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Building a Dinner Theater w/ DIY Speakers, Subs, etc... - Page 5

post #121 of 585
Quote:
Originally Posted by dutchswan0311 View Post

MK....We're you actually running 500W through your drivers? Lilmike had advised not to run more than 300W... even through a 500W driver; but he never attempted nor measured such a thing. It would be exciting if I can safely run 500W through the 390HF with clean results. :-)

Been through this before. It is not worth the risk. The difference between 300 and 500 watts per driver will not likely be measurable in real world conditions. The SPL increase at best will only be 2.22 dB, but some of that will be lost due to compression.

(log(500) - log(300))X10 = theoretical increase in dB

(2.699-2.477) * 10 = 2.22

The actual increase WILL BE LESS than this. The risk to your equipment rises quickly as you approach (or exceed) the thermal and mechanical limits. You're applying 67% more power to get maybe a couple of dB under ideal circumstances. This is crazy. The risks outweigh the benefits in my opinion. Applying power that does not make more SPL is a waste - all it does is take the equipment that much closer to the point where damage results. As soon as watts in don't equal SPL out, there is no need to put more watts in.



With the MFW 15, I hit that limit at about 300 watts when I measured it, but I ran out of amp, so I am not 100% sure that I hit the driver limit or the amp limit first. Those sweeps should be separated by 5 dB each, as you can see, the top one is not.



The T-6 with the W-8 740C shows this a little better. I did the plot a little differently too, I overlaid all of the plots with the power offset taken out. By 64 watts (1/2 the driver's rated power handling) I was showing signs of reaching the driver's limit. By 128 watts, the effects are clear. At 256 watts, I heard lots of bad noises... I did not bother including that plot. This time I did not run out of amp, I clearly ran out of driver.

Added power will result in thermal rise to the voice coil, increasing Re, which results in a decrease in the efficiency of the driver (power compression). With the additional power, you also increase excursion by about 40%. With an xmax of 14 mm, 500 watts exceeds this limit (15 mm). More importantly - with an xmech of ~20 mm, 500 watts is well past that limit (32 mm).

300 watts should not damage drivers, and with 4 cabinets fed 300 watts, you're approaching 130 dB at a meter, in a groundplane setting.

I'd certainly hope that's enough.
post #122 of 585
Thread Starter 
Quote:
Originally Posted by lilmike View Post

Been through this before. It is not worth the risk. 330 watts should not damage drivers, and with 4 cabinets fed 300 watts, you're approaching 130 dB at a meter, in a groundplane setting.

I'd certainly hope that's enough.

Haha. Okay okay... :-)
post #123 of 585
Thread Starter 
I asked Parham at what point should high pass the 4pi mains and his response is below. He mentions that I should low pass my subs at the "Schroeder Frequency" which he says for our room size would be around 80Hz. Guess I lucked out there. Without further research, I don't understand a lick of what he said in answer to my question on where to high pass the 4pi mains. Anyone care to translate?

(Quoting Parham)
"High-pass at the Helmholtz frequency of the mains. The multisub configuration is not limited to direct radiators, but can be employed with hornsubs as well. Delay on the mains is really used to match the acoustic centers, to compensate for the extra depth of a basshorn.

Helmholtz frequency of each model
You delay the mains to match the hornsubs, to provide in-phase summing without a multi-cycle shift. But in a multisub configuration, this takes on a different meaning, since in-phase summing is non-sequiter in the modal region. What you really want is for the sound sources in the modal region to be staggered in time. It's the varying amounts of "delay" from various sources in different positions that make the multisub configuration work.

In the end, since the reflections are delayed, there is no way to get them all in-phase. That's what room modes are all about. The take-away is you will want to delay the mains to nearly match the flanking subs, but do not worry about the more distant subs. The flanking subs should actually be just behind the mains, to fill in the hole from the reflection of the nearest wall just behind them.

