Amp/speaker matching
 

Hi All

Our bands practice room PA Amp is a prosound 1600 by maplin
Heres its Spec:
4Ω stereo: 2 x 500Wrms 8Ω stereo: 2 x 250Wrms

For a long time weve ran two phonic 250w rms 8ohm 3 way speakers with it- but the range of them ain't great and our bass player has blown one of the 15" drivers- we're gonna replace this and add another pair and run them in series.

I know we'd be better with a crossover etc. but moneys too tight.

I've seen some cheap speakers that have a good range and 15" drivers- but they are 400w RMS at 8 ohms- I'm guessing that we are we limited to adding another two 250w rms at 8 ohms- but I was hoping one of you knowledgable chaps might be able to confirm wether this is the case?

Run them in parallel; the amp is then loaded by four ohms, which it's happy with, and you've got twice as much power (not the same thing as twice as loud, but you can spread the sound out better). Series= higher impedance, and since a crossed-over multiway system can't be trusted to have a constant impedance, probably weird frequency response. But parallel is the obvious way to wire it, anyway.

So, your 400 watt speakers are not being driven to their limits; they'll get the 250 watts available, and might even survive the speakerivore bass player.

Thanks very much for your advice- running them in parrallel means I simply go out of the first speaker into the second one (on both sides)?
(I thought i was pretty bright until i tried to learn about speaker matching-it doesn't make any sense to me at all!)- So just to be sure -I should clarify that I want to use one 250W RMS and one 400W RMS on the right hand channel and the same again on the left channel-all these speakers are 8ohms- though i understand that doubling them up effectively reduces the ohms to 4 ohms-
So i'd be running 650wrms speakers at 4 ohms through each channel even though the amp spec. is max at 500wrms at 4ohms- and this won't hurt the amp?

(aren't ALL bass players speakerivores!?)

Exactly that. A 400 watt loudspeaker doesn't oblige the amp to give it four hundred watts; that's what it can survive as a maximum. So the amp runs a bit hotter and gives maximum power, and each of the speakers grabs 250 watts of this, and everyone's happy. That's transistor amps for you (tubes are a little more complex).

As regards bass players, yes, they do tend that way. Something to do with needing a 250 watt bass amp to sound as loud as 30 watts of guitar, I think.

Thanks again for confirming this Chris-don't know what I'd do without forumns like this- and generous people like yourself manning them!!


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Hi,

You'll probably be better off adding bass only cabinets to an existing pair
of PA speakers, pairs of PA speakers can have interference problems.

Ideally a pair of 500W 4 ohm sub cabinets with built in crossover, and
experimenting with putting a large bipolar capacitor * in series with
the main speakers when used with the sub cabinets (if they are
not built into the sub cabinet).

rgds, sreten.

* can be a number of capacitors in parallel.

Thanks screten, but a lack of knowledge/funds mean we're trying to keep things simple- can we not just add a capacitor around the cabling between the linked cabs to reduce interference?-

Sorry-I meant to say can we put magnets around the cables to reduce interference- like they do with computer leads- :ferrite chokes- (you may have gathered by now I know little about this subject!!)

That's not the kind of interference sreten was talking about. Unless multiple speakers are designed to be used together in groups, don't. The sound will interfere with one another if the coverage patterns don't line up over a wide band. If ferrite beads can fix that everyone's job would be a whole lot easier.

Ah I see- that does make sense-THANKS FOR POINTING THAT OUT.

In that case we'll probably go for using just the cheap wider range 2 x 400wrms 8ohms- the amp may run a bit hot but we should be okay (i'm a bit cynical that these claim to have a frequency response as low as 30hertz!?):
AUNA PW-1522 DJ PA PASSIVE SPEAKER 800W 3 WAY 15" BASS PARTY MOBILE DISCO NEW 4260130928339 | eBay

Though I am now looking at a low cost crossover and a single second hand powered bass bin as an option:-Stereo signal from mixer into 2 way stereo crossover which i'm assuming will split the stereo signal into four -two of which can go into our existing amp/speAker set up and the other two can go into the one powered bass cab (that bit doesn't make sense).

The sort of money we're after paying will probably mean laughable quality to you chaps but heres a links to the stuff I'm now looking at:

600 WATT DISCO PA ACTIVE SPEAKER SUB CABINET | eBay

New Citronic CX23 / CX 23 2/3 Way Active 19" Rack Mountable Crossover 170.929 | eBay