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Old 5th March 2014, 11:42 PM   #21
labjr is offline labjr  United States
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I like those pill bottles. Addicted to audio
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Old 6th March 2014, 01:41 PM   #22
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Quote:
Originally Posted by labjr View Post
I like those pill bottles. Addicted to audio
It is great to hear from you. Your remark inspired these thoughts. It connected, pills [e.g. Statins], addiction [ingested daily] and audio [promotes good health]. Addicted to audio is mostly diyaudio; which differs in meaning from audiophile. Come to think of it; life is one mother sum of countless addictions.

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Old 7th March 2014, 08:18 PM   #23
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Default This is it.

The attached diagram of the Acoustic Absorber is a practical device like that taught by Mr. Pass in his attendant patent. Note the following which also include recent improvements and simplifications:
  • The schematic is the same as a phase inverting [operational] amp.
  • Except that the voice coils [VC1 and VC2] of the subwoofer are the input and feedback elements instead of classical resistors.
  • I removed the 0.33 Ohm degeneration resistors which appeared in the full-blown schematic of the amp in a previous post.
  • Thus, this revised current source power amp [CSPA] operates at a certain maximum open loop voltage gain or transconductance [TBD].
  • VC1 is bypassed with a 1uF film capacitor. This is a must to prevent oscillation. Higher cap values are not relevant.
  • A Zobel [0.2 Ohm in series with 47 uF electrolytic] between the output Vo and common lowers output noise down to ~5 mVp-p; as seen on scope.
  • Note the phase [shaded triangles] on the voice coils. These connections go with a phase inverting CSPA. This is the correct/right connectivity which enables the destruction of standing waves.
  • The Acoustic absorber is stable [did not oscillate] when the leads of one voice coil were reversed relative to the other. But; it may augment rather than destroy standing waves which is contra to the desired objective.
The upcoming post will discuss bench testing the Acoustic Absorber so as to demonstrate its operation.

Best regards.
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File Type: pdf AcAb2.pdf (18.4 KB, 11 views)
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Old 8th March 2014, 07:05 PM   #24
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Default Testing The Acoustic Absorber

The Acoustic Absorber [AcAb] was tested as follows. Its subwoofer has a twin [I actually bought 3 such subwoofers at the time] which is fully operational; meaning I did not disable its commercial crossover network; like I had already done to the AcAb subwoofer. Both loudspeaker boxes were put on the floor with their loudspeaker drivers facing each other; like Kissing Gouramis, or mirror images. The attached picture is the testing setup, and shows the following.
  • The Right subwoofer is the intact twin. It is driven by a voltage source power amp [brown wire] fed by a signal generator. The pill tubes contain 8 Ohm power resistors. They attach to the satellite ports as loads.
  • The Left loudspeaker is the AcAb subwoofer. The green cable goes to VC1 and is the "microphone". The red cable goes to VC2 and is the "speaker".
Here is the stepwise procedure:
  1. Turn power on to the signal generator and set frequency at 50 Hz.
  2. Turn power on to voltage source power amp [VSPA]. It has a built in volume control which is ideal in this set up.
  3. The current source power amp [CSPA] in AcAb is not powered yet or is off.
  4. Put the leads of a scope between Vo [of CSPA] and ground.
  5. Advance the volume control on [VSPA] to energize the Right subwoofer [sound wave generator], and to simultaneously get a 400 mVp-p at Vo of CSPA. I had a standing wave at the cone of cone of AcAb, and vibrating it too.
  6. Measure also with the scope [Vi] which was 200 mVp-p.
  7. Now turn power on to CSPA.
  8. The new Vo as measured by the scope dropped to ~15 mVp-p. This was a roughly 26 fold reduction.
  9. The new Vi as measured by the scope diminished to ~7 mVp-p. This was roughly a 28 fold reduction.
  10. Points 8 and 9 said that sound pressure at the cone of AcAb is greatly dimished [a factor of ~27]. Or the parent sound wave impinging on the AcAb cone was effectively neutralized. This is how I see and explain via this test setup this invention by Mr. Pass.
  11. Points 8, and 9 also showed that the initial voltages at Vi and Vo were reduced together to ~zero volts; not one or the other. This system is not fighting itself, and both VCs are working together toward the same objective to null air pressure at the surface of their common cone.
I'll put the AcAb subwoofer in a corner of the music room, and test it in action.

