AudioCircle
Other Stuff => Archived Manufacturer Circles => AudioKinesis Loudspeakers => Topic started by: Duke on 13 May 2017, 12:54 am
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Apologies in advance to readers of Robert Green's Yahoo group... much of this is re-cycled...
Often discussions of "which sub for Maggies or Quads" includes recommendations of dipole subs, and for good reason: Dipoles blend well with dipoles! Let's take a look at WHY dipoles work well, because I think there's a common misconception. And let's look at multiple monopole subs, and see what they do better and what they do worse, and see if there might be a "best of both worlds" approach (spoiler alert: I think there may be two "best of both worlds" approaches).
Okay let's start by dividing the bass region into two zones (and I realize these aren't new concepts for most of you): The "modal zone", where we get those familiar and unwelcome room-interaction peaks and dips; and the "pressure zone", down below the modal zone, where the wavelengths are so long relative to the room dimensions that all of the first reflections occur within 1/4 wavelength of each other, which tends to put all of the in-room bass energy in-phase. We will come back to these concepts later.
Another concept we want to look at is "de-correlation". This concept is less well-known, but it is the primary acoustic smoothing mechanism for in-room bass in both dipole bass systems and distributed multiple monopole bass systems. We get good de-correlation when the in-room bass energy is adding in semi-random phase. De-correlation is desirable because it results in smooth bass, because no particular frequencies have enough energy to stick out like sore thumbs (or "peaks"). To help you visualize what we mean by the term, good "de-correlation" would be like the foot-falls of a highschool football team running out onto the field. On the other hand, strong "correlation" would be like the foot-falls of the Wehrmacht on parade. The thing to remember is, good de-correlation = smooth in-room bass.
And smooth bass is "fast" bass, literally and perceptually. Because room + sub(s) = a minimum phase system, in-room peak = slower energy decay at that frequency = "slow" bass. So if the perceptual goal is "fast bass", the road thereto is the one marked "smooth bass".
In general, dipole bass really is smoother than monopole bass! In 2002 researcher James M. Kates published a paper in the Journal of the Audio Engineering Society showing that dipoles have smoother in-room bass than monopoles. This wasn't news to the Gradient and Quad and Maggie and SoundLab and Apogee owners out there, but it WAS long-overdue officially-sanctioned peer-reviewed validation.
Now most people who talk about the "speed" (in-room smoothness) of dipole bass attribute it to the figure-8 radiation pattern exciting fewer room modes. But if only few-and-far-between room modes are excited, that's an indication of strong correlation (Wehrmacht)! And we'd expect those few-and-far-between peaks and dips (especially the peaks) to stick out like sore thumbs. So, I think that attributing the in-room smoothness of dipole bass entirely (or even mostly) to the figure-8 radiation pattern is a misconception. Kates' data shows smoother in-room bass for dipoles, which implies good de-correlation, so something else must be going on. Here's what I think is happening:
The primary smoothing mechanism for dipole bass is, the phase relationship between the frontwave and the backwave energy. The figure-8 radiation pattern also plays a role here, so it does matter, but not all by itself. Because of the radiation pattern, the normal-polarity frontwave goes off in one general direction, and the reverse-polarity backwave goes off in the opposite direction. After a few room boundary bounces the twain shall meet again, but their phase relationships are now generally semi-random - which means good de-correlation - highschool football team!
[Not that I'm necessarily the world's biggest fan of highschool football teams, whose members were often the dispensers of wedgies and noogies to us little nerdlings, but at least football gave them someone else to hit and hit hard.]
In general, it takes two intelligently-distributed monopole sources to get the same approximate in-room smoothness of a single dipole source. The energy from the dipole source sums in-room in semi-random phase because the frontwave and backwave start out in opposite polarity and are launched in opposite directions, and the energy from two intelligently-spaced monopole sources also combines in semi-random phase because of their physical distance from one another and dissimilar physical distances from most of the room's boundaries.
So the same mechanism - semi-random phase summation - is at play in smoothing the in-room response of both dipole bass systems and Swarms in the modal region. But the two approaches totally diverge as far as what happens down in the pressure zone! If the energy in the pressure zone is all in-phase (like with four monopole subs), then it sums in-phase. This can result in boom, because in-phase summation is inherently 3 dB louder than the semi-random-phase summation we were getting up in the modal zone. And because of the ear's heightened sensitivity to relative loudness at low frequencies (which is shown in the bunching up of equal-loudness curves south of 100 Hz), a 3 dB emphasis below 40 Hz can sound as big as a 6 dB emphasis up in the midrange region. (This is also an argument for most systems having significant room for improvement in the bass region.)
With a dipole, at very long wavelengths the situation is kinda the same but the outcome is totally different. In the region where all of the reflections are happening within 1/4 wavelength, we have half of the energy with one polarity and half with the opposite! The net sum would be complete cancellation ( making it a "no-pressure zone"?). In practice the cancellation isn't complete, but it is severe, and as a result dipole bass tends to have poor impact unless a) the room is very large (pushing the "no-pressure zone" down very low in frequency) and b) the dipole bass system actually does go very low (which requires a very large baffle and/or a lot of EQ).
So intelligently-distributed monopoles can match the in-room smoothness of dipoles in the modal zone as long as we use enough monopoles. But down in the pressure zone, the monopoles tend towards having about 3 dB of excess energy, while the dipoles tend towards complete cancellation (virtually no bass energy). Neither situation is ideal, and subjectively "too much low bass" can be even more distracting than "not enough low bass".
But, the Swarm has one final trick up its sleeve! We can reverse the polarity of one of the four subs! Now as we move down into the pressure zone, we have 3/4 of the energy in normal polarity and 1/4 of the energy in reverse polarity, so we end up with neither the low-end over-emphasis of the pure monopole (all woofers in-phase) approach, nor the trending-towards-complete-cancellation of the dipole approach. And by reversing the polarity of one sub, we are also improving the de-correlation up in the modal zone. So we end up with smooth bass all the way down, with no over-emphasis anywhere. And remember, smooth bass is "fast" bass.
