Amps and speakers

I'm not familiar with the particular equipment you mention, but guitar combos and cabs are not usually designed to handle the low frequencies of bass (below about 70-80 Hz.), regardless of their wattage rating. I would guess you could easily damage those 10" drivers with a strong low E on your bass. Therefore, I recommend either unplugging the 10" drivers and using a bass cabinet instead, or somehow attenuating (via a filter or biamp set-up) the frequencies below 70 Hz. to it.

I don't know anything about the Marshall 15". If it is a guitar cabinet, same comment. If it is designed for bass guitar (BTW: will not have a big open back, but perhaps a smaller vent/port opening), then that's the one to use. Pay strict attention to impedance so that the amp is loaded properly.

To save money, you might initially use the guitar head from the combo to drive a bass guitar speaker cabinet, then upgrade the head in the future if you wish.

- Mike

 

Okay. I haven't looked up your combo, so it's hard to make specific comments. I'm assuming the MM is a mono amp head (not stereo) and its speakers are for guitar. Those speakers would really enhance the punchiness if you could keep the low bass away from them (to prevent damage). If you had a stereo amp (meaning separate power amplifiers, not dual input channels) or a separate amp that you could slave off the MM, it would be relatively easy to do this via a filter or bi-amp at the pre-amp stage. Short of doing this, I don't think there is much you can do, short of keeping the volume way down and/or cutting your low bass EQ way down while using the 10" drivers.

I'm not sure I understand this. Usually the outputs on the amp are in parallel. If you are talking about the jacks on the 15" cabinet, they are usually wired in parallel as well. If you have two cabinets, each 8 ohms, they will result in 4 ohms when connected in parallel. If you use only one of the cabinets, set the output for 8 ohms. If using two in parallel, set it for 4 ohms.
- Mike

 

I don't agree with MikeyD....

I'd say get an electronic crossover, and send the lows to the 15, and everything else to the guitar speakers. Do you know what I'm talking about? I think you can get one at Radio Shack for about $50.

I think this would solve your problems, IF you keep impedance (ohms) where they need to be. You would keep most of that punchiness you like, and also get a lot of bottom.

Mark

 

Yes, I agree. If you are talking about a bi-amp crossover, it splits line level signals at the pre-amp stage, and you'd have to have two power amps. If you are are talking about a passive (loudspeaker) crossover network, typically the crossover frequency is much higher than 1 kHz (2.5-3.5 kHz is common). This is okay, but the 15" may not do very well up at that frequency. Might be worth a try, though. The content above the crossover frequency, fed to the 10" drivers, might be enough to brighten the sound a bit. It won't help the 15" be "punchy" though. The punchiness from 10" speakers typically happens around 300-500 Hz., IMO. This is why most bass guitar systems bi-amp at lower frequencies.
- Mike

 

good point. Maybe Yvette could use a 3-way loudspeaker crossover and send the mids and highs to the guitar cab. Is that possible? That's actually what I was thinking about. Or isn't there such thing as a variable crossover? I guess it would then be ideal to send the 15" cab freq. of about 250Hz and less, and everything else to the guitar cab.

I'd say since Yvette says the amp is "plenty loud", he/she just needs to be able to get the lows away from the guitar cab....

 

This is difficult/expensive to do at lower frequencies, which is why most subwoofer systems use active crossovers upstream of the power amps, rather than passive crossovers downstream. It has to do with the impedances involved. Upstream impedances are typically in the 10's of thousands of ohms, so capacitors and inductors required to achieve the desired cutoff frequency are reasonable in size; whereas downstream impedances are around 4-8 ohms, requiring huge components to achieve low crossover frequencies. It can be done, but who wants to haul around a crossover network that costs $400 and weighs as much as the whole speaker cabinet? Besides, better phase characteristics can be achieved with a higher-order active crossover.
- Mike

 

yikes, now I'm getting out of my league!!

But doesn't every 2 and 3-way full range speaker made have a crossover in it? I think you can buy a 3-way crossover for less than $100 at Radio Shack (don't know if they have that where Yvette lives?).
Wouldn't that do the job?

Mark