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Multi-Way Conventional loudspeakers with crossovers

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Old 2nd September 2011, 03:43 PM   #51
Frode is offline Frode  Norway
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Invert half of the drivers and you have something like djk's PPSL: A Thread for those interested in PPSL enclosures

Frode
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Old 2nd September 2011, 05:39 PM   #52
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I would anticipate that (unlike the drawing above) you would invert the
drive polarities. I think this has been pointed out elsewhere (probably
Linkwitz) that it allows some cancellation of 2nd harmonic.

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Old 2nd September 2011, 05:54 PM   #53
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Quote:
Originally Posted by Nelson Pass View Post
I would anticipate that (unlike the drawing above) you would invert the
drive polarities. I think this has been pointed out elsewhere (probably
Linkwitz) that it allows some cancellation of 2nd harmonic.

Yes, the cancellation can yield quite an improvement when you are using less expensive drivers. Historically, I think there was a commercially available design from Electrovoice that used such a design

Keep in mind that the geometry of the cavity will act as a low pass filter. The smaller the better, although some clever person might actually use the LPF to their advantage in order to decrease higher harmonic distortion.
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Old 2nd September 2011, 05:54 PM   #54
Frode is offline Frode  Norway
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Quote:
Originally Posted by Nelson Pass View Post
I would anticipate that (unlike the drawing above) you would invert the
drive polarities. I think this has been pointed out elsewhere (probably
Linkwitz) that it allows some cancellation of 2nd harmonic.

Yes, that is correct. I was a bit sloppy with the drawing.

Frode
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Old 2nd September 2011, 07:39 PM   #55
Rudolf is online now Rudolf  Germany
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Quote:
Originally Posted by otto88 View Post
Rudolf

What do you think of the dispersion pattern: OB - would you build it slot loaded?
It is a matter of what you want to achieve. Folding a baffle will lead to some sort of quarter wave transmission line easily. That will define an upper frequency limit. But it will allow for a much narrower baffle in the bass region.
Combining a (folding) slot with a wide baffle doesn't make much sense to me. WRT the 9 dB difference I am very much with sreten. Simply tripling the air velocity by diminishing the area to a third doesn't give more efficiency. It is NOT the same effect as AMT.
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Old 2nd September 2011, 11:11 PM   #56
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Perhaps you are simply looking at it the wrong way.

Let's analyze it from another angle using a little physics:

You will agree that the volume of air displaced to the front and back
will have to be the same for practical purposes, the acoustic equivalent
of Kirchoff's law.

Acoustic energy is the product of volume displaced at a given pressure,
the acoustic equivalent of watts = volts X amps.

For a given signal, the pressure out the front is measurably higher at any
reasonable position or distance and it is in phase with the displacement of
the woofers. Therefore, there is more energy going out the front than the
rear.

If it is not sound, where did the energy go?

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Old 2nd September 2011, 11:43 PM   #57
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Accelerating the same mass a few times faster? I think that's what happens, but I'm not sure how well this higher velocity gets coupled to a greater area by abrupt dumping at the floor and middle of the baffle panel. I guess the simulator can show that.

Last edited by Andrew Eckhardt; 2nd September 2011 at 11:48 PM.
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Old 3rd September 2011, 12:09 AM   #58
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This is a simple physics problem. I don't think the simulator is particularly
going to help you with that.

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Old 3rd September 2011, 12:40 AM   #59
sreten is offline sreten  United Kingdom
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Quote:
Originally Posted by Nelson Pass View Post
You are saying my whole fallacy is wrong, and Heil transformers
obviously don't work as described.

But it's a fact that air moving at a higher velocity carries more energy
and this shows up as greater pressure.

When I said near field, I did not mean that I was sticking the microphone
in the slot - it is true that the farther away you get and as the frequency
goes lower the effect is diminished. I find that the effect is perfectly
adequate for listening purposes.

Hmmm .... your calling it a fallacy, if it is, it must be wrong.

How Hiel "air" transformers work has nothing to do with this case.

Efficiency is simply volume displacement at a given level, that is it.
The point of the Heil arrangement is to increase VD over planar,
it actually does this by more efficient use of the magnetic field.

By your "theory" the narrower you make the slot the greater the
efficiency increase, this simply does not happen, in the same way
small ports with high velocity are no more efficient than larger ones.

There is no useful effect, other than the phase and dispersion issues,
which may improve, and horizontal braces in the slot would also give
force cancelling - a reason I've seen something similar before.

Forward output is no greater than the rear output, inevitably.

rgds, sreten.

Regarding very dodgy physics, some of the arguments above would
apply to nearfield listening, hardly the intended purpose here ........

To have more frontal energy requires greater acoustic coupling.
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Last edited by sreten; 3rd September 2011 at 12:56 AM.
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Old 3rd September 2011, 12:54 AM   #60
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You are not addressing the problem I presented.

BTW, the "fallacy" statement is a famous joke by Marshall McLuhan.



ps "Efficiency is simply volume displacement at a given level, that is it"

That's not it.

Energy (work) is volume displacement times pressure.

Last edited by Nelson Pass; 3rd September 2011 at 12:58 AM.
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