ATC SM75-150S Dome Mid Measurement Data

Rob,

I don't think anyone is saying this is severe. Just that it is IME enough to give a slight edge to the sound - a little additional bite if you like. Obviously if you are listening off axis of the midrange dome, the severity and audibility of this will be substantially reduced.

 

Said bite being of use in their professional role which addresses that issue.

 

How can something that is already 'slight' be regarded as having any 'severity' and be 'substantially reduced'?
Or, how do you substantially reduce a little additional bite-turn it into a gentle suck?
Without plotting the graphs for the units employed either side of this unit you cannot even get close to interpreting the sonic effect of this minor resonance on the overall output of the ATC's-it aint just the slopes employed its how the driver responses overlap and further eq their combined responses(you guys know this already I'm sure)respective polar responses also probably influence ATC's choice of xover point(you know this too).

Oddly enough I've never found the larger(300's?) monitors to be entirely transparent in the mids myself and felt a slight papery taint to the sound but thats me-I'd still have a pair they're excellent speakersIMO.

 

Using your ears? I feel you should register on the Naim forum without any further delay, particularly since you know someone who is an expert, and who once worked in the hifi industry, Jek.

"Musicality" will appear in your posts before very long, I predict.

 

Bub, some used their ears only to be told they are deaf - after all Pink Floyd can't be wrong

You've then been presented with measurements and an explanation as to the likely affect of some of the recorded irregularities. These you dismiss as irrelevent. I've then shown that they are not - that Bob Polly confirms their relevence and the rumours you've been spreading are ill founded.

Some have experience of moving crossover points to attenuate drive unit resonances. I do and were it not for my having sold the DEQX I'd be only to happy to demonstrate this to your Southern representative so you too can understand that issue. You can see the evidence in the spectral decay plot, energy stored and smeared in the time domain.

There is no need for words like "Musicality" There is both objective and subjective evidence to suggest ATC have made a compromise that some will be sensitive to and find objectionable. It was always rumoured (nothing more I might add) that ATC never listened to their speakers. That they designed and did QC purely based on measurements. Maybe they might be advised to listen more?

I suspect if I bought a pair of SCM 50's, ripped out the electronics, and used my own amplification and crossover topology I wouuld be very happy with the results.

 

Since you are seemingly in almost daily contact with Bob, why don't you suggest it?

You have to admit you are trolling Mike.

 

Anyone having the temerity to point out compromises in your hallowed system appears to be trolling to you Bub. I'm sure in five years time when you are complaining about the resonance in the midrange of ATC monitors that don't compare at all with your new ****, we'll all find this highly amusing.

 

I apologise, but I was going along with you until you posted these last two paragraphs.

ATC didn't have an on-site guest listening facility at their factory until the mid-late nineties although their then sales manager, the rather outspoken Ashley James, lived nearby and had a dedicated listening room given over to ATC's clients.

OF COURSE THEY LISTEN!!! Mostly in their clients' studios - the actual environments the speakers are used in. How many domestic speaker manufacturers get the chance to do this? Rather, they may do musical evenings if they're Naim and demonstrate their products in dealers showrooms but it's not the same!

I also take issue with your disguised condemnation of ATC's active amp packs - and therefore your disrespect of Tim Isaak, ATC's electronics designer and director of the company. If you actually bothered to talk to him, I'm sure he'd enlighten you as to what he does with his (mainly heavily Class A biased) amps and, more importantly WHY!!!

Thank God ATC don't pander to the likes of us. Their speakers would be a dogs dinner and change spec every other month as they pandered to the latest capacitor, fancy cable, measurement technique and the latest fantastic "this years" tweeter that calls for constant crossover changes..... - you know what I mean -...

ATC DO improve their products, but it's a gradual thing over tens of years rather than tens of weeks or months and as a result, you know what you're buying (or not, as the case may be).

I said before that commercial considerations often mean that a good, consistant tweeter that can be easily serviced if it fails is far more important to ATC than a finely produced expensive one that may expensively fail if the soft clipping doesn't act quickly enough. This far more important to them than a slight resonance in the mid dome that's well down in level and IN PHASE with the tweeter. The distortion measurements back this up I think.

 

Another disgruntled ATC owner/dealer I believe. I am sorry if you don't like my comments regarding the amplification packs but I'm not the only one who suspects they are a limiting factor - indeed ATC themselves went for a slightly better design in the Anniversaries. The the small heatsink is surely insufficient for the heat dispersion of over 200 watts of Class A output so I'd be interested in measurements indicating the biasing of the amp packs - both standard and upgraded. Having seen the amplifier boards, I can quite understand the upgrade offered on the Anniversary.

