Another 70 volt Critique Request - AVS Forum
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post #1 of 11 Old 06-04-2013, 01:32 PM - Thread Starter
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Hello guys,
I've been lurking for a while now trying to learn as much as I can about 70v systems, and hope you can help me out. We are taking over a restaurant/bar space that has a cd player with a couple speakers wired up providing background music. The space is mostly square, about 1000sqft and mostly open beam ceilings and no division between the bar and dining area. What we intend to have is decently clear background music, louder if needed depending on atmosphere, and occasionally show sports games, we're talking Saturday/Sunday big games (college/NFL), big name sports events. This is what we have planned out with a $2000 budget:

5 JBL Control 25AV Surface Mount Speakers tapped at 60w
Atlas Sound CP700 Amplifier
Crown 14M Mixer

Anything wrong with this set up for what we'd like to do? My pricing puts this at just over $2000, but we want to make sure we're not going to go limp when the game is in overtime.

I was looking at Crown's XLS and XLI lines, but I do not see the options for 70v system set up. Can we wire a transformer from the amp before reaching the speakers or is this not an option?

Also, when JBL lists nominal impedance as 8 ohms, what does it matter if it's a 70 volt system, and why does a 70 volt amp have different ohm set ups? At this point I believe we'd just bridge the channels at 8 ohms. Any help on clarifying this would be great!

Intended speaker set up (x's):



X - - - - - -X
- - - - X - - -
X - - - - - -X
|- - - Bar- - |
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post #2 of 11 Old 06-05-2013, 06:18 AM - Thread Starter
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Just to add, I read that 5'' speakers won't last that long if they are driven hard often, in addition to them conflicting with people's normal voice frequencies. I'd prefer to use JBL Control 29AV with a Crown XLS 1000 or XLI 900 if I could, but I can't find anything about how to drive these speakers that way.

It must be really simple and require no real explanation for a dumb guy like me if it's possible huh. biggrin.gif
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post #3 of 11 Old 06-06-2013, 06:30 AM
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You definitely want speakers that are larger than 10" for that size space.

You can buy 70V transformers separately and use them for any speaker; just watch the power rating of the transformer and make sure it is high enough.

Full Compass has 100 watt transformers for 70V setups for around $90 each (Lowell 10070). Those should work with almost any speaker system for your application. You will not exceed 100W.

You can get the JBL JRX112M speakers for only $100 each from Amazon, and those are the ones that will do the job for you. get 4 or 5 of those and you will have some serious sounds in there.

The transformers have 70v input taps to connect to the amp and 8 ohm and 4 ohm output taps to connect to the speakers. The multiple input taps on the transformer allow you to set the volume of each speaker relative to the other speakers in the system in case one physical location requires more or less volume relative to the other speakers in the system.

You should be able to get a 300-400 watt 70v PA amplifier for $300-600.

Mixers are available from any pro audio store for various prices. A good 8-channel mixer should not cost more than $300.

The "70v", by the way is the approximate output voltage of the amplifier when it is turned up to FULL VOLUME. It will put out a much lower voltage at normal volume levels.
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post #4 of 11 Old 06-06-2013, 07:14 AM - Thread Starter
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Quote:
Originally Posted by commsysman View Post

You definitely want speakers that are larger than 10" for that size space.

You can buy 70V transformers separately and use them for any speaker; just watch the power rating of the transformer and make sure it is high enough.

Full Compass has 100 watt transformers for 70V setups for around $90 each. Those should work with almost any speaker system for your application. You will not exceed 100W.

You can get the JBL JRX112M speakers for only $100 each from Amazon, and those are the ones that will do the job for you. get 4 or 5 of those and you will have some serious sounds in there.

The transformers have 70v inputs to connect to the amp and 8 ohm and 4 ohm output taps to connect to the speakers. The multiple input taps on the transformer allow you to set the volume of each speaker relative to the other speakers in the system in case one physical location requires more or less volume relative to the other speakers in the system.

You should be able to get a 300-400 watt 70v PA amplifier for $300-600.

Mixers are available from any pro audio store for various prices. A good 8-channel mixer should not cost more than $300.

Thanks for the response.

Since I do want the ease of use of the 70v system, you're suggesting I use the 100 watt tap on the transformer. Wouldn't I want at least a 600 watt amp if I have 5 speakers tapped at 100 watts?

I was thinking I'd be mounting these speakers with the grill side facing down hanging from the beams. After reading their mounting description of only a 10 degree change possible with it's own mounting hardware, am I going to be looking at poor acoustics with a hang down installation?

Thanks for the help.
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post #5 of 11 Old 06-06-2013, 11:57 AM
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You need 600 W/8 ohm to provide a full 70 V output. Whether you actually need that much, who knows. You should be able to use one of the Crown amps; the transformers at the speakers are for load-balancing (among other things) and impedance matching so the amp does not see as severe a load compared to say putting them all in parallel.

