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Topic: Soundhead to processor

Dan Chilton
Expert Film Handler

Posts: 191
From: Springfield, MO
Registered: Mar 2004

posted 04-01-2005 04:12 PM

How does the sound get from the optical sound head to the processor/receiver (i.e. what kind of wires are used)?

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Stephen Furley
Film God

Posts: 3059
From: Coulsdon, Croydon, England
Registered: May 2002

posted 04-01-2005 04:48 PM

They are balanced signals, so two core screened cables are used, two of these cables are used for each projector, one each for the Lt and Rt signals. The screen is normally connected at only one end.

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Dan Chilton
Expert Film Handler

Posts: 191
From: Springfield, MO
Registered: Mar 2004

posted 04-01-2005 05:48 PM

So the sound travels from the pick-up in the soundhead, through two core screened cables (left and right), into a processor (dolby, stereo, etc.), into an amplifier/receiver, and then out to the speakers. Is that about right?

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Aaron Sisemore
Flaming Ribs beat Reeses Peanut Butter Cups any day!

Posts: 3061
From: Rockwall TX USA
Registered: Sep 1999

posted 04-01-2005 06:00 PM

Yes, that's right.

-Aaron

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Dan Chilton
Expert Film Handler

Posts: 191
From: Springfield, MO
Registered: Mar 2004

posted 04-01-2005 06:11 PM

The reason I ask is because the sound system we've been spec'd is actually TOO big for what we need. I think our equipment dealer envsions us more as the smallest auditorium in a multiplex, rather than a high-end home theater, which is pretty much what we are. I don't see a need for the giant old Altec A7-500 when we can get a nicer 5.1 surround system.

I'm trying to figure out exactly where the projector equipment components stop and the high-end consumer level stuff would take over. I suppose the processor could be fed into a standard receiver/amplifier, right? So everything from that point on could be supplied and installed through another source... ??? [Confused]

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Scott Norwood
Film God

Posts: 8146
From: Boston, MA. USA (1774.21 miles northeast of Dallas)
Registered: Jun 99

posted 04-01-2005 06:33 PM

A modern Dolby (or similar) processor has line-level outputs (balanced or unbalanced, depending on the model) for each channel. You can connect these to whatever type of amplifier and speakers you want.

Whether this is a good idea or not is a different issue. Films are mixed to sound good on "typical" theatre systems and may or may not sound good on other types of equipment. Also, good consumer-grade amplifiers are probably not much cheaper than models designed for theatre use and will likely not be as reliable.

The "5.1" concept only applies to digital sound systems (and some 70mm formats). If your source material is 35mm optical, then you will have at least one (center/mono) and at most four channels (L/C/R/S) plus subwoofer. You would probably want to wire the system for separate left/right surround channels now in case you ever upgrade to digital sound later.

Note that some older sound systems (Kelmar, etc.) connect to the solar cell(s) on one end and speakers on the other. The preamp and amplifer are one unit and not (easily) separable. Unless you are installing older equipment, you can safely ignore this paragraph.

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Bruce Hansen
Jedi Master Film Handler

Posts: 847
From: Stone Mountain, GA, USA
Registered: Dec 1999

posted 04-01-2005 06:37 PM

Wet strings with a little salt on them. [Big Grin]

The output of the solar cells in the sound head is at mike level, which is much lower than line level, such as an AUX input. To use the AUX input on a consumer receiver, you will need a mike preamp (such as a mixer with mike inputs). A mag phono input is not usable, due to the EQ used. Most 35MM films today use Dolby SR noise reduction. A consumer receiver will not have this, and the sound will be a bit strange sounding.