Okay, is there another approach that can give similar results? I think so, and it's something Siegfried Linkwitz has been doing for decades: Use dipole bass down to the transition between the modal and pressure zones, and use monopole bass down in the pressure zone. Both approaches work well.
Not all rooms will have a significant pressure zone - open-floorplan rooms won't - so not all of the distinctions made above will be equally applicable. The best answers are probably arrived at on a case-by-case basis. But I think that a good distributed multisub system, well set-up, is competitive with a good dipole system across the modal zone and superior to both dipole and pure monopole (all woofers in-phase) down in the pressure zone.
Duke
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Good read Duke. Thanks for re-posting :thumb:
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Thanks for sharing Duke.
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Thank you both very much! I admire your determination if you actually managed to read all of that. I hadn't realized how long it was until it actually posted.
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Duke,
Thanks for posting! Correlates with what I have experimented completely! In fact, to satisfy my own curiosity and dipole bass aficionados, I experimented with "multisub dipole bass" specifically with Rythmik drivers (so theee would be no argument from naysayers with regards to "quality" and benefits of "servocontrol"). What did I find? Although it sounded good, it failed in the "impact" and "realism" department compared to my current setup that is using multiple high efficiency subs (95 dB in my case) in the modal region, and 1 or 2 subs (depending on room size, preference) for the 1st mode. A simple FR curve wasn't able to discern the differences between the 2 setups (as they both measured great) nor did other measurements like waterfall, etc...I imagine it will come down to things I can't measure and can't prove either like more freedom from compression, lower THD & IMD of the drivers used at that particular SPL, etc, etc...
Best,
Anand.
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I've posted this a couple times already:
https://secure.aes.org/forum/pubs/conferences/?elib=17270 (https://secure.aes.org/forum/pubs/conferences/?elib=17270)
An overview of about 30 bass studies.
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A fascinating and well-written paper. In the past I have owned big dipoles (double KLH-9; Infinity Servo Statik; Acoustat 4; Sound Lab; Maggie. OK, so I'm restless). My attempts to mate monopole subs with them never came off well, for reasons that Duke has outlined quite cogently. Now I have OB main speakers (GR Research LS9s) mated with a three-stack of GR Research (Rhythmik) OB servo woofers per side. Aaah! Much better.
But I'm still restless. Although my system presents a good "startle" factor, I'm thinking it could have more. Duke's post plus Anand's suggest that a combination of monopole and dipole subs might be worth trying. So maybe I should just add a couple of monopole subs. But, boy! That sounds like a huge complication: amps (with volume controls), cables, positioning. And can my preamp handle a third output? This may be an itch I'll never really be able to scratch.
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THROWBACK, if you can swing it, I know from hearing basically your same setup (Mockingbird LS-X with two triple stack OB servo subs) at RMAF, with and without a pair of sealed servo subs firing out of phase from the back of the room, the result from adding the sealed subs is well worth it. I would from my experience compare it to taking what you have now, with all its goodness, and adding the foundation in the bass the boxed LS-9 brings to the table compared to the same speaker OB. Evolutionary rather than revolutionary, but definitely not subtle.
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Duke,
Thanks for posting! Correlates with what I have experimented completely! In fact, to satisfy my own curiosity and dipole bass aficionados, I experimented with "multisub dipole bass" specifically with Rythmik drivers (so theee would be no argument from naysayers with regards to "quality" and benefits of "servocontrol"). What did I find? Although it sounded good, it failed in the "impact" and "realism" department compared to my current setup that is using multiple high efficiency subs (95 dB in my case) in the modal region, and 1 or 2 subs (depending on room size, preference) for the 1st mode. A simple FR curve wasn't able to discern the differences between the 2 setups (as they both measured great) nor did other measurements like waterfall, etc...I imagine it will come down to things I can't measure and can't prove either like more freedom from compression, lower THD & IMD of the drivers used at that particular SPL, etc, etc...
Best,
Anand.
Thank you Anand!
Hopefully one day measurements will catch up to perception... right now measurements are usually excellent tools for telling us why we hear what we hear, but your experience is an example that there is still ground left to be covered.
I have these two somewhat similar bass guitar cabs and when you compare the measurements, one should have "more bass", but perceptually the other one does. This has been reported by all of my customers who own both or have heard both side-by-side, except for one... and that one is the guy who does measurements for a magazine. I suspect that his ears are calibrated better than all the rest of ours, but serious bass players are extremely good at this sort of thing, so that doesn't explain the majority's perceptions. It would be really nice if I can figure out how to optimize for best perceived low end.
It seems to me that sometimes the better the "grip" the motor has on the air, via larger cone area for instance, the better the impact. A heavy cone can still work if the motor is powerful enough, but power-to-weight ratio seems to matter too, which trades off against cone area. I've tried woofers that looked good through this lens and were distinctly "mushy" down low, so it's more complicated than that. Your approach of modal-region-optimized high efficiency woofers + pressure zone woofers may be the way to really nail it.
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I've posted this a couple times already:
https://secure.aes.org/forum/pubs/conferences/?elib=17270 (https://secure.aes.org/forum/pubs/conferences/?elib=17270)
An overview of about 30 bass studies.
Thank you AJ!
My membership expired during the Great Recession a few years ago, and I haven't renewed it yet. I'll buy the article if it's really valuable. Can you give me a few sentences that describe what you learned from it?
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Thank you AJ!
My membership expired during the Great Recession a few years ago, and I haven't renewed it yet. I'll buy the article if it's really valuable. Can you give me a few sentences that describe what you learned from it?
Multiple subs in mono results in smoother amplitude, but loses ability to recreate spatial info in recordings.
Gradient (cardioids) showed the highest immunity to modal issues/placement in rooms and offered lower decay times. Lower decay times increased discrimination of spatial effects.
The least researched (2006) was 5(+) full range channels, each driven by appropriate signals (like JJs PSR).