I have not looked at the speakers, but I would go with standard ceiling-mounted speakers (perhaps in boxes) to provide a broader radiation pattern. A "regular" speaker typically radiates less in its normal vertical axis than in the horizontal. There are also special speakers with broad radiation patterns used for sound reinforcement in churches, auditoriums, and clubs. For a sports bar, and background music, I do not see the need for extended LF response.

You could go with a powered mixer if you want to save space (and perhaps a little money).

You might call up Sweetwater Sound and ask for some help. Their sales consultants deal with a lot of places like yours and can suggest what you need for agiven price range. A local sound consultant might be well worth the money to at least provide some general on-site guidance.

"After silence, that which best expresses the inexpressible, is music" - Aldous Huxley
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post #6 of 11 Old 06-06-2013, 04:14 PM
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100 watts is the maximum rating of the transformer. You will seldom if ever run the system at full power, so the transformers are really overrated.

The tap you choose on each transformer is determined by the relative volume you want from each speaker.

For example, if you decide that speaker B needs to be a bit less loud than speaker A, then you might select the 100W tap to use for A on its transformer, and the 50 watt tap to use for speaker B on its transformer.

I very much doubt that you need a 600 watt amplifier, but if you want to be bullet-proof, it couldn't hurt. 300 watts is probably fine.

If you use the JBL JRX112M speakers I mentioned, I would mount them on the end walls about two feet below the ceiling facing straight into the room, or maybe tilted downward VERY slightly. This will give the most effective dispersion, with minimum absorbtion by keeping the sound projected HORIZONTALLY above the people and furnishings, so that it reaches their EARS with less attenuation.

I think four of them will be all you need; two at each end of the space. Facing speakers straight down, vertically, gives very poor sound dispersion; the power is absorbed by the bodies and the floor and does not travel far from the speaker. You really do not want to do that.

As a matter of fact, one of the reasons for using down-facing speakers in an office or other PA system is that it limits the sound from a given speaker to a small area, and then you can avoid disturbing other nearby areas too much by strategic placement. If you go to a restaurant or other venue with ceiling speakers, you will observe that you don't hear them worth a damn unless you are almost right under them. Think about that...lol.

I would use at least 12 speakers if they were going to be downward-facing speakers. You will need them.
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post #7 of 11 Old 06-08-2013, 08:40 AM - Thread Starter
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Quote:
Originally Posted by DonH50 View Post

You need 600 W/8 ohm to provide a full 70 V output. Whether you actually need that much, who knows. You should be able to use one of the Crown amps; the transformers at the speakers are for load-balancing (among other things) and impedance matching so the amp does not see as severe a load compared to say putting them all in parallel.

I have not looked at the speakers, but I would go with standard ceiling-mounted speakers (perhaps in boxes) to provide a broader radiation pattern. A "regular" speaker typically radiates less in its normal vertical axis than in the horizontal. There are also special speakers with broad radiation patterns used for sound reinforcement in churches, auditoriums, and clubs. For a sports bar, and background music, I do not see the need for extended LF response.

You could go with a powered mixer if you want to save space (and perhaps a little money).

You might call up Sweetwater Sound and ask for some help. Their sales consultants deal with a lot of places like yours and can suggest what you need for agiven price range. A local sound consultant might be well worth the money to at least provide some general on-site guidance.

I guess this is where I'm confused. I thought I do want to wire the speakers in parallel, wiring that way to keep it simple to add on if necessary? I looked at some of the powered mixers but they all seem to be able to handle low power ratings. One Crown powered mixer has two channels at 80w, that'd be great if I tapped two speakers on each channel at 30 watts, but is that going to be loud enough?

I will definitely get in touch with Sweetwater Sound, sounds like a good idea.
Quote:
Originally Posted by commsysman View Post

100 watts is the maximum rating of the transformer. You will seldom if ever run the system at full power, so the transformers are really overrated.

The tap you choose on each transformer is determined by the relative volume you want from each speaker.

For example, if you decide that speaker B needs to be a bit less loud than speaker A, then you might select the 100W tap to use for A on its transformer, and the 50 watt tap to use for speaker B on its transformer.

Got that. My question now is even a 50 watt tap going to be loud enough? I'm only used to examining stereo systems in cars, not sure how ratings work out with open spaces.
Quote:
I very much doubt that you need a 600 watt amplifier, but if you want to be bullet-proof, it couldn't hurt. 300 watts is probably fine.

If you use the JBL JRX112M speakers I mentioned, I would mount them on the end walls about two feet below the ceiling facing straight into the room, or maybe tilted downward VERY slightly. This will give the most effective dispersion, with minimum absorbtion by keeping the sound projected HORIZONTALLY above the people and furnishings, so that it reaches their EARS with less attenuation.

I think four of them will be all you need; two at each end of the space. Facing speakers straight down, vertically, gives very poor sound dispersion; the power is absorbed by the bodies and the floor and does not travel far from the speaker. You really do not want to do that.