It's not a case of pandering to audiophiles, it is a case of producing the least compromised monitor for both professional clients and music lovers. If their more successful rivals such as Dynaudio and B&W see fit to put extremely good tweeters in their professional product, I cannot see the reason ATC choose not to other than to save money. Look at Dynaudio M3. Look at Westlake BBSM. Look at Adam monitors with their Heil tweeters. ATC owners for some reason give the company an almost religious significance - bizarre given their limited share of the professional and domestic market. They make very good loudspeakers, but so do many other manufacturers and all are compromised to one degree or another. Please don't place ATC on a pedestal. They are not beyond criticism IME.

 

I bet he will have PMC and an Sp10 by then!

 

I believe Bub does have his on a pedestal!

 

Thank you for your respectful and considered reply. I'm afraid I got rather cross this am and this discussion kept coming to the surface all morning, distracting me from my studies... I'm only a bit disgruntled with your last two paragraphs, NOT my speakers I should add.

Of course ALL speaker manufacturers' products have compromises somewhere, some more than others I'll admit. ATC's amp packs would be awful driving anything else as they were ONLY designed to drive the 16 Ohm drivers in their monitors and the drive units are 16 Ohm too, to assist the amp/speaker synergy. if the latest mid driver is 2db more sensitive then that can only be of benefit as the amp only has to use around 2/3 the power than before.

I can assure you that the heatsinks are fine and never get too hot to touch (their Class A biassing is about 50W into their output as I recall, meaning the tweeter is Class A driven). I did replace the (floor length) cloth cover on one of my 20aSL pros recently when it was switched on and much later that day my wife discovered it, switched it off and found the whole carcass very hot indeed without ventilation...

I'd like to ask a genuine question as to why you dislike the active boards having seen them. I believe ATC publish circuit diagrams so there's nothing secret about them unless I am mistaken.

From what I've heard (ok, some years ago), ATC have three levels of reproduction; the passives, the actives up to the 100a's and the biggies (200 and 300) - I haven't heard the 150 but think the greater efficiency of the bass unit may close the gap.

I think ATC have put drive unit engineering before almost anything else since day 1 and almost certainly don't see any upper mid resonance as a major problem area, now they use 4th order active filters as some on here have (I'm sure they acknowledge it, but they have other priorities). I've always found Billy's staff very open and honest in their dealings with my clients and myself and they never tried to hide anything from me when I was a dealer for them.

 

It's nothing to do with your repetitive and dogged criticism of just about every hi-fi component I own, as I have become very accustomed to reading this type of post from you.

The reason why I think you are trolling is that there is absolutely no credible evidence that the ATC midrange dome displays the problems which you are claiming. I am far from being the only person here to disagree with you about this, but you seem to want to single me out for some reason.

Um, yes.

 

Bub,

it is clear you don't understand the measurements presented on this thread, so debating the issue with you will sadly quickly become circular.

There is a resonance indicated on the published measurements. The audibility of this is in question. My experience suggests it will be audible. Shinobiwan seems to suggest the same. With due respect, both of us have spent more time playing with loudspeakers and crossover topologies than you. It might therefore be more than a wild unsubstantiated guess.

DJSR,

I think it was a general impression when looking at the boards in the factory to be honest. My active crossover comprises entirely discrete componentry, the amplification the same. I hear an electronic haze, subtle but there, when I listen to ATC's and I can't help feeling that the amplifier packs are basic. I still cannot see how that heatsink copes with the heat dissipation of a total of 200 watts class A power ( ATC claim 2/3rds output in class A I believe). My ATC SCM50ASL's got warm but not that warm!

 

The resonance is outside the intended usable bandwidth, as has been pointed out several times. It's also not apparant on Paul Ranson's measurements, and none of the ATC users here appear to be able to hear it.

This is getting extremely tedious, as usual, so I think I will leave you & BBV to it. Have fun.

 

Bub,

how would you recognise a resonance when listening to the mighty Floyd?

 

I probably wouldn't be able to hear it Mike. Especially if it wasn't there.

Go on: have the last word.

 

Buffy. Buffy. Buffy.

Quick. I'm powerless here. Would a ZG mod lock this thread now?

Joe

 

So either the heatsinks were fine, or the amps aren't quite as much class A as stated, which I don't think is true.

The only way to prove your point regarding amps and active crossover is to obtain a pair of passive ones, remove the passive crossover from its chamber and make a new back panel (ATC may even have this option already for all I know) so you can actively tri-amp them. That would prove your point once and for all (I do think you have a point...............).

 

One amateur measurement appears to show a resonance. Another amateur measurement appears not to.

Unless you can demonstrate this resonance on an actual speaker then discussion of its audibility is moot.

I've had a look, I can produce relevant curves that don't show it (the FR graph from upthread is not one of these) but this doesn't mean it's not there. Perhaps you could borrow a bare unit from Stuart or Bob and we'll go back to basics on the measurement front and see it the result is reproducible.

Look deeper into ATC's claim. The 'substantially Class A' bit refers to the mid and treble, and of course the mid is 16 Ohms and so runs at less current implying less standing dissipation.

Paul