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Alright I'm new at this whole seperate head and cab thing. I know that the head must be of equal or more wattage than the cab. Yet some say at different ohms they are differen wattages. Say you have a 400 w at 8 ohms cab, would a 400w at 4 ohms head be able to power that or what?

Thanks for your help

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400 watts into 4 ohms usually equals 240-300 watts into 8 ohms.


People use cabs with amps that don't have the maximum reccomended wattage all the time. 400 into 4 ohm heads and 400 watt 8 ohm cabs are very common. Some people seem quite satisfied, using such a rig for years. If you're getting enough sound from your setting and not straining anything, you're all set.


It really depends on who you're playing with and how loud they get.


If you routinely use the maximum power and distort (clip) the power amp, that will damage the speaker. If that's the case, you'll be needing to upgrade, either with a second 8 ohm speaker and/or a more powerful amp.

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Yeah, what Jeff said.


Don't worry about a perfect match. Try to get into the general range. It also depends on the equipment you're looking at. Look at the Acme Low B-2; 350-watt RMS rating for that cabniet, yet there are people on this forum that use 1,200-watt amplifiers with that beast. However, SWR's Goliath III cabinet is rated 700-watts RMS, I believe, yet most people power it with between 200 to 500-watt amplifiers.


Your best bet is to narrow down what you're looking at and ask on the forum what others are using as a gauge. I'd bet dollars to doughnuts that you'll get a couple of good responses.

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Here are my thoughts on the subject....for what it's worth.


I just put a QSC PLX 1602 in my rack. I run an SWR Grand Prix into it. I am running the power amp bridged into my 8 ohm SWR 4X10 cab. The amp puts out about 900 watts bridged mono into 8 ohms. The cab is rated at 700 watts. I know it sounds like overkill, but I have never heard this cab sound like this before. I used to use about 300 watts into it. The added headroom makes all the difference. The low end thunders! Best thing...the amp isn't breaking a sweat and I have it at about 1/2.


I was debating getting new cabs, but after hearing this set up, I am VERY pleased. I also like having the option of running two cabs parallel. I tried this as well with my 8 ohm 4X10 and an 8 ohm 2X15. Each cab got 300 watts and sounded really nice. (I may have to add a 1X15.) I can also run two cabs at a HUGE 1,600 4 ohm bridged mono.


Anyway to make a long post short (too late) I would get as much power amp as you can. Get something that will be flexible so if you change your set-up (like I often do) you won't have to get a different amp.


There are many nice pre-amp out there. I really love SWR so I got the Grand Prix. They are discontinued (I don't know why) but you can find them used. I also had a Demeter and liked it alot, but it was a little clean for me. My friend has an Alembic and really likes that.


Good luck and welcome to the forum. Let us know what you decide.

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Also realize that multiple cabs will be louder than a single cab given the same head wattage. I have a Crate BX100 combo (100 watt, single 15") - good amp but not usually what people think of as top of the line. When I added a 4x10 to its built-in 15", it sounded significantly louder AND much better! The 10s give more 'punch' to accompany the 15's bottom, and the extra speakers physically move more air.

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