As a matter of fact, one of the reasons for using down-facing speakers in an office or other PA system is that it limits the sound from a given speaker to a small area, and then you can avoid disturbing other nearby areas too much by strategic placement. If you go to a restaurant or other venue with ceiling speakers, you will observe that you don't hear them worth a damn unless you are almost right under them. Think about that...lol.

I would use at least 12 speakers if they were going to be downward-facing speakers. You will need them.

Got it. Thanks for the help. I am still a little confused on how to use all these amps. Some are 70v specific while others aren't, how can you use the non 70v specific ones and continue to wire them parallel in a distributed audio format and not overdraw like Don said?
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post #8 of 11 Old 06-08-2013, 04:40 PM
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The 70 V speakers have transformers built-in so yes you just wire them in parallel. The transformers provide impedance matching and load balancing (volume leveling). I have not looked at many powered mixers but many companies offered fairly high-power units last time I looked (Mackie is one company that makes inexpensive powered mixers). However, that was just if you wanted to save space and money; my preference would by far be for a separate amplifier. There is nothing special about most 70 V amplifiers these days. Some have a transformer output, but many forego the transformer and just provide a direct low-impedance output as you would get from any amp. A two-channel amp run in mono or bridged mode is often used for the job. As commsysman said 70 V is the maximum output; nothing happens if you use a less powerful amp (well, the max volume is less, of course). In your diagram wall speakers would probably work as well as ceiling and would be easier to install (and repair if needed), and should cover that area (about 30' x 30" ?).

HTH - Don

"After silence, that which best expresses the inexpressible, is music" - Aldous Huxley
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post #9 of 11 Old 06-09-2013, 06:16 AM
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If you use a NON-70V amplifier, you could wire 4 speakers up by putting two of them in series with each other on each channel of a stereo amplifier (wire + of one speaker to the - on the other and the other two terminals to the amp).

If you put 2 or more of them parallel with each other, the load impedance will be too low for the amplifier.

That is why a 70V system is preferred. With a 70V system you can wire many speakers in parallel.

Actually, the JBL JRX115 speakers would be better for you. They have more bass and are perfect for what you want to do. Four of them will give you more sound than you can use.

Sweetwater pro audio has them for $224 each, which is about 40% off of list price.
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post #10 of 11 Old 06-09-2013, 06:21 PM - Thread Starter
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Quote:
Originally Posted by DonH50 View Post

The 70 V speakers have transformers built-in so yes you just wire them in parallel. The transformers provide impedance matching and load balancing (volume leveling). I have not looked at many powered mixers but many companies offered fairly high-power units last time I looked (Mackie is one company that makes inexpensive powered mixers). However, that was just if you wanted to save space and money; my preference would by far be for a separate amplifier. There is nothing special about most 70 V amplifiers these days. Some have a transformer output, but many forego the transformer and just provide a direct low-impedance output as you would get from any amp. A two-channel amp run in mono or bridged mode is often used for the job. As commsysman said 70 V is the maximum output; nothing happens if you use a less powerful amp (well, the max volume is less, of course). In your diagram wall speakers would probably work as well as ceiling and would be easier to install (and repair if needed), and should cover that area (about 30' x 30" ?).

HTH - Don

Ok, so if the speaker has a transformer built in, or if a transformer is wired to a speaker, the impedance matching has been taken care of. Got that.

The room is about 30x30, I'll have exact dimensions and pictures of the ceiling shortly, but it is a pitched open beam ceiling.

Quote:
Originally Posted by commsysman View Post

If you use a NON-70V amplifier, you could wire 4 speakers up by putting two of them in series with each other on each channel of a stereo amplifier (wire + of one speaker to the - on the other and the other two terminals to the amp).

If you put 2 or more of them parallel with each other, the load impedance will be too low for the amplifier.

That is why a 70V system is preferred. With a 70V system you can wire many speakers in parallel.

Actually, the JBL JRX115 speakers would be better for you. They have more bass and are perfect for what you want to do. Four of them will give you more sound than you can use.

Sweetwater pro audio has them for $224 each, which is about 40% off of list price.

Can I bridge the two channels on a NON 70v amp, wire transformers at each speaker, and run it "70v style"? I'd like to have an amp with extra capacity just in case we need more speakers or if we have a band or something. The Crown XLS 1500 is something I was thinking about using, but I want the flexibility of a 70v installation.

I like what I've read about the JBL speakers (both models) that you've suggested. Sounds like they'll allow for vocals to be clear on music and sports broadcasts which is obviously what we want.
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post #11 of 11 Old 06-10-2013, 03:21 PM
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Did we reference this Rane Note?

Constant-Voltage Audio Distribution Systems:
25, 70.7 & 100 Volts

http://www.rane.com/pdf/ranenotes/Constant_Voltage_Audio_Distribution_Systems.pdf

Kevin
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