Also, do not "crossover" subs to mains like you might outdoors. Instead, low-pass the subs around 80Hz, which is the Schroeder frequency for your room. Blend every sound source you have in this region. Only high-pass the mains to reduce energy below their Helmholtz frequency, to prevent over-excursion. Do not high-pass them higher than that, because the goal is to have multiple sound sources below the Schroeder frequency."
(End Quote)
post #124 of 585
post #125 of 585
If the baffle wall is all absorptive material, you will lose some boundary loading for the 4Pis, it will be as if they were more like in free space. Enough to matter? Hard to say. mouting the speakers close to the screen material will help if you use reflective material for the baffle wall, or use a thin absorption layer to eliminate HF reflection problems but still retain some boundary loading lower in freq. I say use drywall, listen, hang the screen, listen. If there is a problem, use 1" of fiberglass in front of the drywall, rehang the screen, listen. If the problem is solved, done. If not, another 1" of glass. 2" of 3lb per cuft fiberglass will absorb any freqs reflected back by the screen and then some.

L and R speakers should be around 24-28 degrees off axis.

I think of multiple subs cancelling room modes either by not exciting them due to position (even order modes), or by cancellation of odd order modes. Either way, you get the same result. Wayne is right, spreading out the subs will get you the largest area of similar (NOT FLAT) response (with large variations in response outside of that area), with one EQ solution (which may require more headroom than you have). What Parham fails to address is that multiple, spread out subs lose efficiency compared to clustered subs, depending on the chosen sub locations, and IIRC you do not have a whole lot of headroom to begin with (with 4 F20s) if you plan to run at reference level in the middle of the theater space.

The ONLY way to see the difference in your room will be to measure and experiment with sub locations, which will take time, and which may not be a part of the overall decor you are going for. I do realize that you have limited placement options, hence my recommendation to cluster the subs under the screen. Sure, in an ideal world, you would have subs with 10dB of headroom above reference anywhere in the seating area, spread out around the room to cancel modes, and even running a JBL BassQ to optimize the system fully.

Some general reading that may help w/ LCR placement:

http://www.jblpro.com/pub/cinema/cinedsgn.pdf


JSS
post #126 of 585
Thread Starter 
@max: Thanks for the info. I read the entire manual and printed the 20 pages that appeared relevant to our application. There was a lot of good information in there that I will definitely employ. I find it interesting that JBL cinema professionals recommend one 18" sub powered at 400W for every 25,000 cubic feet of theater space. That is right about the size of theater that we will be. I wonder how many 15" 300W subs equal an 18" 400W sub. My guess is they are probably almost 1:1. Not to mention JBL is talking about a ported sub, not a high efficiency horn sub. So, with four F20s, I would meet the needs of a 100,000 cubic foot cinema....in my dinner theater that is 1/4 that size? Is four F20s overkill then? Would two be more appropriate? Then again, JBL was listing minimums and specifically stated that you can put more sound in a smaller theater but not less sound in a larger one. Whew...so much to learn.

On a different note; I seem to have accidentally built the exact number of surround speakers recommended for a theater our size: the right number at the right wattage and power handling capability. Interesting.

@everyone else: I have updated the F20 build on the first page of this thread. I have also changed the placeholder post to include many images and thoughts on my 4pi and 1pi builds. Just thought I would mention it in case no one visits the first page anymore (I know I had not been there for a while).

Also, I believe this will be the final setup (depicted below). The JBL cinema sound manual that Max referred me to stated that the L & R channels should be as far out to the edge of the screen as possible. It also said they should be directed to the ear level of the middle of the theater @ 2/3 the distance from the screen to the rear wall. That's something to consider as I build my baffle wall.

post #127 of 585
Thread Starter 
CHOOSING AMPS, AVR, & OTHER COMPONENTS

Perhaps the list will need change as my understanding of everything evolves; but what I have put together so far is depicted below. I am working within the confines of a $15,000 budget, so that is a major consideration. I welcome input as to the amps that I have selected so far, and the combination in which they are employed.

The "JBL Cinema Sound System Manual" had nothing against running each surround channel in parallel, as long as each speaker was wired with its own "home run" wire, and then put into parallel at the "booth". Perhaps I should run fewer, stronger amps in order to accomplish this? It might save money?

