Question how to PA setup with Subs & crossover & multiple amps

  • Thread starter Thread starter Trainwrecked
  • Start date Start date
T

Trainwrecked

New member
I'm not a sound engineer & don't know one unfortunately. Bigger gear setups are greek to me. I've only done small bedroom stuff with a small amp & speakers. I've been asked to do a party for people who know less about music/gear than me.

There is a power conditioner. I figure this goes first & TT/CD & mixer plug in here.
I have to set up 4x (2way) mains and 2x subs. With these are a bunch of single 1/4 phone to phone cables that match speakers & the amps.
There are 3 amplifiers (smallest one is 1000 W, other 2 are 2500 W, all three have bridged, mono, stereo switching)
That's the gear supplied.

I don't know what rack gear other than a crossover will be needed or what kind of crossover to get (or even how to do the setup) Is it wired in after the mixer, and then feeds to the amps?

I have no clue what I'm doing for setup, but I can lay down a mix as smooth as Betty Crocker :4theloveofgod:please advise...
 
Your subs and your main boxes - what are the power ratings for each into what load?

i.e. the sub might say something like 600RMS@8Ω

The numbers you quote on the amps seem inflated, are they the Peak Program Power, can you find out the RMS values.

you will need a crossover and comes after the mixer and before the amps as you guessed.

Choose your crossover frequency to advantage both the top boxes and the subs.

The low output of the crossover goes to the two large amps, which are probably set in bridge mode and each will feed one sub.

The high output of the crossover goes to the inputs on the small amp, with the outputs being sent to a pair of boxes each. this can be done from the amp itself or by connecting cables between the two speaker boxes on each side.

dubSubMultHi.png
 
Wow, awesome diagram. Nice!

I looked at the speakers and the subs say 8 Ohms at 400 Watts. The mains just say 8 Ohms normal impedence.

The small amp (on the back) reads:
700 W 8ohms Channel
1200 W 4 ohms Channel
2400 W 8 ohms Bridged

*I was told that 8 ohms is one channel normal output for one speaker, and linking 2 together makes it 4 ohms. True?

The big audio amps just say 3400 W Max on the back.

Thank you for the setup instructions! What kind of crossover would you recommend btw?
 
Ok, so now that you have given me some additional info, I would make the following changes to my advice:

  1. hook up each speaker box to a separate channel of each amp - 1 side of each amp connects to 1 speaker box.
  2. connect the small power amp to the subs - they seem to be matched properly.
  3. the larger power amps probably run at 850WRMS, so shouldn't be a problem with main speakers.
  4. don't push the amps too hard as they could burn out your speakers - use the level controls on the amp and set them to about 1 o'clock.

Updated image

dubSubMultHiB.png


When you combine speakers it depends entirely on the way you wire them together what the resulting impedance will be:
  • If you wire in parallel then it is equal to the sum of each speakers impedance divided by 2
  • If you wire in series then it is equal to the sum of each speakers impedance.
  • There are other ways to wire them togehter but you won't have need to do so for this job.

As for a crossover get what you can afford - unless you are going to spend more than a grand they're all much of a muchness.
 
Thank you for the reply!
hm, I obviously need to learn more about speaker impedance. I'll do as you suggested because I'm not sure how to hook them up together unless I was using the 1/4 phone jacks on the back that read "to ext speaker" - I'm not sure what way it came wired from the factory. Is there a standard?

Found a sweet deal on a crossover. It's made by Ashly, I tried to post a picture but apparently you need 20 posts to link pictures - sorry
 

Attachments

  • 750-XR2001_img_rear.webp
    750-XR2001_img_rear.webp
    50.6 KB · Views: 5,545
On wiring of speaker boxes for extension speakers, generally the sockets are wired in parallel - hot to hot, ground to ground.

On speaker impedance - we use a nominal value to describe it, but it varies in a complex relationship to frequency, as the driver is a complex ac circuit involving both resistance and reactance - it is a coil of wire suspended in a magnetic field that has an ac voltage applied to it.

To simplify impedance calculations we limit ourselves to the nominal value and treat it as though it were a dc resistance and the apply standard electronics theory for combining resistances in series or parallel or combinations thereof.

Is this your x-over

xr1001-f.jpg


or this

xr2001-f.jpg

or this

xr4001-f.jpg
 
it is the 2nd one down, the 2001. I was surprised to see it loaded the back panel picture anyway and not the front!
 
Hmmm....


yeah, the 2001 would have been a deal as it is no longer manufactured, according to Ashly's site. Interesting layout and selling point of it being a 4 channel 2-way x-over rather than a stereo 3 way. Good luck with the party.
 