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Stephen Furley
Film God

Posts: 3059
From: Coulsdon, Croydon, England
Registered: May 2002

posted 04-01-2005 06:39 PM

To simplify things a bit, two signals are read from the film, Lt and Rt, these have been encoded from a four channel, left, centre, right and surround (L,C,R,S) mix. These two signals are fed into the Dolby, or similar, cinema processor, where they pass through several stages of processng. Firstly is the optical pre-amp, which amplifies the signals, and also applies some equalisation to them. Next comes two channels of Dolby noise reduction, originally the professional 'A' type, but now the improved Dolby SR. The next stage is the matrix decoder which takes the two Lt and Rt signals, and decodes them into L,C,R and S. Total separation is not possible, there is a certain amount of 'leakage' between channels with a matrixed system. The S signal is also delayed slightly, by an amount which depends on the size of the auditorium. The L,C and R signals are passed through equalisers whose main purpose is to compensate for varying accoustics of different auditoria. A simplified equalisation is usually applied to the S signal. Up to this point we have been dealing only with the signals from the analogue optical soudheads, but at this pont it is possible to select other sound sources, non-sync sources,such as a CD player, for example; many cinemas are also equipped for digital soundtracks, and some for analogue magnetic tracks. Whatever sound source is selected passes through a multi-channel fader, operated by a single knob, either on the processor front panel, or remotely. That is the end of the processor function, the signals then go to the main power amplifiers, and then to the speakers.

That's about it; it varies a bit between processors, and depending on what other equipment is installed.

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Steve Guttag
We forgot the crackers Gromit!!!

Posts: 12814
From: Annapolis, MD
Registered: Dec 1999

posted 04-01-2005 07:08 PM

The size of the room matters very little in the big picture of setting up a room, as far as money is concerned. The film does not know it is showing in a small room.

What changes are typically the lamp size(s), speaker size and amplifiers.

The Altec A-7 isn't really a "big" speaker persay. It is also a reasonably good sounding one.

However, if you look at really good "little" speakers you will find they will cost quite a bit...and guess what...they typically have lower efficientcies than their bigger brethern...as such, the amplifier size increases to accommodate the lower efficientcy. So even little rooms don't always work well with little amplifiers. Often, I find it is a wash.

On the surround side...sure you get to go with smaller speakers there too...but you need more of them to cover the space...again a wash.

I've done rooms for homes, 20 or so seat theatres and for grand auditoriums...just looking at the bottom line, you would not always know which went where.

If you are running film, your designer would be correct in thinking of the theatre as the smallest auditorium in a plex rather than a home-theatre. You'll have less trouble. BTW...Home-Theatres often cost more than commercial theatres.

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Dan Chilton
Expert Film Handler

Posts: 191
From: Springfield, MO
Registered: Mar 2004

posted 04-01-2005 07:17 PM

Ah ha. It all makes sense after I read everyone's comments. The problem with our theater is two-fold: space and money are at an EXTREME premium. If space weren't an issue, I'd pull the screen out about 3 feet and stick the Altec behind it. Unfortunately, that would be a little TOO close for the front row patrons.

We could do a cut out in the screen wall and shove the butt of the speaker into the hall, but that would put a very irregular looking wall jut within head bumping height... albeit a very tall head.

If money weren't an issue, we could keep the screen against the back wall, or very close to it, and place our L and R channels on each side. This would mean upgrading our processor, which is currently only set for center/surround, but again, I'm pretending like money isn't an issue.

So, is there any way to conserve space (i.e. keep the screen against the wall) and use a left, right, center, sub, surround model that wouldn't end up costing us 10K more than what we had budgeted?

And if it helps make things a little more clear, here's the equipment we've been spec'd:

- Ultra Stereo JS 5/95 center/surround stereo processor
- 2 Smart TA-242 power amps
- KC TS-18 subwoofer
- Altec A7-500 backstage speaker
- 6 surround speakers (JBL)

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Steve Guttag
We forgot the crackers Gromit!!!

Posts: 12814
From: Annapolis, MD
Registered: Dec 1999

posted 04-01-2005 11:47 PM

Everyone's project has money and space at an extreme premium! There is nothing new there....speaking of nothing new.

