Ohms and connecting combos

frenfrins · #1 12-07-2012, 11:54 AM

Hi everyone, congrats for this amazing forum, very useful anytime I need any information using the search options.

This time I hope someone could give me a hand:

A week ago, I bought the Harley Benton BA5110C combo (you probably know it, 250w 8ohm or 500w at 4ohm, similar to the Ibanez Promethean), I'm very happy with the sound I can get with it, also one of the reasons that made me buy it was the possibility of getting those 500w adding another speaker.

To get that power, I wanted to use the speaker of my Fender Bassman 250/115 combo, just to try, or unless until I could buy another speaker.

I don't know why, but I was sure that the Fender's speaker was a 250w @ 8ohm. Today I bought the wire, and then I realized that it is 4ohm!

Is there anything I can do or just forget about that idea?

I hope I explained it clear enough, English is not my native language.

Thanks in advance

Bass_Pounder · #2 12-07-2012, 12:07 PM

Short answer - NO

Mixing a 4 ohm speaker with a 8 ohm speaker gives a total impedance of 2.67 ohms - which is BELOW the safe operating range of your amp.

RickenBoogie · #3 12-07-2012, 12:07 PM

No, you cannot connect a 4 ohm spkr to your HB combo, it must be an 8 ohm ext cab.

frenfrins · #4 12-07-2012, 12:17 PM

OK, so it is as I suspected

Thanks a lot for your help

RickenBoogie · #5 12-07-2012, 02:05 PM

Yeah, sorry, but welcome anyway. What you really want, it as close to a matching 8 ohm cab to whatever's in the combo. IF it's a 1x10 combo, another 1x10. But realise that no 1x or 2x 10 will ever handle 500 watts.

frenfrins · #6 12-10-2012, 10:49 AM

Yes, I understand, but if I get something similar as the speaker included, I mean a 250w 1x10 8ohm, I assume I could get those 500w, and that could be something similar size of a 2x10, right?

scottfeldstein · #7 12-10-2012, 11:06 AM

Quote:

Originally Posted by frenfrins

Yes, I understand, but if I get something similar as the speaker included, I mean a 250w 1x10 8ohm, I assume I could get those 500w, and that could be something similar size of a 2x10, right?

Well, there's "getting" and there's getting. Adding a second 8 Ohm 10" speaker will "get" you the full 500w...but you'll never be able to use them. No pair of 10" speakers alive can handle that much power. Although it'll be there, in the volume knob, you won't be able to turn it that far.

RickenBoogie · #8 12-10-2012, 11:17 AM

+1 speakers are rated for thermal limit's, NOT actual mechanical limits. It's usually around half. So, a 250 watt 1x10 will actually handle approx 125 watts before it starts to "fart", which is a sign the spkr is being stressed beyond it's capabilities, and about to destroy itself. Yes, you will have the full 500 watts available, but the 2 10's will never handle the whole lot. Doesn't matter though, most of the volume comes from the first 50 watts or so anyway, and wattage is NOT a measurement of volume, regardless.

frenfrins · #9 12-10-2012, 01:48 PM

OK, it really makes sense, thanks for the info. So, which option will you consider to get those 500w without having to carry something really big? How about adding a 2x10 cab?

scottfeldstein · #10 12-10-2012, 01:56 PM

This is where you start going "why did I buy a combo?"

Because it has an 8 ohm 10" speaker already permanently in the equation, the most sensible thing to add on to it is a second 8 ohm 10" speaker cab.

You could theoretically add on a larger cab instead. Maybe a 15 or even a 410. But you won't be able to turn the volume knob up to where you're getting the most out of that larger cab. Your volume knob is going to be limited to what the single 10" can take--far less.

Adding a larger 8 ohm cab will be louder. You will just have to be careful and understand what you're doing.

Unless there's a way to disconnect the built-in speaker.

I'm sure that's all clear as mud. Sorry.

frenfrins · #11 12-10-2012, 02:11 PM

Your answer is totally clear, and I really appreciate your help.
It is very easy to take off the head of the combo, just have to remove four screws. So, it looks that the only way I can be sure to get all the power is forgetting the combo speaker and getting a 4ohm cab.
At the moment the combo is working fine, I did a gig with it last saturday and had no problems with volume. Now I know what I should do in case I need it to be louder.
Thanks again!