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Old 5th September 2007, 07:15 PM   #11
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Thanks Ian for a very informative post;

Since starting this thread I've learnt a few things about the Sensurround horns - for one, it is a pair of the model 'M' horns I wish to construct, and these would be stacked and operated into a corner as originally intended. The frequency response doesn't centre about 15 Hz as I originall thought; The signal consisted of frequencies in the octave or so above 15Hz, meaning sound between 15 or so up to 30 and probably higher.

I have also heard that the Cerwin-Vega drivers used to fail on regular occasions, but I'm wondering why - was it a mechanical failure due to over-excursion, or overheating? Builing a driver to accept 250 watts continuous (500 watts into 2 X 8 ohm drivers) was a bit of a problem in the '70s, after all.

Anyhow, I would indeed be very interested in any information you have, especially the PDF file you mentioned.

Thanks for replying.
Andy.
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Old 6th September 2007, 04:14 PM   #12
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Greets!

Had to be over-excursion based on driver specs and acoustically huge compression chamber (CC) volume (Vb) to get them to play below the ~33 Hz cut-off at high SPL unless many boxes with horn extensions were used.

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Old 7th September 2007, 06:51 AM   #13
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Hi Andy. As I am new here and under "observation", I cannot email you, so I will convert the PDF into JPG and post it here. Actually the drawings are for a cabinet for a 189ES driver which was similar. The 189E was an incredibly robust monster with sand cast basket, paper cone and linen/wax suspension surround. I will post a photo of one of mine here. I do not know the reason for failure, but guess its a travel thing. Cheers, Ian
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Old 7th September 2007, 06:51 AM   #14
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Another page for the drawings:
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File Type: jpg cab2.jpg (52.9 KB, 585 views)
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Old 7th September 2007, 06:51 AM   #15
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Photo of a 189E driver (and friend)
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Old 7th September 2007, 11:53 AM   #16
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oops...looks like the first plan didn't upload...try again:
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Old 7th September 2007, 01:48 PM   #17
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I went and saw "Earthquake" in some cinema in Melbourne at the time, purely to hear the sound. Couldn't care less about the movie! Not long after, another movie Midway came along also using Sensurround. That was hopeless. Every time a bomb dropped there was an identical 50Hz blurt from the big speakers. Very monotonous.

Anyway, just before Earthquake hit the screens, Electronics Australia magazine ran an article telling all about the hardware used in the cinemas including IIRC drawings of the speaker boxes. They stated the 18" drivers used had a p/p movement of 1.5 inches and displaced about 300 cubic inches when doing so. No, I haven't got a copy of the article; that's from memory.
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Old 7th September 2007, 10:20 PM   #18
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Thanks Ian for the uploaded plans - I've saved the image for reference when I actually get around to cutting wood.

I've also heard about the rather large displacement these Cerwin Vega drivers were supposed to have, but I wonder what the Xmax was? I doubt the designers of the Sensurround system would have bothered about distortion or other non-linearities caused by moving the cones beyond this point, as hi-fi was unnecessary here - it was all about decibels.

I notice that the Precision Devices PD1850 has a maximum excursion limit of 1.26 inches, although whether that's peak to peak or one direction only I don't know; Quite a bit for a PA driver anyhow, Xmax rather less than this, obviously.
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Old 7th September 2007, 10:28 PM   #19
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XL-18S = 4.2 mm
CW 189E = 5.2 mm
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Old 8th September 2007, 02:13 AM   #20
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I have included a photograph showing the old-fashioned corrugated suspension of the 189 E driver. I suspect that the Xmax of 5.2 mm quoted by GM is accurate. The cone travel of the drivers as mounted in their sealed enclosures was quite small during a test in which I ran a portable CD player through the A-3000 I amp to the drivers while playing the opening track of the Varese Sarabande CD soundtrack from the 1977 Dracula movie (VSD-5250) which has amazing rumble content for testing purposes. The cones hardly moved but the crockery in the kitchen did and and that was without any horn loading! Actually I have a feeling that the use of a long throw speaker driver in a folded horn cabinet might create too much turbulence in the throat. I considered using more modern drivers but dismissed the idea given that the effect that I wish to achieve was to be as close as possible to real Sensurround. I will post a few more photographs in subsequent links for interest.
Ian
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