|
|
This topic comprises 3 pages: 1 2 3
|
|
Author
|
Topic: Long speaker runs VS. short runs.
|
|
|
|
|
|
|
Frank Angel
Film God
Posts: 5305
From: Brooklyn NY USA
Registered: Dec 1999
|
posted 04-23-2018 08:46 PM
Definitely with you on Class Ds -- someone sold these folks a bunch of Crown XTi2 Series -- the ones that Crown claims sound as good as Class ABs. says so right in their manual, :-) So far I haven't heard them in any real setup because the rooms are being treated and haven't been B chain calibrated yet.
The question about hookup run is because the screening room has a control "Smart Podium" at the front of the room which controls their Barca in the booth. So they have these 7 Crown amps and they want to put them in the podium. This will require them running an additional set of cables from the podium back to the booth for no good reason really, except to have manual control of the amps at the podium. Why, I asked would that even be necessary, once the room is calibrated, as long as the "processor" (a Marantz receiver is in the podium to make minor adjustments, no one should be playing with the amps, ESPECIALLY professors. Plus,building them into the podium will mean a concentration of heat in a small space.
But it's hard convincing the client once someone has read on the internet that if you wrap speaker wires in magazine paper (must be the clay coated type at that), it will do wonders for the sound. Me thinks acousticlly treating the hard plaster walls and ceiling in this all-parallel-walled room might have a bit more affect on the quality of the sound than wrapping the wires wth paper (no doubt the fire code will require sprinklers for that, ya no?). ![[evil]](graemlins/evil.gif)
| IP: Logged
|
|
Steve Guttag
We forgot the crackers Gromit!!!
Posts: 12814
From: Annapolis, MD
Registered: Dec 1999
|
posted 04-24-2018 08:15 AM
First, there are some electrical facts to this:
Shorter speaker runs means lower resistance, which improves damping (or doesn't reduce damping is more accurate). That said, the driving determination of actual damping is the voice ccoil of the driver itself, the speaker wire is relatively insignificant compared to that unless you run REALLY small stuff.
Long analog lines tend to beget ground loop issues since keeping the same ground potential at varying distances can prove challenging.
So, with conventional amplifiers, I prefer them in the booth and deal with the longer, larger, more expensive speaker runs.
Now with various DSP systems (RANE's former HAL system, QSC's DCP200 or DCP300) where the audio signal can be delivered behind the screen digitally such that the analog amplifier can be delivered a clean hum-free signal, there are cases were I prefer that method and it makes for a cleaner, lower-cost installation that has all benefits and little-to-no downsides.
As for Class D, I'm experimenting with it now. QSC has their DPA series that is Class D and despite Mark's claims, has MORE RESERVE power than a DCA amplifier. They typically run with 155V power rails and can gain share between the channels (The LF section of a stage speaker is bound to need more power than the HF section). I'm building a set of speakers and plan to do some critical listening to the quality difference between the DCA and DPA-Q series of amps. Sure QSC says their Class-D is good but there is ample opportunity to mess up the sound with the whole PWM conversion of the audio.
With a platform like QSYS, DPA-Q amps make a lot of sense (it is like they were designed with each other in mind!) And with that, putting amps behind the screen right at the speaker also makes a lot of sense. Shorter, cheaper speaker runs and just CAT6 between the CORE and Amplifier with the ability to have dual redundant QLAN connections for reliability. With a minimal mount of amplifiers, you can run your stage channels sans any passive crossovers. Personally, I think QSC could take the next step and just put the appropriate amplifier IN the speaker and just have QLAN ports (and analog in for non QSYS) on the outside and a power connector. You'd always have the right amount of power and it would be a fast installation that is essentially already tuned.
However for surrounds, you are still going to have long speaker runs but I don't put surrounds in the same critical listening category as stage channels.
