[woodsyi]

I came across this description from Huff Loudspeakers.  http://www.huffloudspeaker.com/subs.html

Sub One (the pair that's on sale on Audiogon for $3800)

The Sub One is a no compromise design. It uses twin extremely long throw 12" woofers in a push - pull configuration for quick, tight, accurate bass.

The push - pull configuration allows for very deep bass (and a low Q response curve) in a relatively modest enclosure size. A manufacturer would have to build a cabinet twice as large to go as low without compound loading.
   
Sub

18" Sub One shown in Quilted Maple

(Click on photo for a larger view.)
A note on compound loading: the two drivers are mounted face to face, doubling the motor power. The inner woofer drives the enclosure, providing a neutral atmospheric pressure area between the drivers, so the outside driver can move instantly and effortlessly against little resistance. Most importantly, it provides quicker acceleration and braking for the outer driver. This allows it to start and stop instantly when the signal starts and stops, so there is no overshoot to muddy the sound. You will feel the difference.

The woofer cabinet is a sealed design, so there is no "box echo", or resonant cavity effect coloring the music. The flatter low frequency response curve rolloff of the sealed design (12 dB slope per octave vs 24 dB rolloff for a ported design) closely matches the typical "room gain" at the rolloff frequency, therefore producing flat bass to below 20 Hz. in most rooms, without the inevitable coloration induced by ported or even servo designs. This design produces the most natural sounding bass possible. Non-downfiring.

The Sub One comes in two sizes: 16" diameter x 36" tall, and 18" diameter x 26" tall. Both have the same internal volume, and the same response characteristics. You may choose the one that best fits your room decor and the sub location. We recommend using them in matched pairs.

Sub Ones are available in beautiful wood veneers to match the satellites, or in solid colors.

I am having a conceptual problem understanding how this works.  Would some body explain please.  I have put two speakers face to face (driver to driver) and run them out of phase to break them in.  In this case the two speakers pushed and pulled their way to a cancellation of sound output.  What is the difference here?

[Jazz and Baroque]

Rim,

Your set-up had both drivers exposed to the room.  So the two pressure waves cancelled out. 

In the Huff configuration they say
"The inner woofer drives the enclosure, providing a neutral atmospheric pressure area between the drivers, so the outside driver can move instantly and effortlessly against little resistance." 

I think that this means that the inner woofer is between a sealed box and a second chamber that also contains the "external" woofer.  The inner woofer sucks back on the second chamber to provide reduced back pressure on the outer woofer.  The outer woofer is what creates the pressure wave. 

The only purpose of the inner woofer is to reduce the back pressure on the outer woofer.

Does this help??
Mike

[woodsyi]

Mike,

Yes, it helps.  How does the back wave of the inner driver dissipate?

[Mike Dzurko]

Mike,

Yes, it helps.  How does the back wave of the inner driver dissipate?

Just like any other sealed box woofer. The compound (or isobarik) loading simply cuts the Vas of the driver pair in 1/2 from what a single driver would be. A fairly costly way to 1/2 box volume . . .

[Jazz and Baroque]

Some people really like small sub-woofers.

[woodsyi]

Mike D,

If volume was the limiting factor, would this get to the lowest frequency at a given volume?

[Mike Dzurko]

Mike D,

If volume was the limiting factor, would this get to the lowest frequency at a given volume?

It's one way. It essentially cuts the required box volume in 1/2, but of course you need space for the extra driver so you don't gain the full space. 15 years ago and previous to that this was how we did our subs. However, we have since found that well designed sub electronics can gain you even more.  With a compound load you are still limited in extension by the TS parameters of the driver. With electronics, you can reduce box volume and lower extension . ..  . limited only by the power available and driver excursion limits. 

[Imperial]

Like Vince Bruzzese does with Mani-2 (Totem acoustics) albeit with more freq range in mind..
(Totems inner driver actually only work in parts of the outer drivers range. Below 400-200hz?)
What you also achieve is that the drivers cancel out some of the inherit non-linearity's of each other.
If you guys know of the Whise patent (Parametric Acoustic Modeling, PAM) this is also a very interesting type of approach regarding subwoofers to achieve flat in-room response.
Arnie Nudell (Pipedream/Genesis) and Martin Schützenauer(WLM) Also uses this push-pull tech I think.
Their subs are also "cylinders".. Actually, the Huff looks very much alike the Nearfield "Tribal drums"...

Imperial

[Imperial]

The only purpose of the inner woofer is to reduce the back pressure on the outer woofer.

Does this help??
Mike

I think this is a slight simplification...

What happens is that the inner woofer + chamber presents to the outer woofer a small volume of air (the volume between the two drivers that "behave" like a very large volume of air, but with a tricked out set of properties, helping the outer woofer to track the signal much more closely. What the outer woofer "see" is a volume far greater than just double the internal volume of air.
This volume of air can be given quite a lot of different extra functions as well. Lots of ways to do this.
This setup also function as a sort of built in low pass filter, so that the outer driver will not be able to go higher than a given freq.

