new Heil AMT type driver

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Santiago53

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Joined 2009
#1
This may be useful to those looking for good AMT type drivers

For a long time I've been looking to get a reasonably priced AMT type driver, and never felt excited about buying used Heil AMTs with cracked and aging diaphragms for 350+ a pair!


So afterMUCH looking, I was able to get and test the dm2a driver from Mark & Daniel. Their on axis response was pretty scary, but if loaded with a diffusor to get an Omni type response they did great.

So yes, a good AMT at a fair price BUT....be careful, they require some special acoustical loading.
You can get them from Jason Terpstra, contact him at:

jterpstra@markdanielofamerica.com

About the tests:

I measured with a calibrated Mic using a Behringer DEQ2496 pink noise... SPL isn't shown correctly, but I referenced to a known 88dB source, so the levels can be extrapolated fairly easily.
The divisions between dotted lines are 5dB.

1) Direct Radiation Response: see picture dm2a on axis direct radiation

the dm2a has an average sensitivity of about 82 dB followed by a "tilted shelf" response starting at 7KHz. The 10KHz level is at about 88dB and the 20KHz level is about 95dB and appears to continue on a strong rising trend.

Comments:
The dm2a response makes it a little tricky to integrate without resorting to lots of equalization. If used in a system at 82dB it will be smooth from 1KHz to 5KHz with a 4 dB dip at 6Khz, but will then have a MAJOR high frequency emphasis and sound quite sizzly.


One could put in a first order roll-off on the top end but this would aggravate the dip at 6KHz, make it very inductive.. and still end up with only 81 to 2dB on axis sensitivity.

Also note, even though the level at 450Hz is about 84 dB, that is due to a major mechanical resonance. The crossover should be at least 3 to 4 times higher to avoid exciting this resonance. Don't even THINK about a 900 Hz crossing unless you like a very resonant vocal band!

Not so good if you want to use these with even a medium sensitivity midrange or woofer. But read on, there IS a way to make this work and work WELL.

2) Where one could say that the dm2a is not a great choice for direct radiation, it can be SPECTACULAR if used as shown in the picture entitled "dm2a omni mount with deflector"

If you look at the series of pictures of the Omni w. deflector response, you will see that the use of a properly proportioned and spaced deflector adds an acoustic impedance load which brings the response of the combination to a level that is much more than just acceptable, it is very, very good.

Because of the improved acoustic loading (and dig that fancy cut glass deflector!), the average sensitivity goes up to near 88dB across the band and is now very flat, within a +/- 2dB band from 1.5KHz to 20KHz. See the pics of response for the Omni array at 5 degrees below horizontal as well as the responses at 10 degrees above and below.

This array puts out very FLAT response well beyond 20Kz


PLEASE NOTE: 88dB at 2.83V is decent efficiency, but because this response is nearly identical at ALL of the 360 degree circle (It's omni ! It's OMNI !!), the acoustic power output is equivalent to that of a ScanSpeak AirCirc D3004/6600 direct radiator at 94dB. This level of output is about the same as that of the AirCirc … and the impedance is also about the same at 4 Ohms for the dm2a vs 3 Ohm for the AirCirc


I really like the AirCirc... but I may like the dm2a even more...need more time to tell for sure, but this omni array really works wonders.


But please note! the deflector shape and distance play a CRITICAL role in smoothing out the dm2a response. IT WILL NOT BE THE SAME UNLESS YOU USE THE DEFLECTOR ARRAY!! What you see in these pictures is the result of very careful adjustment of the distance between driver and deflector (23mm). other shapes and sizes give different (and mostly inferior) results. I tried other deflectors, this one worked the best... there may be others that work better, so please let me know what you find.


So how does the Omni array sound? Crossed over at 2KHz with a simple 1st order slope, and mid bass drivers at 88dB, the sound is spectacular: open, clear, quick, tremendous impact (impact? From a tweeter? YES!!) and uncompressed clarity that is very hard to beat, even at very high SPL.

