I am hoping to use a pair of Dayton AMTPRO-4 planar drivers as part of a dipole project. After some recent testing I have figured out how low I can cross these drivers and other info about the response pattern.
I would like to cross over the AMT to a tweeter no lower than 5kHz, maybe as high as 7kHz, to a front firing dome tweeter. The purpose for this is to create a system that is fully dipole up to this point, and then forward only radiation above. One tweeter I am considering is a compact small dome (3/4", 18mm) unit that is transitioning from monopole to controlled directivity around this frequency. The other tweeter I am considering has a 4" flange with a waveguide for a 1"/25mm dome and is close to CD all through this range up to its top end.
I am stuck on how to best integrate the AMT with one of these tweeters. From what I have read, the AMT's diaphragm is connected to the frame at the ends (in the long direction) and the rest is free to move, although I am not sure about this. In any case, the radiating area is long, vertically (the AMT will be mounted in the normal way with the "long" axis oriented vertically). I could place the tweeter above or below the driver but this will put the dome far from the "center" of the diaphragm. I could also put the dome right next to the middle of the AMT, to one side. In the former case, the lobing would be in the vertical plane and the latter the lobing would be laterally. In the former the distance from the center of the AMT to the dome would be about 5" and in the latter the distance would be about 2.5". At 5kHz, the wavelength is about 2.75 inches, so in either case there will be some lobing.
I'm throwing this out for comments.
I would like to cross over the AMT to a tweeter no lower than 5kHz, maybe as high as 7kHz, to a front firing dome tweeter. The purpose for this is to create a system that is fully dipole up to this point, and then forward only radiation above. One tweeter I am considering is a compact small dome (3/4", 18mm) unit that is transitioning from monopole to controlled directivity around this frequency. The other tweeter I am considering has a 4" flange with a waveguide for a 1"/25mm dome and is close to CD all through this range up to its top end.
I am stuck on how to best integrate the AMT with one of these tweeters. From what I have read, the AMT's diaphragm is connected to the frame at the ends (in the long direction) and the rest is free to move, although I am not sure about this. In any case, the radiating area is long, vertically (the AMT will be mounted in the normal way with the "long" axis oriented vertically). I could place the tweeter above or below the driver but this will put the dome far from the "center" of the diaphragm. I could also put the dome right next to the middle of the AMT, to one side. In the former case, the lobing would be in the vertical plane and the latter the lobing would be laterally. In the former the distance from the center of the AMT to the dome would be about 5" and in the latter the distance would be about 2.5". At 5kHz, the wavelength is about 2.75 inches, so in either case there will be some lobing.
I'm throwing this out for comments.
For a pretty complete set of measurements that I made on this driver, see this post:
http://www.diyaudio.com/forums/plan...ow-cross-when-used-open-back.html#post5009411
http://www.diyaudio.com/forums/plan...ow-cross-when-used-open-back.html#post5009411
The AMT does not make any movement in the direction that a planar does i.e. in the direction towards the listener. It moves sideways, like the middle piece in an accordion, and squeezes out air towards the listener. I assume all 4 sides are anchored in the frame. I think you should try to maintain an equal directivity throughout. A WG is good and not that big for that range.
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Hmm, not sure about that. I am using this driver in an open baffle type speaker. A waveguide doesn't really fit with that kind of application, and does not help when it comes to crossing over to the tweeter. I think it would make the situation worse because the extra material in the waveguide around the periphery of the tweeter will push the acoustic centers farther apart. Can you point me to a waveguided dipole using this AMT?
Thanks for clarifying how the AMT membrane is working. I forgot about that...
I wonder about this driver OC25SC65-04: Peerless by Tymphany OC25SC65-04 1" Textile Dome Tweeter
It could very well be very good above 7khz. Glue 2 back to back with a thin wall between them? I have a need for a very small footprint dome for duty above 6-7 khz but I cant find any good reference on these on the web.
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It could very well be very good above 7khz. Glue 2 back to back with a thin wall between them? I have a need for a very small footprint dome for duty above 6-7 khz but I cant find any good reference on these on the web.
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Not off-axis. Look at my measurement data:
http://www.diyaudio.com/forums/plan...ow-cross-when-used-open-back.html#post5009411
Even on axis it's not good above 8kHz. Too many problems.
Could you please... pretty please, make some measurements on these - it would be much appreciated - distorsion please.
Have you played them? OK?
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Have not played them, but I put a lot of trust into Zaph measurements. Also, from this forum, you will find "nude" frequency response measurements (driver was hung by a string) performed by member Joachim Gerhard here:
http://www.diyaudio.com/forums/multi-way/178350-zdl-7.html#post2403471
Download the pdf attachments to view the plots. Not many angles, but he did make a measurement at 180deg. The limited data looks good to me!
I'm attaching the Zaph data, including distortion. He mounted them in a beveled hole.
Attachments
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Judging by the distortion and CSD plots, a 3k crossover point would be the lowest I would try with this dome. It is a 3/4 (18mm) unit after all. Anything about that should be fine. For this price it is an awesome little guy. Maybe that is why it has been continuously made available for quite a few years now?
So, at what frequency would you suggest crossing the AMTPRO-4 over to this dome? Anyone?
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In my experience you really can't judge an AMT like anything else looking at the FR response. They measure kinda wonky, but don't sound anything like what you'd expect it to. I used mine full range and to compensate for the top end roll off, I used the AMT-mini from like 10KHz up with great results.
I will give the 'mini' a look. Can it be run open back (dipole)?
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Hiy'all, very interesting thread as I'm nearly finished my first ever DIY speaker build with the AMT PRO-4 in an open backed housing on top of a tower speaker with two RS180-4's and a 12" tapped horn sub. They will be active with eq and I was thinking that would do but I'm now having second thoughts! An AMT Mini would be easy to add on top. Maybe limited in output? Are you using it with a passive? I could buy another amp & go 4 way?
Martin.
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