How Much Power?

Stevens R. Miller

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Apr 11, 2016
Location
Loudoun County, Virginia, USA
I suspect this is asked (and answered) a lot, but most of the online guidance I've found has been (understandably) a bit vague. I'm hoping, though, that maybe someone has had experience in nearly the same setting as the one in which I'm seeking guidance.

After our last community theater musical wrapped, I made it clear to my colleagues that I have had my lifetime desire to work with badly maintained, curiously wired, largely undocumented dusty humming audio equipment of nostalgic vintage completely satisfied by our latest experience. Accordingly, I am pushing for us to get our own powered speakers, so we can stop using the in-house stuff in the middle schools we use as venues. The response has been cautiously supportive. But the threshold question, of course, is how much will this cost? That, naturally, depends on what we need.

Our typical venue is a middle school auditorium, with a seating area of about 4,000 square feet (roughly 80 feet wide by 50 feet deep), that seats about 480 people. They usually have a single center cluster of three speakers mounted on the ceiling, just above and in front of the proscenium arch. As far as I can tell, it is driven by a QSC CX1102 amplifier. I do not know the impedance of the speakers. If they are 8-ohm, QSC says both channels driven gets you 700 watts (I am not entirely sure, but I think both channels are used in a bridged configuration). If they are 4-ohm, QSC says that gets you 1,100 watts. The masters on the amplifier are down about one-third from their least-attenuation position, and I know we could be driving the amp with higher line levels than we send it, so we have a lot of overhead that, I am guessing, we mostly never use.

So here's my question: if we're going to use a pair of self-powered speakers on stands, instead of the single center cluster on the ceiling, in a 4,000-square-foot, 480-seat middle school auditorium, how much power should each speaker provide?
 

jkowtko

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Joined
Jan 9, 2007
Location
Redwood City, CA
... I have had my lifetime desire to work with badly maintained, curiously wired, largely undocumented dusty humming audio equipment of nostalgic vintage completely satisfied by our latest experience.
Everyone always has at least one interesting thing on their bucket list ... ;)

So here's my question: if we're going to use a pair of self-powered speakers on stands, instead of the single center cluster on the ceiling, in a 4,000-square-foot, 480-seat middle school auditorium, how much power should each speaker provide?
I run the semesterly instrumental music concert at the local middle school. Similarly sized auditorium with pull-out bleachers along one side wall where the ~500 parents sit.

For this I use two Mackie SRM450s on tripod stands at the corner edges of the "orchestra" area on the gym floor -- about 75-80 feet apart, 10 feet from the base of the bleachers -- and one Anchor AN-1000x speaker on a small stand in front of the conductor's riser as the center fill.

The center fill makes a BIG difference in sound ... it fills the entire space evenly. The center runs off an Aux so is a mono mix of LR.

The above setup has way more than enough horsepower to blast the parents in the auditorium. I run the speaker volume knob at ~10 o-clock (12 o'clock is the halfway point). The Anchor runs at 12 o'clock (halfway point). I've also used the exact same setup for a school assembly the following morning (spirit week) with rowdy screaming kids in the audience instead of relatively polite and quiet parents, and again had no problem pushing the band and the emcee up over the crowd noise.

If you don't have access to the SRM450, then QSC K-12 should be equivalent in volume, maybe with slightly cleaner sound. I wouldn't suggest anything less powerful.

And make sure you have that center fill.
 

Stevens R. Miller

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Joined
Apr 11, 2016
Location
Loudoun County, Virginia, USA
I use two Mackie SRM450s on tripod stands at the corner edges of the "orchestra" area on the gym floor
Wow! Those are a thousand watts each, right? That does seem a bit potent.

and one Anchor AN-1000x speaker on a small stand in front of the conductor's riser as the center fill.
I may be misreading their Web site, so let me know if I'm right or wrong: that one is only 50 watts(?). Is that enough to get the fill you're creating?

The center fill makes a BIG difference in sound ... it fills the entire space evenly.
That's a very helpful point, thanks.

Sounds like you're in a bigger space than I'm using, but otherwise dealing with similar issues.

