TL design questions

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Hello,

I am currently designing my first loudspeaker cabinet and chose to build a TL for Fostex FE126 drivers.

I thought I’d first practice with cheap drivers I have at home. They are JVC VGS-1001-018 ,10cm, 15W fullrange salvaged from an early 90ies micro-component system that sounded decent despite having such tiny drivers in a bass reflex enclosure. I think I can make them sing a lot nicer in a TL. I measured their Fs at 110Hz.

I’m still hesitating between a straight or once-folded design. If I go straight, I’ll place the driver 1/3 down the air column to smooth out the second (3/4) harmonic mode. If I go for the folded design, I’ll place the driver 1/5 down the air column to keep it at a decent height, not to have it too close to the fold and to smooth out the third (5/4) harmonic mode. Either way, I will initially stuff the area above the driver to “slow down” all higher harmonics pressure antinodes and re-adjust as needed.

I know how I want things sized-up, but in case I’m missing something big or get an unexpected answer to my questions, I ask you the following:

1. Just how much can you get out of a TL tuning? Assuming typical driver roll-off of 12dB/octave below Fs. Just how low can you tune the TL before it’s worthless? My guess would be not to go any lower than 1 octave below Fs for quarter-wave resonance mode. Any thoughts and experience on that?

2. What about the cross-section of the TL? I am making mine straight, no-taper and was thinking of a X-section about 3-4 time Sd, which is around 0.0054 square meters for my drivers, with a mouth area equal to Sd and a depth-width ratio of 1.4142. How does a X-section of say, Sd, differ from one of many times Sd, say 5-6 times?

Thanks in advance,

IG81
 

GM

Member
Joined 2003
Greets!

I recommend educating yourself on current TL, etc. design theory and in particular the Classic TL designer tutorial to help with your specific design: http://www.quarter-wave.com/

If you don't measure T/S specs, then figure the pipe's total volume (Vb) will need to be at least 4x and maybe as much as 10x the mini-monitor's to allow sufficient tuning flexibility/max gain, so its cross sectional area (CSA) is a function of its Vb divided by path-length, not any correlation to the driver's Sd.

GM
 
Hi,

FWIW assuming you make some effort to make them look nice
I'd suggest you start off with a driver with known parameters,
at least you will not be guessing and whatever you learn will
be more predictable for the second time round.

Though in maximising possibilities a MLTL (mass loaded TL)
should not be ignored, e.g. the Metronome is very appealing.

:)/sreten.
 
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