Question about "transmission line bass" and Heil tweeters (1 Viewer)

[Matt Stryker]

My dad is finally giving up his AMT mains to me, and I asked him about using them in HT; he said they were probably too "hot" for my theater and mentioned that the transmission line bass design would not work well with my existing speakers (Boston Acoustics VR series).

Can anyone explain to me how/what transmission line bass is, as well as the Heil tweeter? Just wondering how I should set them up (distance from walls, equalization, etc) in my 2-channel system. Not familiar with all this 70's technology.

 

[John Garcia]

Transmisson line refers to a tuned "chamber" through which the bass travels, usually exiting in a slot. Chamber design (length, size, angles) depends on the driver and enclosure, and can be a single, long tunnel, or a what looks like a maze through the speaker. This is what Bose uses in their wave radio. It works very similar to a basic round port, as it is used to tune at a given frequency, but I believe it also helps accentuate the bass by making use of reflections within the chamber.

I can't help you on the tweeter.

 

[Stasulos]

Does anybody know how the TL box frequency should relate to woofer resonance frequency? Should it be higher, lower, equal?

 

[BrianLund]

Matt,
I own a set of ESS Heil AMT4's that I got when I was newly married in 1974. I can't give the exact inner workings or really much on placement. The AMT stands for Air Motion Transformer and refers to the tweeter. Basically if you think of a sheet of mylar like material folded in small accordian pleats standing vertically between two magnets thats the AMT. It works by compressing and relaxing the pleats just like an accordian. I guess this would classify it as either bipole or dipole. The wiser experts here should be able to clarify that. The 4's did not have the TL bass. Just a single 10" woofer to make it a 2-way system. I have changed the woofers out a couple of times due to age but they are still going strong and provide very nice sound to our living room through an equally old Harmon Kardon 930B. I have never known them to be terribly sensitive to location and we have had them in about 5 different rooms/configurations over the years. Thats about all I can tell you and I hope it helps.
Brian

 

[John Garcia]

Does anybody know how the TL box frequency should relate to woofer resonance frequency? Should it be higher, lower, equal?

This question is probably better asked in the DIY forum, if you are really curious. I know what a TL is, but not how to design and tune one.

 

[Chris Carswell]

You might want to talk with Mark Smith. I believe he knows a lot about that speaker system. He's even pulled the AMT tweeters out of some old pairs and designed some speakers around them. He has also designed a center with a similar ribbon tweeter (Raven1 or Hi-Vi RT2, think it was the RT2) to complement the new mains. I'll see if I can't get in touch with him.

 

[Mark_E_Smith]

I assume you have large AMT. One of the sweetest tweeters around, they handle lots of power, very efficient and are mostly crossed over in the 800 Hz range. They are not shielded and have a VERY strong magnetic field. If you Are going to use a modern sub you could build a MMT tower using some 6.5 drivers cross over at 1200 Hz and It would be very sweet. ESS is still in business you can go here:
http://www.essspeakers.com/
If the woofers are OJ, the surround material dies after so many years. You are in for a real treat. I have 4 AMT monitors and I still haven't found a speaker, including some high-end $4000 each, that have the imaging and clarity of these speakers, this is solely because of the Heil AMT tweeter, I think the Raven tweeter is the closest to it. They are not sensitive to room placement. The Heil has incredible horizontal dispersion and very limited vertical. so you don't have to toe them in, the are very efficient "hot" and can easily over spl other speakers in the system. All speakers will sound dull after you get used to these.

 

[Michael Roderiques]

Here are some links on TL design and use.
http://www.t-linespeakers.org
Link Removed
http://www.aspen-media.com/transmis.htm