problem.... with TL length

[AudioGeek]

ok.. i worked out that if I used 2 peerless 1727 per side in a TL config i need a length of 8 feet.

1/4 wave tuning is 35Hz unstuffed to 15Hz stuffed.
sealed box tuning is 35Hz to 32Hz stuffed.

This is with a 8 foot long tube at 12in in diameter... or about 6.3 cu ft.

I was going to just have the drivers at bottom in a push -push config and the tube out the top to ceiling...

problem is I do not have 8 foot ceilings.

If i cut it back to say 5 feet:

1/4 wave tuning is 55hz to 30hz and sealed box is approx 42Hz to 38Hz or something like that.

It still overlaps but not as good.

what would happen if I cut it back to 5 feet vs 8 feet????

[Nelson Pass]

What's the resonant frequencie of the Peerless?

[AudioGeek]

it is 22Hz free air.

pretty low!!

[cheesehead]

AudioGeek:

It's not just about 1/4-wave lengths anymore!

Take a look at some of the threads involving TL's, especially mass-loaded TL's. Then see Bob Brines' web site , Martin King's , and Planet10's sites.

Then get Martin's Mathcad sheets and find a way to make them work. The math isn't even that hard, Martin's sheets do the work.

There's lots of help available here on this forum... and TL's are (relatively) easy to do (in my meager humble understanding ).

[AudioGeek]

i don't want to do a ML TL.... just a straight TL with S0=SL

was going to use sonotube or PVC pipe.

plus my mathcad doesn't work some reason.

[MJK]

AudioGeek,

Try scoping out the TL geometry using my alignment tables. I don't understand your lengths, something does not look right to me.

Also, please read the models page on my site, I bet you can get the MathCad running after looking at the known problems people have encountered on this page.

[BillFitzmaurice]

You also want to reconsider how much lower you'll go stuffed versus unstuffed. The reality of it is perhaps 10% at best. The notion that stuffing will alter the speed of sound to allow a shorter line/lower F3 is valid, but not to the extent that your figures presuppose.

For a pure TL with your drivers the F3/Fs ratio is about 1.5/1, so an F3 of 35 Hz or so is achieveable. The F3 to Fp ratio is about 1.2, which means you'll need a pipe that is 1/4 wavelength long at about 30Hz, making it about 9 feet long. If you go 8 feet long for a Fp of 35 Hz you can realistically expect an F3 of about 42 Hz.

A five foot pipe will likely result in an F3 around 68 Hz.

[GM]

Normally, the point of using a TL is to get ~IB response from a semi-reasonable sized cab so a ~1/4WL of Fs and Vb = Vas is a good ROT for drivers with a Qts <0.403. For two of these it means a ~154.168" long pipe with a ~106.176" CSA, with the drivers offset ~43.16" down from the closed end (preferably in a bipole layout) and stuffed with 0.5lbs/ft^3 (~4.81lbs) of polyfil distributed along its length.

As you shorten its length, F3/Fc rises, which means the transient response progressively degrades as it moves away from controlling the driver at resonance, defeating the point of making a TL, so progressively more stuffing density is required to flatten the response and ~preserve the transient response of the longer/larger pipe.

Shortening it to 5ft, with the same CSA/stuffing to maintain the proper scaling and positioning the drivers at ~21.4", F3 = ~56Hz/half space, rolling off at ~12dB/octave below this point.

Anyway, from this you can scale driver position to whatever the max size you can tolerate. If you shrink the CSA also it will skew the driver location plus cause an even higher F3/Fc than the shorter pipe dictates, so better in this case to stick them in a sealed cab IMO.

GM