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Author Topic: Starting off with stereo sound Adam Martin I'm not even gonna point out the irony. Posts: 3686 From: Dallas, TX Registered: Nov 2000 posted 12-18-2006 06:47 PM                     Over-simplified, but here goes: split surrounds - Optical surround sound was mono with the same signal going to all surround speakers. Digital systems are capable of splitting the surround speakers into groups (left and right) or (left, right and rear). Bi-Amplified / Tri-Amplified - How the signal is amplified and sent to the stage speakers from the processor. Amplified = the whole signal is sent to the speaker where it goes through a crossover (see below) and is split to low, [mid] and high range. Bi-Amplified and Tri-Amplified use a crossover before the amplifier to separate (either low and high [Bi-Amplified] or low, mid and high [Tri-Amplified]) the signals before they get amplified and sent to the stage speakers. 2-way systems - A two-way speaker has a woofer and tweeter mounted together in one assembly rather than individual speakers for low and high-frequencies. crossovers - a device that takes the audio signal and splits it up into multiple signals so that the low-frequency goes to the woofer, the mid-frequency goes to the mid-range and the high-frequency goes to the horn (et al). Sometimes this is built into the speaker electronics itself. (SR) emulation Dolby owns the rights to the process of A-type and SR-type noise reduction. Non-Dolby systems must emulate (do the same thing in their own different way) the noise reduction process in order to properly reproduce the encoded audio tracks.  |  IP: Logged Andrew McCrea Jedi Master Film Handler Posts: 645 From: Winnipeg, Manitoba, Canada Registered: Nov 2000 posted 12-18-2006 10:37 PM                        Thanks Adam!  |  IP: Logged Cameron Glendinning Jedi Master Film Handler Posts: 845 From: West Ryde, Sydney, NSW Australia Registered: Dec 2005 posted 12-19-2006 02:19 AM                     More information please What shape is the cinemas? Parrallel walls? Will there be curtains on the wall? Stadium style or flat floor? Big soft seats or older style? Answer those questions and I'll let you know about what speakers would be ideal. In my opinion one size does not fit all. PS Later Dolby processers also have SR emulation and analogue sound is not as good as the earlier models were.  |  IP: Logged Dave Macaulay Film God Posts: 2321 From: Toronto, Canada Registered: Apr 2001 posted 12-19-2006 10:51 AM                     Technically whatever Dolby® does to get Dolby® SR® is Dolby® SR®, not an "emulation". The original Dolby® analog cards are considered the best sounding, but there are several implementations using digital signal processors. The CP45 has pretty poor digital SR®, the CP500 is quite a bit better, and the CP650 is quite good IMO. If you want to hear what a really bad emulation sounds like, try a DTS 6AD. Considering the price for an analog SR® card it's understandable that the DSP version is used nowadays, particularly as fallback for digital sound.  |  IP: Logged Sam D. Chavez Film God Posts: 2153 From: Martinez, CA USA Registered: Aug 2003 posted 12-19-2006 10:56 AM                       The CP45 is not digital in any way. It is the last of the analog processors from Dolby. If memory serves, it uses a 222/SR "Lite" card which is analog.  |  IP: Logged Andrew McCrea Jedi Master Film Handler Posts: 645 From: Winnipeg, Manitoba, Canada Registered: Nov 2000 posted 12-19-2006 11:40 AM                        So, how are amplifiers chosen regarding speaker sizes? Here's the equipment I've narrowed down so far for these two rooms: Cinema 1 45' long and 38' wide 130 seats (older style model, sloped) 35' screen maxed in scope 43' Throw Cinema 2 37' long and 28' wide 70 seats (older style model, sloped) 25' screen maxed in scope 35' Throw QSC's ISA Amplifiers JBL 4675C screen channel speakers JBL 4645C subwoofers JBL 8330A surround speakers (Above links are Adobe PDF files for specifications) Which of the amps would you select for each speaker/speaker set? What about speakers for the rooms? 6 surround on each side wall in both houses? Bi-Amp in larger house? Thanks for the help!  |  IP: Logged Scott Norwood Film God Posts: 8146 From: Boston, MA. USA (1774.21 miles northeast of Dallas) Registered: Jun 99 posted 12-19-2006 12:17 PM                        Speakers have a characteristic called "sensitivity," which is measured in dB/watt at one metre. Given the dimensions of the room, the efficiency of the speaker, any sound absorbing characteristics of the room, and the desired maximum SPL, you can calculate the necessary amplifier power. In general, newer speakers are less efficient than older ones. With an Altec A-4, you only need about 25-50 watts of power to fill a 2000-seat theatre with sound. You will need considerably more power to reach an equivalent SPL with modern JBLs. The right way to do this is to hire an acoustical consultant when designing the room and then hire a competent service company to design and install the sound system, assuming that you actually want to build or renovate a theatre, as opposed to just being interested in the process. As a side note, I will point out that I think that your rooms are too small (too few seats) and that your screens are too big for those room sizes. Your "cinema 2" reminds me of a screening room where I have worked. For the record, that room was about 30' deep and the screen was about 14' wide for scope and the proportions seemed reasonable (see photos of "GCC screening room"). That place doesn't exist any more, but they had the small EV stage speakers (and sub), biamped with QSC 1400 amps, and some type of EV surround speakers. This was probably serious overkill for that room. Also, why are your throw distances less than the length of the room? Does the booth stick out over the last row of seats, or is there some other reason for this?  |  IP: Logged Andrew McCrea Jedi Master Film Handler Posts: 645 From: Winnipeg, Manitoba, Canada Registered: Nov 2000 posted 12-19-2006 12:52 PM                        The room sizes include space behind the screens, plus the throw includes 1' away from the port. From the back wall to the screen in #1 would be about 42'. This is just interest for the process. Some people said the room sizes were quite good. The screens are maxed in scope, as well. The flat screen in #1 ends up being about 27'.  |  IP: Logged Cameron Glendinning Jedi Master Film Handler Posts: 845 From: West Ryde, Sydney, NSW Australia Registered: Dec 2005 posted 12-19-2006 04:50 PM                     Ok, I would not recomend the 6575c, as the horn has a high and wide coverage pattern and unless you have very good acoustics (THX style, thick curtains and acoustic treatment on the side/ back walls) the advantage to the midrange sound quality that a large horn makes will be lost to early reflections that make inteligibility difficult. The 90 x 40 smaller horn would probably work better and be easier to aim, to avoid the bounce from the back and side walls. aim to place speakers on stands 2/3 the hight of screen and aim the hi frequency horn down through the screen into the middle of your seating area, so that the seats and audience break up / absorb the sound, before it bounces of the flat auditorium walls. Remember to angle the left and right speakers horns inwards. QSC is simply a very high quality amplifier, as for size, you have small rooms, so 200w would be fine the jbl 2677 from their small cinema rangeweb page please note that the whole box needs to be angled as it has a fixed horn. Also that the THX model features a 90 x 90 horn ( correction 100 x 100 )and is probably not suitable. In small rooms there is no need to bi amp unless you prefere the sound that way(try before you buy) to me the difference is not huge. The next model up 4760d would be ideal. I suggest 8 surround speakers per auditorium, 2 on the back walls 3 per side walls starting 1/3 back from stage. Your cinemas are small so you dont need big for quality [ 12-20-2006, 12:39 AM: Message edited by: Cameron Glendinning ]  |  IP: Logged Steve Guttag We forgot the crackers Gromit!!! Posts: 12814 From: Annapolis, MD Registered: Dec 1999 posted 12-19-2006 09:07 PM                     Sorry...the Cat 222SR/A IS SR emulation...not SR...for it has NO SR IN IT. It has a cascaded "S" (consumer) circuit in it. It does not track like SR so it can only be classified as emulation...just like all of the rest of the real SR products Dolby made (Cat 300, 350 and Cat 280).  |  IP: Logged Andrew McCrea Jedi Master Film Handler Posts: 645 From: Winnipeg, Manitoba, Canada Registered: Nov 2000 posted 12-20-2006 11:23 PM                        I was looking at this JBL document and they suggest picking an amplifier with twice the wattage output for a surround speaker than the speaker's power... so a 100W surround speaker channel would get a 200W amp, as far as I understood. It says that the sub should get an amp that is rated as close to the sub as possible. It doesn't say anything about the screen channels. I thought if you overdid the amplifier, it would blow the speaker?  |  IP: Logged Gordon McLeod Film God Posts: 9532 From: Toronto Ontario Canada Registered: Jun 99 posted 12-21-2006 10:05 AM                     Andrew said"I thought if you overdid the amplifier, it would blow the speaker? " actually the reverse situation damages more speakers by being driven into clipping  |  IP: Logged Andrew McCrea Jedi Master Film Handler Posts: 645 From: Winnipeg, Manitoba, Canada Registered: Nov 2000 posted 12-21-2006 10:12 AM                        So if a speaker's average power capability was 300w, then an amplifier of 300w or a little bit more would be the choice?  |  IP: Logged Gordon McLeod Film God Posts: 9532 From: Toronto Ontario Canada Registered: Jun 99 posted 12-21-2006 01:48 PM                     You choose your amplifiers based on the power you require as based on the speakers sensitivity to get the desired SPL in the theatre and then a bit of headroom  |  IP: Logged Andrew McCrea Jedi Master Film Handler Posts: 645 From: Winnipeg, Manitoba, Canada Registered: Nov 2000 posted 12-21-2006 02:08 PM                        quote: Scott Norwood Speakers have a characteristic called "sensitivity," which is measured in dB/watt at one metre. Given the dimensions of the room, the efficiency of the speaker, any sound absorbing characteristics of the room, and the desired maximum SPL, you can calculate the necessary amplifier power. So, how do I use this formula?  |  IP: Logged

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