Filter capacitors with speakers

[NaBo]

Well I've searched this forum and the usual lores of info, as well as googling... but I haven't really been able to find a good explanation of how to use filter caps with speakers...  too much power supply info :roll:

Can someone direct me to a good resource that explains how and why to implement them (maybe with equations, diagrams, frequency charts, etc... calculator?)... perhaps with a 'working example' approach?  That'd reeeeeally help me out so I can work on finishing up my little "mini-head-amp slash talkbox-stomper" project, and apartment-sized cab  

Really appreciate it, thanks a lot
Nabo

[aron]

I typed in:

capacitor speaker

in google.com and got this:

http://www.bcae1.com/capspkr.htm

http://www.bcae1.com/passxovr.htm

[NaBo]

Thanks Aron!!!  I think that site's exactly what I needed!

I'll mull this over for a bit and see if anything else comes up, but I think I'll be fine!

[NaBo]

Alrighty, plowed through relevant pages on that site and get the jist of it... caps in series rolloff lows, inductors highs.

But the site pretty much just deals with using these simple filters to divvy up frequencies between multiple speakers, eg, lows to woofers, highs to tweeters...  in my situation, i'm looking to protect my compression horn driver from harmful freqs, as i was advised to.

Now, in the case of my talkbox, the driver specs say frequency response is 600-11,000 Hz .  Is my goal to limit anything outside of that range from reaching the driver at full volume?  Should I therefore have a capacitor that rolls off frequencies below 600 Hz and an inductor that rolls off highs above 11 kHz, both in series?  Is it possible/necessary to have both?  I assume it's probably the lows from my amp that would cause the damage... just a cap then?

Getting there...  thanks

[Cabezahead]

It is my completely unknowledgeable unreasearched uninformed opinion that you would only need to filter stuff that goes below what your speakers at - as that causes the big movement in speakers - stuff that goes above won't affect a speaker negatively...

I think.

-CH

[NaBo]

Yeah, I'm of the same still unsure yet common sensical mind... lows are the ones that rattle the cone when a speaker's being pushed above and beyond.

Some reassurance?  Rolloff below 600 Hz and I'm set?  

[Mark Hammer]

The output caps just ahead of speakers are intended to block DC.  Of course, DC is just a very, very, VERY low frequency of AC when you think of it.   When you consider things like how a neighbourhood's use of air conditioners might cause a slowly increasing fluctuation in line voltage over a couple of hours, and even days, sometimes, it might be best to think of zero volts DC as *really* being something more on the order of a .000000001hz AC.

So, why am I telling you this?  Because when you block DC, you're really blocking AC.  And if you're blocking AC, then it now becomes your choice as to how far down you want to block it, and how you go about doing so.  Usually, when one tries to simply "block DC", what you're really talking about is rolling off AC below a point where you'd notice the loss, given speakers with exceptional bass response.  Of course, in most instances, the speakers will not have that response, or at least the amp will not have a stiff enough power supply, etc., to be able to deliver solid bass response to the speakers, in which case the choice is generally made to not make promises that can't be kept - i.e., shave off any bass that can't be cleanly delivered by means of a smaller coupling cap.

In the case of mini practice amps, there are a couple of considerations.  First, it is often (though not always) the case that they will be used with small-ish speakers and small-ish cabinets, and these will not deliver big bass under any circumstances, so why oblige the power-amp stage to deliver what can't be used or heard?  Second, such power-amps will often be used with battery supplies, and the current required to provide the bass will ultimately be larger, and the consequent battery drain faster.

One of the things about crossovers and frequency-dividers is that, being passive systems, they lose signal.  Indeed, that is one of the chief rationales for using active crossovers and bi/tri-amping - ALL the amp output is used.  Consequently, even though a cap/inductor arrangement would provide a steeper rolloff for purposes of limiting bass to the speaker, it would achieve such a clearer distinction between wanted and unwanted bass content by sacrificing power, which obviously one doesn't want in a battery-powered system.

Obviously, the more desirable choice is to simply use a "single-pole filter" (i.e., a cap in series with the speaker), though if there is some desire to have a better sounding high end, that "cap" may well be achieved by means of a few caps of different values in parellel; for instance a smaller value like <1uf for the highs.  

