Pioneer B20FU20-51FW 8 TL?

aznboi3644

Member
2007-12-15 3:00 am
aznboi3644 said:

Should I design the enclosure based on the 1/4 wavelength of the drivers FS??

Will it even sound good in a TL??

Greets!

I don't see why not, it's worked well in a wide variety of cab alignments me and others have designed/built already, though only Nelson Pass's is a TL per se AFAIK, which is buried in this recent thread along with some other designs: http://www.diyaudio.com/forums/showthread.php?s=&threadid=113210&highlight=

Anyway, typically you design it a bit < 1/4 WL of Fs since the stuffing's resistance will shift Fp lower. MJK's Classic TL alignments will calc them based on Polyfil's resistance: http://www.quarter-wave.com/Theory/Alignment_Tables.pdf

GM
 
I resemble that remark! ;) If I couldn't 'slam' a pair together in an afternoon I was goofing off way too much. Not that having power tools helped, though in my defense it was just a proof-of-concept made from house repair scraps to showcase Dave p10's doped/plugged 40-1197s:

Anyway, I normally left the finishing to the end user. For myself I didn't care since they were always big/loud enough that hiding them behind open weave drapes was easiest.

GM
 

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Ok...well for the sake of simplicity I am going to try a regular transmission line.

Ok for the line length the length should be a little higher than the drivers fs...the polyfill stuffing will make the speaker "see" a longer line

What should I do for the area ratio?? tapered or a 1:1???
 
aznboi3644 said:
Ok for the line length the length should be a little higher than the drivers fs...the polyfill stuffing will make the speaker "see" a longer line

You get no siginificant apparent increase in line length from the stuffing.

If the line is tapered (bigger at the closer end) the line will need to be shorter, if tapered the other way it will need to be longer.

At least use Martin's tables (if not he entire sw package). Do not use classic design methodology.

Or as GM says, just build Nelson's

dave
 
Alternatively, if simple is wanted, an MLTL is even easier: http://www.diyaudio.com/forums/showthread.php?s=&threadid=113210

WRT traditional TL designs, as Dave says, stuffing does not significantly affect the apparant line length the driver 'sees.' One of the (many) myths of TL design, that. Assuming a semi-resonant line is what is desired, rather than a near-aperiodic or pure transmission line, then the principle affect of adding damping materials is to help attenuate the unwanted harmonic resonances of the pipe, and to change the system roll-off characteristic to something shallower.

For example, here's the frequency response of a simple, untapered pipe with a Peerless midbass & the driver mounted at the far end, with no damping applied:
 

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And here's the exact same pipe / driver, but with 0.5lbs ft^3 of Dacron hollow-fibre stuffing added throughout the line (different materials will need different packing densities for the same level of damping).

Note that the final cut-off frequency doesn't change much. However, what you do get is a much more balanced response overall, closer to the driver's natural sensitivity (where the undamped pipe boosts it signficantly above this), the attenuation of the harmonic modes, and the shallower roll-off described above.
 

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