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sound sytem advice for a school dance

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Anonymous
June 21, 2005 1:43:07 AM

Archived from groups: rec.audio.pro (More info?)

At our school dances (held in a small-medium sized gym) we 've been
powering a pair of crate micro series pe-12h (8 ohms 100 watts)
speakers AND a pair of Crate ps-115hp (8 ohms 125 watt) all with a
little ol' mackie 808s powered mixer. I knew nothing about power
requirements and bought the powered mixer for the school on the
recommendation of someone whom I thought was knowledgeable. Needless
to say, the mackie has been overheating and cutting out. Aiming a fan
at the heatsink helps, but I want to make things right with a different
speaker configuration. I've spent about 8 hours online studying some
audio basics, the most important being the rule of thumb that says you
should drive speakers with an amp that has continous output 2x the RMS
rating of the speaker.

The Mackie delivers 240 watts (continuous) per channel into 8 ohms.
That means I should run speakers with an rms rating of no more than 120
watts. Yes? Or am I still not understanding this principle?

So why do I see lots of folks with a pair of Mackie c300 passive
speakers hoked up to the 808S? These are 300 watt speakers...don't
they require a bigger amp? I'm stumped!

I'd like to go with the c300s and then buy a powered Subwoofer and hook
it into the 808S (through a crossover). But I'm not sure it will get
the job done.

Obviously, I'm a novice at this. Any advice would be most welcome.

Colin
Anonymous
June 21, 2005 8:50:01 AM

Archived from groups: rec.audio.pro (More info?)

what mic position
and what recording system
hard drive or flash


opps thought this was a professional recording listserv
but given the number of stereophile and pa questions

maybe kevin doyles students were right and this group has died as a
true
professional recording group
Anonymous
June 21, 2005 9:28:47 AM

Archived from groups: rec.audio.pro (More info?)

On 6/21/05 12:43 AM, in article
1119328987.195456.242030@g44g2000cwa.googlegroups.com, "spamhades@yahoo.com"
<spamhades@yahoo.com> wrote:

> At our school dances (held in a small-medium sized gym) we 've been
> powering a pair of crate micro series pe-12h (8 ohms 100 watts)
> speakers AND a pair of Crate ps-115hp (8 ohms 125 watt) all with a
> little ol' mackie 808s powered mixer. I knew nothing about power
> requirements and bought the powered mixer for the school on the
> recommendation of someone whom I thought was knowledgeable. Needless
> to say, the mackie has been overheating and cutting out. Aiming a fan
> at the heatsink helps, but I want to make things right with a different
> speaker configuration. I've spent about 8 hours online studying some
> audio basics, the most important being the rule of thumb that says you
> should drive speakers with an amp that has continous output 2x the RMS
> rating of the speaker.
>
> The Mackie delivers 240 watts (continuous) per channel into 8 ohms.
> That means I should run speakers with an rms rating of no more than 120
> watts. Yes? Or am I still not understanding this principle?

You're REALLY not understanding.. And that's ok! read on MacDuff...
\
>
> So why do I see lots of folks with a pair of Mackie c300 passive
> speakers hoked up to the 808S? These are 300 watt speakers...don't
> they require a bigger amp? I'm stumped!
>
> I'd like to go with the c300s and then buy a powered Subwoofer and hook
> it into the 808S (through a crossover). But I'm not sure it will get
> the job done.
>
> Obviously, I'm a novice at this. Any advice would be most welcome.

First... You;re looking at this sideways (and if, as it seems, you have no
real idea about electronics, then that makes sense... Don;t sweat it, just
hang in there with this craziness!).


THE Mackie rates at 240w into eight ohms...
Assuming EACH of your speakers is rated at 8 ohms, then with TWO speakers on
a single output, the impedance drops by 1/2 = FOUR ohms
and you;re asking the mackie to deliver much more power to those 2
speakers.
(it's basic electronics math... However unintuitive, Take it on faith for
now!)
What's the Mackie rated at running into a load of FOUR Ohms?
It may not be able to do supply enough and thus is overheating trying to.

Let's see...
MACKIE 808s
Maximum Power at 1% THD, midband,
both channels driven
600 watts per channel into 2 ‡
450 watts per channel into 4 ‡
300 watts per channel into 8 ‡
Continuous Sine Wave Average Output Power, both
channels driven (rated power)
340 watts per channel into 4 ‡ from 40 Hz to 20 kHz, with no
more than 0.15% THD
240 watts per channel into 8 ‡ from 40 Hz to 20 kHz, with no
more than 0.10% THD

What sort of eq and tone control settigns are you using?
Related resources
Anonymous
June 21, 2005 12:09:25 PM

Archived from groups: rec.audio.pro (More info?)

dale wrote:
> maybe kevin doyles students were right and this group has died as a
> true
> professional recording group

Welcome to Endless September. The divisions between newsgroups have worn
a bit thin, and there's an endless supply of newbies who are still
learning why keeping things divided is useful. I must admit I've gotten
sloppy about it myself.

