Full Review of ATC SM75-150S Midrange Driver

[ligs]

Re: Full Review of ATC SM75-150S Midrange Driver

Regarding the listening impression,
“The midrange is so clean, undistorted, and natural sounding that vocals are almost life-like. Dynamics are clean and powerful.”
How much of the sound quality is attributable to the dome shape and or softness/stiffness of the diaphragm?I remember in the 70’s dome midranges were very popular. AR and ADS and many other companies had dome midranges in their top models. Then, dome midranges became more or less disappeared. What happened?

[Jeff B.]

Re: Full Review of ATC SM75-150S Midrange Driver

Jeff,

Thanks for the great review and starting a thread on this classic driver. I have certainly never "voted" on a thread before, just figured out how to do it...

Anyways, it was great to see the measurements, comments, references and some nice pics all in one place. I am sure more than a few folks will download that PDF even though they may not comment here. I have always been fascinated by this mid and a few topics that always seem to come with it:

1) Can a cone or planar ever match its performance? I believe around the time of its introduction, the leading contenders were the small scanspeak paper cone and the larger lowther drivers, so today I suppose we would add the illuminator mid, the accuton, the morel you recently referenced, the SB Satori, Tang Band and Dayton full rangers, the BG Neo 10, the Beyma 12P80Nd and the AE 10 or 15 M series. All seem to garner big fans in various designs and get mentioned as being among the very best midrange transducers. Of course, there is no real answer to what is best, but it is fun to get various opinions and occasionally get a chance to hear them in a design every now and then. Few drivers ever seem to get such consistent praise as this large mid dome however, and in the end I find that fact a bit depressing given how hard it is for anyone in DIY to get their hands on it, especially those of us with real budget constraints.

2) What exactly is the "midrange" frequency range anyways? For me anyways, I like that this driver forces the designer to dive into crossover points that are usually avoided, at least by many of the designers I have followed over the years. The lower crossover point of 300-500 Hz I suppose is not that uncommon for 3 way designs, but certainly presses the 200 Hz or lower crowd of which I have been a subscriber (as an armchair designer of course), and even more so those that like to stay at 100 Hz or less. Then there is the upper limit which doesn't quite go far enough to get out of the danger zone of mid/tweet transitions so that you would just add a super tweeter and call it a day. Nope, you gotta work the crossover real close to where we are the most sensitive to freq, phase, and location between drivers... And yes, this is all up for debate and I know that you specifically have responded to my posts before with the notion that you let the math drive the selection of crossover points and don't worry about any folk lore around some points being better than others. I am sure this particular design will be as good an example as any to support that position.

3) Flange and overall physical size vs range covered... I believe the only time I have ever seen this driver used in an MTM design was one of the ProAc floor standers. Given the frequency range issues described in #2 above, is it possible to get any combination of drivers on a baffle and have them integrate well with two rather than one of these mid domes? That seems like a very difficult task given the lobing issues at the upper range and the flange of these drive units. Is there even a reason to ever need to? Probably not, but you know the first thought is always that if one is great, then two has the potential to be super great! At least that is where idiots like me always go for lack of any more profound insight.

Anyways, thanks again for the review, it really was a nice read and brings back a lot of memories of various folks giving this driver a try over the years. I will go back to bugging Dave Pellegrene about his experiments with the TB 75 even though I am starting to feel the pull of line arrays again and looking at the Neo 8PDR among other things...

Greggo, let me give my thoughts on a few of your questions and comments –


Comparing this driver to other mids can be difficult. Although they differ in a lot of ways, there are a number of drivers that can produce absolutely fabulous midrange reproduction. I have found simple coned drivers from SBA, Scanspeak, Morel, Audio Technology, PHL and others that excel at it. I have also heard speakers like Dan N.’s Echelons which use the BG Neo10, and its midrange was beautiful as well. There are lots of ways to skin a cat. The key is using a driver in a range and in a manner that it is best suited. The usable range and directivity of a 6” cone and 3” dome in a short waveguide will be different. What you need makes a difference.


It should also be noted that distortion below a certain threshold will be less and less of a factor, and linear, smooth frequency response will be the biggest factor. Because of this quite of few drivers under the right circumstances can provide state of the art midrange performance.


The ATC SM75 is a package. That package includes the directivity of a 3” dome in a waveguide, 94 dB sensitivity, extremely low distortion, very smooth frequency response, relatively high output, and a pretty high price.


I feel the Satori, or the Morel, offer very high-end midrange performance at a much more reasonable price point, and they can cross over much lower (or operate at bass-mids). However, they will not be able to extend quite as high if that matters, and their sensitivity will be quite a bit lower in actual application, so will their max output. So, again, it call comes down to how you want to use the driver.


