Ohms

[BigLicks67]

If you have an 150 watt amp with a maximum at 4 ohms. What speaker rating do you need to match this up with? IE do you need a speaker cab rated at 4 ohms for it to work?
Many thanks in advance for your help.

[discreet]

Not necessarily. You could use an 8 ohm speaker - you just won't get the full 150 watts from the amp.

Edited February 10, 2013 by discreet

[Bill Fitzmaurice]

[quote name='discreet' timestamp='1360520614' post='1971681']
Not necessarily. You could use an 8 ohm speaker - you just won't get the full 150 watts from the amp.
[/quote]Not that it matters, as few speakers can make use of more than half their rated power anyway. It's always prudent to use a speaker twice the amp's rated impedance, should you need to add another down the road.

[BassBus]

This might help you understand Ohm's Law. Taken from a post somewhere on the net in a forum, might even have been this one.


[i]"The best description of ohm's law I read talked of it as two hose pipes. If you are trying to squeeze water through a 1cm pipe it can only flow as quickly as that pipe can take it, the resistance. If you then attach another 1cm pipe along side it you have twice the flow rate and half the resistance.

Therefore, an amp that is rated 500w at 8 ohms can only push about 300w of power through to an 8 ohm speaker. If you connect a second 8 ohm speaker you reduce the resistance to 4 ohms and are able to use the full 500w".[/i]

[RandomBass]

[quote name='discreet' timestamp='1360520614' post='1971681']
Not necessarily. You could use an 8 ohm speaker - you just won't get the full 150 watts from the amp.
[/quote]

Indeed. I'd go with an 8 Ohm cab to start with, I doubt you will notice much (if any) difference volume-wise. A high sensitivity 8 Ohm cab could easily sound louder than a lower sensitivity 4 Ohm one. At a later date you can then add another 8 Ohm cab which will increase the perceived volume level because you are moving more air, and have more power.

Assuming you have a SS amp, it's important the total combined speaker load does not go below the 4 Ohm rating of your amp. That will be one 4 Ohm cab, or two 8 Ohm cabs, or four 16 Ohm cabs (erm well).

However, to what extent things happen depends on your amp and choice of cabs.

Cheers

Geoff

[RandomBass]

[quote name='BassBus' timestamp='1360524137' post='1971781']
This might help you understand Ohm's Law. Taken from a post somewhere on the net in a forum, might even have been this one.


[i]"The best description of ohm's law I read talked of it as two hose pipes. If you are trying to squeeze water through a 1cm pipe it can only flow as quickly as that pipe can take it, the resistance. If you then attach another 1cm pipe along side it you have twice the flow rate and half the resistance.

Therefore, an amp that is rated 500w at 8 ohms can only push about 300w of power through to an 8 ohm speaker. If you connect a second 8 ohm speaker you reduce the resistance to 4 ohms and are able to use the full 500w".[/i]
[/quote]

I'm assuming you mean the amp is rated at 500w @ 4 Ohms?

[BigLicks67]

Many thanks for your lucid and well informed replies.

[BassBus]

[quote name='RandomBass' timestamp='1360524467' post='1971798']
I'm assuming you mean the amp is rated at 500w @ 4 Ohms?
[/quote]

Yes. It's the same for all 500 waters. [size=4] [/size]

[RandomBass]

[quote name='BassBus' timestamp='1360528104' post='1971898']
Yes. It's the same for all 500 waters.
[/quote]

Really? I know of one that goes to 2 Ohms, with some internal limiting going on (which is what the Terror Bass does too, albeit for 4 Ohms).

[BassBus]

Hmm. I think you missed the joke a little.

[Mr. Foxen]

[quote name='BassBus' timestamp='1360524137' post='1971781']
This might help you understand Ohm's Law. Taken from a post somewhere on the net in a forum, might even have been this one.


[i]"The best description of ohm's law I read talked of it as two hose pipes. If you are trying to squeeze water through a 1cm pipe it can only flow as quickly as that pipe can take it, the resistance. If you then attach another 1cm pipe along side it you have twice the flow rate and half the resistance.

Therefore, an amp that is rated 500w at 8 ohms can only push about 300w of power through to an 8 ohm speaker. If you connect a second 8 ohm speaker you reduce the resistance to 4 ohms and are able to use the full 500w".[/i]
[/quote]

Problem is signal from amps is AC, and the rated impedance as nominal, so it doesn't work nearly as well in practice when applied to speakers. Especially anything to do with watts, since the watt ratings on speakers started off a bit irrelevant.

[RandomBass]

[quote name='BassBus' timestamp='1360530251' post='1971954']
Hmm. I think you missed the joke a little.
[/quote]

Oops yes I missed your 2nd typo lol