Monday, February 13, 2012

Tweak #1b you can do on almost any speaker

Resonances are everywhere and the more you eliminate, the better the sound will be.  Take your existing speakers, for example.  Go up to the cabinet and reap your knuckles against the side. What you hear, sounding similar to a door knock, is the natural cabinet resonance, hopefully occurring at a pitch higher than that of the operating frequency of the drivers inside.

Everything resonates at some frequency, including the individual components of the speaker drivers themselves. The cone or dome resonates at one frequency, the mechanical motion in and out resonates at another, the interaction between the cone and the magnetic pole piece deep inside resonates at yet another, just to mention a few. How well the manufacturer controls these resonances will determine how little these resonances alter the natural ability of the driver to uniformly reproduce sound.

Some resonances can be controlled even after a speaker is manufactured and some cannot. One resonance that can be controlled is the one the driver makes against the baffle board. In tweak 1a, you were shown that three mounting screws reduces the number of undulations a driver basket makes when attached to a baffle board. But the basket still creates resonances, although with three mounting points they are greatly controlled.

To reduce the remaining basket undulations there is one more tweak. Now note that I said REDUCE and not ELIMINATE. Regardless of what you do, some undulations will remain and the goal is to lower their audible impact. This tweak requires the removal of the driver from the baffle board and installing a different seal in place of the existing seal.

Most loudspeaker manufacturers use one of two methods for mounting a driver to a baffle board:
  1. Use a cardboard gasket between the driver basket and the baffle board
  2. Use caulk between the driver basket and the baffle board
The third method is a thin compressible foam gasket, probably the best method for absorbing minor resonances at the edge of the driver basket. However, removing the driver, removing the cardboard or caulk seal and replacing it with a simple foam seal is an equally viable and very inexpensive option.

If you have already removed the redundant screws in tweak1a, removing the three remaining screws is a small task. To do this without harming the speaker, lay the speaker on its back, remove all screws from the driver basket, and carefully remove the driver.

Once removed, you can add a thin piece of closed-cell weather stripping to the back of the basket and reinstall the driver using the three-screw triangular pattern described in the earlier article.

In the image above, I removed the driver from the speaker wire but it is not necessary in most cases to do so. The new gasket is applied in a uniform smooth manner around the edge with a small amount of overlap. The other option is to apply the gasket in a similar to the baffle board itself and then put the driver back into the baffle board.

Whichever method you use, keep the edge of the driver basket away from the recessed cutout hole for the driver (center it as best you can). Then tighten down the three triangular-pattern screws until the seal is compressed and the screws are snug. Be careful not to over-tighten these screws since in doing so will strip out the hole. If this happens, you must rotate the speaker slightly, drill pilot holes for the screws, and be more careful when tightening these three screws.

There is one more tweak you can do before putting the driver back into the hole on some speakers. We will learn about that tomorrow.

Yours for higher fidelity,
Philip Rastocny

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