Some live sound help

[matt99camero]

I'm getting a pair of JBL dual 15in cabs pretty cheap, $150 for the set. I'm not exactly sure which line these are but they look like the TR line, so that would put them somewhere in the range on 500w rms and 1000w peak. So now I guess I'm gonna have to get a power amp and better mixer. I'm looking at getting a Beringer UB2222fx-pro since they are pretty cheap. But how much power would sufice for those speakers. Would one 1000w power amp do? I'm pretty much illiterate when it comes to live sound stuff so I want to get a little knowledge on this.

 

[jeremy]

Re: Some live sound help

find out what impedance those cabs are and what the power rating is. if its 4 ohms and 500w then youll want to get an amp that can give you at least 500w at 4 ohms per side

 

[TwilightOdyssey]

Re: Some live sound help

I would say 500-1000W will be okay for those cabs ...

 

[Thames]

Re: Some live sound help

Behringer PA products are great units for the price.

 

[matt99camero]

Re: Some live sound help

When we played the other night one of the other bands let us use their brand new mixer that I talked about above. I liked the look of it and it's pretty cheap. I'm not really in a giging band right now but we play once or twice a semester and for the price of those speakers I couldn't pass them up. I plan on doing alot more once I get out of school so I'm sure they will come in handy in the future.

 

[Kent S.]

Re: Some live sound help

Remember, peak is roughly 2.5 times the continuous power rating, so if the cab is rated at 1kW peak, and you are running an amp that's rated at continuous power of say 500W, and you hit a loud peak that clips the power amp, you'll be asking that cab to handle about 1.5kW instead of the 1kW they were designed to handle. Of course that's one cab, and we must assume that the two cabs are running in parallel, which would cut the impedance in half with two of the same cabs, don't know what the amp is rated at impedance wise either at this point.
Do yourself a favour for the future (and this touches ALL aspects live, recording, etc.) ... Invest $40 and get the Yamaha Sound Reinforcement Manual ... available from Hal Leonard Publishing ... you'll thank me later.
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No, ... you really will. :cool3:

 

[skyydogg01]

Re: Some live sound help

I've read on the peavey site that it's good to get amps that are TWICE the wattage that your speakers can handle ... but run them at half. it'll give you more headroom (no clipping) which will give you better sound. It makes perfect sense if ya think about it.

 

[matt99camero]

Re: Some live sound help

Thats kinda what I was thinking, get something with more power than I need and just keep it turned down where it's not overpowering the speakers. I'm surely going to get more pa stuff in the future and I'll already have the power there if I need it.

 

[matt99camero]

Re: Some live sound help

Well I just went and picked up the speakers. They are a bit more beat up than I first thought but they work fine and I guess that's all that matters, they just need a little TLC. They are the TR series, which I read is JBL's lowest line but still a good deal at $150 for both. They are 4ohm with a continous power rating of 450w and peak power at 1800w. So I'm guessing putting around 600w to each would be ok?

 

[matt99camero]

Re: Some live sound help

Ok so say I get that Behringer mixer and run out from that to the power amp. Then run one speaker to Ch. A & one to Ch.B, that would split the ohms in half, so since the speakers are 4ohm they would be running in 2ohm right? So I'd need to look at how much power an amp puts at at 2ohms.

If that is the case I found a Nady for $300 that is 2x800w@2ohms and a Behringer for the same price that is 2x700w@2ohms.

I'm not sure how bridging the speakers works but am I right about the other stuff? Any other suggestions about what to buy. I know that I'll need monitors and a small power amp to run those but right now I'm focusing on the mains since that's what I have at the moment. Thanks so much for any help.

 

[LesStrat]

Re: Some live sound help

The ohm load does not split when you plug into separate channels. Daisy-chaining does that. To reiterate, when you plug the cabs into separate channels, they remain at 4 ohms.

Bridging is in the amp, not the speakers. It is one way to maximize power output, but it runs the cabs in mono (same signal to both cabs). This is not necessarily a bad thing. Many people do it (that's why it is a setup option). There is also parallel mono.

Keep asking questions and get satisfactory answers before you invest, bro. You're on the right track. But get good info first.

Sorry I'm not more informative. It's been awhile since I had to deal directly with PA equipment setups.

 

[matt99camero]

Re: Some live sound help

Here are some pics after I gave them a good shine

There are two places the wood is a little cracked but I don't thing it affects it. The crack in the second pic looks like it has already been sealed with something and I guess I'll just get some wood glue and patch the one in the third pic.

 

[Kent S.]

Re: Some live sound help

I've read on the peavey site that it's good to get amps that are TWICE the wattage that your speakers can handle ... but run them at half. It'll give you more headroom (no clipping) which will give you better sound. It makes perfect sense if ya think about it.

