2445 condenser

[GCT]

HI
Just got my 2445's and I'm using an electronic crossover at 600-1000Hz. A quick listen 600 sounds sweet to me.

Is it standard practice to use a condenser tuned to 500Hz to protect against misuse? This is for PA use and controls could get moved and buttons pushed by accident. Do JBL cabs always have a condenser in series even when BI-amping or does the switch remove this?

Cheers

GCT

[Lee in Montreal]

I would use a condenser, but at a much lower frequency and only to cut DC. I am thinking doing it too on my 2445 and 2405, and most likely cutting at 100Hz, well below the drivers' range.

When I had my Kef 105-2, there were two generations of crossovers. One with 480µF of caps and one with 900µF to protect the woofer, midrange and tweeter from DC. That capacitor was well away from the sound spectrum. Remember it is only to cut DC, not to protect drivers from bad operators...

51748
51749

[Eaulive]

HI
Just got my 2445's and I'm using an electronic crossover at 600-1000Hz. A quick listen 600 sounds sweet to me.

Is it standard practice to use a condenser tuned to 500Hz to protect against misuse? This is for PA use and controls could get moved and buttons pushed by accident. Do JBL cabs always have a condenser in series even when BI-amping or does the switch remove this?

Cheers

GCT

I always put a capacitor in series with the compression drivers.
You can not "tune" a capacitor since it's not a resonant device, it will give you a smooth rolloff and can not be used as a crossover.

A 100µF will have a 2.65 ohms reactance at 600 Hz, to give you a example.

In my setup I have 2425Js crossed at 1500Hz and a 47µF in series. This gives me a 2.25 ohms reactance at cutoff.

http://www.sengpielaudio.com/calculator-RC.htm

[GCT]

A 100µF will have a 2.65 ohms reactance at 600 Hz, to give you a example.
In my setup I have 2425Js crossed at 1500Hz and a 47µF in series. This gives me a 2.25 ohms reactance at cutoff.


I don't want a crossover, I want protection, so I was thinking a 40mF cap should protect aganst DC and give a 12dB/Oct rolloff below 500Hz should anyone connect the horn wrongly - probably me. In the event of wanting to cross over low, it will be with a 24dB/Oct LR type, so I could lift the crossover to higher than 500Hz and all's well.

Or no?

GCT

[GCT]

Remember it is only to cut DC, not to protect drivers from bad operators..

Mmm... I think I need protection from the latter more than the former, hence I'm thinking 40mF.

GCT

[Lee in Montreal]

Mmm... I think I need protection from the latter more than the former, hence I'm thinking 40mF.

GCT

The only ways to protect your drivers from a bad operator are twofold.

1. Lock the active crossovers (all digital crossovers can be protected). Or put the analog crossovers behind a locked panel.
2. Use fixed passive crossovers.

There's nothing you can really do against an operator who decides to tweak the system.

Also, you may still need to protect each driver from DC anyway. Power amps that are used to their limit will induce DC which will destroy your drivers. Amps that don't have a protection circuit may also send DC on start-up.

[Eaulive]

I was thinking a 40mF cap should protect aganst DC and give a 12dB/Oct rolloff

You were thinking wrong, a single cap in series will give you 6dB/ oct rolloff.

http://www.electronics-tutorials.ws/filter/filter_2.html

[GCT]

Right, so 6dB/oct is not much protection. And yes I was thinking of hiding the crossover knobs behind a panel.

Thanks for the info. Will digest over the next few days.

Cheers

GCT

[louped garouv]

......


Thanks for the info. Will digest over the next few days.

Cheers

GCT

here's another thread with some more info/links that may be useful...

http://www.audioheritage.org/vbulletin/showthread.php?30388-HF-protection-capacitor-compensation-in-active-setup

:)

[boputnam]

You were thinking wrong, a single cap in series will give you 6dB/ oct rolloff.

http://www.electronics-tutorials.ws/filter/filter_2.html


This is a great post. I think I'll preserve the Link in the Technical References section, under General Audio Discussion. The question of the phase impact of filters comes up again, and again...

[penngray]

Right, so 6dB/oct is not much protection. And yes I was thinking of hiding the crossover knobs behind a panel.

Thanks for the info. Will digest over the next few days.

Cheers

GCT

Why would you say 6dB/oct is not much protection? It will still save the CD from a low frequency signal (ie.DC thump!!)


I have always used single large Caps for 6dB/octave protection with ALL my CDs when testing (I have 15 different CDs sitting around).

I do have to ask about your post the word "condenser", Im curious about that definition instead of just saying "Compression driver" ??

[speakerdave]

Your protection capacitor should be targeted at a frequency an octave or more below the crossover frequency. I think 100 Hz is too low. Its capacitance should be based on the load impedance of the driver. You can find charts for this in various places including the manuals for the UREI crossovers. I'm using 40uf for my nominally 16 ohm drivers crossed at 700Hz.

[Allanvh5150]

Your protection capacitor should be targeted at a frequency an octave or more below the crossover frequency. I think 100 Hz is too low. Its capacitance should be based on the load impedance of the driver. You can find charts for this in various places including the manuals for the UREI crossovers. I'm using 40uf for my nominally 16 ohm drivers crossed at 700Hz.

For DC protection, as long as the cap is under the response curve of the crossover, ot will be fine. The cap will block DC no matter what the size and in general, anything above 40 or 50 uf will be fine. Some crossovers even use a lamp to soak up excess power.

Allan.

