Interesting.
May I kindly enquire about this measured driver?
What’s the approximate serial number of yours?
NOS or new?
A friend has a pair of drivers serial numbers 4xxx and they don’t appear to measure like the above.
As Chris mentioned, did you have to run them in, or was it a measurement of a fresh unit?
@Cask05
How do yours measure? Like @Robh3606 ‘s unit?
The initial measurements of the AMT-1 that I bought in December 2018 look like the bottom solid trace in Rob's measurement. After a few days, it looks like the top trace.
The band around 5 kHz doesn't look like Rob's. I believe the amplitude response disturbance corresponds to the ribbon supports/magnet assembly reflecting energy and being summed with the main portion of the ribbon output.
Here is what the DSP PEQs look like for a fully broken in set of two AMT-1s stacked on top of each other with 7-inch wings, showing the corrections from 4-7 kHz as a local rise in amplitude that needs to be attenuated. Note the vertical scale is in single dB increments to highlight the corrections in SPL vs. frequency:
The 4-7 kHz area is affected by using two AMT-1s and side wings--thus raising its relative output a bit around the 5kHz disturbance.
Also note that microphone radial position is pretty critical when taking measurements. I recommend being a little off-axis (about 5 degrees horizontally) in order to catch the local higher SPL just off-axis that I showed in the polar plots, above.
Chris
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I'd really like to do something with my vintage AMTs. The diaphragms look awful, but they work. Not sure if original diaphragms in bad shape are better or worse than the new ones. The price on new diaphragms is a little steep IMO. I'd probably rather buy whole new units instead.
They were purchased new and serial numbers are 2992 and 2993 November 2018 Christmas Holiday Sale.
When I started a build thread at Lansing Heritage there were numerous questions about measured Heil FR measurements. There is a comparison with my measurement compared to a magazine posted will add it here. Apparently they seem to have varied over time.
The original measurement was new no real time on the driver. Used that to design a network. Ended up going active 24db L/R with a passive a 5K notch filter to help smooth the on axis a bit. So no real break in time.
For clarification the light grey is raw and the black is with a passive18 db network and notch I didn't end up using.
Rob 🙂
https://www.audioheritage.org/vbull...l-with-a-JBL-woofer&highlight=HEIL+JBL+WOOFER
Attachments
When you say they change their SPL response over the first few hours on a new pair, can you elaborate...do they become louder ( more efficient) after some break in?...
FYI, I just received a new pair that I purchased from ESS and was quite surprised how well they sounded from the " get go"...I am crossing them over at 950 hz, 2nd order Butterworth and they sound very impressive.
They replaced some very nice Beyma CD. I am attenuating the back wave with some 2 inch foam.
I also have an old pair of ESS AMT transformers that I was evaluating. They are probably original from the 70's. Anyway the new pair is definitely more efficient...at least 2 to 3 db....perhaps the older AMT's loose efficiency over time.
I was thinking of adding a second pair in a stacked arrangement, however with out any "wings"...Can you tell me if a stacked pair will work down to 6 or 700 without any bad side effects?
Thanks.....
Personally, I did not like the sound when wings were added to stacked Heil AMT-1's. Also did not like the sound with foam absorbing the back wave. Both ways made the sound less open, airy, and natural in my room.
Also, even though stacked Heils are capable of reaching lower, especially with wings when they can technically be crossed over at around 600-700Hz, I prefer the sound when crossed at 1000 kHz, without wings or foams. Then the sound is just super smooth, natural, open, sweet, yet very detailed and unforced. YMMV.
Also, even though stacked Heils are capable of reaching lower, especially with wings when they can technically be crossed over at around 600-700Hz, I prefer the sound when crossed at 1000 kHz, without wings or foams. Then the sound is just super smooth, natural, open, sweet, yet very detailed and unforced. YMMV.
Their response below ~4-5 kHz changes, like the diaphragm is stretched initially, then loosens up. The low-end response below 2 kHz especially changes-loosened up. The response was heavily overdamped and attenuated before diaphragm break in. I wish that I had the REW measurements to show, but I lost the files in an external HD that hit the floor in April 2020 that I had inadvertently overlooked in backing up.
It was dramatic, not subtle. It was also from the batch of four AMT-1s that I bought in December 2019 when they went on sale for $125/ea. There were a fair amount of diaphragm failures during that period that I experienced (1 failure) as well as others that also bought during that time. There was apparently a huge increase in demand then and the manufacturer was struggling to keep up with sales. My guess, perhaps the QC on the diaphragms was a problem then. I haven't heard of any problems since that one period of time.
Chris
I've heard many complaints about having the driver too close to the front wall or too far forward on top of the loudspeaker cabinet, but not the wings. In fact, just the opposite.
Chris
Gentlemen, thanks for your responses. I notice that with the supplied rubber mounting base the AMT is slighltly angled back a few degrees. What negative response might happen if the top AMT in the "STACK" was reversed and the top one angled downward. The bass bin I am using is 39 inches tall and my ear height is approximately 40 to 41 inches.
