ATC SM75-150S Dome Mid Measurement Data

The evidence is incorrect Mike.

As I said, I asked Bob Polley about any available upgrades whilst my speakers were with him at the factory over Easter. The only upgrades for my speakers were new tweeters & baffles, as I already had the SL bass drivers. I gave him a completely free hand, and emphasised that I wanted the speakers to be identical in specification to brand-new ones.

Check with the ATC factory if you are in any doubt at all about any technical aspect of their monitors. You'll find they are extremely courteous, professional and helpful.

 

Paul,

Ralph(Aeronet) was fully credited in the opening lines of my original post and I quote:

"I should also thank Ralph who's FR and impedance data I have borrowed. 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."

I bought and used the SM75-150S 16ohm so any data presented here from myself is of that driver.

EDIT: I see you cleared up the misunderstanding amongst yourselves. Ignore this.

 

Simon, all the lspCAD 'justMLS' plots are Ralph's. He posted them in my ATC build thread over on DIYA and I asked if it was OK to use them in a measurement summary. I then abridged the data with my own distortion and CSD measurements to provide a more complete picture.

He later put the data up on his website.

 

This should clear up a few things. I dealt with ATC direct and built up a fairly good client relationship with Bob Polley down at ATC. Here's what I've heard from ATC themselves and isn't guesswork or rumour.

The ATC mid comes in two guises, standard and super with an 8 and a 16ohm variant of each. They are exactly the same as the ones used in their commercial models.

The difference between the standard and super is simply the magnet. The super has a larger type which increases BL product or in other words, there's more flux in the voice coil gap and so is more sensitive.

ATC have released one revision of their mid dome since its release in the late seventies. This happened in 1999 and saw a refinement of the wave guide used.

The only drivers you or me cannot buy from ATC is the SL(Super Linear) model bass drivers and instead will only supply the LC and SC models. The SL drivers are exclusive to the larger SCM monitors that were released from 1996/7 onwards.

 

I used the 16ohm version.

Paul, Mike has the general idea and I think this very thread was originally much larger but got pruned back because of heated debate surrounding just what was and wasn't the correct implementation for the ATC mid.

I championed my own implementation which attempted to circumvent the obvious short comings of the drivers and ones which ATC wander quite close to in their own implementations.

The driver has a large breakup at about 4.4Khz and ATC use 3.8Khz 24db/oct slopes. The low end has the driver Fs or resonance frequency at approx 320hz and ATC use 380hz with the same 4th order slopes.
If it isn't apparent from this, then I'll just say that's cutting it fine on both counts.

My own experiments and ATC orientated build yielded better objective and subjective performance from moving further away from these issues and that was done with either steeper filtering and/or narrowing the passband away from the problems.

Driver engineering isn't quite voodoo and good common sense design in light of component behaviour applies is something you'll find in all good and particularly accurate loudspeakers. ATC isn't a special case here, at least not if linearity is an issue.

This is obviously controversial because it implies that ATC have a sub optimal implementation of a driver they themselves engineered and that I, a simple enthusiast, did it better. This was exactly why the thread turned sour all that time ago. I've long since sold the ATC's and have no further interest in debating just what is and isn't right for the driver nor do I wish to antagonise happy ATC owners.

Consider this post another opinion on how loudspeakers should be designed and file it with the thousands of others you'll find scattered around the internet.

 

Of Course it is Bub. Would you be able to produce anything to back that assertion up other than a load of slutz pontificating on the internet?

Bub are you not reading my posts. I did check with Bob and have already posted what he said. I asked about the dome in the D100 which is the lower sensitivity, non S variety. Stewart uses this because he prefers it to the S. As I have already posted, the amplitude response of both drivers is the same, and I believe Shinobiwan's post squares the circle on the issue and puts to rest the internet rumours you were clinging to.

 

Mike, quite frankly I am not certain what has happened to you recently. I used to think you were quite entertaining, and probably quite a good laugh in person, but these days, the good humour seems to have evaporated.

