# A question regarding my amp.

Discussion in 'Amps and Cabs [BG]' started by Cambass, Dec 16, 2001.

1. ### Cambass

Jan 25, 2001
Australia
I currently own an Ashton 40 watt bass amp. On the back of it is a jack with 'External Speaker' and '4-8ohms' below it. My question is: Does this mean I can attach an extra cabinet to it? I've read that it is possible to attain more loudness doing this but would it be worth doing? I assume if I bought a cab I could always buy a head later on. (Unfortunatly I didn't get manual with the amp)

This leads me to another question: When looking through catalogues, the descriptions for the heads always say 'xxxwatts at 4ohms' or something similar. Does this mean you have to match the watts of the head and cab or do you only worry about matching the ohms?

Thanks.

2. ### JMXVorsprung durch Technik

Sep 4, 2000
Cologne, Germany
With amp you probably mean a combo (amp and cabinet/speaker in one housing), right?
With small combos like yours, the internal speaker ususally is 4 Ohm and delivers the full power, and the external out offers the possibility of using another speaker while bypassing the internal one.

So you won't gain any loudness (from the amp).

Even if the internal speaker is 8 Ohm, I wouldn't add an external speaker. You'd then gain some loudness, but 40W is far too small to even bother.

Better get a new combo or amp and speaker with at least 200W.

BTW: The most important spec for matching amp and cabs is impedance (Ohm).

Dec 16, 2001
Aridzona
Remember that when you hook up multiple cabinets the total impedance load (what the amp "sees") changes as follows.

(cab1 x cab2) / (cab1 + cab2)

The product divided by the sum.

This formula is really important. Most people know that two 8s make a 4. But they're not sure why.
I blew up my first amp figuring it out.

So if you combine 2, 8 ohm cabs:
(8x8)/(8+8) = 64/16 = 4 ohms

But if you combine an 8 and a 4:
(8x4)/(8+4) = 32/12 = 2.67 !!

If your amp says 4 ohms, don't feed it less, unless it's really pissing you off... because you'll kill it. On the other side of the coin, if you feed it more than it's rated for, the amp is less efficient (because it's "pushing a heavier load." (won't be as loud)

Note, this assumes a "parallel" configuration, which 99.999% of all speaker jacks (amps and cabs) are configured with. If they're in series, you add them together. But you're unlikely to find that scenario.

Typical 410 cabs (or 412s) are wired with 2 parallelled, series pairs. (pairs of 8s are wired series to 16, then the two pairs are parallelled back to 8).

TMI? Sorry for the lecture.

4. ### Cambass

Jan 25, 2001
Australia
Thanks for the replies.

I have another question regarding buying a head and cab. Say I buy a 200watt cab and a 100watt Head, does this mean that I will only get 100watts of power? (Assuming the ohms are matched)