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Here’s a whacky idea

Paul's Posts — 11 April 2012

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Here’s a whacky idea

We’ve been focusing on the importance of the room to a stereo system over the past couple of days.  Let’s dive a little deeper.

Nelson Pass designed an interesting product called the Shadow a while ago.  It was an active bass correction device that made sense – because instead of correcting the output of the speakers for bass problems in the room – it fixed the room itself and left the main speakers alone.  Not sure whatever happend to it but it mirrors an idea I’ve had for years: fixing the room has to be better than fixing the output of the speakers with what’s incorrectly referred to as “active room correction” (because it doesn’t actually correct the room).

“Active room correction” through DSP is really something of a can of worms.  This technique basically changes what comes out of your loudspeakers to correct for problems of the room.  So, for example, you have too much bass at your listening position because of the room – so the DSP reduces how much bass your loudspeakers generate to compensate.  While this works I think it’s wrong headed because it is fixing a symptom instead of the problem.

Imagine something entirely different for a moment: instead of correcting what comes out of your speakers, correct what the room is doing by adding a series of wall-hugging modules around the room – one on each wall.  These modules are somewhat like Nelson’s idea only full range and much more powerful – each with a microphone, amplifier, DSP and loudspeaker “listening” to what’s around them and eliminating the room according to the user’s instructions.  Designed properly you could walk into any room and change the perceived dimensions and acoustics of that room with the touch of a button.  You could make a large hall for one type of recording and a small and intimate one for another.

I know this is totally whacky, only for Audiophiles, unfriendly to wives, small children and dogs.  But I can dream can’t I?

I picture being at a consumer audio show with a group of people sitting in the room.  I ask everyone in the room to close their eyes and “feel” the space they are in as I talk.  Then I touch a button on my remote activating the modules and ask “ok what size room am I in now?”  The room just grew to huge – those sitting in the audience are now in a large hall, or a small one, or perhaps even “outside”.  The important feature here is the audience is IN the room.  The main loudspeakers or even a live group playing in the room sound completely different BECAUSE of the room.

Perhaps some young designer out there will have a lightbulb go off after reading this.  I’d be his first customer.

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About Author

Paul McGowan

Paul McGowan is the CEO and co-founder of PS Audio Inc. a Boulder Colorado design and manufacturing company of high-end audio products and services. McGowan has been designing and building high-end products for nearly 40 years. Hobbies include skiing, music, hiking, artisan bread baking, kick boxing and cooking. He lives in Boulder Colorado with his wife Terri and his 4 sons.

(13) Readers Comments

  1. April 11, 2012 at 6:46 am

    That IS a great idea – and I would actually be surprised if no one is developing it. It would need to be subtle, creating interference patterns that cancel or augment selected frequencies, relieving “congestion” in the room due to peaks and troughs.

    Mics may need to be positioned separately from the speakers, depending upon your room’s issues and dimensions. Omni-ish speakers or perhaps just repurposed home theater side-wall bidirectional jobs. May require subs as well, since that’s where a lot of room issues are – but I could see that getting sonically messy – maybe just stick to higher frequencies? They seem to have more influence on localization and perception of “size” and “depth”, etc. Sign me up, too!

    • April 11, 2012 at 6:57 am

      Thanks. I kind of doubt anyone’s working on it as this has been an idea rattling around in my head for nearly 10 years – there’s a lot of rattling in my head – and aside from nelson’s Shadow product and another version of Nelson’s product called the “Black Hole” I have never seen or heard of this.

  2. Gannon

    April 11, 2012 at 6:50 am

    My first guess would be to devise a system which is an acoustic analogy of that ‘invisible vehicle’ video feedback design…only using microphones which sample the reflection characteristics of the surfaces directly perpendicular to it. The worst of flutter echos and frequency shifts due to combing could be removed…those caused by the parallel surfaces, while angular and circular ones…the stuff which diffuses reflections…would be ignored.

    Now, what is the nature and proper scalable size of the active absorber? I’d say we’ve finally found a valid use for those invisible speakers…where the transucer connects to a membrane which, when surfaced with a thin layer of drywall spackle and paint, becomes the correction element.

    if you need more amplitude than what it can provide…you’ve got bigger problems!

