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 Multi-Way Conventional loudspeakers with crossovers

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Patrick Bateman
diyAudio Member

Join Date: Oct 2006
Location: San Diego
Quote:
 Originally posted by MaVo You have to take into account that this box uses a 12 inch coaxial driver for mid, so the crossover point will be probably 3 octaves below this 2250hz and thats why the holes wont have much effect.
If that's the case, then my first guess, in post #2 makes sense.

The designer is using a chamber in front of the woofer to roll off the highs, just like a bandpass box.

That's quite clever I think - he's getting the dipole radiation pattern of a dipole, along with the distortion-filtering aspects of a bandpass.

Let's do the math real quick, to see if my hunch is valid.

To figure out the tuning frequency of the chamber, we use this formula:

(2 * fs) / qes

for an Eminence Alpha 15A, that's (82 hz / 1.53 ) = 53.59hz

http://www.parts-express.com/pe/show...number=290-407

And then you tune the backchamber to that frequency.

But there IS NO backchamber. So the Fb of the backchamber is the same as the Fs of the woofer which is...

41hz.

So yeah, looks like this would work. The Fb is off by a third of an octave, but that won't make much of a difference.

 31st July 2009, 04:42 PM #12 dlneubec   diyAudio Member   Join Date: Jan 2006 Location: Indiana FYI, The specs say the woofers to mid crossover is at 100hz (LR8-DSP active) and the mid to tweet is at 900hz (BW3-passive). __________________ Dan N.
 31st July 2009, 04:48 PM #13 Godzilla   diyAudio Member     Join Date: Nov 2005 Location: New York >>> The "Aperture Bass Propagation technology" works by impressing the customer with fancy words and by this raising the amount of money he will spend for the speaker. In its own way, this is an impressive technology. LOL... i don't see where the other driver is? Godzilla
Patrick Bateman
diyAudio Member

Join Date: Oct 2006
Location: San Diego
Quote:
 Originally posted by jamikl I'm at work and can't sim this now. It seems to be the same as a slot loaded box without the box. Could be modelled in Horn response with no rear chamber, front chamber same as speaker volume on inside of cone and surround and a conical horn with maybe 25mm length and no expansion. Might look good until combined response is done for back to front cancellation. I have been looking at slot loading an open baffle myself to keep the directivity higher. As I said, can sometimes look good until the cancellation comes into the sim. jamikl
I modeled it a different way. I modeled it as if the enclosure was backwards. So there's a ported *rear* chamber, with a six inch port that's one half inch deep. (We don't know the depth, but we can guess.) The volume under the cone should be about 3.3liters. Again, we can only guess. Reducing the volume will change the tuning frequency of the bandpass.

Here's the modeled frequency response.
Attached Images
 alpha2.jpg (38.6 KB, 946 views)

Patrick Bateman
diyAudio Member

Join Date: Oct 2006
Location: San Diego
Quote:
 Originally posted by jamikl I'm at work and can't sim this now. It seems to be the same as a slot loaded box without the box. Could be modelled in Horn response with no rear chamber, front chamber same as speaker volume on inside of cone and surround and a conical horn with maybe 25mm length and no expansion. Might look good until combined response is done for back to front cancellation. I have been looking at slot loading an open baffle myself to keep the directivity higher. As I said, can sometimes look good until the cancellation comes into the sim. jamikl

Here's the parameters I used. Note that the "horn" is actually the cone of the woofer itself. It has a diamter of fifteen inches and a depth of 1.5". I also added a baffle that's 20" wide.
Attached Images
 alpha1.jpg (60.0 KB, 908 views)

Patrick Bateman
diyAudio Member

Join Date: Oct 2006
Location: San Diego
Quote:
 Originally posted by MaVo You have to take into account that this box uses a 12 inch coaxial driver for mid, so the crossover point will be probably 3 octaves below this 2250hz and thats why the holes wont have much effect.
I don't know why I didn't think about the obvious reason to use a bandpass chamber in a dipole.

It reduces the excursion!

duh, how did I miss that?

So you tune the front chamber carefully, and you can double or quadruple the power handling, by reducing the excursion.
Attached Images
 alpha3.jpg (32.2 KB, 913 views)

Patrick Bateman
diyAudio Member

Join Date: Oct 2006
Location: San Diego
And a schematic of this strange beast. Cone on the right, coupling chamber on the left. The port is is 6" in diameter by 1/2" in depth. (just guessing based on the pics)
Attached Images
 alpha4.jpg (24.0 KB, 949 views)

gedlee
diyAudio Member

Join Date: Dec 2004
Location: Novi, Michigan
Quote:
 Originally posted by Patrick Bateman I don't know why I didn't think about the obvious reason to use a bandpass chamber in a dipole. It reduces the excursion! duh, how did I miss that? So you tune the front chamber carefully, and you can double or quadruple the power handling, by reducing the excursion.
Hey John

I don't follow the cone excursion reduction. With a 100 Hz LP there will be no effect to the excursion below 100 Hz.
__________________
Earl Geddes Gedlee Website

Patrick Bateman
diyAudio Member

Join Date: Oct 2006
Location: San Diego
Quote:
 Originally posted by gedlee Hey John I don't follow the cone excursion reduction. With a 100 Hz LP there will be no effect to the excursion below 100 Hz.
There's a 48db/octave electronic filter at 100hz.

But the coupling chamber in front of the woofer forms a physical lowpass. If they tuned it at ((2 * FS) / qes), then the reduction in excursion would occur at 53.59hz.

So that seems quite clever. You get a reduction in excursion at the tuning frequency, a reduction in 2nd and 3rd harmonic distortion, and a dipole radiation patterns.

If you're into dipoles, this seems like a serious improvement.

 1st August 2009, 09:58 AM #20 cnclld   diyAudio Member   Join Date: Jan 2005 Location: - How much does this affect the front response below the xo point versus the rear? I guess that could lead to a very strange radiation pattern (not a dipole).

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