Good Cheap Bass Reflex Fullrange

You can get some fairly good sound for not much money with a bass reflex box using Radio Shack's 40-1909 5-inch fullrange. Price $9.99 according to the 1997 Radio Shack catalog.

This speaker can only handle continuous power to about 2 watts, and peaks to about 10 watts RMS. It may suffer distortion and/or thermal power compression with wattages much over about half these.

Please note that these designs have some significant resonant character centered at a frequency very slightly below the port frequency. Depending on your tastes, this is not too likely to be objectionable to those who like bass reflex speakers. This resonance is of slightly higher Q than average for bass reflex (ported) speakers.

Thiel-Small Parameters for the 40-1909:

Fs=84 Hz
Qts=.56
Vas=.315 cubic foot

Reference Sensitivity = 90.5 dB at 1 watt, 1 meter

Plan A:

Box Volume = .65 cubic foot
Possible internal dimensions: 15.5"H * 10.625"W * 6.875"D
External dimensions using 3/4 inch wood: 17"H * 12.125"W * 8.375"D
Port tuning: 62 Hz
Port dimensions (There are others that work) 2" inside dia, 1.65" long
Bass -3 dB point: 54 Hz

This speaker gives fairly full bass with fairly good efficiency. The midrange response is fairly good, especially if the speaker is not equally distant from the four sides of the box. The treble response is good enough to hardly need a tweeter.

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.

Plan B

For use with an octave equalizer with a 63 Hz control:

Use a slightly larger box volume of .70 cubic foot and a lower port tuning of 52 Hz. Boost the 63 Hz control of the octave equalizer by 3-4 dB. This extends the bass -3dB point to 45 Hz.

Internal dimensions that make .7 cubic foot: 15.875"H * 10.875"W * 7.0625"D
External dimensions using 3/4 inch wood: 17.375"H * 12.375"W * 8.5625"D
Port dimensions for 52 Hz with .7 cubic foot: 2: inside dia. * 2.75" long

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