Thanks for the reply!
 

jkowtko

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Joined
Jan 9, 2007
Location
Redwood City, CA
Yes the 400 watt model ... I may have the V1 ... mine are over ten years old.

The AN-1000x packs a punch. Not great music quality but gets fairly loud. As a fill it does what it needs to. if you want to put a larger speaker in there you could, but larger speakers will also start to physically block the view. The AN-1000X lays horizontally with side mount points so it can be tilted up.

My entire sound system for this concert including two SRM450s, two AN-1000x (another one for choir monitor), 4 wireless receivers and sound board, all run off of a single standard (15a?) 110v outlet from the wall ... nothing special. I've been doing this for several years now with the same speakers.

Also, I will caution you against getting the smaller speakers (SRM350 or QSC K-10) ... IMHO they pale in comparison in power and sound quality.
 

FMEng

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Tacoma, WA
It's time to break some myths again...

The size of the amp has little to do with how loud the speaker is under normal operating conditions. All it means is how much power can be delivered to the speaker, if called upon by the input signal, without clipping distortion. You'd be surprised how many speakers are doing their job every day being driven by an average of a few tens of watts from a 1000 Watt amplifier. Having extra headroom is never a bad thing. Plus, there is always a certain amount of spec-manship with speakers. 1000 Watts sells better than 700, though you'd be hard pressed to hear the difference.

Another myth is that the setting of the volume control on the amplifier has anything to do with how much power is going to the speaker. All the volume control does is adjust how much input signal is required to drive the amp to a given amount of output. You can drive the amp to full output with the control set at 9 O'clock or 5 O'clock.

Mackie SRM450s, were excellent for their day, but subsequent generations of that product don't compare that favorably to the plethora of self powered speakers available today. They are fine for a tight budget, though. If the budget allows, consider Yamaha DXR/DSR series, QSC K/KW series, or EV EKX series, among many others. I would look for something with a 12" or 15" woofer.
 

RonHebbard

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Premium Member
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Jun 12, 2004
Location
Waterdown, ON, CA
It's time to break some myths again...

The size of the amp has little to do with how loud the speaker is under normal operating conditions. All it means is how much power can be delivered to the speaker, if called upon by the input signal, without clipping distortion. You'd be surprised how many speakers are doing their job every day being driven by an average of a few tens of watts from a 1000 Watt amplifier. Having extra headroom is never a bad thing. Plus, there is always a certain amount of spec-manship with speakers. 1000 Watts sells better than 700, though you'd be hard pressed to hear the difference.

Another myth is that the setting of the volume control on the amplifier has anything to do with how much power is going to the speaker. All the volume control does is adjust how much input signal is required to drive the amp to a given amount of output. You can drive the amp to full output with the control set at 9 O'clock or 5 O'clock.

Mackie SRM450s, were excellent for their day, but subsequent generations of that product don't compare that favorably to the plethora of self powered speakers available today. They are fine for a tight budget, though. If the budget allows, consider Yamaha DXR/DSR series, QSC K/KW series, or EV EKX series, among many others. I would look for something with a 12" or 15" woofer.
Hello @FMEng, possibly you'll write a few words about sensitivity and efficiency, 1 Watt/1 Meter.
Toodleoo!
Ron Hebbard
 
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jkowtko

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Jan 9, 2007
Location
Redwood City, CA
Don't forget that 400W vs 1000W is only 4dB...
I agree the volume level difference is probably not that noticeable ... maybe the more relevant point of this is that two of these speakers plus other sound equipment for the gig would collectively be rated to run under one 15 amp circuit.

I also won't dispute the speaker quality issues with the newer versions of the Mackie. I would just say it's safer to audition them yourself before buying ... or buy from a place you can return them to if not satisfied when you first use them.
 

Stevens R. Miller

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Joined
Apr 11, 2016
Location
Loudoun County, Virginia, USA
Okay, looks like a general consensus is forming around two 400-watt speakers, with jkowtko making a good case for a low-power center-fill speaker. We are on the typically tight budget for a community theater company, but I certainly don't want to "save" money by wasting it on bad equipment.

