ATC SM75-150S Dome Mid Measurement Data - diyAudio
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Old 25th September 2006, 01:00 PM   #1
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Default ATC SM75-150S Dome Mid Measurement Data

There's always plenty of heated debate regarding ATC's dome mid so I finally decided to put together measurement data and post it here to perhaps remove some of the subjectivity and also the bashing for the sake of bashing.

I should also thank Ralph who's FR, impedance data and accompanying notes/comments I have borrowed(excellent work Ralph!). Ralphs measurements followed my own very closely so thats reasurring regarding accuracy, it also saves me much time capturing, editing, converting and uploading that data.

Just a couple of very quick notes:

The distortion test was performed outside and at 90dB average measured at the mic which was exactly 2m from the driver. The driver itself was mounted in a Perceive Satallite enclosure with no crossover in place for both distortion and CSD tests.

Cumulative Spectral Decay and distortion measurements were taken in ARTA and STEPS software(v1.1.0) using a Behringer ECM8000 mic, both ARTA and STEPS were calibrated using a true RMS DMM, the mic sensitivity was taken as per manufacturer specs.

On Axis:
Click the image to open in full size.

The amplitude response is not as smooth or as flat as might be expected for driver that costs so much or is held in such reverence. However the phase response is remarkably smooth between 300Hz-4kHz. The above plot is a 'nearfield' LF response merged at 700Hz with a 'farfield' high frequency response taken at 0.5m. The first major breakup occurs at about 4.5kHz and is also evident in the impedance plot below. Below 1kHz the response rolls off smoothly.

As mentioned, in order to use this driver in a system requires considerable EQ. This isn't easily achieved with a passive crossover, and the driver benefits from an active implementation.

Off-axis:
Click the image to open in full size.

The off-axis response is where the driver really shines. It's easy to eqalise a driver to be flat on axis, but not so easy to equalise it for a flat power response as well. Only a driver with a consistent power response can be equalised to achieve both.

Below is an example of the ATC's consistent off-axis performance. EQ has been applied to flatten the response somewhat, and the consistency in amplitude response as the measurement microphone is moved off-axis is easily seen; at 45 degrees the amplitude response remains within +/-1dB between 400Hz and 2kHz. Only above 2kHz does the driver start to beam and the power response fall away consistent with size of the driver's diaphragm.

Note that the vertical scale is 1dB/division. By augmenting the ATC mid with a controlled directivity HF driver, a smooth roll off in the system power response can be achieved. By 4.5kHz things are getting nasty, so to use the driver up to around 3.5kHz as is found in ATC's own speaker systems suggests quite steep crossover filters are needed.

Impedance of 8ohm version
Click the image to open in full size.

The impedance plot is well behaved with just a small glitch at 700Hz and a larger one at 4.5kHz. The driver resonates at 320Hz which is only marginally outside the claimed operating range of 380Hz to 3.5kHz. Normally a midrange driver is not used close to it's resonance frequency. But in the case of the ATC mid, it works very well down low, sounding better crossed around 300-400Hz than higher up. Of course, when used below 400Hz, a steep filter is recommended or power needs to be limited not exceed Xmax.

Distortion:
Click the image to open in full size.

CSD:
Click the image to open in full size.

Hope that helps demystify the fog of hype/BS that surrounds this driver. Make of the measurements what you will and please note the test conditions - it makes all the difference.

If anyone is interested in other measurements/conditions I'll should be able to provide them given time.

There also seems to be a distinct lack of measurements for the Scan R2904 ring radiator, if anyone wants those I do have them.
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Old 25th September 2006, 01:44 PM   #2
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Hi Shin,

Thanks for your informative post. It's always very interesting reading about "high-end" products.

How does this thing manage such low non-linear distortion?

Even down to 100Hz, at 90dB/2m (96dB/1m) this thing manages 0.3% THD?

That can't be right. That's actually better than most 8" bass drivers, and competitive with the tens...
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Old 25th September 2006, 02:44 PM   #3
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Quote:
Originally posted by tktran303
Hi Shin,

Thanks for your informative post. It's always very interesting reading about "high-end" products.

How does this thing manage such low non-linear distortion?

Even down to 100Hz, at 90dB/2m (96dB/1m) this thing manages 0.3% THD?