Btw, AES membership ($125/yr) gives full access to entire library. No need to purchase individual papers any more. I can't think of $125 better spent if one has the slightness interest in "Audio".
cheers,
AJ
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the "pressure zone", down below the modal zone, where the wavelengths are so long relative to the room dimensions that all of the first reflections occur within 1/4 wavelength of each other
Hi Duke, could you clarify the "pressure zone" definition? The above seems to suggest that the room might need to be 1/8 or less of a wavelength in the longest dimension (i.e. if I sit on top of a sub located on the short wall).
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But I'm still restless. Although my system presents a good "startle" factor, I'm thinking it could have more. Duke's post plus Anand's suggest that a combination of monopole and dipole subs might be worth trying. So maybe I should just add a couple of monopole subs. But, boy! That sounds like a huge complication: amps (with volume controls), cables, positioning. And can my preamp handle a third output? This may be an itch I'll never really be able to scratch.
IF your main amp is sending a fullrange (rather than highpassed) signal to your main speakers, perhaps you could build a voltage divider network which would derive a line-level signal from the amp's output, and use that to drive one or more subwoofer amps.
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Multiple subs in mono results in smoother amplitude, but loses ability to recreate spatial info in recordings.
Gradient (cardioids) showed the highest immunity to modal issues/placement in rooms and offered lower decay times. Lower decay times increased discrimination of spatial effects.
The least researched (2006) was 5(+) full range channels, each driven by appropriate signals (like JJs PSR).
Thank you AJ, very interesting. I'm under the impression that very few recordings actually have stereo bass. Some Swarm users are using two amplifiers, probably in stereo in most cases, and driving the two subs on one side of the room with one amp and the two on the other side with the other amp. At least some of them are also using the phase controls to put the subs on one side of the room in phase quadrature (90 degrees apart) from the subs on the other side, which is a technique suggested by researcher and acoustician David Griesinger for synthesizing hall ambience from recordings with mono-summed bass.
Very interesting that cardioid sources are the most immune to modal issues! Since cardioid subwoofer require two woofers per unit (one of which is used to partially cancel the other) along signal processing and separate amplifiers, it's probably relatively expensive compared to implement.
I wonder how four monopole subs with one in reverse polarity would have compared. Oh well, we'll probably never know, as that's a pretty obscure technique.
Hi Duke, could you clarify the "pressure zone" definition? The above seems to suggest that the room might need to be 1/8 or less of a wavelength in the longest dimension (i.e. if I sit on top of a sub located on the short wall).
My definition of the "pressure zone" was quite sloppy! Thanks for catching that!!
Here is a better one: The "pressure zone" is the region below the frequency that has a wavelength of twice the longest internal room dimension. In this zone, sound behaves very much like changes in static air pressure. The longest room dimension is actually the oblique dimension, going from one bottom corner to the opposite top corner.
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I used to have some crazy bass systems that could do very high output down to 16hz, and I found that I didn't actually like it very much. It pressurized the room and made me basically feel like I was under water. Very uncomfortable feeling for me. I ended up with OB (servo) bass because it gave a lot of punch, but specifically did NOT pressurize the room like a high output box(es) solution. Plus, most of the 'percussive' bass is 50hz and above, that's where the 'kick you in the chest' feeling comes from.
Even though my subs were pretty crazy, they were nothing as insane as my friend Thomas' system, the "12 Shivas Dancing" infinite baffle which was able to put out prodigious bass, to say the least. And same problem, for me - the pressure on my inner ear was just downright uncomfortable. It felt like I was swimming.
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I used to have some crazy bass systems that could do very high output down to 16hz, and I found that I didn't actually like it very much. It pressurized the room and made me basically feel like I was under water. Very uncomfortable feeling for me. I ended up with OB (servo) bass because it gave a lot of punch, but specifically did NOT pressurize the room like a high output box(es) solution. Plus, most of the 'percussive' bass is 50hz and above, that's where the 'kick you in the chest' feeling comes from.
Even though my subs were pretty crazy, they were nothing as insane as my friend Thomas' system, the "12 Shivas Dancing" infinite baffle which was able to put out prodigious bass, to say the least. And same problem, for me - the pressure on my inner ear was just downright uncomfortable. It felt like I was swimming.
Thanks for posting your experiences with uberdeep room-pressurizing subs. I don't feel so bad now that my subs only go down to about 20 Hz.
By any chance did you ever try something like the four-subs-with-one-in-reverse-polarity setup? Not that there would have been any obvious reason to do so, just curious.
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No, I think at the time no one had even thought about a swarm approach, let alone tried it.
As you know from my RMAF reporting, I do really like the AK Swarm :thumb:
Mainly my point was more of a "be careful what you wish for", especially with high output low bass. For me, room pressurization was a very real negative.
But I think a lot of people haven't had a super high output low bass system and might end up with a nasty surprise if/when they finally get one.
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Thank you AJ, very interesting. I'm under the impression that very few recordings actually have stereo bass.
Paper 41 of 45 in the study I linked addresses just that http://www.aes.org/e-lib/browse.cfm?elib=13358 (http://www.aes.org/e-lib/browse.cfm?elib=13358), as did this thread in diyaudio http://www.diyaudio.com/forums/lounge/247583-can-human-ear-really-localize-bass-18.html (http://www.diyaudio.com/forums/lounge/247583-can-human-ear-really-localize-bass-18.html).
Some caveats: The vast majority of popular music recordings don't. Usually acoustic music types that might actually be performed in actual spaces. Jazz, classical, etc.
which is a technique suggested by researcher and acoustician David Griesinger for synthesizing hall ambience from recordings with mono-summed bass.
Griesingers work is referenced also, as are other decorrelated maximum separation (+/- 90 degree) lateralization methods. He is one of the early advocates of smooth amplitude alone (free of peaks) being not the sole arbiter of bass SQ.
Since cardioid subwoofer require two woofers per unit
They do not. There are many examples of flow resistance enclosures that generate cardioid response, ME Gethain, Music & Design (John K), http://kimmosaunisto.net/CardSub/CARDSUB.html (http://kimmosaunisto.net/CardSub/CARDSUB.html) etc.
