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Old 21st February 2014, 11:56 PM   #11
ra7 is offline ra7  United States
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I don't think you need to do this instantaneously, as is being proposed here. The standing waves can be determined based on room dimensions and the source (i.e., loudspeaker) locations in the room. Once you determine the variations at the listening position, you can apply EQ to your sources, or you can place more sources, as in the patent, around the room to cancel the effect of the standing waves. In fact, I am running my system this way.

You need DSP (miniDSP), multiple amps and subs, and measurement programs, such as REW. REW will even generate the EQ for you. It has a superb room modeling module as well.
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Old 22nd February 2014, 12:31 AM   #12
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Quote:
Originally Posted by Nelson Pass View Post
I think you have this reversed. Pressure which pushes the cone in, met with
forces which push the cone out, will result in greater pressure.

We want zero pressure, practically speaking, reduced pressure.

Thank you for the correction. I made the mistake of equating Air Pressure [Force per unit area] with Force. There are 3 possible outcomes from AcAb:
  • The cone does not move at all [i.e. locked] when the external and internal Forces acting on it are equal. Get an ideal zero Air Pressure at the cone's surface. The offending standing wave is no more.
  • The impinging external force somehow exceeds the reactive internal force. Get a diminished air pressure at the cone's surface. This standing wave is partially wiped out.
  • The internal force somehow exceeds the external force. Get a phase inverted outgoing wave. As if the original wave is reflected, and the loudspeaker now behaves as a normal subwoofer.
Best regards.
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Old 22nd February 2014, 12:58 AM   #13
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Quote:
Originally Posted by ra7 View Post
I don't think you need to do this instantaneously, as is being proposed here. The standing waves can be determined based on room dimensions and the source (i.e., loudspeaker) locations in the room. Once you determine the variations at the listening position, you can apply EQ to your sources, or you can place more sources, as in the patent, around the room to cancel the effect of the standing waves. In fact, I am running my system this way.

You need DSP (miniDSP), multiple amps and subs, and measurement programs, such as REW. REW will even generate the EQ for you. It has a superb room modeling module as well.
Thank you ra7 for your comments. You have a sophisticated system , and I admire your ability to understand and manage it. Way above my abilities; but I hope to understand too. Maybe in the future you may consider comparing the Pass approach with your current system; as you already have amps and subs.
Best regards.
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Old 22nd February 2014, 02:11 AM   #14
The Dastardly Dad of Three
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Antionel, this can't be right ?
"The cone does not move at all [i.e. locked] when the external and internal Forces acting on it are equal. Get an ideal zero Air Pressure at the cone's surface. The offending standing wave is no more."

If the cone is in fact locked all that would happen is that the waves get reflected back into the room ? So a few bricks could have the same effect ?

Maybe the cone needs to move inwards to create rarefaction instead?

Interesting investigation btw, thanks...
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Old 22nd February 2014, 09:52 AM   #15
Zen Mod is offline Zen Mod  Serbia
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Old 22nd February 2014, 12:29 PM   #16
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Quote:
Originally Posted by kasey197 View Post
Antionel, this can't be right ?
"The cone does not move at all [i.e. locked] when the external and internal Forces acting on it are equal. Get an ideal zero Air Pressure at the cone's surface. The offending standing wave is no more."

If the cone is in fact locked all that would happen is that the waves get reflected back into the room ? So a few bricks could have the same effect ?

Maybe the cone needs to move inwards to create rarefaction instead?

Interesting investigation btw, thanks...
Hello kasey197. Great to hear from you. Thank you for your comments. The undetlined in your post got me thinking of this example which I hope may clarify your question. Envision two athletes who are arm wrestling. Their arms are upright,they grimace, pant,etc... But are they faking this duel [zero force exchange], or are they truly competing. Either way, their arms appear or actually are motionlessr to a spectator. Either way, athlete1 moves its arm one degree of vertical to the right while athlete2 senses this motion of athlete1, and reacts with a force to restore the original status quo; be it faking or competing. Also, It seems to me that I am explaining [to myself] the mechanism of a DC servo and/or loop feedback, and/or my understanding of Le Chatelier's Princinple.
Best regards

Last edited by Antoinel; 22nd February 2014 at 12:34 PM. Reason: correct Chatelier
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Old 22nd February 2014, 09:50 PM   #17
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Default Amplifier schematic of Acoustic Absorber