At the low end of the price spectrum, I see a lot of products offered by Gemini. Example: Gemini AS-08P, 8-inch woofer, 500W, $99.95. That's an awfully attractive price for that many watts, but I'm naturally dubious when, for comparison, the Electro-Voice ZLX-15P, 15-inch woofer, 1000W, is $449.00. Twice the power and twice (or, four times, if you consider area instead of diameter) the speaker cone, but also about four times the price. Now, we can allocate more than $100 for each of two powered speakers, but $450 is out our range. I'd hazard to say that we'd like to keep it under $250, more like $200, if possible.

Any particular recommendations for a 400W device for $200?
 

TJCornish

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Joined
Mar 27, 2012
Location
St. Paul, MN
Wow! Those are a thousand watts each, right? That does seem a bit potent.


I may be misreading their Web site, so let me know if I'm right or wrong: that one is only 50 watts(?). Is that enough to get the fill you're creating?


That's a very helpful point, thanks.

Sounds like you're in a bigger space than I'm using, but otherwise dealing with similar issues.

Thanks for the reply!
As others are alluding to, you don't hear watts, you hear sound pressure level - SPL. The efficiency of various speakers can vary a lot - some take a lot of watts to make a certain amount of SPL; others that are more efficient can do the job with fewer watts. All of that is irrelevant, though, and most newer-generation products tend to have large amplifiers because it can now be done cheaply, whereas 10 or 15 years ago, high power amps were more expensive.

What kind of material are you working with? An 80' x 50' room isn't all that big, so I agree with the others that any reasonable model of modern powered speakers will likely be just fine unless you're looking for concert volume.

The JBL SRX800p, Yamaha DSR112, and EV ETX all sound really excellent and have much of the tuning work done at the factory, so you will get good sound by plugging them in and turning them on. The lesser offerings - JBL PRX, Yamaha DXR, and the lower-end EV series will work too, trading off performance for cost savings.

In my opinion, QSC is a bit behind at the moment with their powered speaker offerings.

I agree with FMEng that you probably want 12" woofers, as smaller speakers will have lower output and/or less bass ability. Often (again in my opinion) the extra weight and size of a 15" speaker doesn't really buy you very much. Any of the above speakers will do 95dB+ at 50'.

I also agree that the width of the room may be a challenge without a front fill speaker. I am partial to the Yamaha DXR-10, which is the best of the bunch of the 10" speakers and is a great value. If you want to stick with the same brand, a pair of Yamaha DSR-112 speakers for left/right and one DXR-10 as a center fill would be a great system. You could chain the center fill off either the left or right main and it would be close enough. You'll want to turn the level down lower than the left/right speakers; it's purpose is to fill in the hole from the main system.
 

TJCornish

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Joined
Mar 27, 2012
Location
St. Paul, MN
Okay, looks like a general consensus is forming around two 400-watt speakers, with jkowtko making a good case for a low-power center-fill speaker. We are on the typically tight budget for a community theater company, but I certainly don't want to "save" money by wasting it on bad equipment.

At the low end of the price spectrum, I see a lot of products offered by Gemini. Example: Gemini AS-08P, 8-inch woofer, 500W, $99.95. That's an awfully attractive price for that many watts, but I'm naturally dubious when, for comparison, the Electro-Voice ZLX-15P, 15-inch woofer, 1000W, is $449.00. Twice the power and twice (or, four times, if you consider area instead of diameter) the speaker cone, but also about four times the price. Now, we can allocate more than $100 for each of two powered speakers, but $450 is out our range. I'd hazard to say that we'd like to keep it under $250, more like $200, if possible.

Any particular recommendations for a 400W device for $200?
I didn't carefully read over your budget numbers.

Gemini, Nady, Fender, Alto, Samson, Phonic, et al are all garbage and your current feelings of frustration will continue into the future. For new gear, a pair of Yamaha DXR-12 would be the bottom of the range that would be worth your time new (IMO). If your absolute max budget is $200, you're in trouble, even for used equipment. I recently sold some 15-year old Mackie SRM-450 speakers for $300 each. There's not much even used for $100 each.

Once again - forget watts. It's as meaningless as comparing fuel pump pressure on cars. Think SPL!
 