It should be also noted from the studies that there is significant differences in ability to lateralize among the population.
So as usual, YMMV, depending on many factors, including music preferences.
cheers,
AJ
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Very interesting that cardioid sources are the most immune to modal issues! Since cardioid subwoofer require two woofers per unit (one of which is used to partially cancel the other) along signal processing and separate amplifiers, it's probably relatively expensive compared to implement.
site top corner.
If you are after a cardioid pattern from a subwoofer, wouldn't it be more easily achieved with a U-shaped open baffle (a boxed sub with an open back) or maybe a H-frame with different depths to the wings front or back? This would eliminate the signal processing and one amp per sub?
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If you are after a cardioid pattern from a subwoofer, wouldn't it be more easily achieved with a U-shaped open baffle (a boxed sub with an open back) or maybe a H-frame with different depths to the wings front or back? This would eliminate the signal processing and one amp per sub?
Jonathan,
I built a pair of U-frame cardiod subs designed by John Kreskovsky, several years back. It definitely required EQ and of course amplification. The driver was specifically designed for dipole and cardioid applications. So I have no idea where you are coming from with the notion that a U-frame and H-frame eliminate or even minimize the need for signal processing. Of course they sounded quite good but due to the relative inefficiency of the drivers used, they were SPL compromised, and as such, I moved on.
I think some degree of signal processing and/or EQ will always be needed to achieve a flat bass response in room. It however is minimized the more subs that are used in the room as long as the subs are somewhat asymmetrically placed and not grouped together.
Best,
Anand.
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They do not. There are many examples of flow resistance enclosures that generate cardioid response, ME Gethain, Music & Design (John K), http://kimmosaunisto.net/CardSub/CARDSUB.html (http://kimmosaunisto.net/CardSub/CARDSUB.html) etc.
Thank you very much for the link! I didn't realize that flow resistance was practical down into the subwoofer range. EQ is probably still called for, I think I saw 10 dB at 30 Hz mentioned in the article, but I haven't yet taken the time to really read it closely.
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Anand, my suggestion was in response to Duke's proposition of needing subs using a pair of drivers each, thinking that being able to reduce that to one driver per sub in handling the pattern shaping with the cabinet would reduce having to manage processing for two drivers independently and having to have two amp channels per sub (how I interpreted Duke's idea) to create the desired radiation pattern directly through manipulating driver output. I thought this might at least make it a little easier to put together a system based on cardioid radiation pattern subs.
I'm sorry if that sounded like I was suggesting no EQ or amplification was needed at all; just a little bit less. Of course, this might then add the complication of having to aim the subs physically as well as limit placement options for them. Also, of course, if a system already is using a signal processor capable of handling the requisite number of channels and the number of available amp channels isn't a problem, the concern becomes a non-issue.
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EQ is probably still called for, I think I saw 10 dB at 30 Hz mentioned in the article, but I haven't yet taken the time to really read it closely.
Yes, unless using a high Qts driver or specialized one like from AE et al, just like many sealed subs, a bit of EQ is needed if one wants to get really deep.
However, there is really no benefit to doing so below 40 hz or so, where modes are sparse. There, monopoles still rule, as many as one would wish. Even in mono. The research I linked does not suggest otherwise.
cheers,
AJ
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Yes, unless using a high Qts driver or specialized one like from AE et al, just like many sealed subs, a bit of EQ is needed if one wants to get really deep.
However, there is really no benefit to doing so below 40 hz or so, where modes are sparse. There, monopoles still rule, as many as one would wish. Even in mono. The research I linked does not suggest otherwise.
cheers,
AJ
That's pretty much the conclusion I was coming to, i.e., that the benefits of cardioid bass started to be outweighed by the EQ requirements at very low frequencies.
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Jonathan,
Thanks for the clarification! The internet unfortunately isn't the best place for a sequential conversation and hence my concerning query, and my apologies if I sounded a bit obtuse.
AJ & Duke,
Below 40 Hz where you are dealing with very few modes, yes, large psychotic monopoles are key. But as far as the area from 40 Hz to a little below the Schroeder frequency of the room, can we agree that this is the modal region and that another option (other than multiple asymmetrically placed monopole subs receiving a summed mono signal) is a pair of cardioid subs receiving a stereo signal? And that this cardioid sub pair can then maintain spatialization and minimize the FR ripple as well as multiple assymetrically placed monopole subs?
I need to download that paper AJ linked! And I need to become an AES member!
Thanks,
Anand.
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No, I think at the time no one had even thought about a swarm approach, let alone tried it.
As you know from my RMAF reporting, I do really like the AK Swarm :thumb:
Thank you very much, Tyson.
I think that any enhanced sense of image size or spaciousness or whatever that any of my systems produced at RMAF were more due to the "late ceiling splash" energy than anything else.
Mainly my point was more of a "be careful what you wish for", especially with high output low bass. For me, room pressurization was a very real negative.
But I think a lot of people haven't had a super high output low bass system and might end up with a nasty surprise if/when they finally get one.
And you made that point very well - thank you for taking the time to do so!
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AJ & Duke,
Below 40 Hz where you are dealing with very few modes, yes, large psychotic monopoles are key. But as far as the area from 40 Hz to a little below the Schroeder frequency of the room, can we agree that this is the modal region and that another option (other than multiple asymmetrically placed monopole subs receiving a summed mono signal) is a pair of cardioid subs receiving a stereo signal. This cardioid sub pair can then maintain spatialization and minimize the FR ripple as well as multiple assymetrically monopole subs?
I don't know enough about cardioids to say whether two cardioid subs are better, worse, or about the same as four monopole subs in the modal region. AJ knows more about cardioids than I do, and has read (and understood!) more research on the subject than I have, so he can probably answer that better than I can. My inclination is to think that four monopoles will be smoother in-room that two cardioids, especially if we either reverse the polarity of one or, if it's a two-amp setup, do the Griesinger phase-quadrature-thing.
