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TOPIC: Screen's A'round

Re: Screen's A'round 17 Oct 2003 04:34 #28436

  • outaframe
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Well, the friend I helped repair the screen was delighted with the result, and it was his decision to make...

I'm surprized that the only fault you found with my sound setup was the DNR noise reduction... As you know, the pro-logic decoder already has Dolby B noise reduction built in, and the DNR just supplements the additional boost that Dolby SR has above Dolby A... It may not be exact, but it very close to the real McCoy... The rest may be somewhat overkill, but the additional headroom may account for the fact that it does sound damned good... I have heard a lot of sound systems fed with all the various formats, including all three of the digital systems, and have yet to hear the night and day difference you might expect... I only hope that Cyan tracks will not degrade what I now have...

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Re: Screen's A'round 17 Oct 2003 13:31 #28437

  • KingJoe
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Thanks guys for your imput. Let me clear up a few things.
The Simplex speaker=I will NOT be using it.....I just thought it was neat that it was still there. I will NOT throw it out. I am not a big fan of throwing things out. Someone somewhere may have a use for the thing. If not, it will look cool in my office or my employee lounge.

The Screen=believe it or not, I think it is in perfect condition. There are no visible tears/scratches. I ran my hand across the piece I could reach, and it seemed to respond with some flexibility. It is a silver, or 'gunship grey' colour so I don't know if it is useable. Again, I just thought it was neat to see.

IF the screen could be saved, that would have some nostalgic benefits. If it can be used as silver, GOOD. If it can be used but recoated matte white GOOD. If not, a new (or used) screen it is.

I can sympathise with the people on a shoestring budget, since you are talking to the owner, manager, accountant, chief negotiator, crew trainor, purchaser, installer, handyman, cleaner, projectionist......you get the picture.


I want to have a top shelf operation, but I need to trim the budget as much as possible. There is a good chance my chief creditor will have an employee by the name of 'Vinny" or 'knuckles'


What I am REALLY looking for are options, on what would be the best for my situation. there is still much to consider.

I may have found a good deal on some equipment, so that may open the door to a new screen, but only time will tell.

So, what do you guys know about needing speakers that are digital ready? Is this some sort of sales trick, or is there something really to it????

The King

'The King is only as wise as his Jester'
'The King is only as wise as his Jester'
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Re: Screen's A'round 17 Oct 2003 13:45 #28438

The Dolby B in your prologic is only on the surround output
It was put there originally to help hide the noise of analouge bucket brigade time delay chips
The only active NR on the stage channels is the DNR
I don't knowck DNR I have made my own CAT22 NR replacement boards to plug into CP200's for MAG NR on older non encoded mag prints(prints with no dolby noise reduction) that have gotten hissy over time
But it is a filter not an expander
The essence of the DOlby scheme is to provide compression during recording and expansion in playback (the cleaver part of there system is in fact they use expansion in recording and subtract it from the original and compression added to the original during playback to do the same thing with less artifacts)

The dynamic range without that style of NR is about 98db at max

If you wanted to better it one should look at a used DBX 3 band expander as it will provide some increase in the dynamic range

Also all prologic decoders have a limited Time Delay on the surround channels of usually 35msec and most cinemas need in the range of 70msec

As for speakers I am not a fan of any bass horn design and W bins in particular as they behave much like an organ pipe there mouth size plus length determins the peak of the response and as such they have definite colourations to them Also there response is very uneven

The thiele small direct radiator ported cabenets though less efficient have much better response and less overall distortion than a horn

For highfrequency response unless someone wants to spend the bucks on the SA or Alcons ribbon tweeters one needs a horn

For those a large mouthed constant directive horn is best cellular horns (such as example of the old one in question) beam at different frequencies. Also the older drivers and horn geometry cut off at about 12K in practical pureposes and if it is a 288 driver it is limited to 15watts

The crossovers also used tend to have very wide crossover bands so power handling is even more limited.
In several circuits that we install and service that use older horns we biamp them even though they ae small rooms as an electronic crossover removes all problems of driver impedance mismatch to a passive crossover and a very tight crossover point
And amps are very cheap these days

