Decouple Your Speakers

A simple and inexpensive trick to improve sound quality

By Frank Moldstad

Auralex MoPads

Looking for an easy tuneup for your audio system? One good thing to try is decoupling the speakers. This is an old audiophile trick for minimizing the sound transmission between a speaker cabinet and the surface upon which it rests.

Decoupling can noticably improve the sound. There are several different ways to accomplish this, including inexpensive acoustic foam, polyurethane and rubber products. They are designed for placement under the speakers, and will improve the sound of any speaker, whether it's a computer multimedia product or a high-end studio monitor.

Speaker systems will transmit vibrations to a floor, a shelf or even a dedicated stand. In a sense, whatever surface speakers are placed on becomes part of the speaker box, and low-mid frequencies (aka mud) are exaggerated. As a result, the sound is duller and less distinct than it should be. Decoupling prevents this transmission, so the sound you hear is what the speaker system was designed to reproduce.

MoPads

I use an Auralex product called MoPads for decoupling a pair of bookshelf monitors. The MoPads cost less than $30, and the speakers sound cleaner and more precise with the MoPads than without them. They're made of polymeric acoustical foam, which is a much higher density material than what you'd pick up at a foam mattress store. One box contains four pieces, and two are placed under each monitor. They can be angled up, down or flat, using a small wedge-shaped insert. They measure 12"x 4" per section and will support up to 100 pounds. http://www.auralex.com/sound_isolation_mopad/sound_isolation_mopad.asp

IsoWedge

A similar product is PrimeAcoustic's IsoWedge, made of a "high-density low compression foam" material. IsoWedges also come in sets of four (two per monitor), and are priced at $29 per box. Each piece measures 12.8 x 4 x 2. They are reversible, with a 6 degree slope for angling the sound up or down. http://www.primacoustic.com/isopad.htm

Another option is Sorbothane, a material that is designed to dampen shock and vibrations in everything from computers to industrial bushings. It is a Visco-elastic material, meaning that it has properties of both liquids (viscous solutions) and solids (elastic materials). A distributor called JMK Audio sells 1"x.5 thick Sorbothane pads for decoupling monitors, priced at $17.50 for a set of eight. The company says four pads this size will support up to 65 pounds. http://www.jmkaudio.com/

Some do-it-yourselfers have come up with inexpensive and creative ways to decouple their speakers. One method is to slice tennis balls in half, making sure to affix the montors securely so they don't topple. Another is to place Neoprene mousepads under the speakers. Or, speakers can be put on pieces of rigid fiberglass that are wrapped in fabric to absorb reflections. Although some solutions are more effective than others, nearly anything that reduces vibrations has some benefit.

Speakers are also sometimes "coupled," to a surface -- which is an opposite strategy for achieving the same result -- better clarity. This involves the use of small ceramic or brass cones or spikes that are affixed to the speaker. Many audiophile speakers have threaded screw holes for just this purpose. The idea is to provide a small footprint and a rigid connection down through the floor by eliminating slight movements or vibrations that may occur when a speaker system rests on a solid and heavy table or carpeted floor.

But decoupling is an effective solution for most bookshelf or nearfield speaker systems -- and it's easier (and usually cheaper) than attaching little cones to the speaker bottoms.