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Matching amp and speakers
Years ago, when I was working my way through college working for Radio Shack, we made sure that the power handling capability of the speakers was bigger than the power output of the amp. This makes sense, right? Clearly if you feed 1000W into a tiny little 25W speaker, you will do some damage to the poor little speaker.
When I recently talked with Bob (my favorite sound guy), I got a totally different story. He told me that the important thing is that you make sure the amp is big enough to drive the speakers. Ideally, you want the amp to be able to deliver twice the power that the speakers are rated for.
This blew my mind. If I have speakers that will handle 250W, then I want to drive them with an that will amp will deliver at least 500W?
The folks at Musician's Friend agree with Bob. I quote from their PA System Buying Guide:
Make sure to buy an amp with plenty of power for your speakers plus enough headroom. Many speakers are damaged by getting too little power, causing clipped waveforms that will ruin your gear. You will probably want an amp with twice the wattage of your speaker's rated power handling to ensure clean power gets to them.
The buying guide is not clear on which watts are what. You have an amp, and it has wattage ratings in peak and RMS and it lists wattage for 8 ohms and 4 ohms and maybe two ohms. You have a speaker and it has peak and program and continuous and RMS... How to figger it all out?!?!?
Step 1: Determine the ohms for the speakers and how many speakers you will be plugging into one channel. Generally speaker, you will have one speaker per channel - one in the right channel and one in the left. And generally speaking, the speakers will be 8 ohms. But, just in case you have two speakers plugged into one channel, or just in case they are four ohm speakers, you need to figger out the ohms for the speaker combination. In case you forgot, I mentioned how to do this in the post on amps, under the heading "Ohms".
- Will your amp handle the ohms? If your amp is only rated for 8 ohm speakers, then you can't plug in a pair of 8 ohm speakers, dude.
Step 2: Determine the RMS power rating of your speakers. I gave a very simple way to convert any of the plethora of speaker specs into RMS in the previous post on speakers:
If there is a spec for peak power, divide by four to get RMS power.
If there is a spec for program power, divide by two to get RMS power.
If there is a spec for continuous power, then multiply it by 1. Or divide by 1. Or add zero. The RMS power handling is the same as the continuous power handling.
Matching amp and speakers
Years ago, when I was working my way through college working for Radio Shack, we made sure that the power handling capability of the speakers was bigger than the power output of the amp. This makes sense, right? Clearly if you feed 1000W into a tiny little 25W speaker, you will do some damage to the poor little speaker.
When I recently talked with Bob (my favorite sound guy), I got a totally different story. He told me that the important thing is that you make sure the amp is big enough to drive the speakers. Ideally, you want the amp to be able to deliver twice the power that the speakers are rated for.
This blew my mind. If I have speakers that will handle 250W, then I want to drive them with an that will amp will deliver at least 500W?
The folks at Musician's Friend agree with Bob. I quote from their PA System Buying Guide:
Make sure to buy an amp with plenty of power for your speakers plus enough headroom. Many speakers are damaged by getting too little power, causing clipped waveforms that will ruin your gear. You will probably want an amp with twice the wattage of your speaker's rated power handling to ensure clean power gets to them.
The buying guide is not clear on which watts are what. You have an amp, and it has wattage ratings in peak and RMS and it lists wattage for 8 ohms and 4 ohms and maybe two ohms. You have a speaker and it has peak and program and continuous and RMS... How to figger it all out?!?!?
Step 1: Determine the ohms for the speakers and how many speakers you will be plugging into one channel. Generally speaker, you will have one speaker per channel - one in the right channel and one in the left. And generally speaking, the speakers will be 8 ohms. But, just in case you have two speakers plugged into one channel, or just in case they are four ohm speakers, you need to figger out the ohms for the speaker combination. In case you forgot, I mentioned how to do this in the post on amps, under the heading "Ohms".
Step 2: Determine the RMS power rating of your speakers. I gave a very simple way to convert any of the plethora of speaker specs into RMS in the previous post on speakers:
If there is a spec for peak power, divide by four to get RMS power.
If there is a spec for program power, divide by two to get RMS power.
If there is a spec for continuous power, then multiply it by 1. Or divide by 1. Or add zero. The RMS power handling is the same as the continuous power handling.
Step 3: Find the RMS power per channel for the amp, using the ohms that you determined in step 1. The amp probably list different ohm values, 8, maybe 4, and maybe maybe 2. Pick the watts for that particular ohmage. If they happen to list a maximum power or a peak to peak power, ignore that inflated number.
Step 4: Compare the rating for the amp (from step 3) with the power handling for the speakers (from step 2). Ideally, the ratio will be 2.0. That is, the watts for the amp will be twice the watts for the speakers. Don't get anal about this... there is some leeway. To get a feel for how much leeway, let's look at some systems that were put together by the pros.
I turned to the Musician's Friend website and started looking for live sound systems. The first thing I found was an interesting tidbit. All their systems fell into one of two categories. Either the system included a powered mixer and passive speakers, or it included a mixer and a pair of active speakers. There were no systems that they offered that was all components, that is, an unpowered mixer, an amp, and passive speakers.
Hmmmm... that makes sense. I guess? Having all components, you are of course more flexible. But combining one way or the other means less stuff to carry around. For a KJ, this is important.
Musician's Friend had a long long list of systems to pick from. I picked three of these to compare. All were around the $700 mark.I picked different brands to keep it interesting. I also just looked at systems with a powered mixer and a set of passive speakers. I chose this not because I am partial to that type of system (I am, by the way, but only slightly). I chose this type because you need to match amp and speakers with this type of system. If the amp and speaker are in the same box, the matching has already been done for you.
The Phonic system
The Phonic system includes their Powerpod 1860 Plus powered mixer, coupled with the Phonic S715 speakers.
Step 1: The speakers are 8 ohms. We will plug one speaker into each channel of the amp, so each channel of the amp will see 8 ohms. The amp has a rating for 8 ohm operation, so we are cool.
Step 2: The speakers have the following power handing: Power handling: 600W (Peak), 400 W (Program), 200W (RMS). Which spec do we want? Yes, of course, the last one, the RMS power handling of 200W.
Step 3: The amp has the following ratings:
Step 3: The amp has the following ratings:
260W per side at 8 ohms
400W per side at 4 ohms
800W bridged mono
400W per side at 4 ohms
800W bridged mono
We first note that the amp does say "per side", so they aren't pulling anything funny like combining the power from both sides. Since we determined that our speakers are 8 ohms, we choose the 260W number. Note also that they did not specify whether these are peak watts or RMS, so we will assume that the numbers are RMS. If we were actually buying this piece of equipment, we might want to take a close look at the manual to verify this.
Step 4: Compare the two numbers. The output of the amp (260W) divided by the rating of the speakers (200W) is 1.3.
So, is this good? My opinion, the speakers are perhaps a bit underpowered, but nothing to really be concerned about.
If I am figgering how big a crowd I could handle, I would use the wattage of the amp (260W). Since the amp has two channels (right and left) I would multiply this number by 2 to get 520W. In the section on amps, I used the conservative number of 10 watts per person. Based on all this calculation, this system should be ok with crowds of 52. Get that 53rd person in and you need to run out for another bucket of watts.
Well, no... I'm just kidding. You can go ahead and have 53 people.
The Behringer system
The Behringer system includes the PMP1000 powered mixer and a pair of VP1220 speakers.
Step 1: The speakers are 8 ohms. We will plug one speaker into each channel of the amp, so each channel of the amp will see 8 ohms. The amp has a rating for 8 ohm operation, so we are cool.(Gosh that sounds familiar.)
Step 2: The speakers are referred to as Behringer EUROLIVE VP1220 800W 12" PA Speaker, so they must be 800W, right? Tricky folks. You have to read further down to get the spec that we want: 200 Watts Continuous / 800 Watts Peak Power. Continuous power is the same as RMS power, so we will go withe the 200W number.
Step 3: The amp has the following spec: Ultra-compact 2 x 250-Watt stereo powered mixer (500 Watt bridged mode). I'm gonna call this a non-spec, since they don't tell you whether the spec is for driving 8 ohm speakers or 4 ohm or what. You would think that maybe, since this is all sold as a system, that they would pick the spec that is relevant to the set of speakers that are in the system?
But, no. They make you work a little to get at the number that is really important. When I click on the "Spec" tab, I find all kinds of numbers. In particular, the 250W is clearly much larger than the number we want. First, 250W is peak power, not RMS. Second (I reach for my blood pressure medication), this number is the power when driving 4 ohm speakers.
Peak Power, both channels driven:
8 Ohms per channel: 135W
4 Ohms per channel: 250W
Step 1: The speakers are 8 ohms. We will plug one speaker into each channel of the amp, so each channel of the amp will see 8 ohms. The amp has a rating for 8 ohm operation, so we are cool.(Gosh that sounds familiar.)
Step 2: The speakers are referred to as Behringer EUROLIVE VP1220 800W 12" PA Speaker, so they must be 800W, right? Tricky folks. You have to read further down to get the spec that we want: 200 Watts Continuous / 800 Watts Peak Power. Continuous power is the same as RMS power, so we will go withe the 200W number.
Step 3: The amp has the following spec: Ultra-compact 2 x 250-Watt stereo powered mixer (500 Watt bridged mode). I'm gonna call this a non-spec, since they don't tell you whether the spec is for driving 8 ohm speakers or 4 ohm or what. You would think that maybe, since this is all sold as a system, that they would pick the spec that is relevant to the set of speakers that are in the system?
But, no. They make you work a little to get at the number that is really important. When I click on the "Spec" tab, I find all kinds of numbers. In particular, the 250W is clearly much larger than the number we want. First, 250W is peak power, not RMS. Second (I reach for my blood pressure medication), this number is the power when driving 4 ohm speakers.
Peak Power, both channels driven:
8 Ohms per channel: 135W
4 Ohms per channel: 250W
The relevant number is considerably less impressive: 8 Ohms per channel: 90W.
Step 4: Compare the two numbers. The output of the amp (90W) divided by the rating of the speakers (200W) is 0.45.
Ouch. The speakers are pretty seriously underpowered. Remember, this number is ideally around 2.0. I'm not gonna recommend this powered mixer with these speakers.
But, let's say you decided to go with this system. How big a crowd could you handle? Each channel is 90W, so the total wattage is 180W. Figgering 10W per person, I put the crowd size at 18. Maybe 20? Definitely a small gig.
The Yamaha system
Finally, let's do a little spec check on a Yamaha system, which pairs the Yamaha EMX212S powered mixer with a pair of Yamaha A12 speakers.
Step 1: The speakers are 8 ohms. We will plug one speaker into each channel of the amp, so each channel of the amp will see 8 ohms. The amp has a rating for 8 ohm operation, so we are cool. (Gosh that sounds familiar. Most speakers are 8 ohms.)
Step 2: We have the following spec for the power rating on the speakers: 300W program handling (600W peak). Hmmmm.... program handling is twice the RMS rating, so the number we want is 150W.
Step 3: The amp is rated rather sparsely: Dual 200W amps. We need to dig further, since we have learned the the numbers at the front are not necessarily the ones we want. Unfortunately, Musician's Friend does not have the spec that we want.
To get that spec, I had to go to the Yamaha website. On this page we see the important number 130W+130W, which means 130W in one channel and 130W in the other.
Step 4: Compare the two numbers. The output of the amp (130W) divided by the rating of the speakers (150W) is 0.87.
Gosh. This is better than the Behringer system, but it still falls short of the magic value of 2.0. If I were considering this system, I think I would lean toward using the Yamaha EMX312C powered mixer instead of the EMX212C. This amp is rated at 190W per channel, which is a little better suited to the speakers. But... it costs $110 more.
Let's say we bought this system. How big a crowd could we host? We have 130W per channel from the amp, so the total power is 260W. When we divide this by 10W person, we get a maximum crowd of 26 people.
I have looked at three systems. Of the three, the Phonic system comes off the best in terms of matching amps with speakers and in terms of total wattage output. (Time for the weasel words) These specs are only part of the story. I have equipment from all three manufacturers and I tend to think of the Phonic equipment as the best value for a low end system, and the Yamaha as the better value for a slightly higher end system.
Copyright (c) 2010, John Seymour
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