MTM Project Advice

jimbones · 11th October 2011, 01:22 AM

I have some Dynaudio 17W75's laying around and I was thinking of building up an MTM. Any suggestions on what tweeter? I have done a little research and what little I do know is that you need to get the tweeter and woofers as close as possible and the XO point as low as possible. Thanks. Oh and do the woofers have to be angled in? That would make the cabinet assembly more complex.Thanks.

wintermute · 11th October 2011, 02:34 AM

Is it the original 17W75 or one of the later ones with more extended frequency response? The original looks like it would need to be crossed fairly low (maybe 2K) though you might be able to simply use at notch filter at around 2.5K and cross it there. It is a bit hard to tell the natural rolloff from that graph but it appears to be greater than 24db/octave!

I'm looking at the pdf on David's site http://www.gattiweb.com/images/dynaudio/17w75_data.pdf

some of the morel tweeters may be a good match

Tony.

AllenB · 11th October 2011, 04:53 AM

The reason you want to cross low is because the two drivers will behave a little like one driver as big as the two are spaced. I.e. they will become directional and the highs will cancel off axis. Your tweeter won't have this issue so if you cross too high, you will have a power loss in the midrange.

The aim of the MTM is to use the crossover to phase the drivers so you reduce the vertical lobing, i.e. normally there are cancellations between woofer and tweeter just at the crossover region where you either need to suffer a power loss, or allow an on axis peak to make up for it.

You can treat an MTM like a conventional speaker in which case it will appear a little like an offset coax (two-way car speaker), and you'll probably want to phase it carefully around the crossover.

jimbones · 11th October 2011, 12:17 PM

Update: Madisound recommended some tweeters Seas H1499, H1189 DXT tweeter that is used in the IDUNM and a morel with a 94mm flange. Since the Dynaudio is flat out to a few k and then peaks I was thinking of an xo point of 2k or 2.5k

11th October 2011, 01:22 AM	#1
jimbones diyAudio Member Join Date: Nov 2004 Location: ny	MTM Project Advice I have some Dynaudio 17W75's laying around and I was thinking of building up an MTM. Any suggestions on what tweeter? I have done a little research and what little I do know is that you need to get the tweeter and woofers as close as possible and the XO point as low as possible. Thanks. Oh and do the woofers have to be angled in? That would make the cabinet assembly more complex.Thanks.

11th October 2011, 02:34 AM	#2
wintermute just another diyAudio Moderator Join Date: Aug 2003 Location: Sydney Blog Entries: 22	Is it the original 17W75 or one of the later ones with more extended frequency response? The original looks like it would need to be crossed fairly low (maybe 2K) though you might be able to simply use at notch filter at around 2.5K and cross it there. It is a bit hard to tell the natural rolloff from that graph but it appears to be greater than 24db/octave! I'm looking at the pdf on David's site http://www.gattiweb.com/images/dynaudio/17w75_data.pdf some of the morel tweeters may be a good match Tony. __________________ Any intelligence I may appear to have is purely artificial! Some of my photos

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11th October 2011, 04:53 AM	#3
AllenB diyAudio Member Join Date: Oct 2008	The reason you want to cross low is because the two drivers will behave a little like one driver as big as the two are spaced. I.e. they will become directional and the highs will cancel off axis. Your tweeter won't have this issue so if you cross too high, you will have a power loss in the midrange. The aim of the MTM is to use the crossover to phase the drivers so you reduce the vertical lobing, i.e. normally there are cancellations between woofer and tweeter just at the crossover region where you either need to suffer a power loss, or allow an on axis peak to make up for it. You can treat an MTM like a conventional speaker in which case it will appear a little like an offset coax (two-way car speaker), and you'll probably want to phase it carefully around the crossover.

11th October 2011, 12:17 PM	#4
jimbones diyAudio Member Join Date: Nov 2004 Location: ny	Update: Madisound recommended some tweeters Seas H1499, H1189 DXT tweeter that is used in the IDUNM and a morel with a 94mm flange. Since the Dynaudio is flat out to a few k and then peaks I was thinking of an xo point of 2k or 2.5k

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