I am glad to say that I see in it contributions from Mr. Pass, Zen Mod, lhquam, buzzforb, generg, Tea-Bag and all of you who posted in the diyF6 Amp thread. Note the following:
  • The amp inverts the phase of input signal [Vi].
  • It is a current source amp prior to loop feedback which is mediated by the subwoofer driver.
  • This particular negative feedback can be called "Transformer-Coupled Schade and/or Pass". A similar name maybe "Electromagnetically-Coupled ...."
  • The dual coil subwoofer driver is written as a 1:1 transformer. Note the phase symbols on it.
  • As shown, the amp is stable or silent. But it oscillates when the connection of VC1 or VC2 is reversed; due to Schade and/or Pass positive feedback.
  • Four versions of the subwoofer exist; with and without a passive low pass filter ahead of the voice coils.
  • Vo centers at ~0 V with a trivial DC offset of <50 mV.
  • Each voltage regulator chip operates like a depletion device. Idle current is ~300 mA through each.
Coming up will be pictures of the prototype amp, and the subwoofer which was a commercial product by MCM.

Best regards
Attached Images
File Type: jpg AcAbAmp.jpg (297.4 KB, 563 views)
Attached Files
File Type: pdf AcAbAmp.pdf (25.7 KB, 8 views)

Last edited by Antoinel; 22nd February 2014 at 09:52 PM. Reason: tweak
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Old 23rd February 2014, 09:36 PM   #18
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Default Prototype AcAb Amplifier

The picture of the prototype AcAb amp is shown. Nothing fancy. I will continue to use it to generate data. Note the following:
  • The tubes are plastic pill containers. Two identical sets are shown flanking the heatsink.
  • Each set has a container for a 10,000 uF/50V cap, for a 4 Ohm/40W non-inductive resistor, for a 1 Ohm/5W and wirewound resistor, and for 1/2 Ohm/5W and ww resistor. The ww resistors are connected in paralell to give 0.33 Ohms as shown in the schematic of the previous post.
  • The tube housings protect against shorts.
  • The + and - 15 VDC regulated PSU is not shown.
  • The input [Vi] for voice coil 1 is the centerpoint of the 1,000 uF capacitor as shown on the far right of the picture sitting atop a small block of wood.
  • The output [Vo] to voice coil 2 is shown on the far left side of the picture.
  • The heatsink gets lukewarm with the chips dissipating ~9 W.
Best regards
Attached Images
File Type: jpg img_2803.jpg (541.4 KB, 526 views)
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Old 23rd February 2014, 11:39 PM   #19
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Default A dual coil subwoofer for the Acoustic Absorber

I bought a pair of the pictured subwoofer from MCM Electronics a while ago. The white background under the loudspeaker is snow. This subwoofer was designed to sit in the corner in a floor or a wall joist. In the second photo, I show its [speaker] connectors to the power amp. Immediately beneath them is a dual crossover; with individual outputs to R and L satellite speakers. I bypassed both crossovers for this study. But I have the twin of this subwoofer with its crossovers in place for a comparison of perfomance to be done in the future.

Best regards
Attached Images
File Type: jpg IMG_2801.jpg (483.8 KB, 497 views)
File Type: jpg IMG_2799.JPG (891.6 KB, 338 views)
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Old 5th March 2014, 04:15 PM   #20
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Default Moving forward

Hello everyone. The voltage gain of the current source amp driving an 8 Ohm non-inductive power resistor is [Av = 40 at 100 Hz.]. Divide this result by the value of the load [8 Ohm] to get a transconductance; Gm = 5 Amps out per unit input Vi.


The attached pictures declare these important observations.
  • The impedance of each voice coil is 8 Ohms.
  • I disabled the commercial crossover network which came with the subwoofer.
  • Must have a Zobel across VC1 to prevent oscillation of the assembly. Its purpose is to neutalize the rising impedance of "inductance" with increasing frequency. This Zobel [not optimized] is an 8 Ohm non inductive resistore in series with a 70uF NP electrolytic.
  • The Zobel across VC2 is less important than that across VC1. It is the classical 10 ohms in series with a 0.1uF film cap seen in commercial amps. Its presence sharpens the low frequency noise trace seen on the scope, and/or gets rid of blur riding on it.
  • There is room for a Low Pass filter in series with VC2. This is like that shown and taught in Fig. 3A of the article by Mr. Pass which is entitled "Current Source Crossover Filters"
The upcoming post will show the method[s] used to test the operation anof the Acoustic Absorber.

Best regards.
Attached Images
File Type: jpg AcAb1.jpg (249.3 KB, 326 views)
Attached Files
File Type: pdf AcAb1.pdf (21.3 KB, 8 views)
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