JBL recommended a 2:1 ratio for the amp wattage to the RMS power rating of the loudspeakers, but a 1:1 ratio for the sub amp to the ohm rated wattage handling of the sub driver. I wonder if I have given myself too much head room on the sub amps and not enough on the 4pi amps. Thoughts?

Also, I am starting to research AVRs for our application. Does anyone have a recommendation as to what AVR might be appropriate for us? It seems like it should have high/low pass abilities, but one thing I am having trouble finding is a rack mountable AVR of any kind. Advice from my forum friends is appreciated!

(Footnote: While I imagine it is completely unnecessary, I liked that I was able to find my needs in the same brand and model of amp. Then again, I am a little crazy when it comes to symmetry.)

post #128 of 585
One amp for multiple surrounds may be better since it might be hard to drive more than one amp from the pre-out on the AVR.

I think the Onkyo PR-SC5508 may be available in a pro version with rack mount ears. Way over your budget though. It also has XLR outputs, that you won't find on a receiver.
post #129 of 585
Thread Starter 
Quote:
Originally Posted by petew View Post

One amp for multiple surrounds may be better since it might be hard to drive more than one amp from the pre-out on the AVR.

I think the Onkyo PR-SC5508 may be available in a pro version with rack mount ears. Way over your budget though. It also has XLR outputs, that you won't find on a receiver.

Petew...thanks for the reply. I will check that AVR out. Even if it ends up being too pricey, it might get me in the right track. With regard to the 2 amps/channel on the surrounds; I figured I use a Y adapter to send the signal from the preamp to the amps. Is this not a wise thing to do?
post #130 of 585
dutch,

For a quick angle measurement, a fist at arm's length (knuckles horizontal, not including thumb) is approximately 10 degrees of angle. From the middle of the theater, if you have 2 fists between center and L or R, you should be good. If it is closer, consider mounting the L/R just outside of the screen...

Looks like a pretty good plan, thanks for the 1st post updates! Looking forward to seeing this completed....

JSS
post #131 of 585
Thread Starter 
Quote:
Originally Posted by maxmercy View Post

dutch,

For a quick angle measurement, a fist at arm's length (knuckles horizontal, not including thumb) is approximately 10 degrees of angle. From the middle of the theater, if you have 2 fists between center and L or R, you should be good. If it is closer, consider mounting the L/R just outside of the screen...

Looks like a pretty good plan, thanks for the 1st post updates! Looking forward to seeing this completed....

JSS

The baffle wall will be built out (obviously) to conceal the speakers and subs behind the AT. The max width of the baffle wall is 14' due to windows on either side if the baffle wall; hence the 13' wide (180" dia) screen. So, the only place the L&R speakers can go is the outer moat limits of the screen. I have the floor plan drawn up in cad, so determining the angles of the L/R will be easy.
post #132 of 585
Thread Starter 
I have been attempting to learn how to possibly hook up the surrounds in parallel. I found a calculator online that showed me how wiring four 1pi speakers rated at 8Ohm in parallel would change the impedance to 2Ohm. Does that mean I would need to find an amp that was capable to one of these two (assuming I wanted to double the 100W RMS rating in my 1pi to 200W RMS rating in the amp):

800W x 1 @ 2Ohm in Bridged Mono Mode

or

400W x 2 @ 4Ohm in Stereo Mode

post #133 of 585
Wiring in parallel may help you reduce the amount of amps you will need. If the amp is stable to 2 Ohms and can provide the needed power, then do it.

JSS
post #134 of 585
Wire two in series, which will give you 16Ω. Then wire those pairs together in parallel, which will get you back to 8Ω.
post #135 of 585
Thread Starter 
Quote:
Originally Posted by petew View Post

Wire two in series, which will give you 16Ω. Then wire those pairs together in parallel, which will get you back to 8Ω.

@petew: I found a diagram for wiring speakers in series, and in parallel, but couldn't find one that did both. I put together a diagram that I believe incorporates what you are talking about. Did I do it correctly? If I do both, then I would just need an amp that has an RMS rating of 400W per channel @ 8Ohms (assuming I wanted my amp to double the RMS rating of my 100W speaker). Is that right?

post #136 of 585
Quote:
Originally Posted by dutchswan0311 View Post


@petew: I found a diagram for wiring speakers in series, and in parallel, but couldn't find one that did both. I put together a diagram that I believe incorporates what you are talking about. Did I do it correctly? If I do both, then I would just need an amp that has an RMS rating of 400W per channel @ 8Ohms (assuming I wanted my amp to double the RMS rating of my 100W speaker). Is that right?

