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foul_owl 23rd January 2012 07:08 AM

Cheap DIY PA System
 
Alright, here is the band setup. Metal band, two guitar players, each guitar player has a 100 watt tube amp and a full stack, bass is a mesa 400+ in a 4x10 and a 1x15. We play pretty loud, but try to keep things manageable. We have tried turning down, but the problem there is that the drums just don't have the right punch and attack as when louder. At any rate, the volume level is comparable to bands in the same category. So not looking for replies here about turning down or whatever. We all wear earplugs when playing of course.

This PA would be used for 4xvocals + 2xacoustic guitars + violin + cello. Violin, cello and probably 1 or 2 vocals at a time for louder parts, quieter parts would be all 4 vocals + acoustic guitars + violin + cello.

Anyway, onto my question! I am considering a DIY tube PA head, but due to the high number of channels, I think something solid state might be easier. I would like to build an appropriately powerful 8 channel PA head, but more importantly, first I would like to build appropriately powerful speaker cabs.

So first of all, what sort of wattage do you think would be good? I was considering 400 watts total (200 per channel) but of course if you think more is needed, let me know.

For the cab, I was thinking two cabs (would more at lower wattage sound better?), each cab has a horn and 2x15 speakers. Or even better, a cab with just a 15" and a horn.
I was thinking two of these:
Goldwood GW-1538/PA 15" Guitar Speaker 290-394
That gives a rating of 280 watts per cab. Not sure how the power rating works with the crossover and horn involved.

Basically, here are my questions.
1. How much power would you estimate I need for this PA?
2. What sort of cab configuration do you think would sound good? It would be nice to consider budget (less than $100 per cab), midrange ($100-$200 per cab) and high end (more than $200 per cab) Basically, what speakers should I get from parts express haha?
3. How to calculate how much power goes to the horn when using a crossover. My guess would be once you are fully in the horn's frequency range, ALL the power goes to it, but I can't find horns rated high enough...(200 watts per cab at least, right?) It would be nice if the impedance of the cabs was something tube compatible (4,8, or 16)

Anyway, how would you design this PA system?

(For the head, I might just borrow a solid state PA head from a friend, but ideally I would love to have an 8 channel tube preamp/mixer => 300 watt stereo tube power amp powered by 4xKT120s haha (but maybe not enough power?) )

Thanks! :D

Mike Caldwell 29th January 2012 04:02 PM

What your thinking you need and what your really need are worlds apart. I am going to say it you guys need to turn down! The days of full 100 watt guitar stacks are long gone. Yes you may still see them on some big stages but in reality many of them are just for show. Sometimes behind the stack is small combo amp or even no amp at all.
A PA to keep up with what you want and are doing would be at the very least a REAL double 18 cabinet and a solid double 12 x 2 inch top box per side ran tri-amp with about 2000 watts per double 18, 1200 per side for mids and 300 to 400 on the horns.
Stage monitors that would have the guts to stay on top of your stage volume in addition to your ear plugs would be another story.

foul_owl 29th January 2012 11:03 PM

We have full stacks on guitar, but the reason I like full stacks is having more speakers higher up so that I can hear what I am playing. Usually the places we play will have a decent PA for vocals, but no way to mic up cabs, no stage monitors, and no time between sets to mic up anything and balance the levels in the monitors for what people want. The band usually sets their levels, and the sound person sets the vocal levels, and that's that.

Now for practicing, yes we have full stacks, but we don't run master volumes very high. I would say, for example if I was to use someone's 5150, we would run the volume for that at about 11 or 12 oclock, perhaps even lower. But of course that could mean anything in terms of decibel levels. Probably ~115-120 db at where I am standing?

Maybe it would be a better idea if I measured min, max, and approx average decibel levels next band practice? (Ill measure at various places around the room)

You know what I'm saying though about drum attack? For example, if I told my drummer to play softer, the tone of every single drum would not be the same. Personally I don't care about turning down, its just a matter of being heard over the drummer. Although I do like having speakers up in the air behind my head. (bottom cab could just be an empty box)

Haha yeah and I know the walls of stacks are usually fake. We are never planning on playing well funded shows though. (see my comment about the house sound systems at places we play) Usually it's a DIY warehouse, and there may or may not even be a sound guy (thus the need for our own PA haha although we would rather not bring a PA on tour, but it's better than playing a show without one!)

