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Author Topic: Newbie Sub Woofer Question  (Read 1804 times)

Arthur Beaulieu

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Newbie Sub Woofer Question
« on: August 11, 2007, 02:43:41 pm »

Hi,

I am new to PA's and sound reinforcement.  I won the job of building the PA for our band.  Most things are going well, but I have an impedance question about sub-woofers and amps.

I have two 18" subs, one a JBL and the other a Peavey.  The JBL is rated at 4 ohms, the Peavey at 8.  If I run these in parallel from a mono bridged amp what impedance is the amp seeing?  Is it 6 ohms?  The amp is a crown XLS 402. The spec only mentions bridging into 8 Ohms.  If I bridge this into my less than 8 ohm situation as mentioned above am I risking the amp?

Thanks for your help in advance.  I have a ton of questions but I will do my best not to drive you all crazy.

Arthur
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Ivan Beaver

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Re: Newbie Sub Woofer Question
« Reply #1 on: August 11, 2007, 02:57:07 pm »

You are looking at a total impedance of 2.67 ohms, NOT good on a bridged amp.  I would run one per side of the amp and use the level controls to match levels-if needed.
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Scott Smith

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Re: Newbie Sub Woofer Question
« Reply #2 on: August 11, 2007, 03:02:57 pm »

An 8 ohm speaker paralleled to a 4 ohm speaker will be 2.67 ohms total.  Your XLS402 amp is only rated to do 8 ohms bridged, or 4 ohms/ch stereo.  While it is not ideal to mix subs, the only way to safely do it with your amp is to run the amp stereo, and hook the subs to separate channels.  You can NOT run both subs on this amp bridged, and you can NOT run the 4 ohm sub on this amp bridged either.
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Tony "T" Tissot

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Re: Newbie Sub Woofer Question
« Reply #3 on: August 11, 2007, 03:05:13 pm »

Ivan Beaver wrote on Sat, 11 August 2007 11:57

I would run one per side of the amp and use the level controls to match levels-if needed.

This is the way to do it.
And adding - if you run two completely different speakers on a single bridged channel - one speaker is likely to be at a very different volume level from the other.
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David A. Parker

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Re: Newbie Sub Woofer Question
« Reply #4 on: August 12, 2007, 09:42:11 am »

You need to get started off right. Sell one of the subs and buy another one identical. Unlike subs cause all kinds of problems. The problem you ask about today is just the beginning.
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