I'm done using THHN for speaker wire. It has to be twisted to prevent inductive crosstalk and there is no good way to twist it in the field. Most use a drill and that is just flat out wrong, I don't care how many times you've done it. It stresses the copper strands as it adds a rotation to the individual conductor for every twist put on the cable. I've found West Penn's 2522xB series to be pretty cost effective and Plenum rated (available non-plenum by omitting the first "25" and the "B" at the end). it isn't esoteric but it gets the job done at a fair price.
| IP: Logged
|
|
Carsten Kurz
Film God
Posts: 4340
From: Cologne, NRW, Germany
Registered: Aug 2009
|
posted 04-24-2018 08:26 AM
I guess it also depends a lot on passive vs. active. The long speaker runs are no big issue with passive crossovers, but once you go active EQ, I would immediately place at least the screen system crossovers and amps behind the screen. And yes, it is easier, even cheaper, to transport balanced line level analog or digital audio to that location than multiple runs of speaker cable.
What is your general experience concerning the choice between 'general use' amplifiers vs. dedicated system/networked/smart amps?
I understand the general benefits of using networked/monitored amps, but are they reliable enough to not come across replacement issues once they fail? They are also usually a lot more expensive than general use PA amps, so, it hurts smaller operators to keep replacements on site.
- Carsten
| IP: Logged
|
|
Tony Bandiera Jr
Film God
Posts: 3067
From: Moreland Idaho
Registered: Apr 2004
|
posted 04-24-2018 09:59 AM
I went through this exact discussion nearly 30 years ago, and had a few locations in my service "kit" with amps located behind the screen.
I can tell you that putting the amps behind the screen in ANY location EXCEPT private screening rooms is a very bad idea for a number of reasons:
- As Mark pointed out, fire codes often require a sprinklered space;
- The area behind a screen is far too often crammed with junk storage, blocking access and creating a fire hazard;
- The area behind a screen is extremely filthy, with dirt, dust, popcorn and other food residue often building up;
- Unauthorized persons can easily tamper with settings or just steal the equipment;
- The projectionist has NO IDEA if the amps are on, working or going up in smoke unless they constantly go into each auditorium every show;
- Connecting the amp outputs to a booth monitor requires runs of wire all the way back to the booth anyways (and using a single multi-conductor cable to do this often results in crosstalk or RF pickup.) ;
- It would be impossible for the projectionist to repatch a failed amp "on the fly" without totally disrupting the show by going behind the screen with a flashlight and tools, whereas in the booth it can be done with minimal disruption to the show.
In real life, the drawbacks I mentioned above, IMHO, make it one of the dumbest things to do in cinema design. Even UC Irvine's screening room (see the pics in the warehouse) suffers from the junk storage, dust build up, no way to readily spot an amp that has failed, and no output monitoring issues.
As for having powered speakers behind the screen, that would be even worse, as now a failed built - in amp cannot be repatched during a show or intermission, and good luck getting that module out with the speakers on skinny stands up in the air with only inches of clearance to the rear wall. (Plus having powered speakers behind the screen WILL in most places make sprinklers mandatory, yet another added cost.) And speaking of added costs, now you'll have to have an electrician wire in power, receptacles and extra circuit breakers to EACH speaker location, which will cost a LOT more than a single large conduit that the system installer simply pulls wire through later.
Historical installations have proven why having a true projection booth, with ALL equipment (including lighting control) located in that booth, has proven to be the most efficient, cost effective and more importantly, SAFE way to construct a cinema or screening room. Just because the industry has gone digital is no reason to change that. (And don't even get me started on how retarded this whole "Boothless" concept for digital is... I don't care what anyone tries to claim, the costs and ongoing maintenance of projector lifts and "hush houses" and the more complicated cooling setup does NOT SAVE MONEY in the the long term. It is cheaper during construction to provide a simple open plan booth space.)
To address Frank's installation:
1: Crown amps suck ass. They are overpriced, unreliable, bad sounding pieces of shit. You would be better off to sell them off and buy some used QSC DCAs.
