Now, another way to look at the whole issue of isolating the subwoofer is if you have already isolated all of the electonics and front end is it really necessary to isolate the subwoofer? The answer lies in the low pass filter characteristics of the isoaltion systems employed for the electronics/front end AND the lowest frequency produced by the subwoofer. Let's say the subwoofer is capable of producing 20 Hz plus or minus 3 dB which would be really good performance, right? And let's say the iso systems employed for the electronics and front end have resonant frequencies of 3 Hz. Then the effectiveness of isoaltion at 20 Hz is something like 95% based on the rate of attenuation for low pass filters. So the answer is no, it is not necessary to isolate the subwoofer if you have resonably good isoaltion for the electronics and front end already.

Geoff Kait
Machina Dynamica

Kal Rubinson wrote:

OK but consider that isolating the subs would also moderate their ability to excite resonances in floors, walls and furniture.

Am I missing something? Are you saying the subs should have the ability to excite resonances in floors, walls and furniture?

Geoff Kait
Machina Dynamica

Nt

David Harper wrote:

My B&W powered sub kept moving across the hardwood floor. I took two 2x4's (about a foot long each), went to True value and got some 5/8ths in. foam rubber weatherstripping and stuck it to the top and bottom sides of the 2x4's, and put them under the sub. Now the sub stopped moving (which was real annoying), but I'm not real clear about whether this would isolate the sub. It would seem it does, right? When you say mechanical isolation, you're not talking about low frequency waves in the air, right? Or bouncing off the floor? Or the walls?
You're talking about physical vibration of the sub?

Yes, when I say "isolate" I mean de-couple the subwoofer cabinet vibrations from the floor so they won't migrate to the electronics and front end. And when I refer to isolation I'm referring to "mass-on-spring" mechanical isolation which normally entails some sort of spring, steel spring or airspring design. I separate damping techniques from isolation techniques although there is a little overlap I suppose. Since traffic and Earth crust motion produce vibration with extremely low frequencies damping won't work so more stringent methods must be employed.

Geoff Kait
Machina Dynamica

Kal, you gave me quite a scare. I thought for a moment you had gone over to the dark side.

Geoff Kait
Machina Dynamica

David wrote,

"correct me if I'm wrong, but isn't interaction between the low frequencies from a sub and walls and floor part and parcel of the music? I mean, if you had a sub suspended four feet off the ground, hanging from a wire, in an open field, outdoors, you wouldn't hear any bass at all.(at least, almost none)"

That's part of the debate that's been going on here, whether it's better to allow vibrations to roam free in the room, in the system, in the signal, or to constrain them, attenuate them, perchance to uh, kill them. I would not lump the acoustic waves produced by the woofer cone with cabinet vibrations,, the latter of which I propose should be minimized. The acoustic waves are a different issue and can be dealt with separately as one sees fit, by subwoofer placement, room treatment, setting the crossover frequency, setting the output level, etc. But I am proposing that vibrations from the sub should be constrained from migrating to the electonics and front end via the floor, walls and furniture where they would undoubtedly degrade the sound. The only good vibration is a dead vibration. Whilst I am am favor of dissipating,,attenuating and reducing the amplitude of mechanical structureborne vibration the folks over at TuneLand seem hell bent on preserving vibrations, allowing them to roam free, providing a path for them to get into the electronics and front end, and encouraging vibrations to run along with the pure music signal in the conductors. I implore you,, gentle readers, sign the petition now, stop the madness!

Geoff Kait
Machina Dynamica

I almost forgot. The landmark article on vibration isolation that was written by Shannon Dickson and that appeared in Stereophile magazine has it really been 20 years ago? Link to the article, Bad Vibes, below. This article appeared shortly after the introduction of the Vibraplane isolation device and was the inspiration for your humble scribe entering the big wide wonderful world of vibration isolation.

http://www.stereophile.com/reference/52/#OwKdwBm0pBHqSBRr.97

Geoff Kait
Machina Dynamica
Give Me a Stiff Enough Spring and I Will Isolate the World

Nt

If you don't mind too much, Michael, how 'bout instead of tuning ....Ooops! Freudian slip ....instead of TURNING this thread into another one of your idiotic shit and git bulletin boards why don't you actually do something constructive and discuss whatever it is that's killing you to say. Besides it's way too much trouble to login to your website. If you have something to say spit it out, cowboy!

The vibrations must be free to flow, the system is a musical instrument and the audio signal is vibration. Everything is vibration. There, I said it for you! Nevermind.

Geoff Kait
Machina Dynamica

David Harper wrote:

correct me if I'm wrong, but isn't interaction between the low frequencies from a sub and walls and floor part and parcel of the music? I mean, if you had a sub suspended four feet off the ground, hanging from a wire, in an open field, outdoors, you wouldn't hear any bass at all.(at least, almost none)

An ideal subwoofer has no cabinet resonance and no acoustic wave interaction with the room boundaries. Thus hanging subwoofers outside should actually produce excellent bass response as the woofer diaphragm would be producing a purer signal as it were. It is the amount of air that the woofer diaphragm produces that determines the bass response, no? As Kal says it's the interaction of subwoofer mechanical vibration AND acoustic vibration with the room that is generally undesirable what with standing waves and reflected waves but also the unfortunately influence on the cabling and wall outlets and such but also the effects of structureborne vibration on the electronics and front end. Would you believe that many folks are sitting right smack dab in the middle of a standing wave or reflected wave? Not to mention the walls and ceiling act as drum heads whilst music is playing which can be quite undesirable in terms of comb filter effects.

Pop quiz: why do many speaker manufacturers measure speaker frequency response in an anechoic chamber instead of in a "real listening room?"

Geoff Kait
Machina Dynamica

Some speakers are designed to be placed near wall boundaries but most speakers including subwoofers yield a flat response out in the room away from walls and room corners. Bass frequencies are reinforced when the speaker is placed in a corner or near a wall. More so in the corner since the bass reinforcement is produced by three boundaries, two wall and the floor. But subwoofers are generally not designed for wall or corner placement so as to avoid boomy or thumpy bass. So, in effect, you are trying to minimize or avoid room interactions with subwoofers, not maximize them. Obviously standing waves and reflected waves for subwoofer frequencies 20-100 Hz or whatever in the room are not a good idea, either. Nor is the low frequency shaking of windows, furniture, audio racks, candelabra, TVs, what have you. While I'm at it, a pet peeve of mine is the high frequency squealing and distortion produced by the dust cap in the center of most subwoofers.

Geoff Kait
Machina Dynamica

The room is part of the system. Wow! Talk about a news flash. Are you guys for real?

Geoff Kait
Machina Dynamica