Speaker impedence and performance

[kanihoncho]

I've installed four head units (HU) with speakers in my life and one complete system with HU, amp, wiring, and crossovers with never an issue. I can do the work if the instructions are clear. I'm no genius when it comes to all the issues matching components and installing them.

Question: If a speaker is rated at 3Ω and an amp is rated at 50W RMS per channel at 4Ω, will the 3Ω speaker have slightly more performance in terms of output . . . say 60-65W?

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[Doxquzme Premium Member]

The amp will need to be stable at 3 ohms or you will burn up the amp. If the amp is 2 ohm stable then you will see about a 16.5% increase at 3 ohms over 4.

 

[kanihoncho]

How do I know if an amp is STABLE at 2Ω? If it's rated in the spec? These are the specs for that amp. In my ignorance I thought I would need to have 2Ω speakers to get 75W output. Would these speakers be somewhere between 50 and 75W because of their 3Ω rating? I do understand that power is logarithmic, so a 3Ω speaker would not quite get close to 75W, is this correct? I guess I'm a little confused as to what a speaker draws and what an amp puts out.

5-channel car amplifier specs

• 50 watts RMS x 4 + 300 watts x 1 at 4 ohms
• 75 watts RMS x 4 + 500 watts RMS x 1 at 2 ohms
• 150 watts RMS x 2 bridged at 4 ohms + 500 watts RMS x 1 at 2 ohms

 

[Doxquzme Premium Member]

Your 5 channel amp is 2 ohm stable on the primary 4 channels at 2 ohms if it lists that capability/spec, which it does. I assume you are running the 2 front L/R and 2 rear L/R and they are 3 ohms each. At three ohms, that amp would provide about 62.5 watts of power x 4 to the 3 ohm drivers. You'll not likely hear any difference between 62.5 and 75 watts. It's less than 1 db.

 

[kanihoncho]

That is correct. Thanks for making that clear. One last question . . .How does the amp know whether the speakers are 2, 3, or 4? Is it a setting or is it just a function of physics?

 

[Doxquzme Premium Member]

That is correct. Thanks for making that clear. One last question . . .How does the amp know whether the speakers are 2, 3, or 4? Is it a setting or is it just a function of physics?

The impedance (resistive load) is built by design into the driver - physics.

 

[kanihoncho]

Thanks again have a good weekend . . . .