2: Never, and I mean NEVER install any critical equipment in a podium used by professors and/or students. Most professors can't figure out how to use a smartphone, much less operate an A/V system. They need simple controls for source selection, (and play, pause, stop, etc.), volume and room lighting and NOTHING ELSE. Giving them any other equipment to get into is begging for serious trouble. Install a mixer/source switcher in the booth or whatever A/V space, set up the levels during install and lock the equipment up. My 12 years at UCI proved this over and over again.
3: Putting the marantz receiver in the podium is a disaster waiting to happen, and it will happen soon. How are you going to prevent someone from boosting the bass or treble all the way up, not to mention the volume? (Kiss your speakers goodbye.) How about keeping them from playing with any DSP effects? Cranking up the radio because they are bored? NO ONE NEEDS TO BE DOING "minor adjustments" to the system, through the receiver. A properly set up system would only require the users to use the master volume control provided for them.
Candidly, I must say to Frank, if YOU cannot take over the design of this install and get things done right, keeping all the equipment isolated from users, then you need to either walk from the job or be ready for YEARS of constant service calls and complaints. (And carry hefty liability insurance.) Again, I tell you this from my 12 years at UCI and setting up two screening rooms there.
| IP: Logged
|
|
Scott Norwood
Film God
Posts: 8146
From: Boston, MA. USA (1774.21 miles northeast of Dallas)
Registered: Jun 99
|
posted 04-24-2018 12:04 PM
Having worked in a number of multi-use facilities as described here, I agree 1000% with everything that Tony has said.
Really, the best option is to have a "good enough" system for professors to use (including a separate video projector) and a "professional" system to be operated only by knowledgeable people (which could include responsible, trained students).
And, if you do this, be sure to power the D-cinema projector up from time to time. At least with the Christies, the crypto board will fail if the unit is powered off (or even left in standby mode) for six months or more.
I can't really speak to the new-technology stuff that Steve discussed above, but, as an operator, I like having the ability to monitor sound off of the amplifier outputs, and I do worry about dust accumulation behind the screen.
| IP: Logged
|
|
|
|
Steve Guttag
We forgot the crackers Gromit!!!
Posts: 12814
From: Annapolis, MD
Registered: Dec 1999
|
posted 04-25-2018 08:28 AM
quote: Tony Bandiera Jr
I can tell you that putting the amps behind the screen in ANY location EXCEPT private screening rooms is a very bad idea for a number of reasons:
As Mark pointed out, fire codes often require a sprinklered space
In this area, you already need sprinklers in that space, so amps behind the screen or not, it is a non-issue, cost wise.
quote: Tony Bandiera Jr
The area behind a screen is far too often crammed with junk storage, blocking access and creating a fire hazard
It depends where you locate the amps or the mini rack as to the difficulty to get to it. If you have a speaker loft, it would be no more complicated than getting to the speakers themselves.
quote: Tony Bandiera Jr
The area behind a screen is extremely filthy, with dirt, dust, popcorn and other food residue often building up;
Unauthorized persons can easily tamper with settings or just steal the equipment
Well yeah, I guess if you just throw the amps on the floor that they will get filthy with food stuffs on them and kids will steal the blinkly light boxes. But gee what about, I don't know, just securing them? Put them in a rack, wall mount if desired or even up at the speaker level? For a typical 5.1/7.1 theatre, we are only talking about 4U of rack space or 6U if you'd like a spare Center amp.
Given that HVAC is typically above the ceiling anyway, it wouldn't be rocket science to drop a small supply/return just to the rack but really a decent filter would be all that is needed. They aren't moving that much air, with a sufficient sized filter, your change would be what? Every year or two?
quote: Tony Bandiera Jr
The projectionist has NO IDEA if the amps are on, working or going up in smoke unless they constantly go into each auditorium every show
Um NO! In fact, in a modern DSP system like QSYS (which, by the way, is one of the conditions I set forth on doing a split system), the projectionist or NOC will know of an amplifier failure BEFORE you would ever know in a traditional system. All of that data is already at whatever user interface you choose including amp presence, temp or any other failure.
quote: Tony Bandiera Jr
Connecting the amp outputs to a booth monitor requires runs of wire all the way back to the booth anyways (and using a single multi-conductor cable to do this often results in crosstalk or RF pickup.)