Comparing against the ScanSpeak AirCirc revelator, the dm2a in the omni array will give similar levels of neutrality, MUCH wider dispersion at high frequencies, and apparently higher levels of low distortion output with what seems like more impact. And the fact that it can be had for USD100 each instead of USD250+ for the Revelators, well that makes up for the shiny plastic faceplate which covers the (adequately substantial) painted metal housing.


More later, maybe test em with controlled directivity waveguides and the foam bung like GedLee... but that will come MUCH later, if at all. I like this in omni so much that I may never get around to it.

So, anyway, looks like great choice when used in this way.
 

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#5
Hi Santiago53 - and Welcome to diyAudio! 😀

Impressive work you are doing and I am interested in your findings and progress. I already have AMT1's and have loved them from the 1st time I listened to them back in '75. I lived in Sacramento California where the ESS plant was at and had a couple of friends that worked there and introduced me to the AMT's. I would need to come up with a different diffuser from the one you are using because if the wife sees that thing she will want one too! :clown:

Your AMT's from M&D cost $100 USD each? Did I read this correctly???
If this is correct it is one heck of a deal!!! :bigeyes:
 
#6
AMT cost

yes, Jason is making them available at $100USD each...

I think it's a fairly good price given the performance these are capable of. But I do advise users to respect this one warning: they really sound excellent, but again ONLY if used with an Omni diffuser similar in distance, size and angle to the one I used...

and please no jokes about "crystal clear highs" 😀 ....

and , no, I don't really believe the diffuser has to be made of crystal:whazzat:
 
#7
M&D use their Omni-Harmonizer from 7K on up - and it is made out of marble (they like to use marble don't they). Something a little bigger along the same design lines should work out. If I used 2.5 KHz for the targeted lowest fs then the diameter of the cone should work out to 5.4 inches and 8.76 inches high (golden ratio). So - make a little "snow cone" shaped mold out of heavy paper and mix up a little acrylic plastic and "presto" - I have a diffuser. Or I could turn one out of a nice hard wood - that might have some WAF to it. I would finish things off with BudP's EnABL pattern just for S&G's. Hmmmm - currently have two speaker projects in the Q - plus a couple of class A mono blocks in assembly - so that would make the ETA on this thing - ????? 🙄 Damn - I just luv this little hobby!!! 😎
 
#9
DM4

Sorry, I haven't been able to measure or hear the DM4 yet, although i am quite interested as they may be able to be crossed in lower than the DM2a

I believe there is a newer version in the works, the DM4a.

Still, with the deflector, the DM2a gives good measured performance and subjectively a highly musical and transparent sound, coupled with tremendous dynamics, rhythm and pace. Superb for crossing in over 2KHz

So, i guess you could say I like em!
 
#10
DM4 measurements

Hi, I just found this series ofDM4 measurements at ZaphAudio, check his site at

http://zaphaudio.com/tidbits/

A few comments:

1) the freq response looks fairly similar to that of the DM2a, meaning that this driver will likely benefit from a similar omni deflector to what I described previously for the dm2a...
I would echo Zaph's comment about the FR seems unusable without major eq'ing aqnd DEFINITELY echo his comments on the midrange honk if crossed in too low

BUT...
the omni deflector, as used for the dm2a may reslove many of these issues (not the honk at 400Hz though)

AND... the deflector probably has to be bigger in order to extend the acoustic loading to lower frequencies

2) The distortion figures look fairly good, even very good in the lower ranges

SO, despite looking like a difficult driver, similar to the dm2a, a properly conceived omni load/deflector may turn this into an excellent performer

enjoy!
 
#11
Thanks for the links. I plan to use it as a supplement to other full range speakers. So it will run in parallel with the full range. The concept of omnidirectional certainly is appealing and will give it some serious thoughts....

Now back to the omni reflector. Will the use of a high grade diamond make the sound brighter (sorry couldn't resist😀 ).

I am sure when you built that the wife approvalbility factor was quite high...

