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Old 5th November 2009, 03:47 AM   #21
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Quote:
Originally Posted by rcw View Post
Having a steep high pass filter about an octave lower than this is also advisable since bass guitars produce a very large d.c. component that causes a large cone offset, and this can be greatly increased by the technique of damping the strings with the hand.
Sounds like nonsense to me. I bet you can`t find a commercial bass amp that doesn`t have either cap, transformer, or servo on the output.

andrewskaterr, wake up and smell the coffee. Lose the crossover.
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Old 5th November 2009, 03:54 AM   #22
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Originally Posted by leadbelly View Post
Sounds like nonsense to me. I bet you can`t find a commercial bass amp that doesn`t have either cap, transformer, or servo on the output.

andrewskaterr, wake up and smell the coffee. Lose the crossover.
ok I'm not understanding him with the octave lower deal. can you break it down?
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Old 5th November 2009, 04:10 AM   #23
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I'm not sure I understand that last bit, are we getting confused between amp and speaker here?

I've built a couple of bass cabs for my daughter and one was 2-way, 15inch with a 5.5mH coil in series and 12 inch with a cap in series, both 4R drivers and sharing a sealed box, it was OK, especially for practice using her head-unit.

Personally I think 15s are too small for bass guitar and if I was going to build an open back box I would be using a low frequency high pass to stop the driver going thru to X-DAMAGE if she really pounded the volume and bass boost at the same time, large capacitor bank in series with the input.
Depending on the impedance you need around 1500/1900 uF and that will not be cheap but it filters a lot of the infra-sonic and gives a slight boost to the low bass, works best on high Qms drivers.
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Old 5th November 2009, 04:26 AM   #24
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Originally Posted by rcw View Post
This type of box is a part of a musical instrument and not intended to reproduce sound, look on it as the body and sound hole structure you find in a bass viol.

Bass guitar boxes in general have a 60Hz. punch peak, and you will find the typical bass guitar driver is uptimised for this. In general it is best to design the box for the formant you want, then tweak the tone controls.

Having a steep high pass filter about an octave lower than this is also advisable since bass guitars produce a very large d.c. component that causes a large cone offset, and this can be greatly increased by the technique of damping the strings with the hand.
The effect of this offset is to soak up large amounts of power and produce no more sound.
rcw.

can you explain the last paragraph?
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Old 5th November 2009, 04:39 AM   #25
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You gonna have a funky load anyway, as neither speaker is Zobel'd flat.
I'm not suggesting you do that. Funkiness is fine in an MI application,
as long as you don't go too far off into the weeds....

Just remember you got a huge impedance peak around resonance, and
also a rising impedance with frequency. That doesn't mean you need to
panic and change how you cross it. Merely abusing the opportunity to
open your eyes to another can of worms thats maybe not relevant...
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Old 5th November 2009, 04:42 AM   #26
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Low-cut or Subsonic filter I think he means?
One probably already in most amps.
But don't hurt to make sure.
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Old 5th November 2009, 04:55 AM   #27
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You didn't mention the type of amplifier you are using.
Bass guitar amplifiers do not go down much lower than 30-40Hz.
Hi fi type amplifiers go down too low and the speaker spends much of its excursion capacity in d.c. pulsing, and in this case a steep high pass filter is advisable.

You can make a quick and dirty one by putting a capacitor somewhere in the amp input, and another, (back to back electro), in series with the drivers.
rcw.
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Old 5th November 2009, 05:28 AM   #28
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Quote:
Originally Posted by rcw View Post
You didn't mention the type of amplifier you are using.
Bass guitar amplifiers do not go down much lower than 30-40Hz.
Hi fi type amplifiers go down too low and the speaker spends much of its excursion capacity in d.c. pulsing, and in this case a steep high pass filter is advisable.

You can make a quick and dirty one by putting a capacitor somewhere in the amp input, and another, (back to back electro), in series with the drivers.
rcw.
well I own a power amp so that's what I use, but I've used guitar and bass amps on it. I see what you were talking about now with the high pass, i was thinking in the mids, not at 30hz. my power amp has a 30hz filter on it. 18db i think. it's a tapco juice amp 2500
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Old 5th November 2009, 05:42 AM   #29
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30Hz should be fine, and if it is 3rd order that should be steep enough.
HiFi amps usually have it at 18/25 Hertz.
Just out of interest; do you go though an effects box or are you plugging straight in to the power amp?
My daughter blew up one of my amps by plugging her bass- axe into the mike inputs, well she was 12 at the time so I forgave her ( it was an old amp after all )
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Old 5th November 2009, 06:36 AM   #30
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Quote:
Originally Posted by Moondog55 View Post
30Hz should be fine, and if it is 3rd order that should be steep enough.
HiFi amps usually have it at 18/25 Hertz.
Just out of interest; do you go though an effects box or are you plugging straight in to the power amp?
My daughter blew up one of my amps by plugging her bass- axe into the mike inputs, well she was 12 at the time so I forgave her ( it was an old amp after all )
I can't remember if I've done it straight. The day I really tested it I ran a guitar to an Art tube preamp ($30 it's nice) then to the power amp. we also ran it through a fx pedal and when we had it on clean, the amp led actually started going orange, which i've never had happen before. i was pushing around 575w or more.
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