TEST: ATC SM75-150 mid-dome

[watchnerd]

Thought this was interesting, given the number of decades this driver has been in continuous production:

http://www.troelsgravesen.dk/ATC-SM75-150.htm

 

[March Audio]

I seriously considered the ATC for my speaker design (requiring 800Hz to at least 4.5kHz range), however cost and availability were an issue. I ended up with a Morel EM1308 which has excellent dispersion properties. I am somewhat bemused by the choice of mid range drivers made in many 3 way speakers whose size is above 3". Above that is simply to large to retain decent dispersion into the higher frequencies.

http://www.madisound.com/loudspeaker_specifications/EM1308.pdf

https://www.supersonic.se/dokument/Morel EM1308 Test Voicecoil.pdf

 

[watchnerd]

I seriously considered the ATC for my speaker design (requiring 800Hz to at least 4.5kHz range), however cost and availability were an issue. I ended up with a Morel EM1308 which has excellent dispersion properties. I am somewhat bemused by the choice of mid range drivers made in many speakers whose size is above 3". Above that is simply to large to retain decent dispersion.

http://www.madisound.com/loudspeaker_specifications/EM1308.pdf

https://www.supersonic.se/dokument/Morel EM1308 Test Voicecoil.pdf

View attachment 18690

Why only 800 Hz?

The ATC seems to be used down to 380-400 Hz, and up to 3.5k, so arguably could claim to cover the all of the critical midrange without a crossover in the path.

 

[March Audio]

I actually use it from 700Hz which is just about below the most "critical" range

Remember driver excursion and potentially distortion goes up with reducing frequency. The mid is limited in this respect. The SB Acoustics woofer is more suited to cover this lower range.

 

[watchnerd]

I actually use it from 700Hz which is just about below the most "critical" range

Remember driver excursion and potentially distortion goes up with reducing frequency. The mid is limited in this respect. The SB Acoustics woofer is more suited to cover this lower range.

So why have dome mids fallen out of favor?

Cost?

 

[bigx5murf]

Interesting, my two favorite speakers in my collection right now use large domes, one as a mid (ADS L710 and Thiel CS 04a). They both happen to have fairly complex crossover as well. Especially the Thiel, 15 components for a 2 way.

 

[Wombat]

FWIW: http://www.troelsgravesen.dk/large_domes.htm

 

[March Audio]

So why have dome mids fallen out of favor?

Cost?

Buggered if I know, I dont see cost as an issue.

Going back to the "critical range" its actually does extend a bit higher in frequency than many think. most sensitive in the 2 - 5kHz range.

 

[andreasmaaan]

I consider using them sometimes, and actually have a pair of the Tang Band 3” dome mids atm that I’m planning to try out in something at some point, perhaps this ultra budget design I mentioned in the other thread. The advantages tend to be the wide treble dispersion and (often) low levels of higher order distortion and IMD. The disadvantage is of course the lack of low frequency extension.

Can’t speak for others, but whenever I’ve decided against a dome mid it’s been because of that disadvantage. If you’re crossing the midrange up over 600 or 700Hz, and if you want to actually gain from the benefits a dome mid can offer, you're generally looking at a mid-tweeter crossover up over 3 or 4KHz. Although that keeps the xover out of the ear's most sensitive band, usually I want to avoid the kind of lobing inherent in having such a high crossover frequency, preferring to use a lower frequency crossover to a cone midrange, and often to horn-load the tweeter to some extent to get it extending down below 2KHz i.e. the other end of the critical band. Just my 2c though...

 

[bigx5murf]

FWIW: http://www.troelsgravesen.dk/large_domes.htm

The Audax TW034 is the modern version of the HD13D34. My Thiel 04a had open coils on both tweeters when I found them. Unwinding one coil dropped their impedance from 8ohm down to 2ohm, so I went looking for replacements. The Audax TW034 was the first one I tried, they distorted in the mid range with the Thiel phase/time aligned 1st order crossovers. I hunted down a pair of HD13D34, and transferred the domes/coils from them and the distortion was gone. So there's definitely a difference there. Specs say only 100Hz difference in resonance frequency.

