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There is a big question when putting a karaoke system together. How big? How many watts do you need?
Naturally size matters. Especially if you are a guy. More horsepower... more terabytes in your iPod... more watts in your karaoke system. All that stuff. I think it's part of the natural selection process. Male peacocks with the biggest tail feathers are the most successful at attracting mates, and so it is with KJs and watts.
But how much do you really need?
Bad news
The bad news is that watts are expensive and that you probably need a lot of them.
In an earlier post on how bands got their names, I reported that Deep Purple once held the Guinness record for the loudest band. The record is currently held by KISS, with a performance that reached 136 decibels. For reference, hearing damage starts at around 120 decibels, and the "threshold of pain" is above 130. Unfortunately, I have not been able to find a reference to that wattage for that concert.
Just how expensive is an amp? The chart below is a plot of dollars per watt for a series of amps that I trust from an online vendor that I trust. As a rule of thumb, divide the wattage in half and add thirty. If you figure you need 500W, then the amp will cost about $280. I made this chart, by the way. Did I mention that I am a mathematician?
In future generations, this rule of thumb will become known as Seymour's Rule of Amp Pricing. In future generations, this rule of thumb will be obsoleted by inflation, and eventually, by technology. This is in accordance of Seymour's Rule of the Obsolescence of Rules.
Enthusiasts of the history of science will recognize a similarity of this rule to Stigler's law of eponymy, which states that "No scientific discovery is named after its original discoverer." This law was first discovered by Robert Merton, so naturally, it was named after Stigler.
Enough digression. Here is an important corollary of Seymour's Rule of Amp Pricing. It is more cost effective to buy a single amp with twice the power than it is to buy two amps.
For example, the Crown XLS 202D sells for $200 and generates 300 watts. I could get 600 watts if I buy two of them, and it would cost me $400. Alternately, I could buy the Crown XLS 602D, which is rated at 600 watts, and it would cost me $300. Not only is the bigger amp cheaper, but it is less total weight and less to schlep around.
Watts and specs
Before we talk about how many watts a KJ needs, we need to set some ground rules about specing of amps. The problem is, it is confusing.
First, there is the issue of the units that one uses. Some manufacturers spec out their amps in terms of watts peak-to-peak and some use watts RMS. Peak to peak numbers are given when a manufacturer wants to artificially inflate their specs, since peak-to-peak numbers are almost six times as large as RMS numbers.
Another very helpful way that a manufacturer can confuse a prospective KJ is to speak in terms of total power rather than watts per channel. Another bad thing. Well... it's actually not all that terrible. If an amp has two channels (i.e. stereo), you just add the watts RMS. Just be careful when reading the specs.
The next confusing thing is exemplified in a spec on the Crown XLS 202D: "330W/ch @ 2 ohms, 300W/ch @ 4 ohms, 200W/ch @ 8 ohms, 660W bridged mono @ 4 ohms, 600W bridged mono @ 8 ohms." Depending on which number you look at, the amp could be rated at anywhere from 200 watts per channel to 660 watts per channel.
Isn't this deceptive advertising? Actually, not at all. The specs merely reflect the power output that you get with different configurations of speakers. You just have to know a bit about your speakers in order to properly read the specs. In particular, you need to know a bit about ohms.
Ohms
To clarify right off... I am not talking about the kind of oms involved in transcendental meditation.
Speakers are generally described in terms of their resistance, which is measured in ohms. What does that mean? Well, I could explain it, but the simple explanation requires some explanation of electronics, and the correct explanation says that ohms are actually meaningless when you talk about speakers.
So, let's just say that a typical speaker is 8 ohms and forget the details. Generally speaking, if the speaker has one woofer, it will be 8 ohms. Not always, but usually. If you plug one speaker into each channel of the amp, then the spec from the amp that is relevant is the "watts per channel at 8 ohms" number. In the case of the Crown amplifier, this relevant number is 200W.
With this particular Crown amp (and with most decent amps, for that matter) you can plug two 8 ohm speakers into each channel without blowing up the amp. How can you tell if an amp will blow up with two sets of speakers?
