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Old 06-20-2011, 12:42 PM   #1
Audiosyncrasy
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Default Matching a dual-mono speaker set up with an amp

Hello Everyone,

So, I've been tasked with putting together a dual-mono speaker setup in a small room (roughly 12ft. x 8ft.). I'm looking at using these speakers with this amp.

As I understand it, the general rule is that you want to "over-power" your speakers at a ratio of about 3:1 to 5:1. I realize this is a little overkill for the 60W (8 ohm) rated speakers, but does this look like it'll work?

Thanks in advance!
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Old 06-20-2011, 01:09 PM   #2
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What is this for?
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Old 06-20-2011, 01:52 PM   #3
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I'm installing ceiling speakers for the Mother's Room in my church. So, it's a feed off the main mix to play at moderate levels (probably 65 to 70 dB).
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Old 06-21-2011, 05:19 AM   #4
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I would possibly go for another amplifier brand.

It seems somewhat over powered for an 8 inch public address/muzak system to my mind.

It should work though.
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Old 06-21-2011, 06:58 AM   #5
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I don't think overpowering for headroom is very important for ceiling speakers, esp. considering you won't have any low end. That amp is serious overkill, you need what, 10 watts to get as loud as you want to.
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Old 06-21-2011, 08:51 AM   #6
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Thanks for all the responses!

So, basically, I only need to "overpower" speakers when I want to have crystal clear frequency response across the full spectrum (20Hz - 20kHz)? For instance, passive studio monitors or loud speakers?

Thanks again!
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Old 06-21-2011, 09:44 AM   #7
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Okay, so I found an old amp of ours laying around . . . here's the manual for the unit.

If I run two speakers in the Mother's Room, at 8 ohms apiece, I can drive them in parallel, off one channel on the amp, which will yield 75 watts (according to the manual) given the following:

Zp = (Za x Zb)/(Za + Zb)

Where Zp = total impedance when running speakers in parallel.
Za = impedance of speaker 'a'
Zb = impedance of speaker 'b'

Plugging in the numbers . . .

Zp = (8 x 8)/(8 + 8)
Zp = 64/16
Zp = 4 ohms

Does this seem kosher?
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Old 06-21-2011, 09:54 AM   #8
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That will be perfect. Feed one channel of the amp a mono (L+R) signal, and you'll have the other channel available to feed something else. Typically you might feed the other channel a microphone.
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Old 06-21-2011, 09:59 AM   #9
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Quote:
Originally Posted by Audiosyncrasy View Post
Thanks for all the responses!

So, basically, I only need to "overpower" speakers when I want to have crystal clear frequency response across the full spectrum (20Hz - 20kHz)? For instance, passive studio monitors or loud speakers?

Thanks again!
Yes and no. Part of the "overpowering" is so the amp doesn't distort trying to drive the speakers since distortion via clipping is worse for a speaker than being slightly overpowered. There are two major types of speaker failure, massive overpowering and eventual coil failure due sustained heat from distorted signals...

So you really only need enough headroom to allow driving the speakers without distortion from the amp. That being said that amp is probably still a little overkill or just use one channel. Based on the speakers being wired in stereo you'll get about 350 watts RMS and 700watts peak from that amp which could result in the other type of damage to the speakers "massive overpowering". I think something close to 1/2 that power would be closer (provided those specs reflect the actual performance of the amp).

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Old 06-21-2011, 10:16 AM   #10
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Quote:
Originally Posted by karbomusic View Post
Yes and no. Part of the "overpowering" is so the amp doesn't distort trying to drive the speakers since distortion via clipping is worse for a speaker than being slightly overpowered. There are two major types of speaker failure, massive overpowering and eventual coil failure due sustained heat from distorted signals...

So you really only need enough headroom to allow driving the speakers without distortion from the amp. That being said that amp is probably still a little overkill or just use one channel. Based on the speakers being wired in stereo you'll get about 350 watts RMS and 700watts peak from that amp which could result in the other type of damage to the speakers "massive overpowering". I think something close to 1/2 that power would be closer (provided those specs reflect the actual performance of the amp).

Karbo



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Awesome! That makes sense.

Quote:
Originally Posted by JHughes
That will be perfect. Feed one channel of the amp a mono (L+R) signal, and you'll have the other channel available to feed something else. Typically you might feed the other channel a microphone.
Cool. Thanks for taking the time to look over this stuff. I took circuits classes in college for the fun of it (yes, I enjoy torturing myself with electronic circuits theory at 7:30 am in the morning ), but I'm having to dust out all the cobwebs.
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Old 06-21-2011, 11:59 AM   #11
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Default Think ahead...

Most likely, sooner rather than later, someone will ask you to run more speakers to other rooms. That being said, you need to seriously consider going with a 70-volt system. Please see the link for more explanation.

http://www.alectrosystems.com/audio/...ion/70volt.htm
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Old 06-21-2011, 04:58 PM   #12
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I was about to recommend a 70 volt system myself. Definitely, especially for a church. In the future they'll be able to add rooms and even mics to address people through them as well.
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