amplifier output and speaker spl - AVS Forum
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Old 09-02-2012, 01:51 AM - Thread Starter
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Hello forum!

through basics and formuals i am wondering this:

I´m connecting 4 outdoor speakers of 8 ohms in parallel to an amplifier with 4-16 range. This is a 35W RMS per channel multizone amplifier.

I have called the manufacturer of the speakers and the amplifier to take some advice and considerations for a Terrace audio design.
He told me i´m insane to pretend a good intensity audio level with a 35W amplifier. He recomends me a 100W for this kind of applications. My doubt is this:

My speaker sensibility is 89DB/1W/1m.

So if my amplifier output is 35W then,

10xlog(35)=15.44

So the spl at 1m with that speaker should be: 89+15.44= 109 DB

I THINK THAT´S LOOOOUD! Why this guy told me that i wouldn´t have a decent volume level.

Am i right?
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Old 09-02-2012, 05:46 AM
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When you connect the speakers in parallel, the AVR will see them all as 4-ohm speakers, effectively requiring far more power to attain the same volume than when connected as 8-ohm speakers (think of going from a 1/2" water hose (8-ohm) to a 1" PVC pipe (4-ohm)). Although you will get some volume, as the mfr indicated, you won't be able to get a "good intensity audio level."

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Old 09-02-2012, 01:58 PM - Thread Starter
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thanks jdsomoothie for the reply,

at the amplifier manuel saids:

Power/Channel (RMS, 2 channels driven into 4 Ohms) 45 Watts @ 1kHz

So for example if im connecting 2 speakers of 8 ohm for right channel, and my receiver sends a 1 khz tone i should have 45/2=22.5W for each speaker. I know that a song has many frequencies at different amplitudes but in this particular case if my speaker sensibility is 89DB/1W/1m, my calculus (as far as i think i´m right) is:

10xlog(22.5)=13.5dB

So, at logarithmic scale if im standing 1m straight o the speaker i with sound meter i should have:

13.5+89 = 102.5dB

Considering this calculus for only 1 right channel speaker i think its a really decent volume for a terrace right?

so why you state:

Although you will get some volume, as the mfr indicated, you won't be able to get a "good intensity audio level."

i think 102.5db it´s really good for backgroud music, that´s why i don´t understand why the tech support of the amplifier told me that. YOU NEED AT LEAST A 100W AMPLIFIER FOR THIS KIND OF APPLICATION.

thank you for advance for the help.
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