Vifa p17wj-00-08 & D25AG-35-06 crossover. - diyAudio
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Old 15th May 2012, 04:16 AM   #1
shmb is offline shmb  Australia
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Default Vifa p17wj-00-08 & D25AG-35-06 crossover.

Hi all,

As many would know, this is an old driver combination commonly used in the past.

I'm currently trying to design a crossover for a centre speaker with these drivers in an MTM horizontal config. (Tweeter mounted slightly higher than woofers)

The biggest issue I'm having, is trying to reduce variations in response horizontally. I realise this is inherently hard with MTM and I'm only doing this by ear. I've tried many variations by experimentation but just wondering if there is a trick to this? Or is there anyone that has done this before with these drivers? Basically I'm after crossover schematics that I can work from.

I've done heaps of searches but most of the crossover schematics seem to have gone.
I have found a couple but they are based on a single woofer in a vertical array.

Tweeter: http://www.wescomponents.com/datashe...25AG-35-06.pdf

Woofer: http://www.sea.vg/vifa/P17WJ-00-08.pdf

Anyone have any advice/links re the x-overs?

Any help will be appreciated
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Old 16th May 2012, 04:38 AM   #2
shmb is offline shmb  Australia
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I made some progress yesterday and I'm now fairly happy with the result, but still would like some more tips if possible.
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Old 16th May 2012, 05:01 AM   #3
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this may help: Red Spade Audio: Etude TL crossover

edit: oops, no, it won't help much for a horizontal box...
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Impedance varies with frequency, use impedance plots of your drivers and make crossover calculations using the actual impedance of the driver at the crossover frequency

Last edited by PeteMcK; 16th May 2012 at 05:12 AM.
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Old 16th May 2012, 05:23 AM   #4
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well maybe it could be useful; these guys:
Outlaw Audio
use a 2.5 way xover in a horizontal MTM, ...???
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Impedance varies with frequency, use impedance plots of your drivers and make crossover calculations using the actual impedance of the driver at the crossover frequency
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Old 16th May 2012, 09:37 AM   #5
AllenB is offline AllenB  Australia
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Quote:
Originally Posted by shmb View Post
I realise this is inherently hard with MTM
You'll be fairly restricted in your crossover frequency, somewhere around 1700Hz in your case.

You'll want to get the phase difference between the drivers correct. Without this you kind of defeat the purpose of the MTM. A crossover specifically for an MTM wouldn't be the same as any other for the same drivers.
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Old 16th May 2012, 12:54 PM   #6
shmb is offline shmb  Australia
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Did more listening/tweaking tonight and I'm certainly getting there.

I have seen the red spade audio link before, but the outlaw one is an interesting one. Osborn use this principle in their MTM centres too.

AllenB: Regarding xover point, if this helps, the tweeter is mounted higher than the two woofers and the acoustic distance (centre to centre) between the tweeter and either woofer is just under 130mm. Reason is the woofers are mounted on top of the frame of the tweeter so they can be closer. Doesn't that equate to a 2700Hz or less xover, or am I way off the track? Can I ask how you worked out 1700Hz? I think that's way too low for this tweeter anyway.

Thanks so far guys.

Last edited by shmb; 16th May 2012 at 01:11 PM.
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Old 16th May 2012, 03:22 PM   #7
AllenB is offline AllenB  Australia
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I was probably just a little more conservative given that there are a few reasons why it is better to err on the low side with an MTM

By the way, that tweeter may not normally be crossed that low, but it could be if you were careful. It's also not a bad thing to keep crossovers low so they are less obtrusive.
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Old 18th May 2012, 12:49 PM   #8
shmb is offline shmb  Australia
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Well, after reading this, I've now gone for a lower crossover frequency and it seems to have helped.

For now, I have settled on a single 0.82mH coil in series with the 2 woofers (connected in parallel).

For the tweeter, a 6.8uF and 0.82mH second order, with an l-pad after that consisting of an 18 ohm in parallel, and a 0.47ohm in series with the tweeter.

I've tried impedance equalisation as well as a second order slope on the woofers, but those all cause more horizontal variation.

The crossover frequency, at a guess is probably around 2kHz now, hope the tweeter can handle it.

Thanks.

Last edited by shmb; 18th May 2012 at 12:53 PM.
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Old 19th May 2012, 04:57 AM   #9
AllenB is offline AllenB  Australia
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Quote:
Originally Posted by shmb View Post
I've tried impedance equalisation as well as a second order slope on the woofers, but those all cause more horizontal variation.
Have you considered this may be a phase issue.

Quote:
The crossover frequency, at a guess is probably around 2kHz now, hope the tweeter can handle it.
There are tradeoffs between performance, distortions and the design goal. FWIW, I've done worse.
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Old 19th May 2012, 12:53 PM   #10
shmb is offline shmb  Australia
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I have no doubt, its a phase issue, I'm assuming adding the extra capacitor is causing extra phase shifts which are not needed.

Anyway I'm having fun playing with it, if I can get it as good as possible, I'm happy.

BTW: it was from reading you're thread on 'designing crossovers without measurement' which inspired me to get back into this. After the centre, I'm going to redo the crossover on my rear and front speakers too. (all my diy design from many years ago)
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