ATC SCM 40A Active Speakers
- Thread starter Isobarik
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JezmondTutu
pfm Member
I’ve never heard much difference.
My digital is balanced, vinyl not, both sound great. The Naim pre is likely to be a weak spot though.
They are pretty much double the price!
John Phillips
pfm Member
I had a pair of both in the same demo room for a morning before taking the 50A home to try. For a domestic system I would say there is not as big a step between the two as some write about.
Compared to the 40A the 50A dig deeper into the bass (38 Hz vs 48 Hz at -6 dB). They have lower distortion as the volume goes up (clearer low level detail is maintained) because the 50A's SL drivers have stronger magnetic motors as well as reduced magnetic hysteresis.
For domestic listening the 40A may be good enough if you like the ATC presentation, and maybe even better for not being too revealing. I even encountered someone in another online forum who downsized from 50A to 40A in a new house and was perfectly happy. If you want the deeper bass adding a subwoofer would, I think, be a less costly way forward.
Rationally I should have bought the 40A but how rational is this hobby?
Nail on head. I’ll end up with 50s just because I want a pair. They will not be twice as good.
You know it is inevitable. Just give in.
I recently bought an expensive road bike so the funds need to be topped up. Always choices to be made.
S-Man
StrivingON
Unfortunately ATC chose to use a ported enclosure for the Classics. On paper this seems like a good idea: deeper bass, higher SPLs at lower distortion. However for domestic use this is not a compromise I would choose, I find the bass quality is poor and would rather have better LF transient response even if it incurred the penalty of lower maximum SPL capability.
The perfect ATC speaker would be one with the classic series mid and treble - which is superb - but a better bass alignment.
So the size and direction of the "step" depends on what you value and what your ears are sensitive to.
darrenyeats
pfm Member
Sealed boxes have a 2nd order roll off. Your typical ported box has a 4th order roll off. ATC and Tannoy ports 3rd order. From a pro magazine:
SCM100 (ported)
http://www.avreport.ru/tests/home/audioreproduction/loudspeakers/floorstandas/item/316/measurements/
JMlab Chorus 816V (ported)
http://www.avreport.ru/tests/home/audioreproduction/loudspeakers/floorstandas/item/320/measurements/
KEF Q900 (passive radiator)
http://www.avreport.ru/tests/home/audioreproduction/loudspeakers/floorstandas/item/665/measurements/
Click graphs for better view.
I think ATC should get credit for their implementation.
- SCM25 (ported): "....with a 3rd-order roll-off with -10dB at around 30Hz."
- ME Gethain RL944K (ported): "....with a 4th-order roll-off."
- Klein & Hummel 0410 (ported): "....with a rapid 5th order roll-off."
- Focal Twin6 Be (ported): "....with a 6th-order roll-off, indicating the use of an electronic high-pass protection filter."
SCM100 (ported)
http://www.avreport.ru/tests/home/audioreproduction/loudspeakers/floorstandas/item/316/measurements/
JMlab Chorus 816V (ported)
http://www.avreport.ru/tests/home/audioreproduction/loudspeakers/floorstandas/item/320/measurements/
KEF Q900 (passive radiator)
http://www.avreport.ru/tests/home/audioreproduction/loudspeakers/floorstandas/item/665/measurements/
Click graphs for better view.
I think ATC should get credit for their implementation.
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Here’s a bit about ATC‘s design philosophy:
”The reason that this ported speaker sounds like a sealed cabinet is down to ATC’s unique design. All ported cabinets have a resonant frequency, which is related to relative dimensions of the port and cabinet. Most designers use this resonance to artificially enhance bass response, particularly in smaller enclosures, which is why they often sound boomy and slow. By contrast, ATC doesn’t use the port to extend the bass, merely to reduce distortion by controlling the motion of the bass driver. ATC designs for a relatively low damping factor (Q) of around 0.5, which produces a gradual low-frequency rolloff similar to a sealed cabinet. By contrast, most ports are tuned to a Q of 0.7 or more, which reduces port damping and gives the impression of a more powerful bottom end—but often gives a “one note” bass response. A high-Q ported cabinet also has a much steeper rolloff than a sealed-cabinet design.”
Full review:
which concludes:
”In my experience, there’s no other loudspeaker that comes even close to its immense power, neutrality, bandwidth, speed, and sheer visceral impact at anywhere near the price.”
”The reason that this ported speaker sounds like a sealed cabinet is down to ATC’s unique design. All ported cabinets have a resonant frequency, which is related to relative dimensions of the port and cabinet. Most designers use this resonance to artificially enhance bass response, particularly in smaller enclosures, which is why they often sound boomy and slow. By contrast, ATC doesn’t use the port to extend the bass, merely to reduce distortion by controlling the motion of the bass driver. ATC designs for a relatively low damping factor (Q) of around 0.5, which produces a gradual low-frequency rolloff similar to a sealed cabinet. By contrast, most ports are tuned to a Q of 0.7 or more, which reduces port damping and gives the impression of a more powerful bottom end—but often gives a “one note” bass response. A high-Q ported cabinet also has a much steeper rolloff than a sealed-cabinet design.”
