Film-Tech Forum ARCHIVE: IMAX SR speaker crossover point

This is topic IMAX SR speaker crossover point in forum Large Format Forum at Film-Tech Forum ARCHIVE.

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Posted by Paul Trimboli (Member # 1509) on 03-17-2005, 04:40 AM:

I need to find out at what point a 2 way Sonics speaker as used in an IMAX SR setup is crossed over. Is there anyone that makes high power (600watt ish) PASSIVE crossovers?

Posted by Gordon McLeod (Member # 33) on 03-17-2005, 09:35 AM:

Why would you want to passively crossover it since they will introduce far more distortion
Also the crossover slope of a passive is probably to shallow to protect the drivers

Posted by Dan Suomi (Member # 2585) on 03-17-2005, 11:08 AM:

I would also like to add that that type of info would probably considered confidential to prevent anyone from copying speaker design.

Posted by Paul Trimboli (Member # 1509) on 03-19-2005, 03:35 AM:

Well what might be happening is I will be doing the setup at a now closed IMAX cinema. The speakers are still in place, but no amps or crossovers. OK so passive does not seem the way to go. My question is still at what point should I cross the speakers over at and what should my crossover slop be? Is there anyway to work this out with out the driver specs?

Posted by Mark Gulbrandsen (Member # 72) on 03-19-2005, 07:39 PM:

Paul, I have to chuckle, another closed Imax....... I guess you have "bean counters" down there too!

Anyway if you have a good spectrum analyzer, preferably one with at least 4 mics, and access to a programmable x-over with adjustable time delay this is a workable thing to do. While I can't reccomend any exact x-over points and time delay settings if one looks at what each driver is doing by itself its pretty easy to determine reaosnable x-over points and delay settings. The use of a TEFF analyzer probably would be needed to determine exact delay settings. Once you determine as close as you can what each driver is up to then building a system around them is fairly easy. I would definately reccomnend the use of a digital x-over for this. You will need LOTS of power... Dont skimp here! Hope this gives you some clues.

BTW: Those Imax SR sound systems just use Crown power amps in disguise....... inside the Sonics case you will find a Crown... not very original!

Mark

[ 03-19-2005, 11:45 PM: Message edited by: Mark Gulbrandsen ]

Posted by Adam Martin (Member # 641) on 03-19-2005, 08:11 PM:

Only the SR (and maybe the MPX) systems use Crown amps. The higher-end systems use much better amps and run three-way.

Paul doesn't have the amps, he just has the speakers.

Posted by Paul Trimboli (Member # 1509) on 03-19-2005, 08:43 PM:

Thanks for the help Mark. I can get my hand on such equipment so hopefully will be able to work it out. Was hopeing someone could say-oh sonics crossover at such and such and the slope is this number. But as Dan said, this might be confidential info. I was looking at around 600watt for HF and 600watt LF drivers. A couple of thousand for subs. Those numbers seem OK?

Your right Mark, we have been counters in Australia too. We only have IMAX Sydney and Melbourne left in Australia. When I was over in Sydney for work a couple of weeks ago I visted IMAX, building is a little run down but I think they are running at a point where they are turning over a profit.

Posted by Gordon McLeod (Member # 33) on 03-19-2005, 09:24 PM:

I doubt you would need much more than 200 watts for the HF

Posted by Paul Trimboli (Member # 1509) on 03-19-2005, 09:34 PM:

Anyone has much experience with Biema amps? Any good?

Posted by Gordon McLeod (Member # 33) on 03-19-2005, 09:47 PM:

I know David Johnson at Hoyts has been using them so maybe you should ask him

Posted by Mark Gulbrandsen (Member # 72) on 03-19-2005, 11:43 PM:

quote: Adam Martin
Only the SR (and maybe the MPX) systems use Crown amps. The higher-end systems use much better amps and run three-way.

Yes, am aware.... Thanks, I stand corrected and so does the post. You mean theres someting better than Crown amps????? [Big Grin]

quote: Paul Trimboli
When I was over in Sydney for work a couple of weeks ago I visted IMAX, building is a little run down but I think they are running at a point where they are turning over a profit.

Seems like an example of having to let the building go to heck because the profits have to go elsewhere.....by contract.

Good luck getting the system back up... shouldn't be too hard! Just don't blow any of those mysterious drivers or you may have to install something that can be easily delt with [thumbsup]

.

Mark

Posted by Paul Trimboli (Member # 1509) on 03-20-2005, 12:07 AM:

That was another question I had Mark,what if I need driver replacments? Got the spare parts speaker at the top of the screen I guess! [Big Grin]

Posted by Gordon McLeod (Member # 33) on 03-20-2005, 09:50 AM:

Another issue to be addressed is bass summing to a sub since the screen channel speakers were designed for that form of bass management

Posted by Mark Gulbrandsen (Member # 72) on 03-20-2005, 01:39 PM:

quote: Gordon McLeod
Another issue to be addressed is bass summing to a sub since the screen channel speakers were designed for that form of bass management

Actually Gord if they install a DTS XD-10 which is most likely to end up in a replacement for that system they an go eiither with a dedicated sub or with bass summing. DTS will format it which ever way you want it onto your playback disk or per the director/producer. I recomend a Panastereo CSP-1200(even in its basic form!) as all the sub card slot is able to run full range if needed. Most LF DTS stuff is 6 track discrete with channel 6 as the sub channel. In leiu of that sub channel it can be used asa full range channel for high center in which bass summing is then necessary. For that slot you will need to add 1/3 octave eq which is bybassable in sub mode. BTW: The CSP-1200 also sounds WONDERFUL in a large format system!