When you plug two speakers in, the resistance (that is, the ohms) of the speakers gets cut in half. If you plug two 8 ohm speakers into each channel, the load for each channel becomes 4 ohms. And now the applicable spec on the amplifier is "300W/ch @ 4 ohms". Just by virtue of the fact that the amp has a power rating for 4 ohms, you know that you can plug in two 8 ohm speakers.
So... hmmmm.... we doubled the number of speakers and the power went from 200 watts per channel up to 300 watts per channel? That doesn't seem fair! We didn't get twice the power. :(
I agree that it's not fair, but it's reality. There is a certain amount of inefficiency when you plug two speakers into the same channel. And this leads to another important point: It is more cost effective to run a single set of speakers per channel.
These important points lead in the same direction. Buy a bigger amp, dude, and use a single set of speakers.
That said, I am going to make a case for plugging in multiple sets of speakers. You probably have noticed this, but the closer you get to a speaker, the louder it is. If I have one speaker, and try tomake it loud enough on the opposite side of the room, it will necessarily be too loud near the speaker. If I add a second speaker, with proper spacing, the overall sound levels are more consistent around the room. Each set of speakers that I scatter throughout the room makes the sound level more even.
In a larger room, I will run with two sets of speakers to get this evenness.
Caveats
For the more technically adept: I need to clear some stuff up. I have made a whole bunch of simplifications in describing this stuff above.
When I talked about the resistance for speakers plugged into the same channel, I was assuming that the speakers had the same resistance. The formula is more complicated if the speakers have different resistances.
Another simplification is thatI have assumed that the speakers are combined in parallel, rather than in series. If you go out of your way with a soldering iron you could combine speakers in series. But, if you use standard plugs and cables in the way they were intended, your speakers will be in parallel.
The third simplification was in my discussion of using multiple sets of speakers. I neglected to say that if the listening areas of the speakers overlap, you will get dead spots from phase cancellation. Analyzing this is very complicated. Don't go crazy with it.
Yet another simplification was that I completely avoided talking about the bridged mono mode for an amp. Let's agree to ignore this. Well... unless you get a passive subwoofer. Then I recommend bringing in a sound pro just to make sure.
How many watts do I need?
Boy... good question.
"It all depends" is a good answer, although probably not all that useful. But of course wattage requirements do depend on a lot of things. I should be honest, though. The real reason I say "depends" is to avoid having to accept any responsibility for my actions.
The first big question to ask is whether you want to do outdoor gigs. If a gig is outdoor, the PA is going to be a lot less efficient. A lot. I mean, a lot. There is nothing to contain the sound, so it will just get lost. Most importantly, the bass will get lost. My opinion... if you are playing a gig outside, you should look into adding a subwoofer. You only need one because the stereo effect is less pronounced at low frequencies. But you do need one.
Another important variable is the efficiency of the speakers. I will discuss this in the section about speakers.
(Now I will actually get down to giving some advice.)
There is a big question when putting a karaoke system together. How big? How many watts do you need?
Naturally size matters. Especially if you are a guy. More horsepower... more terabytes in your iPod... more watts in your karaoke system. All that stuff. I think it's part of the natural selection process. Male peacocks with the biggest tail feathers are the most successful at attracting mates, and so it is with KJs and watts.
But how much do you really need?
Bad news
The bad news is that watts are expensive and that you probably need a lot of them.
In an earlier post on how bands got their names, I reported that Deep Purple once held the Guinness record for the loudest band. The record is currently held by KISS, with a performance that reached 136 decibels. For reference, hearing damage starts at around 120 decibels, and the "threshold of pain" is above 130. Unfortunately, I have not been able to find a reference to that wattage for that concert.
Just how expensive is an amp? The chart below is a plot of dollars per watt for a series of amps that I trust from an online vendor that I trust. As a rule of thumb, divide the wattage in half and add thirty. If you figure you need 500W, then the amp will cost about $280. I made this chart, by the way. Did I mention that I am a mathematician?
In future generations, this rule of thumb will become known as Seymour's Rule of Amp Pricing. In future generations, this rule of thumb will be obsoleted by inflation, and eventually, by technology. This is in accordance of Seymour's Rule of the Obsolescence of Rules.