If you actively direct people to the right groups rather than just
complaining about it, that helps a bit.
Anonymous
June 21, 2005 1:02:13 PM

Archived from groups: rec.audio.pro (More info?)

<spamhades@yahoo.com> wrote:
>At our school dances (held in a small-medium sized gym) we 've been
>powering a pair of crate micro series pe-12h (8 ohms 100 watts)
>speakers AND a pair of Crate ps-115hp (8 ohms 125 watt) all with a
>little ol' mackie 808s powered mixer. I knew nothing about power
>requirements and bought the powered mixer for the school on the
>recommendation of someone whom I thought was knowledgeable. Needless
>to say, the mackie has been overheating and cutting out. Aiming a fan
>at the heatsink helps, but I want to make things right with a different
>speaker configuration. I've spent about 8 hours online studying some
>audio basics, the most important being the rule of thumb that says you
>should drive speakers with an amp that has continous output 2x the RMS
>rating of the speaker.

Have you considered turning it down?

>The Mackie delivers 240 watts (continuous) per channel into 8 ohms.
>That means I should run speakers with an rms rating of no more than 120
>watts. Yes? Or am I still not understanding this principle?

This is a very rough estimate, but it doesn't seem like a terrible one.
What you -really- care about is the sensitivity rating, though. There's
a number on the data sheet for the Crate speakers which will tell you
how loud a signal they'll produce with a given power input.

I'm assuming you have one speaker per channel, right? You aren't paralleling
two speakers per channel for a four-ohm load, right?

>So why do I see lots of folks with a pair of Mackie c300 passive
>speakers hoked up to the 808S? These are 300 watt speakers...don't
>they require a bigger amp? I'm stumped!

They probably aren't running them as loud as you are. Just because the
amp will produce 240W doesn't mean you always need to be producing 240W
all the time. (And they are running 8-ohm loads. So are you, right?)

>I'd like to go with the c300s and then buy a powered Subwoofer and hook
>it into the 808S (through a crossover). But I'm not sure it will get
>the job done.

You may need an external amp to use the crossover, unless you have a
mains insert on the Mackie that you can use to intercept the signal
between the main out and the power amp.

>Obviously, I'm a novice at this. Any advice would be most welcome.

You need to run out and get a copy of the Yamaha Sound Reinforcement
Handbook. Your local library can probably get it.
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."
Anonymous
June 21, 2005 6:10:28 PM

Archived from groups: rec.audio.pro (More info?)

"There is a handfull of long-time stalwarts that continue to show up
and take
seats in the corners, backs to the wall, and watch as the neighborhood
goes
to hell. They are as good as ever but nobody wants to bother."

I volunteer for an opera house guild and do school and community bands.
what directions can I give to a person who post an obvious PA question
on a Recording usenet.
If they can not use the resources of what they have locally and can not
use the internet resouces
what help can I give verbally to explain how a PA system works.

but the real question to ask him is how is he wiring the speakers
together.
is he giving the amp some outrageous ohm value??? 2 ohms????
which mr dorsey did, as a true gentleman should.

I was just reacting to the postings here that show a real ignorance of
sound.
the diatribes that can become shallow.
and then this question

"What sort of eq and tone control settigns are you using?"

hey, the question is how are you wiring the speakers!

thanks mr dorsey for doing the right thing.
the BS sure gets to be a mite thick and redneck here.
god forbid
Anonymous
June 21, 2005 9:58:13 PM

Archived from groups: rec.audio.pro (More info?)

On 6/21/05 7:50 AM, in article
1119354601.678732.174360@g49g2000cwa.googlegroups.com, "dale"
<dallen@frognet.net> wrote:

> what mic position
> and what recording system
> hard drive or flash
>
>
> opps thought this was a professional recording listserv
> but given the number of stereophile and pa questions
>
> maybe kevin doyles students were right and this group has died as a
> true
> professional recording group

There is a handfull of long-time stalwarts that continue to show up and take
seats in the corners, backs to the wall, and watch as the neighborhood goes
to hell. They are as good as ever but nobody wants to bother.
Anonymous
June 21, 2005 10:52:38 PM

Archived from groups: rec.audio.pro (More info?)

spamhades@yahoo.com wrote:

> At our school dances (held in a small-medium sized gym) we
've been
> powering a pair of crate micro series pe-12h (8 ohms 100
watts)
> speakers AND a pair of Crate ps-115hp (8 ohms 125 watt)
all with a
> little ol' mackie 808s powered mixer.


> I knew nothing about power
> requirements and bought the powered mixer for the school
on the
> recommendation of someone whom I thought was
knowledgeable.

On the face of it, a Mackie PPM808S doesn't look like a bad
choice.

> Needless to say, the mackie has been overheating and
cutting out.

Why, needless to say?


> Aiming a fan at the heatsink helps, but I want to make
things right with a
> different speaker configuration.