For most smaller theatre we have used the pyramid pa1000 which is about 250w into 8 ohms and retails in canada for about 400.00

In larger theatres I use QSC almost exclusivly or Smart AB serries

For processors we usually use the Smart mod6 in smaller venues as it is cost effec tive and the new mod7 is even cheaper listing for in the area of 1400.00 us
If you add up all the boxes of a preamp switching prologic decoder noise reduction and equalizers of any quality then the smart is cheaper
It also does changeover and has a 5.1 input that is level compatable with a DTS 6d or DA20

When one weighs the simplisity of designing a proper packaged system and the fact on installation and service cost very little more I find it difficult to figure some cost cutting moves people make


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Re: Screen's A'round 17 Oct 2003 15:25 #28439

A Silver screen will appear grey
If it is in good shape use it
During the 50's some of the best silver screens were made as they were usually foil coated on lenticular cloth backing
The gain is good and on a curved frame look spectacular
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Re: Screen's A'round 17 Oct 2003 20:08 #28440

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OK, GORDON <> We're not as opposed on things as it originally appeared... Yes, all the various Dolby noise reduction types work on the same principle, and ARE a clever idea... By reducing the selected band playback levels by a mirror image of what they were boosted during recording, the noise floor is driven down by the amount of the recording boost, and becomes nearly inaudible... Not unlike the RIAA recording curve system that permitted full range stereo LP recordings... There are some minor differences in the frequency bands, and the amount of boost between A, B, C, and SR, but they are mostly compatible, and can be managed by some high frequency rolloff... That explains why the DNR works, but I recently bought a used DBX unit to see if it is an improvement... My surrounds are powered by the Pyramid amp you mentioned, and it's a very decent unit for the money... I originally intended to tri-amp the screen channels for all the reasons you mention, but 5 stereo amps and 10 pairs of speaker wires gets to be ridiculous, and by juggling impedences, crossover points and slopes, and building passive crossovers to suit, I came up with a smooth mesh using 2 big amps, and active crossover only for the W horn sub... In defense of the W horn, it's only rated to play up to 200 Hz, and limiting it to 50 Hz eliminates problems and floor/wall mounting adds to its efficiency and low end... You can't really hear anything below 30 Hz, but this thing has "punch" and moves a lot of air that you can FEEL... The debate over bass horns vs direct radiators will probably still be going on long after we're BOTH pushing up daisies, and there's no sense in beating that horse here: you prefer vanilla, I prefer chocolate... The NEC pro-logic unit I am using has up to a 50 ms delay, and seems to be adequate... That old horn of Joe's probably has too wide a dispersion pattern, both horizontally and vertically for what he'll need, but there are people around who love 'em... IF Joe's screen is a lenticular foil/fabic type, it's the best of the silver... Maybe it won't be delaminated, or yellowed/darkened too much to use, but cleaning other than a light vacuuming is very iffy...`
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Re: Screen's A'round 18 Oct 2003 14:25 #28441

Dolby B is a single band nr system compared to the 4 band of Dolby A
The SR is 4 fixed bands and 4 variable bands
The DBx nr systems are a single band 2:1 expander and as such will not work that well but the DBX 3BX dynamic rnage expander is at max 1.5:1 and is in 3 bands to prevent pumping and breathing
If digital is being installed the sub has to be able to handle 25-80 Hz
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Re: Screen's A'round 18 Oct 2003 18:28 #28442

  • KingJoe
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Uh.....I like movies......


Sooooo......Can, for example, an old speaker( NOT the Simplex) say 10-20 years or less, be setup to run digital sound? Can the driver or cone be changed?

I have a quote from a company that includes a penthoues Dolby digital reader and a CP650 with a full compliment of speakers. That is pretty expensive, but I think the average patron is looking for at least digital sound.

Do you guys know where I can find this stuff used? AKA cheap!!??!!

Still working on the digi pic of the screen. I'll try this weekend.