Based on the equipment listed...it appears your person is using whatever sh/e had laying around so I doubt you are spending very much money, as theatres go.

The Ultra 5/95 is a bit of an old piece and a poor choice if you plan to run modern films. Mono-Surround is not how films are mixed and with a small room, the lack of stereo will be noticable. The 5/95 predates SR noise reduction by two generations of Ultra processors too so you will not be hearing the sound properly.

If you are not looking for digital sound right away...look into a Panastereo CSP1200. It is quite flexible and will handle modern film soundtrack just fine...it has a bunch of inputs to allow for future expansion. I've even been known to place a "Prosumer" type of A/V receiver in the rack to feed the Pana home-theatre video sound...it works quite well, if you plan to have video in this room.

The Altec A-7 is 2-feet deep...modern cinema speakers often require about as much (18-inches) unless you go with shallow speakers....without exception, I haven't heard shallow cinema speakers do sound justice. Often the HF Horn doesn't go low enough or the LF cabinet go high enough to have good sound. In any event, I would suspect that the price you are being charged for the A-7 is less.

You can use small high-power speakers if your room is small enough but as I said previously, these things are not cheap and they will consume more amplifier power. While that A-7 may need 100-watts for your room...a little speaker in the same room may need 400-watts for the same volume level....it is all a matter of the physics of the room and equipment.

An advantage to having speaker "pockets" is the ability to service the speaker later...if you bury the speakers behind the screen...you might have to plan on pulling the screen just to service the speaker later on.

Again, looking at the equipment list you just posted...I wouldn't call the space (any space) as "over sold"...quite the contrary...more like undersold.

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Stephen Furley
Film God

Posts: 3059
From: Coulsdon, Croydon, England
Registered: May 2002

posted 04-02-2005 05:49 AM

Cinema processors don't have a great deal in common with home theatre amplifiers/receivers.

Cinema processors have pre-amps and slit loss equalisation for connecting the cells of optical sound heads; home equipment does not. Cinema processors have Dolby 'A' type and SR noise reduction; home equipment does not. Cinema processors have the 2:4 channel matrix decoder only for use with 35mm analogue optical tracks; home equipment has a similar decoder, but can put any 2 channel input through it. I'm not sure if the decoder in home equipment has the surround channel delay, since the auditorium size is much smaller. Cinema processors have the equalisation modules, which are set up by a technician at the time of installation, using specialised test equipment, and are not normally altered unless amplifiers, speakers or acoustics are changed in some way; home equipment has simpler tone controls which are adjusted by the user to their own preferrence by ear. Some also have pre-set 'modes' which can be selected. Home equipment has many inputs to which different type of video and Hi-Fi equipment can be connected; cinema processors do not. Home equipment provides switching for video signals; cinema processors do not. Home equipment has built-in power amps; cinema processors generally do not, although as Scott has said, there are exceptions. Home equipment usually has built in decoders for Dolby Digital, and sometimes DTS and/or Mpeg layer II audio. SDDS is not used in home equipment. Cinema processors either do not have digital inputs, and require extra external equipment to handle digital sources, or they have Dolby Digital, DTS or SDDS processing built in. They don't normally provide more than one type of digital processing, to get that you need external equipment. The theatrical and home versions of DTS are different, the versions of Dolby digital are similar, but home equipment won't work with cinema sound heads, and most Dolby cinema processors won't work with home Dolby digital equipment. Mpeg audio is not handled by normal cinema processors, though Dolby do make an add-on unit, the DMA8 Digital Media Adapter, that dan handle just about any type of digital signals, including things like Dolby E which you certainly won't find on home equipment. I've got a feeling that the Dolby CP-650 processor can handle the home version of Dolby digital, but I'm not sure. Some home equipment has an imput for the Dolby AC-3 modulated onto an RF carrier signal, that was used by Dolby Digital NTSC Laserdiscs, and nothing else.

