How Much Power?

Stevens R. Miller

Well-Known Member
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

Well-Known Member
... 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

Well-Known Member
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.

Stevens R. Miller

Well-Known Member
Ah, wait... I didn't do my Googling. The SRM450 is available in different versions. The v3 is a kilowatt, but the v1 is 400 watts. I'm betting you're using the 400-watt model, correct?

jkowtko

Well-Known Member
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.

Chris15

CBMod
CB Mods
Departed Member
Don't forget that 400W vs 1000W is only 4dB...

FMEng

Well-Known Member
Fight Leukemia
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

Well-Known Member
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

Well-Known Member
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.

BillESC

Well-Known Member
I'd suggest looking at the speaker offerings from Electro Voice.

The ZLX, EKX and ETX lines merit consideration and can adjust to any budget.

Stevens R. Miller

Well-Known Member
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.

TJCornish

Well-Known Member
Efficiency is NEVER irrelevant.
Toodleoo!
Ron Hebbard.
!? Can you elaborate with regards to this context?

EdSavoie

Well-Known Member
Efficiency is NEVER irrelevant.
Toodleoo!
Ron Hebbard.
It is when you're not paying the bill

(I'm kidding, I'm kidding)