All correct. The room being sealed is critical to this kind of gain. It would be hard to predict other than to say that if your room isn't as tight as mine - which is very rare, my room is sound proof - it isn't going to do this. Yes, only a monopole could achieve this particular trick. My situation is the exception, but certainly doable in a proper design.
Hey Duke,
While I can fully understand your reservations on designing bandpass subs, as I've been playing with models and still don't feel fully confident enough to build any of them, I would imagine that the overlapping aspects could still be achieved with your designs. For instance, the bandpass filtering could be achieved with low pass filters on the subs in a fashion that would roughly match the type of low pass filtering that Dr. Geddes gets with his bandpass designs and the associated low pass filters used. It would still seem very beneficial to me, based on my understanding, to have this overlap as this is the area of greatest modal density. by not overlapping in this area, you end up lowering the number of low frequency sources you have in the one area it would matter most, no?
Also, Dr. Geddes has talked a bit about the benefit of slightly different subwoofer tunings for the main two or three subs covering the upper bass range, and then having the corner sub being one designed for ultra low frequencies. While I know that using 4 identical subs is fine and can still benefit a great deal by using the asymmetric arrangement,given that you are the manufacturer, have you considered changing this to more closely match Dr. Geddes suggestions? For instance having two or three of the subs use a driver with a lower moving mass and greater efficiency, and then having the fourth sub, the ULF sub, being more like what you have now.
While I can fully understand your reservations on designing bandpass subs, as I've been playing with models and still don't feel fully confident enough to build any of them, I would imagine that the overlapping aspects could still be achieved with your designs. For instance, the bandpass filtering could be achieved with low pass filters on the subs in a fashion that would roughly match the type of low pass filtering that Dr. Geddes gets with his bandpass designs and the associated low pass filters used. It would still seem very beneficial to me, based on my understanding, to have this overlap as this is the area of greatest modal density. by not overlapping in this area, you end up lowering the number of low frequency sources you have in the one area it would matter most, no?
Also, Dr. Geddes has talked a bit about the benefit of slightly different subwoofer tunings for the main two or three subs covering the upper bass range, and then having the corner sub being one designed for ultra low frequencies. While I know that using 4 identical subs is fine and can still benefit a great deal by using the asymmetric arrangement,given that you are the manufacturer, have you considered changing this to more closely match Dr. Geddes suggestions? For instance having two or three of the subs use a driver with a lower moving mass and greater efficiency, and then having the fourth sub, the ULF sub, being more like what you have now.
Pjpoes thanks for your suggestions, but in order to make one sub go much deeper than the others at comparable efficiency it would have to be much larger (remember I use one central amp), and I think that would add disproportionately to the cost and be a tough sell. But if someone requested it and was willing to pay a premium, sure I'd do it.
Now at times I have tuned one enclosure deeper than the others, and will do that for customers who have a vented Swarm (or I'll tell them how to do it themselves by changing the port length; it's a modular Precison Port with the sections taped together). But instead of having lots of subs working in the upper and middle bass region and only one working ultradeep, I tune all my subs to have a gentle 3 dB per octave rolloff down into the mid to lower 20's (for a vented Swarm). Two authors I'm aware of have published "typical room curves" which show approximately 3 dB per octave of gain below 100 Hz. My sealed Swarm has Qtc = .5 sealed boxes so the rolloff there is fairly gentle as well. So in the low bass region instead of having one big sub, I have four small subs that are each theoretically ballpark 6 dB down anechoic relative to 100 Hz. Note that in the modal region the subs combine in semi-random phase, but below the modal region they combine approximately in-phase, so in-room those little subs probably sum approximately in-phase below the modal region resulting in a few dB boost of the ultradeep bass. Now I'm not saying this is superior to a dialed-in full bore Geddes two-subs-plus-ubersub overlapping system, but I do think it's better than just about anything else in its price range, and with some types of main speakers even a viable alternative to the Geddes system.