The King

'The King is only as wise as his Jester'

[This message has been edited by KingJoe (edited October 18, 2003).]
'The King is only as wise as his Jester'
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Re: Screen's A'round 18 Oct 2003 19:04 #28443

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All the Dolby systems can be acceptably played without any noise reduction by rolling off the high frequencies... It's not by the book, but it does produce listenable sound... Dolby nr was chosen, in part because of this, so that it will play even in mono houses... DBX specs come closer to Dolby specs than DNR does, however using a good adjustable graphic equalizer, there is no reason that both A and SR can't be duplicated Exactly by attenuating the seperate bands according to Dolby specs (which I have listed somewhere, but can't lay my hands on at the moment)... I have not found this is necessary, but I have the equalizer to do it with, if necessary... I may hunt this up and give it a try...

The W horn is spec'd to play down to 20 hz, when augmented with "wings," and up to 200 Hz... I don't need the boost at 80 Hz, and rolled it off at 50 Hz to eliminate boosting the harmonic of the lowest octave of male chest tones... There is no reason that it couldn't be rolled in at whatever frequency range up to 200 Hz... The NEC prologic decoder has active sub output at 80 Hz 12db/oct... I wanted both a lower and steeper crossover, so went with the outboard Proton 24db/oct... The flush wall mounting, at the floor junction is much better than adding "wings" but serves the same purpose...

Sound below 30 Hz is not audible by most people (myself included), but the SPL meter confirms that it's there, and as I said you can certainly feel it...

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Re: Screen's A'round 18 Oct 2003 20:55 #28444

A couple of points Dolby is very clear that SR is not mono or A type compatable and is very plain on there disclaimers of the signal degregation involved
The NR system is not a attenuation of certain frequencys but a dynamic attenuation that below a threshold occurs at varrying levels
The SR system also contains several other circuits to reduce distortion and saturation

As a condition of licensing a Digital playbck from dolby you must have a SR capable processor to connect it to

The DBX system as I have said is a full range single band expandor and is incompatable with every thing dolby has done
Their 3BX variable expander can help put some of the lowlevel stuff back but not all and definetly will have some artifacts

In fact listen closely to any dialogue in a rain or windy field scene with out SR and it is almost unintelagable

As I have said before there is a minimum level that a paying customer has a right to expect.

Also on a sub system the band area of the digital sub is 30-80 Hz and needs 10 db above the centre channel headroom and it is discretely recorded expecting that level. It is a misnomer in a lot of ways as the optical sub is actually properly termed Optical bass extension and was designed to take part of the load off the stage channels
Digital assumes that the stage channels can each reproduce from -3db at 40Hz to flat to 2Khz with a 3db per ocatve rolloff above that

Film done right is the only survival technique when in a competative market

A while ago we did several distributor requested alignements and before in a competative market the theatres in question had to prove they could meet the industry specs before they got a print and I failed 3 theatres that didn't get a print because of it because of cut corners in there systems

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Re: Screen's A'round 19 Oct 2003 01:17 #28445

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Thanks for the update: some of this information is a revelation... My understanding was that when SR debuted, it like Dolby A, COULD still be played in mono... I was still playing mono at the time, and DID notice that in situations like the one you mention, the sound effects seemed extremely loud compared to the dialogue, but most prints were still Dolby A at that time, and I put this system together before the major switchover to SR... Now, I wonder what the mono houses have done to be able to play the SR prints in mono (there are still a lot of mono houses around)... Also, I have a redundant mono mixer/amp that I have standing by to switch into the center channel, to stay on the screen in case of a failure in the regular sound system... Thankfully, I have never needed it, but as long as I have solar cell output, and a center channel speaker, this will keep me onscreen... And, I have dual exciter supplies that I can switch between... I switch the standby amp in every six months or so, to verify that it's operational and watch a few feet of film... Understandably, it doesn't sound nearly as good as the main system, but it doesn't sound THAT bad, either... Now, I am wondering if I should try to add some sort of noise reduction to it...

