Dual Opposed Subwoofer Theory?

[sigbergaudio]

Enjoyable post, @RealityCheck18

I'm afraid giant horn loaded subwoofers aren't in great demand. People want ever smaller subs these days, so more and more subs are sealed. Adding two drivers dual opposed in the same cabinet, will give you more oomph while still having a reasonably small box if you compensate for the lack of volume with lots of watts.

 

[Vytauts]

I'm thinking two DOS for 2.2 setup. Similar to Amphion Basetwo25 or Barefoot stack subwoofer. So only vibration and volume are all of issue?

Hi, What speakers will you use?
Also considering 2.2 setup. Will speakers put on subs ar separate stands?

 

[Juhazi]

Subs can be a piece of furniture too! 2x235 liters make a bench! The cover plate only weighs about 60kg and is 3x90x220cm.
SEAS T18 coaxials in sealed boxes as LCR. Bass traps and resonators are essential to get good sound as well!

 

[Putter]

WinISD is perhaps the most popular bass box simulator, worth investigating

View attachment 104770

Some obvious questions come to mind. Has Child Protective Services been called? Are you sure it's not a full range speaker since it includes a tweeter?

 

[RealityCheck18]

Enjoyable post, @RealityCheck18

I'm afraid giant horn loaded subwoofers aren't in great demand. People want ever smaller subs these days, so more and more subs are sealed. Adding two drivers dual opposed in the same cabinet, will give you more oomph while still having a reasonably small box if you compensate for the lack of volume with lots of watts.

Preach it, bro!

Some nut designed a dual 12" push pull tapped horn tuned to 18Hz--I was smitten! It was only 6 feet tall, 2.5 feet deep but less than 15 inches wide. Put on my top hat, did the "you won't notice a pair of those in the living room" dance but my wife demanded a drug test. The designed called those beasts "Kraken" because they had the output of the mythical sea monster, were about as large as a sea monster and if near a wall...your drywall will be cracken... those 12 inch subs used in the design went out of production shortly after that so I went with 15" PPSL for the garage to boost efficiency and called it a day.

My living room subs--wanted dual 12" PPSL--not a chance. Dual 10" PPSL was the right size as an end table but the cost was actually higher than the 12 incher (high Xmax 10" and 2 ohm stable amps cost a lot more) Again, my CFO wife disapproved funding so I countered with a single 15" end table--approved and funded.

So yeah, I'm a poser, a hypocrite and a wuss... no PPSL/opposed for me in my living room. Before you send the people with torches, I do have them in my garage in their giant box gloriousness which means something! I've built two isobaric subs but tend to stay away from them as the 6dB loss compared to opposed is a cost I'm unwilling to pay.

Fully understand why it is not common to see dual driver subs be they push-pull, push-push, push-pull slot loaded and so on. They are big, they are heavy, they are expensive and that does not sell very well. Size matters and manufacturers have to pay the bills so will build what the consumer wants. Throw in with push-pull, they look bizarre and although technically correct, they are FN ugly to most people.

If you want to go full "audiophile sub", just get two of them per spot and a few ratchet straps later you are golden! I do find it odd when I see subwoofers with two drivers and they are not opposed at the minimum--because aesthetics is a real thing. I can pull the tops off my end tables subs and make them opposed and post the results. Then again, my wife would throw me out and the local bridge where I would be living does not have WiFi so I guess that's out.

 

[Juhazi]

Some obvious questions come to mind. Has Child Protective Services been called? Are you sure it's not a full range speaker since it includes a tweeter?

My lovely daughter Aino just wanted to check my seams!

By the way, I couldn't find this kind of sub at local hifi store, so I had to DIY.
By the 2nd way, if you DIY in the first place, do something you can't buy!

 

[Chromatischism]

The dual opposed configuration (woofers on opposite sides of the cabinet to cancel vibrations) was patented, and at least one company went with a three-woofer triangular-opposed configuration to implement the vibration-cancelling concept without violating the patent.

I don't know whether the patent has expired or lapsed or gone undefended, or whether the invention has been licensed. I just remember bumping into it about fifteen years ago when I was researching multiple woofer patents.

I used to build isobaric subwoofers as a hobbyist. I made a direct comparision (using close-miked response curves) between a single-woofer sealed box system and an isobaric system half the size. Both used the same woofer. The published equation indicates a halving of effective Vas for isobaric loading and therefore the frequency responses should have been essentially identical. The actual measured response was very different; the isobaric system had much deeper bass than predicted, so I think the published equation is incomplete.

Definitely not patented:

http://www.rythmikaudio.com/G22.html

 

[sloth_kwj]

I'm not talking about isobaric, just DOS in phase.

Hi, What speakers will you use?
Also considering 2.2 setup. Will speakers put on subs ar separate stands?

Linearaudio.pro Model M is my main speaker. Still improving with developer in many ways so asking in this thread.
I'll put speaker on subs similar to Amphion Basetwo25 concept.

 

[Frank Dernie]

I think the isobaric part is the constant pressure between the cones of the front and rear drivers, since the air volume never changes there.

True, my speakers use "isobaric" installation.
What the OP is asking about is not this, though, in fact the opposite, which is why the pressure between them will be high and the requirement for double the cabinet volume.

