Ok, I just got more or less commissioned by a friend to design him a pair of speakers for a $17 Goodwill reciever for playing mostly country music. I have been itching to built a Transmission Line, and this offers me my chance. I am planning on using Tangband drivers. The Tangband W4-656S shielded 4" midbass offers a relatively smooth response to where I want to cross over, which is first order at 4500 Hz. From there, I will have a Tangband 25-669SD shielded dome tweeter handling the highs. This, I think, is the same tweeter that is the GR-Research T1 tweeter. I used MJK's alignment tables and discovered that the line length I need to get response down to 65 Hz (the W4-656S's Fs) is 51.7". The enclosure I designed gives me a line length of 65". Is this a bad thing to have a line that is too long? Or am I still ok? Also, the driver is not at the exact end of the line, but is down the line about 5". Can I just put a piece of BlackHole 5 and some open-cell foam at that end of the line and have everything be fine as long as I account for the offset in my line length?
Having built two ML-TQWTs my experience is that it's better to have the line length equal to 1/4 Fs and maybe even tune the pipe just above resonance frequency. I quickly ran the numbers in MK's program and the line length looks bad. Even added stuffing didn't offset the response. I recommend sticking pretty close the MathCAD numbers and try different port sizes and So and Sl ratios. Something else to consider is adding another woofer in bipole configuration for BSC.
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