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Amps and speakers

Discussion in 'Amps and Cabs [BG]' started by Yvette, Sep 4, 2001.


  1. Hi all
    I'm thinking about getting a new amp. What I'm worried about with my current set up is damaging my favorite speakers in my beloved amp, that's why I thought of buying the new amp. Thing is I play throu a Music Man 130 watt all tube guitar amp combo with two 10" speakers. I have added a Marshall 15" cab (250 watts 8 ohm).
    I'm absolutely shure the amp can handle it. Also I never use it harder then pre amp on 4 and power amp at 5 to 6, so there are no way clipping tones it's almsot totaly clean, just little tube compresion. But my drummer said that in time the spearkers might get damaged just melt because of all the low I put in. I'm not shure he is right since they can handle 150 watts and I'm only feeding them 65 (due to the two cabs) and I never even use close to full power (it's absolutely loud enough allready (that's what this amp is weel known for). So I might still use it as I wish, but then if he is right, jesus that will be a disaster with tears and everything.
    Well I would love to hear your opinions on this, thanks in advance,

    Yvette

    PS I have not much money so if I go for a new amp it's just to keep my MM okay, I was thinking about Hartke 4000 or 3500 or Peavey Nitro Bass, lots of power for the price.
     
  2. MikeyD

    MikeyD

    Sep 9, 2000
    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
     
  3. Thanks for reply. The Marshall is bass all the way, closed back indeed. I think I just must indeed disconnect the internal speakers. It gives a less punchy cutting sound then, but with the open back of the combo that probably will only be so the first few steps in front of the amp, it will be lost further on anyway.
    Other question I have is the ohm setting. The speaker outs are serial. What does that do to ohm setting? Are two 8 omh cabs still 4 ohm? Or will it stay 8 ohm? Replies are very welcome here, thanks in advance,

    Yvette
     
  4. MikeyD

    MikeyD

    Sep 9, 2000
    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
     
  5. 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
     
  6. Thanks again.
    The speaker out are absolutely serial. Someone said it to me and I checked it and it's true, so still curious about that.
    For the other sugestions I think I go try to split the high and low signal indeed.

    Yvette
     
  7. MikeyD

    MikeyD

    Sep 9, 2000
    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
     
  8. 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....
     
  9. MikeyD

    MikeyD

    Sep 9, 2000
    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
     
  10. 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