Golly this takes me back to my car audio days. I used to be decent at this but now I can't remember much other than loud bass, what does that mean? Can't be good
post #137 of 585
Thread Starter 
@max: That is what I was thinking. Could save three amps; or a total of $1,000.

Please critique my diagram and amplifier selections, and let me know if my design is flawed in any way. As always, thank you in advance to anyone willing to lend their feedback. It is greatly appreciated!



post #138 of 585
Quote:
Originally Posted by dutchswan0311 View Post

@petew: I found a diagram for wiring speakers in series, and in parallel, but couldn't find one that did both....

That's exactly what I had in mind. All of your diagrams look correct, however, I'd wire up the surrounds to load the amp at 8Ω instead of 2Ω. Look at the specs for the amp - distortion rises from .1% to 1% which I would think means the amp is really straining to hit the mark. Also keep in mind that the speaker impedance is not a fixed value. It varies with frequency. Look at the graph below from Wayne's site. The impedance of the 2π drops to 4Ω between about 6kHz and 13kHz. That will put a 1Ω load on the amp with four wired in parallel.
post #139 of 585
Thread Starter 
Your point is well taken Petew. I will look for the model that puts out ~800W per channel into an 8ohmelectrical load. I think th EPQ1200 does that, but I am on the work site right now and will have to check later.
post #140 of 585
Thread Starter 
Worked all day on construction at the winery today. I just thought I would share a couple of non-AV related pictures in to give you some context as to where our dinner theater is located. The contractors will be installing our exterior stone over the next 2-3 weeks. The pictures below depict how it looks so far (without grout).





Today I ran wire for 9 of the 19 speakers that will comprise our dinner theater's sound system. I purchased 1,000 feet of CL3 rated 14/2 speaker wire, but I have already used 600 feet of wire and still have 10 home runs to go. When it's all said and done, I think I will have used about 1/4 mile of speaker wire!



The orange spray paint approximates the size of the 180" screen that we plan to use. That is about 13' wide and 7.5' tall. The baffle wall will be built 26" from the main wall using 2x6s, bringing the F20s flush with the audience side of the baffle wall. I really appreciate Mike taking the time to show us how to cut the mouth of the horn on the side; but in the end I decided to take up the extra 10" out of my 45' room so that the subs could actually be grouped together more effectively. The width of the baffle wall will stretch to about 6" on either side of the orange spray paint.

Side Note: The wall cavities that you see will be insulated with spray foam in a few weeks. I thought this would do well to absorb sound, but Parham tells me that spray foam insulation is actually very bad at absorbing sound and will, in fact, reflect most of it. Any suggestions on what kind of wall covering I should use after the spray foam is installed? This is, of course, the wall that is behind the baffle wall.

post #141 of 585
Quote:
Originally Posted by dutchswan0311 View Post

Worked all day on construction at the winery today. I just thought I would share a couple of non-AV related pictures in to give you some context as to where our dinner theater is located. The contractors will be installing our exterior stone over the next 2-3 weeks. The pictures below depict how it looks so far (without grout).

Today I ran wire for 9 of the 19 speakers that will comprise our dinner theater's sound system. I purchased 1,000 feet of CL3 rated 14/2 speaker wire, but I have already used 600 feet of wire and still have 10 home runs to go. When it's all said and done, I think I will have used about 1/4 mile of speaker wire!

The orange spray paint approximates the size of the 180" screen that we plan to use. That is about 13' wide and 7.5' tall. The baffle wall will be built 26" from the main wall using 2x6s, bringing the F20s flush with the audience side of the baffle wall. I really appreciate Mike taking the time to show us how to cut the mouth of the horn on the side; but in the end I decided to take up the extra 10" out of my 45' room so that the subs could actually be grouped together more effectively. The width of the baffle wall will stretch to about 6" on either side of the orange spray paint.

