What tweeter??

[Gargoyle]

Like some advice on a tweeter to match the Vifa M18WO-09-08

Cabinet will be a 25l Vented enclosure tuned to 36hz with a 50mm x 146.66mm vent

I had in mind (read easily obtainable) the following

all Vifa's

XT25TG30-04
D27TG-35-06
D25AG-35-06

I have limited ability to tune so was looking at a Butterworth second order crossed at basically 2500 to 2800 to match the Mid/woofer as all 3 tweeters should handle this.

As an aside is a front mounted vent preferable in this application??

Any comments, advice or criticism will be most welcome

Cheers

Gargoyle

[sreten]

find a design on the web using using your bass driver ,
they exist.

should allow for Baffle Step Compensation.

sreten.

[5th element]

Ok im not sure how much you know about speaker design. So ill say a few basic things here.

"I have limited ability to tune so was looking at a Butterworth second order crossed at basically 2500 to 2800 to match the Mid/woofer as all 3 tweeters should handle this."

Yes all tweets will handle this but with regards to the butterworth?? Well, you would use xover values presumably calculated from a formula in a book or on the net. This would provide you with an electrical 2nd order butterworth into an fixed impedance. Lets assume the tweeter will have a perfectly flat 8ohm impedance so your calculations will yeild the correct slope, so it actually generates the butterworth electrically. Will you have a butterworth filter?? Nope, coupling the 2nd order butterworth with the tweeters frequency response could give you anything from a 2nd order to 4th order acoutic roll off, with any of the standard filters, ie linkwitz butterworth bessel.

But the tweeter doesnt have a flat even impedance for the xover to work on so the calculated values probably are not giving you an electrical butterworth at all!

Also with regards to the woofer I dont think you can get away with just a simple xover, I have heard that you should cross as low as you can with this driver, and you can see why! The freq response is pretty ragged above 2.5k if you ignor the slight peak and dip around 1.5k.

If I were you I'd get loudspeaker workshop from Adua (its free) and SPL trace, then do some simulating. This is at the very least.
What would be even better is if you built the wallin jig for speaker workshop and measured all the drivers yourself. This would give much more predictable results then just throwing a text book xover at the drivers.

One last note - hunt for a tweeter which can be crossed LOW as in about 2k, I wouldnt personally want to go much higher with the M18W0. Tweeters to consider would be the Scan D2905/95, probably the 93 although I havnt used this one. The 95 does 2k no probs so the 93 shud too. A cheaper alternative would be the SEAS 27TFFC which from what I have read can do 2k also.

Obviously this is only one persons views and I have not used the M18, but from what I can see with this driver I would certainly not want to cross high.

Oh and that peak at approx 1k can be dealt with via a RLC, but again you will need to simulate to get the values correct for this because it is dependant on what crossover you use with the M18.

Regards Matt