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4 ohm vs. 8 ohm  

post #1 of 4
Thread Starter 
<n00b><not electrical engineer either>
what is the difference between 4ohm and 8 ohm speakers? (I know, 4 ohms! but seriously folks...)

why would you want 4ohm vs 8ohm?

why are most DIY plans ~4ohms?

could I take the crossover design for a 4ohm DIY plan, tag an extra 4ohm resistor on the tail and make it an 8ohm speaker? would this produce a total crapfest of a speaker?

why are most commercial speakers 8ohm?
</not electrical engineer either></n00b>
post #2 of 4
Quote:
Originally Posted by gonar
<n00b><not electrical engineer either>
what is the difference between 4ohm and 8 ohm speakers? (I know, 4 ohms! but seriously folks...)

why would you want 4ohm vs 8ohm?
If you are designing, it may depend on availability. Also, it may depend on the amp you intend to mate with it.

Quote:
why are most DIY plans ~4ohms?
See above.

Quote:
could I take the crossover design for a 4ohm DIY plan, tag an extra 4ohm resistor on the tail and make it an 8ohm speaker? would this produce a total crapfest of a speaker?
Yes and yes. Adding the series resistor will make the load 8ohms but half the power will be dissipated in heat by the resistor.

Quote:
why are most commercial speakers 8ohm?
</not electrical engineer either></n00b>
Easier mating with commercial amplifiers.

Kal
post #3 of 4
4 ohm and 8 ohm are the nominal impedences, and just depends on what the speaker designer wanted to do. 4 ohm draws more current, and you need to check to see if your amp is designed for 4 ohms. It also means that a 4 ohm speaker gets more power for the same voltage. Also, the 4 ohm and 8 ohm ratings are the NOMINAL, so the actual impedence varies with frequency. A 4 ohm speaker could easily dip below 2 ohms at some frequencies, and be well over 8 ohms at other frequencies.

8 ohm is easier for an amplifier to handle, it draws less current.

No, you cannot add a 4ohm resistor to a crossover and get anything decent. It will change the crossover frequency and characteristics. You'd also need a HUGE resistor to handle even 100W, and you'd be wasting half your amplifier's output power. If your amplifier can handle 4 ohms, then why worry about it? If the DIY plan you want is 4 ohms and your amplifier isn't rated for 4 ohm, you should probably get a new amplifier (hey, an excuse to buy new stuff!)

I'd put more thought and effort into what the speaker sounds like than what its ohm rating is.
post #4 of 4
1. Well that's the net effect but understand that the impedance of a speaker varies with frequency and depending upon the particular speaker, you'll find impedances of 2 or even 1 ohm at certain parts of the audio spectrum. If you look at some speaker reviews in say Stereophile, check out the sections where they do measurements to get a better understanding. Also, bear in mind that as the impedance drops, your amp or receiver will need to be able to provide more current (amperage). Not all amps are capable of doing this without running into voltage or current (clipping) limting. Hence, if you've got a 4 ohm speaker, depending upon things like room size, the volume you listen to, etc. you may find your receiver can't drive them properly.

2. You don't. You want a speaker that works for you by whatever criteria you deem important. Then it's your responsibility to make sure the amp or receiver is capable of driving them.

3. Because those are the drivers they chose.

4. There's more to crossover design than simply adding resistors. A thorough explanation is beyond the scope of my post but you might want to take a look at books like Vance Dickason's on speaker design and in one of these forums is an ongoing discussion on crossovers.

5. You'll find nominal impedances all over the place. I don't know if there's a preponderance of one over the other. In the end though, it comes down to what drivers the designer chose in order to achieve their goals.
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