Planetarium Sigma system

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Duke

Planetarium Sigma system
« on: 10 Oct 2015, 06:27 am »
At the Rocky Mountain Audio Fest last weekend, our new Planetarium Sigma system made its debut.  Here's a shot taken just before we hooked everything up on Thursday afternoon:



The Planetarium Sigma is an eight-piece system (ten if you count the stands), certainly going off in a different direction than most of the home audio world, but doing some things that a pair of regular stereo speakers really can't do as well.

Here are things this configuration does better than a conventional two-speaker system:  Smoother (i.e. "faster") and more natural-sounding in-room bass, and more realistic overall presentation.

The smoother bass comes from the distributed multisub system.  I'll go into detail for anyone who's interested, but briefly each sub will generate a unique in-room peak-and-dip pattern and the sum of these dissimilar peak-and-dip patterns is inevitably much smoother and more natural-sounding than a single ubersub.

The more realistic presentation comes from more closely approximating the sound field we find in a good live venue.  Studies were done on what makes a good seat (as opposed to a lousy seat) in a concert hall. A critical factor is whether or not we have a clear differentiation between the direct sound and the reverberant sound.  Let me quote David Griesinger on the subject, he uses the word "envelopment" to describe the experience of immersion in the soundfield that I'm aiming for:

"Envelopment is perceived when the ear and brain can detect TWO separate streams:  A foreground stream of direct sound.  And a background stream of reverberant sound.  Both must be present if sound is to be perceived as enveloping." 

When the direct and reverberant sound are run together (in the time domain) so that the one is not clearly differentiated from the other, we don't get this sense of envelopment, and that result in a poor seat in a concert hall.  And that's usually what we have at home, because they usually do run together too much.

The Planetarium Sigma system is designed to provide these two distinct streams that Griesinger calls for, by using a highly directional main array and then supplementing it with a pair of dedicated reverberant-field-only speakers optimized and aimed so that their output arrives after a fairly long time delay (ten milliseconds constitutes a "fairly long time delay" in this context).

Conceptually, this is like the improvement you get when you position Maggies a good five feet out into the room, except that the angled/upfiring Space Generators allow you to get away with much closer-to-the-wall placement because they take advantage of the ceiling height to get the desired path-length-induced time delay for the "backwave" energy.

Another way of looking at it would be this:  It's like we took the radiation pattern of a good conventional speaker and chopped it up into two parts, both spectrally correct.  We fire one part at the listening area, and fire the other part off in a direction that results in a much more natural-sounding arrival time because it better mimics what happens in a good seat at a good hall.   

The ear/brain system judges the size of an acoustic space largely by the time delay between the direct sound and the onset of significant reverberant energy (after the floor and ceiling bounces), and this surge of late-onset (and spectrally correct) reverberant energy from the Space Generators makes the room sound bigger than it is, and correspondingly expands the soundfield.   So this system will make it sound like you have a significantly bigger room, all the way down into the bass region, where the Swarm does that as well!

Tube amp friendliness is retained (93 dB, 8 ohm load when the Sigma Mains and Space Generators are driven in parallel), and we have the dynamic liveliness of prosound drivers (negligible thermal compression on peaks).  I've been told by many listeners, at this RMAF and at previous shows, that my speakers are a welcome break because they are so relaxing to listen to.  I don't emphasize audiophile fireworks; I want something that you can leave on all day and never begin to get tired of (owning SoundLabs for many years ruined me as far as being able to tolerate fatiguing speakers).

I've been told that I need to spend more time emphasizing how user-adjustable my speakers are, because that seems to be a fairly unusual, perhaps even unique, attribute.  So here goes:

The Swarm subwoofer modules can be used sealed, ported, or some of each.  Many users get best results with reversing the polarity of one of the subs.   Aside from the normal subwoofer controls (frequency, gain, and phase), the subwoofer amp has a single band of parametric EQ and a bass-boost switch (normally engaged for sealed box mode, and disengaged for ported box mode). 

The top end of the Sigma main modules can be gently tilted up or down by changing the value of a high-quality resistor in an external terminal cup on the back of the cabinet.  Sound too laid-back for you?  Use a lower value resistor.  Also we have four pluggable ports on the back, so we can fine-tune for how much boundary reinforcement the mains are getting (or not getting).   Most stand-mount speakers are weak in the lower midrange/upper bass, but not these.  And the midwoofers have enough excursion that you can run the mains fullrange (no protective highpass needed) with all four ports open (worst case scenario) and they won't be at risk going into over-excursion until you get to about 114 dB at one meter.  So if you've agonized over trying to find a truly transparent highpass filter that is affordable, you can stop.  You don't need one. 