Best regards.
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Old 9th March 2014, 11:04 PM   #25
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Default The proof is in the pudding

I listened to the songs Billie Jean [Jackson], Borderline [Madonna],and Sweet Dreams [La Bouche] to assess the performance of the Acoustic Absorber [AcAb]. The subwoofer of AcAb was put in the corner behind the Left speaker of the audio playback sysytem. The objective performance of AcAb was as follows:
  • To start, electrical power to the current source power amp [CSPA] in AcAb was not turned on.
  • Attached the probes of a scope to Vo of CSPA; set at 5 mV per division.
  • Played a song from the above set and watched the trace of the scope. It detected sine waves of various amplitude [up to 40 mVp-p] dancing on the screen. Clearly there was a detectable set of sounds across VC2.
  • Turned on power to CSPA. The trace of the scope became flat at ~0 V. The set of sounds at the cone have practically disappeared; akin to the action of a notch filter.
The subjective performance of my audio system wirh AcAb engaged agreed with the patent's objective which is to improve the quality of a reproduced audio event on a playback system in a generally rectangular room. The impulse bass in the opening statements of the above songs was clear, detailed with a fast attack and decay. Music filled and easily expanded in the room. The sound from the main Left speaker was affected more so than the R speaker. The Left speaker [AcAb behind it] presented a 3-D performance with a rich/vibrant output as compared with the R speaker.

I'll add more detail in a future post.

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Old 10th March 2014, 12:08 AM   #26
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Congratulations on a successful experiment.
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Old 10th March 2014, 12:21 AM   #27
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Quote:
Originally Posted by BobEllis View Post
Congratulations on a successful experiment.
Thank you. Any great sound system will soundeven better after taming/breaking up standing waves in the music listening space.
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Old 17th March 2014, 10:05 PM   #28
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Default Additional useful tests on Acoustic Absorber

Hello. The attached picture shows two schematics for the Acoustic Absorber [dual voil coil subwoofer plus current source power amp; CSPA].
  • The upper schematic uses the Acoustic Absorber as a phase inverting power amp having a voltage gain of 1. It is driven by a power signal generator at 50 Hz. It is stable, and has a pleasing 50 Hz signal hum.
  • The bottom schematic allows the user to compare the performance of its stereo system with the Acoustic Absorber engaged or not. The mechanical toggle switch [at input] is at the remote listening chair/couch. It is connected to CSPA with a 20 foot three conductor cable. This was a round green power cable commonly used outdoors, and has the normal black, white and green conductors.
  • Played a song [Rush by Paula Abdul] with the switch connected to the 8 Ohm input resistor. I noted the scope trace dance to the opening statement at Vo and Vi' [similar levels ~100 mVp-p].]. The switch was then connected to VC1. Replayed the start of the song and noted that both scope traces at Vo and Vi' were now at zero/flat baseline.
  • The switch was encased in an opaque pill bottle, so that I will not be able identify position [VC1 or 8 Ohm]. Also, the scope was not used after this to detect [cheat] on the identity of its position.
  • What power level requirement to this CSPA? I talked about ~100 milliVolt peak-to peak across a minimum 8 Ohm voice coils. Let's be conservative and use 1 Vp-p instead. This calculates to ~20 milliWatt.
Best regards
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Old 17th March 2014, 11:34 PM   #29
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Quote:
Originally Posted by Antoinel View Post
The attached diagram of the Acoustic Absorber is a practical device like that taught by Mr. Pass in his attendant patent.
Looking at it, I am unsure that you are not simply using the feedback to
freeze the motion of the cone. It looks like when a positive pressure is
applied, the result is negative voltage on the sensing coil which is then
inverted and amplified to a secondary coil, causing a force to push the cone
against the incoming pressure.

It might work (I'm uncertain) if you reverse the phase, but that would tend
to oscillation, I think>

I suggest that you consider two woofers in separate enclosures but close
next to each other instead of two voice coils on one woofer, and use a
non-inverting amplifier (or reverse the wiring of one of the coils).

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Old 18th March 2014, 01:05 AM   #30
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Quote:
Originally Posted by Nelson Pass View Post
Looking at it, I am unsure that you are not simply using the feedback to
freeze the motion of the cone. It looks like when a positive pressure is
applied, the result is negative voltage on the sensing coil which is then
inverted and amplified to a secondary coil, causing a force to push the cone
against the incoming pressure.

It might work (I'm uncertain) if you reverse the phase, but that would tend
to oscillation, I think>

I suggest that you consider two woofers in separate enclosures but close
next to each other instead of two voice coils on one woofer, and use a
non-inverting amplifier (or reverse the wiring of one of the coils).

Thank you Mr. Pass for your constructive comments. Your analysis in the first paragraph makes complete sense. It is an elegant explanation of the observed result of no sound. I will show another schematic which uses the identical components whereby the cone does not freeze; but continues to vibrate to put out an inverted acoustic signal.

Reversing phase [second paragraph] caused an incurable oscillation as you expected.

I will gladly pursue your suggestion of the 3rd paragraph. More food for thought.

Todate, my "assemblies " are capable of only three possible outcomes. Oscillation, and cone freezeup are not the answer to the standing wave problem. The third outcome is for the assembly to generate an inverted acoustic signal of a certain controlled level.

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