No (again) you are once again using prior knowledge of traditional analog linear amp systems to a current DSP system. With a System like QSYS (though it can be done with other DSP), you can have "amplifier out" at your booth monitor of any channel of any section of any channel all you want. In fact, you can have it on your phone or monitor it from your house if you desire. All with out the extra runs of cable. That CAT6 cable, information (signal) goes BOTH WAYS.
quote: Tony Bandiera Jr
It would be impossible for the projectionist to repatch a failed amp "on the fly" without totally disrupting the show by going behind the screen with a flashlight and tools, whereas in the booth it can be done with minimal disruption to the show.
Guess what I'm going to say here? Wrong again. In fact, the projectionist (manager, NOC) can repatch every bit as fast in either system. Why? Well, at the press of a button, you can have Center come out of Left/Right (with left and right) or vice-versa (depending on what has failed) or in a 5-screen channel ATMOS, use LC/RC as backups in addition to their role in an ATMOS track. But wait, since we are all DSP here, add a spare amp to the screen rack and always feed "Center" to it, in the even of the main Center amp failure, again press a button and you are on your backup amp with just the addition of a suitably sized relay connected to GPIO. And this isn't theoretical, people already put a spare amp in for center and with DSP, feeding one signal to two sources doesn't cost anything extra and carries no potential for interaction.
quote: Tony Bandiera Jr
In real life, the drawbacks I mentioned above, IMHO, make it one of the dumbest things to do in cinema design.
Open your mind and don't apply a set of rules that were quite valid for traditional system and think that they apply to different systems. The only really valid points you make (and are a concern of mine too) is the dirt level and equipment longevity as a result.
I have been doing split systems for years, with zero incidents. In some situations, it was the only practical method of accomplishing what the space needed (even the speakers are portable and roll out of the way) In the venue, I had about 400A of electrical service to supply the amps (the room was designed for traveling shows and such) but NO conduit paths from the booth to the stage for speaker wires. The original design presumed that the cluster speakers for PA would be used for cinema. The results were so unsatisfactory that they rented cinema sound systems for each performance! Getting a couple of plenum CAT cables was going to be a LOT easier and more efficient than getting speaker wires to go that distance. From the booth they have full audio monitoring of the amps (audio and diagnostics), control over the amps going on/off as well as fault indication. Also, by doing it as a split system, we could wire the speakers as 4-ways and quad amp each speaker.
Another site, the amps are in the organ loft and not in any danger of jujubees and again, significantly lowered the cost of the retro fit since electricity (sufficient for the needs) was available but connectivity to the booth was very limited.
quote: Tony Bandiera Jr
As for having powered speakers behind the screen, that would be even worse, as now a failed built - in amp cannot be repatched during a show or intermission
See above about "repatching" in a DSP system. As for getting a different amp onto the Center speaker, you are right, that would be decidedly more difficult. I'm not completely behind the power-speaker idea but I've heard the idea floated. The primary reason it is floated is that it allows a self-contained system whereby the amplifier is appropriately sized and whatever tuning the particular speaker needs is built in. It is "EQed" out of the box. As such, installation is VERY fast because you are merely connecting a small cable and plug them in.
Then again, the amp will probably do well cooling wise and dirt wise living in the speaker rather than completely in the elements. The self powered speakers I've used (studio monitors) have been rather reliable and amplifier failure just about non-existent.
