• WANTED: Happy members who like to discuss audio and other topics related to our interest. Desire to learn and share knowledge of science required. There are many reviews of audio hardware and expert members to help answer your questions. Click here to have your audio equipment measured for free!

Active Crossover Tweeter Protection

YSDR

Active Member
Joined
Sep 5, 2019
Messages
273
Likes
287
Alternatively you can use the protection capacitors as part of the total filtering. This way, the prot cap can be much smaller.
For example, instead of 47uF, you can use a 4.7uF cap. Just measure the driver response with the cap in place, then flatten this response at least 1 octave past xover point at the low-end (and as much as possible up top if you wants a flat response), then apply your desired xo slope. Done.
 
Last edited:
OP
G

gabo4au

Member
Joined
Apr 18, 2022
Messages
57
Likes
52
There are two issues here.
Firstly, protecting tweeters against overload. That is by far best done by limiters in the DSP crossover. I've set mine to around 40 watts which is similar to what B&W used for their APOC protection with the same tweeters. Fast-acting iimiters cause no additional distortion, and don't allow clipping.


Secondly, there's protecting the tweeters against an amplifier fault that could put 50v or more DC on the tweeters, and that's most easily done with a series capacitor sized so it doesn't affect the crossover point. I used 47uF for the tweeters, and 250uF for the midrange, if I remember correctly.

S

That's probably a good approach. Amp faults, at least with old school amps like I have, tend to fault DC to the speakers and the rest typically comes from upstream of the DSP. I'm not sure how class D amps fail, probably the same as the MOSFETs are still switching the DC supply to create the PWM output.
 

restorer-john

Grand Contributor
Joined
Mar 1, 2018
Messages
12,579
Likes
38,274
Location
Gold Coast, Queensland, Australia
In real terms, tweeters in active systems should be protected by voltage monitoring to ensure they are not overdriven or destroyed during amplifier failure events, transient noise events or being fed frequencies and power levels their tiny voice coils cannot absorb.

The revelator tweeter has just 0.3gram of moving mass. That is the diaphragm and the voice coil. There is no way on earth, more than ~5-10 watts could be continuously dissipated by such a VC- if that. The 160W rating is system, not tweeter. Such a number is utter fantasy for a tweeter.

1651546074635.png
 
Last edited:

sergeauckland

Major Contributor
Forum Donor
Joined
Mar 16, 2016
Messages
3,440
Likes
9,100
Location
Suffolk UK
Are you using film or electrolytic? A film 250 uF cap costs way more my midrange drivers.
Non polar electrolytic. I don't see any value in anything else considering there's no significant voltage across the capacitor as it's not acting as a crossover component, just for DC protection.

S
 

richjoh

New Member
Joined
Mar 10, 2023
Messages
2
Likes
0
Active crossovers or dsp can't protect tweeters. You need an inline electrolytic capacitor (50uf to 200uf say), a value below crossover to protect from LF excursion damage and amp turn on surge. An incandescent bulb type 511 or 211-2 automotive for 1" tweeter. For compression drivers 1 3/4" or 2" a 1156 automotive bulb works. Thanks to DJK, I came across this thread on diyaudio years ago. I installed bulbs on all my DJ DIY speakers and its always prevented blown out bullet tweeter from there on.
 

valerianf

Addicted to Fun and Learning
Joined
Dec 15, 2019
Messages
691
Likes
442
Location
Los Angeles
I never got a damaged tweeter.
But I fully understand that you want to protect it as it is an expensive unit.
First you have to verify that the tweeter has a very high quality and high voltage capacitor placed in serie.
This capacitor is the first level protection.
If the capacitor fails, then the tweeter will be dead as it will not survive to DC.

Second level of protection could be what was used by Bose 20 or 30 years ago: you just add a Polyfuse (re-armable fuse) in serie before the capacitor.
 

richjoh

New Member
Joined
Mar 10, 2023
Messages
2
Likes
0
A polyfuse will cut sound and remain off until high power signal is removed and polyfuse cooled down. Incandescent bulb give instant protection from high power peaks while keeping the music playing. The bulb goes momentarily high impedance on musical peaks glowing while providing sound output with no dropout of sound.
 

fineMen

Major Contributor
Joined
Oct 31, 2021
Messages
1,504
Likes
679
In addition your tweeters look quite robust ...
Hope dies last ...

- if there is a level matching necessary, do it passive with resistors
- use a *smaller* capacitor and egalize the loss with the active crossover; because all these filters are 'minimum phase' all properties are the very same once the frequency amplitude response is the same, frequency response implicates phase response

In short, exploit the headroom the power amp offers.

Best move, though, avoid such costly delicate devices. Diminishing returns ...
 

Sokel

Master Contributor
Joined
Sep 8, 2021
Messages
5,836
Likes
5,762
Hope dies last ...

- if there is a level matching necessary, do it passive with resistors
- use a *smaller* capacitor and egalize the loss with the active crossover; because all these filters are 'minimum phase' all properties are the very same once the frequency amplitude response is the same, frequency response implicates phase response

In short, exploit the headroom the power amp offers.

Best move, though, avoid such costly delicate devices. Diminishing returns ...
Resistor,cap...
Then he will only be an inductor away from an ordinary passive crossover :)

(the paranoid me has demanded my installers that mid and tweeters has passive crossovers,power is cheap these days after all)
 

fineMen

Major Contributor
Joined
Oct 31, 2021
Messages
1,504
Likes
679
Resistor,cap...
Then he will only be an inductor away from an ordinary passive crossover :)

(the paranoid me has demanded my installers that mid and tweeters has passive crossovers,power is cheap these days after all)
Sure. The tweeter may be considered to be a second order filter in itself, having its inherent resonance frequency and Q. I myself use a) digital + b) analog signal level+ c) passive on power level + d) enclosure esp. for midrange ... the complexity doesn't bother me,
 
Top Bottom