My understanding is that two stereo cardioid subs would have better spatial resolution than the distributed monopole subs, assuming the latter are all receiving the same summed mono signal. How far that carries over when we have left and right channel signals going to the respective left and right pairs of monopole subs, I don't know.
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Which is the best Guys,dipole or multiple monopole subs,too much tech jargon ,for us with limited tech knowledge,my opinion is the bass should be at the same loud level and spatial level as the other drivers,there are some car subs that have tones of bass!(for me a no no in hifi)
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It seems like, based on this conversation if I'm reading it correctly, that the answer is actually a combination of the two. Assuming we're talking about a two-channel stereo setup, the ideal appears to be a pair of stereo subs (ideally cardioid in radiation pattern, although a dipole would seem a desirable second option due to similar pattern control improving issues dealing with room modes) playing down to roughly 40Hz. From there to as far down as one would like to go, the research AJ references suggests a distributed set of monopole subs (like Duke's swarm setup) is the way to go, as sound localization no longer stands as an issue.
This combination of subs would theoretically present the smoothest, most even response below a frequency where spatial perception fails people, while maintaining proper stereo separation and imaging between there and up to where whatever chosen main speakers are in the system take over. The interesting wrinkle in bass management presented so far in this discussion suggests that between 130Hz and 40Hz-ish there is a great need for processing and EQ to make that range work well with the stereo pair of subs, but below that, saturation to even out room response through summed dissimilar sources is key to the exercise, with whatever little processing or EQ one chooses to do being mostly a function of calibrating the swarm of lowest frequency subs to most optimally compensate and correct for each other.
Do I have that about right?
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Which is the best Guys,dipole or multiple monopole subs,too much tech jargon ,for us with limited tech knowledge,my opinion is the bass should be at the same loud level and spatial level as the other drivers...
A well set-up multiple monopole system does a very good job of having the same loudness level across the bass region. It also can have very good spatial level, with a little bit more cost and complexity.
But I would not try to tell someone what is "best" without knowing a lot about their situation, because what is best for them depends very much on the situation.
It seems like, based on this conversation if I'm reading it correctly, that the answer is actually a combination of the two. Assuming we're talking about a two-channel stereo setup, the ideal appears to be a pair of stereo subs (ideally cardioid in radiation pattern, although a dipole would seem a desirable second option due to similar pattern control improving issues dealing with room modes) playing down to roughly 40Hz. From there to as far down as one would like to go, the research AJ references suggests a distributed set of monopole subs (like Duke's swarm setup) is the way to go, as sound localization no longer stands as an issue.
My understanding is that, among recordings, there is a continuum that extends from "pure mono bass" (below say 100 Hz or so) to "true stereo bass", and that most recordings are pretty close to the "mono" end of this continuum, with classical music recordings most likely to be the exceptions. In other words, I think that most recordings have essentially mono bass, from a perceptual standpoint if not literally.
Now I don't think there is anything wrong with having a stereo subwoofer system, and about 1/4 to 1/3 of my Swarm customers use two amps, so they can either set them up for stereo, or use the Griesinger phase-quadrature configuration, or both.
I'm not ready to concede that a stereo pair of cardioid subs offers more than a minor spatial advantage over a stereo-configured four-piece Swarm-type system. And if the recording has insignificant stereo separation down low, then a two-amp phase-quadrature Griesinger setup would probably tip the scales in favor of the Swarm, because it would synthesize the sort of spatial impressions we get from good stereo bass. I believe Griesinger's word for it is "immersion".
Now if you are going to use stereo cardioid or dipole subs, then it may very well make sense to add a monopole sub for the very low frequencies. This may or may not correspond to the transition from the modal zone to the pressure zone - it may simply be a matter of not having the amplifier headroom and/or woofer excursion capability called for by the equalization that would be needed to extend the response low enough.
However if we are able to make the transition from dipole/cardioid to monopole in about the same frequency region as the transition from modal to pressure zone, we might be able to get away with just using a single monopole sub.
This combination of subs would theoretically present the smoothest, most even response below a frequency where spatial perception fails people, while maintaining proper stereo separation and imaging between there and up to where whatever chosen main speakers are in the system take over.
I think dipole/cardioid over most of the bass region + monopole (perhaps in multiples) down low would work very well.
The interesting wrinkle in bass management presented so far in this discussion suggests that between 130Hz and 40Hz-ish there is a great need for processing and EQ to make that range work well with the stereo pair of subs, but below that, saturation to even out room response through summed dissimilar sources is key to the exercise, with whatever little processing or EQ one chooses to do being mostly a function of calibrating the swarm of lowest frequency subs to most optimally compensate and correct for each other.
This is an area where multiple monopole subs, with one in reverse polarity, does well: Very good results are not limited to the few with powerful measurement and signal processing capability. One of my Swarm customers has a very powerful Meridian processor that he had had a technician calibrate for his system previously. When he got the Swarm, he set it up according to my guidelines, reset all the filters in the Meridian processor to "flat", and called in the technician to fine-tune the system. The ONLY thing the technician did to the Swarm was, tweak the level - no EQ was needed! Quoting now from his e-mail:
"... The other big change I made was replacing my single [competitor's sub] with your AudioKinesis Swarm asymmetric four-subwoofer array this past summer. Results - unbelievable bass with no suckout anywhere in the room !
"The MRC program can insert up to 60 digital filters between ~10hz and 250 hz to eliminate the dominant room resonant nodes. The previous calibration resulted in 16 filters distributed across 5.1 speakers, (the left and right Vandersteen Quatro Woods, VCC-5 center channel, the two VSM-1 surround speakers, and the [competitor's subwoofer]. The VCC and the two VSM's were crossed over at 80 hz, while the Quatros were set for full range. The speakers are in a 16' wide by 22' deep symmetric room using the ITU 5.1 placement standard). With your Swarm taking the place of the [other sub], the MRC only inserted 2 filters - one for each VSM-1 ! (I think this may due to their proximity to the ceiling corners in the back of the room.) The Quatro Wood 11-band analog equalizers were set flat, and the Meridian processor left them that way.