 

[pozz]

A DIYer took an impulse response from his listening position comparing a monopole and dipole: http://elias.altervista.org/html/Dipole_vs_monopole_bass.html

Interesting simulations. This is just a guess, but if he had made same kind of analysis with multiple distributed subs I think the result would be similar to the dipole.

 

[egellings]

So long as the cones themselves move in phase with respect to each other, then you have the isobaric approach, however the drivers themselves are oriented/connected.

 

[tusing]

Do force-cancelling subwoofers (aka KC62 and KF92) eliminate the need for dual subs?

 

[jhaider]

Do force-cancelling subwoofers (aka KC62 and KF92) eliminate the need for dual subs?

No. All it does is keep the cabinet from shaking and walking.

 

[audiofooled]

Enjoyable post, @RealityCheck18

I'm afraid giant horn loaded subwoofers aren't in great demand. People want ever smaller subs these days, so more and more subs are sealed. Adding two drivers dual opposed in the same cabinet, will give you more oomph while still having a reasonably small box if you compensate for the lack of volume with lots of watts.

And this is where the practical use for it ends. For the same box size, dual opposed isobaric will lower the Qtc and smooth the rolloff as if the box is twice as big but at a cost of 3 times more power for the same output. Also, it wouldn't go as low as a single driver in twice the bigger box. Though, if you really want to put 2 drivers in a single box and really can't go for a bigger one, dual opposed isobaric would still be much less boomy (normal alignment would raise the Qtc and bump the output for more than 2 or even 3 db but only above Fsc... Subs need big boxes which sadly are hard to fit anywhere. Dsp to tailor the response is more practical and available nowadays.

EDIT: Sorry, mixed up dual opposed with isobaric

 

[digitalfrost]

For the same box size, dual opposed will lower the Qtc and smooth the rolloff as if the box is twice as big but at a cost of 3 times more power for the same output.

Please explain. You're simply putting two drivers in the same box, how does having them arranged "dual opposed" change anything with regards to Qtc?

 

[audiofooled]

Please explain. You're simply putting two drivers in the same box, how does having them arranged "dual opposed" change anything with regards to Qtc?

The interaction between the two. Think of it in a similar way when you stuff the box with polyfill and the driver "sees" as if the box is bigger. With isobaric the effect is much greater, also at much greater cost of output.

 

[audiofooled]

Please explain. You're simply putting two drivers in the same box, how does having them arranged "dual opposed" change anything with regards to Qtc?

Sorry, my bad, this refers to isobaric loading (see my edit). Dual opposed would bump the output (raise the Qtc) and reduce the vibration.

 

[Chrise36]

There is also the 6 order isobaric bandpass where both drivers radiate sound

Also a reason why the the dual system plays lower is probably because there is added mass from the air enclosed bringing the fs of the system
down

 

[Putter]

WinISD is perhaps the most popular bass box simulator, worth investigating

Dual opposed woofers share same airspace typically. Air volume in the box is an important factor that affects the low end behaviour of drivers when long excursion and air compression/movement happens. This will show in spl response of the unit and maximum spl it can give per frequency. Bass reflex tuning depends on box volume and port length, number of radiators is negligible.

Many dogmas and traditions of loudspeaker's bass performance come from era of drivers with short Xmax and poor power handling, and passive designs without use of signal eq or motional feedback. In this millenium we can bend those rules quite a lot (at least for domestic use) simply and with low cost by DSP and modern driver units, driven by cheap and efficient classD amplifiers.

Dual opposed in my eyes best suited for hifi 3-way speakers, as seen in eg. Vivid Audio Giya. Home theater and PA subwoofers aim for very low freq and high spl capacity, which still means very large cabinets and often some sort of horn to maximize efficiency, then dual opposed is not best giving benefit. I have personal experience with a DIY PPSL dual opposed with two sealed boxes side by side, with 15" woofers. A single Hypex DS2.0 easily drives it to intolerable spl in my HT room!

View attachment 104769View attachment 104770

I think you've got the wrong driver in there. That looks more like a tweeter than a woofer. I have seen that pic before and hope I'm not stealing a joke.

 

[Duke]

For the same box size, dual opposed isobaric will lower the Qtc and smooth the rolloff as if the box is twice as big but at a cost of 3 times more power for the same output. Also, it wouldn't go as low as a single driver in twice the bigger box.

That has not been my experience.

Back in the early 80's I built several homebrew isobaric subwoofers. To my ears they seemed to outperform what the math predicted. I borrowed some test equipment from the college I was attending and made some close-miked frequency response measurements, comparing a sub with two woofers in a sealed isobaric configuration in one cubic foot total internal volume, versus a single woofer (same woofer, a large Dynaudio) in a two cubic foot sealed box. My measurements seemed to confirm what my ears were saying, the isobaric enclosure behaved as if it had a higher system Q and it went deeper.

I don't claim to have an explanation for my observations, but I speculate that the published math for isobaric woofer systems fails to take into account the addition of at least some of the airmass in the isochamber to the moving mass of the cones. [Edit: That speculation now seems implausible to me, as the airmass in the isochamber was only 12 grams.]