The Space Generators have a wider range of tonal adjustability as far as tilting the top end of the response goes, to accommodate a wide range of room acoustic situations, and to compensate for the typically dull off-axis spectral balance of most conventional speakers (when they're added to an existing system).  They have a level control as well, and can generally be set to work well with main speakers having a 2.83-volt sensitivity ranging from the lower 80's to the lower 90's.  They present a nominal 20 ohm load at their loudest setting (and a correspondingly higher impedance load at their lower settings), so the Space Generators can safely be run in parallel with most speakers.  They can be connected in normal polarity, reverse polarity, or one of each, depending on what works best in your room.   One of each seems counter-intuitive, but that introduces more de-correlation into the reverberant field, which is actually desirable.

The net result is, aside from getting the basics right (timbre, clarity, imaging, dynamics, lack of listening fatigue), the Planetarium Sigma system is more engaging because it recreates the cues that you would get at a live performance in a good seat at a good venue.  The Planetarium Sigma brings what most systems are missing.

Specifications:

Main Modules:  Two-way ported (but seal-able) MHM; 8" prosound woofers; 1" Beryllium-diaphragm compression driver on a waveguide-style horn; 65 Hz to 20 kHz; 16 ohms; 95 dB/watt and 92 dB/2.83 volts; 28" x 18" x 10"; 55 pounds.  $6000/pair + shipping, not counting stands.

Space Generators:  Two-way 10" sealed box coaxial; 60 Hz to 19 kHz; 20 ohms or more (depending on passive level setting); 78 - 88 dB sensitivity (2.83 volts); 12" x 12" x 19" tall; 35 pounds. $1800/pair + shipping (introductory price).

The Swarm:  Four-piece 10" multi-sub system; typical in-room response -3 dB @ 18 Hz ported and -3 dB @ 23 Hz sealed (bass boost engaged on the amp for sealed mode); typical in-room smoothness (as reported by many customers) +/- 3 dB, 1/3 octave smoothing; each module 12" square by 23" tall and 44 pounds.  $2800/set + shipping, kilowatt-class shelf-mount subwoofer amp included. 

« Last Edit: 13 Oct 2015, 06:03 pm by Duke »

G Georgopoulos

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Re: Planetarium Sigma system
« Reply #1 on: 10 Oct 2015, 06:33 am »
look great,congrats on the show,all the best!.

FullRangeMan

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Re: Planetarium Sigma system
« Reply #2 on: 10 Oct 2015, 11:59 am »
The main speaker are 2 ways?
Any photo with no grills?

Duke

Re: Planetarium Sigma system
« Reply #3 on: 10 Oct 2015, 09:49 pm »
look great,congrats on the show,all the best!.

Thank you very much!

The main speaker are 2 ways?
Any photo with no grills?

It's not a FullRange driver, sorry Man!  But I did have one person who owns speakers with fullrange drivers ask me if that's what it was (the grilles were on), so I take it as a compliment that he couldn't tell it wasn't.   And the few people we popped the grilles for were usually surprised to see a horn. 



Now, it's not just any horn.  It's an extremely low-coloration device, described as a "super-elliptical oblate spheroid waveguide", and I think it's the best available.   The configuration I use (MHM) results in excelent pattern symmetry in both the horizontal and vertical planes, particularly in the crossover region, where we don't want any abrupt pattern changes. 

Jim Romeyn designed the grille and the stands.  Not that my speakers well ever be considered audio jewelry, but I think they look pretty good with the grilles on.   The finish is natural Cherry. 

FullRangeMan

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Re: Planetarium Sigma system
« Reply #4 on: 10 Oct 2015, 10:51 pm »
Thanks for sharing Duke, I appreciated it.
I wish best luck to your project It is very
much refined and easy to live with.

Iam not stringent w/speakers as some think,
if it have a big bass I can use 2 way happily.

fakamada

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Re: Planetarium Sigma system
« Reply #5 on: 15 Oct 2015, 11:54 am »
Hi. Duke. Glad to see another design using ceiling splash!
I noticed that you've switched from 12" woofers to 10" and now 8" woofers. (also 15" and 6.5") I'm very interested in your opinions on different sizes. Especially 2 factors:

-How you'd compare midrange clarity
-How you'd compare integration with subwoofers.

My experieces tell me that bigger woofers (15"-10") are a bit warmer and have a bit less clarity/resolution (XO 1khz-1.5khz), but integrate better with subs.
« Last Edit: 15 Oct 2015, 02:37 pm by fakamada »

JoshK

Re: Planetarium Sigma system
« Reply #6 on: 15 Oct 2015, 12:56 pm »
That looks like a great system!