Oon
 
#12
more thoughts on dm4

hey Oon,
given that the DM4 has that big bump at 400Hz, like Zaph said, I would suggest crossing it over high enough to keep the mids from honking - it's right in the vocal range - ouch -

so i would suggest a lowest xo at 2Khz if using 1st or 2nd order

to go lower then i would say maybe 1.5 KHz with a 3rd order and 1.2KHz with a 4th order

as for sparkly highs, well I think "crystalline clarity" will surely beat "hard as diamonds" so I would still opt for the crystal deflector hehe, just a matter of personal preference I'm sure

but we should never rule out the sparkle appeal when it comes to the ladies, so yeah, go ahead and use that extra pair of 500 Carat diamonds you have lying around in your safety vault....

that way the sound could be .... "sparkly but rich"








:smash: :smash:
 
#13
Hi Santiago,

Thanks for the advice. Since I am using two different drivers handling the same frequencies, the sound will come out the average of the two. So the honk might not be so objectional. Might try and crossover at 1KHz with simple capacitor. Will have to try that and see.

I am hoping this one will be used more for picking up the low level treble and to improve the overall detail.

The speaker I plan to pair it with is a markaudio alpair 6. More info of it is available in full range forum.

I like it so far, the details and airiness coming out of that thing is quite amazing.

I think you should also consider lighting up the diamond from below..... Could look quite spetacular.

If i had a few 500 carats, I might sell it off and get a few other wives....

Oon:devilr:
 
#14
Hmm, using the Dm4 with the Alpair could be a good combo...

I would think that you could put the Alpair at a 60 degree angle, almost pointing up, this would give a near omni response up to about 3KHz or more.... plan on using a coil in series with the Alpair...

definitely use a rolloff on both drivers, don't try to use them in parallel... unless you like screaming mids... I don't!

The detail on the Alpair is probably very good up to at least 6KHz... and putting the crossover point up around 3KHz should give you good results.

Seriously, you want to avoid crossing the dm4 at 1KHz with a 1st order..

Hey I like the idea of the lights... multi-colored LED lights could look really cool, especially if they pulse and glow with the music...

it would give the sound more of that "lit from within" quality...

all the best!
 
#15
Hey Oon, more thoughts for you...

the MArkAudio Alpair probably has good on axis beyond 18kHz, but probably starts to get very beamy from 6kHz on up... if you looked at a hemispherical average, it would probably start rolling off as low as 3 or 4kHz... this would be closer to the acoustical power output from that driver...

and we definitely will hear that as "soft" top end, lacking in air, unless we like sitting with our head held rigidly in one position and aiming the Jordans or the Alpair directly at the ears

so then, yes it makes sense to add some air to the top of that, but NOT at 1kHz

So where to start?

I would advise you to leave the Alpair in "direct connect" mode, with no network to preserve the single driver benefits.... if you angle it at 45 to 60 degrees, the on axis response will look much like the power response

and then, to add some air and sparkle, you would use the dm4 with a single series cap, but at 10kHz (yes, TEN kHz)

So you will ask, why so high?

well the DM4 runs at about 94dB at 14kHz on axis, well above the level of the Alpair

AND

because a 1st order rolloff at 10kHz still has very substantial output at 5kHz, only a few more dB down!

in practice, you will still clearly hear the DM4's contribution until it gets to about 15 to 20dB below the level of the Alpair


Since the dm4 has goodresponse above 10kHz, you could mount it on top as a front firing dipole and get good results.... even so, i would still advise using it with an omni-diffusor, I think it will be better yet.

if you can't aim the Alpair up, just give it lots of toe in, so the angle is more like 45 to 60 deg from your ear, and aim the dm4 forward into the room.

Maybe also play with 4kHz, 6Khz or 8kHz crossings, but my hunch is 10kHz will do the best job of adding air to the Alpair while preserving its full range attributes.

Happy experimentation!
 
#16
Hi Santiago,

Thanks for the lengthy response.

Actually my plans for the speakers are a bit wild and not quite what a lot of people have in mind. I am thinking of building something of a cross between a line array and a MTM. But instead of using woofers for the MTM I will be using alpair6. They will be spaced approximately 1 foot apaprt on separate boxes. That will give the speakers 2 foot from M to M. The DM4 will be in between. And that is why I am planing on crossing it low. It will effectively a third driver, not just a supertweeter.