It should be noted that the person I am making these speakers for is just an average guy, much like the rest of us. Yes, he is a professional in the music business, but that doesn’t change the fact that these are still costly hard to find drivers for him too. I am a professional in the automotive industry but I still have to buy cars like the rest of us. This person heard the ATC driver in studio monitors and made the decision that it was what he wanted so he pieced his dream speaker together over several years and now has asked me to help bring it all together for him. I think any of us could do the same if we decided what we wanted and set our minds to it.


I consider the midrange to begin at around 180 Hz, but that’s a loose number. It is certainly the lower end of vocal fundamentals with harmonics rising below that. It tapers off at about 3 kHz. The high frequency range begins much lower than most people think.


One of the things that has surprised me over the years is how my personal experience can really differ from all of the “rules” I learned in the beginning reading about speaker design. I no longer follow some of these rules, determining in my own mind that they are meaningless. When I hear them repeated on-line I assume they are simply restating what they have read and not what they have actually found. One example of these things is “acceptable or optimum crossover points”. For what it’s worth, and maybe it’s not worth much, but I have found that of all of the three-way speakers I have worked on the best crossover point always seems to be in the 350 - 400 Hz range. And this has been almost without exception. A crossover in this range seems to give me the best overall midrange and vocal balance while it allows you to control floor bounce and baffle step the most effectively. In my opinion, no one can really argue with the acoustic advantages of crossing in this range. I find it easy to get good phase alignment and flat frequency response here too. This has become a golden zone for me after making a lot of speakers. Just my two cents here.


The ATC is a huge driver. However, if you look at the speaker I am making you will see that my midrange to tweeter spacing isn’t that excessive – no worse than any other driver with a waveguide. Having said this, I would also add that I personally wouldn’t use a driver like this in an MTM. I used to make a lot of MTM’s. I make very few now days. I have found that the apparent advantages are less than you might think, and when combined with the cost of an additional driver, it may not always be the best approach. There are still advantages though – higher sensitivity, power handling, max SPL, and symmetrical lobing, so I won’t throw out MTM’s; with small stand mounted speakers it can make good sense. But, with the last two larger dual woofer two-ways I designed I found I liked the small tower, MMT with the tweeter at the top at ear level the best. I will be demo’ing one of these at the InDIYana event too.


I don’t know if these thoughts will answer any of your questions or not, but good luck on your endeavors. And if you decide on the BG Neo8PDR then you should have a very nice midrange.


Jeff B.

[jinjuku]

Re: Full Review of ATC SM75-150S Midrange Driver

Thanks for the thorough write up. When I saw those in person my wallet ran and hid somewhere. Evil bastard.

[raiderone]

Re: Full Review of ATC SM75-150S Midrange Driver

Not from me as I like to read about unobtanium drivers and fantasize about how I could use them. I'm guessing that most of like to read about exotic cars and watch Top Gear and also read about expensive stereos (Absolute Sound, Stereophile, etc). And even though I'm attracted to "best bang for your buck" speaker drivers, I'm just as intrigued or more so, by expensive/reputed to be great speaker drivers like the ATC or RAAL, Accuton, etc. So, I really liked reading your write-up/implementaion/graphs of the ATC though, I wished you would have disclosed a schematic of the crossover.

Having said this, and this being a diy forum at PartsExpress.com (no less) there are some who would be jealous/envious about a driver they could not obtain let alone afford. You know that you cannot please everyone, so don't let it discourage you from posting about more exotic/expensive/unobtainable drivers in the future.

Hmmm.... this thread has a pretty poor rating. I thought I provided a fairly informative evaluation of this driver.
Jeff

[Greggo]

Re: Full Review of ATC SM75-150S Midrange Driver

Jeff,

Thanks so much for that thoughtful reply. It was great to get your perspective on the three points I brought up. Yes, all of those impressions are just the summary of many years of soaking up opinions of various forums and doing my best to qualify and rationalize with my own gut instincts and listening impressions. This is all far less optimal than rolling my sleeves up and doing some experimenting myself, but that day is coming soon enough. It will be interesting to see if the new AE TD8M-8 manages to hit the sweet spot with sensitivity, dynamics and frequency range smoothness to compete with the other drivers you mentioned. I do still like the idea of crossing at certain points depending on general scenario, but I am moving more towards the point of view that there are no hard and fast rules other than letting drivers play to their strengths.

[jonasz]

Re: Full Review of ATC SM75-150S Midrange Driver

Hi Jeff, any idea how the 94 dB B&W FST middriver tested over at Zaph would compare to the ATC driver? I believe it's still available to diy'ers as a replacement part for $300 or thereabout.

[Paul K.]

