How do you "size" an amp? I want everyone to hear it, without making anyone's ears bleed.
Situation could be anything from a 12' x 50' conference room with 10' ceiling to a 100' by 100' showroom with a 30' ceiling.
Surely there's a 'formula' for this sort of thing?
Situation could be anything from a 12' x 50' conference room with 10' ceiling to a 100' by 100' showroom with a 30' ceiling.
Surely there's a 'formula' for this sort of thing?
Well, considering you gave us no idea of the application. Is it just spoken word? One guy talking? A folk trio singing? Small rock bands auditioning?
100 foot square showroom? OK, what do you want in that showroom? A whole rock band music presentation for all to actively listen to? Or some background music to set a mood, but not interfere with conversations? Or a lecture to a hall full of people?
How tall should a ladder be? Two steps to reach the kitchen top shelf? 8 feet to reach the top of the doorways? 30 feet to reach the eaves troughs?
100 foot square showroom? OK, what do you want in that showroom? A whole rock band music presentation for all to actively listen to? Or some background music to set a mood, but not interfere with conversations? Or a lecture to a hall full of people?
How tall should a ladder be? Two steps to reach the kitchen top shelf? 8 feet to reach the top of the doorways? 30 feet to reach the eaves troughs?
I've played churches with seating for 120, 40'x80'x10', brick walls & sparse crowd, with 35 W stereo. That is a quiet attentive crowd.
Another church is 30'x50'x10', seats ~70, brick walls, has a QSC RMX800. 400 w/ch. Only one speaker on one channel. That is overkill in watts IMHO. They should have been sold a Peavey MMA-75t or Crown MA-180. I have the Peavey in my house, 14'x33'x11' music room; quite capable of symphony or cantata reproduction.
Another church 100'x50'x30' stone walls had an organ equipped with two 100 watt amps for two channels. Huge heat sink, that S100 could do 100 watts all day.
Bar crowds shouting at each other & whistling, quadruple or 8x wattage.
Another church is 30'x50'x10', seats ~70, brick walls, has a QSC RMX800. 400 w/ch. Only one speaker on one channel. That is overkill in watts IMHO. They should have been sold a Peavey MMA-75t or Crown MA-180. I have the Peavey in my house, 14'x33'x11' music room; quite capable of symphony or cantata reproduction.
Another church 100'x50'x30' stone walls had an organ equipped with two 100 watt amps for two channels. Huge heat sink, that S100 could do 100 watts all day.
Bar crowds shouting at each other & whistling, quadruple or 8x wattage.
It's not a matter of Watts per, rather it is an "average" sound pressure level measured in decibels. Loudspeakers of course are all over the map on decibel levels per watt, a sensitivity level.
We must take into consideration the frequencies you are intending to cover, the true public address, with those big horns are the easiest to implement.
When I worked at Radio Shack in my twenties, I had a guy come in for a PA system he wanted to assemble for a metal-fab shop. I got him an amp, a pedestal microphone & three of those giant RS "Powerhorn" PA jobs.
A few days later he came by kinda confused, didn't know what to do, had lines strung thru the shop, but couldn't get anything to work.
I stopped by his shop, wired things up, loud & clear..."Jerry, come to the office"...while noisy work was in progress.
------------------------------------------------------------------------------Rick.....
We must take into consideration the frequencies you are intending to cover, the true public address, with those big horns are the easiest to implement.
When I worked at Radio Shack in my twenties, I had a guy come in for a PA system he wanted to assemble for a metal-fab shop. I got him an amp, a pedestal microphone & three of those giant RS "Powerhorn" PA jobs.
A few days later he came by kinda confused, didn't know what to do, had lines strung thru the shop, but couldn't get anything to work.
I stopped by his shop, wired things up, loud & clear..."Jerry, come to the office"...while noisy work was in progress.
------------------------------------------------------------------------------Rick.....
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If there is it will be a long list of variables.