 

[March Audio]

I consider using them sometimes, and actually have a pair of the Tang Band 3” dome mids atm that I’m planning to try out in something at some point, perhaps this ultra budget design I mentioned in the other thread. The advantages tend to be the wide treble dispersion and (often) low levels of higher order distortion and IMD. The disadvantage is of course the lack of low frequency extension.

Can’t speak for others, but whenever I’ve decided against a dome mid it’s been because of that disadvantage. If you’re crossing the midrange up over 600 or 700Hz, and if you want to actually gain from the benefits a dome mid can offer, you're generally looking at a mid-tweeter crossover up over 3 or 4KHz. Although that keeps the xover out of the ear's most sensitive band, usually I want to avoid the kind of lobing inherent in having such a high crossover frequency, preferring to use a lower frequency crossover to a cone midrange, and often to horn-load the tweeter to some extent to get it extending down below 2KHz i.e. the other end of the critical band. Just my 2c though...

Not really found lobing to be a major issue in my Acourate implementation. NT linear phase XO.

 

[andreasmaaan]

Not really found lobing to be a major issue in my Acourate implementation. NT linear phase XO.

View attachment 18695

Yeh, of course these things are much less of an issue with steeper filter slopes

Would be interested in seeing the vertical polars from that system if you have them? I'm guessing the lobes are very narrow but begin at rather near to 0° (with the deepest null @ +/- 15° or so perhaps)? A reasonable trade-off for the nice low IMD and fast decay of the dome mid I'm sure.

 

[hvbias]

I seriously considered the ATC for my speaker design (requiring 800Hz to at least 4.5kHz range)

If you were making that decision now it would be much easier for you, ATC will not sell the SM75-150 to anyone other than people that own their speakers. Even then it might need to go through a dealer. You used to be able to build a "poor man's" version with a Wilmslow kit though with only passive crossover. Someone on DIYAudio managed to find their active amp packs and turned them fully active. Prior to me learning about Geddes'/Toole's papers/book (and listening to constant directivity speakers) respectively I was planning to go the ATC route.

 

[andreasmaaan]

The Tang Band also measures very well although I can't work out if it's still in production or not. Either way, the Monacor DM75-TB seems to be more or less an exact copy.

 

[March Audio]

Interesting, that 75 looks good. Is there any off axis data for the TB?

 

[andreasmaaan]

Interesting, that 75 looks good. Is there any off axis data for the TB?

Cut and paste to save you scrolling down the page:

I'll take some measurements myself when I get a chance and will post them, likely in January

 

[watchnerd]

https://www.hifi-selbstbau.de/daten...9-tangband-tb75-1558se-wie-ein-ei-dem-anderen

 

[Frank Dernie]

The first really jaw dropping hifi I heard had a pair of Proac EBS speakers in it. They use the ATC mid dome and their 9" bass unit with a tweeter I know nothing about.
My home system never seemed satisfactory after that.
I eventually bought a used pair on ebay and have then in my study. There is an occasional buzz so I have been planning a strip down but mys study is so full of junk and the speakers are so big I haven't made space yet.

 

[watchnerd]

The first really jaw dropping hifi I heard had a pair of Proac EBS speakers in it. They use the ATC mid dome and their 9" bass unit with a tweeter I know nothing about.
My home system never seemed satisfactory after that.
I eventually bought a used pair on ebay and have then in my study. There is an occasional buzz so I have been planning a strip down but mys study is so full of junk and the speakers are so big I haven't made space yet.

Wow, I had never heard of these. I didn't ProAc once used ATC drivers.

That's a lot of poundage of speaker.

 

[watchnerd]

The first really jaw dropping hifi I heard had a pair of Proac EBS speakers in it. They use the ATC mid dome and their 9" bass unit with a tweeter I know nothing about.
My home system never seemed satisfactory after that.
I eventually bought a used pair on ebay and have then in my study. There is an occasional buzz so I have been planning a strip down but mys study is so full of junk and the speakers are so big I haven't made space yet.

Pretty simple crossover, too: