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Using A and B speakers really requires 16ohm speakers?

 
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Silvertone
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PostPosted: Sat Sep 05, 2015 6:32 pm    Post subject: Using A and B speakers really requires 16ohm speakers? Reply with quote

I have an old home theatre amp (cheap Sherwood brand) that actually says it is advisable when using both A and B speakers at once, that speakers be at 16 ohms. I have never seen this on any other of my amps.

I am using this to amplify signals from an electronic drum set and will play through 15 inch subwoofers and 6 inch speakers for drums and cymbals. Both types of speakers are 8 ohm.

I have done this successfully before with other amps. Do I really need to worry about this?

Also, I don't really care if the amp melts down in a test, only if my speakers are damaged.

Thanks for any tips.
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vtech



Joined: 08 May 2006
Posts: 1264
Location: USA

PostPosted: Sat Sep 05, 2015 10:26 pm    Post subject: Reply with quote

When using both A & B speakers at the same time, you are in effect halving the total impedance seen by the amp section.(hence 16 ohm speakers) Rather common issue with many, many low end receivers without any such warning to the end user.

Point being, the specific Sherwood is not designed to operate under 8 ohms load. Anything below that will strain the unit and you are running a chance of damaging the amplifier section. Inability of the units current capability is mainly the cause. As you reduce the ohms, you are asking for more drive current.

In your application, when you have both A&B speakers on, the amp sees 4 ohms which is already too low. It will work but very likely to eventually kill the amp; Whether it will damage the outside load is usually dependent on what type of protection scheme used in the amp. It is NEVER a good idea to risk valuable speakers..........as I saw many examples during my time in consumer electronics business.
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Silvertone
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PostPosted: Mon Sep 07, 2015 12:27 am    Post subject: Reply with quote

Thanks for the succinct answer. That is what I had thought in the back of my mind, though now that it might damage the speakers, I will change my plan. Since the drums can be mono, I will send only one channel through the my dedicated subwoofer amp to the large speakers for bass and the other channel through the Sherwood and on to smaller speakers for cymbals. You have helped very much.
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