Driver protection?

[X_X]

When running an active crossover- It has been suggested that I place a cap on the terminals of the drivers for protection. I understand the need for this but I do not understand how to calculate the values. Is there a formula?

[rs237]

The Cap for the Driver is a first Order Network. The Crossover Point should be appropriate for at least 1 Oktave (half frequency) below that the active Crossover.

Example :

Aktive Crossover 1100Hz
Cab for Crossover 550Hz

here you find a pasive Crossover Calculator

http://ccs.exl.info/calc_cr.html#first

only the Higpass its interest

for 8 Ohm Driver at 550Hz = 32µF

i hope you understand my bad english

regards

juergen

[louped garouv]

http://www.audioheritage.org/vbulletin/showpost.php?p=169444&postcount=3


:)


does a cap inline flip the phase or have any other effects?

[rs237]

http://www.audioheritage.org/vbulletin/showpost.php?p=169444&postcount=3


:)


does a cap inline flip the phase or have any other effects?




"does a cap inline flip the phase" yes

"have any other effects"

have you an ideal Cap ? then no
have you an real Cap ? then yes

use good Caps as in Crossovers with bypass Cap etc.


regards juergen

[Earl K]

does a cap inline flip the phase or have any other effects?


"does a cap inline flip the phase" yes

- Juergens' answer is ambiguous and begs for some clarification .

So;

- The reason for setting the F3 point of an inline DC-Blocking cap at least 1.5 octaves below the Actives' F3 point / is to minimize adding in the phase change caused by the cap .

- Simplistically speaking, the phase changes happen down in the stop-band ( below the crossover point ) not in the signals pass-band ( above the crossover point ). They ( phase rotations ) do reach a little above the F3 point but they are generally gone when one is well into the signals' pass-band ( something like 1.5 octaves above ) .


:)

[rs237]

Hello Earl,

thanks for the detailed explanation. Unfortunately my English for it was not sufficient.

regards

juergen

[Allanvh5150]

Hi,

I have built electronic crossovers for years. The cap you talk of is usually always built into the crossover out put. It is quite large so to pass all frequencies except DC. Its job is to protecr the input of your amplifier from DC, which of course is not your beloved speaker's best freind. you shouldn't need additional protection in your speakers but it is worth protecting expensive horns and tweeters. The caps will add a phase difference of course. Hope this helps.

Allan.:)

[Zilch]

When running an active crossover- It has been suggested that I place a cap on the terminals of the drivers for protection.Just to be sure nobody misunderstands this, the cap goes in series with the driver, not across it.... :yes:

[Baron030]

In addition to a series capacitor, I would also recommend adding a damping resistor across the driver’s voice coil. In a way, a series capacitor acts like a series resistor. So, it decouples the driver's voice coil from the amplifier's output. And as a result, any resonant peaks in the driver’s impedance will also impact the driver’s frequency response. Here is a link to a site that explains the impact that resonant impedance peaks has on a driver's frequency response, in a way far better then I ever could:

http://sound.westhost.com/lr-passive.htm

In my own system, I found that adding a 40 ohm resistor across the voice coil of my 2446h drivers made a very noticeable improvement. The 2446h/2382a combination has a very large resonant peak at around 700Hz and while I have my Ashley set at 1200Hz. The resonant peak was quite noticeable without the damping resistor. For drivers that do not have any resonant impedance peaks, a damping resistor is very much optional. I found that adding a 40 ohm resistor across my 2405s had very little impact in how they sounded. That is because the 2405 does not have any large resonant impedance peaks.

If you are going to add a damping resistor, remember that it is going to lower the impendence that the series capacitor sees within the circuit. So, the lowered impedance must be taken into account when calculating and selecting a protection capacitor value.

And I can also recommend "Charge Coupling" (A.K.A. Bypassed and Biased capacitors) for speaker protection circuits as well. :thmbsup:

Baron030 :)

[X_X]

Hi,

I have built electronic crossovers for years. The cap you talk of is usually always built into the crossover out put. It is quite large so to pass all frequencies except DC. Its job is to protecr the input of your amplifier from DC, which of course is not your beloved speaker's best freind. you shouldn't need additional protection in your speakers but it is worth protecting expensive horns and tweeters. The caps will add a phase difference of course. Hope this helps.

Allan.:)


This answer had me re-reading the manual and it turns out my active crossover does indeed have a good measure of built-in protection. Thank you! I can even program notch filters. This is going to be fun. :)

I still want to understand these aspects of passive protection.

Is the "half-freq/1st order" calculations rs237 suggested protecting the driver from DC "thumps" or excessive volume levels...or both?

And what about the junk the amp itself can spew out? I have a 2a3 based amp that puts out a notorious 120Hz filament hum (I need to alter the AC/DC filament feed). If I run that amp on my tweeters- I fear the 120Hz noise could damage them when connected direct and driven loud. How do I filter out that particular freq region using a passive component?

[louped garouv]

And what about the junk the amp itself can spew out?

as i understood it, that was the purpose of the cap paralleled inline between the amp and the driver, no?

[rs237]

This answer had me re-reading the manual and it turns out my active crossover does indeed have a good measure of built-in protection. Thank you! I can even program notch filters. This is going to be fun. :)

I still want to understand these aspects of passive protection.

Is the "half-freq/1st order" calculations rs237 suggested protecting the driver from DC "thumps" or excessive volume levels...or both?

And what about the junk the amp itself can spew out? I have a 2a3 based amp that puts out a notorious 120Hz filament hum (I need to alter the AC/DC filament feed). If I run that amp on my tweeters- I fear the 120Hz noise could damage them when connected direct and driven loud. How do I filter out that particular freq region using a passive component?

You say :
"active crossover does indeed have a good measure of built-in protection"
That does not help in the case of an error in the Amp
The Cap is only for DC Protection, not for excessive Levels.
With a Tubeamp you could do without DC Protection. The Tubeamp has a transformer in the exit. That is also DC Protection . You must absolutely eliminate the filament hum. The Protection Cap reduced also this however it always disturbs.



as i understood it, that was the purpose of the cap paralleled inline between the amp and the driver, no?

here a schema :