Stevens R. Miller

Well-Known Member
Joined
Apr 11, 2016
Location
Loudoun County, Virginia, USA
As others are alluding to, you don't hear watts, you hear sound pressure level - SPL.
That makes sense, given what I'm learning about speakers. I was shocked to find out how inefficient they are. Apparently, it's common for 99% of the power sent to a speaker to be lost as heat, not converted to sound. I'd have lost a bet on that one.

Let's see if I'm doing my homework right: SPL is the logarithm of the ratio of pressure created by a sound source and the pressure created by a reference sound. The common reference sound for audio work is 20 micro-pascals, chosen because it is at roughly the lower limit of human hearing. Expressed as decibels, SPL is 20 log10(p/p0), where p0 is the reference sound. The Yamaha DXR-12 quotes a maximum SPL of 132 dB (about 157,000,000 times the reference pressure). Am I correct in assuming that SPL must be measured at some standardized distance from the speaker? If so, is it safe to assume that all vendors are quoting SPLs that are measured the same way, thus making them directly comparable?

What kind of material are you working with? An 80' x 50' room isn't all that big, so I agree with the others that any reasonable model of modern powered speakers will likely be just fine unless you're looking for concert volume.
We do musicals with pre-recorded soundtracks. Examples are "My Fair Lady," "The Little Mermaid," and "Fiddler on the Roof." You know, the usual stuff ;). We need a fairly fulsome level of sound, but we're not doing head-bangin' heavy metal.

I agree with FMEng that you probably want 12" woofers, as smaller speakers will have lower output and/or less bass ability. Often (again in my opinion) the extra weight and size of a 15" speaker doesn't really buy you very much. Any of the above speakers will do 95dB+ at 50'.
My Googling suggests that the standard distance for measuring SPL is one meter. 50' is about 15.24 meters, and pressure should drop by in the inverse square law, so 132 dB at one meter would be about 116.6 at 50'. If I want 95dB, then, that DXR-12 would appear to be good enough (although their spec is 132 dB is maximum peak, not RMS; is maximum peak what I should be looking at?).

I also agree that the width of the room may be a challenge without a front fill speaker.
Agreed, I think this is a very appealing layout and I have recommended it to my colleagues.

I learn so much at this site, but it's like drinking from a fire house. Add to that the fact that I'm advising other people on how to spend their money and it's a bit intimidating. I sure do appreciate all the guidance I get here.
 

RonHebbard

Well-Known Member
Premium Member
Joined
Jun 12, 2004
Location
Waterdown, ON, CA
As others are alluding to, you don't hear watts, you hear sound pressure level - SPL. The efficiency of various speakers can vary a lot - some take a lot of watts to make a certain amount of SPL; others that are more efficient can do the job with fewer watts. All of that is irrelevant, though, and most newer-generation products tend to have large amplifiers because it can now be done cheaply, whereas 10 or 15 years ago, high power amps were more expensive.

What kind of material are you working with? An 80' x 50' room isn't all that big, so I agree with the others that any reasonable model of modern powered speakers will likely be just fine unless you're looking for concert volume.

The JBL SRX800p, Yamaha DSR112, and EV ETX all sound really excellent and have much of the tuning work done at the factory, so you will get good sound by plugging them in and turning them on. The lesser offerings - JBL PRX, Yamaha DXR, and the lower-end EV series will work too, trading off performance for cost savings.

In my opinion, QSC is a bit behind at the moment with their powered speaker offerings.

I agree with FMEng that you probably want 12" woofers, as smaller speakers will have lower output and/or less bass ability. Often (again in my opinion) the extra weight and size of a 15" speaker doesn't really buy you very much. Any of the above speakers will do 95dB+ at 50'.

I also agree that the width of the room may be a challenge without a front fill speaker. I am partial to the Yamaha DXR-10, which is the best of the bunch of the 10" speakers and is a great value. If you want to stick with the same brand, a pair of Yamaha DSR-112 speakers for left/right and one DXR-10 as a center fill would be a great system. You could chain the center fill off either the left or right main and it would be close enough. You'll want to turn the level down lower than the left/right speakers; it's purpose is to fill in the hole from the main system.
Efficiency is NEVER irrelevant.
Toodleoo!
Ron Hebbard.
 

