[poseidonsvoice]

From Thilo Stompler's new company, Audiopulse, he has compiled a very nice primer on Subwoofer Truths & Myths. In particular, is the notion of there is "no replacement for displacement." The statement is true but only within one context of subwoofer design. That's in very low frequencies, i.e. the first 1/2 to full octave. After that there are other parameters that come into play. As I start building the sub portion of my system, I have come to realize that I will probably have a pair of subs for a so called 'midbass' region. Something between 50Hz to 100Hz, in addition to a pair of subs from 20Hz to 50Hz. It would need to be high spl and probably won't have a driver with high xmax, but will have one with a higher sensitivity.

Anyway, Read and have fun.

Anand.

[Bob in St. Louis]

Interesting article. But it seems geared to car audio too much with the constant reference to "SPL competitions". They talk about less watts, less Xmas and more sensitivity, yet their flagship driver is 38mm Xmas, 87 dB and needs 5000 watts to drive it. 

A couple comments made my head lean over to the side, much like a dog would.
Here are a couple:

- .....most of the bass frequencies for music are really limited by {driver} sensitivity..... (#7)
- .....For low frequencies, the cone {material} on a driver makes no difference in the sound whatsoever.....(#10)

I'm not an expert, but those sound odd to me.

They also use the word "box" too often for my liking. As an OB guy, that offends me.   

Bob

[Kevin Haskins]

I've just scanned it but overall, there is nothing glaringly wrong.    Many of the topics are more complex than the simplifications needed to communicate the situation to the average user.    That is why you get many of these "myths".    They evolve out of an effort to simplify what is occurring and it is a way for people to try to make sense of the complex.

The power rating thing drives me crazy because people insist upon a fixed number so that they can be assured they will never overdrive their speaker.   The situation is just more complex than that but good luck trying to explain that to the masses. 

And Bob... I'd agree with the statement about cone materials.   It is largely a choice based upon marketing.   None of the cones are anything but pistonic in their range of use.   

[Bob in St. Louis]

And Bob... I'd agree with the statement about cone materials.   It is largely a choice based upon marketing.   None of the cones are anything but pistonic in their range of use.

Meaning you believe that (for lower frequencies) the cone material will not change the FRG or the sound?
I'm not "testing" you Kevin, I sincerely don't know. It seems illogical to me that it wouldn't make a difference. But this is from a guy that's never heard anything but paper for lower frequencies.

Bob

[Kevin Haskins]

Interesting article. But it seems geared to car audio too much with the constant reference to "SPL competitions". They talk about less watts, less Xmas and more sensitivity, yet their flagship driver is 38mm Xmas, 87 dB and needs 5000 watts to drive it. 

The reason is that for maximum SPL, these car sound competitors design a large resonant peak in the system.   The easiest place to locate that peak, while maximizing output (to get the highest SPL) is typically around 60Hz.    You are playing with cabin gain, power available, and then the physical limitations of the transducers when balanced against the allowable artificially designed metrics for winning/losing.     Those artificially designed metrics are such that you don't have to have wide bandwidth, for a given SPL, just a maximum number.    As you go lower, you need to displace about four times as much air to achieve the same SPL but that is transposed against a cabin gain curve, which rises as frequency drops.    When you also add in the limits of power available you quickly see that the best way to maximize SPL at a given frequency, is to pick a point on those curves that gives you a maximum.   That is in the 50-70Hz range for most vehicles.     For that type of application, you want high efficiency and the ability to withstand high power with minimal thermal/Cms/BL compression.    That is what "wins" under those circumstances.

None of that has any applicability to high-end audio or HT though.   It is just to counter the beliefs of the car audio crowd who are impressed by SPL contest numbers and whom might chase high X-max as the solution for winning an SPL contest.   

[Bob in St. Louis]

None of that has any applicability to high-end audio or HT though.   It is just to counter the beliefs of the car audio crowd who are impressed by SPL contest numbers and whom might chase high X-max as the solution for winning an SPL contest.

Bingo....Gotcha Kevin. That's what I was thinking. Thanks for that.
They confused me and had me second guessing myself for a minute.

I never saw the point of SPL competitions though. 
Not sure what it proves.

Bob

[Kevin Haskins]

And Bob... I'd agree with the statement about cone materials.   It is largely a choice based upon marketing.   None of the cones are anything but pistonic in their range of use.

Meaning you believe that (for lower frequencies) the cone material will not change the FRG or the sound?
I'm not "testing" you Kevin, I sincerely don't know. It seems illogical to me that it wouldn't make a difference. But this is from a guy that's never heard anything but paper for lower frequencies.

Bob

No problem... I'm not worried about being "tested".     Yes... as long as the cones are pistonic, they do not have differing FR curves outside of what is set by their intrinsic mass and its effect on the T/S parameters.     

That wouldn't be the case necessarily with a midrange driver.   The size and shape of the transducer have an affect on the dispersion, so you could have two drivers, both pistonic with the same on-axis FR measurement that would sound drastically different due to their differing off-axis behavior.   

At low frequencies (1st/2nd octave), we don't have those issues because they are all omindirectional over that bandwidth.   

[Kevin Haskins]

None of that has any applicability to high-end audio or HT though.   It is just to counter the beliefs of the car audio crowd who are impressed by SPL contest numbers and whom might chase high X-max as the solution for winning an SPL contest.