"The asymmetric Swarm array works so well that the only "calibration" really required is for level. (We were able to get every speaker within 1/2 dB, prior to the processor burst noise sequence and resultant filter build). It has rendered both the MRC and Vandersteen's analog equalizers unnecessary for my room [emphasis in the original]. After reading Earl Geddes and Fred Toole's papers, I knew it would force the room nodal distribution to be inherently flatter, but I had no idea how much improvement was going to occur.
"The tech., who has performed dozens of these calibrations, said he has never seen anything like this. The room is rendered literally flat in frequency response and spatial energy distribution - sonically the room disappears. We played one of Kal Rubinson's recommended demo discs, the 100th anniversary for the San Francisco Symphony Orchestra using the John Adams piece, "Short Ride on a Fast Machine", and you would swear you were in the hall. You can "feel" the ripple in the tympani skins ! Very impressive."
In other words, zero equalization was needed to achieve results that the technician felt could not be improved on by using the Meridian processor's filters. All he did was correct the gain setting on the Swarm amp. I'm not saying that you can't get equal or better results with a more complicated cardioid/monopole hybrid system, but it's probably going to be a lot harder to get dialed in.
Returning to the spatial issue for a moment - in my opinion there is a LOT more spatial information that can be made good use of north of 100 Hz. But that's another thread for another day.
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I'm been looking for examples of cardioid subwoofer setups. Do they require DSP? It seems like that is a way to do it, but I get a lot of odd ball things that are just canceling phase of everything behind the subwoofers from what I can tell.
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A well set-up multiple monopole system does a very good job of having the same loudness level across the bass region. It also can have very good spatial level, with a little bit more cost and complexity.
But I would not try to tell someone what is "best" without knowing a lot about their situation, because what is best for them depends very much on the situation.
I've never listened to multiple subs,so i don't know what you're talking about,my situation is average room,i'm interested to know about the spatial of multiple subs and how they work,is it the same with surround sound?,thanks Duke...
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I'm been looking for examples of cardioid subwoofer setups. Do they require DSP? It seems like that is a way to do it, but I get a lot of odd ball things that are just canceling phase of everything behind the subwoofers from what I can tell.
Yes, they do require EQ/DSP. Read Music and Designs primer here: http://www.musicanddesign.com/NaO-II-U-frame.html
And here: http://www.musicanddesign.com/u_frame.html
John Kreskovsy has done quite a bit of work with cardioid designs.
Best,
Anand.
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I've never listened to multiple subs,so i don't know what you're talking about,my situation is average room,i'm interested to know about the spatial of multiple subs and how they work,is it the same with surround sound?,thanks Duke...
You need to learn how to walk before you run. We all have "average" rooms, so don't worry. It also has nothing to do with surround sound.
Theory:
Very technical: http://www.wghwoodworking.com/audio/low-frequency_optimization_using_multiple_subwoofers.pdf
Less technical: http://www.wghwoodworking.com/audio/multsubs.pdf
http://www.gedlee.com/Papers/multiple%20subs.pdf
Application:
http://www.hifizine.com/2011/06/bass-integration-guide-part-1/
http://www.hifizine.com/2011/09/bass-integration-guide-part-2/
http://www.hifizine.com/2012/06/bass-integration-guide-part-3/
Best,
Anand.
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I've never listened to multiple subs,so i don't know what you're talking about,my situation is average room,i'm interested to know about the spatial of multiple subs and how they work,is it the same with surround sound?,thanks Duke...
I will try to explain without using too much tech jargon.
The worst problem that a single subwoofer has is, what the room does to its frequency response. As the bass energy bounces around the room, the reflections combine in a way that causes peaks at some frequencies and dips at others. We can move the subwoofer or move the listening position and that changes the peak-and-dip pattern, but does not eliminate it.
The main idea of multiple subs is, to solve this problem. The peaks are the worst part if this problem.
In the kind of multiple sub system I manufacture, the four subs are scattered around the room. If we look at each sub all by itself, the room will cause its response to have big peaks and dips. But the peaks and dips are at different frequencies for each sub because they are each in a different location. All of these different peaks and dips added together actually result in much smoother response than we could get from just one sub, no matter how carefully we position it. And no matter where you are in the room, you have the sum of four different peak-and-dip patterns, so the bass is smooth throughout the room.
And smooth bass sounds "fast", because it is the peaks that sound slow.
To answer your other question, multiples subs usually are not like surround sound, where each speaker gets a different signal. Multiple subs usually all get the same signal.
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Yes, they do require EQ/DSP. Read Music and Designs primer here: http://www.musicanddesign.com/NaO-II-U-frame.html
And here: http://www.musicanddesign.com/u_frame.html
John Kreskovsy has done quite a bit of work with cardioid designs.
Best,
Anand.
Thank you Anand! I was hoping you would reply to Folsom because you know a lot more about cardioids than I do.
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I will try to explain without using too much tech jargon.
The worst problem that a single subwoofer has is, what the room does to its frequency response. As the bass energy bounces around the room, the reflections combine in a way that causes peaks at some frequencies and dips at others. We can move the subwoofer or move the listening position and that changes the peak-and-dip pattern, but does not eliminate it.
The main idea of multiple subs is, to solve this problem. The peaks are the worst part if this problem.
In the kind of multiple sub system I manufacture, the four subs are scattered around the room. If we look at each sub all by itself, the room will cause its response to have big peaks and dips. But the peaks and dips are at different frequencies for each sub because they are each in a different location. All of these different peaks and dips added together actually result in much smoother response than we could get from just one sub, no matter how carefully we position it. And no matter where you are in the room, you have the sum of four different peak-and-dip patterns, so the bass is smooth throughout the room.
And smooth bass sounds "fast", because it is the peaks that sound slow.
To answer your other question, multiples subs usually are not like surround sound, where each speaker gets a different signal. Multiple subs usually all get the same signal.
Duke,has been tried before,thank you for your easy explanation,all the best with it.
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Yes, they do require EQ/DSP. Read Music and Designs primer here: http://www.musicanddesign.com/NaO-II-U-frame.html
And here: http://www.musicanddesign.com/u_frame.html
John Kreskovsy has done quite a bit of work with cardioid designs.
Best,
Anand.
It drives me nuts there's no pictures of his subwoofers. And his have no DSP. As nice as they are in graphs, I'd have to hear them to know if the bass actually sounded good with all the dampening; so perhaps DSP makes more sense.
Then again the swarm is pretty easy :D
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It drives me nuts there's no pictures of his subwoofers. And his have no DSP. As nice as they are in graphs, I'd have to hear them to know if the bass actually sounded good with all the dampening; so perhaps DSP makes more sense.
Then again the swarm is pretty easy :D
There are pictures of his subs (it's just a box with an open back). Look in my gallery under XJ-12 (http://www.audiocircle.com/index.php?action=gallery;album=1151). The U-frame sub design that he has incorporated into his dipole speakers use DSP as did mine. He recommends a MiniDSP (or equivalent) with all his current builds as well.
Best,
Anand.
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Below 40 Hz where you are dealing with very few modes, yes, large psychotic monopoles are key. But as far as the area from 40 Hz to a little below the Schroeder frequency of the room, can we agree that this is the modal region and that another option (other than multiple asymmetrically placed monopole subs receiving a summed mono signal) is a pair of cardioid subs receiving a stereo signal? And that this cardioid sub pair can then maintain spatialization and minimize the FR ripple as well as multiple assymetrically placed monopole subs?
Anand, I should be clear that there is no one size shoe that fits all. There are dipoles and cardioids than extend to below 20hz and may prove all one persons needs for bass. The fact is monopoles are simply more efficient in this area and there is no real benefit to gradient output in this region below 40-50hz, or non-mono reproduction.
But a very common misunderstanding is that gradients are less efficient than monopoles. This is false. Above F equal, they are more efficient. So it all depends on what frequency F equal is in the system.
The other issue regards both spatial reproduction and localization. Multiple subs can indeed yield smoother amplitude response, but that is limited to around an upper end of about 80-90hz, due to localization. There are lots of modal issues above this, in typical rooms, up to several hundred Hz, typically around 400hz or so.
Multiple subs are useless between 90-400hz. Most folks then resort to both EQ and/or so called "treatments", but these have there own issues.
Gradient systems can address issues in this region where monopoles by themselves, cannot.
I need to download that paper AJ linked! And I need to become an AES member!
Yes :wink:
It's the best $125 spent in audio, if that is ones interest.
cheers,
AJ
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My understanding is that two stereo cardioid subs would have better spatial resolution than the distributed monopole subs, assuming the latter are all receiving the same summed mono signal. How far that carries over when we have left and right channel signals going to the respective left and right pairs of monopole subs, I don't know.
Hi Duke,
As noted earlier, there is no one size shoe fits all. Ability to discriminate lateralization (low frequency spatial effects) varies quite a bit. Then there is the issue of content and preferences. For the HT crowd or rock/pop music types (the vast majority of audiophiles I've encountered), smooth amplitude via spatially averaged monopoles should be a no brainer. It sounds better than response with peaks and over a wider area to boot.
However, if one's preferences lean more heavily to non-amplified music that contains LF spatial info, then there is no chance of reproducing this in summed mono.
So as always YMMV. Keep in mind that the gradients not only increase discrimination of spatial effects (being fed a non-mono signal), but also have increased clarity due to the lower amount of power resulting in a decrease in decays. This effect can be mimicked with a lossy room as Dr Geddes advocated for (3' of absorber on front wall alone iirc), as this will reduce the far field power to levels similar to gradients.
But as Sean Olive says, why create power only to absorb it, very wasteful in these green times. :D
cheers,
AJ
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AJ,
As I try to read up on gradient/cardioid in-room bass effects it seems that stacking out of phase subs and a delay (perhaps 4 ms, but I understand that is frequency dependent) applied, with one pair per channel is the practical ideal to achieve the effect (for non-amplied music). True?
And is it not true that the cardio effect is only about 10 dB and that overall it reduces output significantly?
BTW I'm primarily interested in lower frequencies (20 - 60 Hz).
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AJ,
As I try to read up on gradient/cardioid in-room bass effects it seems that stacking out of phase subs and a delay (perhaps 4 ms) applied, with one pair per channel is the practical ideal to achieve the effect (for non-amplied music). True?
Hi JLM,
To an extent, one would achieve a cardioid patter over some bandwidth by doing so, yes. Ideal? Well, maybe ;-). There are several ways to do it (see Kimmo link). One benefit of a "single" enclosure, either flow resistance or multi-source (dipole+monopole, rear delay driver, etc), is that they can be rotated, so the null is directed at different angle, possibly better coupling to modes. This is true for dipoles also.
And is it not true that the cardio effect is only about 10 dB and that overall it reduces output significantly?
Not quite sure what you are referring to. Rear output (nulling)? Far field?
cheers,
AJ
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Anand, I should be clear that there is no one size shoe that fits all. There are dipoles and cardioids than extend to below 20hz and may prove all one persons needs for bass. The fact is monopoles are simply more efficient in this area and there is no real benefit to gradient output in this region below 40-50hz, or non-mono reproduction.
But a very common misunderstanding is that gradients are less efficient than monopoles. This is false. Above F equal, they are more efficient. So it all depends on what frequency F equal is in the system.
The other issue regards both spatial reproduction and localization. Multiple subs can indeed yield smoother amplitude response, but that is limited to around an upper end of about 80-90hz, due to localization. There are lots of modal issues above this, in typical rooms, up to several hundred Hz, typically around 400hz or so.
Multiple subs are useless between 90-400hz. Most folks then resort to both EQ and/or so called "treatments", but these have there own issues.
Gradient systems can address issues in this region where monopoles by themselves, cannot.
Yes :wink:
It's the best $125 spent in audio, if that is ones interest.
cheers,
AJ
Ah! Thanks for the eye opener. Indeed, my high efficiency Geddes bandpass/passive radiator subs (midbass modules actually) which I love work from about 40 Hz to about 100 Hz and smoothly blend into the mains (no electrical crossover, all acoustic due to the bandpass design, only electrical manipulation I have done is with phase). That being the case, I had to be careful about dealing with SBIR from 100 hz to 250Hz, so positioning of the mains, as well as having very decent room treatments around the corners near the mains and also behind the mains on the side walls made a nice difference. The midbass modules were useless in that bandwidth. This was partially because they are bandwidth limited but also because of what you stated earlier that multiple subs are less useful in that region above 100 Hz.
I will be happy to share my measurements which are a few years old, if Duke doesn't care/mind.
I would like love a demonstration one day with different recordings (that truly do have stereo bass) to illustrate to me the importance of preserving spatialization. I think I will have to read the article you referenced and take a trip down to Tampa. Unfortunately, I do not think I really own any recordings that have 'true stereo bass.'
Thank you once again for the knowledge. In fact, I feel yet another book can be written on all the vagaries of bass reproduction. It is a pity since most audiophiles' "reference" systems have pathetic bass reproduction.
Best,
Anand.
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Duke, thanks for clarifying the definition. Have you considered the way in which response of dipole vs monopole varies with distance from the listening position?
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I find this discussion interesting as I have always shied away from subs or using electronic crossovers. Living happily with my Spendor monitors or Duke's Jazz Modules in their native form. However, I have always been intrigued by the Swarm and lately I have been using a similar set up to it that was brought to my attention by Roger Modjeski of Music Reference.
Roger builds his own ESL speakers and designs them to cut off at 100 Hz. He supplements them with a pair of woofers in a bi-amped set up. His RM-10 driving the panels and a generic Class A/B solid state amp with his low pass filter built into it. The filter is 4th order Linkwitz Riley but with a passive EQ that goes to 32 Hz or lower if desired. The drivers Roger selected are designed to fit into a small enclosure where they resonate above 100 Hz. It's quite a nice set up.
For me, I went a slightly different route. I have a Beveridge RM-3 using high and low pass filters with the same 4th order L/R configuration and 32 Hz EQ. The RM-3 allows me to use my RM-10 to drive my ESL 57s and a Luxman M-02 amp that has connections for two sets of speakers to power 4 of the bass boxes. I have spread the boxes asymmetrically around the room and have to say the results are quite satisfying. I did some additional re-positioning to dial in the sound a bit more. What I haven't done is reversed the polarity on any of the bass boxes. I really don't feel any excess bass energy so I just left well enough alone. If anything I may change the EQ to push below 30 Hz.
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So, how does EQ figure into the strengths/weaknesses of various sub setups? ... My specific question involves using something like a miniDSP unit as an active crossover. The unit has the capability of EQ. If I EQ a full-range speaker, would that overcome the need for multiple monopole subs to smooth out the frequency? Also, would that provide a smooth bass response in one position, but not do as good a job of smoothing it out room-wide? And, would monopole or dipole subs matter if I am using EQ? ... A related question, with or without EQ, would augmenting to full-range speakers with two subs provide similar benefits to four subs?
Thanks for any input!
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Duke will have to pardon me on his forum, but I see no reason not to use your mains full range and use subs to smooth the response and increase output/headroom.
The benefit of the minidsp is it also allows delay (along with EQ, phase, etc), so that the added subs can be placed in various spatial positions that work best for whatever one is hoping to accomplish.
The key of course, mains that are as capable at LF as subs, in extension, power, inaudible levels of distortion, etc.
One of the setups mentioned in the paper are 5 fullrange speakers (no "subs").
cheers,
AJ
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Thanks AJ. Duke, any thoughts on this?
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Hi skvinson,
A combination of DSP and multiple bass sources is probably better than either one alone. Imo DSP alone is not as effective as multiple subs alone for smoothing out the modal region over a large listening area, but DSP alone can do a very good job in a small listening area.
Personally I'd prefer only having DSP in the signal path to the subs, and not in the signal path to the mains, but that's just my personal prejudice.
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Thanks Duke! ... Makes sense.
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Hi skvinson,
A combination of DSP and multiple bass sources is probably better than either one alone. Imo DSP alone is not as effective as multiple subs alone for smoothing out the modal region over a large listening area, but DSP alone can do a very good job in a small listening area.
Personally I'd prefer only having DSP in the signal path to the subs, and not in the signal path to the mains, but that's just my personal prejudice.
I agree - multiple subs are great at evening out room modes, especially the ones created by the front/rear walls and the side walls. Floor/ceiling tends to NOT be addressed by multiple subs, and DSP is a good option to knock that mode down.
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I agree - multiple subs are great at evening out room modes, especially the ones created by the front/rear walls and the side walls. Floor/ceiling tends to NOT be addressed by multiple subs, and DSP is a good option to knock that mode down.
Would a few ceiling mounted and/or wall mounted subs take care of the floor/ceiling mode issue?
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I agree - multiple subs are great at evening out room modes, especially the ones created by the front/rear walls and the side walls. Floor/ceiling tends to NOT be addressed by multiple subs, and DSP is a good option to knock that mode down.
Why can't subs be mounted above the room centerline?
Yes, aesthetics is a concern for some but if you are already doing multi-sub then you should do it right. Your room is 3D so you should think about trying to energize as many room modes as possible throughout the space. Keeping all subs on the ground is not optimum as Geddes has shown.
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Why can't subs be mounted above the room centerline?
Yes, aesthetics is a concern for some but if you are already doing multi-sub then you should do it right. Your room is 3D so you should think about trying to energize as many room modes as possible throughout the space. Keeping all subs on the ground is not optimum as Geddes has shown.
One of my subs is about 1 foot off the floor relative to the other 2 subs. And I have a 4th one to add soon, as a result of a project that I recently collaborated with Duke...and yes, I wish one of my other subs was hanging a bit from the ceiling. That being said, the only frequency response area that I am using DSP is right around the 1st mode (i.e. below the modal region) to boost 20Hz which is expected given the lossy nature of all small rooms.
Best,
Anand.