Another Ohms Post...

[Morpheus77]

Ok, I'm still a little confused about the whole Ohms thing. I have read back several reviews, and its all jiberish to me, like a foreign lanuage. I know its simply the amout of resistance the speaker has to the current coming in? At least that's what I gathered. My question is this....Is it easier to push a four ohm speaker, or harder? In other words do I need more watts to move a four ohm speaker or less? Thanks again for all the input in advance.

Tommy

[GMichael]

Ok, I'm still a little confused about the whole Ohms thing. I have read back several reviews, and its all jiberish to me, like a foreign lanuage. I know its simply the amout of resistance the speaker has to the current coming in? At least that's what I gathered. My question is this....Is it easier to push a four ohm speaker, or harder? In other words do I need more watts to move a four ohm speaker or less? Thanks again for all the input in advance.

Tommy

I'm not the best at this but I'll give it a shot until someone else comes along.

It's not the wattage that's in question for lower ohms. As the resistance goes down, the need for more Amps go up. This can burn up a receiver if turned up too loud. Most people here seem to think that you are OK with 4 ohm speakers if you are only driving 2 and not driving them too loud. I would think that amps made for 4 ohm speakers would be, and sound better.

What speakers and amps/receivers are you looking to mate?

[kexodusc]

Is it easier to push a four ohm speaker, or harder? In other words do I need more watts to move a four ohm speaker or less? Thanks again for all the input in advance.

Tommy

Not really easier or harder to "push" (we use the word "drive" conventionally when talking speakers, not sure it's any better) a 4 ohm speaker than an 8 ohm speaker, but there are some considerations.
I suppose in a literal sense, it's easier to drive a speaker of lower impedance (ohms) than higher. But as GM mentioned, it trades one problem for another - low impedance leads to higher current demand. This is fine until you reach the current limits of the amplifier (which can happen quite fast depending on which speakers/amps you're using). A 4 ohm load will reach that limit twice as fast as an 8 ohm load. That's the danger when driving lower ohm speakers. More wattage is better here usually, because in most solid state amplifiers that means the power supply has a higher current handling ability. So more watts gives you more headroom. But you really need to think in multiples of 2 X or more when adding watts if you're worried about power handling. CV's are pretty high sensitvity speakers usually, and need fewer watts to play as loud as many other speakers, so that helps balance out the low ohms thing for you....

[nightflier]

Not to add any more confusion, but speakers rated at let's say 4 ohms don't necessarily stay at 4 ohms. They can easily dip down to 2 ohms (Martin Logans for example). An inexpensive receiver will easily clip with a hard to drive 4 ohm speaker.

[Dusty Chalk]

It's harder to drive a four ohm speaker than an 8 ohm speaker. Same voltage drop leads to higher current demands requires more wattage.

[kexodusc]

It's harder to drive a four ohm speaker than an 8 ohm speaker. Same voltage drop leads to higher current demands requires more wattage.

Yeah, bad voltage drops would, and do, suck. All depends on what factors you wanna manipulate in your scenario. You increase the DC resistance of a drivers voice coil, one of the largest contributors to the impedance profile and you'll decrease sensitivity.
A lot of 4 ohm speakers (especially Cerwin Vega boomers) are of higher sensitivity than a lot of 8 ohms speakers, which compensates for the current demands. A 96 dB sensitive 4 ohmer would handle voltage drops far better than an 91 dB sensitive 8 ohmer, if maintaining the same SPL was the goal, etc. There's also a pragmatic side to this...if you listen to your music at 90 dB or less in 15 x 15 room, even most 50 watt amps ( at 8 ohms) or HT receivers will be fine driving a 4 ohm speakers to all but obscene levels.

When in doubt, more watts are better.

[hermanv]

I have not run into a modern amp that cared very much whether it was driving 4 Ohm or 8 Ohm speakers. Tube amps generally have transformer taps for both so those don't care at all.

Watch out if you parallel more than one pair of speakers. This is still true even if your amp has A and B speaker outputs, they are just paralleled inside the amp when you switch to "both" or "A & B". Paralleling 4 Ohm speakers can get you into trouble with smaller amps.

(nightflier; I'm pretty sure my M-L ReQuests manual says 1 Ohm at 20 KHz).

[Smokey]

Good reading guys, and here is more

Most good amplifiers tend to keep their output voltage the same. So usually speakers have
about 20 volts cross their input when connected to amplifier output.

And since speakers ohms is an “average” numbers (speaker ohms vary from 2 to 20 ohms), the voltage is the same. The only thing that change is current. So if we put an 8 ohm speakers cross the amplifier, the current would be around 20v/8 ohm= 2.5 amp.

But if we put a 4 ohm load cross the amp, the current would be 20v/4 ohm= 5 amp. So as one can see, the lower the load, the higher the current would be. And harder on the amp.

[Coilgap]

The impedence means the resistance to a AC signal and music is an AC signal. Also Impedence will change with frequency. I have a pair of Cerwin Vega the woofer is marked 8 ohms so is the tweeter horn and the 2 midranges. Now dc resistance at the speaker terminals reads around 6 ohms. But some time while I am playing some tunes the impedence will be around 4 ohms maybe even lower. Some modern day receivers don't get along well with such speakers even though they do get rather loud with mderated input power. The face plate reads 102db with 1 watt. WOW! I have drive them with an Adcom 555II they get very loud but the woofer I believe can't take what that thing can dish out. I have heard it pop and the the air in the room actually shakes. So what you need is a high current amp section be it a seperated unit or a reciever with a high current amp built in.