Re: Full Review of ATC SM75-150S Midrange Driver

I found your writeup interesting and thorough. I never rate threads and don't pay attention to the ratings anyway.
Paul

Hmmm.... this thread has a pretty poor rating. I thought I provided a fairly informative evaluation of this driver.
Jeff

[jonpike]

Re: Full Review of ATC SM75-150S Midrange Driver

FWIW... I have seen one of these, though I don't recall now which version. A coworker friend of mine has a pair of ATC speakers, and one of the drivers opened up on him. He was able to order it as a spare, with only some difficulty.

It was an experience, being handed the bad one to look over. First of all, I recognized it from the Zaph review, second off, its the size of a small barbell weight, third off... it FEELS like a small barbell weight 'cause that's how heavy that magnet is!!

His ATC's sounded pretty nice, and I've heard another model of them at the THE Newport show being played way louder than comfortable or even safe, while the vendors marveled over how clear the mid was... ("Check that out, I've never heard clarinet sound that loud without being harsh!") They were right, but I was wondering nwhat shape their ears were going to be in by the end of the day... All that adds up to a heck of a midrange, I'd say.

[tkollen]

Re: Full Review of ATC SM75-150S Midrange Driver

Hi everyone,

I have been asked to design a studio monitor using the ATC SM75-150S 3" dome midrange driver. Since this driver is so hard to get your hands one, and since it has near-legendary reputation as a mid, I thought I would submit of full review with measurements and subjective listening thoughts. You can download the full review in pdf form here: https://app.box.com/s/j1pwj8exbmioz350nu0n

Comments are welcome,
Jeff B.

Thanks for a great review. I have modified my Dahlquist DQ10 and among other things I replaced the madiocre 1 1/2" Midrange dome with a Dynaudio D54 (the best dome midrange at its time), a replacement that made a substantial improvement. My only issue with the D54 is that it has its -6dB point at 6 kHz with a sharp downward slope, whereas the Peerless goes up to 10 kHz before filter attenuation starts. Looking at the frequency response curve for the ATC driver it appears the response slopes down very gradually and well beyond 10 kHz. I have been thinking for some time to try out the ATC driver in my system although recommended upper crossover point is 3.8 kHz. What does the polar pattern look like and how good does it sound (low distortion) between 4 kHz and 10kHz?

[Jeff B.]

Re: Full Review of ATC SM75-150S Midrange Driver

Thanks for a great review. I have modified my Dahlquist DQ10 and among other things I replaced the madiocre 1 1/2" Midrange dome with a Dynaudio D54 (the best dome midrange at its time), a replacement that made a substantial improvement. My only issue with the D54 is that it has its -6dB point at 6 kHz with a sharp downward slope, whereas the Peerless goes up to 10 kHz before filter attenuation starts. Looking at the frequency response curve for the ATC driver it appears the response slopes down very gradually and well beyond 10 kHz. I have been thinking for some time to try out the ATC driver in my system although recommended upper crossover point is 3.8 kHz. What does the polar pattern look like and how good does it sound (low distortion) between 4 kHz and 10kHz?

Distortion stays low, but the off-axis response is rolling off above 4 khz. The graphs are posted above.

[scholl]

hello Jeff and others!

How does this midrange still rate today, is there something much better, or any better? Is it still available to DIYers, where? I
d like to keep the crossover around 400hz.

I'm going threw some life decisions and looking to finalize my main system. Cost isn't much of a concern. I'm selling down a bunch of junk that'll easily cover an expensive midrange. The AE TD15S will stay of course!!

Thanks!!

Scott

[Drummer]

hello Jeff and others!

How does this midrange still rate today, is there something much better, or any better? Is it still available to DIYers, where? I
d like to keep the crossover around 400hz.

I'm going threw some life decisions and looking to finalize my main system. Cost isn't much of a concern. I'm selling down a bunch of junk that'll easily cover an expensive midrange. The AE TD15S will stay of course!!

Thanks!!

Scott

https://www.diyaudio.com/forums/multi-way/327594-source-monkey-box.html

Check this out, Scott. The ATC is not available for diy, but the Volt 752 3" dome is. The open source monkey box uses the Volt, and the thread contains tons of measurements . Glenn.

[scholl]

I found the Voice Coil review and distortion is very low but I've yet to find it in the US, I'll keep looking.

[Wolf]

TMK, it's only available in the northern neighboring country, and from the same place as that makes their own caps in France.
Later,
Wolf

[Jeff B.]

TMK, it's only available in the northern neighboring country, and from the same place as that makes their own caps in France.
Later,
Wolf

It shouldn't be available there either. ATC changed their policy a while back and they will not authorize the sale of the mid to individuals anymore unless it is a trade-in on a damaged unit.