Isolation pad with a downword firing port? - AVS Forum
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post #1 of 7 Old 01-13-2013, 05:32 AM - Thread Starter
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I have 4 subs in my ht which is in my basement. I am looking to get some Auralex Iso pads to hopefully cut down on that rattling that occurs (glasses on the bar, door against frame, wall studs etc.) one of mysubshas a downword firing port. Is it ok to use an iso pad with that and should using pads under all 4 help with the rattling?

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post #2 of 7 Old 01-13-2013, 06:31 AM
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I have 4 subs in my ht which is in my basement. I am looking to get some Auralex Iso pads to hopefully cut down on that rattling that occurs (glasses on the bar, door against frame, wall studs etc.
They'll have no effect. Next to high priced cables and power conditioners isolation pads and spikes are the biggest scams in audio. The following quoted claims are taken straight from the websites of manufacturers of these devices:

The Isolation Claim: ‘Its purpose is to prevent sound from transmitting through your subwoofer to surrounding surfaces. Subwoofers create big vibrations (low frequencies) that you can feel in the floor and in objects placed nearby. When the source of the vibrations is coupled directly to the floor it causes these objects to vibrate or resonate…’

The Truth: The source of these vibrations is the movement of the driver cone. The claim would only be true if you coupled the driver cone to the floor. If the cabinet panels vibrate enough to cause the floor to vibrate, the speaker is defective.

The Decoupling Claim: ‘Isolators for your speakers…will decouple your speakers from the surface they rest upon, resulting in a more pure, accurate tone. Low frequencies will be projected and will no longer lack the definition you desire. Mid and high frequencies will be crisp and intelligible. Rattles and resonances will be a thing of the past.’

The Spike Claim: ‘By rigidly coupling a loudspeaker enclosure to a floor by means of a spiking system, it is possible to dramatically improve clarity, stereo imaging and bass response. This is very apparent with subwoofer systems.’

The Quandary: These sources claim the same benefits from coupling and from decoupling. Who’s telling the truth?

The Truth: Both are lying. Isolation and coupling makes no difference. To test this I measured the response of my THT and my David with the test mic in the room, in the next room, and in the room below, with the cabinet sitting on the carpeted floor, on four inches of high density acoustic foam, on rubber feet and on spikes. I’d post the measured results for each set of comparisons, but there would be no point. In each case the measured responses of the four options were identical.
Note that this was on a carpeted floor. There may be some slight benefits to isolation devices or rubber feet on a bare floor, or on a bare shelf or stand. But you never want a bare floor, it’s an acoustical nightmare. If you only have area rugs in your listening room stick a piece of felt carpet padding, a carpet scrap or rubber feet under your speaker. If you're using bookshelves on a bare shelf or stand small rubber feet or felt pads are all you need to prevent spurious vibrations.

The Endorser Claim: ‘I tried them and they work, I know what I’m hearing!’

The Truth: The first thing you learn in an acoustical engineering course is that you don’t know what you’re hearing. If you did you’d be able to listen to a speaker, take pencil and graph paper in hand, and draw a frequency response chart, THD chart and waterfall plot, all with 1/24 octave resolution and 1/10dB accuracy. Our ears just aren’t that good, not by a very wide margin. But our imagination works very well, and that clouds our audio judgment, leading to placebo effect. In short, if you think something will make a difference in the sound, it will.

For an in depth examination of why we really don’t know what we’re hearing check out this video:
http://www.youtube.com/watch?v=BYTlN6wjcvQ

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post #3 of 7 Old 01-13-2013, 06:53 AM - Thread Starter
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Thanks for the in depth, informative reply. I figure any guy who has Yoda as an avatar must be an expert in the field. I guess I'll just have to turn them down. mad.gif

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post #4 of 7 Old 01-13-2013, 07:34 AM
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Thanks for the in depth, informative reply. I figure any guy who has Yoda as an avatar must be an expert in the field. I guess I'll just have to turn them down. mad.gif
That, or remove or isolate the stuff that's vibrating. Putting four inches of foam for a few hundred bucks under the subs won't do anything, but 3/32 inch of rubber shelf topper for five bucks under the glasses will silence them, as will a weatherstrip on the door frame, etc.

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post #5 of 7 Old 01-13-2013, 10:03 AM
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I have wood flooring in my house (built in the 1920's) and my HT is located in an upstairs room. Using Auralex Gramma's under my towers (cut one in half) and my subwoofer does in fact cut down on the floor vibration noise that is heard in the room below by a good amount. They do not at all make speakers or subs "sound better", they simply help reduce problem vibrations, resonance, etc. that might exist in an installation.

Bill's seeing of no difference, as far as annoying vibrations cause by his equipment, is probably more of a testament to how well acoustically his HT room is than anything. Now keep in mind that these things will not affect the amount of low frequencies transmitted through the floor, they will only reduce the amount of vibrations in the floor and rattles caused directly by those floor vibrations. So if your door is rattling against the door frame, these things will not help with that since that rattle is cause by the pressure that the cones of your subwoofers are creating.

So these Gramma's etc, do have there place, but not everyone needs them if they do not have problem areas.

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post #6 of 7 Old 01-13-2013, 10:05 AM - Thread Starter
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I am going to do that, the main problem is the stud(s) that rattle. I can try to figure out which one(s) they are and put a few more screws in them.

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post #7 of 7 Old 01-13-2013, 12:03 PM
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I am going to do that, the main problem is the stud(s) that rattle. I can try to figure out which one(s) they are and put a few more screws in them.
This is one case where a band aid works a lot better than surgery, and is a lot cheaper too. Screws work, and at perhaps ten cents each you can afford to be liberal with using them.
Quote:
I have wood flooring in my house (built in the 1920's) and my HT is located in an upstairs room. Using Auralex Gramma's under my towers (cut one in half) and my subwoofer does in fact cut down on the floor vibration noise that is heard in the room below by a good amount.
I have wood flooring too, dating to 1938. Mine is carpeted over. A Gramma will aid with a bare wood floor, but no more than will a thick piece of carpet.

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