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Mundorf AMT 27d
Mundorf AMT 27d
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Old 11th February 2015, 01:45 PM   #21
phazer99 is offline phazer99  Sweden
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Quote:
Originally Posted by annerholm View Post
So even if a shorter driver has better vertical disperion (due to it's size), that will increase when stacked?
You will get the same dispersion pattern of a driver of double height (if the drivers are totally uniform (which they never are) and with no spacing between them (which is impossible)), i.e. a more focused dispersion pattern. Whether that is better or not depends on your application, listening distance etc.
Quote:
Originally Posted by annerholm View Post
So a line source of a certain length - regardless of if it's one or many drivers - has theoretically always the same vertical dispersion?
Yes, but a line array is never a perfect line source, that would require an infinite number of drivers placed infinitely close together.
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Old 11th February 2015, 01:48 PM   #22
solhaga is offline solhaga  Sweden
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And as the two AMTs will not be that close you will get combing that will reduce hf response.
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Old 11th February 2015, 08:35 PM   #23
annerholm is offline annerholm  Sweden
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So if we boil this down to a comparision of a single 27d or a single 25d - which one is to prefer?
I can some see pros and cons:
27d
+ better dipole pattern, possible lower xo.
- too focused listening window
25d
+ better vertical dispersion/bigger listening window
- higher xo (or does it have to be? FS is 1250Hz)

What do you guys think?
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Old 11th February 2015, 09:32 PM   #24
solhaga is offline solhaga  Sweden
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Quote:
Originally Posted by annerholm View Post
snip

trying to achieve constant directivity

snip
Only to raise more questions , have you considered a CD wave guide in front of the AMT?
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Old 11th February 2015, 10:20 PM   #25
phazer99 is offline phazer99  Sweden
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Quote:
Originally Posted by annerholm View Post
So if we boil this down to a comparision of a single 27d or a single 25d - which one is to prefer?
I can some see pros and cons:
27d
+ better dipole pattern, possible lower xo.
- too focused listening window
25d
+ better vertical dispersion/bigger listening window
- higher xo (or does it have to be? FS is 1250Hz)

What do you guys think?
Personally I would go for the Dayton driver, as it seems to be able to go down to 1200-1500 Hz according to the comments on Part Express (but it would interesting to see some distortion graphs). For the Mundorf drivers the 27D looks much better in the distortion plots (but it's a really expensive driver). The 25D doesn't look usable below 2 kHz.
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Old 12th February 2015, 07:52 AM   #26
annerholm is offline annerholm  Sweden
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Quote:
have you considered a CD wave guide in front of the AMT?
I'm not a big fan of waveguides... How could that improve the constant directivity in terms of keeping a dipole pattern? The best thing about Mundorf's dipole AMT's is that they are about the most narrow dipole driver you can find. The shortest distance between the front wave and the back wave is what dictates how high you can keep that 8-pattern. IMO these drivers would be far superior to other dipole solutions such as double dome tweeters.
Quote:
Personally I would go for the Dayton driver, as it seems to be able to go down to 1200-1500 Hz according to the comments on Part Express (but it would interesting to see some distortion graphs). For the Mundorf drivers the 27D looks much better in the distortion plots (but it's a really expensive driver).
I know this would be a risky project since it's so expensive;-)... That's the main reason for posting it here and make some research. I've also emailed Mundorf themselves to hear what they say, but no answer so far. Will post if I get one:-)
My concern about the Dayton driver is that it's much wider and also have a kind of u-frame at the back.
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Old 20th February 2015, 07:51 AM   #27
annerholm is offline annerholm  Sweden
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Now I got some info from the manufacturer themselves. The narrow vertical dispersion of the 27d is of course confirmed, and this driver is intended to be used x3 in a dipole array.. Which explains the 12 ohm. (a quick calculation gives that it will cost you 6x549 EUR for 1800-30kHZ...) It can be xo at 1600Hz but needs compensation for the resonance freq peak with a prarallell LCR. Can somebody explain the LCR? Sorry for lacking the knowledge. Could that be done digitally since it would be active?

The 25d should have a much better vertical dispersion and could be xo down to 1800Hz.
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Old 20th February 2015, 08:53 AM   #28
phazer99 is offline phazer99  Sweden
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Quote:
Originally Posted by annerholm View Post
The narrow vertical dispersion of the 27d is of course confirmed, and this driver is intended to be used x3 in a dipole array.. Which explains the 12 ohm. (a quick calculation gives that it will cost you 6x549 EUR for 1800-30kHZ...)
Whoa, that's a pair of really expensive speaker with limited bandwidth.
Quote:
Originally Posted by annerholm View Post
It can be xo at 1600Hz but needs compensation for the resonance freq peak with a prarallell LCR. Can somebody explain the LCR? Sorry for lacking the knowledge. Could that be done digitally since it would be active?
That's a notch (or band-stop) filter. It can be done digitally (all filters can).
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Old 31st May 2017, 01:22 PM   #29
audiomagnate is offline audiomagnate  United States
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Quote:
Originally Posted by annerholm View Post
Now I got some info from the manufacturer themselves. The narrow vertical dispersion of the 27d is of course confirmed, and this driver is intended to be used x3 in a dipole array.. Which explains the 12 ohm. (a quick calculation gives that it will cost you 6x549 EUR for 1800-30kHZ...)
This makes a lot of sense to me. The 27d shape (and dispersion patterns) is close to that of the Aurum Cantus G3si ribbons I use. If you want your speakers to sound right using drivers like this when sitting down AND standing up, the line has to be the length of the difference between where your ears are when sitting and standing. For me, (I'm 5'10"/1778mm) that's about 30 inches, which happens to be the length of three 27d (774 mm). The longer your legs, the more drivers you're going to have to buy! I'm using two now (four total), but three would be better, or four when my tall friends drop by to listen. It has been proven that tall people earn significantly more money throughout their lifetimes than short people, so this seems only fitting.

Last edited by audiomagnate; 31st May 2017 at 01:37 PM.
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Old 31st May 2017, 03:48 PM   #30
lowmass is offline lowmass  United States
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The issue is you usually ether want a very long line or a very short one. Both give good vertical response. Everything in between will have some issue (not always a bad thing) with vert dispersion.

The AMTs are nice units BUT everyone wants to take tweeters lower now and although some AMTs show response to 1khz I would caution trying to crossover too close to this as these drivers cut off sharply and that response will show up in the crossover curve. As well there is some coloration associated with sudden response cut offs as it generally reflects mechanical limits in the diaphragm.

As well the horizontal dispersion tends to be a bit more narrow in these designs due to wider dimension than most domes or ribbons

Last edited by lowmass; 31st May 2017 at 03:53 PM.
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