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Speaker Asylum General speaker questions for audio and home theater. |
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Speaker Asylum General speaker questions for audio and home theater. |
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In Reply to: Strengths / Weaknesses of a TL subwoofer? posted by WithTarragon on December 20, 2009 at 08:58:39:
I've neither built nor measured a TL sub, but have built maybe fifty or so TLs that weren't subs.
The output from the end of a TL emerges in-phase with the frontwave at the frequency where the path length is 1/2 wavelength. If the woofer is well chosen and the line isn't too narrow, we can hope for good bass output down to the frequency where the line length is 1/4 wavelength. However at the frequency where line length is equal to 1 wavelengh, the output from the end of the line emerges 180 degrees out-of-phase with the frontwave, causing a cancellation dip. Stuffing the line to reduce the magnitude of output at this 1 wavelength frequency will also reduce the beneficial output down lower (though not as much). There is a technique that results in good bass extension with minimal cancellation dip, but it also results in a fairly low efficiency box and suitable woofers are rare.
You can see this dip in frequency response measurements of TL-type speakers, such as models from PMC and the Zu Druid (the Druid isn't exactly a TL, but it's still a resonating tube). You will also see this dip, and usually a sequence of higher dips, in the frequency response measurements of bass horns. The energy that causes the higher dips is normally absorbed by the stuffing in a transmission line, but they'd be there in an unstuffed line.
So my suggestion is to take the anticipated 1 wavelength dip into account and expect a TL sub to cover a bit less than 2 octaves.
Duke
Me being a dealer makes you leery?? It gets worse... I'm a manufacturer too.
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- RE: Strengths / Weaknesses of a TL subwoofer? - Duke 10:12:19 12/21/09 (0)
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