Capacitor value for Horn tweeters in a bass speaker cab?

[ultradust]

Hello guys, I know this is kinda' off topic but I really need help about my DIY Bass Speaker Cabinet... THe design is plain and simple... A 300 watts 8 ohms 15 inches bass speaker and with a high-end 100 watts Horn tweeter driver. The problem is that I can't make the tweeter to sound as it's supposed to. Then I remembered that every tweeters needs a capacitor in series with the positive terminal in order to make it work.

My big problem is I don't have any idea what value of capacitor to use?

Any suggestions and help would be very much appreciated...


THanks,

Chad

[rockgardenlove]

I have a setup like this...but its upstairs, if you'd like I can check the capacitor value and post it tomorrow...I'm just going to bed.

[ultradust]

I have a setup like this...but its upstairs, if you'd like I can check the capacitor value and post it tomorrow...I'm just going to bed.

It's ok... Gonna wait for your post tomorrow... Thanks. 

[Gus]

you need to give much more information.   Piezo tweeter or coil drive.
15" to a small tweeter will be hard to match without a mess in the mids.  what type of sound do you want etc.........

[WGTP]

Depending on the tweeter, a single capacitor with a 6db/oct. roll off might not be enough protection.   

[RedHouse]

Try a .47uF 400v poly film cap

[ultradust]

you need to give much more information.   Piezo tweeter or coil drive.
15" to a small tweeter will be hard to match without a mess in the mids.  what type of sound do you want etc.........

A coil drive to be specific... I just wan't to make the cab sound a little bit flexible... Lotsa bottom with some nice treble boost.

[ultradust]

Try a .47uF 400v poly film cap

Would this give me the nice treble boost that I'm after? Well just asking, gonna try it out anyway...

Btw, Is there a range of capacitor values that I can experiment with?

[George Giblet]

I seriously doubt a single cap is good enough, you could blow your tweeter.  You will need at least a cap and an inductor.

Start with say 3.3uF (non polar)  and ~0.5mH (say less than 1 ohm DC resistance, 0.5ohm better).
The connection goes input, cap, other side of cap to speaker, inductor across speaker, other side of speaker and inductor to ground (and back to input ground)

Things to try:
- try reversing the polarity of the tweeter(don't mess with the woofer polarity).
- You could try a 4.7uF or 2.2uF cap.  Strictly you should change the inductor but it will cost you more to play around and these crossovers are rough anyway.
- use an attenuator on the tweeter to balance the level of the tweeeter and woofer - this is very important.


If you are going to be cranking the crap out of your amp I suggest puting a PTC protection device or a car incandescent bulb in series with the tweeter for protection.


Oh, for professional results there's a lot more to this than just chucking a crossover on a tweeter!!!

[ultradust]

I seriously doubt a single cap is good enough, you could blow your tweeter.  You will need at least a cap and an inductor.

Start with say 3.3uF (non polar)  and ~0.5mH (say less than 1 ohm DC resistance, 0.5ohm better).
The connection goes input, cap, other side of cap to speaker, inductor across speaker, other side of speaker and inductor to ground (and back to input ground)

Things to try:
- try reversing the polarity of the tweeter(don't mess with the woofer polarity).
- You could try a 4.7uF or 2.2uF cap.  Strictly you should change the inductor but it will cost you more to play around and these crossovers are rough anyway.
- use an attenuator on the tweeter to balance the level of the tweeeter and woofer - this is very important.


If you are going to be cranking the crap out of your amp I suggest puting a PTC protection device or a car incandescent bulb in series with the tweeter for protection.


Oh, for professional results there's a lot more to this than just chucking a crossover on a tweeter!!!

Would all these mods be done with the tweeter only and no changes with the woofer's circuit?

What's an attenuator? Is it the same as the Marshall Power brake PB100 or something small to fit inside the speaker cab?

[George Giblet]

There is no crossover connected to the woofer.

I had a closer look and came up with something a little better than the "recipe crossover" I gave before.   A good start would be a 3.3uF polyester cap, 330uH inductor with less than 0.5ohm resistance (a 20AWG wire 330uH inductor will be about 0.36ohm, which is fine).  I doubt you will need to change the values.  I'm not going to go through the details but the idea was to make life easy as possible for the tweeter.

The attenuator is a resistive divider placed between the crossover output and the speaker.

At the bottom of this page is a calculator and a schematic:
http://www.apicsllc.com/apics/Misc/filter2.html

To work out how many dB's attenuatoin you need you perform the calculation

tweeter sensitivity - woofer sensitivity

If the woofer is more sensitive than the tweeter, which is highly unlikely, you don't need an attenuator (and you might have to live with the tweeter being slightly down in level).

That assumes you know these parameters for the woofer and tweeter.  If not you have to work it out by ear.  I suggest starting with 6dB attenuation then knocking the level down in 3dB steps until it sounds right, then go  up or down 1.5dB on the last step.  If the tweeter sounds way loud perhaps drop in 6dB steps.  In the final design use say 10W wirewound resistors.  You can do your initial tests using cheap 1W resistors provided you don't crank the amp up too far.

An alternative to the attenuator is to buy an Lpad (with suitable power rating) which lets you dial-up the tweeter level - like the SWR cabinets have.  These can cost quite a bit.

http://colomar.com/Shavano/lpad.html

[RedHouse]

Try a .47uF 400v poly film cap

Would this give me the nice treble boost that I'm after? Well just asking, gonna try it out anyway...

Btw, Is there a range of capacitor values that I can experiment with?