I am also surprized to learn that the sub needs only to play down to 30 Hz... I was under the impression that when digital was introduced, a 20 Hz low end was specified... Is that 30 Hz a SRD spec, or for all digital?... I dismissed both SRD and Sony's digital as being too complicated and expensive to justify the results in my situation, but I am still thinking positively along the lines of adding DTS at some future time...

I calculated the W horn's output in light of your specs... Adding nothing for the "wings" (in this case, floor/wall junction placement) and with both speakers in parallel (4 ohm load) driven by the 400 watt amp it is now connected to, it should produce 119 db spl mid-house before clipping... I can't imagine a situation that would require more than this, but the speaker pair could supossidly safely handle 800 watts, and add another 3 db... I use it to supplement the R&L screen channels LF which will play down to 25 Hz, and set the level of the SUM of the 3 (rather than just the sub's level) at 30 Hz, 10 db above the level of the system, to compensate for hearing insensitivity at very low frquencies, and to emulate what I understood to be digital sound specs... Would this be correct for SR?... Thanks!...
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Re: Screen's A'round 19 Oct 2003 05:22 #28446

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HELLO JOE <> My apologies for seemingly ignoring you... I don't want to "hog the ball" here, and I hoped that Gordon would answer your questions, as he is an expert on the subject, and I am just a reasonably well informed amatuer... It is hard to give you a purely factual answer as there are so many variables involved, and even amoung recognized experts there is not complete agreement... But in general, cinema speakers need to be extremely efficient, cover the entire frequency range of 20 to 20K Hertz (or very close to that), have high power handling capacity, have very low distortion, and be ruggedly built... And these terms are meaningless without a reference point and detailed specifications, which are difficult to come by... Speaker manufacturers print up glossy sales brochures that are heavy with glowing rhetoric, but short on hard facts... The pat answer is to find a good reputable dealer and leave it up to him... When you buy a car do you do this?... Will the Chevy dealer send you to the Ford dealer because the Ford better serves your needs?... He will most likely convince you that what he has for sale, is what you need, and he may actually believe it himself, but that doesn't necessarilly make it so... With used equipment, it is even more likely because it isn't like he can order something else: that's what there is at the moment, and he wants to sell it... Your only protection is to have enough technical knowledge to make a decision based on what you can verify as to how it meets your needs... Speaker specs for digital use are only slightly more stringent than for high quality analog sound, and yes, there are certain speakers designed in the late 1960's that will fill the specs, but you have to have the detailed specs to know... Woofer cones should not need replacing unless the speaker has been damaged or abused, or is just worn out, and in such cases it is usually best to pass on it... Horn driver diaphrams are far more delicate, and replacing them is not unusual... Many times a 12 or 16 ohm driver will also have an 8 ohm diaphram available, and by changing the diaphram it can be used with modern direct coupled transistor amps... There are many sound systems installed with speakers that do not allow the potential of the electronics to be fully realized... Moderate quality electronics can sound great playing thru excellent speakers, but the finest electronics will sound crappy playing thru poor speakers... I would suggest that you buy this book and read it so that you can ask the technical questions that you need to know to predict what speakers you really need... The book is "Designing and building you own speaker system" by David Weems, 2nd edition 1984... It is the most complete and easy to understand book on the subject I have ever found, and you will understand what the various type speakers are, how each works, and enough about the subject to ask the questions you need answered... I don't think you probably want to build your speakers: you can skip the building details, and concentrate on just the hows and whys... I have checked online and found used copies for sale by booksellers in the $5 to $10 range... If you have any problems finding it, let me know & I'll help you find a copy... Then, measure your theater's auditorium, and we can figure out what you need, and how large the amps will need to be to power your system to specs...
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Re: Screen's A'round 19 Oct 2003 12:21 #28447

The digital sub need really to only go down to 30Hz and extend up to 80 Hz
On used speakers replacing a diaphram that was 12 or 16ohms with a 8 or 4 ohm will effect the behaviour of the passive crossover. It will cause a shift of either the crossover frequency or slope either creating a hole in the response or two much of the alternate band getting into the driver in question usually in the case of high frequency driver catastrophic failure

