Low Pass Filter

Whoever gave you that circuit should be unfriended. It's a high-pass circuit and will cut the bass. Also, it shows a polarized capacitor which is not appropriate.

Also, this post would be better served in the Amps and Cabs forum.

 

For the vast majority of people regular old tone controls in our amps and/or basses do the job perfectly well. What is your situation that makes you feel the need for a passive first order low pass filter at speaker level?

TLDR version: if you have to ask you probably don't need it

 

Your speaker already acts as a low pass filter. To me, LPF's are better used in PA systems, where if you run a DI, it will likely run full frequency range up to 20 khz, so you'd use an LPF to knock it back down to 4 or 5K like your speaker does.

 

I agree with Passinwind and JimmyM. If you want more truncation than the physical characteristics of a 15-inch speaker, just turn down the treble on the amp or the tone on the instrument. If the trace in the opening post is of the driver that is being considered, then notice the natural rolloff. Any treble cut will take care of the spike above 5kHz.

Remember, you don't want too much roll off, because you need some overtones to make sure you are articulate and present out front in the mix, whether your rig is carrying the house, or if there is either a mike or d.i. from the rig to the house mains carrying the load.

 

I installed a switchable low pass filter in my 15 cab but it isn't supposed to be a full range speaker. I use it with a couple of different top boxes, one of which (my old Eden 210) is quite midrangey. being able to roll off the treble and upper mids from the 15 gives the pair just the right response for me.

the other top box I use (aguilar light weight 12) is very scooped in the mids, so I switch off the filter for this combo.

if memory serves, the filter is simply an LC low pass. (actually it may even just be an inductor on its own, it was a few years ago I did this.) I wound the inductor myself. I may have some photos somewhere...

 

I always interested in seeing how other people approach those sort of configs, as I have built and enjoyed quite a few top box implementations myself. That's a much different thing than what the OP asked about though, of course.

 

I found some photos, but not of my 15 cab. This was another little project. This has a simple cross-over (one cap, one inductor) and a horn attenuator. The coils are wound on plywood formers with a piece of copper clad circuit board with two solder pads "dremelled" on it. Use an online inductor calculator for the sizes, then drill an inner hole for the start of the coil. Winding by hand with such heavy guage winding wire, you'll need to paint some super glue across the coil every few layers to keep it all tight. It's quite hard work keeping it all neat and tight. Your fingers will be sore at the end! Near the edge, drill a second hole, thread, then solder the outer end of the coil. Oh, and you'll need to scrape the coating off the wire to solder. It won't burn through like pickup wire.



As you can see, the 0.56mH inductor has a single hole through the middle to be mounted with a bolt through the metal plate in the speaker box.




The 0.9mH was the one I used for the 15 cab. It has two holes and IIRC was mounted with self tappers into the timber frame of the speaker box. The little red thing on top is simply a join. I ran out of wire from one spool and instead of starting again, I drilled to exit holes right next to one another, stripped, twisted, soldered, insulated, then glued the join in place.

 

Cool, thanks. For those playing along at home, a number of software apps have inductance measuring facility these days, including Room EQ Wizard, which is freeware. You just need a decent soundcard and a pretty simple reference jig. Lots of people using commercially available coils start high and de-wind to get custom values.