Side Note: The wall cavities that you see will be insulated with spray foam in a few weeks. I thought this would do well to absorb sound, but Parham tells me that spray foam insulation is actually very bad at absorbing sound and will, in fact, reflect most of it. Any suggestions on what kind of wall covering I should use after the spray foam is installed? This is, of course, the wall that is behind the baffle wall.

I like the exterior. Nice choice on color. Cables look like they are run well and secured nicely. The only thing drawback to those staples is that if you ever want to pull new wires through that it'll be tough but that might not be a consideration. Nice work.
post #142 of 585
Thread Starter 
@sx: where those cables are, spray foam will go...so there won't be any pulling of more cables through there after a month from now.
post #143 of 585
Thread Starter 
The following represents the settings that I am attempting to achieve, and the subsequent amps that I have found so far that most closely meet those stated objectives. Please chime in if you know of a better or more efficient way of going about this (or if you see something wrong with my "ohm math"

4pi Speaker: As of now, I plan to run each of these three LCRs on their own Amp in bridged mode. The JBL Pro Cinema manual recommends doubling the RMS rating on the amp when compared to the RMS rating of the loudspeaker. As the 4pi speakers are rated at 600W RMS @ 8ohm, I am looking for a loudspeaker that puts out 1,200W RMS in Bridged mode @ 8ohm.

1pi Speaker (Left Surround x4 & Right Surround x4): Since each of these channels have four speakers in them, I am looking for an amp that can either (1) Provide 800W RMS in bridged mode @ 8ohm to connect to four 1pis wired in parallel and serial. This would require two amps; one to run the Left surrounds and one to run the right surrounds (or)
(2) Provide 800W RMS x 2 Channels @ 8ohms to run the left and right surrounds wired in parallel and series. This would run all eight L/R Surrounds with one amp.

1pi Speaker (Left-Rear Surround x 2 & Right-Rear Surround x 2): Provide 400W RMS x 2 @ 4ohms to connect to two 1pis wired in parallel on each channel.

post #144 of 585
Thread Starter 
Update: After further research, I believe the two charts above represent the best options available for our application with consideration to our budget constraints. The real question at this point is beyond my expertise, and I would truly appreciate some guidance. The question is: Ignoring price, which is the better amp; the Crown XLS series, or the Behringer EPQ series?
post #145 of 585
Crown
post #146 of 585
Thread Starter 
Quote:
Originally Posted by flyng_fool View Post

Crown

Trust me when I say I have no sense of brand loyalty; but can you qualify why these particular Crowns might be superior to these particular Behringers?
post #147 of 585
Quote:
Originally Posted by dutchswan0311 View Post


Trust me when I say I have no sense of brand loyalty; but can you qualify why these particular Crowns might be superior to these particular Behringers?

In the case of pro gear, most value assessments come from criteria that has little to do with subjective sound quality and more with things like reliability, road worthiness, portability (read weight),etc. As to your choice of amplifiers, I suggest you narrow down your AVR/ preamp processor to determine it's output interface and level. You're going to want avoid having to use output level matching devices between the two or suffer limited dynamic range or output. Amplifiers that have selectable input gain stages are obviously more flexible.

In the case of your need for sound deadening in or behind the baffle wall, Roxul is the preferred material.
post #148 of 585
+1 to the level-matching. I have some Behringer stuff, but none of the above models.

Are you planning on using an AutoEQ package onboard an AVR for final adjustment/tweaking of the system?

JSS
post #149 of 585
Thread Starter 
@mayhem...I will look into the roxul ...ty.

@max...one of the reasons I changed how things are wired was to eliminate three amps which will allow me to invest in a better AVR. The plan was to EQ through the AVR. Is this a bad plan?
post #150 of 585
Quote:
Originally Posted by dutchswan0311 View Post

@mayhem...I will look into the roxul ...ty.

@max...one of the reasons I changed how things are wired was to eliminate three amps which will allow me to invest in a better AVR. The plan was to EQ through the AVR. Is this a bad plan?

Since you'll be using discrete amps would it make more sense to use a preamp rather than an AVR since you won't need the amps in the AVR?
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