I think the overlapping has to be done as a systems approach; if the mains are rolling off at 18 or 24 dB per octave, I'm not sure significant amounts of overlap would be benefical. Now the last time I modelled Earl's sealed box mains the rolloff was more like 6 dB per octave, in which case overlapping by lowpassing the various subs at different frequencies makes sense, killing two birds with one stone (smooth transition as well as giving lots of low frequency sources in that region).
My top-of-the-line systems approach is different from what Earl is doing, but it does address the issue you raised. I use controlled-pattern offset bipoles for my mains. By "offset", I mean that the rear woofer is at a different height from the front woofer. When toed-in as recommended, the front and rear woofers are now each a different distance from all of the room boundaries so each is interacting with the room modes differently. When Robert Greene had a pair of my (Swarmless) offset bipoles in his room he hooked 'em up to his favorite automated room correction system, and it did almost nothing to change the speakers' response, indicating that the in-room response was already exceptionally good. I can link to his post to that effect on his Yahoo forum if anyone would like to see it. Anyway, my point here is that I do have a systems approach that gives smooth upper bass above the region covered by the multisubs.
Now at times I have tuned one enclosure deeper than the others, and will do that for customers who have a vented Swarm (or I'll tell them how to do it themselves by changing the port length; it's a modular Precison Port with the sections taped together). But instead of having lots of subs working in the upper and middle bass region and only one working ultradeep, I tune all my subs to have a gentle 3 dB per octave rolloff down into the mid to lower 20's (for a vented Swarm). Two authors I'm aware of have published "typical room curves" which show approximately 3 dB per octave of gain below 100 Hz. My sealed Swarm has Qtc = .5 sealed boxes so the rolloff there is fairly gentle as well. So in the low bass region instead of having one big sub, I have four small subs that are each theoretically ballpark 6 dB down anechoic relative to 100 Hz. Note that in the modal region the subs combine in semi-random phase, but below the modal region they combine approximately in-phase, so in-room those little subs probably sum approximately in-phase below the modal region resulting in a few dB boost of the ultradeep bass. Now I'm not saying this is superior to a dialed-in full bore Geddes two-subs-plus-ubersub overlapping system, but I do think it's better than just about anything else in its price range, and with some types of main speakers even a viable alternative to the Geddes system.
I think the overlapping has to be done as a systems approach; if the mains are rolling off at 18 or 24 dB per octave, I'm not sure significant amounts of overlap would be benefical. Now the last time I modelled Earl's sealed box mains the rolloff was more like 6 dB per octave, in which case overlapping by lowpassing the various subs at different frequencies makes sense, killing two birds with one stone (smooth transition as well as giving lots of low frequency sources in that region).
My top-of-the-line systems approach is different from what Earl is doing, but it does address the issue you raised. I use controlled-pattern offset bipoles for my mains. By "offset", I mean that the rear woofer is at a different height from the front woofer. When toed-in as recommended, the front and rear woofers are now each a different distance from all of the room boundaries so each is interacting with the room modes differently. When Robert Greene had a pair of my (Swarmless) offset bipoles in his room he hooked 'em up to his favorite automated room correction system, and it did almost nothing to change the speakers' response, indicating that the in-room response was already exceptionally good. I can link to his post to that effect on his Yahoo forum if anyone would like to see it. Anyway, my point here is that I do have a systems approach that gives smooth upper bass above the region covered by the multisubs.
Hi Russell... here's the link. Second paragraph:
http://groups.yahoo.com/group/regsaudioforum/message/23243
http://groups.yahoo.com/group/regsaudioforum/message/23243
Ha! Thanks Earl, but apparently I haven't quite found the magic combination of words just yet. My marketing department is still working on it, though they spend most of their time complaining about being underpaid.
I looked through a guitar magazine recently, and apparently the key to success there is to use the words "crushing", "monster", and "tone" in the same sentence. The order of the words doesn't matter, nor does the product they're applied to. Extra points for using a really big font.