That can't be right. That's actually better than most 8" bass drivers, and competitive with the tens...
It might actually help if I'd uploaded the correct file

Click the image to open in full size.
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Old 25th September 2006, 03:40 PM   #4
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I now I've only got the pleb version of the ATC dome but straight out of the box I much prefer the Audax HM100Z0 to it. The ATC just sounds a bit wrong.
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Old 25th September 2006, 03:55 PM   #5
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I wonder how the first 0.75 ms of the CSD would look like.
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Old 25th September 2006, 04:34 PM   #6
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Quote:
Originally posted by BlackCatSound
I now I've only got the pleb version of the ATC dome but straight out of the box I much prefer the Audax HM100Z0 to it. The ATC just sounds a bit wrong.
Well, Shin has both, so he can tell us!
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Old 25th September 2006, 05:24 PM   #7
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Default Re: ATC SM75-150S Dome Mid Measurement Data

There's always plenty of heated debate regarding ATC's dome mid

Can you elaborate? I don't ever recall reading where people
didn't like this driver. The ATC dome midrange is probably
the only real good dome midrange on the market, the rest don't
compare.

As mentioned, in order to use this driver in a system requires considerable EQ. This isn't easily achieved with a passive crossover, and the driver benefits from an active implementation.

I think you can say the same for many other drivers, lol....

The off-axis response is where the driver really shines.
You didn't need measurements to know that dome midranges
are sweet in this regard. Their drawback is the inability to perform
at a lower crossover point that a good midrange or midwoofer
can do. Data suggested long ago that this driver is best with
a > 500hz crossover point, perhaps ~700hz, the 300hz range is
far too low if you want to get any SPL. The steep slope recommendation will help alot and should be implemented
if you cross low.

The ATC is on my 'unique driver list' good for certain types of
designs
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Old 25th September 2006, 08:47 PM   #8
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Quote:
Originally posted by BlackCatSound
I now I've only got the pleb version of the ATC dome but straight out of the box I much prefer the Audax HM100Z0 to it. The ATC just sounds a bit wrong.

Quote:
Originally posted by pinkmouse


Well, Shin has both, so he can tell us!
Its very easy to get the implementation of the ATC wrong, I even believe that ATC aren't completly on the ball here and its their own driver.

Without being armed with the measurements this driver is almost impossible to maximise the performance of. So not sure what or blackcatsound implementation was I can't comment, like I said the driver has problems which need to be avoided and address.

Its obvious weak spots are distortion low down, nasty resonances up high and a crooked FR. The strengths are good CSD and distortion in the optimium operating ranges, excellent off axis response lending well to good power response and excellent impulse response. There's also the subjective side where dynamics, transparency and great tonal realism show through, of course this is only once its been correctly implemented into a loudspeaker system with well matched drivers.
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Old 25th September 2006, 08:58 PM   #9
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Default Re: Re: ATC SM75-150S Dome Mid Measurement Data

Quote:
Originally posted by thylantyr
There's always plenty of heated debate regarding ATC's dome mid

Can you elaborate? I don't ever recall reading where people
didn't like this driver. The ATC dome midrange is probably
the only real good dome midrange on the market, the rest don't
compare.


I originally posted this on a UK forum where there's an anti-everything that's well regarded faction. I wanted to provide and alternative to the subjectivity and actually provide measurements.

Since I copied and pasted that, it ended up here without actually meaning anything because we all tend to be more grown up about such things. Sorry for the confusion.

Quote:
As mentioned, in order to use this driver in a system requires considerable EQ. This isn't easily achieved with a passive crossover, and the driver benefits from an active implementation.

I think you can say the same for many other drivers, lol....

The off-axis response is where the driver really shines.
You didn't need measurements to know that dome midranges
are sweet in this regard. Their drawback is the inability to perform
at a lower crossover point that a good midrange or midwoofer
can do. Data suggested long ago that this driver is best with
a > 500hz crossover point, perhaps ~700hz, the 300hz range is
far too low if you want to get any SPL. The steep slope recommendation will help alot and should be implemented
if you cross low.

The ATC is on my 'unique driver list' good for certain types of
designs
Those comments were made by Ralph but echo my own thoughts and I'd completely agree. So I posted them. The main interest is the measurements rather than the text.

One thing I realised when I posted these measurements was that they are far from perfect, in actual fact they aren't exactly stella considering the 390 each asking price for the drivers. TBH measurements are very important but so is the sound and the ATC's have an undeniable character that tradition cone mids don't have, if you've heard horn setups they're like that but without the distortions some of those present. Very powerful live sound rather than soft and polite, more true to a real performance IMO.
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Old 25th September 2006, 09:07 PM   #10
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Which forum was that?

I've been testing your old dome mids with a Volt B2500.1 and a Morel USA MDT-32. 3 way active from an ultradrive. Crossover points and levels set by ear, no EQ at all.

Got some spanky new MDT-33s to play with now
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