#1
Hey everyone.  I know very little about powered mixers, PA's etc.  At a small gig the other night we only connected one speaker and our monitors to our PA mixer vs the whole setup as space was an issue.  That got me to thinking about how you have to be careful with tube amps and not having the correct load etc. can cause issues.  Which brings me to my question.  I have a 5 channel powered mixer, is it bad to connect only one speaker like we did?  It is a solid state powered mixer btw.  One of the reasons I ask is because I use a little champ SS amp speaker to test things at my house as well as the time we played with just the one big speaker connected to the back vs two like normal.  Everything sounds fine and it worked perfectly but don't want to be doing any damage or anything so thought i'd ask, thanks for any advice.
#2
SS amps need a minimum speaker load or no load at all. If it says "minimum 8 ohms load", you need at least an 8 ohm load. Do NOT supply it just a 4 ohm load or anything lower. If it required an 8 ohm load and you supplied a 16 ohm load, that would be fine but you will drop the wattage down by half. So if it was 200w at 8 ohms, it will be 100w at 16 ohms. If it is minimum 8 ohm load per SIDE, and you are using just one side with an 8 ohm speaker, that should be okay.

However, you also have to take into consideration the output power of the power amp. If it says 8 ohm load, 250w, and you supply it an 8 ohm speaker rated only at 150w, you'll likely blow the speaker. Now two 4 ohm speakers, at 150w each, connected together in series would be 8 ohm total load, 300w power handling. Two 4 ohm speakers, 150w each, connected in parallel would be 2 ohm total load, 300w power handling.

Some basic rules, I think this is all right:

Two speakers of the same ohm rating wired in series adds the two ohm ratings together, or multiples one of the ohm ratings by 2. So two 8 ohm speakers is 16 ohms total load.

Two speakers of the same ohm rating wired in parallel subtracts the two ohm ratings together, or divides one of the ohm ratings by two. So two 8 ohm speakers is 4 ohms total load.

The total wattage handling of the speakers is the lowest wattage speaker rating multiplied by the number of speakers. So if you had a 50w and a 25w speaker together, your total wattage handling is 25 X 2 which is total 50w.

Output wattage is halved every time you double over the recommended ohm rating. So an amp rated 200w at 16 ohms will be 100w at 32 ohms.

Ohm ratings that are halves/doubles of themselves are easy to calculate (16, 8, 4, 2) but numbers that are not (10, 3, 5, 6) require actual math.
Last edited by Will Lane at Jun 1, 2017,
#4
Thanks guys, it is a Behringer Europower 5 channel, here is the link to it:

http://www.musiciansfriend.com/pro-audio/behringer-europower-pmp550m?cntry=us&source=3WWRWXGP&gclid=CK6Fnsvln9QCFQNahgodLu8EXg&kwid=productads-adid^156727059247-device^c-plaid^143952845322-sku^J18422000000000@ADL4MF-adType^PLA

It says on the back it can be 2 X 4 ohm at 250 watts or 2 X 8 ohm at 140watts.  Because it had the "2 X" is why I was concerned.  There is zero in the manual, it is like 2 pages long and basically legalese.  So what we've connected is one 8 ohm speaker.  I have no idea if it is wired series or parallel and yes I understand that the wattage could blow my small 8ohm speaker but I didn't turn it up much.  I think I'm ok, I was just wondering if it had to be balanced, I asked an audio/visual guy at GC and he said it was fine you couldn't hurt it.
#5
OK, there appears to be lots of bullshit in the ad and the manual appears to be written by an idiot of the first order - not a electronics engineer - but from the controls and the connection details, and the size and weight, this is a MONO amplifier with only one output (the two sockets are connected in parallel to the same power amplifier). The power amplifier is 500W (not convinced these are real, r.m.s. watts anyway) into 2 ohms. So connection of two 250W 4 ohms speakers gets the full output of the amp. A single 8 ohm speaker connected should get about 280W on full. You should be OK using your small speaker provided that you do not turn it up so the speaker distorts HOWEVER if it is rated at less than, say 50W, and you get sudden clicks from poor connections to your guitar or mic's then you could damage it. Connecting one speaker will not affect the amplifier.

For the price it looks quite a reasonable mixer amp, and the anti-feedback should provide some protection for your smaller speaker too.
Last edited by PSimonR at Jun 2, 2017,
#6
Yes, 1x8ohm speaker connected to the back as long as it is rated to 140w or greater will work fine with no damage to the amp.

http://www.musiciansfriend.com/pro-audio/behringer-europower-pmp550m?cntry=us&source=3WWRWXGP&gclid=CK6Fnsvln9QCFQNahgodLu8EXg&kwid=productads-adid
"Your sound is in your hands as much as anything. It's the way you pick, and the way you hold the guitar, more than it is the amp or the guitar you use." -- Stevie Ray Vaughan

"Anybody can play. The note is only 20 percent. The attitude of the motherfucker who plays it is 80 percent." -- Miles Davis

Guthrie on tone: https://www.youtube.com/watch?v=zmohdG9lLqY
Last edited by Cajundaddy at Jun 2, 2017,