[fergs1]

Greetings, I have been thinking about this for a while, could you use two drivers  in the h frame clamshelled and wired out of phase, and would it be worth it. If it seems like a worthwhile thing to do, ( i guess less distortion, greater sensitivity) would someone whose name begins with M and ends in artin J King care to simulate it Or anyone else for that matter. The depth would have to be increased slightly so the magnets of the alphas didn't stick out the end of the H frame. I'm interested to hear what you all think
                                                              cheers  fergs

[panomaniac]

Clamshell?  Do you mean sorta face to face at an angle?

Gary P runs 2 15s in an H-frame that are "nested" at an angle. (about 43 degs, IIRC).  Both face the same direction. Maybe it's actually a W frame.   Works great. Very clean, very deep bass.

[fergs1]

Greetings Panomaniac, I certainly do mean face to face but in the standard baffle of MJK's h frame so each speakers arse points out towards the opening on either side.          cheers  fergs

[scorpion]

Hi fregs,

I'll give you some flesh on the bones. Clamshell or not, just test, opinions differ !
Three simulations should give a good picture of what to expect.

All are with an H-frame 32" (H) x 16" (W) x 16" (D) inner measures including internal baffle.

1st, No LP crossover applied:



2nd, LP at 125 Hz 2nd order Linkwitz-Riley:



3rd, LP at 80 Hz 4th order Linkwitz-Riley:



/Erling

[D OB G]

Hi fergs1,

Not quite what you are talking about, but in light of Linkwitz using woofers facing backwards and forwards, and wired out of phase to reduce second harmonic distortion, two interesting issues arise.

I contacted Tymphany in regard to using XXLS woofers.  They insisted that mechanical noises, if they occurred at all, would be greater than the second harmonic distortion reduction. i.e. don't worry.

And Geddes insists insists that second harmonic distortion, and indeed total harmonic, whilst measurable, unless ridiculously high does not correlate in double blind trials with audibility!!! i.e. don't worry!!!

With surprise,

David

[panomaniac]

Right, it certainly ins't the 2nd harmonic that we need to worry about.

[Viridian]

Greetings Panomaniac, I certainly do mean face to face but in the standard baffle of MJK's h frame so each speakers arse points out towards the opening on either side.          cheers  fergs

Hi Fergs,

I would wonder what might happen as well. I would have thought the same things as yourself: greater sensitivity and lower distortion. I might just try it in standard OB since I don't have an H-frame to try it with.

Add: In looking at Linkwitz I don't see that he shows there to be an advantage. Perhaps I'm not looking in the right spots.

[JohnR]

Clam-shell will have half the sensitivity compared to a single driver (i.e. 3dB less). The main reason for doing this is the reduced Vas i.e. smaller box (*). But for open baffle I think it would be better to use the two drivers separately - greater sensitivity and displacement.

(*) Here's an example of subs with clamshelled drivers:

[mcgsxr]

I explored isobaric loading of OB woofers years ago, and found the disadvantage to be swept area - by using 2 woofers mounted conventionally, you double the swept area, and drive more air.

I use a clamshell loaded isobaric sub box in my car, cause I did not want to use up trunk space...

[scorpion]

My limited English, interperting clamshell, probably led me wrong, my simulations show what will happen with two Alphas in an H-frame. If they are pointed in the same direction and wired in parallel or in different directions and connected out of phase in parallel, like in the Linkwitz Orion and Phoenix prototype, doesn't matter but they are certainly not mounted isobaric. Perhaps my given measures for the H-baffle could have indicated that. Isobaric mounting has no advantage in OB at all.

/Erling

[iON]

I'm still not sure what clamshell means but.. as I understand you want to mount the alphas in a push-pull config?

Aside from the fact that push-pull (and isobaric) setups don't have a stellar reputation in hifi circles, Think of it this way:

Mounting the two elements push-pull would, if we simplify things, be the same as having one single element with a stronger motor. That would effectively lower the Qts. Usually that is not what you strive for when dealing with OB's.

Add also the consideration that you are only using half of your available driver area to move air and I think you would agree that such a design would not considered optimal. 

Hope you found the information helpful.

Cheers!

- Jon