If the problem is just a matter of amplifier power, a ready
alternative would be to get a second power amp, hook it to
the mixer outputs of your powered mixer, and use it to drive
the second pair of speakers.

> I've spent about 8 hours online
> studying some audio basics, the most important being the
rule of
> thumb that says you should drive speakers with an amp that
has
> continous output 2x the RMS rating of the speaker.

If the mixer you have is really a Mackie PPM808s, then it
seems like it has lots of power. If you run the speakers in
parallel, you create a 4 ohm load, and the Mackie

http://www.mackie.com/pdf/ppm808s_ss.pdf

is rated at 340 wpc into 4 ohms. Your speakers sum to 225
watts, so you are close with a power amp with about 1.5 x
the power ratings of your speakers.

> The Mackie delivers 240 watts (continuous) per channel
into 8 ohms.

Yes, but you have a 4 ohm load. OK, your current situation
is a bit of a stretch, but you aren't missing the mark by
that gosh awful much.

> That means I should run speakers with an rms rating of no
more than
> 120 watts. Yes? Or am I still not understanding this
principle?

You are right that your amps are a bit undersized but you
missed the fact that most good solid state power amps
deliver more power into lower impedance loads. By hooking
your speakers in parallel, you create a lower impedance
load.

>So why do I see lots of folks with a pair of Mackie c300
passive
>speakers hoked up to the 808S? These are 300 watt
speakers...don't
> they require a bigger amp? I'm stumped!

Well one thing - power ratings aren't the only relevant
speaker specification. Another relevant spec (one that is
lied about, lots) is speaker efficiency. Most people turn
the volume up until the music is loud enough. How loud
speakers get is dependent on both how much power they
receive and how efficient they are.

Another variable is the size of the room, and how reflective
or absorbtive it is. Then there is the slight matter of how
loud you want to play the music. No doubt if you backed off
on the loudness, your amps would be less likely to overheat.

>I'd like to go with the c300s and then buy a powered
Subwoofer and hook
> it into the 808S (through a crossover).
> But I'm not sure it will get the job done.

Here's where the fun begins. My examination of vendor spec
sheets says that both the Crate and the Mackie speakers have
about the same efficiency. However like I said, efficiency
is one of those specs that cannot always be taken at face
value.

At any rate, a far less expensive approach, and one that is
pretty much assured to work, would be to get another power
amp, and take a lot of load off of your speakers. The
Behringer EP2500 power amp comes to mind as a possible
choice.
Anonymous
June 21, 2005 10:53:32 PM

Archived from groups: rec.audio.pro (More info?)

Correction:

> At any rate, a far less expensive approach, and one that
is
> pretty much assured to work, would be to get another power
> amp, and take a lot of heat and power load off of your
Mackie Mixer.
Anonymous
June 22, 2005 9:05:24 AM

Archived from groups: rec.audio.pro (More info?)

On 6/21/05 5:10 PM, in article
1119388228.789798.234370@g49g2000cwa.googlegroups.com, "dale"
<dallen@frognet.net> wrote:

> I volunteer for an opera house guild and do school and community bands.
> what directions can I give to a person who post an obvious PA question
> on a Recording usenet.
> If they can not use the resources of what they have locally and can not
> use the internet resouces
> what help can I give verbally to explain how a PA system works.

There's no PROBLEM politely asking in ANY forum any particular question.
Those who yell at you for that should be hung out to dry and the others will
eather try to answer of give you a good isead where to find better advice. I
refer many questions here back over to the live sound or movie sound groups
when approriate for the real answers.

>
> but the real question to ask him is how is he wiring the speakers
> together.
> is he giving the amp some outrageous ohm value??? 2 ohms????
> which mr dorsey did, as a true gentleman should.
>
> I was just reacting to the postings here that show a real ignorance of
> sound.
> the diatribes that can become shallow.
> and then this question
>
> "What sort of eq and tone control settigns are you using?"
>
> hey, the question is how are you wiring the speakers!

Yes.. AND No. The question was NOT about speaker wiring but why was his amp
overheating and cutting off. (as I asked in your reqote there) there indeed
may be an issue with someone who's not sure what they;re doing, that they
push the extremes of a graphic or a tone control, trying to make average
speakers do exteneded bass that they;re not capable of and blowing amp power
uselessly (sky-ing the 30Hz band for example) adn thus making the system
overheat and have problems.

>
> thanks mr dorsey for doing the right thing.
> the BS sure gets to be a mite thick and redneck here.
> god forbid

That's why we wear the waders.
Anonymous
June 22, 2005 12:32:00 PM

Archived from groups: rec.audio.pro (More info?)

want to bet his "knowledgable friend" suggestted thst he run the
sysytem mono,
because stereo is not best for his situation, and he has the speakers
wired on the same side!
and what does his expert say about his problem????
has he had that person over to help??

are you one of kevin's students?
!