I can't be bothered to argue with you any longer.

I'm off to make breakfast for my lads. See you later, no doubt.

 

Bub,

if you stopped arguing against the facts when it comes to ATC, then there would be no need to point these facts out would there and we could all have more fun.

As I said, enjoy your ATC's - they are inherently a fine loudspeaker. Just please don't berate those of us who have issues with them. We all hear differently, as Paul pointed out when he last visited. Just because you choose to rely on the crutch of professional studio users, doesn't make all of the other major studio's like Stirling Sound, Skywalker Ranch, Abbey Road and Master Disk wrong does it?

 

This is getting silly. Why didn't you post consistent data?

ATC claim 3.5kHz.

Paul

 

Mike.

I am not knocking non-ATC users.

Shin's post is actually rather ambiguous. He said:

"The ATC mid comes in two guises, standard and super with an 8 and a 16ohm variant of each. They are exactly the same as the ones used in their commercial models."

So, which version is in the Active SCM series: 50s, and up? And which version's data is presented in this thread?

 

We haven't yet established the facts.

Paul

 

So which is right? The review you link to? As I've pointed out already, even 3.5khz would be too close for comfort IME.

Well we have reviews from a respected publication, the words of Bob Prolly, and confirmation from two sets of measurements. What would you like to know?

 

I'd like an answer to that question, Mike.

 

Bub,

Shinobiwan has already posted that the measurements refer to the 16ohm varient fo the 150S - the exact same drive unit as used in the ATC Monitors.

Bob Prolly has already stated that this unit and the other measure exactly the same in terms of amplitude response so even if another set of measurements were taken from a speaker employing a different varient, the FR plot would be identical.

In short, the rumour being stoked on Gearslutz and PFM is unfounded and untrue.

 

i am guessing the entertainment stopped when Mike dissed the ATCs and dumped the SME for the better performing SP10. Take it easy bub.

If the crossover is just under 4khz and the breakup just above then it would certainly explain my subjective listening experiences. This flaw would unlikely have any effect on the professional role for which ATC are used which is why the pro users don't complain.

 

I know this is an attempt at reconciliation (which I don't want to jeopardise)... but (if) ATC use a crossover which has audible problems for the audiophile, then these problems are clearly going to be equally a problem (if not more so) for a studio engineer.

Surely?

 

They are usually concerned more about tonal balance and being able to "hear" what is going on. A bit of added zing might actually help. As a pro tool on the front desk it is one of the very best. But you dont see them in mastering suites where they assess the finished product - which is a bit telling.

 

You're the man with all the facts.

No he hasn't. The base FR, dispersion and impedance measurements were done by Ralph on an 8 Ohm unit of some form.

Paul

 

How could anyone possibly quality monitor or EQ something as common as human voice with such an audible flaw? You really don't know what you're talking about.

Paul

 

I'm sorry to be thick headed, but I fail to see what the problem is with the amplitude responce of the mid dome in the range in which it's used. +/- 1db is quite good I think.

To answer an earlier reply to my former post, ATC have NEVER recommended passive versions of the 50's upwards as, by their own admittance, they use the mid driver as wide as they can get away with and this can cause problems with the passive crossover, which can't be tweaked out, or at least minimised, as they can with with the active ones - I should add the active setting up at the factory is quite thorough and a far cry from the Linn and Naim way ('scuse me while I wash my mouth out...).

I've just remembered a discussion I had a while ago with a couple of good geezers from Northamptonshire, both of whom had active ATC's (50's I think). The SL updates involved retuning/re-voicing the bass-mid balance, removing the slight (BC1 style) tubbyness in the upper bass/lower mid and appearing to extend the bass down a little further - I think HiFi News measured both versions as I recall and the response around 100-200Hz was certainly different in level by a couple of db on the previous and current versions.

What I'm getting at is that one of these chaps disliked the change in sound the SL upgrade made and commented on the increased perceived "brightness" - as far as I know, only the bass units were replaced and the mid-top balance wasn't altered.