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Dayton AMTPRO-4: how low to cross when used open back?
Dayton AMTPRO-4: how low to cross when used open back?
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Old 7th April 2016, 03:05 PM   #1
CharlieLaub is offline CharlieLaub  United States
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Default Dayton AMTPRO-4: how low to cross when used open back?

I am gathering drivers and parts for my next speaker project and one of these is a pair of Dayton AMTPRO-4 AMT. After doing some modeling I plan to use this without the pads and located at the top of an open baffle, about halfway in/out of the baffle (the unit will stick out halfway above the baffle with the lower half mounted in the baffle). This seems to result in good CD-like off-axis response.

I thought I would try to get some opinions from people on just how low I can cross over to the woofer with this arrangement. There should be a little more low end support in the frequency response when it is partially in the baffle. The infinite baffle response is usable down to 800Hz, but I am thinking 1kHz might be possible. Would that result in too much strain on the driver?

The crossover and speaker are both active, so I can shape/EQ the driver's frequency response as needed.
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Old 26th May 2016, 02:44 AM   #2
frangus is offline frangus  Australia
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Did you ever get to test these Charlie?
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Old 5th March 2017, 06:34 PM   #3
CharlieLaub is offline CharlieLaub  United States
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Yes, I just took off axis measurements with the driver hanging by strings. I will post these later today when I can get the data off of my measurement rig.
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Last edited by CharlieLaub; 5th March 2017 at 06:46 PM.
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Old 5th March 2017, 06:45 PM   #4
TNT is offline TNT  Sweden
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Dayton AMTPRO-4: how low to cross when used open back?
Mine measured very low distorsion. But what about "the sound"... I wasn't so sure. But I'll keep them for future endeavours. A rock-box sealed back for the ATM and a smaller seald for a 15" with a Hypex 2x400W inc. X-over plate amp :-D

CL - what did you think about the SQ? Do they improve by time?

//
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Old 5th March 2017, 07:19 PM   #5
CharlieLaub is offline CharlieLaub  United States
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OK, here are my measurements on the AMTPRO-4. I collected all this data by suspending the driver in free air and using gated impulse measurements. I was able to get about 50Hz frequency resolution using this approach. For the HD and IMD measurements I did not check the level but I would estimate that it was at least 90dB@1m with the "10dB louder" HD measurement increased by that amount.

Attachments:
  • Horizontal FR at 0deg and about every 11 degrees off axis until 90 deg, taken in FRONT of the driver at a distance of 16inches (0.4m)
  • Horizontal FR at 0deg and about every 11 degrees off axis until 90 deg, taken in BACK of the driver at a distance of 16inches (0.4m)
  • Vertical FR at 0deg and about every 11 degrees off axis until 90 deg, taken in FRONT of the driver at a distance of 16inches (0.4m)
  • Vertical FR at 0deg and about every 11 degrees off axis until 90 deg, taken in BACK of the driver at a distance of 16inches (0.4m)
  • Harmonic Distortion vs frequency on axis in front at 16inches (0.4m)
  • Harmonic Distortion vs frequency on axis in front at 16inches (0.4m), with level increased by 10dB
  • IMD (using 10kHz and 11kHz tones) on axis in front at 16inches (0.4m)

Conclusions:
This is a unique driver in that the front and rear frequency responses are similar, and the rear response is without peaks or nulls above 2kHz (this is often a problem with a cone driver because of the magnet and backet). Because of the length of the diaphragm the vertical response is already starting to narrow around 2k-3k Hz but this is about the only shortcoming of the driver when used in this way. The distortion is pretty low between 1kHz and 8kHz and this distortion profile remains about the same when you increase the SPL another 10dB. IMD also looks good. Based on the harmonic distortion plot I think one could use this driver down to 1.5kHz if crossed steeply. Where to cross over to a tweeter depends on how close you want to get to the high end distortion rise, narrowing response pattern and diverging response between front and rear.


NOTE: to figure out which plot is which, hover the mouse pointer over the attachment thumbnail and then look for the name at the bottom of the browser window.


.
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Last edited by CharlieLaub; 5th March 2017 at 07:22 PM.
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Old 7th March 2017, 04:00 PM   #6
bentoronto is offline bentoronto  Canada
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Dayton AMTPRO-4: how low to cross when used open back?
A few years ago, I concluded it made no sense to lock-into the details of crossing-over before putting a mic at your seat and choosing freq and maybe slope empirically with REW, at least as far as the bits and pieces and components I fool with.

Just as nobody makes a car with windows with manual winders (I think), so it makes little sense today for music enthusiasts to make their main system anything but a multi-amped system with an adjustable crossover.

B.
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Old 9th March 2017, 09:46 PM   #7
wreckingball is offline wreckingball  United States
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Wonder if people are using these with no tweeter above their FR and just EQing?
I'm going to assume yes and "to heck with the added 2nd-order distortion up-to and around 10-12k".

I bought a pair of these, but because they weren't what I was expecting, may be selling them...
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Last edited by wreckingball; 9th March 2017 at 09:54 PM.
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Old 10th March 2017, 02:26 PM   #8
Fenalaar is offline Fenalaar  Norway
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As there is a peak in the frequency response at the same frequency, EQing this will reduce the distortion by the same amount.

Johan-Kr
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Old 10th March 2017, 02:43 PM   #9
TNT is offline TNT  Sweden
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Dayton AMTPRO-4: how low to cross when used open back?
Distorsion is not this drivers problem. I wonder why people seem to not really take a liking on them?

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Old 11th December 2020, 01:11 AM   #10
hollowboy is offline hollowboy  Australia
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To reply to TNT's old question:

"I wonder why people seem to not really take a liking on them?"

I got a pair. They were OK, but didn't work for the niche application I had in mind. I wanted to make a high efficiency coaxial by removing the faceplate

(this thread shows what they look like without it):

AMT tweeters - explored by Critofur -

Techtalk Speaker Building, Audio, Video Discussion Forum


...and mounting them in the mouth of a midrange horn. I was using some big JBL compression drivers, and I wanted to use the AMTs to fill in the range where the JBLs were spiky.

For me, the vertical dispersion of the AMT was too narrow to work well in this setup. For an always seated listener, it might have been fine.

In general:

- these particular AMTs take a bit of eq to flatten.
- if you use a big planar as a wide range driver (up to 10kHz), the vertical dispersion will be quite limiting.
- IF you use them only in the midrange (1-5kHz), the dispersion would be fine, but there are tons of reasonably priced conventional and horn drivers that do 1-5kHz happily. The only reason to choose the AMT over them is if you were into the dipole thing.
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