• TalkBass has been independent since 1998. Add your voice.
    Create a free account to reply to discussions, view embedded media, and browse with fewer display ads.
    Join free Log in
    Want zero display ads or expanded classifieds tools? Compare plans.

capacitor selection for tweeter

S

squawker

Apr 25, 2007
5
0
#1
I’m trying to install a tweeter in a bass amp speaker cab but I’m having a little trouble in selecting a value for the capacitor. I have an 8 ohm tweeter with a recommended crossover point of 2.5KHz. Calculating that value is easy enough – 8uF. The odd part that goofed me up is that I have a brand new amp (same brand) that works fine, already equipped with a tweeter that I planned to copy but the value it has makes no sense – a 4 ohm tweeter with a 1uF capacitor which comes out to be almost 40KHz.
How does this work? Also, do bass cabs with tweeters typically cover the full range or is there a large gap in the mid range?

Mark
 
#3
Here's a capacitor calculator: (bottom of page)

Invalid Link Removed

For me, a 6.2uF or so should do the trick for full range but the existing design is what has me so puzzled. I guess I'll experiment with reality to determine what is needed.

Mark
 
#4
Using only a capacitor is a recipe for a blown tweeter. Even in hi-fi use the minimum slope required for even moderate protection of a tweeter is 12dB (2nd order), while for professional use 18dB (3rd order) and 24dB (4th order) slopes are preferred. Read about crossovers and how they work here:
http://www.lalena.com/Audio/FAQ/XOver/

Also, do bass cabs with tweeters typically cover the full range or is there a large gap in the mid range?
Click to expand...
There is a large gap. Even though many woofers have axial response good to 3kHz or so their off-axis response is pretty much non-existent above 2kHz at best.
 
#5
I certainly agree with the possibilty of blowing the tweeter.
The reason I ask about the gap in the mid range is because the drivers I have a capable of covering the whole range but the designers chose a very high crossover point which leaves the mid range out. I was thinking that maybe bass amps sounded better this way - I didn't know if there was a common practice with this or it was just my amp.
Mark
 
#6
squawker said:
I certainly agree with the possibilty of blowing the tweeter.
The reason I ask about the gap in the mid range is because the drivers I have a capable of covering the whole range but the designers chose a very high crossover point which leaves the mid range out. I was thinking that maybe bass amps sounded better this way - I didn't know if there was a common practice with this or it was just my amp.
Mark
Click to expand...
Doing as they did, with a ludicrously high filter frequency, allows the use of a 1st order filter without blowing the tweeter. That is an economic decision, not an engineering one. Multiply the ten bucks thus saved per cab by the number of cabs sold per year and that makes a tidy sum.
 
#7
Just a question for you; why not forget the tweeter and install a midrange speaker such as a 4-6" with a crossover at something around 1500hz and a lot more power handling so it doesn't burn out like a tweeter might. Bass cabs don't really need anything higher than around 5khz response anyway.


These are only $10, for example:
[Invalid or Expired Link Removed]

Usable response from 500Hz up to 5,000Hz with 50 watt power handling, 4 ohm, 94dB. I use these in two of my cabs and they sound great without a tweeter, but of course there's no shortage of good inexpensive mids available.
 
#8
Those are great web sites! Thank you! A mid range is a good idea. Its my fault for not fully explaining what I have. I was thinking it but I never typed it out - I have a woofer with an upper limit of 3K and the tweeter I have is 2k - 16k, 60 watt, 8 ohm. I guess I'm actually aiming for the midrange with the 6.2uF cap I mentioned previously. That would put me at about 3.2k or a 6.8uF at about 3k. If there's not much above 5k, I would guess there's not a lot of energy for the tweeter to burnout?

Mark
 
#9
squawker said:
If there's not much above 5k, I would guess there's not a lot of energy for the tweeter to burnout?

Mark
Click to expand...

The energy that kills tweeters is that from below the crossover frequency which an inadequate crossover slope allows to come through.
I have a woofer with an upper limit of 3K
Click to expand...
Axial response, maybe. But it's off-axis response that counts.
 
#10
If you don't mind guys,i want to jump in with a simular qeustion.
My 12Lf and La6 will come soon, but have to crossover the mid driver.
Is it possible to make a ''one way'' second order filter with just one cap and a coil?
I know a cap allone will not work for a cutoff of 800Hz.

