A question on Bridged Mono

[dar1us]

Ok, i warn you, i am about as n00b as they come, this is probably in completely the wrong place (not a physics student, but an English one)

We do a mobile disco, at the moment, i got 2x700 (1400max) RMS Peavy HiSis4 speakers (1980 something i reckon), they are beasts, but we wanted a little more sound. I got a McGregor amp that delivers 625watts RMS per channel and a Carlsbro PowerLine 2000 - this is a 2000 watt RMS amp, 1000 watt RMS per channel (2000 max), at 4ohms.

Firstly, i swear that the McGregor amp (1250watt) is louder than the 2000watt Carlsbro one with the Peavy HiSys4's (700watt), why might this be, or am I just stupid?!

How can I get more power out of the thing, "Bridged Mono" would give me 2400watts RMS, can i run both speakers off this to deliver 1200watt per speaker if i run them in parallel? I know the idea is to run one speaker at 2400watt, but can I run it at 2400 watt over 2 (disregard using these with the peavy ones, more speakers are on the way - is it possible?). What can I do, stereo isn't required because it is just mobile disco, it isn't that important, loudness is all that matters.

i searched the forum and all i can find is very technical threads that confuse me


harrison

[Stocker]

The problem is that the explanation needs to be at least a little technical in order to make sense.

Things vitally important to consider:
*Internal circuitry of the amp: if already bridged inside, then no more bridging outside. What about overcurrent protection / low impedance ratings? An amp stable into 4 ohms but not 2 will not be bridgeable into 4 ohms.
*So you need to consider the type of speaker impedance you want to be dealing with as well. Paralleled 8 ohm speakers are 4 ohms. A systematic approach is neccessary.

Oh, and one amp may be louder than another for various reasons, not all of them physical fact, but especially either over or under rating by the manufacturer or the ability to drive the load you give them.

[anatech]

Don't forget that 1200W vs 2400W is only a 3dB difference. Just noticable. In other words, not a big difference and not worth while in most cases. Also remember that all that power has to come out of the AC outlet. In North America, that means 1800W at best, less losses as heat, if that's the only amp on that circuit. 2400W is starting to look shakey here.
-Chris

[psychosteve]

input sensitivity may be an issue, if your running a single mixer, the two amps may need different input levels to take them to max output, i had this with a peavey CL 1000 that sounded quieter than my old carlsbro 400.

it is very speaker dependent as well, what are the eficiency ratings of the speakers? there is a big difference between 80db and 95db speakers.

hope this is of use, see you soon, steve.. ..

[dar1us]

In the UK, 13A at 240volts, 3120 watts max, so there is something to play with. Bigger amps require 16amp plugs (they are the fat and phat ones found in theatres...). That level of technicality was bang on, got everything there, that 8ohm in parallel equaling 4 ohm helps loads. That means that, well our new speakers are 600watt sub (all RMS values) and 400 three-way, they are 8ohms each, that will total 1000watts max at 4ohms right, or are there more sums to do?


harrison

[dar1us]

Also, sorry for the addition, but can I run a multimeter across my amp to see what wattage is actually occuring? Could any multimeter handle it, or is there a better way of seeing, or will doing anything like that blow it all up straight away?


harrison

[Stocker]

Touching the output leads of the amplifier together will blow some stuff up, but...

For one sub in with one 3-way that are nominally 8 ohms each, you should end up with 4 ohms.

But

What about a crossover?

Not a problem for a bandpass sub, sealed and vented need at least a (huge) choke in there. Otherwise it may sound like sh..

You can run a voltmeter across the leads and see the instantaneous voltage...better still, one that has a max-hold feature. volts/ohms=amps, amps*volts=watts. indirect but it gives you an idea. If you want to do a little customizing and some math ahead of time and all you want is an ooh-ahh meter, take a cheap analog voltmeter / panel meter, make a custom faceplate showing watts instead of volts... Precision measurement is possible, but a bit more complicated.

Here's a one for you: Speakers don't suck watts. They are a load for something that makes watts for them. A 600W speaker will blow up with something more than 600W. You will hear a quite-loud signal with 5W going to it, which out of an amplifier would be single-digits of volts to a 4-ohm speaker The amplifier will usually put out a variable voltage and the speaker dictates the current drawn, thus the watts consumed. A 1000W amp will also play at 1W, with a low-enough input signal.

You could possibly blow out the 400W speaker with 1000W to the set, while the sub was all happy. You could also be underutilizing your amplifier and not realize it because of the tremendous racket it's making. But you could be fine. Best bet is put a 400W speaker to a 400W amp and you will likely underutilize them both and be happy. Or better still, get some super-efficient speakers.

Which reminds me... if you parallel the sub and main speaker, and the sub is not as-or more-efficient than the other, it will have weak bass, which I think you DON'T want as a PA/DJ setup! With multiple amps, you can adjust the levels easily.

[anatech]

Hi dar1us,
Yes you can measure the voltage across the outputs and figure out the wattage from that. Be aware that most multimeters are wildly inaccurate much above 60 Hz. All speakers change their impedance as the voicecoils heat up. The resistance varies with frequency ... a lot. You might consider a dummy load.
-Chris