Since adding two speakers of the same power will effectively increase the SPL by 3dB, or is it 6dB, I intend to put a resistor to the DM4 to attenuate it so it is a few db softer than the alpair6. This should change the overall response a bit, but by not too much.

I will probaby try and get the sound level to match at approximately 10KHz. I find the alpair 6 benefits from this. My initial experimentation, spacing the speakers apart also creates a bigger sound. Since there is quite a bit of overlap, they don't sound disjointed as in a tweeter and woofer situation.

Oon
 
#17
OK, got the picture. More ideas then:

1) Toe in the Alpairs at about a 60 degree angle, run them "naked', no crossover. This preserves the "direct attack" without the added distortions, phase and impedance interaction fr changes from a series coil. If they are sufficiently toed in, the direct signal will look much like the average response, i.e. like they are dropping off at about 3 or 4KHz

2) Using a pair increases the apparent sensitivity by 6dB (yes, it's really 3dB, but because the impedance drops by factor of 2 you are doubling the power from the amp at the same output voltage)
Now the Alpairs will look like they are at 93-94dB

3) Mount the dm4 with the Omni type array similar to what you see in the first pictures on this thread.

4) With double Alpairs, probably no need to attenuate the dm4

5) Because the dm4 is crossing in with a 1st order slope, to preserve the proper phase relationships, it must be at a Fxc of at least 4 to 5 times the low frequency rolloff on the driver

why?
because the LF rolloff of the dm4 behaves like a 2nd order highpass at 400Hz.... and when that combines w. the1st order electrical filter it becomes an effective 3rd order electro-acoustic filter, requires inverting the phase, blah blah... no good!

so with a 1st order, cross in no lower that 1.6kHz....otherwise you will surely get some cancellations in the lower mid band

again...
near 4kHz would be the optimum, it would require no choke on the toed-in alpairs

Also, the resolution from the dm4 is likely not better than the Alpairs until you get up into the cone breakup areas.. 5kHz and up, so you are not likely to hear any improvement if you cross them in much lower... and it will probably sound worse

look at the waterfall displays on zaphs site and you will see the dm4 is not all that fantastic when it comes to the midband.... so despite M&D's hype about crossing in low...with the dm4.... it's a BAD idea!

the lower crossing adds so many more problems... and the dm4 honks at 400 Hz... etc, etc.... this is precisely why so many experienced listeners are going full range!!

Try it the 4kHz way first,THEN if you want to experiment and feel you must go lower, at that point you will almost surely need a series inductor on the alpairs ... hmm, that loss of transparency..oy vey



BTW these"Uncle Santiago" hints come from long experience in this field... BSEE in Electroacoustics, followed by 30+ years of working in the industry, so if it seems useful, take the free advice.

And you can always use this as a starting point and modify to suit your listening preferences along the way.

Seems to me you've got the makings of a pretty special system there, let me know how it sounds when it's up and running.

Happy Listening
 
#18
Omnis have always interested me, since I first saw The Ace Horn with the big impressive diffusor mounted right in the middle of the Lowther driver

I did once build the Super Ace, but with 10" Coral, and they are long gone now

At the moment I am focused on designing something very easy to build, and have also thought about OB

But now I think I will try an omni and use thick plastic tube
I will build a couple of simple protos first, but when my lathe is up and running again in my new home, I will be able to do a better finish

Driver are all Tangband, 6.5" and 4", and maybe a small Fountech on top
Xo will be quite simple, I hope
Cost should be low
Goal is that they should be easy and pleasing to listen to, at avarage SPL
 

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#20
Spaceships?

Hey Tinitus, that space ship looks pretty cool. Looks like it has good potential.

Here is a picture of something I've built that works pretty well with either the Scanspeak Aircirc in front firing mode or with the M&D dm2a

Yup, it's an Omni, and it sounds pretty dang good!

Needs a little more work on the filters, currently am using a Behringer DEQ2496 in digital in/out to correct for some freq response aberrations in the 1kHz and 4kHz bands

I may not change anything further.... it's really good as is. Sounds excellent whether far away from walls or right up against them.

More details later, i may be offering these in kit form once some details are ironed out.
 

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