Duke

Re: Planetarium Sigma system
« Reply #7 on: 15 Oct 2015, 07:40 pm »
Thank you, FullRangeMan and Josh!

Hi. Duke. Glad to see another design using ceiling splash!
I noticed that you've switched from 12" woofers to 10" and now 8" woofers. (also 15" and 6.5") I'm very interested in your opinions on different sizes. Especially 2 factors:

-How you'd compare midrange clarity
-How you'd compare integration with subwoofers.

My experieces tell me that bigger woofers (15"-10") are a bit warmer and have a bit less clarity/resolution (XO 1khz-1.5khz), but integrate better with subs.

Good questions!

If there is a difference in midrange clarity that is caused by cone diameter, I haven't noticed it.  Of course that goes against the conventional wisdom, so let me mention a couple of extremely well-respected speakers that likewise go against the grain:

When JBL set out to design what is becoming the new standard in high-end studio monitors, they chose a two-way format with a 15" woofer crossed over to a constant-directivity horn at 800 Hz.   And their M2 is indeed dominating the high-end studio monitor market.

And then there's Earl Geddes' Summa, which uses a 15" prosound subwoofer driver(!) crossed over at 1 kHz.  The Summa is very well respected for many things, and in particular how natural it sounds through the midrange region.   Earl has other similar-format designs, and because of radiation pattern considerations the crossover point moves up as the woofer diameter decreases, but I'm unaware of anyone finding his 8" and 10" models to have better midrange clarity than his 15" model. 

I think that the cues we interpret as "speed" occur above the midrange region, and I think that the outstanding performance of these big-cone two-way speakers demonstrates that there are other things that matter a lot more than cone diameter as far as midrange clarity goes.   What's happening to the backwave of the midwoofer matters a lot more in my opinion, as far as clarity goes - remember that it's going to reflect back through the cone rather easily, because the cone isn't much of a barrier to sound transmission in comparison with the walls of the cabinet.

As far as integration with subs, again can't say that I've noticed a major advantage of one cone size over another, but generally I do prefer large cones down low (or multiple small cones).  The frequency response is the dominant factor in my opinion, but ime better lower midrange/upper bass impact does seem to correlate with larger cone area.   Larger cones can have the advantage of not needing a protective high-pass filter to prevent driving them into over-excursion, and being able to leave that component out of the main signal chain can be beneficial to clarity.

We humans like to understand cause and effect in the world around us, and so when we hear a difference, we look for things to attribute that difference to.  Cone diameter is easy to see, and so we are inclined to attribute audible differences to cone diameter when that may not be the main reason for the difference.  In other words, we are inclined to mistake correlation for causation. 

I see this a fair amount of this over in the bass guitar cabinet world, where the prejudices can run pretty strong ("tens are too middy", "fifteens are too muddy", "twelves are just right", "no, twelves do nothing well"), when the differences heard are actually far more a function of the woofer's T/S parameters and frequency response curves, plus the box design, than of cone diameter.  Yes there are general trends that follow cone diameter, and radiation pattern width at a given frequency is very much a function of cone diameter, but the specifics of a particular design are what matter most.

The main reason I tend to use large cones is for radiation pattern control, but there are beneficial side-effects that come along with it.  Of course I pick and choose my large cones carefully.  And then there's the obvious downside that big speakers are becoming less and less popular in the price ranges where I'm competing, so maybe I'll do a fairly compact low-to-medium efficiency speaker some day after all... if I can figure out a way around the thermal compression issue.

JLM

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Re: Planetarium Sigma system
« Reply #8 on: 15 Oct 2015, 10:31 pm »
Duke I understand the basics behind the thermal compression issue, but I've also read that it's primarily a concern in professional sound reinforcement where 110 dB (or more) is the goal in arenas and stadiums versus average 80 - 90 dB in home use.  Care to comment?

Duke

Re: Planetarium Sigma system
« Reply #9 on: 15 Oct 2015, 11:56 pm »
Duke I understand the basics behind the thermal compression issue, but I've also read that it's primarily a concern in professional sound reinforcement where 110 dB (or more) is the goal in arenas and stadiums versus average 80 - 90 dB in home use.  Care to comment?

Excellent question!  There are other thermal compression mechanisms aside from magnet heating (which usually happens slowly) and the consequent (usually temporary) loss of magnetic flux. 