Again, I think it is a bit of a false economy since a DSP system with the speaker's parameters has the benefits without tying two different failure points together so if either fails, you are completely down.
quote: Tony Bandiera Jr
And speaking of added costs, now you'll have to have an electrician wire in power, receptacles and extra circuit breakers to EACH speaker location
Oh stop, now you are reaching. Getting sufficient AC behind the screen on a new-build would add near zero to the cost. They are running AC anyway. The cost of getting two circuits of AC from the booth to the screen is nowhere near the cost of getting large conduit runs (with just AC, they can run MC cable if not small, easy to bend EMT), with the larger conduit, everything is more expensive and every bend is larger ordeal. One chain found it cheaper to buy all Plenum speaker cable (which typically doubles cost) then pay for the dedicated speaker conduit run.
What I suggest is open your mind to some changes in technology that negate some of the negative effects you've experienced in the past (as I have experienced them too). I've never had a split system, all analog where, noise didn't find its way in but not so with DSP/Digital systems.
I'm not saying you have to do it, but it is a viable alternative now where it was a poor choice in the past because the negatives out-weighed the positives. I think the balance has shifted now where the benefits are there with minimal negatives.
| IP: Logged
|
|
Tony Bandiera Jr
Film God
Posts: 3067
From: Moreland Idaho
Registered: Apr 2004
|
posted 04-25-2018 10:00 AM
Steve, IF we were discussing a setup as you described using all the latest technologies you pointed out, I would be in full agreement with most everything you said (except the increased cost of electrical power vs. single large conduit.) I have been an electrician longer than I have been a cinema tech, and have been involved in the bidding processes of all kinds of jobs..and sorry, you are wrong. The costs of individual runs of smaller conduits (or MC cable) WILL always be greater than one larger conduit capable of holding the same amount of wire. (By how much though does vary depending on the individual job and construction.) It is the material, and to a somewhat lesser extent, the labor that adds up fast in that case. (And in a large room, I would always have each powered speaker on it's own circuit, especially with the dynamics of today's soundtracks.)
But we are NOT talking about a full cinema, with a budget to accommodate the latest technologies. We are talking about a public facility where multiple users and operators are involved, and seeing as they are talking about (used?) Crown amps and a marantz receiver, a facility with no idea what they are doing (not talking about you Frank) and evidently no budget.
As for this: quote: Steve Guttag
Given that HVAC is typically above the ceiling anyway, it wouldn't be rocket science to drop a small supply/return just to the rack but really a decent filter would be all that is needed. They aren't moving that much air, with a sufficient sized filter, your change would be what? Every year or two?
IF that is designed into a new build, sure it is easy and cost effective. Try pricing it out as an add-on, or worse, a change order/refit and now it isn't such a small deal. The HIB100 screening room had NO A/C in the back room where the amp rack is...and to this day it still doesn't. It was deemed too costly to add a 6 foot run off of the duct above the stage. (Plus, as all my HVAC contractors have pointed out, changing an existing system requires new air flow calcs and often changes in dampers, settings and in extreme cases, upgraded air handlers.) Oh, and despite HIB 100 being a relatively clean space, clearing dust from the amps was a quarterly requirement.
Back to the original discussion, and Frank can fill in any errors or omissions in what I am about to say... they are most likely not doing a QSYS or other DSP tech system, they will not be on a NOC to keep an eye on the system, they will not have a full time qualified operator on-hand to address any issues, they certainly will have to call in Frank or another tech as needed to address any problems, the facility owners have no idea what they actually need, and have no realistic budget.
So as far as this particular situation is concerned, (and as applied to non-DSP tech installs) I stand by each and every one of my original points. ![[Wink]](wink.gif)
| IP: Logged
|
|
|
|
Frank Angel
Film God
Posts: 5305
From: Brooklyn NY USA
Registered: Dec 1999
|
posted 04-25-2018 01:09 PM
You guys always give a lively discussion. To answer some points, I am on loan to a film department at the college and just for a short time; they have two 140 seat screening rooms -- SQUARE with bare, plaster walls and a cement floor and hard tiled ceiling. You could clap your hands and then relax and have a cup of coffee while the slap-back echo finally fades. Where they put the Crown amps is the least of their problems.
