Ess Heli Ohms Mismatch

[CHRIS CLEM]

OK,My 1st post.I just got a pair of ESS AMT 1D HELI Air Motion Tweeters only.I want to build only my 2nd speaker system.This will be a 2 way transmisson line,audio only system,with a 6 1/2 woofer which I would like suggestions for.Also the OHMS readings on the tweeters are quite different from each other,1 is 3.4 ohms the other is 5.6 will this be a big issue or not.I listen to LPs in an all tube system and would like a nice smooth sound,no harsness.Any thoughts........

[Tenson]

Use a bigger woofer 12" probably best for an Xover with the ESS.

IIRC ~800Hz?

[CHRIS CLEM]

I should mention that these are the big ESS HEILs DIPOLE the weight I would guess about 15lbs each ? I would like to keep the woofers at 6 1/2 inches if possible.

[matt28sr]

I have built speakers that pair two 6-1/2" woofers with the "Great" Heil (AMT-1 style) unit. They sound wonderful!

Best to use two 6 1/2s, because AMTs are very, VERY efficient! You would be hard pressed to find a single driver that would begin to aproach the AMTs level of output. Also, the radiating surface area of the big AMT driver is (according to ESS literature) more than that of a 12" cone driver! So you would want to have a comparable radiation area for the low end to match.

I used carbon fiber woofers that I had salvaged from an older pair of Altec Lansing towers. Each driver was 8 ohms, so together they amounted to 4 ohms, in parallel. That turns out to be good, because I have learned, through experience, to use woofers with a lower impeadance than the impeadance of the Heil, this helps to make up for the output level difference of the AMT and the cone driver. ESS uses 6 ohm woofers in all of their speakers that I have seen from the inside (which is many).

I have had the pleasure of visiting ESS when they were in Sacramento, and talking at length to an ESS technician. According to him, the "Great" Heil (the big one you have), specs at 8 ohms, and the crossover sould be designed based on this. (However the DC resistance might be different, I can't remeber.) Another good trick is to use an L-pad on the AMT, this will assure that the imeadance is 8 ohms, and you will more than likely need it to strike an output balance with the woofer.

As for your measured impeadance difference between the two units, it may be because one of the digaphragms is damaged or worn out (they do wear out after much use). Best to start with new diaphragms anyway. These are normally are available from a number of sources. (The AMT 1 diaphragm is part #689-1107, don't get any other part number, because it won't fit)

In the past, I could suggest many places to buy replacement ESS diaphragms. Unfortunatly, ESS has recently moved to Germany and it appears that all my sources have disappeared, as has the ESS website.

I have just posted a new thread to see if anyone can help me get in touch with ESS in Germany, or know another source for the diaphragms. Check that to see if anyone has replied. (title: "ESS AMT diaphragms")

Hope this helps. Have fun building your speakers, I'll bet you will love the AMT's sound!

[matt28sr]

Hey Chris:

Thanks to the helpful links sent to me by a DIYAudio member, I think I have come across some info that might be helpful to you, and prove me to be wrong about the impeadance of your Heils.

http://www.hifisound.de/oxid/oxid.ph...8c2b0.50716260

Copy and paste the above into your browser window (or better go to the reply to my post: "ESS AMT diaphragms" in the "ribbon/planar/alernative" section and click on the second link provided by Badman)

You'll see a photo of your Heil on the page. Click the button by it that says "Mehr Infos", then scroll down the page until you see a little British flag on the left sidebar and click "english".

You'll have more technical specs on a Heil than I have ever seen. You'll also note that the stated impeadance is 4 ohms, not 8.

But also note that the stated DC resistance is 3.4 ohms, the bottom end is 1500Hz and the power rating is 100 watts.

Here's the thing. It's comming back to me. Last time I took a DC resistance on a big Heil it was 5.6 ohms. Also, I have old literature from ESS that clearly states the crossover point on an AMT-1, 1b, 1c, and 1d is 800Hz and the power rating is 350 watts.

Could it be that there is a 4 ohm and an 8 ohm version of the diaphragm? I have never seen such a thing listed by suppliers, even from ESS when they were in Sacramento. But then I have never had to get diaphragms from Europe either.

Perhaps you have one of each diaphragm, a 4 and an 8 ohm.

Either way, you might want to persue getting new diaphragms while you still can. The new yellow diaphragms seem to last a lot longer than the older clear ones, perhaps they last indefinitely. In which case you'll only need to get them this one time.