Enthusiasts of the history of science will recognize a similarity of this rule to Stigler's law of eponymy, which states that "No scientific discovery is named after its original discoverer." This law was first discovered by Robert Merton, so naturally, it was named after Stigler.
Enough digression. Here is an important corollary of Seymour's Rule of Amp Pricing. It is more cost effective to buy a single amp with twice the power than it is to buy two amps.
For example, the Crown XLS 202D sells for $200 and generates 300 watts. I could get 600 watts if I buy two of them, and it would cost me $400. Alternately, I could buy the Crown XLS 602D, which is rated at 600 watts, and it would cost me $300. Not only is the bigger amp cheaper, but it is less total weight and less to schlep around.
Watts and specs
Before we talk about how many watts a KJ needs, we need to set some ground rules about specing of amps. The problem is, it is confusing.
First, there is the issue of the units that one uses. Some manufacturers spec out their amps in terms of watts peak-to-peak and some use watts RMS. Peak to peak numbers are given when a manufacturer wants to artificially inflate their specs, since peak-to-peak numbers are almost six times as large as RMS numbers.
Another very helpful way that a manufacturer can confuse a prospective KJ is to speak in terms of total power rather than watts per channel. Another bad thing. Well... it's actually not all that terrible. If an amp has two channels (i.e. stereo), you just add the watts RMS. Just be careful when reading the specs.
The next confusing thing is exemplified in a spec on the Crown XLS 202D: "330W/ch @ 2 ohms, 300W/ch @ 4 ohms, 200W/ch @ 8 ohms, 660W bridged mono @ 4 ohms, 600W bridged mono @ 8 ohms." Depending on which number you look at, the amp could be rated at anywhere from 200 watts per channel to 660 watts per channel.
Isn't this deceptive advertising? Actually, not at all. The specs merely reflect the power output that you get with different configurations of speakers. You just have to know a bit about your speakers in order to properly read the specs. In particular, you need to know a bit about ohms.
Ohms
To clarify right off... I am not talking about the kind of oms involved in transcendental meditation.
Speakers are generally described in terms of their resistance, which is measured in ohms. What does that mean? Well, I could explain it, but the simple explanation requires some explanation of electronics, and the correct explanation says that ohms are actually meaningless when you talk about speakers.
So, let's just say that a typical speaker is 8 ohms and forget the details. Generally speaking, if the speaker has one woofer, it will be 8 ohms. Not always, but usually. If you plug one speaker into each channel of the amp, then the spec from the amp that is relevant is the "watts per channel at 8 ohms" number. In the case of the Crown amplifier, this relevant number is 200W.
With this particular Crown amp (and with most decent amps, for that matter) you can plug two 8 ohm speakers into each channel without blowing up the amp. How can you tell if an amp will blow up with two sets of speakers?
When you plug two speakers in, the resistance (that is, the ohms) of the speakers gets cut in half. If you plug two 8 ohm speakers into each channel, the load for each channel becomes 4 ohms. And now the applicable spec on the amplifier is "300W/ch @ 4 ohms". Just by virtue of the fact that the amp has a power rating for 4 ohms, you know that you can plug in two 8 ohm speakers.
So... hmmmm.... we doubled the number of speakers and the power went from 200 watts per channel up to 300 watts per channel? That doesn't seem fair! We didn't get twice the power. :(
I agree that it's not fair, but it's reality. There is a certain amount of inefficiency when you plug two speakers into the same channel. And this leads to another important point: It is more cost effective to run a single set of speakers per channel.
These important points lead in the same direction. Buy a bigger amp, dude, and use a single set of speakers.
That said, I am going to make a case for plugging in multiple sets of speakers. You probably have noticed this, but the closer you get to a speaker, the louder it is. If I have one speaker, and try tomake it loud enough on the opposite side of the room, it will necessarily be too loud near the speaker. If I add a second speaker, with proper spacing, the overall sound levels are more consistent around the room. Each set of speakers that I scatter throughout the room makes the sound level more even.
In a larger room, I will run with two sets of speakers to get this evenness.
Caveats
For the more technically adept: I need to clear some stuff up. I have made a whole bunch of simplifications in describing this stuff above.
