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Double Bass Impedance Matching question.

J

James Gibson

Mar 3, 2007
266
4
Brooklyn, NY
www.myspace.com
#1
I'm putting together a new rig, primarily to be used for my double bass. The head I've bought lists Ohm ratings for 2Ohms and 4Ohms. The cabs I use with my old bass guitar rig are rated at 8Ohm. Will these cabs work with the new head?

I guess basically what I'm asking is, can you assume that the 8Ohm power rating for the head will be half of the 4Ohm rating specified on the head? Could pairing an 8Ohm cab with this head be detrimental to the cabs since it is not an impedance rating specified on the head?

Thanks! Love this forum!
James
 
#2
As a general rule, the only problem is when your speakers present too little impedance to a head, ie., if you use 2 ohms when the amp is only designed to handle 4 ohms. There should not be a problem using an 8 ohm cabinet when the amp is rated for 4 and/or 2 ohms. However, you didn't specify how many cabs you have, or how you plan to connect them. If you plan on using two 8 ohm cabinets with an amp rated for 4 (or 2) ohms, then that won't be a problem as the impedance will be 4 ohms. Three 8 ohm cabinets would be 2.66 ohms, which should be ok because you said the amp is rated for 2 ohms. I wouldn't connect more cabs than that, though, because then the impedance would be too low.

As for the power rating; no, you can't just assume the 8 ohm power rating will be double the 4 ohm rating, though it may be something close to that.

BTW - Above I said there "should" not be a problem because, if you hook it up and it causes a problem, I don't want you to be mad at me. However, if it was my rig, I wouldn't hesitate to hook up 8 ohm speakers to an amp rated at 2 or 4 ohms. I have worked in electronics for over 25 years and I know that this won't be a problem. (I would have had it hooked up 2 seconds after I got it home.)

However, because we always have to have disclaimers...
YMMV, FWIW, IME, IMO, etc., etc.
 
#3
Skunk11, thank you so much for you input. You're right, I didn't specify. Until I can get a smaller speaker, I'm planning to use a single 4x10 cab with this head.

I'm putting a smaller rig together to use with double bass. I'm tired of using my tried and true BG rig on DB gigs.

So, just to specify; for the time being, I plan to use one of my old Peavey 4x10 cabs (rated at 8 Ohms, wattaged rated at 350, with peak at 700.) with my new EA iAmp 800. This should work *for the time being*?

Additionally, I read recently that it's best to never leave a tweeter turned all the way off. The cab has a tweeter, but I usually don't like using it when I'm playing DB. Does anyone have anything to say about this?
 
#4
Skunk11 said:
As for the power rating; no, you can't just assume the 8 ohm power rating will be double the 4 ohm rating, though it may be something close to that.
Click to expand...

If anything, as James suggested, the power developed into 8 ohms will be LOWER than that into 4 ohms.

Skunk11 said:
BTW - Above I said there "should" not be a problem because, if you hook it up and it causes a problem, I don't want you to be mad at me. However, if it was my rig, I wouldn't hesitate to hook up 8 ohm speakers to an amp rated at 2 or 4 ohms. I have worked in electronics for over 25 years and I know that this won't be a problem. (I would have had it hooked up 2 seconds after I got it home.)

However, because we always have to have disclaimers...
YMMV, FWIW, IME, IMO, etc., etc.
Click to expand...

No need for disclaimers, you are absolutely correct. Going above the impedance rating is not a problem. BTW, with most solid-state amps, you never even get close to "impedance matching" in terms of maximum power transfer but that's another thread...

Skunk11 said:
Additionally, I read recently that it's best to never leave a tweeter turned all the way off. The cab has a tweeter, but I usually don't like using it when I'm playing DB. Does anyone have anything to say about this?
Click to expand...

Hmm... can't immediately think of a reason why that would be true unless the design of the control vis a vis the total impedance is strange.
 
#6
Originally Posted by Skunk11
As for the power rating; no, you can't just assume the 8 ohm power rating will be double the 4 ohm rating, though it may be something close to that.
Click to expand...

drurb said:
If anything, as James suggested, the power developed into 8 ohms will be LOWER than that into 4 ohms.
Click to expand...


Oops! I misspoke (mistyped). You are absolutely correct drurb. The power will be lower into an 8 ohm load.
 

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