Film-Tech Forum ARCHIVE: Use of Horn Loaded Subwoofer In A Baffle Wall

This is topic Use of Horn Loaded Subwoofer In A Baffle Wall in forum Film Handlers' Forum at Film-Tech Forum ARCHIVE.

To visit this topic, use this URL:
https://ft-forum.com/ft/cgi-bin/ubb/ultimatebb.cgi?ubb=get_topic;f=1;t=005373

Posted by Mark Gulbrandsen (Member # 72) on 09-25-2003, 12:33 PM:

I have a customer that wants to re-use his Cerwin Vega "W" horns in a baffle wall that is part of an upcomming project in a large single screen sound system.
Long ago in THX class they told us briefly the physics of why this will not work well. That was long ago and I've forgotten that part. Can anyone refresh me on this topic? I realize there there would be phasing problems, but I also think the "W" horn may have lower output when its in in a full baffle wall.
Mark @ CLACO

Posted by Mark Seaton (Member # 1398) on 09-25-2003, 12:44 PM:

As a maker of a few potent bass horns, I can confirm that in general, a baffle wall greatly helps most bass horns. The question of how they were designed is an entirely different discussion. I recall that some of the old CV horns were meant to be corner loaded to extend and load the horn more properly.

If a horn is operating properly, output should hardly be an issue. That said, there are plenty of bad sounding bass horns out there. So far as not working well, that depeneds... A horn has a path length wrapped up inside the box. It takes sound time to travel this path length. As such, the mid-highs must be delayed appropriately to better overlay the impulse from each device. With modern signal processing this is a pretty trival task, and you can get yourself in the ballpark by figuring ~1ms per foot of additional path length. Since there will be a low pass filter on the subwoofer, which introduces it's own delay, you want to err on the longer side of this rule of thumb.

Hope this helps some,

Regards,

Posted by Gordon McLeod (Member # 33) on 09-27-2003, 04:34 PM:

The CV's from earthquake were designed to use the room corners as an extension of the horn
I often have placed them at the side of the screen near the wall

Posted by Mark Gulbrandsen (Member # 72) on 09-27-2003, 05:11 PM:

I've never run into a customer wanting to do this sort of thing. After disscussions with other techs and industry engineering folk, plus taking in Mark Seatons post above we decided to go with two of the BGW M2200 sub woofers running on 220 volts in this system to keep it all direct radiator. It was decided that if the horn was placed at the front of the baffle wall that it would probably work ok, but it would also require a DSP system of sorts to time align all the screen channels, in this case the JBL 5674, to the horn. I am wanting to keep this system DSP free and have the highest quality possible. The 5674 is probably the finest direct radiator system made for cinema use and although we are using digital x-overs they are of the 96khz/24 bit type, not DSP based. I hope the building survives the subwoofers [Big Grin]

!!

P.S. I once had the pleasure of using Marks phenominal subwoofers outside at Lincoln Park in Chicago for an outdoor 70mm film showing. With twelve of his subs we were able to seriously irritate a large number of high rise dwellers about 300 yards away by rattling their windiows when we ran pink noise!! No small feat indeed...many came down to see what the noise was and give us a piece of their mind [Eek!]

...... NASA also uses them to levitate objects......
Mark @ CLACO