Bingo....Gotcha Kevin. That's what I was thinking. Thanks for that.
They confused me and had me second guessing myself for a minute.

I never saw the point of SPL competitions though. 
Not sure what it proves.

Bob

It is just a drag racing event.   You are just testing man against materials.   

[Bob in St. Louis]

Damn....Despite my best efforts I learned something today. 

Thanks for your time and the clarification(s) Kevin. 

Bob

(I still think SPL drag racing is silly). 

[Kevin Haskins]

Damn....Despite my best efforts I learned something today. 

Thanks for your time and the clarification(s) Kevin. 

Bob

(I still think SPL drag racing is silly). 

Ha... you have to go out of your way to stay ignorant.    

I'm not much for drag racing either.   None of my drivers are good SPL drivers, at least for car audio.    If you want to talk about a maximum output capability @ 20-30Hz, it is all about displacement baby.   

[Bob in St. Louis]

I would venture a guess that there aren't very many (if any at all) drivers found in these pages that would be good for the drag. And as far as I'm concerned, that's a good thing.

And yes, max SPL at frequencies that low has quite a bit to do with area but I'd add to that, that alignment would play a big part of the equation.  aa

Bob

[poseidonsvoice]

Interesting article. But it seems geared to car audio too much with the constant reference to "SPL competitions". They talk about less watts, less Xmas and more sensitivity, yet their flagship driver is 38mm Xmas, 87 dB and needs 5000 watts to drive it. 

Bob

Ya, I agree with that. Their drivers are generally average to low sensitivity, but he does talk about 'more sensitivity' as being advantageous. He doesn't seem to offer drivers like that though!  AE does. This again, seems to depend on what 'range' we are talking about. And of course the topic gets a lot more complex once you depart into dipole land, cause you need a lot more of these drivers to get into higher SPL territory. Again, this is my experience with Home Hifi not car stuff which I know nothing about.

I'm not much for drag racing either.   None of my drivers are good SPL drivers, at least for car audio.    If you want to talk about a maximum output capability @ 20-30Hz, it is all about displacement baby.   

Now that's the point. Note the frequency range and then the method on which we achieve that. But at higher frequencies, it seems that sensitivity (say north of 50 Hz) plays more of a role.

I am just glad that companies like Exodus Audio and AE exist. For diy'ers its like a buffet line. And I agree at low, low frequencies the driver composition (as far as Kevlar, paper, etc...), makes nada difference. Its all marketing. With a well designed woofer like the Tempest Mark 2...then the room, the box alignment, and amp make the differences.

Anand.

[Kevin Haskins]

Now that's the point. Note the frequency range and then the method on which we achieve that. But at higher frequencies, it seems that sensitivity (say north of 50 Hz) plays more of a role.


Anand.

My comments are limited to and applicable only for the SPL contest where you are building a system with a huge single resonance peak inside an automotive environment.    Those comments do not necessarily apply to other situations.   You would have to treat each situation differently because the variables at play are not simple and generalizations tend to lead to wrong conclusions. 

Here is an Seas CA18-RNX (6.5" midwoofer) next to a 21" Maelstrom.   The Seas is about 87dB/1W/1M and the Maelstrom is about 89.6 dB/1W/1M.    I could add some mass easily to the Maelstrom to decrease the efficiency number but there is no comparison between these two drivers in their ability to play-back a 60Hz signal at high output.   Both thermal & mechanical capability are needed to hit high SPL at anything under 80Hz.    Sure... you can analyze the system and point your finger at the limiting factor at 80Hz being thermal when playing back a single test-tone, and mechanical at 30Hz, but that doesn't necessarily give you useful information about playing back music which is a complex waveform made up of both.     




I'm not sure the efficiency number is all that meaningful unless you consider all the factors.   People tend to get myopic and focus on one number or another and the situation is just too complex to be nailed down to such a simple analysis.    You have to look at a number of variables and have a grasp of how they all interplay to come to useful conclusions. 

[poseidonsvoice]

Kevin,

Got the picture, and thanks. That 21 inch Maelstrom looks a tad small no

I think one of the problems I have (or maybe some of us have) is that because of the complex interplay of multiple variables with a particular audio topic, in this case, subwoofer design (SPL, Xmax, power compression, etc)...sometimes the internet medium is really not the best to explain as it doesn't involve a sequential dialogue. You are right about generalizing and trivializing details or even more so, not realizing what aspects of subwoofer design are most important depending on your end goals. I admit, I am still learning here and picking up the phone and calling is probably best  .

My concern with lower sensitivity drivers seems to be with calling them for duty at 110dB at 1m and wondering if power compression is just as much of a concern as it would be for an equivalent sized driver that was say 10 dB more sensitive (of course its Fs is much higher, etc...). Again, both drivers are built incredibly well, aluminum shorting rings, blah, blah, blah. The frequency range I would be concerned with is exactly as you state around 60-120Hz. What I am really wondering is (cost no object) if using a pair of subwoofers to span the range from 150Hz to 15hz is what is best, or if this is just making it a lot more complex than it should be. In my particular case, it would be mating with a woofer on my monitor that is 95dB sensitive/2.83V/1m. I don't know what your experience has been in that regard or if you have any advice at all. And what I really mean is for playback of music, not test tones of course. The usage of multiple subwoofers has advantages with evening room modes, etc....all of this has been hashed and published before.

There might be no easy answer to this question except for built it, measure it and try it.

Anand.