When I talked about the resistance for speakers plugged into the same channel, I was assuming that the speakers had the same resistance. The formula is more complicated if the speakers have different resistances.
Another simplification is thatI have assumed that the speakers are combined in parallel, rather than in series. If you go out of your way with a soldering iron you could combine speakers in series. But, if you use standard plugs and cables in the way they were intended, your speakers will be in parallel.
The third simplification was in my discussion of using multiple sets of speakers. I neglected to say that if the listening areas of the speakers overlap, you will get dead spots from phase cancellation. Analyzing this is very complicated. Don't go crazy with it.
Yet another simplification was that I completely avoided talking about the bridged mono mode for an amp. Let's agree to ignore this. Well... unless you get a passive subwoofer. Then I recommend bringing in a sound pro just to make sure.
How many watts do I need?
Boy... good question.
"It all depends" is a good answer, although probably not all that useful. But of course wattage requirements do depend on a lot of things. I should be honest, though. The real reason I say "depends" is to avoid having to accept any responsibility for my actions.
The first big question to ask is whether you want to do outdoor gigs. If a gig is outdoor, the PA is going to be a lot less efficient. A lot. I mean, a lot. There is nothing to contain the sound, so it will just get lost. Most importantly, the bass will get lost. My opinion... if you are playing a gig outside, you should look into adding a subwoofer. You only need one because the stereo effect is less pronounced at low frequencies. But you do need one.
Another important variable is the efficiency of the speakers. I will discuss this in the section about speakers.
(Now I will actually get down to giving some advice.)
The wattage requirement also depends on the size of the venue. Here is one advisor that gives a specific number: "If you intend using the machine at parties or small social events you will need at least 80 watts (2 speakers at 40 watts each)." Sounds pretty cool. We can get off really cheap!
I am not so excited about 80 watts. The only gig that I have run where 80 watts is sufficient is my New Year's Eve party. This is maybe 20 people, in my living room. And we are generally somewhat older, so we don't need to have music quite so loud. And with 80 watts, the music doesn't interfere much with conversation.
Musician's Friend has a "PA System Buying Guide" that I recommend reading. They offer some advice on power requirements that I find more reasonable:
"The size of the venue you play in can help you determine the continuous power handling (wattage) your system will need. For example, smaller gigs, conferences, lectures, and outdoor meetings may need about 350-500 watts, while club bands, garage bands, and mobile DJs may need 500-1,000+ watts."
Here is a different expert who gives a number in terms of people. If we assume that karaoke fits into the category of "bands and average size venues", then 3 to 4 watts per person (in the audience) is recommended. So, if there are 50 people listening to karaoke, you need something like 150 to 200 watts.
The karaoke pundits put a slightly larger number on it. The number tossed about in this forum is around 10 watts per person. So, if you have a venue with 100 people, then they might recommend 1,000 watts.
The Crown amp that I mentioned above (the XLS 202D) puts out 200 watts per channel into a pair of 8 ohm speakers. So, with one set of speakers, you get a total of 400 watts. With two sets of speakers (the equivalent of one 4 ohm speaker per channel, the amp will put out 300 watts per channel, for a total of 600 watts.
I have this amp. I have run gigs where 400 watts (with one set of speakers) is fine. I have had other gigs where 600 watts (two sets of speakers) falls a bit short... I wind up pushing the amp a bit harder than I would like.
For larger gigs, I now bring one set of passive speakers (speakers that run from the amp) along with one set of active speakers (speakers with their own amps). My active speakers are the Behringer B212A speakers, that put out 250 watts each. Thus, I get a total of 400 watts from the passive speakers and 500 watts from the active, for a total of 900 watts. Still, I sometimes feel I would like to push a bit more. I have my eye on a Crown XLS 802D...
So, I am gonna agree with that range of 200 to 1,000 watts. To make most customers happy, I think a KJ should be set up to deliver something like that amount of power. o make the KJ happy, you need to push toward the other end.
Now for the weaselwords. If you are running outdoors, you should really consider getting a subwoofer. And more power. And if you are running a large club, then you will probably need a whole lot more power, but (my experience) large clubs usually have their own sound system. And they will usually allow you to hook into their system.
Copyright (c) 2010, John Seymour
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