That idea originates in the hi-fi world (quoted no less from the Yamaha sound manual), problem is that if the program clips the amp on a musical peak, your still asking your speaker to handle more power than it's peak is capable of without damage. Now if your speakers are say rated at 400watts program and 1500 watts peak, then you don't want an amp that will delver more than 1500watts when it clips.
Yes you want enough power to have the headroom that you need (about 12dB for example), so that you don't clip the amp ... BUT your drivers must be able to stand the power produced if they do.
You can do the above if you want; however you need limiting to ensure that the input voltage to the amp will not exceed the maximum power output that the speakers will handle. Get a bigger power amp ... sure ... But those speaker have to be overated for it.
The best thing to do, is go spend sometime at the local shop with the head sound reinforcement guy ... not guitar joe, the guitar sales guy ... there is to much heresay on this topic ... go to a pro and ask .... then go by the book.

 

[Kent S.]

Re: Some live sound help

Well I just went and picked up the speakers. They are a bit more beat up than I first thought but they work fine and I guess that's all that matters, they just need a little TLC. They are the TR series, which I read is JBL's lowest line but still a good deal at $150 for both. They are 4ohm with a continous power rating of 450w and peak power at 1800w. So I'm guessing putting around 600w to each would be ok?

Continous is a worst cases scenario rating ... program is what you want to look for ... if all three (continous, program ,and peak) are not given, and if unclear as to which the manufacturer actually means, again go by the peak rating, and ball park that a power amp peak is roughly 2.5 times the program rating (or incorrect as it is named *RMS Power*), make sure each your cabinets can take that power level. Going from the above ... program would probably run about 720watts, so if continous is in fact continous, rather than program ... 600W should suit you fine. Don't know if you are running independent channels (some powered boards do),or mono bridging (more common with stand alone amps).

 

[Kent S.]

Re: Some live sound help

Ok so say I get that Behringer mixer and run out from that to the power amp. Then run one speaker to Ch. A & one to Ch.B, that would split the ohms in half, so since the speakers are 4ohm they would be running in 2ohm right? So I'd need to look at how much power an amp puts at at 2ohms.

Nope ... see LesStrat's comments ...

I'm not sure how bridging the speakers works but am I right about the other stuff?

If you connect speakers to a brdiged amp, or bridge the amp incorrectly ...
It's gone, might take the speakers with it also (some newer desgns might just have a switch incorporated that allows you to keep the conections the same while doing it all internally)... Basically a bridged amp uses one channel to drive the positive half of the wave, and the other to drive the negative half, like a push/pull guitar amp ... you get more power that way ...See your local SR Pro, and BUY the book ...

Any other suggestions about what to buy. I know that I'll need monitors and a small power amp to run those but right now I'm focusing on the mains since that's what I have at the moment. Thanks so much for any help.

I'll say it for the last time, get off the internet, and haul your butt down to the local SR pro guy ... tell him the size of the venues you play or plan on playing, what you got, and ask what you need, and how the hook the stuff up. ... Then once again ... go buy the book, or another similar book.

 

[matt99camero]

Re: Some live sound help

Ok, ok I get it, get my arse out of here are go ask somebody. Well the only place I know of that even really deals in pa stuff close to me is Guitar Center and that's 45mins away. We don't even have a guitar shop here in town unless you consider the crappy pawn shop place and I'll never go back there because of what they did to my tele. Hmm there has got to be sombody around here that knows about that stuff. Maybe I can talk my mom in adding that book to my Christmas list or for my B-day. Well actually I have my Mom's credit card # and she told me to just charge about $250 worth of what I wanted. :firedevil

 

[Kent S.]

Re: Some live sound help

Ok, ok I get it, get my arse out of here are go ask somebody. Well the only place I know of that even really deals in pa stuff close to me is Guitar Center and that's 45mins away. We don't even have a guitar shop here in town unless you consider the crappy pawn shop place and I'll never go back there because of what they did to my tele. Hmm there has got to be sombody around here that knows about that stuff. Maybe I can talk my mom in adding that book to my Christmas list or for my B-day. Well actually I have my Mom's credit card # and she told me to just charge about $250 worth of what I wanted. :firedevil

Yeah, that's the other side of the coin ... I'd call GC or whereever and ask to speak to someone in that department ... doesn't cost anything ... actually there is another book as well ... much simpler, but still very good, and I think it costs a bit less too ...it's a HL publication as well. I'll post it in a minute, let me dig it up.

 

[Kent S.]

Re: Some live sound help

Okay Matt, the first book that I spoke of ...
Yamaha Sound Reinforcement Handbook ... By Gary Davis and Ralph Jones
# HL 00500964 ... was $34.95

Not sure if that's the current price or not, mine's a second edition.
And the second (but this first as i think this will do you, it ddoesn't delve into the math and detail like the other) ...

Sound Check ... The basics of sound and sound systems ... by Tony Moscal
# HL 00330118 ... was $14.95.

Both of those are really good, the math might scare you in the YSRH at first, but they just want to tell you everything ... But htere are some cool things in there regarding recording and broadcast stuff, and even a bit of history when applicable. Both books are really good. Get the second one first, then if you want delve deeper into it.

 

[matt99camero]

Re: Some live sound help

Well I had to get some other stuff at musicians friend so I went ahead and picked up that book called Sound Check for $11.99