foul_owl 30th January 2012 06:51 AM

Alright, measured decibel levels at practice. Measured where members were standing, at ear level. Looks like it is pretty evenly around 112-115 decibels that reaches our ears.

indianajo 31st January 2012 03:54 PM

Gee, I bet your vocals are muddy and inaudible like the other amateur bands I've heard. You've got to understand you're performing for the audience, not yourselves. You have too much music on the stage for yourselves. Jeff Beck last spring didn't have any stacks behind him, but he had about 10000 watts to the sides and in front of the stage. All the big watts went into the bass, he wasn't blasting my eardrums with treble. But I could understand the words when the girl bass player sang.
And if the drummer is not loud enough, put him up front and blow off the mikes. When I played a drum in high school you could hear me from the press box at the top back of the stadium. Of course our bass drum was 36", not one of these wimpy drums the bar bands play. When 24 of us played a drum hit you could hear the echo bounce off the freeway retaining wall a mile away 2 seconds later. If your actually going to buy the 4 or 5 drum mikes it takes to do it right, make sure your power is 1.3kw peak or more. Drum and piano take tons of power, much more than mushy guitar.
I don't understand the problems of playing in bars, but I understand cheap PA gear. I got a PV1.3K for $55 and have put $120 in parts in it. By the time I convert the stupid speaker crowbar PCB burner into a O.T. meltdown detector and speaker disconnect relay, parts will be $150. If I were running a band on a shoe string now, I'd get a pair of burned out Peavey SP4's, replace the speakers myself, and set them to the side of the stage. Else a pair of SP2's on 6' stands and a 218 subwoofer, but that takes three channels of amp and takes longer to set up. I'd buy a burned up Peavey or crown amp of 800-2000 watts and repair it. All new electrolytic caps in it, speaker disconnect relay if is is not a modern CS800s or x, plus whatever else is toasted, Dual banana jack or nutrix speaker plugs, no 1/4 phone jacks. The only 1/4 phone jacks you want on the stage are the guitar inputs: no high powered 1/4 plugs to burn out your amp inputs. Then I would not buy or power stage monitors. I would buy an FM radio transmitter from a hobby supplier, and wear FM radios and Plantronics telephone gear in one ear for the monitor feed. That is if you can afford a sound man (woman? any girlfriends, siblings? parents?) to set the balance after you start. I'd use cabled microphones. There are lots of cheap radio mikes on Craigslist, which probably means they don't work well enough anymore. The one at church sure doesn't work. Probably just bad nicad batteries, but diy radio transmitter repair is not legal.

foul_owl 1st February 2012 03:45 AM

Quote:

Originally Posted by indianajo (Post 2885647)
Gee, I bet your vocals are muddy and inaudible like the other amateur bands I've heard.

Depends greatly on the PA being used at the venue. Thus my question.

Vocals are crust punk style but this isn't a forum for debating which genre of music is better...

Quote:

Originally Posted by indianajo (Post 2885647)
You've got to understand you're performing for the audience, not yourselves.

No ****.

Quote:

Originally Posted by indianajo (Post 2885647)
You have too much music on the stage for yourselves.

Too much music? Do you mean too many instruments or levels set too high? Every other metal band I have seen perform in underground venues sounds great (or can sound great!) at similar levels, but like I said, it depends greatly on the PA they are using. Thus, I would like to build some PA speaker cabs that would work for what I want, using the speakers found on partsexpress, for the best price for the sound given my approximate budget. That is the goal here.

Quote:

Originally Posted by indianajo (Post 2885647)
And if the drummer is not loud enough, put him up front and blow off the mikes.

The drummer is plenty loud enough, thus the need for big guitar and bass amps. And like I said before, if the drummer plays quieter, you don't get the same sound out of the drums, and again, this isn't a forum for debating genre preference, it's a forum for building audio projects.

I don't know how common it is to find the burned out speakers you mentioned, but I wouldn't mind building from new parts, even though it might cost a little more.

