Re: The "rotary" subwoofer

On a sunny day (Mon, 25 Aug 2008 09:47:47 -0700) it happened "Paul Hovnanian P.E." wrote in :

Exactly. AC3 / Dolby 5.1 none of the channels goes lower then 20 Hz, the subwoofer has teh same minimum: 20-120Hz.

on

Maybe they could play back some seismometer data.

On a sunny day (Mon, 25 Aug 2008 10:43:28 -0700 (PDT)) it happened Richard Henry wrote in :

Yes, there were some tests recording audio in the underground railway (tube). There (think very long tuuuube) the low frequency response of different camera audio systems showed big differences. But with THAT system you can actually reproduce the wind from the approaching trains ! (given a suitable pressure sensor????) Realistic, somebody donate one, I will try.

The lowest note I have noticed on a music CD is E0, slightly over 20 Hz. I have done spectral analysis of bass notes in that CD and found general lack of content below about 30-33 Hz. The lowest notes lose their fundamentals.

- Don Klipstein ( snipped-for-privacy@misty.com)

I agree with what everyone has said about the sub 20Hz response being pointless. However, if you investigate the real response of most subwoofers, they have dropped off severely at 20Hz.

So, if you're willing to pay their price (about $20K total) for superior performance in the 20Hz-40Hz range, they are worth a look see.

Bob

Maybe, but the "fan" woofer still needs an enclosure, and it's still much cheaper, easier and more reliable to collect a few used cheap car subs from eBay with low Fs (25-30 Hz), medium Qts (0.4 or so) and decent Xmax (10+ mm) and optimize big reflex or bandpass boxes for them - they will easily fill out the 20+ Hz bottom octave or two. Tony

The problem with conventional subwoofers is that they have very poor transient response. There are several expensive solutions that offer nice tight and fast midrange and top end (as is possible with electrostats and/or magnestats) but they're only good down to (about) 50Hz. It's easy to ruin the total experience by adding on a clunky-sounding subwoofer. Infinity got close with their electrostatic Servo-Static 1A by adding a servo-controlled subwoofer.

I don't know what the transient response of this rotary device is like, but it better be effing good (on the A-F scale) for $20K.

I guarantee you that any eBay-concocted subwoofer would not be able to keep up with a true high-end system.

Bob

On Mon, 25 Aug 2008 17:30:55 -0700, "BobW" wrote:

.....snip!......

Transient response for a subwoofer doesn't need to exceptionally fast, you can calculate it based on the highest frequency req'd, and the order of the effective low-pass filtering. That effective low pass filter will ensure a fairly slow input waveform to the woofer cone, so there's no need for a "fast subwoofer". A fast subwoofer is a full range speaker! The fan will also have a limited transient response, since the vanes must turn (change pitch) in response to the signals. Their weight (and inertia) will probably be sufficient to restrict the bandwidth (and transient response). The nature of the mechanical system will determine the transient response, it should be a function of the upper (-3db) frequency response, and the nature of the response (just like the woofer's). The manufacturers specs suggest an upper cutoff of 30 Hz, which I think is quite remarkable. That means the pitch changes from + to - and back at a rate of 30 times per second. A conventional subwoofer has a radiating surface that moves all at once, and more or less uniformly. The fan has a severe limitation in that the pressure wave is non-uniform ( the blade acts like a wing surface, so there are pressure variations as you measure across the blade). On the trailing edge of the fan plade the pressures vary all over the place, and there are air vortexs that will be created. That means the desired wave front will be modulated by the fan rotation (usually a hum or whine). There will be added noise from the vortexing (usually a wooshing sound). You can't get laminar flow from a device like this! Your wave front would very ragged and its shape would vary with time due to the fan rotation. Even at low fan speeds, the vortexing should cause some interesting non-linear effects. My guess is the fan speed multiplied by the number of blades should modulate the sound in strange ways. Even if that is sub-sonic, it would have significant harmonic content. In short, this device will have added noise and distortion that you wouldn't expect. The manufacturer says 3% distortion..... That might not include all the modulation and noise effects. It might also be at full output, where the extraneous noises are small compared to the signal. It would be an interesting device to try, were it not for the approximate $13,000 price tag. Listening tests would be pretty difficult due to the nature of SUB-sonics. Even if you could hear these lows, and even if the music source had significant content at these frequencies, the fan woofer sounds like a bad choice. It would probably be cheaper, and more effective to use a bank of large cone woofers. Sorry.... I just don't trust high-end audio stuff. I seen just too many weird silly products that sell for a fortune, and are just sucker bait.

-Paul G.

A fan with electrically controlled pitch like this might make a windmill that could adapt its torque to use light breezes more efficiently than a fixed pitch blade.

BobW wrote: >

For hundreds of years organ builders have been using 32 foot pipes to go as low as 17 Hz - and it's a wonderful sound. If there is no point, why did they do it?

G=B2

Weird silly products? Are you saying that plugging in a digital clock to align the electrons in your home wiring is silly? Painting the edges of your cds with a yellow highlighter and them freezing them is silly? Placing small bits of exotic wood around your living room...silly?

Hmmm....you may be right.

Bob

And yet people wonder why i like pipe organ in person. They have one on Balboa park in San Diego. It even gets regular play. At least it used to some 25+ years ago.

In the mid 1960's an engineer at Ford insisted we stop by his house, before we flew back to Phoenix, to see his organ.

My first response, kept to myself, "Oh-mi-gawd, we have to go see his kit-built electronic organ" :-(

We get to his house, go down in the basement, and there's a complete PIPE organ in his basement!!

Seems the Fox Theater in Detroit had been closed to make way for "development", and the engineer had bought and reassembled the organ in his basement.

MAN! There's nothing quite like being IN a pipe organ while it's being played ;-)

...Jim Thompson

Still does, every Sunday during the summer with occasional other performances.

On a sunny day (Sun, 31 Aug 2008 14:30:58 -0700 (PDT)) it happened Richard Henry wrote in :

When specified 20-120Hz that does not mean there is nothing below 20 Hz. It is not very likely a 'brick wall' filter, but more likely a -3dB point. Even the normal PC sound card, for example my soundblaster on Linux, running into my sub woofer (that is mounted on the wooden floor, so the floor motion works to give that extra thing to the sound), sounds when driven at 10 Hz like this: sgen sin 10 makes the chair vibrate.... but you hardly hear anything. sgen sin 15 is stronger, feels like a starting earth quake, hardly hear anything. sgen sin 20 starts shaking stuff on the tables, still hear not much. sgen sin 25 Now I hear something. Great fun, 10 minutes past midnight here :-) I am using this for bass amp:

I had the eerie and unusual experience, about 30 years ago, of touring the interior of the Balboa Park pipe organ while it was being played. The "wind chest" is large enough to walk through; all those little solenoid valves going click-click-click are louder than the music itself. Outside, of course, it's blasting away but in the chest all that sound is moving away from you so it's relatively quiet.

There was one in a huge restaurant in Cincinnati once as well, but it has since been dismantled.

I do not recall hearing about the one in Balboa Park, and I have been out here since '94. I think it too, must be gone.

ItsASecretDummy wrote: >

Doesn't seem so as you missed the concert _yesterday_ !

G=B2

Even though it was not playing when i took the tour it is an extraordinary experience.