As always, limiting low end via a series cap also lets through low end, albeit at a lower amplitude.  So, what can be done to keep unneeded bass out of the circuit/path?  There are a few things.  First, the gain loop between pins 1 and 8 on a 386 can be used creatively.  The cap in that loop sets the low end response.  Usually you'll see 10uf indicated, but that's to preserve full bandwidth.  If you didn't want the bass, you could use 2.2uf or 1uf.  The same gain boost can still be achieved, but it will be applied to a more restricted segment of the spectrum.  As well, series caps in the signal path can also be reduced to limit low end.  The general idea is to stick in a 6db/octave rolloff here, another there, and yet another there, so as to achieve a combined 18db or 24db/octave rolloff.  Naturally, the desire is to coordinate these rolloffs so they all start about the same place, producing a stepp rolloff below a given frequency, but essentially flat respoonse above it.  Alternatively, what one does is use an active filter ahead of the power amp to limit low end.  This concentrates in one locus what might be otherwise distributed about.  Look for online articles about designing active crossovers for more info.  I suspect what you want is a highpass design aimed at carving up the spectrum into sub-bass vs everything else.  As a a great many chorus/delay pedals demonstrate, quite powerful 18db/octave highpass filters can be built up around a single transistor.

Given the range of guitar fundamentals, you probably don't want to aim too much lower than 150hz or so.  That may not seem like all that much restriction of bass at first glance, but if you use 20hz as a benchmark that's actually shaving off 3 octaves or so.[/b]

[NaBo]

Once again, Mark to the rescue with a wealth of info!  Thanks a bunch!

This info, with some of the other stuff I read on the site aron linked to, (not to mention that great frequency response thread that popped up recently) has led me to the conclusion that there's no way around it, some experimenting is in order.

Ultimately, the amount of bass I'll need to cut out will depend on how much volume I wanna get out of the horn (of course).  When this little-head-slash-talkbox was a practice amp, I'd always have to cut a touch of bass at higher volume on the clean channel.  So I guess I'll try setting the volume and adjusting my amp's EQ before permanently cutting bass at the horn.

Since the mini-cab I'd use it with is actually comprised of the speaker that was wired to it (and two smaller ones that I can switch out) I know I have nothing to worry about there... whatever's coming out of the amp is specifically designed to be fed directly into that speaker.

First things first though, I better get to building the new chassis and wiring in the additions

[aron]

I would start by rolling off lows and if necessary, then move on to the highs.

[Duff]

AAAAAAnnnnndd I´m Back!    Back in business and ready to make some DIY shit. First of all       :shock:  :shock:  WWHHOAAA!! That is certainly some explanation Mark, it sure has been a while since I´ve read one of theese, I´d ask you to speak spanish, but since I´m in an english website :lol: ,   please speak for the dumb ones like me, Ok I´m not dumb per say (first time I used that expression) but I have to really read some things that are written in theese websites.

So anyway, just baught me a brand new horn driver, it´s a 75w 16 ohm GBR, I don´t know if that brand is as known (good?) as I think it is, someone let me know, it seems ok, got a hose, no piping, and it´s too small, so I´m going shopping in a few days for all the stuff, I´ll try to buy a non cyanide hose. :lol:

NaBo, there´s a schem in generalguitargadgets that shows a 15uf 50v cap in series with the driver, I can´t say anything about the frequency or anything but I trust it  :? , also, when I went to buy it I couldn´t find a 15uf so I bought two 33´s to hook them in series, and silly me I forgot it had to be non polarized, does someone know about this, does it have to be NP? if it can be polar. which way? I think I read somewhere that you could put one one way and the other the other way round (that´s a strange set of words), I´ll check that website on crossovers.

Something else, I´m planning on using a small Kustom amp for the driver, it doesn´t say about the watts but I would gess 10??, I remember discussing this in an old post, the buyer told me the horn should be 99db, that should be ok to the amp,... I don´t really understand theese things, I mean, the amp (combo) with its tiny speaker gets saturated (the speaker) at max vol. because of the bass an all, and is unhearable with a band playing, but when I used it with a 10" Invader speaker (INVADER rules! ) the thing rocked, when I use my 25w Laney/10" Invader Combo it rocks, when I hooked it up to a smalish (15w? amp)´s speaker, ANY REASONABLE MIND WOULD THINK IT WOULD BLOW UP! well it doesn´t, it just sounds as if the amp was designed for that less power speaker,, AND WHEN I CONNECT IT TO A 15" SUPER HEAVY CONE, it knocks walls down!! (and no overheating involved).
So what is the deal with this intrincate amp-speaker relationship? Are all the things we´ve heard about blowing amps a lie? Or are the amps so intelligent to self adjust themselves to the needs of the speaker? in this case who´s the guy and who´s the girl? :lol:  just kiddin´ , I only hope it sounds good and as loud as I need.

Just two more things, I undesrtand the need of the cap because the horn is a hi freq device, but i´d really like to give it some bass to have a fuller sound, like I saw the other post about Weezer´s "Beverly Hills" talkbox, and I reaaly think its a weak and empty sound, I like much more Aerosmith´s "Sweet Emotion" or Alice in Chains´s "Man in a box", would it be solved by increasing the lows to the mike?, any suggestions? And NaBo, where are you from? Or rephrasing it, what does NaBo stand for?