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Author Topic: Power amp sizing  (Read 4240 times)

Blake Forman

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Power amp sizing
« on: February 23, 2015, 06:50:43 PM »

I'm no expert in live sound and need some help.  We just purchased two Kustom KPC10M 10" Monitor Speaker Cabinets with Horn Pair (75W RMS handling/150W peak).  We plan to use them as floor monitors for our band.  Can someone help me with power amplifier size?

We are currently using a QSC MX1000A for our mains but I don't think I needs something this big.
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Scott Holtzman

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Re: Power amp sizing
« Reply #1 on: February 23, 2015, 07:25:34 PM »

I'm no expert in live sound and need some help.  We just purchased two Kustom KPC10M 10" Monitor Speaker Cabinets with Horn Pair (75W RMS handling/150W peak).  We plan to use them as floor monitors for our band.  Can someone help me with power amplifier size?

We are currently using a QSC MX1000A for our mains but I don't think I needs something this big.

2 things -

1 - Please update to your Real Name, one of the OP's will lock the thread until you do.  This is explained during the sign up process
2 - This is a $50.00 speaker (on sale Musicians Friend today), they rate it at 60W.  Hope you are not expecting it to work for much more than spoken word
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Scott AKA "Skyking" Holtzman

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Michael Williams

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Re: Power amp sizing
« Reply #2 on: February 27, 2015, 10:52:57 PM »

At the risk of oversimplifying things, basically you want to find an amp that is rated for the same as your speaker's peak power rating.  In your case, the speakers are rated 120W peak and are 8-ohm speakers so a good match would be an amp that is rated ~120W per channel at 8-ohms, assuming you are using one speaker per channel.  The goal is to have the amp's clipping point match the speaker's peak rating.

There are many more factors so that is grossly oversimplified but hopefully it will give you a good rule-of-thumb that will get you close to what you need.

All that said, the Kustom web site says your speakers are rated at 120W peak and have a sensitivity (efficiency of the speaker) that is 93dB.  Pretty poor as speaker go, and certainly not high quality sound at that price, but might be OK for a garage band getting going or similar scenario.

I do not know your circumstances and some times you have to do whatever it takes to get going so I am not knocking your choice of speakers.  Only saying that you should keep your expectations low with those speakers, especially if you have high stage-noise environments and/or musicians with a good ear for sound.
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Taylor Phillips

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Re: Power amp sizing
« Reply #3 on: February 28, 2015, 08:19:18 PM »

I'm no expert in live sound and need some help.  We just purchased two Kustom KPC10M 10" Monitor Speaker Cabinets with Horn Pair (75W RMS handling/150W peak).  We plan to use them as floor monitors for our band.  Can someone help me with power amplifier size?

We are currently using a QSC MX1000A for our mains but I don't think I needs something this big.
We have a pair of those cabinets at my church.  They're not as bad as I thought they'd be. If your used to nothing, you'll probably like them just fine.  You just want to do your best to keep your stage volume low enough so that they don't have to be louder than 95dBA because that's when the highs start to get harsh.  With the amp, as it's been said already, the simplest way is to match the peak power ratings. With unpowered speakers though, you can run multiple speakers off of one amp channel, but this will change the impedance (ohms).  If you plan to do this, make sure your amp can handle the reduced impedance.
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Scott Holtzman

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Re: Power amp sizing
« Reply #4 on: March 01, 2015, 06:05:54 AM »

We have a pair of those cabinets at my church.  They're not as bad as I thought they'd be. If your used to nothing, you'll probably like them just fine.  You just want to do your best to keep your stage volume low enough so that they don't have to be louder than 95dBA because that's when the highs start to get harsh.  With the amp, as it's been said already, the simplest way is to match the peak power ratings. With unpowered speakers though, you can run multiple speakers off of one amp channel, but this will change the impedance (ohms).  If you plan to do this, make sure your amp can handle the reduced impedance.

If you change out the Piezo tweeters for some dynamic ones they are a lot less harsh.  I have some I use as confidence monitors for spoken word stuff.

 
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Scott AKA "Skyking" Holtzman

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Jerome Malsack

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Re: Power amp sizing
« Reply #5 on: March 01, 2015, 02:01:04 PM »

If you change out the Piezo tweeters for some dynamic ones they are a lot less harsh.  I have some I use as confidence monitors for spoken word stuff.

Here is the RTA of the updated Kustom with new horn crossover and 10.s 

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Jerome Malsack

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Re: Power amp sizing
« Reply #6 on: March 01, 2015, 02:04:56 PM »

I usually have eq the 16k and up with cut -12.  Boost a little in the 800 to 2 k and cut some from 80 to 120 -3 to -6

100 hz and below is naturally cut to help reduce on stage rumble and you can start from 150 or 160 hz as needed and make the cuts deeper.  4.5 ohm resister in series is dopping the tweeter about -3 db. 
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Jerome Malsack

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Re: Power amp sizing
« Reply #7 on: March 01, 2015, 02:39:35 PM »

The RTA is of a Kustom 10 inch floor monitor with replaced 10, Crossover, and horn. 

The parts list follows. 
MCM Electronics   53-1225 - 1.35'' Compression Horn Tweeter - 3.2'' x 7.4'' Horn
http://www.mcmelectronics.com/product/MCM-AUDIO-SELECT-53-1225-/53-1225

Pyle 10
http://www.mcmelectronics.com/product/PYLE-PPA10-/55-2352

Crossover.
http://www.parts-express.com/dayton-audio-xo2w-25k-2-way-speaker-crossover-2500-hz--260-142




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ProSoundWeb Community

Re: Power amp sizing
« Reply #7 on: March 01, 2015, 02:39:35 PM »


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