Hello there folks
Sorry this might be a bit of a newbie question but im planning on building a sound system for outdoor use with a fairly limited budget (£500 - £700 ish). The system i was hoping to build would comprise of a bass bin (MBP-46) and two, two way pa speakers (midtops).
My question is; can i wire 3 8 Ohm drivers into one amp?
can i maybe wire the midtops in parallel in one channel and the 8ohm bass driver into another or would that present a mismatch in what load the amp see's? (as i said im not very clued up)
or would there be a way of wiring the 3 drivers together so they would be on the same circuit or would that just be impossible?
Or am i just going to have to bite the bullit and buy 2 8 ohm bass drivers (2 bins) and buy an amp for them and then have another amp for the midtops (bi-amping). my problem is that the budget has to also go on; shelter, lighting, transport, tools, ect.
Any advice or ideas would be greatfully welcomed as im at a loss to keep costs down and make this work.
Sorry this might be a bit of a newbie question but im planning on building a sound system for outdoor use with a fairly limited budget (£500 - £700 ish). The system i was hoping to build would comprise of a bass bin (MBP-46) and two, two way pa speakers (midtops).
My question is; can i wire 3 8 Ohm drivers into one amp?
can i maybe wire the midtops in parallel in one channel and the 8ohm bass driver into another or would that present a mismatch in what load the amp see's? (as i said im not very clued up)
or would there be a way of wiring the 3 drivers together so they would be on the same circuit or would that just be impossible?
Or am i just going to have to bite the bullit and buy 2 8 ohm bass drivers (2 bins) and buy an amp for them and then have another amp for the midtops (bi-amping). my problem is that the budget has to also go on; shelter, lighting, transport, tools, ect.
Any advice or ideas would be greatfully welcomed as im at a loss to keep costs down and make this work.
and capability of driving 4ohms is NOT the same as stable into a 4r0 test load.
A 4ohms capable amplifier should be able to drive a 2r0 test load with only a small drop in output voltage (small drop <1dBV and better if the drop is < 0.6dBV) and preferably also able to drive a 1r3 test load for a few seconds.
Thank you JMF, so as long as the amp can run minimum 4 ohms per channel it doesn't matter if its say; 4 ohm one channel and 8 ohm on the other. Its because i can source a 15 inch driver in 8 ohm quite cheaply in my locality, i just needed it confirming so i wouldn't be blowing anything up 
. Thanks again for the reply!
. Thanks again for the reply!Some amplifier retailers/manufacturers tell the truth and do not need to exaggerate power claims to sell their product.
Other retailers/manufacturers put profit above all else and sell rubbish that if truthfully specified would never sell to a knowledgable customer.
These types of sellers will use many ways to describe their Power Amplifiers to make them look as good as or better than those available from competitors.
An example is an 8ohms capable amplifier that is properly specified as a 100W into 8r0 @ 1kHz with distortion <0.1% when the mains supply is @ rated voltage.
This amplifier will be able to drive a reactive speaker because the manufacturer has specified it as suitable for 8ohms.
A consequence of the ability to drive a reactive load is that the same amplifier can also drive a test load that has a much lower resistance than the 8ohms of reactive speaker.
A maximum target for a resistive "test load" would be half the 8ohms, i.e. 4r0. Any half decent properly designed 8ohms amplifier must be able to drive a 4r0 until the heatsink temperature reaches some manufacturer determined limit. A typical power into this half load would be at least 150W into 4r0.
A very good amplifier that can drive very reactive 8ohms speaker will easily be able to drive a 3r0 test load. and achieve at least 170W into 4r0.
An excellent 8ohms amplifier will will drive a 2r0 test load for at least a few seconds before reaching that temperature limit. and acheive at least 180W into 4r0.
If you buy a genuine 4ohms capable power amplifier then it MUST be able to drive a 2r0 test load to at least +50% power, for much more than many seconds and preferably drive 1r5 and 1r0 test loads for a few seconds.
Does that make some sense?
I agree that an eight ohm nominal speaker is likely to drop below eight ohms at some frequencies, so the amplifier has to have a little reserve in the power supply and output stages, but several amp protection circuits current limit, not just temperature limit. In which case, the amp will not drive lower impedances at full drive, but will quite cheerfully deliver rated power into half impedance, and a bit less as the impedance drops further.