My first exposure to the idea of "thermal modulation", a much shorter-term phenomenon than classical thermal compression, was from Earl Geddes.  He talked about how voice coils heat up instantaneously from loud transients (with a corresponding rise in resistance) and then cool down much more slowly, and he applied for a patent on a voice coil wire alloy that did not exhibit a significant change in resistance as it heated up.   Earl didn't go into detail about how much of an issue this is, but he's in the habit of ignoring things that don't matter, and so I figured it must matter.

The solution he suggests?  Big voice coils and fairly high efficiency, so that they don't heat up very much.

My first clear recollection of an encounter with a speaker whose drivers had significantly differing thermal characteristics was a very well-respected $11k (fifteen years ago) three-way.   The spectral balance was mid-scooped at low levels, just right at medium to medium-high levels, and mid-forward at high to very high levels.  Apparently the midrange driver had less short-term thermal compression - what I'd call "thermal modulation" - than the woofer and tweeter.   I've heard something similar at other times, from other speakers, but I'm not a real authority on the subject.

Fortunately a real authority has recently commented on the subject.  Floyd Toole, posting a few months ago on another forum:

"There is more to [loudspeaker thermal behavior] than just getting loud. There is getting loud without changing the frequency response - the sound quality - which happens routinely when different drivers heat up at different rates. Small cone and dome speakers will have the most difficulty in this department, but, for a price, there are drivers that do amazingly well. Horns have no problem getting loud, but getting good sound from them has been a historical challenge. New designs, with short throats and sophisticated flares are different animals, and the best of these can hold their own with "high-end" cones and domes. The difference is that they can get very loud without seeming to be loud."

I asked him about short-term thermal effects, which I think is what you're asking:

"Can rapid voice coil heating (before the magnet has a chance to heat up) cause audibly significant compression on short-term peaks, thereby possibly changing the frequency response of the system on loud peaks even if the average input power remains fairly low?"

Toole replied:

"The audibility of power compression in its many variations probably could use some more research to define what is audible and what is tolerable. The magnet heating that you describe is important in pro audio sound reinforcement systems where the loudspeakers are required to work at or close to their design limits for long periods. Such heating and cooling has a very long time constant. This is not the case in most home systems. Although the modification of motor strength through magnet heating is a factor, most of the audible effects are from voice coil heating, which has a much shorter time constant. I just saw a test of a high-end audiophile speaker that in going from an average level of 70 dB (loud conversation, background music) to 90 dB (a moderate crescendo, or foreground rock listening) lost about 4 dB in output over about 3 octaves in the mid-high-frequency range. It became a different loudspeaker at different listening levels."

That's the best answer I've come across to your question.

If what Toole is saying is correct, and if it's as widespread as he's apparently implying, then this really is a big deal.  So, why don't we see anything about this "dirty little secret" in the audiophile press?  Maybe because very few "mainstream" audiophile speaker brands would measure well by this yardstick.  I seem to recall Audio Magazine conducting thermal testing when the late great Richard C. Heyser was in charge of measurements there, but Stereophile's one article on the topic (that I can recall seeing) dismissed thermal compression as being of no consequence.  I'm inclined to believe Geddes and Toole instead.  I pointed out that Stereophile article to Earl years ago and he said something about the methodology being wrong but I don't remember the specifics.

« Last Edit: 16 Oct 2015, 02:46 am by Duke »

fakamada

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Re: Planetarium Sigma system
« Reply #10 on: 16 Oct 2015, 09:02 am »
Wow! That's very interesting. Thank's for sharing it with us.

brj


Duke

Re: Planetarium Sigma system
« Reply #12 on: 9 Nov 2015, 04:43 am »
Duke, have you ever looked at any of Wayne Parnham's voice coil cooling ideas?

Vented approach:

http://audioroundtable.com/PiSpeakers/messages/15873.html
http://audioroundtable.com/PiSpeakers/messages/17309.html

Heat sync approach:

http://audioroundtable.com/PiSpeakers/messages/17334.html
http://audioroundtable.com/PiSpeakers/messages/17535.html

I was aware of the heatpipe-to-external heatsink approach, but had missed the pump.   I think the heatpipe-to-external-heatsink looks especially effective, and may very well use it in a high-power bass-guitar cab some day.   

As for my home audio designs, I think I have a pretty effective combination of voice coil thermal mass and high efficiency going on, and most of my home audio speakers will probably never see more than 10% of their rated AES power handling even on peaks.   To the best of my knowledge, Wayne doesn't employ these techniques in his home audio design, but rather in his prosound bass horn designs, wherein the relatively small sealed internal chamber can get quite hot.