A+B+C+D+E+F... = watts needed.
A. Sound absorption factor of the listening area(indoor or out, heavily damped - very reflective)
B. Size of area to be covered.
C. Number of persons in the listening area
D. Type of audio presentation to be amplified.
E. Position of loudspeaker relative to the listeners
F. Sensitivity of loudspeaker system
The application varies, that's why I'm looking for a general "rule of thumb".
Case #1: Business conference room, used for conferences and training, anywhere from 2 to 20 attendees + speaker. The amp would not necessarily be for the speaker (not really needed) but for training videos and teleconferencing, something better than just cranking up the volume on the TV.
Case #2: 100' square "showroom". used for demo-ing equipment, playing sales videos, but ALSO used for "events" such as Christmas parties where there might or might not be a speaker and/or recorded background music or a small band. I'm not worried about the band, they'd likely have their own gear. For everything else, they're making do with a single-channel TOA PA mixer/amp and crappy ceiling PA-grade speakers that has about all the clarity of the teacher in the charlie brown films.
Case #3: Wife teaches occasional (maybe 1/month if that) water aerobics classes at the local Y. Olympic-size pool with concrete block walls - the worst possible acoustic environment. Plus, chlorine in the air from the pool, worst possible environment for electronics
Case #4: Cycling class, outdoors, in the parking lot of a local shopping center.
(Personally, I've never understood this. If you're going to cycle outdoors then why not.... cycle outdoors?)
That's EXACTLY the sort of formula that I'm looking for. But I can't find anything anywhere.
An efficient speaker cuts # of watts required. If bass is required I'd buy a Peavey SP2, 84 lb, -3 db @ 54 hz, 98 db 1w1m. If not, a SP5. No point in stereo any of those situations. Get the speakon cables: they don't short the amplifier if tripped on the way 1/4 phone plug cables (cheaper) will. JBL makes some great speakers that I haven't heard here in flyover country. 4722, 4365, 4367 are touted as something to copy by the builders over on multi-way forum.
#2 & # 4 could make use of 150 real watts. Unfortunately most of what is sold now has phantom ratings of 1000 w, 3000 w, 6000 w. (Behringer). The last puts out more "watts" than the power cord will draw. Don't understand those products, if they break are repairable only by authorized shops. #1 & 3 could work with 35-75 watts. I'd buy a disposable speaker for #3, something like a visiton 6 1/2" full range driver in a 14" long cardboard box. A 1" hole in the back boosts the bass.
Peavey MMA-8150t or MMA-81502 could handle all those with 150 watts, are running about $50 on ebay, with issues. (usually bad e-caps, dirty pots, or dirty internal connections). Crown sold MA-1160. Both have transformer protection to keep from blowing up the speaker if wiring faults. Both these have multiple inputs, and the Peavey some inputs can be bought that have phantom power for high quality condensor mikes. I've never seen the crown. Note the Peavey usually comes with telephone input cards, may have to hunt a bit for audio/mike cards. Many of these cards have 2 RCA inputs to mix the 2 channels, which is necessary on CD's that leave out some instruments/vocalists on one channel or the other.
Also possible to buy a powered speaker at 150 w, but lots of these amps show up needing repair on ebay. (klipsch) Not IMHO repairable, switcher supplies.
A speaker stand for getting the speaker above the heads of the crowd does a lot for projecting the sound. See movie 4 Weddings & a Funeral for the setup.
The QSC RMX800 would do the job with some overkill, but requires a separate mixer for more than one input. Also compatible only with dynamic mike, not condensor. Top of line products that don't blow up a lot, Crown, Peavey, Yamaha, QSC. As reported by repairmen on PA thread.
There are powered mixers available with 75 to 100 w/ch stereo output. The old ones are usually IC amps, and a bit fragile if wiring errors occur. New ones will be class D. which has its own sound. Used mixers will have a bad master volume pot.