Don't forget that to get the best out of the system you'll need a crossover to remove the high frequencies from the sub, and lows from the two ways. Not complicated, and greatly improves the performance of both the amp and the speakers.
Have you already got the amp? It would be possible to use two cheaper two channel amps, one (in bridge) for the low end and the other driving the high end in stereo. You'd need to mono up the low frequency signals, but that's no problem, even passively (no, for PA the stereo is not that important, but a fair amount of recorded music was not prepared to sound good in mono, with phase cancellation and odd delays.
Don't forget that to get the best out of the system you'll need a crossover to remove the high frequencies from the sub, and lows from the two ways. Not complicated, and greatly improves the performance of both the amp and the speakers.
Have you already got the amp? It would be possible to use two cheaper two channel amps, one (in bridge) for the low end and the other driving the high end in stereo. You'd need to mono up the low frequency signals, but that's no problem, even passively (no, for PA the stereo is not that important, but a fair amount of recorded music was not prepared to sound good in mono, with phase cancellation and odd delays.
This all sounds a bit odd, as are the replies.
Most sources these days are stereo. If I were approaching this problem I'd wire the source up to the (stereo) amp and the amp to the 2 two-way midtop speakers.
If these are off-the-shelf speakers they will in all probability not suffer from having the bass routed to them, although if the amplifier has tone controls, you can turn the bass down.
If I then wanted to add a bass reinforcement, I'd get a mono amplifier, or a bridgeable stereo amplifier and use it to drive the bass bin. I'd make dual (opamp) buffer to connect to the source, so as not to load it and to keep the channels from mixing and then mix the channels after the buffers with an opamp mixer, pass the output of this to a low-pass filter and thence to the bass amp.
Most sources these days are stereo. If I were approaching this problem I'd wire the source up to the (stereo) amp and the amp to the 2 two-way midtop speakers.
If these are off-the-shelf speakers they will in all probability not suffer from having the bass routed to them, although if the amplifier has tone controls, you can turn the bass down.
If I then wanted to add a bass reinforcement, I'd get a mono amplifier, or a bridgeable stereo amplifier and use it to drive the bass bin. I'd make dual (opamp) buffer to connect to the source, so as not to load it and to keep the channels from mixing and then mix the channels after the buffers with an opamp mixer, pass the output of this to a low-pass filter and thence to the bass amp.
While not (see previous post) entirely disagreeing with your point, most public address (which is after all the origin of "PA") functions are stereo irrelevant; I've frequently used the channel split to balance different regions, or loudspeakers of differing directionality (longthrows on the left main output with a total mix, shortthrows on the right, with mainly vocals and acoustic instruments, no drums or electric bass/guitars). And until quite recently, music was mixed to be mono compatible; not for any hiphalutin' technical reason but because of the number of radios that were still mono. It's only recently with headphone-mixed mp3 intended titles that it hasn't seemed worth making it sound decent reduced to one channel.
And the reason for high passing the satellites is practical; with an eight-inch LF driver (say) in your two way, it's not going to produce much of the 40Hz and down signal. It won't burn out, but all the energy goes into heating its voice coil. Whereas, if you filter this signal (a remarkably large percentage of the total power) off before the amp, for the same result the amp runs cooler and so does the speaker, or you can get several dBs louder. And it's cheap and easy to do.
Most available sources (CD players, mixers, mp3 players…) are low enough impedance not to worry about buffering (unless you want to balance the inputs, which I firmly approve of). If you want an op amp mixer, and an active low pass filter, you need a power supply; why not build a couple of active high pass filters into the box at the same time.
Firstly sorry about the late reply
Thanks for all the replies, @AndrerwT - i kinda understand the test load as a measurement to see how efficient a amp is at certain impedences. The technical side is a bit beyond me but i am really interested in how this works, thanks again.
As for the setup, i've bought a PV 2000 (i would greatly appreciate any advice/tips/warnings from anyone with any experience with this amp) its got an inbuilt 150hz crossover on each channel so the idea now is to run two 4ohm bass bins on one channel (amp can run 2ohm apparently) and then midtops on the other.
Im not sure about if the amp can run mono, it says stereo on the front of it. I think i'll have to see if i can find the little spanish guy called "manual".
Thanks again for all the replies, its been very helpful
- Status
- This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.