DIY the device of US Patent 4,899,387 - diyAudio
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Old 19th February 2014, 04:09 PM   #1
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Default DIY the device of US Patent 4,899,387

This expired patent is entitled "Active Low Frequency Acoustic Resonance Suppressor". It was granted on Feb. 6 1990 to Threshold Corporation; Nelson S. Pass inventor. His inventive device eliminates standing waves [SW] in rectangular music listenning rooms. Thus it enhances the accuracy, perception and enjoyment of music etc...IMHO, this device is a must tool for DIYaudiophiles. For a couple of years, I've had 2 diy stereo resonators, and have recently prototyped a third mono device [for this thread]; all in my rectangular music room.

I hope that Mr. Pass has no objections, and there is interest in diy'ing [his approach] to solve this fundamental and pervasive problem. I'll wait a week before I move forward.

Best regards.
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Old 20th February 2014, 03:16 PM   #2
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I have been thinking about resurrecting that myself.

Have at it.

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Old 20th February 2014, 03:28 PM   #3
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Have a look at patent 6,795,557 which cites 4,899,387 as prior art.

Quote:
2. Description of the Related Art

In U.S. Pat. No. 4,899,387 is further disclosed an apparatus for cancelling low-frequency acoustic resonances in a room used as an acoustic space. The apparatus is particularly suited for improving room acoustics in listening to music. The major single factor causing acoustic frequency response variations typically is the listening room itself that may readily cause deviations as large as 20 dB at some frequency in the amplitude response in a given point of the listening room. These deviations are caused by the interference of sonic pressure waves reflecting from the walls of the listening room with pressure waves radiated directly from the loudspeakers. Obviously, the need for improved listening room acoustics is urgent.

The embodiment described in cited U.S. Pat. No. 4,899,387 attempts to solve the above-described problem by placing cancellation apparatus units in the room at the pressure maxima or in the immediate vicinity thereof. Said cancellation apparatuses comprise a microphone for sensing the sound pressure waves and signal processing means and a cancelling loudspeaker for producing the cancelling pressure waves to the reflected original sound thus measured. In this arrangement, the microphone is located close to the cancelling loudspeaker, and with the help of a feedback circuit, the goal is to alter the acoustic impedance of the cancelling loudspeaker such that the effect of the room acoustics on the smoothness of the sound field is eliminated. This technique bears the risk of instability of the feedback loop that also includes the sound cancellation apparatus itself, whereby the system may start to oscillate.
This might be nothing but salesmanship, suggesting to the patent examiner that all previous approaches are flawed, whereas my new invention glows with burnished perfection.
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Old 20th February 2014, 04:43 PM   #4
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I look at this with multiple microphones at various distances and dsp to make
it work and I say "good luck with that".

I don't expect to see it in operation.

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Old 20th February 2014, 05:17 PM   #5
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Quote:
Originally Posted by Nelson Pass View Post
I have been thinking about resurrecting that myself.

Have at it.

Thank you Mr.Pass.
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Old 20th February 2014, 05:31 PM   #6
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Quote:
Originally Posted by Mark Johnson View Post
Have a look at patent 6,795,557 which cites 4,899,387 as prior art.



This might be nothing but salesmanship, suggesting to the patent examiner that all previous approaches are flawed, whereas my new invention glows with burnished perfection.
Thank you Mark Johnson for this heads-up US Patent# 6,795,557. I looked at its diagrams, and was dismayed as they appeared complex to me; unlike US 4,899,556 which is way simpler, elegant, and highly effective.
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Old 21st February 2014, 09:31 PM   #7
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Default Acoustic Absorber

This diy is a tribute to Mr. Pass, his genius, and a gift to us who are in constant pursuit of the most pleasing and accurate musical experience.


The attendant schematic shows the two building blocks which makeup the Acoustic Absorber [AcAb].
  • A current source amplifier. A diyF6 is used initially as a teaching aid since most of us are familiar with it.
  • A dual voice coil subwoofer, used as a combination microphone and loudspeaker. This approach is totally within the inventive scope of the Pass patent.
Here's how it works which is [a simplified] like that described in the patent.
  • Acoustic pressure [Pa where a is for action] pushes the cone in.
  • Voice Coil 1 [VC1] acts a a moving coil microphone. Thus, it generates an electrical signal which is [Vi] to the input of the amp. Note its phase. The analogous electrical signal in VC2 due to the same [Pa] is irrelevant and is ignored.
  • Vi is amplified and the output of the amp [Vo] is impressed on the second voice coil VC2. Note the phase of Vo in relation to the "phase symbol" of VC2 [bold triangle].
  • The loudspeaker magnet-VC2 "motor" combo then generates an instantaneous reactive force [Pr where r is for reaction] which pushes the same cone outward; in effect opposing or counteracting the action of the incoming [and offending] pressure wave [Pa].
To be continued...
Attached Images
File Type: jpg AcAb.jpg (323.4 KB, 1330 views)
Attached Files
File Type: pdf AcAb.pdf (35.1 KB, 35 views)
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Old 21st February 2014, 10:09 PM   #8
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Hi Antoinel

You are Pablo Picasso of quick schematic !
I like hand drafted with signature my good luck to You.
Keep that diy style please
Greetings
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File Type: jpg picassodotline2.jpg (42.2 KB, 1296 views)
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Old 21st February 2014, 10:20 PM   #9
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Quote:
Originally Posted by soundhappy View Post
Hi Antoinel

You are Pablo Picasso of quick schematic !
I like hand drafted with signature my good luck to You.
Keep that diy style please
Greetings
Hello soundhappy. I'll stay with this style of schematics.
Best regards
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Old 21st February 2014, 11:37 PM   #10
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Quote:
Originally Posted by Antoinel View Post
Acoustic pressure [Pa where a is for action] pushes the cone in.
...
The loudspeaker magnet-VC2 "motor" combo then generates an instantaneous reactive force [Pr where r is for reaction] which pushes the same cone outward; in effect opposing or counteracting the action of the incoming [and offending] pressure wave.
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.

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