Tanx
 
#12
eu
qts said:
If you don't mind guys,i want to jump in with a similar question.
My 12Lf and La6 will come soon, but have to crossover the mid driver.
Is it possible to make a ''one way'' second order filter with just one cap and a coil?
I know a cap alone will not work for a cutoff of 800Hz.
Click to expand...

Sure, you can make a 2nd order high pass filter at 800 Hz. Don't forget to phase reverse the wiring to the top driver. I built a 4th order one for my B&C 6.5" midrange, but found that I preferred just one cap for high pass, plus one inductor to low pass the woofer (Kappalite 3012LF in my case). However, I have no experience with the LA6, so this may be less than germane.
 
#13
Orange County Speaker has a canned 400 watt 2K, 12db /octave x-over at $25. that combined with an attenuator looks like a pretty decent way to go.

(Ken Baker pointed me towards that one in another discussion this morning. I'll getone on order when they open up down there...)

I find that in my rig the 1.5 to 3K area is critical in reducing string and fret noise. Maybe this is a reason that some speaker manufacturer's move the cross over point up to 4K. That gap between the upper end of the woofer's response and the horn/tweet/mid driver might be a good thing ...
 
#14
4Mal said:
I find that in my rig the 1.5 to 3K area is critical in reducing string and fret noise. Maybe this is a reason that some speaker manufacturer's move the cross over point up to 4K. That gap between the upper end of the woofer's response and the horn/tweet/mid driver might be a good thing ...
Click to expand...

I myself prefer to get that with EQ if I want it - or just technique and string choice.

Anyway, it's more likely the crossover point is chosen higher because shallow low-order slopes mean that you need to move it higher to keep those typical Fosterx tweeter horns from blowing.
 
#15
4Mal said:
I find that in my rig the 1.5 to 3K area is critical in reducing string and fret noise. Maybe this is a reason that some speaker manufacturer's move the cross over point up to 4K. That gap between the upper end of the woofer's response and the horn/tweet/mid driver might be a good thing ...
Click to expand...
The crossover is pretty much determined by the tweeter. Few are capable of going lower than 3.5-4kHz unless protected with 3rd order or higher filtering, which is more expensive than lower order filters, and that's by and large the reason why high order filters aren't used. Midranges aren't generally used for pretty much the same reason, both the drivers and crossovers are more expensive than tweeters.
Don't forget to phase reverse the wiring to the top driver.
Click to expand...
Only with a full crossover, and then only if the low pass to the woofer is also second order. Phase shift is 45 degrees per element, so a 2nd/2nd crossover will result in a total of 180 degrees of phase shift and the HF element must be wired with reverse polarity. With a 2nd order HP only total shift is 90 degrees, so the HF polarity is not reversed.
 
#16
I did a search on google, and found a diagram from a filter with a ''cap and a coil in serial'', this was connected on the + of the middriver [ the tweeter had only a cap ]

Winisd filter calculator has the ''coil parallel'' over the middriver, and the ''cap in serial''

Wich one is the real filter??????
 
#17
qts said:
I did a search on google, and found a diagram from a filter with a ''cap and a coil in serial'', this was connected on the + of the middriver [ the tweeter had only a cap ]

Winisd filter calculator has the ''coil parallel'' over the middriver, and the ''cap in serial''

Which one is the real filter??????
Click to expand...

The first one is a full 1st order crossover, the second one is a 2nd order high pass filter.
 
#20
qts said:
Thanx Passinwind, now i realize whats confusing me all the time; it's the difference between '' crossover and filter''
Here in Holland we call it ''a filter'' coffee filter, gas filter, air filter.
So, which one should i use????
Click to expand...

Lots of peoplel call a high pass filter a "crossover", so your confusion in quite understandable.:cool:

As Bill pointed out, the first one is a bandpass, it rolls off both lows and highs on the midrange driver. So, are you going to use a tweeter as well, or just the LA6? You most likely wouldn't want to roll off highs if that LA6 is acting as your tweeter. The more likely question is whether or not you want to roll off highs on that woofer? I have some cabs where I do that, and some where I preferred not to.
 

Latest posts

Top Bottom
Back