Most home equipment has six channel line out connections, which can be fed into a cinema processor if you need to use something like a DVD or Laserdisc player in a cinema for a special event. as has been said elsewhere, most cinema processors have outputs which could feed into a home system, if you need to use 35mm at home. I have done both of these things, but neither is normal; they are just using the front end of one system to provide inputs for additional types of signals not available on the other.

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Steve Guttag
We forgot the crackers Gromit!!!

Posts: 12814
From: Annapolis, MD
Registered: Dec 1999

posted 04-02-2005 07:42 AM

The Dolby DMA-8 will handle both consumer and pro AC-3 varients. It has 8-channels worth of D-A conversion too so you can hook up your Panasonic D-5, digitally, to it. The DMA-8 has several ways into it so you can have multiple sources feed it at the same time.

It has some serious flaws though. There is no indication of what it is doing! No level meters, nothing to show that it is looking at the wrong input (you can, in software give it a priority system but if a DVD player is on, yet not playing, and its input is a high priority...it might be looking at that, and not the thing you just hooked up)...it also likes to hang when power cycled and again no indication that it is in a lock-up state.

I'm not a big fan of the unit in its present state. They should have made it like the DP564...it would have been much more useful. The DMA-8 costs more than the DP564 and all the DMA-8 brings is the Dolby-E part (only a concern if you play video that was for broadcast in origin and not in final form) and the 8-channels of D-A conversion. Probably its biggest feature that no one mentions is the "Global Delay" DCinema projectors typically have at least 2-frames of delay in their processing...so you often need 85 or more msec. of delay to avoid lip-sync issues.

If you want a kick-ass version of an AC-3 and Dolby-E decoder...try a Wohler AMP2-E8DA http://www.wohler.com/overviews/AMP2-E8DA.html

This thing sounds great and will do Dolby AC-3 and Dolby-E decoding....just have a medic standing by when you look at the price.

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Darryl Spicer
Film God

Posts: 3250
From: Lexington, KY, USA
Registered: Dec 2000

posted 04-02-2005 12:29 PM

Audio Control offered a 30 band 1/3 octave precision equalizer for home theatre set-ups. I think you can find them now for around $600. Of course this would be placed between the processing device and the amps.

As far as what you are trying to do, the Ultra Stereo JS 5/95 center/surround stereo processor can be configured to do left/right and surround but you will need the matrix card and another eq card. If there is no way to put the speakers behind the screen you could put them above the screen pointing down torwards the audiance but that would be a last resort in my opinion.

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Jeffry L. Johnson
Jedi Master Film Handler

Posts: 809
From: Cleveland, Ohio, USA
Registered: Apr 2000

posted 04-02-2005 01:26 PM

For cinemas with limited depth behind the screen, Stage Accompany offers cinema speakers that are 230 mm deep.

quote:
Offering an unbelievable depth of only 230mm, the Screen Series S26 and S27 cabinet for instance, requires very minimal space and is specially designed to fit behind the screen in a cinema.

These appear to be marketed to home theaters. Has anyone evaluated them? SolidDrive

quote:
How does the Induction Dynamics™ SolidDrive™ work?

Induction Dynamics™ SolidDrive™ expands and contracts in a magnetized environment up to 20,000 times per second. This allows the SolidDrive™ to convert an audio signal into a powerful vibration that can be transferred into a solid material, evenly delivering sound from the entire surface. Surfaces the SolidDrive™ work with include: glass, drywall, granite, wood, laminate wood. Because the SolidDrive™ utilizes materials already existing in a room, it's ideal for installed home, commercial audio or a theater sound system.

In-Wall Hidden Speakers by Solid Drive Deliver sound to any room with no visible speakers or wiring

Induction Dynamics™ SolidDrive™ installs directly behind walls for a truly inside-wall speaker - turning the entire wall into a sound source. Sound is generated from these large acoustic-radiating surfaces and the listener becomes immersed in sound. The sound is omni directional at nearly all frequencies while channel separation is maintained.

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