• TalkBass has been independent since 1998. Add your voice.
    Create a free account to reply to discussions, view embedded media, and browse with fewer display ads.
    Join free Log in
    Want zero display ads or expanded classifieds tools? Compare plans.

Why 8 ohms?

#4
GabeN said:
Why do manufacturers make 8 ohm cabs? It would make more sense to just make a 2ohm or even 1ohm cab if you can put more power into those. Is there any reason for putting higher impedances in cabs?
Click to expand...
I think that it also has something to do with current technology being able to tolerate or control such a low impedence load. After all, the amp itself has impedence IIRC.

It is a mistake to assume that lower impedence = more power or better tone. It's in how the amp was designed. 8 ohm amps sound no better or worse than 4 ohm or 2 ohm minimum amps.

Right now it is en vogue to get as low impedence a system as possible.

But with modern technology advancing, we now have amps that are '2 ohm stable'. The smart thing to do is to get as big a '2 ohm stable' amp at 8 ohms as you think you will need. That way, should you suddenly find yourself needing to do a big outdoor gig, you can add up to three more 8 ohm cabs. Potentially quadrupling cone surface and power at the same time.

Ideally.

:D

Joe.
 
#5
Lowtonejoe said:
It is a mistake to assume that lower impedence = more power or better tone. It's in how the amp was designed. 8 ohm amps sound no better or worse than 4 ohm or 2 ohm minimum amps.
Click to expand...
On the contrary, I think that Dave (Thunderfunk) insists that 8ohm cabs sound a little better to him than 4ohm ones.
 
#9
The reason for the proliferation of amps that can run low impedance loads at high current is that they're far less expensive to produce than amps that run at higher voltage outputs for the same wattage. Watts=volts x amperes, so you can get more watts by increasing amperage or voltage or both. Increasing amperage is cheaper, you just add more output transistors and a higher capacity transformer. To get higher voltage output you need to use higher voltage transistors, transformers, and power supply componenets, and cost goes up exponentially as voltage capabilities are increased.

In terms of how loud you can go increasing drive voltage is the more effective route, as driver excursion varies with voltage, not current. If wattage increases while voltage doesn't go up then the only way you can increase output is to either lower the driver impedance or use more of them. However, you can only take the impedance so low before current is so high that heat in all the system components, including the speaker cable and driver voice coil, and the A/C supply you're plugged into won't let you go any lower. The 8 ohm standard came about as the best compromise between voltage and current demands on the amp, and that remains the case.
 
#16
billfitzmaurice said:
The reason for the proliferation of amps that can run low impedance loads at high current is that they're far less expensive to produce than amps that run at higher voltage outputs for the same wattage. Watts=volts x amperes, so you can get more watts by increasing amperage or voltage or both. Increasing amperage is cheaper, you just add more output transistors and a higher capacity transformer. To get higher voltage output you need to use higher voltage transistors, transformers, and power supply componenets, and cost goes up exponentially as voltage capabilities are increased.

In terms of how loud you can go increasing drive voltage is the more effective route, as driver excursion varies with voltage, not current. If wattage increases while voltage doesn't go up then the only way you can increase output is to either lower the driver impedance or use more of them. However, you can only take the impedance so low before current is so high that heat in all the system components, including the speaker cable and driver voice coil, and the A/C supply you're plugged into won't let you go any lower. The 8 ohm standard came about as the best compromise between voltage and current demands on the amp, and that remains the case.
Click to expand...

Agree entirely. When an amp is designed the first question is how much POWER do you want to generate, which determines the operating VOLTAGE. THEN you decide how much of a LOAD you want to drive, and that determines the amount of CURRENT you design for. To generate 550-watts into 4-ohms requires a +/-92 volt power supply.

Now, I could add power transistors in parallel to handle higher current for a 2-ohm load which would develop more power, but where would that extra current come from? The transformer is only so big. It's designed for coupling it's power to the output load. To optimize the power output of an amp, you'd need to change the transformer from a 2-ohm model to a 4-ohm model to an 8-ohm model. Each would operate at a different VOLTAGE. SO, manufacturers give you a choice of two impedances. The one that generates less power is a mismatch. But you live with it.

You want three choices? If I designed my amp for 2-ohm maximum power output then you could get 550-watts but ONLY at 2-ohms, 330-watts at 4-ohms, and ~240-watts at 8-ohms. But now all the guys operating 4-ohms and 8-ohms are losing out on power. And there's more of those guys than guys running 2-ohms.

And I hate to say it but I think this 2-ohm question comes from cheap equipment. A manufacturer makes a consumer bass rig and builds a 2x10 to keep costs down, BUT he wants it to be loud so they make the 2x10 a 4-ohm model. That way his amp generates maximum power, but doesn't allow a second box. But it's a consumer amp, so it'll probably never be used with a second box.

Or, it comes from a manufacturer making a 4-ohm 4x10, again to maximize a single cabinet's power making a nice small solution. You want to use 2-4x10's? Buy a pair of 8-ohm cabs. OR plug both of the 4-ohm 4x10 cabs into your 4-ohm amp and burn it up. The question is like asking if you can run your toaster at 240-volts. You see, it'll make toast faster that way, just like a 2-ohm load will (won't) magically generate more power (even though it's limited by the size of the transformer). The toaster is now really popping out toast, but it won't last long. So you complain that it should be designed for 240-volt operation. OK, but now it doesn't toast at 120-volts. There's no secret to operating at 2-ohms. It's just a design choice and a 2-ohm amp doesn't work very well at 8-ohms. That's just the way it is.

And I never said that 8-ohm speakers (cabs) sound better than 4-ohm. I said that an output transformer (tube amps) sounds better if all the windings are engaged. If you have a transformer with an 8-ohm tap, and a 4-ohm tap, chances are the 4-ohm tap is only using half the windings, and won't sound as good.
 
#17
Thunderfunk said:
I never said that 8-ohm speakers (cabs) sound better than 4-ohm.
Click to expand...

But Eden does, and I've also heard this from many people of the years who know what they're talking about. [emphasis mine]:

"We have designed our amplifiers to operate safely at 2 ohms because everyone else is doing it and some users expect it. However, we much prefer operating at 4 or 8 ohms because of the markedly improved quality of tone and dynamic response."
 
#18
Marcus Willett said:
But Eden does, and I've also heard this from many people of the years who know what they're talking about. [emphasis mine]:

"We have designed our amplifiers to operate safely at 2 ohms because everyone else is doing it and some users expect it. However, we much prefer operating at 4 or 8 ohms because of the markedly improved quality of tone and dynamic response."
Click to expand...
That is referring to the quality of the tone coming out of the AMP.

:D

Joe.
 

Latest posts

Top Bottom
Back