Mark

Posted by Gordon McLeod (Member # 33) on 03-20-2005, 02:03 PM:

From what I gather he doesn't plan to run large format and even if he did and put in a xd10 the speaker system design in the first place is designed for the use of bass management and the screen speakers are not full range down to the very bottom of the system
Even the larger 4 sonic systems still use bass management in there design also the "classic systems" used either re branded AB international amps or Bryston amps

Posted by Mark Gulbrandsen (Member # 72) on 03-21-2005, 07:42 AM:

quote: Gordon McLeod
also the "classic systems" used either re branded AB international amps or Bryston amps

Well, I would want to do away with those speakers completely if they did something that dum. BUt I'd be willing to bet that they can be used with or without extra sibs of the appropriate type. As for the other amps. the Brystons are built well but sound bad and AB was/is one of the worst there is. The early ones were taken right out of the RCA power semiconductors manual! So far the Crowns are probably the best they have used.

Posted by Gordon McLeod (Member # 33) on 03-21-2005, 08:43 AM:

Funny if it wasn't for the heat they generate I like bryston they sound very good but the racks get very hot
As for AB they were also the amp used in all the Paramount soundsystems for years

As for bass management that is used in many newer speaker systems nowdays by many manufacturers including the use of the bafflette THX systems use bass management to divert some of the main screen speaker LF to a dedicated sub

Posted by Paul Mayer (Member # 355) on 03-21-2005, 11:10 AM:

The Caesars Palace Omnimax used the same AB amps for its entire life. The old Mitsubishi IMAX in LA (Los Angeles; not Lethbridge, Alberta) used David Hafler amps and THX crossovers even though it was never certified as a THX house.

Posted by Adam Martin (Member # 641) on 03-21-2005, 01:03 PM:

Also note that Imax wasn't in the sound business from the get-go. Many of the older theaters had their sound systems designed by a third party. It wasn't until they purchased (read "ruined") Sonics that they had sound people on staff.

Posted by Gordon McLeod (Member # 33) on 03-22-2005, 05:57 PM:

Why not contact Oxmoor who was the original Sonics people and made most of the electronics
http://www.oxmoor.com

Posted by Adam Martin (Member # 641) on 03-22-2005, 06:11 PM:

The Crown amps in the SR system had a plug-in module on the back. This may have been the two-way crossover, but I don't specifically remember.

Posted by Gordon McLeod (Member # 33) on 03-22-2005, 06:15 PM:

Typically the crossovers were mounted onto the back of the amplifier In the case of teh bryston it was a custom back panel

Posted by Mark Gulbrandsen (Member # 72) on 03-22-2005, 07:12 PM:

"The Caesars Palace Omnimax used the same AB amps for its entire life. The old Mitsubishi IMAX in LA (Los Angeles; not Lethbridge, Alberta) used David Hafler amps and THX crossovers even though it was never certified as a THX house."

No matter.... they are still god awful amps, antique designs about on the same plane as Phase Linear 400's! I have a stack of them in the basement here that I am gong to re-build into Tri-Path Class D amps for my home screening room. Hafler amps actually sound ALOT better but were unreliable and the MOSFETS are now obsolete necessitating somewhat of a rebuild tog et newer MOSFETS biased correctly and working properly. I have an aquaintance at the CBC that does recording andthey have the Brystons there... he says that they have to leave them on all the time for them to sound best but that they still cloud the stereo image considerably and are also some what grainy on the high end. But they are VERY well made!

As for the bass management, there are several ways to do it but the CSP-1200 is very adaptable to just about any method.

Mark

Posted by Gordon McLeod (Member # 33) on 03-22-2005, 07:48 PM:

I know many sound recording engineers mark who will disagree on the quality of the sonic performance of the brystons

Posted by Paul Trimboli (Member # 1509) on 03-24-2005, 09:01 PM:

Thanks for the input so far!
The theatre will be running optical SR and a digital format not any large format system. The processor that is still with the building is an Ultra Stereo JSX-1000, now that obtains its sub signal by summing all channels, will this be suitable? Do OMNIMAX cinemas normally use the same speakers are flat screen IMAX? I am able to inspect the setup at what was the OMNI Dome so if the system is the same I can get my crossover setting from there hopefully, depends on the setup I guess.

Posted by Adam Martin (Member # 641) on 03-25-2005, 01:12 AM:

Typically, no.

Posted by Jimmy Peters (Member # 886) on 04-07-2005, 12:06 AM:

I agree with Mark all the way....the Panastereo is a wonderful box and would sound terrific in large format.

Posted by Adam Martin (Member # 641) on 04-07-2005, 02:18 AM:

Discussion of topics other than "IMAX SR speaker crossover point" should be conducted elsewhere. Thanks.

Posted by Mark Gulbrandsen (Member # 72) on 04-07-2005, 07:15 PM:

quote: Jimmy Peters
I agree with Mark all the way....the Panastereo is a wonderful box and would sound terrific in large format.

I can assure you that it is great in a large format system! Getting back to the x-over issue... I think its pretty safe to assume that if another system used the same boxes, horns, and drivers that are in his system it would x-over at or very near the exact same points. What would probably be different would be the delay settings for time alignment.

Mark

Posted by Stewart Anderson (Member # 1809) on 04-21-2005, 07:15 PM:

Off-topic post deleted by moderator.

[ 04-21-2005, 10:20 PM: Message edited by: Adam Martin ]