PA Speakers - using with a smaller amp???

You're talking about speaker impedance issues. Solid state amps put out different power levels depending on the speaker impedance. Generally lowering the impedance increases the power output, and adding more speakers in parallel lowers the impedance. You have to know the impedances of the speakers that are being paralleled to calculate the resulting impedance. You don't want to overload the amp by running it at a lower impedance than it's rated for.

Tube amps with pentode or beam tetrode output tubes change their power level very little with changing speaker impedance.

Ah....so basically it's not a good idea!!

Thanks Ricochet.

Not necessarily, I'm just saying you need to figure your impedance and power capacities so you don't fry anything.

There's nothing wrong with having speaker wattage rating WAY higher than the amp. What you don't want is something like a set of speakers that works out to 2 ohms if the amp makes its rated power into 8 ohms. You have to know these ratings.

I wouldn't have a clue, and I very much doubt the person who's amp it is would know what it was!

My initial worry was whether they'd have the right cables to connect them. I doubt they'd understand the importance of correct speaker cables and you know what it's like when you try telling someone something like that and they think they know best!!!

Cheers for the help. I think it's about time I learnt about all this impedance stuff!!! I've worked with 4K PA's with a 4 way crossovers and monitors etc for pro bands, but none of the kit was my own and I just put together what was there, so didn't have to worry about whether things were compatable etc, that had already been done!!

Yes, you need to understand impedence. Look on the back of your speakers and it should tell you the ohms. Most PA speakers are 8 ohms, but there are 4 ohms, and even 16 ohms speakers. Ohms is a measure of resistance to current flow, the higher the ohms, the higher the resistance.

Most (not all) PA speakers are wired parallel. So when you connect two 8 ohms speakers this will give you a 4 ohm load. If you connect four 8 ohms speakers in parallel, this would be a 2 ohms load. Think about it, the more speakers, the more conducters you have to carry current. So when you connect speakers together in parallel, more current can flow.

Some, but not many speakers are wired in series. Connecting speakers in series is very different. Two 8 ohms speakers connected in series equals a 16 ohms load. Four 8 ohms speakers in series equals a 32 ohms load. That is a lot of resistance for most PA amps.

Now, look at the back of your amp for "minimum impedence or ohms". It may say "4 ohms minimum" or something like that. This means you cannot go below a 4 ohms load. The lower the ohms, the lower the resistance to current flow. So if your amp says 4 ohms minimum and you connect four 8 ohms speakers to it (a 2 ohms load), you would have too much current flowing through the amp. The amp could quickly overheat and burn up.

Just the opposite is using speaker(s) with too high impedence or ohms. If your amp operates best at 4 ohms and you connect a 16 ohm speaker to it, then your amp will not be able to perform at it's best. I like to say it's like driving with your foot on the brake.

Thanks for the info!! :D

So what difference does the wattage of the speakers or amp make? Say you connect everything with the same ohms how do you know what the end output is? For example the 80w amp to 2x300w speakers, or the 1500w amp to 2x300w speakers.

I'm even confused about my question now!!! :? Basically if you're mixing and matching different wattages of amps and speakers how do you know what output you're getting?

Thanks! :D

Maybe this will help

http://www.teamrocs.com/technical/pages/connectingspeakers.htm

wilbers

"Passive" speakers have no power of their own. When you see a speaker rated 300 watts program, 600 watts peak for example, this means this speaker can safely handle 300 watts of power over a long period of time without damage, and peaks of 600 watts. Better speakers made with better quality components can handle more power than cheaper speakers.

What will really tell you how loud a speaker is is "sensitivity". This is usually expressed in decibels produced with one watt of power applied at one meters distance. This is the standard way of measuring how loud a speaker is. A 100 watt speaker could actually be much louder than a 500 watt speaker. So watts tells you how much power a speaker can safely handle, sensitivity tells you how loud the speaker is.

You will see specs for sensitivity like this 92 dB @ 1W/1M. This means this speaker will produce 92 decibels of volume with one watt of power applied at one meters distance. Then another speaker might be rated 105 dB @ 1W/1M. So this speaker will produce 105 decibels of volume at one watt at one meter. Now, most people would think the 105 dB speaker is better. But this is not necessarily true. It is true that the speaker rated 105 dB will be much louder.

But.... lows like bass draw much more power than highs. A speaker rated 92 dB 1W/1M probably has very good bass response, it will pump a lot of good low end. A speaker rated 105 dB probably does not produce much bass at all. Yeah, it is loud, but it is harsh and tinny. Now, this is not always the case, but don't buy a PA speaker solely because it has a high sensitivity rating. It may not be a very good sounding speaker.

Everytime you double the watts (or power) to a speaker you get about a 3 decibel gain in volume.

So take that 92 dB @ 1W/1M speaker:

1 watt- 92 dB
2 watts- 95 dB
4 watts- 98 dB
8 watts- 101 dB
16 watts-104 dB
32 watts- 107 dB
64 watts- 110 dB
128 watts-113 dB
256 watts- 116 dB
512 watts- 119 dB
1024 watts 122 dB
2048 watts 125 dB

Now the 105 dB @ 1W/1M speaker

1 watt- 105 dB
2 watts- 108 dB
4 watts-111 dB
8 watts- 114 dB
16 watts- 117 dB
32 watts- 120 dB
64 watts- 123 dB
128 watts- 126 dB
256 watts- 129 dB

Compare those two speakers. The 105 dB speaker is louder at only 256 watts than the 92 dB speaker is at 2048 watts! :shock:

This is important to know, because it is often cheaper to buy a speaker with a higher sensitivity rating than buy a much more powerful amp.
So what difference does the wattage of the speakers or amp make? Say you connect everything with the same ohms how do you know what the end output is? For example the 80w amp to 2x300w speakers, or the 1500w amp to 2x300w speakers.

If you hook an 80 watt amp to two identical speakers, each speaker will get 40 watts of power, doesn't matter what the speaker is rated. Remember, the speaker's wattage rating is telling you how much power the speaker can handle. The speaker has no power of it's own. It's loudness depends on it's sensitivity.

If you run the 1500 watt amp into two identical speakers, then each speaker will get 750 watts. Now this is about correct, it is usually advised to use double your speaker's wattage rating.

More power from the amp translates into "clean" sound. An 80 watt amp would have to be cranked to produce enough power and volume for a big crowd or venue. The amp will start to distort. For PA speakers you do not want distortion like a guitar speaker.

On the other hand, the 1500 watt amp can easily produce plenty of volume for a big crowd or venue. It will stay clean and undistorted to much higher volume levels than the 80 watt amp. This is why people want powerful amps.

You will often hear that using an underpowered amp will damage speakers, like using that 80 watt amp to power two speakers rated 300 watts each. This is not really true, it is a misunderstanding. The problem is that the 80 watt will not produce enough volume, so people crank the amp to it's full maximum power. Cranked full the amp will "clip" or distort. The speakers will try to reproduce this distorted signal from the amp, and this distorted signal is what damages the speakers.

But you can also damage a speaker with too powerful an amp. If you crank that 1500 watt amp to max while using two 300 watt speakers, that is way more power than the speakers were designed to handle. So you can blow the speakers this way too.

But you could use both the 80 watt or 1500 watt amps into any speaker as long as you don't clip the amp, or crank the powerful amp too much.

You can hear when speakers distort easily. If you hear that, turn down. :D

I know this is a lot to absorb, go to Scott's PA Tutorial and read there. You will learn a lot about PA systems.

http://members.cox.net/pasystem1/