In one of the rooms the amps are already installed in what they call a "smart" podium -- control panel for a Crestron system simply controls the source selection and source functions for the BluRay, Mac, LaserDisc and even a VHS player. This podium has a Marantz receiver as the processor.
I am not making any decisions here, just making suggestions for them. And yes, professions and non-tech people will be the ones using these podiums which in one room already has the 7 Crown amps installed in that podium; in the other room they have already purchased 7 Crowns which sit waiting to be installed the same way -- in the podium, which is why I started this thread. My instinct was to suggest NOT to do what they have already done in the other screening room, and for exactly the same reason that Tony and Scott immediately jumped on -- you DON'T want anyone messing around with anything except audio level. Having all those blinking lights and control right there where their sticky fingers can muck with them is a huge red flag because it that's just too much of an irresistible temptation to those who think they know what they are doing. And what's worse, there already is a culture of casual FUTZING. I was told they select on of the many MANY DSP presets to make the movie sound better...they are all very different. There are presets that take sources that are 2 channel or even mono and "spreads" the sound out to every one of the 7 speakers with varying amounts of reveb and time delay and phasing crap, and usually with emphasis on the side and rear channels...seems everyone wants to hear stuff coming out of their surrounds no matter what the original mix might be. So even worse than end-users being able to muck with the amps, they can muck with the receivers, which, as Tony and Scott suggest, is a disaster waiting to happen. Imagine someone seeing the word "Cinema Surround" on the fancy LED display panel and thinking, "Oh yah, THAT'S what I want it to sound like," and then cranking up the "spread" control, taking it out of Direct and Original Source, i.e., no processing, and coming up with this reverb crap coming out of every speaker in the room.
They do have a person on site all the time and she is good, but her role and expertise is in network servers and video editing. I don't thing she appreciates that once the B-chain is calibrated, everything but the volume control should be dipped in carbonite like Hans Solo. The college has an IT dept that installs and maintains the smart podiums, but they are the ones set up one room with the center channel speaker just sitting there not connected to anything and with the center channel routed to the rear surrounds. Complaints came in that they couldn't understand dialog (duh!). The other night I saw what one professor's fix was; he turned on the closed captioning so they could READ the dialog! Actually a pretty clever solution, and from a professor, no less (I jest).
I am on the cusp of retiring so they won't be calling me. Any calls will be that someone wants to run 35mm in the PACs big 2500 seat theatre.
At least I was able to get them to agree to treating the walls, which, when that gets done, will be a contribution that will be more important than anything else I can do for them. After the wall treatment, I'll calibrate and voice the room and then what happens with professors playing with all that digital surround nonsense the receivers offer will be up to them. I don't think whether or not I convince them to keep the amps in the booth or in the podium will really change the way the rooms are going to be operated.
BTW, these are the screening rooms in which the seats (hard plastic, no cushioning) are designed for a flat floor but are anchored to the rooms'slope floors so they are pitched forward. Sit in them for an hour and you get back cramps because you are constantly using your leg muscles to keep you from sliding forward. It's almost funny...unless you are a student needing to sit in them for an hour class watching movie on a screen that, btw, has a visible seam about two feet from the bottom, i.e., a permanent solid line in the image. It is what it is.
| IP: Logged
|
|
|
|
|
|
|
|
All times are Central (GMT -6:00)
|
This topic comprises 3 pages: 1 2 3
|
Powered by Infopop Corporation
UBB.classicTM
6.3.1.2
The Film-Tech Forums are designed for various members related to the cinema industry to express their opinions, viewpoints and testimonials on various products, services and events based upon speculation, personal knowledge and factual information through use, therefore all views represented here allow no liability upon the publishers of this web site and the owners of said views assume no liability for any ill will resulting from these postings. The posts made here are for educational as well as entertainment purposes and as such anyone viewing this portion of the website must accept these views as statements of the author of that opinion
and agrees to release the authors from any and all liability.
|
Home
Printer-friendly view of this topic