Thanks for the help! :cheers:

hollbrow 1st February 2012 02:10 PM

If I were in your position I'd be looking for some name brand 'bass bins' with 18" drivers in them that I could recone or replace the drivers in before I started building something from scratch to put in service under the conditions you describe. You're looking for spl & bottom end impact in the 30-40 Hz range for the genre of music you play- You need a TON of bottom end and vocals to keep up with those guitar stacks.
Unless you really know what you are doing you are not gonna get good results building regular boxes. This is one of those deals where there ain't a real cheap way out of your delimma. There are some really good designs out there for DIY bass bins- but the investment in tools and materials (not to mention the skills) to do a professional job building them is pretty expensive.

hollbrow 1st February 2012 02:40 PM

I just re-read the OP- if you are not gonna run the bass and drums through the PA then indianjoes post above is spot on. I'd be looking for some cabinets with a 15 & horn in them- probably 4 cabinets (two on each side) and maybe an 18" sub box ought to do what you need. Peavey, Electrovoice, JBL etc.. I recently picked up a pair of older EV cabinets like that for $400 on craigslist- they are in great shape and they really put out. QSC amps are decent and can be found for sale (craislist etc..) for reasonable prices.

indianajo 1st February 2012 02:53 PM

Getting a speaker right is a matter of design & testing, all of which are expensive & take time. On the other hand speaker repair is not too hard for an amateur. Buy some drivers, replace some capacitors, it's easy. We have a musician's resale shop near the Peavey dealer that sells old band gear. They buy it working for half of what they sell it for, gives me some sort of floor on price idea. Craigslist is your friend, kiji in canada and more so searchtempest.com which will search all the CL catagories (musical instruments, electronics, free, furniture) for the phrase you put in within a distance you choose. Or get some part numbers and post your own ad, looking for blown up gear. The box is what you want, new drivers are a commodity. (See tubesandmore.com for example) I may have overemphasized horns in my previous post, I am a keyboard player and need horns. Guitar-bass-vocal bands with no drums on the PA don't need anything smaller than a 12" speaker, with lots of 15" and 18" speakers for the guitars and bass. I think these should be to the side and front of the stage for the audience. I think the band blend should be in your ear, the way the pros are doing it now. But you don't need all that business band radio stuff with wireless mikes for a non-pro show.
Reducing the sound level on stage is important to proper miking of the vocal. However distorted the vocalist is sounding, you don't want the drum and guitars feeding in there. That is why I think stacks behind the band are a visual prop, not proper sound equipment. That is why I suggest putting the drummer away from the microphones. Electric guitars and bass are not an actual problem, the stacks are.
All you need for level setting is someone on the audience wearing a mike and a FM radio transmitter, the mixer board doesn't have to be out there. The delay from an audience mike can drive some musicians nuts, but somebody in the band could probably listen in and ride the levels. I'm thinking of Ron Pizzarra's band, where the keyboard player is obviously changing the mix during and between songs on a mixer to her side.
As far as power, a blown up 1300 watt amplifier costs about the same as a blown up 200 w amplifier. You'll pay more in output transistors the higher the watts, about $8 each pair. A 200w amp has about 4 transistors, this PV 1.3k has 10 O.T.s, and 4 driver Ts. New rail caps for a 1.3k are about $160 as designed (4 <70 mm 10000 uf) or $48 fooling around the way I do it (8 4700 uf). Rail caps need to be under 15 years (one failed on this amp at 14 years) or 2000 hours. I've looked at some schematics on solid state. I understand some Peavey and Crown stuff. I don't understand the grounding scheme in QSC. Behringer doesn't give away schematics and part number crosses, so they are on my **** list. Stay away from dead amps with switcher power supplies in the beginning, they are for experts. It is hard enough making a transformer amp work in the upper power ranges. Read about light bulb boxes and debug techniques on solid state, saves a bag full of blown (second time) output transistors.
Bottom line, I think repair is easier than scratch building. But I'm not working, so I have an hour or two a day to play with the internet. I love it. Scored a SM27 condenser mike last week for $80, been looking for something that good for my piano for 42 years.

techbiker 1st February 2012 04:51 PM

I just spent 25 minutes typing up a reply and I was logged out before I could post it... :(

Needless to say, this is what I was going to say in a nutshell:

1. Pick an amp to repair carefully! My Crown Comtech 400 has 16 output transistors (as I remember) and 8 driver transistors. Each output transistor costs $8!

2. Acoustic balancing is incredibly important! I've heard tons of bands where the vocalists have been overpowered by tons of guitar amp wattage! This really kills the experience and in my opinion makes the difference between a small-time band and a big-time band. If you have to, have a member of your group sit in the audience and see how your music sounds from their perspective.

Good luck!


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