...

[randytsuch]

Brian from Rythmik talks about two drivers in the same box

Go to the bottom of the page from this link
http://www.rythmikaudio.com/DS12.html#DS12D

Sounds like less cabinet vibration is an advantage to this type of sub.  In a sealed sub, there would be much less pressure change within the cabinet, so less vibration, which should result in lower distortion.

Randy

[Imperial]

The Rythmik pictures does not display the Huff setup.
There, one driver is inside an isobaric. The other driver is the "port", but they are still inside the cylinder, and it is not vented...
It has "slots" that most likely equal a port in function and volume.

Hey... I'm not a subwoofer designer.. so please correct me if I'm off here! 

I think I've read something a while ago that using a pair of the larger Ohm speakers as subs is suppose to be simply amazing?
You'd have to have silly amounts of power I can imagine!!!



Imperial

[randytsuch]

The Rythmik pictures does not display the Huff setup.
There, one driver is inside an isobaric. The other driver is the "port", but they are still inside the cylinder, and it is not vented...
It has "slots" that most likely equal a port in function and volume.

Hey... I'm not a subwoofer designer.. so please correct me if I'm off here! 

I think I've read something a while ago that using a pair of the larger Ohm speakers as subs is suppose to be simply amazing?
You'd have to have silly amounts of power I can imagine!!!



Imperial

Here is a picture from the bottom of the page I pointed to


I was referring to figure A), the Push Pull configuration.

If the drivers are wired out of phase, then you have push pull.  Both drivers will be either going in, or out at the same time (relative to the cabinet), but one will be moving forward while the other is moving backward.

I am a little confused by Huff's page, because it says the drivers are facing each other.  They don't show a picture of the driver mounting, so I am not sure how they do that and get push pull.

Randy

[Mike Dzurko]

The Rythmik pictures does not display the Huff setup.
There, one driver is inside an isobaric. The other driver is the "port", but they are still inside the cylinder, and it is not vented...
It has "slots" that most likely equal a port in function and volume.

Hey... I'm not a subwoofer designer.. so please correct me if I'm off here! 

I think I've read something a while ago that using a pair of the larger Ohm speakers as subs is suppose to be simply amazing?
You'd have to have silly amounts of power I can imagine!!!



Imperial

Here is a picture from the bottom of the page I pointed to


I was referring to figure A), the Push Pull configuration.

If the drivers are wired out of phase, then you have push pull.  Both drivers will be either going in, or out at the same time (relative to the cabinet), but one will be moving forward while the other is moving backward.

I am a little confused by Huff's page, because it says the drivers are facing each other.  They don't show a picture of the driver mounting, so I am not sure how they do that and get push pull.

Randy

Actually A is a simple compound load and B is a push pull design where you'd wire the drivers out of phase electrically and that would put them in phase mechanically.

[Mike Dzurko]

But an even easier and more effective way to accomplish B (for sub use) is to mount the drivers face to face . . . . you eliminate one cabinet structure by doing this . . .

[randytsuch]

But an even easier and more effective way to accomplish B (for sub use) is to mount the drivers face to face . . . . you eliminate one cabinet structure by doing this . . .

Ok Mike, I am now more confused than usual.

You know way, way more about this subject than I do, but I thought the animation from the link below shows push/pull
http://www.avsforum.com/avs-vb/showthread.php?p=12398727#post12398727


Randy

[Mike Dzurko]

But an even easier and more effective way to accomplish B (for sub use) is to mount the drivers face to face . . . . you eliminate one cabinet structure by doing this . . .

Ok Mike, I am now more confused than usual.

You know way, way more about this subject than I do, but I thought the animation from the link below shows push/pull
http://www.avsforum.com/avs-vb/showthread.php?p=12398727#post12398727


Randy

Randy:

Part of why I jumped in was that I saw terms being used incorrectly. That of course does lead to confusion.  To restate, a basic compound load is one in which a second, usually identical driver is installed behind the first. The two drivers together act essentially like a single driver with 1/2 the VAS.  Push - pull refers to one driver being "flipped" and then wired out of phase to be mechanically in-phase.  BTW, you can do a push-pull setup without using a compound load. For example, if you had two identical drivers mounted on the front baffle and one had the magnet end facing out and they are wired out of phase . . .

[woodsyi]

I can understand the compound loading more easily.  The Huff states that their drivers face each other and there are being push/pulled.  Am I to understand then that the Huff set up has air coming out it's rear end, so to speak?   It's a compound farting machine? 

[Mike Dzurko]

I can understand the compound loading more easily.  The Huff states that their drivers face each other and there are being push/pulled.  Am I to understand then that the Huff set up has air coming out it's rear end, so to speak?   It's a compound farting machine? 

Without seeing it, can't say for sure, but sounds right, good analogy!