Subsonic filter bybass?

[jakelm3075]

Hi all, I just registered to the forum. I ave been reading up on everything so I decided to join.

My first question is: I currently have a new box design for my MTX powered sub. I'm using the same plate amp and driver, but the amp has a subsonic filter which drops 18dbs at 30hz. My new box design with be tuned to 20hz but with this filter I wont be able to achieve optimum performance from this sub. Does anyone here no how to bybass this filter, and location to maybe install a jumper? Or is there another way around it?

Thanks
Jake

 

[simon5]

Well, every amplifier is different, but yeah usually you can change some parts to alter the subsonic filter.

You need to contact the manufacturer probably.

 

[anton]

generally there is not " much music" under 25-30Hz , that's why many amps have subsonic fixed around 30 Hz. with subsonic your bass response will be more dynamic, fast and clean. many people wish to have subsonic on the amp but they don't.
.

 

[simon5]

Well I don't agree with this, a 18 dB/octave filter at 30 Hz will not give more dynamic bass response, nor more "fast".

If it's cleaner, then it's just because your driver isn't beefy enough IMHO.

 

[badman]

I agree with simon5. The only reason to high pass a subwoofer at 30 is to keep a cone that can't manage the 'serious stuff' from showing its shortcomings. A high pass in the teens can make sense to keep nonsense like TT rumble and whatnot out of the system, but not up by 30, that's just silly!

 

[jakelm3075]

I just cant have an 18dbs drop at 30hz if I'm tuning the box below that. If anyone knows what to look for on the amp, it would be greatly appreciated. Maybe I can take a picture of the amp and someone can point out what to change or unsolder?

 

[jakelm3075]

Or if anyone knows what the filter looks like or location? I appoligize fopr the ignorence.

Jake

 

[pinkmouse]

It will just be a chip surrounded by capacitors and resistors. You really need to get a schematic from the manufacturers

 

[jakelm3075]

Thanks Al. You think it is between the amp and the input or between the amp and the speaker output? MTX is uncooperative. Very nice people to work with but when it comes to very technical stuff, they are reluctant.

 

[badman]

MTX is uncooperative. Very nice people to work with but when it comes to very technical stuff, they are reluctant.

I think you'll find that's the standard. After all, why should they release their incredible secrets and proprietary technology?
Most companies are reluctant to give up anything, they figure 'give them an inch and they'll take a mile'. I have a neat little sub, for example, a bipole with a highly EQd tiny enclosure. I asked for some information, specifically the transfer function of the amp, so I could work on it: sturdier bigger box. No help was forthcoming, I just wanted to make a bigger stronger box and reduce the EQ accordingly, but retain the same drivers.... no luck.

FWIW: B&W loudspeakers help department was VERY forthcoming when I wanted a little more info on some of their powered towers, to the extent of: crossover schematics, amplifier schematics, construction diagrams, all faxed gratis. Thumbs up to a much maligned company! 🙂

 

[jakelm3075]

Right badman. And I do understand thier hessitation.

If I only knew what to look for on the amp to locate the sub filter. I have full confedence that the driver can produce a much better performance if it wasnt so restricted in airspace and subsonic filter.

Most times manufactures will place filters and gain caps to eliminate warranty issues. They believe (like myself) that most consumers will over drive their system , in turn send it back for repair and warranty claims. Like a govern on a car or truck.

 

[simon5]

You could purchase a new plate amplifier for your MTX subwoofer and use your old amplifier for another project like a small vented subwoofer box where a 30 Hz rumble filter would make sense.

BTW, which MTX driver are you using? Most MTX drivers aren't designed to support 20 Hz at high SPL levels because of the smallish excursion.

 

[Emiel]

The subsonic filter is most likely to be an opamp surrounded by some capacitors in the 100nF range and some resistors. It'll be one of the first stages the unamplified input signal will pass through.
By changing the capacitor and resistor values you could change the frequency to, let's say 17 Hz or so.
Elliott has lots of information on active and rumble filtering on his webpages, see for example:
http://sound.westhost.com/project99.htm
http://sound.westhost.com/project09.htm

I do agree with Pinkmouse though that you should have the schematics before you destroy your amp!

 

[jakelm3075]

Thanks all. What I'll try to do is take a picture of the amp, then maybe yall could give me good pointers as to what to change. I really appreciate all the help.

Jake

P.s The driver and amp in question is on the MTX SW2. If anyone has any pointers on it.

 

[jakelm3075]

You could purchase a new plate amplifier for your MTX subwoofer and use your old amplifier for another project like a small vented subwoofer box where a 30 Hz rumble filter would make sense.

I could but this is a cool project for me. I'm learning so much from this.