A Fair Woofer from Radio Shack

Update 3/22/2011 - this page is likely a historical / legacy one; this woofer appears to me likely discontinued.

You can get some fair deep bass for not much money with a bass reflex box using Radio Shack's 40-1036 10-inch woofer. In addition, this woofer is absolutely excellent for use in rear decks of cars with trunks. Price $39.99 according to the 2001 Radio Shack catalog.

Please note that ported box designs for the 40-1036 have some significant resonant character. Such designs are not audiophile candidates. But they will do an excellent job of deep bass reporoduction, especially with popular music.

Thiel-Small Parameters for the 40-1036, tentative:

Fs=35 Hz
Vas=5.4 cubic feet

Reference Sensitivity = 90 dB at 1 watt, 1 meter

Plan A:

Box Volume = 10.8 cubic foot
Port tuning: 35 Hz
Port dimensions (There are others that work) TWO PORTS 4" inside dia, 1.25" long
Bass -3 dB point: 27 Hz

This speaker gives very full bass with fairly good efficiency. There is a hump in the frequency response in the lower bass, peaking at about +6 dB in the 38-40 Hz range. The response is approx. +3 dB at 33 and 62 Hz.

For best results, a small amount of damping material in the box is recommended. About half an inch of fiberglass or about an inch of "Polyfill" on the bottom, back, and one side of the box should be sufficient. One should use a minimum of damping material, just enough to make standing waves not have a noticeable effect on the sound of the speaker when the speaker is operated in the box. The box itself, with the speaker removed, should have a fairly bass-resonant sound with a slightly noticeable but rather damped standing wave character. Excessive damping material will reduce the bass response.

MODIFICATION TO THIS PLAN - use a port frequency of 28 Hz instead of 35 for a wider hump not quite 3 dB high. -3 dB is at about 23 Hz. Response is full down to 25 Hz. This could be a bit of a waste since it is very rare for music to have significant content below 30 Hz and most is lacking from around 40 Hz on down. Even "bassy" popular music is normally low on content from around 40 Hz on down.

Port Dimensions (others will also work): Two ducts 4 inches inside diameter, 4.5 inches long.

Plan B - in cars with trunks:

Simply put two or four of these in the rear deck of a car with a trunk. You will get more bass than most people would believe possible with 10 inch woofers. The credit goes to the Qts and Vas figures being higher than usual for 10 inch woofers used in cars. The drawback of these woofers is limited power handling. I do not recommend using much more than the output of automotive amps and boosters rated for 40-50 watts into a 4 ohm load. But this will be enough to amaze people - especially ones impressed by the results with limited amplifier power.

For an additional trick, add resistors up to 8 ohms in series with these and then get an appropriate transformer to convert the impedance back down. This will reduce the efficiency a little but the lower bass will have a response hump that many people will like. But without this resistor, there is theoreticaly almost zero response hump.

Written by Don Klipstein.

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