If I had to come up with a buzzphrase to describe your systems, it might be "psychoacoustic-optimized waveguide speakers".
I looked through a guitar magazine recently, and apparently the key to success there is to use the words "crushing", "monster", and "tone" in the same sentence. The order of the words doesn't matter, nor does the product they're applied to. Extra points for using a really big font.
If I had to come up with a buzzphrase to describe your systems, it might be "psychoacoustic-optimized waveguide speakers".
I am so happy to see Duke chime in (in) this thread! Blessings galore to my audio hero.
Duke's sub is the best I've heard at making small (meaning domestic) sized rooms reproduce the bass range w/ the same quality as that of bass reproduced in large (meaning commercial) sized rooms. In that regard it has no known equal. IMHO, once a listener becomes familar w/ this quality it is indispensable.
To become familiar w/ this quality takes only a visit to a commercial space w/ live or moderately flat response reproduced bass. Listen carefully to the bass, how invisibly it blends w/ the rest of the music, how the bass & higher range are in the same musical plane, the bass' effortless dynamic quality, & it's "elastic" quality (elastic in a good way). Immediately go home, not listening to any other music & minimal conversation during the trip, then listen to music at home & compare the bass to what you just heard. The bass will likely sound disconnected & synthetic vs. the rest of the spectrum, like the bass is in a different dimension. It may loose its limitless dynamic & "elastic" quality.
The quality described above more frequently is lacking than any other quality in domestic reproduction systems/rooms. IMO this defect is the single largest impediment to sustaining belief. In moderately OK systems this bass quality makes more difference than any component or speaker swap. It's that big a deal.
Unfortunately most audiofiles usually tend to this last, would rather swap components &/or speakers, or concern themselves w/ bass power &/or getting a few Hz lower cutoff. I pity them. I was them.
The second if not equally great feature about Duke's SWARM is its ability to flatten room modes, performing in this regard better than any digital EQ w/ which I'm familiar. In my current room the modes are so awful that performance is more pleasant minus a normal or EQ'd sub system, prefering the .5cf internal volume standmount monitors alone. W/ a four sub array setup as per Duke's SWARM the modes are close to inaudible.
Once the above two performance upgrades are experienced they would be welcomed for the perceived inconvenience of siting four 1cf subs near walls.
Duke's sub is the best I've heard at making small (meaning domestic) sized rooms reproduce the bass range w/ the same quality as that of bass reproduced in large (meaning commercial) sized rooms. In that regard it has no known equal. IMHO, once a listener becomes familar w/ this quality it is indispensable.
To become familiar w/ this quality takes only a visit to a commercial space w/ live or moderately flat response reproduced bass. Listen carefully to the bass, how invisibly it blends w/ the rest of the music, how the bass & higher range are in the same musical plane, the bass' effortless dynamic quality, & it's "elastic" quality (elastic in a good way). Immediately go home, not listening to any other music & minimal conversation during the trip, then listen to music at home & compare the bass to what you just heard. The bass will likely sound disconnected & synthetic vs. the rest of the spectrum, like the bass is in a different dimension. It may loose its limitless dynamic & "elastic" quality.
The quality described above more frequently is lacking than any other quality in domestic reproduction systems/rooms. IMO this defect is the single largest impediment to sustaining belief. In moderately OK systems this bass quality makes more difference than any component or speaker swap. It's that big a deal.
Unfortunately most audiofiles usually tend to this last, would rather swap components &/or speakers, or concern themselves w/ bass power &/or getting a few Hz lower cutoff. I pity them. I was them.
The second if not equally great feature about Duke's SWARM is its ability to flatten room modes, performing in this regard better than any digital EQ w/ which I'm familiar. In my current room the modes are so awful that performance is more pleasant minus a normal or EQ'd sub system, prefering the .5cf internal volume standmount monitors alone. W/ a four sub array setup as per Duke's SWARM the modes are close to inaudible.