Many lower cost woofers have foam surrounds and rot will eventually set in to them as well as fatigue

BiAmping any system saves a lot of grief and in the long run will produce a better preforming system and amps are not that expensive and crossovers like the 3 channel smart are very cost effective

On the issue of older speakers and digital part of the problem is that like the A5 it had a low frequency limit around 120Hz and the A4 is 80Hz
For optical that wasn't a big issue as a sum of the preamp was fed to the sub and bandpassed at the frequency of your choice to take part of the load off the stage channels (that is why it is reffered to as OBE (optical Bass Extension)

Digital is a dedicated channel (DTS does bury it in the surround and that is why I usually go for a higher cutoff in the sub with a DTS system as there filters are not that great)



[This message has been edited by Gordon McLeod (edited October 19, 2003).]
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Re: Screen's A'round 19 Oct 2003 16:56 #28448

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Thanks for the info, but you didn't answer the most important question: how mono houses are still managing to play SR...

If you change the diaphram in a high impedence driver to 8 ohms, it becomes an 8 ohm driver, which also draws more power, and of course the high impedence passive crossover won't work with the impedence mismatch, but the driver and horn becomes usable with modern systems... If it originally was deficient at HF, you would want to add a tweeter, as well...

Woofers with foam surrounds are not really a good choice for any purpose... They can be refoamed, but fabric reinforced, or butyl reinforced accordian edge surrounds are the only logical choice for power handling and mechanical durability...
The bass section of the A5 is not only deficient in low frequency response, but also in power handling, and efficiency... The 511 horn is great, but by the time you pad it down to match the efficiency of the bass section, you end up with only a marginally efficient system with poor LF response... Biamping won't cure the problem... However, you can mate the 511 horn with either a better existing bass section, or build one, then biamp it, or build a passive crossover that matches the combo, and end up with a very good system...
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Re: Screen's A'round 19 Oct 2003 20:19 #28449

SR is not really even mono compatable but whe you look at the academy curve almost all of the SR gains would be lost anyway in the steep rollof -10db at 4K in the original curve
The use of a different diaphram impedance in a unit effects the RIC values in the crossover so the crossover frequancy will change and the slope will also change with it
typically the crossover point is lowered and the notch of the q is deeper causing a big hole in the midband dialogue parts

Bi amping will cure that as the response is set electronically before the effects of the speaker load Ie the only variable might be the amp input impedance which is not usually an issue

So as such you could tailor the overall accoustic response in a transperent fashion as long as the amps could deliver the required power and the drivers handle it
In effec the crossover becomes a mute point in the equation
remember a passive crossover has 3 values that effect the crossover point C I and R
these components are in the crossover and the reflected load of the driver

In the case of electronic crossovers innbiamp or tri amp devices a high impedance opamp removes the rest of the world from that equation (which is why your electronic crossover on the subwoofer helps you out)

On the A5 the bass cabinet was limited to 120Hz to 500 HZ the standard horn with it was the 1005B (110x40 degree at 1Kz) with a bandwidth of (on a very good day) of 500-14K
(they never did take into account the beaming of the cells)( the only good point of the cellular horns was if you determined you had side wall reflections on the left and right screen speakers you could stick a tube of socks in the cells to stop the dispersion onto the side walls)

Later A5 were sold with the mataray horn to improve the top end but ignored the bottom end issues which is why the OBEy cards from dolbyu had a variable set on the crossover to the sub

But with digital they assume you will be able to go to -3db on all the screen channels at 40HZ

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Re: Screen's A'round 19 Oct 2003 22:26 #28450

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OK, that's about what I expected to hear: the old mono Academy Curve rolls off almost all of the boost that the SR has before going thru noise reduction... Not compatable, but at least playable... Yeah, I've seen a lot of old multi-cell horns with the side cells plugged: necessity is the Mother of invention!... Thanks for the info!...
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