changing cab impedance

[Holliwood]

KK

I know that you can add a driver in series to decrease ohm load from say 8 to 4.
What about taking an 8 ohm cab, rewiring the drivers to make it 4 ohm.
What effect(if any) will this have on performance/sound?

Is there an electronic component that can be installed in line to decrease a cabs impedence? ie: from 8 to 4 ohms

[BassmanPaul]

There is no way to do what you suggest aside from changing all the drivers.

AMPS FAQ!! Info on OHMS, Allsize RIGS-OverUnderPowerCabs DIY TechTalk-Links

Second question: Only a transformer will do what you ask but they are big, heavy and expensive.

[PSPookie]

Not likely. This one has been discussed to death.

Try a search and then try looking up Ohm's Law again because you seem to have some things backward.

[BurningSkies]

Often times this comes up because everyone wants to wring every last watt out of their cab. But the reality is that the difference in wattage equals a negligible volume increase, meaning that you probably won't even notice the difference, if you could do it. The best way to get all yer watts and also be louder at the same time is to add more speakers.

When it comes to a device to lower the impedance of the cab you have, yes, theoretically you can do it. You can add a resistive component, like a resistor array. Should you? No. Because there's no free ride. You can add 8ohms of resistors in parallel to your speakers and that will show your amp a 4ohm load...and those resistors will soak up the extra wattage you were hoping to get out of the amp...and your speaker will be none the louder, but your cab will be eating up more wattage and creating loads of extra heat...which is not what you're looking to do...unless you were trying to double up your cab as a space heater.

[billfitzmaurice]

Originally Posted by BurningSkies

Often times this comes up because everyone wants to wring every last watt out of their cab. But the reality is that the difference in wattage equals a negligible volume increase, meaning that you probably won't even notice the difference, if you could do it. The best way to get all yer watts and also be louder at the same time is to add more speakers..

+1. Watts mean nothing, displacement and sensitivity mean everything. Adding a second identical cab gives you more of both.

[gimp]

Lifting this from my own thread (B25-B Cab Modification to get further confirmation. Does anyone see an issue with the following?

Originally Posted by gimp

So I'm putting together a strange rig.

I currently have a B-15NF for home use, and for playing out/practice I use a BT-15 (solid state) into a Mosvalve MV-925 into a 8ohms 1x15. It's not ideal, as the Mosvalve is a 4ohms output, and I need to move a little more air.

I've got the BT-15 and Mosvalve sounding really good after A/B switching it with my B-15NF, so that part is good to go.

I've got a line on a well loved B25-B cab. I'd like to rewire this cab so that the two 15s were independent from each other (two jack plates). This would allow me to load it with two 4ohms 15" speakers and use the full output of the Mosvalve.

That seems pretty straight forward. But, would there be any way to wire this up so I could either have two independent 4 ohms inputs, or a single 8 ohms input? Pretty sure the answer is no, but you guys would know best.

Thanks!

[Rick Auricchio]

Gimp's circuit works, but it's highly dependent on the cab wiring, the drivers, presence of a crossover, etc. It isn't a solution that fits all cabs by any means.

[FunkyScoundrel]

Acmeswitch?

A little light reading for you.

[BurningSkies]

Originally Posted by FunkyScoundrel

Acmeswitch?

A little light reading for you.

The classics never go out of style.

[fdeck]

Okay, here's an idea. Bear with me. Imagine a 6x10, made with 6-Ohm drivers.

Wired one way, the overall impedance is 6*3/2 = 9 Ohms
Wired another way, 6*2/3 = 4 Ohms

These are close enough to 8 and 4 for any practical use. Note that I have no personal interest in a 6x10.

And you read about it here first.

[magic papa]

Correct me if I'm wrong, but you should be able to change the impedance from 8ohms to 2 ohms on a 4-driver cab by installing a switch that changes the wiring from series-parallel to parallel. This assumes the drivers are 8ohm.

I was thinking about getting an Ampeg 410he and doing just that, so I can get away with only one cab for SVR-VR on rehearsals. Then I could use 2x410 in 8ohm mode for the gigs.

[gimp]

Originally Posted by Rick Auricchio

Gimp's circuit works, but it's highly dependent on the cab wiring, the drivers, presence of a crossover, etc. It isn't a solution that fits all cabs by any means.

Much appreciated on the confirmation. I know it's not for everyone, but ti will work well with my setup. I also have a thing for the odd ball setups.