If you want to check a setup in store for accurate sound, use a piano CD with a steinway grand. They have certain sound that is difficult to reproduce, and I had to wait 50 years before I could afford a speaker that was pretty accurate (SP2-XT). Beethoven Appasionatta starts right off with the low notes, no waiting. Solo top octave, also very difficult, is on Peter Nero, When I Fall in Love. Smooth voice is another check, pick your vocalist. Many PA bargain speakers have a bumpy midrange that warp voices, and many don't disperse widely across the room the way the SP2 & SP5 do on stands.
#2 & # 4 could make use of 150 real watts. Unfortunately most of what is sold now has phantom ratings of 1000 w, 3000 w, 6000 w. (Behringer). The last puts out more "watts" than the power cord will draw. Don't understand those products, if they break are repairable only by authorized shops. #1 & 3 could work with 35-75 watts. I'd buy a disposable speaker for #3, something like a visiton 6 1/2" full range driver in a 14" long cardboard box. A 1" hole in the back boosts the bass.
Peavey MMA-8150t or MMA-81502 could handle all those with 150 watts, are running about $50 on ebay, with issues. (usually bad e-caps, dirty pots, or dirty internal connections). Crown sold MA-1160. Both have transformer protection to keep from blowing up the speaker if wiring faults. Both these have multiple inputs, and the Peavey some inputs can be bought that have phantom power for high quality condensor mikes. I've never seen the crown. Note the Peavey usually comes with telephone input cards, may have to hunt a bit for audio/mike cards. Many of these cards have 2 RCA inputs to mix the 2 channels, which is necessary on CD's that leave out some instruments/vocalists on one channel or the other.
Also possible to buy a powered speaker at 150 w, but lots of these amps show up needing repair on ebay. (klipsch) Not IMHO repairable, switcher supplies.
A speaker stand for getting the speaker above the heads of the crowd does a lot for projecting the sound. See movie 4 Weddings & a Funeral for the setup.
The QSC RMX800 would do the job with some overkill, but requires a separate mixer for more than one input. Also compatible only with dynamic mike, not condensor. Top of line products that don't blow up a lot, Crown, Peavey, Yamaha, QSC. As reported by repairmen on PA thread.
There are powered mixers available with 75 to 100 w/ch stereo output. The old ones are usually IC amps, and a bit fragile if wiring errors occur. New ones will be class D. which has its own sound. Used mixers will have a bad master volume pot.
If you want to check a setup in store for accurate sound, use a piano CD with a steinway grand. They have certain sound that is difficult to reproduce, and I had to wait 50 years before I could afford a speaker that was pretty accurate (SP2-XT). Beethoven Appasionatta starts right off with the low notes, no waiting. Solo top octave, also very difficult, is on Peter Nero, When I Fall in Love. Smooth voice is another check, pick your vocalist. Many PA bargain speakers have a bumpy midrange that warp voices, and many don't disperse widely across the room the way the SP2 & SP5 do on stands.
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Thanks for the advice @indianajo.
Yeah, I'm suspicious of power ratings these days too. I mean, a "5000 watt amplifier" with a NEMA-15 power cord on it? LOL.
Heck, being from southern Indiana also, I can remember the '70s when Emerson Lake & Palmer brought "Kilowatt Rock" to Market Square Arena in Indy and their 1,000 watts could be heard for blocks around. (RIP Market Square Arena '01)
Yeah, I'm suspicious of power ratings these days too. I mean, a "5000 watt amplifier" with a NEMA-15 power cord on it? LOL.
Heck, being from southern Indiana also, I can remember the '70s when Emerson Lake & Palmer brought "Kilowatt Rock" to Market Square Arena in Indy and their 1,000 watts could be heard for blocks around. (RIP Market Square Arena '01)
I think the most effective strategy would be to get a system with multiple speakers that can be scaled up from a single to multiple depending on the event.
