Importance of Vas in TL-loading

[Klimon]

Looking for a midwoofer to use in an existing cabinet I've found a candidate with near-identical Fr and Qts compared to the woofers the Tl cabinet was designed for. However Vas of the original woofers is 15; the new woofers state 25l. Will this work properly or if not, what can I tweak to the cabinet to suit the higher Vas?

Thanks!

Simon

[GM]

All else being equal, increase Vas and cab Vb must increase proportionately, so double Vas, double Vb for a given alignment, ergo the TL will be too small in cross sectional area (CSA) for the new driver to work optimally, i.e. once stuffed it will have a higher F3, F6, etc., but depending on the room, etc., it may still perform well, though only one way to know for sure.

GM

[sreten]

Hi,

If the Fs of the drivers is the same this implies the 25L Vas driver
has a lighter cone or a larger effective radiating diameter than
the 15L Vas driver, either way as GM said, a bigger cabinet.

What is the Fs and Qts of the original driver ?

/sreten.

[Klimon]

Fr= 55hz
Qts= 0,52

It's hard to find a driver with same Fr+Qts+Vas as the original; another driver has matching specs except for Qts of 0,4. if Fr dictates length of the line and Vas=diameter, where does Qts come into the equation?

Thanks -- Simon

[sreten]

See measurements at Zaphaudio.com

Hi-Vi F6 is very near, the Tangband-W5-704D not too far away.

this is all assuming the TL does match the specifications.

You can check that here :

http://www.quarter-wave.com/TLs/Alignment_Tables.pdf

Which also illustrates the effect of Qts with Fs and Vas fixed.

/sreten.

[GM]

Basic max flat reflex box formulas:

Vb = 20*Vas*Qts^3.3

Qts = 0.403412*(Vb/Vas)^0.303

Vas = 0.05*Vb/Qts^3.3

---------------------------

original driver:

55 Hz Fs
15 L Vas
0.52 Qts

Vb = 34.668 L, so assuming these specs are ~accurate, then your goal is to find a ~55 Hz Fs driver with a Vas, Qts combination that yields approximately this Vb with the understanding that a lower/higher Qts will raise/lower F3, F6, etc..

GM

[Klimon]

Hi-Vi F6

The TL I'm talking about is 's3tml' from IPLaccoustics.co.uk who formerly used a custom designed driver and now the HIVI m6a, be it with slightly differing specs. What I'm looking for is a driver that works in the given cabinet, has highish efficiency and a relatively smooth midrange. The TB you suggested looks like a peach but is a 5" woofer vs the 6,5" original. Should I make an adapter to ammend the existing hole, wouldn't the change in piston area still affect TL behaviour?

Vb = 34.668 L, so assuming these specs are ~accurate, then your goal is to find a ~55 Hz Fs driver with a Vas, Qts combination that yields approximately this Vb with the understanding that a lower/higher Qts will raise/lower F3, F6, etc..

Thanks, that gives me something to work with.

Thanks again guys, much appreciated.

Simon

[GM]

You're welcome!

Where in the formulas I posted is driver Sd included? If you're referring to MJK using Sd as a reference to defining a TL's, etc. cross sectional area (CSA) it's just that, a reference, and if you use his old worksheets that have this default I recommend converting them to either a width x depth or area dims to save yourself a step in the calcs.

Anyway, Sd only affects its peak SPL rating, which can be compensated for by increased Xmax and/or power handling, so assuming it has enough of each to suit you regardless of whether it measures up to the original, then it's a viable alternative.

GM

[Klimon]

Excellent. The closest thing available in Europe is this http://www.juoiga.nl/download/w5-1611.pdf

Widerange so will certainly allow for a first order at 3k or so.

Cheers

Simon