I roll off my Heils (with the yellow diaphragms) at 800Hz @ 12dB/oct, but then I also use two Heils running in paralell and padded with an 8 ohm L-pad. The only advantage to this that I can see is to split the load betwen them, making each one work less.

I also must apologize, I used two 8 inch woofers, not 6 1/2"s, in the system I was describing to you before. It's been so long since I made them that I forgot. For some time I've thought that they were 6 1/2s! Still, I'd bet that two 6 1/2's will work just fine.

As a matter of fact, check out this address...

www.positive-feedback.com/Issue20/ess450.htm

It's a review of a brand new German ESS speaker with two 7" woofers and a Great Heil. Looks like you can pick a pair up for a mere $12 Grand!

Take care....

Matt

[JohnL]

Hello Chris,

I also use the Heil. I use mine with a pair of 8". Matt is right that they are extremely efficient, even with a pair of 8's I have to pad down the AMTs a pretty fair amount. If you pad them down too much, they do lose something. I had them with a single 6.5 at one point, and I think I had them padded down about 10db and they didn't sound as nice any more. Someone had recommended a transformer attenuator instead of an L-Pad, but I haven't tried that yet.

If I was forced to do a two way with 6.5 drivers, I would probably use PHL 1340s. They are a good mix of efficiency and the ability to play low. If you aren't married to the idea of 6.5s, investigate some 8"s. They really aren't that much bigger. I use mine with RS225s, but it took a tricky crossover to get them to sound good. I have a couple B&C 8PS21's that I tried with the AMT and I think that design had a lot of promise. People tend to over that B&C because it's a 'pro sound' driver, but I think it sounds just like the PHLs that are in that same range.

[dshortt9]

The Heils are technically Bipolar, radiating the same phase in both directions. Dipole radiates opposite phase in each direction.
I use my Heils with a pair of 10" drivers salvaged from Klipsch RF-10's in parallel and bipolar, one facing front and one to the rear. This fills in the baffle step exactly and allows me to use a simple first order series crossover. No padding of the tweeter is needed. The whole thing is very efficient, 98 db, and can be driven with a couple of watts at 4 ohms. IMO they sound comparable to the best I've heard, with excellent bass . The mids are smooth, clear, and dynamic as the Klipsch were designed to cross to a horn around 2K. I have 4 8" speakers from an RF-3 to try with the Heils for a somewhat smaller footprint that should work as well with the same design. I found someone on e-bay selling damaged Klipsch and asked them if they would remove the speakers and send them. They did.
I agree with using 8" or larger. The 8" Klipsh would be an excellent choice, simplify the crossover, and match the efficiency of the Heil possibly better than my 10's. Good luck with your project. It will be worth it.

[sleddogman]

Originally posted by dshortt9
The Heils are technically Bipolar, radiating the same phase in both directions. Dipole radiates opposite phase in each direction.

With all due respect, the Heil AMTs are actually Dipoles. As the front fold Vees are squeezing air and making sound, the rear fold Vees are expanding, and vice versa.

For specific details: http://www.precide.ch/eng/eheil/eheildetails.htm

[spacetransient]

I know this is an old thread but the Large AMT's are here to stay for the DIY Speaker community so I think discussing interesting designs with this driver should continue as well. IMHO there is no other tweeter with its combination of afford-ability, dynamics and transparency with decent tonal balance that has this wide range of frequency response: 800-22000 hz. By design it is extremely fast and requires an extremely fast mid-bass. Two that are successful, within their technological limits are the Audax PR17OMO and the Altec 414's, with the Altecs being a superior and almost seamless replacement for the original AMT1 12"with a slight loss of bass- but increased transparency. No need for x-over changes as the Heil has frequency and output trims, but component upgrades are a welcome addition to the sound. The x-over requires some expertise to redesign as it incorporates the Heils 3.2 ohm an 8 ohm mid-bass driver with trims. Frequency response is somewhat tamed by the "C" version but felt on the horn faces helps to smooth things out even more. The Audax drivers while superb would require additional design implementations and might work well in a transmission line or MTM or MTM 2.5 design. I love my custom pair with a modified 1c crossover and Altec mid-woofers in a transmission line (no passive woofer). Total cost under $1K !!.
Of course the next step up is the Raven 3.2 at $4000 per pair. Sure its better- at nearly 6 times the cost it better be.