Extension speaker from combo amp

You could get any speaker rated higher than 30W as well as more than 4ohm impedance. If the wattage is lower you risk damaging the speaker as you increase the volume, if the impedance is too low you'll damage the amp.

You could plug it into a 4x12 cabinet that is 4 Ohms. Other options would be a 2x12 box thats 4 ohms or a single 12 thats 4 ohm, (off hand I can't think of any single 12" 4 ohm speakers). Basicly any combination of speakers as long as the total Ohms for them are 4. This would be just for the ext. cabinet and not the one already in the amp.

Most celestions are 8 and 16 Ohms, yes, you may want to see jensen they have single 12" 4 Ohm. Crate more than likely has an extension speaker that match's your amp. It will probably a bit costly.

Just a thought

joe

If you were into wiring a cab for yourself, you could take 2 8Ohm speakers and wire them in parallel - that would give you 4Ohms.

So, If I get a passive monitor that is 150 watts peak/  75 watts RMS that is 4ohm, I'll be good to go.  My Crate 30 watt amp will be able to push sound thru that?  By the way what is RMS? Thanks for your replies!

RMS is the root mean square... it's just a way of measuring the power of a sinusoidal signal as an average would be 0.
Your amp would be able to power it ok, and if you got a bigger amp (less than 75W)  later on that wants 4Ohm impedance then that'd be able to power it even louder.

What that's telling you is that the speaker extension speaker should be rated for at least 30 Watts and no less than 4 ohms impedence. I doubt you could find a guitar speaker less than 4 ohms. You can use a higher impedence speaker like 8 or 16 Ohms no problem. However, the higher the impedence the more power to create volume.

The best thing to do if possible is match the speaker in your amp. Different speakers have different properties. Mis-matched speakers can cause frequency cancellations. It could sound worse and maybe even quieter.

Also, you don't want to pair speakers that are different impedence (resistance) Ohms. If one speaker is 4 Ohms (less resistance) and the other is 8 Ohms (more resistance), the 4 Ohm speaker will be quite a bit louder, in effect cancelling out the 8 ohm speaker.

Using a speaker with less than 4 Ohms resistance is bad for the amp more than the speaker. Too much current through the amp (less resistance). As a friend of mine said, you are effectively turning the circuitry and components of your amp into an electric toaster. Not good.

97Reb

One thing you hear over and over is that underpowering a speaker will damage it. That is not so. You can turn down your amp until it's barely audible. Won't hurt the speaker one bit. Here is what is meant by that.

Joe has a 100W  guitar amp into a 1 X 12 cabinet with a speaker rated 200W handling power or RMS.  

Bob has a 30W guitar amp into the identical speaker.

There's 10 people in the club. They are both playing at moderate volume. No problem.

Suddenly 200 people come in. Now volume has to come up so you can hear it above the crowd.

Joe turns his amp up to 5. Plenty loud. No problem

Bob finds he has to turn his amp up all the way to 10. There is the problem. Now, he is pushing his amp too hard. The amp is generating a clipped signal. His speaker is trying to imitate this distorted signal. This clipped distorted signal ruins his speaker.

You can ruin a speaker that's capable of handling 1000 watts of power with just 10 watts if the signal is clipped and distorted.

Also, if the speaker you get is just rated 10 watts handling power, if you don't crank the amp way up, it will handle it easy.

Thanks Wes.  So, are you saying Bob should not try and power anything over 60 watts with his 30 watt combo?

I've found a Line 6 extension cab 1x12 50 watts peak for $150 and a Traynor Custom Valve 80 Watt 2x12 extension Cab for $280.  Not sure which would be better for me at this point.  

I want a little more of a solid sound and could probably use the extension speaker as a monitor if put into a live situation and run the combo to the PA for FOH sound.  Right now, I find myself playing bass for some guys, so that kind of changes things.  

If I go with the Line 6 extension Speaker, it's only $150 and still leaves me room to buy anything I might need for playing bass (another bass or bass amp).

No. You could hook up any speaker to your amp as long as it's impedence is 4 Ohms or more.

You could hook up a speaker rated to handle 10 watts only. As long as you don't turn the amp up too high, it will work beautifully.

You could hook up a speaker rated to handle 1000 watts to your amp. It will work beautifully too.

If the 10W speaker is more efficient than the 1000W speaker, it would actually be louder at the same settings.

What??  How can that be?

It's true.

If the 10W speaker had an efficiency or SPL (sound pressure level) rating of 100dB @ 1W/1M, it would produce 115 decibels volume with 30 watts applied.

If the 1000W speaker was rated 90dB @ 1W/1M, it would only produce around 105 decibels volume with 30 watts applied.  

However, the 10W speaker is not designed to handle 30 watts continuously. After too long the speaker will come apart inside.

The 1000W speaker can handle 30 watts all day long.

BUT- You can still blow that 1000W speaker with your 30W amp.

How?

By cranking up your amp too far. Just the same as if you tried to drive your car too fast. The engine is only designed to take so much. Your amp is just the same. If you crank it up all the way, the amp will begin to distort.

This is not the same as a distortion pedal.

It will send this clipped distorted signal to your 1000W speaker. And that speaker will try to imitate that signal. This clipped distorted signal will cause your speaker to overheat and destroy itself.

So, that Line 6 cabinet will work fine for your amp.

Just don't play with your amp cranked to 10 all the time! ;)

Not being an electrical engineer, I can only tell you what I've read in articles, by electrical engineers, on amps and amp building.

You will damage either your speaker or amp if they are not matched. Solid state amps will take speakers rated slightly higher than their stated output - so you could run 8Ohm speakers on a 4Ohm OP transformer without damage - 16 Ohms would kill your amp.
Tube amps can take a slightly lower impedance so it would be better for an 8Ohm OP transformer to be driving 4Ohm speakers than the other way around.

From my meagre knowledge of electronics, I would say that reducing resistance (impedance) is not going to turn anything into a toaster - toaster wires glow because of high resistance in the wire. This is the reason that wire, connecting the OP transformer to the speaker, should be heavy duty so as not to represent a further impedance in the speaker circuit (and also become very hot due to the resistance).

I'm studying electronic engineering currently so we cover some electrical engneering as well.

I've never seen anything saying a higher impedance will kill your amp if it's solid state.
Most of the time there isn't OP transformer in a solid state amp, so you don't need to worry about burning that out with a lower impedance. Though i'm sure it will over heat various components which will degrade and eventually die.
The reason this happens is because less power is going across the speaker so circuit has to take the rest of the power up with it's own resistance.

I have seen something saying that you should go under the impedance on a tube amp... but it only says by a slight mismatch, best to get a cab/speaker which is rated the same.
Here the mismatch would damage the OP transformer.

Eminence Speakers has a great site to learn. Here is a guide to selecting speakers for many popular amps.

http://editweb.iglou.com/eminence/eminence/pages/resources02/guitarXref.htm

At the bottom of this page it discusses speaker power handling.

http://editweb.iglou.com/eminence/eminence/pages/params02/params.htm

So - Greybeard or any one got any references for buiding your own cabs?  I have two Celestion 75 watt speakers in layaway at SamAsh.  If I can't afford to do a good job on my own  building some cabs in the next month, then I will for sure go with the Line 6.