What powered mixer do I need?

April 23, 2009 12:58 PM

I have two 200-watt, 8 ohm speakers. What PA head do I buy?

I received 2 PA speakers as gift. On the back, its says they are 200 watt, 8 ohms. What would be the proper powered mixer to buy to complete my little PA system? I don't really need any more than 8 inputs, and do not need anything with bells and whistles. Thanks!

posted by rumsey monument to media & arts (14 comments total)

What speakers are they? Does it say anything more than "200 watt"? (such as "peak", "RMS" or "program")
posted by Monday, stony Monday at 2:15 PM on April 23

the brand in KMD and it says nothing else.
posted by rumsey monument at 2:23 PM on April 23

A Peavey XR 8300 would probably do the trick. They also have the more basic (but also less powerful) PVi mixers. Yamaha makes a line of basic powered mixers. Mackie is the other lunchbox mixer manufacturer I'm aware of, but they are currently in some financial trouble.
posted by Monday, stony Monday at 2:30 PM on April 23

What kind of cables does it expect?

The Behringer PMP 1000 puts out 200 watts at 8 ohms when in bridge mode. (essentially mono, driving both speakers at once)

The Behringer PMP 2000 puts out 215 watts at 8 ohms (300 peak) with both channels driven.

$300 at B&H
posted by MesoFilter at 2:39 PM on April 23

If your speakers have 1/4 inch inputs, you can get speaker cable here. They might have speakon inputs (cable here), in which case you may want to get a mixer with speakon outputs or an adapter.
posted by Monday, stony Monday at 2:56 PM on April 23

I have one of these and it works great for my system.
posted by peewinkle at 3:13 PM on April 23

Quick aside- make sure you're using speaker cables to get from the amp to the speakers, not instrument cables.
posted by knowles at 3:18 PM on April 23 [1 favorite]

Woah, mackie is in trouble? That's crazy, their stuff is EVERYWHERE. Losing them would be a sad day in the PA world.
posted by flaterik at 4:27 PM on April 23

Thanks for the recommendations. The specs on all of these mixers are different, so I assume the wattage and ohms of the speakers doesn't matter much? I dont want to destroy them. There is a bit of conflicting info on the interweb about matching ohms and watts.

Knowles - 1/4" instrument cable and speaker cables look a lot alike - whats the real difference?

Thanks for helping a newbie everyone!
posted by rumsey monument at 4:33 PM on April 23

also, the speakers want 1/4" inputs
posted by rumsey monument at 4:35 PM on April 23

flaterik: well, their parent company, LOUD, are in some trouble.

An instrument cable is a coaxial cable composed of a small-gauge (22 in this case -- higher numbers mean smaller cable) central conductor and a shield. It's made to transport low-power signal while protecting them from unwanted noise.

A speaker cable is made of 2 (or more) large-gauge (here, 13) conductors. It's intended to transport a high-power signal.

Using an instrument cable for speakers -> tons of losses and heating due to the high resistance (small conductor).
Using a speaker cable for instruments -> high risk of noise pickup because it's not coaxial.
posted by Monday, stony Monday at 5:05 PM on April 23 [1 favorite]

Also: The Yamaha Sound Reinforcement Handbook should help you clear out the ohms/watts thing. The information in the PSW Study Hall is generally solid, and you can ask further questions in the LAB Lounge (but as with any other forum, you should get a sense of the place before you post and use search [google with "site:srforums.prosoundweb.com" + you terms -- the forum's search is horrid])
posted by Monday, stony Monday at 5:13 PM on April 23

Let me try about the ohm thing:

Suppose that we have an amp that has a maximum output voltage of 28.3 Vrms. If we plug an 8-ohm load into it, the load gets V^2/R = 28.3^2/8 = 100 watts, with a current of 100/28.3 = 3.54 A. Now if we lowered the load's impedance to 4 ohms, and plugged the numbers in the formulas, we'd get twice the power and current, since the denominator was halved. Free power! Except that real amps usually do not output twice the current when you halve the impedance, for practical reason.

What does this mean in practice? That the power output of an amp will vary depending on the impedance of the load it's connected to. So a spec sheet might include something like this:

600 watts per channel into 2 Ω
450 watts per channel into 4 Ω
300 watts per channel into 8 Ω

[taken from the Mackie ppm 808s spec sheet :: pdf]

Now, given that your speakers are 8-ohm nominal, the only number you really care about is the one for 8 ohms.

There are many ways of specifying the power a speaker can take; I don't know which one the maker of yours did. I would tend to play it safe, and not hook them to an amplifier that can give them more than their rating (give or take 10%), especially if they're old.

The first Peavey I linked to gives about 200 watts into 8 ohms, and includes a speaker-protection feature, among some bells & whistles.
posted by Monday, stony Monday at 10:07 PM on April 23 [1 favorite]

and not hook them to an amplifier that can give them more than their rating (give or take 10%), especially if they're old.

Unless of course you don't have a good ear for distortion and would drive the amp all the way. An overdriven amp is worse for speakers than overpowering them a bit.
posted by flaterik at 3:50 PM on April 24