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This topic comprises 6 pages: 1 2 3 4 5 6
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Author
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Topic: Do high-frequency speakers deteriorate over time? Or is it just my ears?
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Monte L Fullmer
Film God
Posts: 8367
From: Nampa, Idaho, USA
Registered: Nov 2004
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posted 03-27-2012 02:30 PM
There's a theatre in Heber City, Utah where a fellow that lived in that town went totally crazy with sound in this theatre moons ago:
He was the originator of Rockford Fosgate.
Had all sorts of amps and E.Q. systems, but his speaker array behind the screen was where the results of all of this ended:
Interestingly enough, there was no baffle wall behind the screen, used VOTT A-7's for the stage speakers, surrounds were JBL units (didn't know the model) but he did make an interesting method for the sub channels:
he mad very large speaker bins made from poured concrete attached to the foundation of the building to mount 4, 18inch subs and had two TUBE amplifiers behind the screen to drive those four subs.
Needless to say, for just Dolby "A" optical sound from a Century R3 soundhead (with exciter lamp) with a Brenkhert Model 80 dbl shutter projector mounted on top and a crapola Christie CH-20 console for the light, presentations in that theatre were outstanding.
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Cameron Glendinning
Jedi Master Film Handler
Posts: 845
From: West Ryde, Sydney, NSW Australia
Registered: Dec 2005
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posted 03-28-2012 01:38 AM
quote: Chuck McGregor
While the results may be well worth it, achieving optimum results, especially with just wings is not just a matter of installing wings and calling it a day. The "logic" behind it does matter in understanding the impact on the sound projection and therefore what to expect.
I disagree, my real world experience says otherwise. In the early 90's having actually hired a large warehouse and experimented with a variety of different wings on the typical set of JBL twin 15" cinema speakers, all I can say is they make a dramatic improvement to the sound when added. The science is very easy to understand and pretty much any width did make a difference, bigger however were better! The only important point that has to be emphisied is that structual strength of the wings or the baffle wall must be extreme, think concrete or more simply put... would you jump up and down on this thing?
Another issue is that a speaker will sound better when its not placed in the dead centre of a baffle (that includes speaker boxes).
Yes the sub bass is dramatically boosted when you add wings but after it is cinema eqed the additional boost disappears and the quality improvement and lower frequency response is all that is left.
On my next generation of cinema loudspeakers I dropped the bass refex port and its inherant distortion in favour of very large infinite baffle boxes with matching wings. The sound was even more realistic and honest, especially noticable in side by side tests with the reproduction of instuments such as the double bass.
Years ago Altecs had a THX aproved cinema speakers that were large sealed boxes, its a shame that the other manufactures did not take note...
quote: Mike Blakesley
How tall does it need to be above the speakers? All the way to the ceiling
The typical THX wall does go foor to ceiling, tripple layered gyprock on a strong steel frame in the cinema.
Does it need to go this high? technically its the width not the hight that is more important, though with the wings that I use to build I would extend them up next to the horn with the black tissue faced fiberglass on the front to remove the early reflections that bounce off the screen. In reality the full wall is the ideal but only if its built solid!
So to be effective to say 50 Hz the baffle/enclosure width must be about 10 feet centered around the loudspeaker.
You have never built a set off wings? firstly the speaker should not ideally be centred, secondly a usable response closer to 30hz in the real world, ( even though the JBL speaker box tested was tuned to 40hz....)
The other practical experiments with cinema audio I did was with trying to contain sound leaking between auditoriums. I got great results with using less reactive (ie smaller magnet and voice coil) 15" and 18" woofers than the typical cinema models.
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Chuck McGregor
Film Handler
Posts: 47
From: Bremen, ME, USA
Registered: Mar 2012
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posted 03-29-2012 01:41 AM
Cameron
I said: "The logic behind it does matter in understanding the impact on the sound projection and therefore what to expect."
You said "I disagree" followed by your discussion how you went to considerable effort to figure out the "logic" so you would know what you were doing!! ![[Razz]](tongue.gif)
Here is where you get five gold stars plus for saying a truth that is pretty much ignored by all manner of audio people ![[thumbsup]](graemlins/thumbsup.gif)
quote:
On my next generation of cinema loudspeakers I dropped the bass refex port and its inherant distortion.
Years ago Altecs had a THX aproved cinema speakers that were large sealed boxes, its a shame that the other manufactures did not take note...
A box with a hole in it is a resonator. Excite the air in the box and it resonates. A big "selling point" for ported loudspeakers (more so some years ago) is that the cone movement is greatly reduced at the port tuning. Well, if the loudspeaker cone isn't moving very much it should be quite obvious the cone isn't "moving" much air, so where is all that low frequency energy coming from? Answer: a box with a hole in it that is resonating. It doesn't take much to get a resonant system going. That is not reproduction. Call it distortion or whatever and it may be sonically convincing but, again, it is not reproduction. It would be more accurate to call it something like a low Q organ pipe driven by a vibrating piston.
The joys of infinite baffles have been well-known for the better part of a century. Loudspeaker designers do know this. However, the economy, practicality, and "ported efficiency" of smaller enclosures drives the designs. Rudy Bozak, was one of the last champions of the infinite baffles and their practical equivalent of enclosures large enough to not appreciably load the rear of the cone. He hated ports for the very reason you cite.
Whether to center the loudspeaker or not depends. With an off center loudspeaker, the effectiveness of the shorter side will be limited to a higher frequency. As well the radiation pattern will be asymmetrical. One only needs to figure out if these things matter or not. As to implying it "must" be centered, I was thinking about my own situation when I wrote that where the wings have be about equal, but for other than acoustical reasons.
"You have never built a set of wings?" Based on your picture, I was designing loudspeakers (professionally) before your were born so let's leave it at that. You are right that the science is easy...at low frequencies. For example however, the screen/baffle reflections can make the science more difficult at high frequencies for high resolution HF horns. Then again, such horns are not at all common so this is more of a moot point.
"Secondly a usable response closer to 30hz in the real world.." 50 Hz was presented only as an example not as any kind of goal if that is what you thought I meant. I should have made that clearer.
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