Cases 1,3,4 would require a pretty modest PA system, one or two 8" powered speakers would cover all those but case 2 is where the plan falls apart, I do lots of event this size and type and I'd bring a something like a pair of EV EKX12p over EKX18sp subs, that is a very capable PA system that can support a band or DJ. But recognizing what is being used now supplementing those 8" powered boxes with some 12" or 15" subs will make it into a proper party system that vastly out performs the current gear. You might get by with just a pair of 12" or 15" PA speakers instead but your wife is not going to want to carry those big boxes to the smaller events, hence my suggestion.
If we were to put some amp power numbers on that this is what it might look like using the suggested speakers. On a budget the Alto TS3 line has products that fit in here but of course you could spend lots more if you want. And you won't beat the convenience of these powered speakers, you can plug both a mic and music source right into one of these so no extra equipment needed.
Case 1: 25w (one 8" top barely turned up)
Case 2: 3000w (both tops and subs running flat out)
Case 3: 400w (both 8" tops at moderate levels)
Case 4: 1000w(Both 8" tops flat out)
Cases 1,3,4 would require a pretty modest PA system, one or two 8" powered speakers would cover all those but case 2 is where the plan falls apart, I do lots of event this size and type and I'd bring a something like a pair of EV EKX12p over EKX18sp subs, that is a very capable PA system that can support a band or DJ. But recognizing what is being used now supplementing those 8" powered boxes with some 12" or 15" subs will make it into a proper party system that vastly out performs the current gear. You might get by with just a pair of 12" or 15" PA speakers instead but your wife is not going to want to carry those big boxes to the smaller events, hence my suggestion.
If we were to put some amp power numbers on that this is what it might look like using the suggested speakers. On a budget the Alto TS3 line has products that fit in here but of course you could spend lots more if you want. And you won't beat the convenience of these powered speakers, you can plug both a mic and music source right into one of these so no extra equipment needed.
Case 1: 25w (one 8" top barely turned up)
Case 2: 3000w (both tops and subs running flat out)
Case 3: 400w (both 8" tops at moderate levels)
Case 4: 1000w(Both 8" tops flat out)
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Case 2 3000W for 254 sq meters ?
You don't want to host a Rock party nor a Techno rave.
I would try a Fender Passport or a Yamaha Stagepas system for a start.
Portable, light, small, mixer included. This would put You in the 600-800 W ballpark.
For outdoors I would install several PA speakers depending on crowd & distance.
Bear in mind, in winter You need more power since sound is absorbed by clothes.
You don't want to host a Rock party nor a Techno rave.
I would try a Fender Passport or a Yamaha Stagepas system for a start.
Portable, light, small, mixer included. This would put You in the 600-800 W ballpark.
For outdoors I would install several PA speakers depending on crowd & distance.
Bear in mind, in winter You need more power since sound is absorbed by clothes.
Hi,
yeah there is no simple rule of thumb, lets think it through why.
if you've got one loudspeaker, it takes more amplifier Watts to get same SPL in a given position in the room compared to a situation you had for example 100 loudspeakers. Or, just put the one speaker right next to the chosen spot and you've got all SPL you need for that spot. Hello headphones.
If you absolutely have to approximate the Watts, measure SPL in the position(s) of interest and calculate. If say 1000 Watts of power doesn't deliver the required SPL with the given speaker system you could calculate how much more Watts you need. Doubling the amplifier Watts gives around 3dB more SPL at a position until the speakers cannot handle the power anymore. Add more speakers, or switch to a more sensitive ones, or distribute the system into multiple locations. Unlimited possibilities.
There is no simple formula to this, as you've noticed, you would have to model the whole situation with the room and the speakers and their positions etc. too complicated math.
If you know the system, and can freely position it in relation to the audience you know how much SPL at what distance with appropriate fidelity is possible since it is your system, you've heard and measured it. Double the distance SPL drops 3db - 6db depending on many things.
