Question on speakers - Ohms

[David St Hubbins]

Can you put a 15 ohm speaker into a cab that says 8 ohm ? I have two 12" Rola Speakers I would like to put into a 2x12 combo. But these Rola speakers are 15 ohm and the ones that are in there are 8 ohm. Are there any issues with doing this? Amp will blow up etc....

Better to ask first.

[tripleG]

Since the wattage rating on your speakers is higher than the amp's original speakers there will be less resistance on the power flowing through the circuit which may damage the Rola speakers you want to install.

You may want to check out the possibility of getting a small device to switch the ohms coming from the amp and install it as well if you really want to use those speakers really loud for a while

.:DevilGuitar:

[Ripper]

Ohms aren't wattage. We don't know what the wattage of Dave's speakers are. For his question at the moment the speaker wattage really isn't an issue.

Dave, you can certainly put those speakers in, but there are few things you have to take into consideration. If you have two 8 ohm speakers in there now, the total impedance of your cab is either going to be 4 or 16 ohms depending on how it's wired. With the new speakers even though they test at 15 ohms, call them 16 for simplicity sake (most speakers don't test out exactly at 8 or 16 ohms). So depending on how you wire these ones in, you are going to end up with either 8 or 32 ohms (32 wouldn't be good). Does your amp allow you to select speaker impedance? Some amps have either separate jacks or a switch to allow you to pick the impedance to match your speakers.

Look up on the net for guitar cab wiring and read about the different ways to wire them etc.

[David St Hubbins]

Thanks for the info so far. The amp is 100 watts, the Rola speakers are G12-30's

The amp is solid state and the speakers are hard wired to the circuit board internally, so I would just be disconnecting them at the speaker connections and connecting the new ones up the same way. There does not appear to be any switch to select impedance.

[bRian]

David, exactly what amp do you have?

[elcabong]

Whatever the way they are wired now, replacing them with the 16 ohm speakers and keeping the wiring the same will double the load, hence reducing the power by half.

If you change the wiring, there is a possibility of having half the load. That is going from 16 now (8 in serie) to 8 total (16 in ||). That may be bad for the output transistors if you dime the amp.

The other possibility is going from 4 to 32. It is going to sound... weak. Or bad.:rolleyes:

You can not match your impedances the way your amp is designed.

[Wild Bill]

Thanks for the info so far. The amp is 100 watts, the Rola speakers are G12-30's

The amp is solid state and the speakers are hard wired to the circuit board internally, so I would just be disconnecting them at the speaker connections and connecting the new ones up the same way. There does not appear to be any switch to select impedance.

Dave, what we are all trying to get you to tell us is if your amp connects to the speakers by "daisy chaining" each speaker (in on a -, out on the + to the other speaker's - and back to the amp's board on the =) OR if it connects the + on both speakers together, the - on both speakers together and then the two common connections connected to the amp as if it were one speaker.

Daisy chaining puts the speakers in series. Tying +'s and -'s together puts them in parallel.

Two 16 ohm speakers in series will add up to a 32 ohm load. The same in parallel will look like an 8 ohm load - TO THE AMP!

You see the problem? If you had two 8's originally in there the amp may have seen either 16 ohms or 4 ohms.

Why is this so important? Solid state amps don't really have a fixed speaker impedance output, like with a tube amp where you have different spkr jacks or a switch to select 4, 8 or 16 ohms. They simply put out as much power as they can into whatever speaker load you hook up. The designer knew that lower speaker loads would mean the amp would put out more power so he set a limit. When you look on the back of a solid state amp it usually will say something like "100 WATTS AT 4 OHMS" but also "DO NOT OPERATE THE AMP INTO LESS THAN 4 OHMS!"

That's because if the transistors see a lower speaker load than 4 ohms they will dump MORE than 100 watts - until those ONLY 100 watt rated transistors overheat from exceeding their ratings and BLOW UP!

Running a higher speaker load than design won't hurt - you just run at less power.

It might be worth your while to spend some time to figure this out...

[David St Hubbins]

Please excuse my ignorance Bill, and everyone else. I really appreciate the info being given. The speakers are wired separately and not connected to each other and then to the amp. They each go to the amp separately. So I would say they are not daisy chained. I will read up on the whole the impedance thing and try and educate myself further.

Appreciate the assistance. :wink:

[Wild Bill]

Please excuse my ignorance Bill, and everyone else. I really appreciate the info being given. The speakers are wired separately and not connected to each other and then to the amp. They each go to the amp separately. So I would say they are not daisy chained. I will read up on the whole the impedance thing and try and educate myself further.

Appreciate the assistance. :wink:

Don't worry about appearing ignorant, Dave! We all start from the same point and learn by asking questions.

The guys that scare me are the ones that never admit to not knowing an answer. This usually means they'll lie... ;-(

We all just don't want to see you have an expensive failure in your amp. As the old blues saying goes: "Some I spent on whiskey, some I spent on women and some I just wasted!"