    Cheers,
    John

    • April 11, 2012 at 6:59 am

      John, that’s actually a really good idea – obviously the transducers have to be speakers and full range at that – but placing them IN the wall as invisible elements is quite obvious and brilliant. Indeed, well thought out young man!

      Maybe the product is a self contained wall mount speaker with every thing built in – you just need to send it power – and it wouldn’t need a lot actually.

  3. Gannon

    April 11, 2012 at 6:51 am

    I want at least 10% off the gross sales for anything which ever is made off of that idea…

  4. Gannon

    April 11, 2012 at 6:54 am

    transDucer…gotta beat up my copy editor again this morning…

  5. Gannon

    April 11, 2012 at 6:56 am

    I can also see a great need for an active LC inter-wall connection system…replacing those cheap aluminum Z and C spacers with those Butt-shaker servor motors linked with sorbothane…

    oh gosh

    this is fun.

  6. Gannon

    April 11, 2012 at 6:57 am

    Talking about LC dual-wall isolation construction techniques…sorry. Brain is now flying at just beyond amorphous…language cannot keep up.

  7. Ed S

    April 11, 2012 at 6:59 am

    I’m thinking of something that operates on the principle of the Bose noise-canceling headphones, but on a much larger scale. (Their noise canceling phones BTW are Bose’s best product.)

    • April 11, 2012 at 7:03 am

      Exactly Ed – but instead of canceling we actually use delay and reflection plus cancelation. The difference between being in a big room and being in a small room is how much of the reflected sound comes back to you and how long it takes to get to you.

      Yamaha has had something like this for years – only they did it back asswards. They used the main loudspeakers to produce the fundamental sounds and then added in room and hall reflections to simulate the larger room – that never worked and only made a mockery of the music.

      The RIGHT way to do it is the opposite – leave the music alone and change the room.

    • Gannon

      April 15, 2012 at 8:48 am

      @Ed,

      Exactly, only instead of the microphones sampling cyclic OUTSIDE sounds, and again removing them from the propogation of music frequencies at the MAIN transducers (which we seem to agree bastardizes the sounds we WANT to maintain integral)…our microphone input to the servo loop auto-correction system would be limited to the specific frequencies emitted from the matching panel on the opposite wall, using very directional panels and mics in order to limit the effect to only parallel surfaces.

      Our servo would NOT operate continuously, it doesn’t NEED to. That would help it save energy, and not become a random problem itself as the music excited the room. We only need to eliminate the specific reflections of parallel surfaces which are the source of the most egregious of the negative room effects…outside the big nodes of the <300Hz pressure waves crashing around. For those, we may need to invent an acoustic vacuum, or active Helmholtz radiator. Ooh…

      Cheers!

  8. coppy

    April 11, 2012 at 8:29 am

    Fantastic ideas… and maybe even practical. Already sounds like it could be done in a way that will not make general use of the room distasteful to normal people. A side benefit is that everyone could then hear those distastefully compressed, artificial contrived mixes so maybe they would start to go away. Imagine, you could actually hear a singer over the loud base lines.

  9. petewilson

    April 11, 2012 at 9:50 am

    Paul

    Clayton Shaw of Spatial has just introduced a product called Black Hole, which is in the same category as your thoughts, but mayhap a little less ..grandiose. Still, the basics are there, I think. The idea of changing the room size isn’t incorporated, but it seems to me it’s a ‘simple matter of software’ (i.e., there just may be a few issues yet to be solved :-)

    Here’s what he says on one forum:

    http://www.audiocircle.com/index.php?PHPSESSID=ajkot39u57ua7tjo4i0q13p9uaf3ddfg&topic=103187.msg1054271#msg1054271

    Note that Clayton also offers a couple of flavours of the evil room/speaker correction approach, using your Mac.

    Info on all the products at:

    http://www.spatialcomputer.com/page9/page9.html

    I’ve got no connection with Spatial save interest and some discussions. The new software-only product sounds interesting to me (i.e. has an interesting price :-)

    – P

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