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Multiple Cabinet Impedance Question

G

gamera

Sep 20, 2004
164
3
Gloucester, MA
#1
To start off please don't jump on me about not using the search feature. I did, and I haven't yet found the answer to my question. Maybe its just because I am bad at math. Besides we are all supposed to help each other out here, right? Isn't that what the board is for?

I have a 307 watt four ohm head. It has two four ohm outputs for speakers.

I have a 4 ohm 2X10 rated at 700 watts.

I want to get an additional 2X12 cabinet.

If I get a 4 ohm 2X12 and plug into the other speaker output aren't I in essence running 2 ohms then? I think that is bad in the bass world.

If I get an 8 ohm 2X12 cabinet and do the same thing I think I am then in effect running six ohms which is better but, I'm not pushing the same amount through each cabinet. The 4 ohm 2X10 would receieve the bulk of the load, right?

How do I fix this and have balanced speakers and not blow my amp? Should I just scrap the whole thing, send back the 2X10 4 ohm cab for an 8 ohmn one and get a 2X12 8 ohm?

Sooner or later I'm gonna get the hang of this stuff. I appreciate everybody's patience.

thanks in advance
 
#2
Speaker jacks on an amp are usually connected in parallel. What this means to you is that plugging in a 4 ohm cabinet (your 210) and an 8 ohm cabinet (proposed 2x12) the amp will see 2.7 ohms. Assuming the amp's minimum load impedance is 4 ohms (as you state) this is a bad thing.

Using a 4 ohm 2x12 makes it worse with a total load impedance of 2 ohms.

As for how the cabinet split the power...using one 4 ohm and one 8 ohm cabinet, the 4 ohm cabinet would get 2/3 of the power and the 8 ohm cabinet 1/3. This is a generalization though as each cabinet's true impedance varies with frequency.

Cabinet efficiency comes into play as well. If the 8 ohm cabinet is 3 dB more efficient, it would sound as loud as 4 ohm cabinet with twice the power.

You would be better off getting an 8 ohm 2x10 and an 8 ohm 2x12. The total load impedance would be 4 ohms, which should keep your amp happy.
 
#4
Aaah, Ok. I understand but I already have the 4 ohm 2X10. So what should I do?

I like having a 2X10. Can I rewire this to 8 ohms? Will that help?

I definitely need something with additional bass response, so I need another speaker cabinet. How do I fix this?
 
#6
No other replies to this? Thanks Billy B. You really helped a lot.

I guess I still haven't figured out yet what to do. I guess if I wire the cabinet in series it'll go to 16 ohms, but then what do I buy to go with it.

If I daisy chain the amps is that the same thing?
 
#7
You are basically stuck. You have a 4 ohm head and a 4 ohm cab.

You could purchase another 4 ohm cab and wire the two cabs in series to get 8 ohms. This would require a special cable or a mod to one of the cabs.
 
#9
gamera said:
If I daisy chain the amps is that the same thing?
Click to expand...

If you mean daisy chaining the cabinets (i.e. plugging one cabinet into another and only running one cable to the amp) yes, doing that will still connect the cabinets in parallel with 99% of the amps that you'll find (I have heard of at least one that has the speaker jacks connected in series).

I forgot to ask earlier...what amp is rated 307 watts into 4 ohms?
 
#10
Thanks Billy. I replied to the pm.

The amp is an Ashdown MAG300. Why its 307 I have no idea. What I was originally going to get was an Ashdown ABM325 and a 2X12 cabinet. In my haste I ordered totally wrong.

If I had taken the time to confirm everything I wouldn't be in this position. So far the people I ordered from have been more than fair and nice. I hope everything works out in the end. I will be sure and post if it does.

Thanks for your help again.
 
#11
ohms faq thread


try the above thread for all yer ohms questions :p
i really with they would make it a sticky, not cause i want the noteriety, i think it would just help a lot of individuals in yor situation

btw, i'm sure someone has already told you this, but.......
in your case your cabinet is probably 2 8 ohm speakers wired in parallel for a net impedance of 4 ohms. the only mod you could do to the cabinet would be to wire it in series for a net impedance of 16 ohms. this is pretty pointless as the cabinet will be very quiet. Hopefully the folks you bought it from will let you exchange it OR exchange the speakers to 16 ohm ones so the cabinet would have a net impedance of 8 ohms
best of luck,
ivan
 
#12
Wow that is great. They should post that as a sticky, seriously. I have always wanted something like this. It is well written too.

The manufacturer/seller is Avatar. Dave has been more than patient with me over this and also been more than helpful. I am exchanging the 2X10 cabinet for a 2X12.
:hyper: :hyper: :cool:
 
#15
You could try the Speaker Mate, made by Sherlock Audio. the Groove Shop is selling them. There was discussion here in the past about the device, but supposedly it allows you to run multiple cabs, matched or not. It may or may not be voodoo, but it sounds like it's what you need if it works. You should do a search for it here. I'd do it for ya, but I gotta go......
 
#17
Yes I am a flying turtle. Yes I shoot flames and protect the earth in my spare moments. Godzilla is a pansy.

Rockit now plays in American Pulverisor. He pretty much kicks my butt. They're a pretty awesome band for those who haven't heard them.

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