TJCornish

Well-Known Member
Joined
Mar 27, 2012
Location
St. Paul, MN
That makes sense, given what I'm learning about speakers. I was shocked to find out how inefficient they are. Apparently, it's common for 99% of the power sent to a speaker to be lost as heat, not converted to sound. I'd have lost a bet on that one.

Let's see if I'm doing my homework right: SPL is the logarithm of the ratio of pressure created by a sound source and the pressure created by a reference sound. The common reference sound for audio work is 20 micro-pascals, chosen because it is at roughly the lower limit of human hearing. Expressed as decibels, SPL is 20 log10(p/p0), where p0 is the reference sound. The Yamaha DXR-12 quotes a maximum SPL of 132 dB (about 157,000,000 times the reference pressure). Am I correct in assuming that SPL must be measured at some standardized distance from the speaker? If so, is it safe to assume that all vendors are quoting SPLs that are measured the same way, thus making them directly comparable?



We do musicals with pre-recorded soundtracks. Examples are "My Fair Lady," "The Little Mermaid," and "Fiddler on the Roof." You know, the usual stuff ;). We need a fairly fulsome level of sound, but we're not doing head-bangin' heavy metal.



My Googling suggests that the standard distance for measuring SPL is one meter. 50' is about 15.24 meters, and pressure should drop by in the inverse square law, so 132 dB at one meter would be about 116.6 at 50'. If I want 95dB, then, that DXR-12 would appear to be good enough (although their spec is 132 dB is maximum peak, not RMS; is maximum peak what I should be looking at?).



Agreed, I think this is a very appealing layout and I have recommended it to my colleagues.

I learn so much at this site, but it's like drinking from a fire house. Add to that the fact that I'm advising other people on how to spend their money and it's a bit intimidating. I sure do appreciate all the guidance I get here.
There are places to get off into the weeds - "peak" SPL, "Program" SPL, "Continuous" SPL, and various weightings - A, C, fast, slow, unweighted, etc. Loudspeaker manufacturers generally reference their specs to 1 meter and for every doubling of distance you subtract 6dB. That much is standard; how the vendor arrives at the initial number is murkier - is it peak SPL? (probably) Is it a level the speaker can reproduce indefinitely without damage? (Maybe) Does it sound good at that level? (Probably not).

Based on owning and having heard many of the current crop of speakers, all of them that are of reasonable quality - >$500 will likely do what you need. I came up with 95dB program SPL as a safe number that pretty much every speaker I mentioned above will be able to do and not sound like garbage doing it. 95dB is fairly loud and I think will meet your needs.
 

RonHebbard

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Premium Member
Joined
Jun 12, 2004
Location
Waterdown, ON, CA
!? Can you elaborate with regards to this context?
I just find too many people get hung up on how many watts they're buying, or how many watts a device can sustain without releasing its magic smoke with little to no regard to efficiency. Those people are the music stores rightful prey.
Toodleoo!
Ron Hebbard.
 

Stevens R. Miller

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Joined
Apr 11, 2016
Location
Loudoun County, Virginia, USA
I came up with 95dB program SPL as a safe number that pretty much every speaker I mentioned above will be able to do and not sound like garbage doing it. 95dB is fairly loud and I think will meet your needs.
We'd have two speakers, and most of our audience is within 10 meters. Losing 6dB at every doubling of the one-meter reference distance means we're losing about 24dB (at 8 meters, but let's keep the math simple and, hey, this is just an estimate). According to this Web page from Crown, you get back about 6dB by being in an enclosed space, so I'm going to guess I'm down about 18dB, which takes to me to 77dB where most of the audience is. Crown seems to think I need at least 90dB for our kind of musicals (I'm putting us in the high end of the "jazz" range), so does that mean I need speakers with about 108 SPL? They (Crown) seem to think I ought to be doing my math only with respect to the nearest speaker and, I guess, ignore the contribution made by the other one of the pair, but I have to doubt that when I'm in an enclosed space (particularly one with cinder-block walls).