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FAST (WAW) build help and opinions
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Old 22nd August 2019, 08:28 PM   #1
seantkezm is offline seantkezm  United States
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Default FAST (WAW) build help and opinions

Hello again audio friends,

I was recently gifted with a pair each of MarkAudio Alpair 6m Gen2 and Dayton RS225-8 and would like to build a set of FAST (WAW if you will) 2-way floorstanders.

Before you ask, I don't have the equipment to take direct measurements myself, so I have been designing the crossover based on the manufacturer graphs. I have included .frd and .zma files I have been working with. Dayton has actual files from partexpress and I used a tracer program for the Alpairs.

I want the front baffle to be 10 inches wide which would be a baffle step at around 450 Hz. As such, I figured that would be a good crossover point. I have been playing around in WinPCD. I tried to do first order on both, but I didn't like how the response looked. So I tried first order on the woofer + zobel and second order on the Alpair (with polarity reversed) and think they look better.
Woofer: 4mH coil, zobel 20uF + 10ohm. Tweeter: 35uF + 2mH.

That said, and I'm sure you could tell, I don't really know what I am doing and would greatly appreciate any recommendations on the design.

Also, if there is anything else you need to know, please don't hesitate to ask.

Thanks so much!
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File Type: jpg Alpair_6m RS225_8 1st order predicted response.jpg (78.3 KB, 416 views)
File Type: jpg Alpair_6m RS225_8 2nd order predicted response.jpg (79.0 KB, 414 views)
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File Type: zip response.zip (12.9 KB, 3 views)
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Old 22nd August 2019, 09:38 PM   #2
planet10 is offline planet10  Canada
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FAST (WAW) build help and opinions
You aren’t crossing that low so a passive XO is doable but typically you want to have the woofer 43-5 db more sensitive than the midTweeter. With this combo and a pasisve XO you are likely going to have to significantly attenuate the A6.2m.

10” gives a nominal Bs(-3) ~ 456 so XO between that and 0.707 times ~320 Hz. Without measures exactly where is bets for the combo to deal with BS. I would probably start XO at about 350 Hz.

An acceptable passive XO is way harder to do than active, and as you go lower in frequency it gets more & more cost effective to biamp. (i rarely design passive XOs).

And ideally you want to keep the XO at a point where the C-C distance between drivers is less than a quarter wavelength of that frequency.

dave
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Old 22nd August 2019, 09:51 PM   #3
xrk971 is offline xrk971  United States
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FAST (WAW) build help and opinions
I have amongst the same speaker you seek. Design is all worked out and RS225-8 is a superb woofer. Almost any 8ohm 2.5in to 3.5in full range can be used with appropriate level adjustment via resistors.

10F/8424 & RS225-8 FAST / WAW Ref Monitor

Here is the XO:
Click the image to open in full size.

Put the woofer on top for best time alignment.

Looks like this:
Click the image to open in full size.
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Last edited by xrk971; 22nd August 2019 at 10:05 PM.
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Old 23rd August 2019, 09:03 PM   #4
waxx is offline waxx  Belgium
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As nerdy as i am, i messed around with this data for maybe an hour and came to this. It's a second order serial crossover without zorbel or bsc as it looks best without, but with a notch filter to tame the treble. 1st order and parallel crossovers did not work well with this setup for one or the other reason. You find the project files included.

Last edited by waxx; 23rd August 2019 at 09:16 PM.
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Old 23rd August 2019, 09:26 PM   #5
planet10 is offline planet10  Canada
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FAST (WAW) build help and opinions
I like series XOs, one of the times i did a passive i couldnít get anywhere w parallel, th eseries just popped.

Isnít this 2nd order:

FAST (WAW) build help and opinions-xo-png

dave
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File Type: png XO.png (6.4 KB, 371 views)
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Old 23rd August 2019, 09:35 PM   #6
waxx is offline waxx  Belgium
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Quote:
Originally Posted by planet10 View Post
I like series XOs, one of the times i did a passive i couldnít get anywhere w parallel, th eseries just popped.

Isnít this 2nd order:

FAST (WAW) build help and opinions-xo-png

dave
Yes it is, altough i'm a big 1st order fan, sometimes it's just not fit like here. Th OP crossovers too high to my taste, and the 6M does not go low enough to crossover low with it in 1st order. I do 1st with my 10M and that works, but here a second order is needed.
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Old 23rd August 2019, 10:15 PM   #7
planet10 is offline planet10  Canada
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What is the turnover frequency? We have often used 250 Hz for the FF85wKeN (PLLXO), the A6.2m moves more air.

But when the guy did the passive XOs for our latest one, he moved the XO up to 450 Hz.

dave
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Old 23rd August 2019, 10:53 PM   #8
waxx is offline waxx  Belgium
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180Hz as you can see in the graph. That's where i like to crossover FR (the 150-250 band) so there is no crossover in the frequency band where i find it disturbing (the 300-4K band). It's there that the phase issues that every crossover has, are most heared by me and where it disturbs me. Above or below is ok for me altough i prefer no crossover at all if possible...

It's because i crossover so low that i need a 2nd order, a first order would cause gaps in the lower part of it as the 6M does not go low enough.
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Old 23rd August 2019, 11:17 PM   #9
xrk971 is offline xrk971  United States
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I am not sure why you want to force the full range down so low. There is no need to go to 180Hz to get the fullrange magic. 500Hz to 700Hz is great as that allows much lower membrane displacement on the fullrange, thereby limiting cone motion induced harmonic distortion. Furthermore, the mid bass punch and slam provided by the much bigger woofer is much more visceral when powered by an 8in or 10in woofer vs a 3.5in “woofer”. A lot of this depends on how well behaved the woofer is so you can let it work up much higher. But making a 3.5in fullrange go to 180Hz really drives audible distortion levels up.
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Old 23rd August 2019, 11:56 PM   #10
planet10 is offline planet10  Canada
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Quote:
Originally Posted by waxx View Post
180Hz
I only cross that low when i have a real wide baffle. Our A7.3eN w 2 SDX7eN is the only example so far.

We tried 180 on an FF85wKeN WAW, it sounded really good, but 250 was better, giving a more viceral impact.

But we always use fairly extended mid woofers ó about 1700 hz on the SDX7 above but all the others good to at least 4k (and th e little Peerless we 1st used with the FF85kWeN could be said to reach out to 10k as does the Alpair 12pWeN. And mostly 1st order XOs and drivers closer than a 1/4 wavelength at the XO which makes them essentially coincident.

dave
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