Low pass filter on a speaker cab?

[Wolfeman]

So I was doing some designing/research for my Wolfe Amplification 4x12 speaker cab, and whilst looking at frequency response graphs for speakers, I got this crazy idea...

Why not throw an inductor on each speaker and 6db low pass them at 12,000 Hz?

When recording, we usually do it around that freq anyway... And most V30 loaded cabs always have that strange high end sizzle going on (if you look at the freq response graph, it has some weird shit going on in the upper frequencies).

I'm very curious as to what this would do to the in room sound, and recorded. 0.10 mH inductors are cheap as hell, so I think I will buy them and test this out. Who knows, maybe I'll be the first person to try this, and maybe it will sound good?

Edit- I also ventured the thought of a high pass filter too. Throwing a 200uF cap in with the inductor would yield a high pass of around 80Hz I think....

Edit- Test Files Here

 

[lolzgreg]

I want to hear it done! CLIPZZZZZZZZZZZZZZZZ

 

[Wolfeman]

I order some inductors and caps for all four speakers. Total damage- $10 haha

I'll give it a go on my Bogner cab and report back. Should be a few days.

 

[AudioPhile777]

clips and pics or it didn't happen!

What you should do, if it works and sounds good, is make something that plugs in between the speaker outs of the amp and the cab (if thats even possible) and see if you can sell it... and maybe add a switch or two to adjust the LPF, incase 12k is too high and you want like 8k or 10k... ya know?

Hell, if it helps the sound in a live situation, I would buy it. Especially with the fizzyness of my new recto...

 

[PlasmaShock]

Actually, this sounds like an exciting idea.

Back when I was studying amplification circuits we worked with guitar amplifiers for testing purposes.

It's shame that I don't have time to test this out at the moment as well

 

[AllanD]

I've always thought about this, but google yielded no results ever. Definitely interested!

 

[Wolfeman]

Yeah I was thinking, almost every other audio 'clique' uses some sort of speaker crossovers/filters- PA setups, Hi-Fi setups, home theater speakers, car audio... Hell, even our studio monitors have filters and crossovers.

 

[Wolfeman]

clips and pics or it didn't happen!

What you should do, if it works and sounds good, is make something that plugs in between the speaker outs of the amp and the cab (if thats even possible) and see if you can sell it... and maybe add a switch or two to adjust the LPF, incase 12k is too high and you want like 8k or 10k... ya know?

Hell, if it helps the sound in a live situation, I would buy it. Especially with the fizzyness of my new recto...

Hmm, yes I think I can do this! I would have to make different ones for different cab impedances, but having the option to have it/not have it in the chain would be great!

 

[AudioPhile777]

Hmm, yes I think I can do this! I would have to make different ones for different cab impedances, but having the option to have it/not have it in the chain would be great!

Don't forget the adjustable LPF/HPF if possible! That would be crucial for me. Just sayin'.

Edit: also, I want 10% of the profits.

:Smug:

 

[Wolfeman]

Don't forget the adjustable LPF/HPF if possible! That would be crucial for me. Just sayin'.

Edit: also, I want 10% of the profits.

:Smug:

The adjustment would be simple to implement, but it would double or triple the cost since you would need X amount of inductors for X amount of switch positions. But like I said, these things are pretty cheap.

 

[AllanD]

Aren't there variable caps for the HPF?

 

[Wolfeman]

Aren't there variable caps for the HPF?

If you want to go garbage pic some 30 year old tuner knob style radios and pull out the variable tuning cap for me, be my guest

Nah, they aren't used much for anything anymore, and would be shitty in an audio path(they are open air caps). I don't even know if there would even be a value of a variable cap that would fit in the range we would need.

Edit- I suppose if it were an active crossover you could make it variable, but you are asking the wrong guy in that area.... And that would just be one more thing to plug in.

 

[Norris-wf]

I remember using variable caps a few years ago, they were very accurate too, but they were at picofarad levels and at that they were pretty big. They were used for test calibration in a lab though, so possibly not a viable option here

 

[kev]

Nice idea!

 

[Omega_Void]

Rolloff with passive filters is 6db for 1st order, which isn't too great. 2nd order passive will have a very gradual knee, might take out too much of what you want along with what you don't.

Output impedance of a guitar amp is not negligible and will affect the turnover frequencies. Zout will also vary from amp to amp, so the filters can't be exactly tuned.

Not that this makes it a bad idea, just pointing up some limitations. I'd be more incline to HP and LP in the guitar's fx loop, it's cheaper and easier to make variable.

A series RLC across the speaker tuned to the speaker's resonant frequency is one thing I've considered to try to reduce the boominess you sometimes get. That would take the impedance peak out of the speaker, so the amp will deliver less of a power peak at that freq (remember high Zout amps are not voltage sources) where the speaker has least control form the suspension. Making the Resistor a pot would allow the effect to be increased or decreased. Whether it's worth trying probably depends on the extent to which the amp's Zout would change the filter tuning, and I haven't done any math on this idea at all, so I'd SPICE model it before you try, but it might be worth a go.

 

[drew_drummer]

This sounds interesting. Because it would come after the amps output; so it'd be different to just using the presence control on the amp.

 

[MarcusGHedwig]

Especially since the presence control is usually centered around 4k

 

[Wolfeman]

Got the parts in for this today. Unfortunately I don't think these would be feasible to sell, at least with the high pass filter, since the 10mH inductor used cost $35. The other parts just cost a few bucks. So to throw it all in a project box, wire it up, etc, I would have to charge around $75 to make any kind of money. So if you want to build one, you are probably better off going the DIY route.

Anyway, I'll hook it all up and throw Jeff's KSE DIs through it in a bit. I'll also throw my measurement mic on the cab and run a sweep through it so we can see exactly what it does at what frequencies.

 

[Wolfeman]

So simple, yet hopefully very effective-

 

[JeffTD]

The only problem I can see you running into is the fact that V30's only have a frequency range of 70hz-5000hz anyways - not sure an hpf will make much of a difference, but it might reduce some fizz from the amp like a graphic eq would?