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20Hz Speaker Fluctuations ??

FuzzBoxVoodoo

FuzzBoxVoodoo

Nov 28, 2008
1,345
11
Sacramento CA
#1
I have been using a BBE BMAX Tube Pre Amp with a Carvin 1500 Amp rated down to 20hz and I just switched over to a GT Tube Preamp made by SWR for GT and now I have noticed that my Speakers move alot more when you are playing the lower notes and if you thump on the strings while muting the string the speakers look like they are going to jump out of the cab.
I guess that the BBE Preamp doesnt go down to 30 or so HZ.
I have a Mackie 1400 that has a built in adjustable crossover that is designed to take out these lower harmful frequencies,I have not tried the Mackie with the GT Preamp to see if I can dial out the unusable lower frequencies.
What do you guys think, should I continue to let the speakers reproduce these lower frequencies or should I switch over to the larger heavier Mackie and try to find the happy medium?
I dont want to hurt my Speakers.
Steve
 
#3
Rick Auricchio said:
You could cut the bass EQ and turn down the power a bit.

If the speakers are moving that much, you're risking overextending them and causing damage.
Click to expand...
You cant hear the sound that is causing the speakers to move.
When I have the Bass Control set where I like it and I play normal then the speakers are only moving a little more than Im used to seeing.
This is probobaly a normal thing for alot of setups (I think) I know that the Gallien Krueger 2x10 Combo that I had did the same thing with what I thought to be unecessary speaker movement.
I just found this info for the Carvin DCM2500 and up.
The LO CUT switch inserts a 40Hz, 3rd order, high pass filter. This will remove sub audio frequencies
from damaging speakers and wasting inaudible power. It is active when the switch is pushed “IN”.
Steve
 
#5
Hi.

Your namesake designed the SWR (pre)amps to behave like that, the extended low range gives them a deep Hi-Fi like capability, but eats A LOT of power. With a proper instrument and cabs, it sounds rather good though ;).

In Your case using the 40Hz Hi-pass filter is justified and recommended as your cabs are most likely ported, and have a tuning frequency around 40Hz.

A ported cab controls the Lo-frequency reproduction and cone movement only down to the tuning frequency, below that the cones are almost completely without dampening so they move uncontrollably, often fart out and are damaged as the result of over-excursion.

If You look at the cone excursion graphs, after the notch at the tuning frequency the excursion skyrockets.

Just my 0.02€
Sam
 
#6
+1 on the above
Very little musical information and nearly impossible to reproduce in the 20 to 30Hz range
Filtering these extreme lows is good protection and while you may hear them slightly when playing alone, it gets lost in a band situation IMO
 
#8
Oh certainly, and in fact most of us live exactly that way since most normal speaker cabs barely project much below 45 Hz anyway. My point was that if he's not seriously down-tuned, and not using a subharmonics generator, he's likely not pushing 20 Hz through anything. But of course he could be very down-tuned or using a low C flat ;) ERB or using subharmonic synth effects, which is why I asked.
 
#9
I play Standard tuning 4 string.
So I have put together many crossovers based on Ohms and frequency but never have made a filter based on voltage and frequncy.
Why couldnt I simply make a 35Hz filter and install in on the Output of the Preamp,there is plenty of room inside as it is a 2U mounting it looks just like a SWR SM-400 Amplifier.
Does anybody here have the capability to help me design a simple 35Hz filter?
Steve
 
#16
T-Bird said:
Hi.

I haven't done any, but search for a rumble filter on the DIY sites.

That GT/SWR pre is the same as in ST220 and SM400 AFAIK.

Or switch to a transformer coupled (tube) power amp. No such problems there ;).

Regards
Sam
Click to expand...
I really like the setup that I have now and would like to somehow filter it a little and I dont want to have to use my bigger and heavier Mackie 1400 with a adjustable low filter to acomplish this.
 
#18
I suspect that your new preamp simply amplifies the fundamental frequencies you do have, from 41 Hz and up, more than the old preamp did at EQ settings that superficially look similar to you. So the overexcursion you are seeing is real, and you are right to want to use a filter to control it, but the actual frequency range causing you trouble is realistically between 40 and 80 Hz.
 
#19
bongomania said:
Your preamp does not generate any frequencies that are not fed into it, and your bass does not produce any frequencies below about 41 Hz.
Click to expand...
Acording to the Carvin DCM-1500 specs the Amp is capable of generating power from 10Hz to 40Khz.
I never had excessive speaker mivement with the BBE BMAX Tube Preamp but now that I am using the SWR/GT Tube Preamp I am getting very low freq coming through my speakers.
I simply want to eliminate the unusable freq
 

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