You are here:

Audio Systems/choosing the right amp


QUESTION: what size amp should i choose to run 8 6 1/2s(40 watts rms)(240 watts max)( 4 ohms)?
what size amp for 8 6x9s(90 watts rms)(500 watts max)(4 ohms)?
could i run 8 4in at 20 watts rms 140 watts max at 4ohms, with
8 4x6s at 30 watts rms 60 watts max at 4 ohms on one amp and what size should i use?

ANSWER: Just to be clear - is the 4 ohms the impedance of each speaker, or the combined impedance for however you have them wired up?

Here's the rule of thumb - just make sure the impedance of the speaker combination is equal to or greater than the output impedance of the amplifier (NEVER EVER less - you'll blow the amp), and the combined wattage of the speaker array is greater than that of the amp - if not, you could blow the speakers.

For example - for 8 speakers combined in a 240watt, 4 ohm array - the amp needs to have a 4 ohm (or less) output impedance, and less than 240 watts output.

I hope this helps.

---------- FOLLOW-UP ----------

QUESTION: the 4 ohms is the impedance of each speaker. should i add up the total watts for each load,or does it matter?( 8 speakers=4000 watts max or 8 speakers at 4 ohms not exceeding 500 watts?

Before I can answer that - how many channels are you planning on running? 2 channel stereo? 5 channel surround? mono?

The amp should list the watts per channel. Whatever that figure is, make sure your speaker array adds up to equal of more wattage (use the RMS values)

Matching the impedance is another story... do you know how to wire speaker arrays in different configurations to change the impedance of the total load?
More on that can be found here in case you're not familiar with it (the article is aimed at guitar cabinets, but the electrical theory is all the same):

Audio Systems

All Answers

Answers by Expert:

Ask Experts


Wayne Tapia


Home Theater Audio Cabling (from HDMI to speaker cable). I WILL REJECT ALL CAR AUDIO QUESTIONS - I am not a car audio guy.


I am a Certified Audio Engineer that also works in the A/V cabling industry. I would like to dispel the myths and outright lies about the cables that connect your home theater systems together. Here's a hint - many of you have been misled out of hundreds of dollars for cabling systems.


Audio Recording Technology Institute Vancouver Film School

Past/Present Clients
Post Magic Studios Khaos Studios Glass Forest Entertainment Funkbuddha Productions The Capital Playhouse Art In Music Global Music Project University of Washington Belle and Wissel

©2017 All rights reserved.