Gig went great! Thanks for the help bandcoach!
Apparently sounded good enough to land another gig. I've picked up some books on sound but none of them really get into PA set up like you described with your diagrams. I was hoping there would be one that would detail similar situations that I might find myself in as the above example. Mismatched amps and speakers etc. Wish our local community college had a course in this...
 
I just got the Sound Reinforcement book. Wow, lot's of good stuff in here!
In case you're curious about my next gig set-up, here's some more info.

I'll be using the same Crossover (Ashly) as listed above and the following speakers and amps.

Amp 1 is a Crest Pro 5200, Rated power 2x8 ohms 290W per channel, 2x4 ohms 525 W per channel, 2x2 ohms 850W per channel. Bridge rated 8 ohms 1050 W, 4 ohm bridged 1700W.

Amp 2 Yorkville Audiopro 3000, Continuous average 2x8 ohms 475W, 2x4 ohms 750W, 2x2 ohms 1200W. Bridged continuous average 16 ohms 925W, 8 ohms 1500W, 4 ohms 2400W.

Amp 3 Carvin DCM 2570. RMS continuous 2x8 ohm 700W, 2x4 ohm 1200W, 2x2 ohm 1250W. Bridged RMS 8 ohm 2400W, 4 ohm 2500W.

Speakers, 4x Mains. JBL SR4722. 8 ohm nominal impedance, 600W

Subs, 2x. EV 18" Eliminator i series. 8 ohm nominal impedance, 400W

Would there be any advantage to bridging one of the amps for the subs and just patching them together in parallel? Or would it make more sense to run them off their own channel in stereo?
I'm thinking the Yorkville (2x8 ohms 475W) is a good match for the subs if ran per channel in stereo and the Carvin (2x8 ohm 700W) is a good match for one set of mains (maybe both run in parallel) question is, how to utilize the Crest (Amp 1) ?

Thanks!
 
Yeah the Yamaha book is great, first bought when it was published, loaned it out. Bought a second copy a few years ago, when my kids were old enough to start learning about PA systems - I own a full rig and don't want it damaged while they are experimenting.

Bridge the Crest and run both of the subs off of that in parallel and keep it under control of it will smell like a bomb went off (and probably sound like it as well when the speakers and the amp blow). Use the other two amps to run your main speakers, one per channel.

Alternatively, get some smaller speakers to use as DJ foldback run by the Crest, then run the subs 1 per channel on the Yorkville and pair the mains two per side on the Carvin in parallel

Good luck.
 
Bandcoach

Liked your posts and hope you could help some?
I have a:
Bbe Max3 2way stereo/3way mono sonic maximizer.
Pyle pt3300 amp.
Pyle pqa 5100 amp.
Harbinger hx 15.2 pair for pt3300. 600 rms/4ohms.
Rockville rsg 15.2 pair for pqa 5100 amp. 1500rms/4ohms.

I currently have ch1 low to pt, hi to pqa.
ch2 low to pqa, hi to pt.
My speaker cabinets all have high, mid, low speakers. Therefore, I don't want to make one amp for low, & the other for high, or else one set of speakers plays only low, while the other set is just high.
I am also daisy-chaining the speakers.
Is there a better way to make this connection better, which I believe so.
Thank you.
 
Last edited by a moderator:
short of buying specifically low mid and high cabinets (separate cabinets for separate freq ranges), and an extra amplifier, no

a possible alternative is to break into the wiring for the individual cabinets and separate out the different speakers to their own inputs and you would still need to buy another amplifier. With this approach, you would need to find a way to bypass the internal crossover so that it did not get back emf from the individual speakers, causing it to burn out or worse adversely interact with the other speakers connected - probably some form of switching matrix would work but seems more effort than the end result warrants - this is the problem of all in one boxes they really do not accommodate the idea of individual amplifiers driving each speaker in the cabinet
 
There it's no alternative way of linking the crossover to the amps, so I can make this work? Can I put both set of speakers, daisy-chained, on the pqa 5100 amp?
However, I still think I would lose either the low, or mid & highs. Depending on what I put to the amp.
 
Last edited:
there is no way to use the external active crossover at this time
 
When I go from high and low of the xover separate channels to one amp & high and low to the other amp. Or high and low to separate amps it still will work using the xover freq control.
Just trying to figure out any better solutions.
 
Already given you the two best pathways -

get new speakers and a new amplifier to go with what you already have or

rewire your boxes (with a switching matrix maybe) so that each driver can be accessed by the relevant amplifier being driven buy the crossover

any other path has your boxes internal crossover still interpreting the input signal and adjusting what goes where accordingly.

even if you just it as a stereo 2-way crossover - you will lose the mids and highs in one box and the lows in the other box by trying this approach
 
Not familiar with what you refer to as a "switching matrix."
Basically a switch to by-pass the built in crossover, & separate the three sets of speakers?
 
You must log in or register to reply here.
Back
Top