Once the above two performance upgrades are experienced they would be welcomed for the perceived inconvenience of siting four 1cf subs near walls.
Earl, it might be worth your while to make contact with Robert Greene. I spoke of your work to him so I'm sure he's aware of you.
He's in the upper level of the mathematics department at UCLA, last I heard working on a follow-up to string theory, so obviously he can think in non-Euclidean dimensionality. He turned down an offer to head Tulane University's math department to take that position. He's also an accomplished professional musician; among other things he was Russell Crowe's violin instructor for the latter's role in Master and Commander. Not only does he have a serious scientific background, but he is a big believer in radiation pattern control AND and he obviously doesn't mind giving recognition to small companies that neither advertise in his magazine's pages nor sell through dealers.
My point being, he's definitely not your average reviewer.
Here's his website:
http://www.regonaudio.com/
He's in the upper level of the mathematics department at UCLA, last I heard working on a follow-up to string theory, so obviously he can think in non-Euclidean dimensionality. He turned down an offer to head Tulane University's math department to take that position. He's also an accomplished professional musician; among other things he was Russell Crowe's violin instructor for the latter's role in Master and Commander. Not only does he have a serious scientific background, but he is a big believer in radiation pattern control AND and he obviously doesn't mind giving recognition to small companies that neither advertise in his magazine's pages nor sell through dealers.
My point being, he's definitely not your average reviewer.
Here's his website:
http://www.regonaudio.com/
It's not often that I get to say this about someone in audio, but you're a class act Duke. You get a compliment upon the performance of your design and pass on much of that to the theorist who inspired you.
Thanks also (belatedly) for a response to an email some months ago on design. Though I eventually went with something else, I got some ideas from you that helped in my experiments.
Thanks also (belatedly) for a response to an email some months ago on design. Though I eventually went with something else, I got some ideas from you that helped in my experiments.
Hi Duke,
I second Brett's sentiment. It is obvious that you are very passionate about everything audio. And it is reflected in your helpful post across many forums.
Also, I would like to thank you for all of the free advice and guidance that you have given me over the past few years.
Hope to see you at LSAF 2010.
Norris
I second Brett's sentiment. It is obvious that you are very passionate about everything audio. And it is reflected in your helpful post across many forums.
Also, I would like to thank you for all of the free advice and guidance that you have given me over the past few years.
Hope to see you at LSAF 2010.
Norris
Patrick Bateman said:I'm really happy with the use of multiple subs. I started with three, and ramped it up to eight, mostly because my mains are so efficient. I am personally using a bunch of DIY subs, but it would be a lot less hassle to just go and buy a bunch of them.
If anyone reading this thread wants to give this a whirl, and do it cheaply, this might be an opportunity to do so.
Newegg has a $250 Polk subwoofer marked down to $100 at the moment. At that price, it's hard to go wrong. Try it out for a few weeks, and if you don't like the sound, go sell them on Craigslist. I wouldn't be surprised if you could RE-sell them for more than $100 each. They are currently $200/each at Crutchfield, and $150/each at buy.com. It's hard to find a plate amp for under $100, much less a finished sub.
Here's the manual:
http://www.polkaudio.com/downloads/manuals/home/PSW10_12_Manual.pdf
Here's the sub:
Polk PSW10
The promo code to get it for $100 is EMCLNLP28.
Ecost has a Boston Acoustics 10" subwoofer for $95 at the moment. Amazon sells it for $400. It has a 250 watt plate amp with a crossover. For some reason the 150 watt model costs more, I have no idea why. You can get the PDF manual for both off the Boston Acoustics website.
It's a refurb, but I've had good luck with this vendor. Purchased two TVs from them and they've been running great for a year now.
http://www.ecost.com/Detail/Speakers/Boston+Acoustics/HPS10HOMDNT/49550960.aspx?navid=155442295