Just try it, if you don't like it you could go bigger a was posted, but never mind "non polar" caps (which are electrolytic, you want poly-film here for this application. Never mind the inductor too, those are for Hi-Fi's

[George Giblet]

>. Never mind the inductor too, those are for Hi-Fi's

Wrong!  Low order crossovers like a single cap let a *lot* more power through to the tweeter.

Here's the problem with first order crossovers:  You can't use a low crossover point because that will blow the tweeter.   The only option is to increase the crossover frequency by using a small cap (some designs use 10kHz or so, a 470nF cap will put the crossover at 40kHz or so!).  The high crossover point means the tweeter doesn't take over the high frequencies smoothly you end-up with a band of frequencies missing between 4kHz and 10kHz.   You are boosting a lot of "junk" at 10kHz and above.   Even with the high crossover point the tweeter still see a lot of power.  You can sometimes get away with it if the tweeter is high efficiency and has to be attenuated down a lot - but that doesn't solve the missing frequency band.

High power applications generally use 2nd order (one cap + one inductor) crossovers because of power issues.   Very common is third order (two caps and inductor) - that's what SWR use.

[rockgardenlove]

I'm not quite learned enough on all this to join in on the technical jargon, but my cap is 8uF.

[Gus]

George Giblet posted some good stuff .

You realy should use an attenuator and > than first order high pass  like posted for the tweeter. 

What type of "sound" do you want? the mids reduced? highs that hurt your ears?.....

I do want to ask why a tweeter with a bass cab?   why do want to hear finger noise on the strings

A good 15 or 18 with a good amp and pre can sound very good with a sealed box of the right size

[RedHouse]

George, apples-n-oranges dude. I appreciate your attempt at schooling me in crossover design but you're barking up the wrong tree my friend. Having been building and testing crossovers (both passive and active) for nearly 30 years now, both back in the bad-ol-days and today.

I didn't jump into this thread to get into a pissing contest, but to un-complicate the issue ultradust brought up, some things you're posting are just making this very basic thing into a complex problem, but then maybe he's looking for a complex solution.

>Wrong!  Low order crossovers like a single cap let a *lot* more power through to the tweeter.

That's a pretty basic aspect of how crossovers work, in fact without exibiting that phenomina we wouldn't have a crossover!
(With any due respect the word Duh comes to mind)

As this thread is about a DIY Bass Cabinet we don't usually want (or care) about a flat band HiFi sound, Butterworth, Bessel, Cheb or +3db response or any of that stuff, it only clouds the very simple issue at hand and complicates life for someone who is just trying to add a tweeter to a DIY Bass Cabinet.

>You can sometimes get away with it if the tweeter is high efficiency and has to be attenuated down a lot - but that doesn't solve the missing frequency band.

Again, in this case a simple capacitor crossover should more than suffice and that is all I suggested, there is no real need for an inductor in this case but it wouldn't hurt. You can get some decent pre-made inductors a Parts Express ($15 or so).

I'd start with just the capacitor and see if it meets your need, if not then add more support components (Inductors, bump the order, add Zobel notch ...etc)

I'm not saying don't ...I'm saying it's not mandatory, trying to difuse the scare-verbiage of blowing the tweeter.

Oh, and there will be no "missing" frequencies, that's just a bit of BS.

In this case, there is quite likely no need for an attenuator, unless he want's some adjustability, again it's just complicating this very basic issue.

The lowest frequency we need to be concerned about is more or less set by the driver's resonant frequency, we must stay above that to keep the driver alive and so as not to experience "honking"

>The only option is to increase the crossover frequency by using a small cap (some designs use 10kHz or so, a 470nF cap will put the crossover at 40kHz or so!). 

A .47uF/400v cap will do quite nicely in this case and should bring him in about 3.5kHz which should be fine. I didn't really get that comment George but if you know anything about capacitors, you should know that .47uF Film cap is nearly an order of magnitude higher than the 3.3uF Electrolytic cap you suggested, in fact yours would work out to bring him in at around ~500Hz which would definately blow the tweeter.
(Not to mention Electrolytics sound worse than nearly any other type of cap)

>You are boosting a lot of "junk" at 10kHz and above

We're not boosting anything in passive networks such as these George, passive crossover networks suck energy from the source signal they don't boost.
(again one could argue transients can be percieved as boost I suppose)

>High power applications generally use 2nd order (one cap + one inductor) crossovers because of power issues.   Very common is third order (two caps and inductor)

Again George, apples-n-oranges, those two are for HiFi designs and not nessessary (but fully useable) in a bass guitar cabinet.



All that is needed here is a simple 6db/Oct 1st order filter formed by the driver and the capacitor.

Things would be different IMO if ultradust was asking about adding a midrange horn like the 'ol JBL's or something, then a 2nd or 3rd order crossover would be appropriate ...but even then I would go to an active crossover and stay away from tone-sucking 2nd/3rd order capacitor/inductor networks.


rockgardenlove, don't worry about the technical jargon, I understand it and it's meaningless in this particular application. Sometimes, with good intentions, people tend to severly over-complicate things, and sometimes in public forums it's just to flex their knowlege.

[George Giblet]

If anyone wants any clarifications send me a personal message.

[ultradust]

Btw, Redhouse has an interesting simplified yet very useful explanation on the subject and will be noting his idea on the subject while George has a nice ideas regarding a more flexible overall horn tweeter driver mods for a speaker cab. However all is well because both ideas were very useful; and it did gave me a better insight in my future Diy speaker cabs... Its the thought that counts and Thanks guys for the ideas.