[Lazz]

I'm not sure if this has been asked before. But what difference does it make if using the 12" woofers with the plate amps but mounting the woofers in the traditional way both facing forward and flush with the front baffle.

[Guy 13]

I'm not sure if this has been asked before. But what difference does it make if using the 12" woofers with the plate amps but mounting the woofers in the traditional way both facing forward and flush with the front baffle.

Hi Lazz and all Audio Circle members.
I have the same question for Danny.
Guy 13

[Jonathon Janusz]

If you're asking regarding the open baffle woofers that most are configuring with an opposed facing in an H-frame baffle, mounting them as you describe with an open back an no change otherwise in overall dimensions gives you:

- a cardioid shaped dispersion pattern (more output to the front than back, nulls not directly to the sides) different than the equal front-back output with nulls directly at the sides in the h-frame design, also causing changes in output with the change from an H-frame to a U-frame

 - additional challenges in dealing with cabinet resonances as the comparative size of the unbraced side panels doubles in size

- without the drivers firing opposite each other, maybe some additional cabinet/baffle vibrations as the drivers would no longer be firing equally and opposing to reduce/deaden/negate these vibrations

In short, a completely different speaker.  Not necessarily better or worse, but a different tool for the job depending on what the rest of your system/room is going for.  I can't remember where I found it (if you search for old threads discussing U-frame baffles you may find it as I think I linked to it from here on AC) but I read a short essay a while back that neatly explained the basic points.

[jparkhur]

Remember too, the woofers are out of phase when wired(they are opposite mounted too)  (if i remember correctly) thus they both push forward and then backwards together..




JON

[Danny Richie]

I'm not sure if this has been asked before. But what difference does it make if using the 12" woofers with the plate amps but mounting the woofers in the traditional way both facing forward and flush with the front baffle.

The problem with making them flush with the front baffle is that you shorten the front to back wave cancellation. This greatly effects the output levels in the lower frequency ranges. You can create a set of wings to each side making it a U shaped frame, but one must be careful not to create a resonance cavity when doing this. There is also a ton of pressure created by these drivers in a U shaped design and the side walls must be very thick and heavy to support the pressure. Heavy bracing will help too but restricts air flow and creates additional pressure.

The H frame is a much better solution. And facing them in opposite directions is supposed to cancel out some odd order distortions. It clearly balances out the load and makes the speaker more stable.

[Lazz]

Thx guys for the response. I'm just trying to understand a little bit more of the ob principles.
Danny if you were to have the open back box surrounding the woofers the same size/depth as the original design but both facing forward, wouldn't that make the cavity resonance the same as per the original. I understand what you are saying in regards to shortening of the back wave cancellation. Mounting them on the same plane above each other in opposite directions looks like it doubles the distance from the front to back wave. Is there any trade off in regards to sound quality that bass is firing at you from one of the rear baskets from one of the woofers, or doesn't it have any affect due to the low xover point. Regards.

[Danny Richie]

Danny if you were to have the open back box surrounding the woofers the same size/depth as the original design but both facing forward, wouldn't that make the cavity resonance the same as per the original.

If they are both on an H frame mounted in the middle of the box the only thing that changes is the cancelling of some odd order distortions and you loose the stability that you get from them facing opposite ways.

Mounting them on the same plane above each other in opposite directions looks like it doubles the distance from the front to back wave.

Actually it is the depth of the side panels that separates the front to back waves. It doesn't matter which way they are facing in that regard.

Is there any trade off in regards to sound quality that bass is firing at you from one of the rear baskets from one of the woofers, or doesn't it have any affect due to the low xover point. Regards.

The woofers sound the same from either direction.

[Jonathon Janusz]

I did a quick google search and found the following links to read up on some theory for you:

http://www.quarter-wave.com/OBs/U_and_H_Frames.pdf

and:

http://www.musicanddesign.com/u_frame.html

Cheers!