ATC SM75-150S Dome Mid Measurement Data

There isn't a problem, but a reference would have been nice. And Shin wasn't clear about who wrote what or who 'ralph' was. It becomes even less clear when reposted by a third party.

So what do they sound like?

Paul

 

What are people's thoughts of JBL K2 S9800's. As anyone here heard or owned a pair? Genuine comments would be most welcome, but please note that I have owned both the JBL's and ATC SCM 150 Anniversaries.

 

Slightly forward in the upper mid which I have little doubt is down to the dome's break up. It's one of the reasons that Proac for instance don't push them so far in the D100. The problem is, the lower you cross them over, the more intrusive that crossover point. Really it could do with remaining pistonic for longer. I suspect modern Berylium domes could solve that issue.

 

You've got too many variables, firstly with the amplification for the JBL. I found the 435Be to be rather ordinary if I'm honest. The 1500AL however is capable of supreme sublety IME - the ATC is more punchy. The JBL is really a mini monitor being -6db at 45hz, the ATC more full range. JBL's equivalent of say a 150 would really be a 4348 or historically, a 4344 or 4345. Those are studio monitors. The speakers you compare are very different beasts designed with different goals.

 

Hi 'Mic:

I couldn't have put it better myself. The bass unit is very special indeed and does things that I've never heard from any other speaker. However, the lack of very low bass frequencies was something I eventually could not live with. The HF driver does seem to have a problem that I never did fully fathom - a very slight and unobtrusive, but pervasive, colouration.

I am extremely pleased with the ATC anniversaries and they are (definitely) the best speakers I have ever had. Again, not perfection, but I'm currently more than happy for them to be 'the last speakers I will ever own' (perhaps!).

 

That'll be a JBL biradial for you -like you say it's unobtrusive. But just like the ATC midrange dome, the 435be requires extensive EQ to flatten the FR and being passive, I'm sure this impacts on performance.

Listen to the Exclusive 2404 or 2402 which Richard owns and you can hear the difference with a ruler flat midrange response.

The JBL 1500AL can be made to work lower, it's just that the K2 is voiced for smaller rooms. I'm not sure what the -6db point is on the ATC's.

The biggest difference between the two speakers is the radiation pattern, and how it will interact with it's surroundings. That will be the most audible change when going from one to the other. I prefer a controlled dispersion if I can get it - and I couldn't get on with the ATC's amplification at the end of the day.

 

I'm sorry to but in, but as far as I know the ATC response of +/- 1 - 2 db doesn't call for extensive eq IMO as it's only usually used before the LF rolloff and again crossed over to the tweeter long before it goes into resonance mode. ATC's active amplification packs ONLY work with the 16 Ohm drivers they use in their own amps.

All this reading on this thread (and the now deleted one on PFM) got me thinking. Why do ATC cross over from the bass unit so low in frequency? Maybe this has already been answered (apologies if so) but ATC make huge reference to consistant dispersion. Am I right in suggesting that crossing over as low as the dome will go maintains mid dispersion consistancy.

ATC did design and make a prototype of a larger dome, but couldn't find a tweeter for it. Perhaps they should try a smaller one which goes up higher?

 

DSJR,

When used passively, typically two notch filters are employed to flatten the midrange response, and often a third to suppress the upper resonance. The upper resonance is dangerously close to the pass band IME at 4.5khz. Without suppression this will be audible, even when using fourth order slopes. Ideally the unit should be linear at least an octave above the pass band.

I wouldn't have though directionality has anything to do with the crossover point, the dome only becoming directional at circa 4khz, the 15" bass driver at around 800hz. The 9" cone in the 50's will be directional earlier of course, yet the same crossover topology is used. It will have no affect at all on the midrange dispersion from what I can see. I suspect that the bass unit throws up spurious 2nd order harmonics much above 400hz, and that is the reason for adopting the low crossover point. Certainly when crossed over at 500hz and properly EQ'ed the dome has none of the charaterisitcs detractors find off putting in the ATC monitors.

 

This doesn't make any sense if the off-putting characteristic is 'forward in the upper mid'.

There's a lot of guesswork, inference and assumption of authority on this thread.

Paul

 

There's also a lot of information garnered direct from an ATC client Paul - not hearsay from internet forums.

What are the crossover points again on the ATC monitors?

 

That's hearsay from an ATC client passed to you and then posted on the internet...

And it doesn't change the essential fact that the midrange fitted to the ATC actives is not the same as the one sold to third parties. You might infer they are equivalent, but we don't know.

Nor how an upper midrange issue is ameliorated by raising the low end of the midrange crossover.

Paul

 

Paul,

Firstly no it's not hearsay I'm afraid. I'll show you the boards at the factory if you would like. It's fact.

Secondly the devices are the same. They do in fact make the S and the standard model , the difference only being in efficency. Both are available to special order at 16 ohm devices should a client require them. There are no special devices made by ATC only for their own speakers that sound better than others. Come on! Do you really think they would tool up for that? Have you watched the domes being made? It's yet another example of ATC owners trying to bypass evidence that suggests there may be some minor issues with their products IMHO.

Thirdly it is not the low end that affects the upper midrange - please read the post. The upper midrange is crossover over too high I believe on the monitors (3.5khz?). That's only a quarter of an octave below the first major resonance. Even with a fourth order slope, it will only be 9db down at that point - not sufficient to remove it's influence IME. As a bear minimum I would crossover half an octave before the resonance fourth order - as other users do. There is of course an issue also at the bottom of it's pass band.

 

Proac using 'x' in their passive crossover this doesn't really generalise to 'typically' although I'd like to see the boards at the factory.

The devices measured by 'Ralph' and 'Shin' were 8 Ohm. We don't know whether the 16 Ohm variant is equivalent or not. At first glance putting more wire onto the coil must change things.

I don't know whether ATC make 'special' units for their own speakers, but I don't see any good reason why they shouldn't.

You said 'Certainly when crossed over at 500hz and properly EQ'ed the dome has none of the charaterisitcs detractors find off putting in the ATC monitors.' which clearly wasn't a complete statement.

I don't know the details of the ATC active or passive crossover so I wouldn't comment on it. It seems to me you don't know either but are happy to jump from effect to cause and then suggest a solution.

Have you ever had any dealings with race engine builders? They're a bit like speaker designers, the other guys compromises are always wrong....

Paul

 

Your acceptance that ATC are making compromises is a good start.

 

When have I not accepted that?

Paul

 

Why would you say that ATC alone see fit to use that dome so close to break up?

 

Mike, the ATC dome seems to have become almost an obsession with you. If you really want answers why don't you phone ATC and ask?

And you could read this, possibly register, and ask some other experts:

http://www.gearslutz.com/board/high-end/10776-opinions-atc-scm20-50-a.html

 

gear slutz is just the pro audio version of zerogain - every deck monkey and his mate is on there spouting off - its less likely to be factually correct even than hifi forums.

 

The obvious irony/o.g. being that you & Mike are spouting off on Zerogain....

All you are doing is flatly contradicting any opinion which you don't like. There's no prospect of progress here.

Never mind.

 

Irony indeed