Since the power is so cheap compared to the speakers you've probably maxed out the amplifier power already and it is the speakers that limit the performance. Amplifier Watts just don't matter unless you have too few.
Peace 🙂
yeah there is no simple rule of thumb, lets think it through why.
if you've got one loudspeaker, it takes more amplifier Watts to get same SPL in a given position in the room compared to a situation you had for example 100 loudspeakers. Or, just put the one speaker right next to the chosen spot and you've got all SPL you need for that spot. Hello headphones.
If you absolutely have to approximate the Watts, measure SPL in the position(s) of interest and calculate. If say 1000 Watts of power doesn't deliver the required SPL with the given speaker system you could calculate how much more Watts you need. Doubling the amplifier Watts gives around 3dB more SPL at a position until the speakers cannot handle the power anymore. Add more speakers, or switch to a more sensitive ones, or distribute the system into multiple locations. Unlimited possibilities.
There is no simple formula to this, as you've noticed, you would have to model the whole situation with the room and the speakers and their positions etc. too complicated math.
If you know the system, and can freely position it in relation to the audience you know how much SPL at what distance with appropriate fidelity is possible since it is your system, you've heard and measured it. Double the distance SPL drops 3db - 6db depending on many things.
Since the power is so cheap compared to the speakers you've probably maxed out the amplifier power already and it is the speakers that limit the performance. Amplifier Watts just don't matter unless you have too few.
Peace 🙂
Same thing in simpler form, even says it is a rule of thumb, kind of 🙂 SPEAKER MEETS AMPLIFIER - HOW TO SELECT THE RIGHT AMPLIFIER - Yamaha - Finland
i could be wrong but it does seem that this is more about intelligibility than SPL,no?
and as a result each situation does require adequate SPL but it's more of question of being able to put the sound where it's needed rather then getting to a particular level, in a reverberant environment like a "mall" court (or public pool) SPL can be your enemy...
the ability to tailor the frequency response of the system to the acoustic environment is more what's needed i think.
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I've have done 100s, perhaps 1000s of business meetings in rooms of about 12x50 with simple powered speakers on speaker stands. More then enough volume for speech, video playback, recorded music, etc. Generally running at 20% capacity Look at how much power is used in speakers like the JBL Eon, the QSC K.2 series, Mackie and similar.
I have also done many shows in a 100x100x30 ballroom. We have used small Meyer Line arrays and the powered Meyer CQ as delays and side fills. Loud enough to do rock bands. I've used 2x or 4X CQs to cover ballrooms about that size, but not for rock band levels. The CQ is a two-way with 620 watts for high and for low. I wouldn't go any lower than that for a large room. The CQ is efficient, so that helps.
Of course I have heard many a Luau in Hawaii covered (outside) by two Mackie powered speakers and it worked just fine. They claim 1000 watts per channel, but I"m not sure I believe it. 🙂
I have also done many shows in a 100x100x30 ballroom. We have used small Meyer Line arrays and the powered Meyer CQ as delays and side fills. Loud enough to do rock bands. I've used 2x or 4X CQs to cover ballrooms about that size, but not for rock band levels. The CQ is a two-way with 620 watts for high and for low. I wouldn't go any lower than that for a large room. The CQ is efficient, so that helps.
Of course I have heard many a Luau in Hawaii covered (outside) by two Mackie powered speakers and it worked just fine. They claim 1000 watts per channel, but I"m not sure I believe it. 🙂
I got called in tonight to install a D&B PA in a school gym/theater. It's got to be near 100x100x30. I'll check on how much power we are using tomorrow.
Sorry, L-Acoustics rig. 4X1800 watts per side (at 4 ohms). Super loud with thumping bass in a space 100x86x45 feet. Loud enough that you can't even shout over it to be heard.
Get yourself a copy of the Yamaha Sound Reinforcement Handbook; it answers all of your questions.