Full review:
which concludes:
”In my experience, there’s no other loudspeaker that comes even close to its immense power, neutrality, bandwidth, speed, and sheer visceral impact at anywhere near the price.”
They’re not the most efficient of speakers so it’s a big ask of any amplifier to drive them passively.
S-Man
StrivingON
That's what they say , but I can't find any measurements to support this. They don't explain how they achieve this either, not sure if they damp/obstruct the port somehow, or if it's just an EBS alignment. Maybe an owner can have a look and see if the port tube is unobstructed?
I think better results are to be had by a pair of extremely well integrated and highly capable subs with smaller ATCs. I spent an evening (at home) listening to SCM7s in exactly this configuration and the sound was absolutely superb!
John Phillips
pfm Member
I hope the OP has had enough input, including mine that I think the SCM40As are superb and I think he need not worry too much about what has been later discussed about their bigger brothers.
Regarding the quote above, when I listened to the 40A and 50A back-to-back I did listen for anything port-related. I had seen online criticisms. However, I heard nothing wrong from the 50A that gets conventionally attributed to a bass reflex loudspeaker when compared to a sealed box.
There are some internal photos of the SCM50P in this review. In particular the port tube is shown in two of the gallery photos at the end. The port tubes on my SCM50As contain no stuffing.
The resonant frequency of the port is revealed, I think, in Martin Colloms' test for HiFiCritic. The zero-phase point in the saddle between the bass peaks is at about 23 Hz or so. I understand that the HF peak being higher than the LF peak means the resonant frequency of the box is lower than the resonant frequency of the driver (source). I think I have the T/S parameters for the driver somewhere but not to hand now.
I don't know if the above reveals anything to those who design reflex enclosures.
However, my listening to reflex loudspeakers over the years has suggested that a resonant frequency below about 30 Hz is good enough to not be problematic to my ears. That's with music where the audio content below E1 on a normal four-string double bass (41 Hz) is pretty limited and the port resonant frequency is well below that.
Certainly I have heard nothing wrong from my SCM50As over the last 6.5 years. I also observe that quite a few people on PFM seem to have SCM50A 'speakers too so they do seem to be broadly liked. YMMV, of course.
S-Man
StrivingON
Thanks John.
As far as I can see the bass alignment in something like what Vance Dickason calls SBB4. His book basically says: rolloff is approx 18dB/oct which is similar to a closed box and the shape of the group delay curves are similar albeit with "much higher absolute delay" for the SBB4.
So ATC hasn't broken the laws of physics. This relative phase shift at LF is easily audible once you know what to listen for.
Anyway, the point of all this is to say that whilst ATC make excellent speakers, they are not perfect, and it might be possible to get a better compromise at lower cost. It all depends how you hear things and what matters to you.
As far as I can see the bass alignment in something like what Vance Dickason calls SBB4. His book basically says: rolloff is approx 18dB/oct which is similar to a closed box and the shape of the group delay curves are similar albeit with "much higher absolute delay" for the SBB4.
So ATC hasn't broken the laws of physics. This relative phase shift at LF is easily audible once you know what to listen for.
Anyway, the point of all this is to say that whilst ATC make excellent speakers, they are not perfect, and it might be possible to get a better compromise at lower cost. It all depends how you hear things and what matters to you.
alanbeeb
pfm Member
I'm not sure the 50s are good for home listening. Maybe great in the studio. I had a pair for a year, impressed by the demo, but I had to give up on them because they were just so hard, unforgiving, relentless, ruthless and so they took the joy of listening away for 90% of recordings. If the 40s are more forgiving then I'd go for them.
John Phillips
pfm Member
Yes. I did a quick peruse and went up the first part of a steep learning curve. Looking at the T/S parameters of the driver in a SCM50 and SBB4's enclosure requirements, SBB4 alignment or close looks like a plausible match. But I am certainly aware that a little learning is a dangerous thing.
AFAICS loudspeakers are all about their particular combination of compromises. I am willing to be corrected but SBB4 looks to me like a very sensible compromise for a studio loudspeaker. I think SBB4 has good transient response within the range available from reflex designs. As you wrote earlier, for home use some might prefer to trade less power handling for improvement in that transient response. OK. I get that. However I genuinely haven't heard anything in 6.5 years of listening to this system that I would change, in contrast to the short list I compiled with my former loudspeakers. In the grand scheme of things I can't see a good reason for some of the criticism I see around the SCM50.
And, with apologies, I don't think I would want to learn to hear LF phase shift. I don't think it's a good idea to learn how to dislike things, but I do observe that other audio enthusiasts would disagree with me. OK if that's their hobby, but it isn't mine.