So what I am saying, stacked in the way described above, my stack will be an angled curve....so to speak......
I don't want to use the AMT without the supplied rubber base, so it will have this angle, unless I want to find an aftermarket rubber base of some kind.
So what I am saying, stacked in the way described above, my stack will be an angled curve....so to speak......
I don't want to use the AMT without the supplied rubber base, so it will have this angle, unless I want to find an aftermarket rubber base of some kind.
Try them in all the possible ways and choose what sounds best in your room and ear height.
In my room, I used the supplied rubber base only under the 1st AMT, then 2nd AMT with thin neoprene stick-on feet so same angle as 1st AMT. 3rd AMT is slightly angled up a couple of degrees on different thickness neoprene, slightly taller in front than back. I also adjust chair height to get the balance just right.
In my room, I used the supplied rubber base only under the 1st AMT, then 2nd AMT with thin neoprene stick-on feet so same angle as 1st AMT. 3rd AMT is slightly angled up a couple of degrees on different thickness neoprene, slightly taller in front than back. I also adjust chair height to get the balance just right.
One would HAVE to use rather large wings to extend the lower range since those folks are usually trying to cross AMT to rather largish woofers, e.g. La Scala-like bass bins, Altec bass bins, etc. There's no choice here, really, and the sound without wings in these cases would be horribly thin in that crossover region.
I'm crossing them to only 8" drivers that have great sound quality well into midrange, and I just find human voices to sound more dense and "supported" when AMT's are not crossed lower.
So if I follow you correctly you are triple stacking 3 Amt's per side?.
Interesting....if you have any pictures of your set up and wouldn't mind sharing....even if it's just a double stack.
Thanks...
Interesting....if you have any pictures of your set up and wouldn't mind sharing....even if it's just a double stack.
Thanks...
This is not accurate-in my experience. In fact, my experience is just the opposite using a miniDSP 2x4 HD to dial in the AMT-1s and bass bins properly.
Chris
I mean it's whatever one prefers. Am I understanding you correctly that you are NOT using wings and still having good response in the crossover region? How large are the bass drivers and crossover point/slope?
I have some photos in this thread and various experiments:
https://www.diyaudio.com/community/...at-midrange-needs-super-tweeter.415360/page-5
I see that most using " Stacked " AMT 's are wiring them in series, due to the 3.7 Ohm rating of an individual ESS Heil AMT...anyone try them in parallel (1.85 Ohm ) using a typical tube amp from the 4 OHM tap ?...
What " nasties " might happen?.
What " nasties " might happen?.
What 'nasties' might happen? Well, your damping factor drops to 'hell no', your amp will say 'gawd, I quit' and your sound will diminish to 'eh, I won't touch that mud with a 10 feet pole'. For a tube amp the impedance match is a real high part of the system. Get the AMTs in series and match that high impedance is definitely not an issue for a tube amp - it's exactly the opposite. So, if you have an issue there, change the load impedance, the OPT or the amp.
I'm using double-stacked AMT-1s on top of Belle Klipsch bass bins with the top AMT-1 leaning back ~15-20 degrees to spread the vertical response--as two-ways with the bass bin only. The AMT-1s replace the midrange and tweeter horns/drivers in the Belles; the top hats are still attached but not in use--to serve as risers to get the centerline of the AMT-1s at or above sitting ear height without having to raise the bass bins above floor level, thus avoiding cavities under the bass bins. The only down side is the increased vertical spacing between the AMT-1s and the centerline of the bass bins,,,a trade that I made while listening to both configurations (on floor and elevated) while moving around the room and listening.
I use a miniDSP 2x4 HD to cross them at ~650-700 Hz and to EQ the amplitude and phase response (min-phase only), yielding less than 180 degrees of smooth phase growth from 20 kHz down to ~50 Hz at the -3 dB bass bin roll-off point (in room boundary effect). No FIR filters are needed and there is no added all-pass phase growth from the crossover, which acoustically achieves about -12 dB/octave slopes,
I'm not using wings because these are serving as my surrounds in a 5.1 array, so they never really play music at >100 dB/1m. The double stack arrangement provides enough efficiency to keep the individual AMT-1 diaphragms below their distortion limits. If I needed more efficiency, I'd add one more AMT-1 on top of each existing stack (I have these in storage right now), and if more efficiency were needed, I'd add wings. I found that I didn't need three-high stacks for this application.
If I were using them in one of the front three in a 5.1 or in a stereo setup, I'd use wings because for my needs they need to be able to play well over 100 dB/1m in those positions without the diaphragms running out of low-distortion excursion limit below ~1.7 kHz.
Chris
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That's great setup. I've been looking locally for LaScala/Bell or Altec VOT bass bins but no luck so far. Not really for AMT stack but for my orphaned round horns, 80x60 horns and various compression drivers. I ended up with too many treble/mid units relative to bass solutions. I do love how different speaker tech gives different mien to music and wouldn't mind having some electrostats too. It's a great time to be an audiophile 👍