Product Review

Auralex GRAMMA Isolation Platform that Will Hold a Subwoofer

April, 2004

Brian Florian



MDF Covered with 1/2" Thick Carpet

2x4 Isolation Foam Rails (Feet)

Size: 15" x 23" x 3"

MSRP:  $59 USA




With my last shipment of acoustical foam from Auralex (see article on the 007 Theater) came a curious piece of hardware that Gavin Haverstick asked me to "check out".  Described as an isolation platform for electric guitar amps, stage monitors etc, Gavin assured me that a home theater subwoofer would also benefit.  "But my room has a carpet covered concrete floor," I explained to him.  "Just try it," he insisted.

The Design

The GRAMMA is a catchy acronym for Gig Recording Amp and Monitor Modulation Attenuator.  Sift through the Star Trek-ese and we see that the GRAMMA is rather simple:  A thick piece of MDF board, covered with carpet, riding on two big strips of VERY dense foam rails (feet).  The gap between the two rails is filled with a piece of Auralex's standard acoustical foam.

So what's the deal here?  When those big guitar amps and stage monitors sit on the floor, they pass a ton of audio energy into the floor, the floor to the walls, the walls to the ceiling.  The room is literally a soundboard.  We're not talking about a room boundary reflecting sound, we're talking about it being a source of sound.  Some may think that in a home theater, a connection between subwoofer and floor is actually desirable in order to "feel it" in your chair during those action movies.  I disagree.  Tactile transducers may rely on direct transmission, but not subwoofers.  With a good subwoofer, when you "feel it" in your chair, virtually all of that energy is being transferred through the air to begin with, not the floor.

By putting the equipment on a GRAMMA, you (in great part) sever the direct mechanical connection with the floor (called "decoupling").  You attenuate from the sound that which is "voiced" by the room and bias the sound in favor of what comes directly from the subwoofer and the reflections thereof bounced around the room.  Essentially, you hear more of what is being passed through the air, and less of what is being passed through the floor.

The isolation foam on the GRAMMA is denser than the sort of acoustic foam you'd put on a wall.  That little fact is very much the key.  The two "rails" of foam did not visibly compress under the 100 pound weight of my M&K subwoofer, and Auralex claims it will support a 300 pound load, no problem.

Even on my carpeted floor, there was no real "rock" or sway to the sub.  I mention this because if you could easily "rock" the sub back and forth, that would be a bad thing.  A freely swaying speaker is one that is expelling power to motion, power which would be better used to transmit the sound out. Ever see a speaker perched on a goose down pillow?  No?  Good for you.  Even better for the poor goose.

The Test

So, I'm pretty confident the GRAMMA can do no harm.  But can it do some good?

I took an impromptu frequency response reading of my sub (gated, "quasi anechoic") while it sat on the floor, then again with it on the GRAMMA.  No surprise: there was no difference and we shouldn't expect one.  There was also no change in impact (back to what we were saying about "feeling it" in your chair).  Lets be clear: the GRAMMA is not a tweak for your sub.  It's better thought of as a treatment for your room!

What we did find is a slight tightening of the bass.  Less "bloat".  Less "fatness".  Not that there was much to begin with: my theater floor is carpet over concrete, and concrete doesn't exactly transfer sound energy (though it reflects it).

I decided to try the GRAMMA in a more typical room with carpet over plywood with floor joists underneath.  Here, the GRAMMA made a more perceptible difference, omitting the slight mud I had previously just accepted was a characteristic of the room.


A monumental-change-your-life-religious-experience?  No.  But at just $59 (regular A/V isolation platforms can cost hundreds of dollars), why not get one!  Or maybe two if you have a Velodyne HGS-18 (JJ has four).  It will also elevate your sub a few inches, something you should do in most situations anyway.  If you've followed my writings at all, you know I'm a no nonsense kind of audiophile, constantly questioning the validity of expensive cables, black magic power conditioners, and anything with the word "tweak" attached to it.  For what it's worth, the GRAMMA gets a thumbs up!


- Brian Florian -

Copyright 2004 Secrets of Home Theater & High Fidelity
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