[Earl K]

This is a great post. I think I'll preserve the Link in the Technical References section, under General Audio Discussion. The question of the phase impact of filters comes up again, and again...

http://www.audioheritage.org/photopost/data//500/fil10_.PNG

And there's the meat of the matter ( nicely illustrating the truth and now bringing me to a pet peeve of mine ) .

All across the internet, I see this as an ever pervasive misconception ;
- ( ie Too many incorrectly assume that the most siginificant phase changes, happen within the Pass Band / when in truth, the total phase rotation is fully realized ,,, out there in the "Stop Band" . )

Eaulive,,, That's a nice website for reference ,,, Thanks !

<> EarlK

[Earl K]

I do have to ask about your post the word "condenser", Im curious about that definition instead of just saying "Compression driver" ??

Condenser is an archaic word ( by North American standards ) for the simple Capacitor .

Obviously, it's a word that still has meaning to some / I'm pretty sure that my old Land-Rover shop manuals, used the word .

<. EarlK

[hjames]

Condenser is an archaic word ( by North American standards ) for the simple Capacitor .

Obviously, it's a word that still has meaning to some / I'm pretty sure that my old Land-Rover shop manuals, used the word .

<. EarlK

Yep my first TC-100 Triumph (500cc twin) manual talked about the condenser , and the Zener too!
Back in the days of KC and valves ... sending signals out into the Aether ... :D

[1audiohack]

It is kind of a funny term but it sort of makes sense as a devise description for what it does in an ignition system as an arc suppressor.

[Allanvh5150]

according to the pic, 45 degrees of phase change happens in the pass band....

[Allanvh5150]

The term condenser is still used in the auto field and in the audio field. Ever heard of a "condenser microphone"?

[penngray]

Condenser is an archaic word ( by North American standards ) for the simple Capacitor .

Obviously, it's a word that still has meaning to some / I'm pretty sure that my old Land-Rover shop manuals, used the word .

<. EarlK


Thanks, the title makes sense to me now. :D

I did understand the discussion was about Capacitor but the title had me confused.

[maxwedge]

Condenser is an archaic word ( by North American standards ) for the simple Capacitor .

Obviously, it's a word that still has meaning to some / I'm pretty sure that my old Land-Rover shop manuals, used the word .

<. EarlK

Thanks, the title makes sense to me now. :D

I did understand the discussion was about Capacitor but the title had me confused.

Condenser is a term that is still used though out the automotive world, including all the major auto manufacturers.

[penngray]

Condenser is a term that is still used though out the automotive world, including all the major auto manufacturers.

This is audio though. There is not a XO desgn book, XO online discussion I have been involved with over the years that used the term condenser. Hence my question/confusion.

You are not putting a condenser in series on the tweeter you are buying and placing a capacitor in series on the tweeter to protect it from DC (ribbons and compression drivers need it!!). Proper definitions make it easier to have discussions.

[Lee in Montreal]

In fact, I have always been puzzled by the use of "capacitor" in the anglo-saxon language. The French denomination is "condensateur" and the Hispanic one is "condensador", wether you are talking about this small piece of electronics used in audio, in cars or the secondary radiator core for the air conditioning. :D

[maxwedge]

This is audio though. There is not a XO desgn book, XO online discussion I have been involved with over the years that used the term condenser. Hence my question/confusion.

You are not putting a condenser in series on the tweeter you are buying and placing a capacitor in series on the tweeter to protect it from DC (ribbons and compression drivers need it!!). Proper definitions make it easier to have discussions.
Well yah duh.;)

What I said is fact and it's also fact that condensers and capacitors are one and the same.

[Allanvh5150]

Well yah duh.;)

What I said is fact and it's also fact that condensers and capacitors are one and the same.

Ah yes grasshopper, but sometimes fact is replaced by point of view.

I am not sure the auto industry will change their terminology and I am pretty sure the music industry will be asking for capacitor mics in the very near future.

Allan.

[maxwedge]

Ah yes grasshopper, but sometimes fact is replaced by point of view.
I think that the OP got what he needs, I was just stating some info.


I am not sure the auto industry will change their terminology and I am pretty sure the music industry will be asking for capacitor mics in the very near future.

Allan.
:D

Scott

[Mike Caldwell]

In some "condenser" microphone descriptions the mic is referred to as a "capacitor" microphone.
As for DC blocking/protection in my systems 8 ohm drivers they get a 30uf cap, that puts them a little more than an octave below the crossover frequency.

[GCT]

Hey , I see you've been having fun with my old English/Spanish terminology!

Glad I put my caps in the horns as the first time out they had the wrong buttons pushed on the xover so the horns got 120-20k and survived a whole rock set. The 2445s are pretty robust. We can try them as subs next time lol
Thanks for all your help
GCT

[Allanvh5150]

Lucky then you had the extra caps in there!!!!

Allan.

[Lee in Montreal]

On page #8 of the JBL 5324a operation manual, there's a list of the various condenser values to use to protect against DC. Values depending on crossover frequency and driver's impedance.

http://www.google.ca/url?sa=t&source=web&cd=1&sqi=2&ved=0CBoQFjAA&url=http%3A%2F%2Fwww.jblproservice.com%2Fpdf%2FVin tage%2520JBL-UREI%2520Electronics%2FJBL-5234A%2520manual.pdf&rct=j&q=jbl%205234a&ei=ltw_TqyRN4i30AH_7e3lBA&usg=AFQjCNFvKw1lpNIspNholAwkncltoVgXyQ&cad=rja

[GCT]

Yeah, I actually did use 2 electolytics in series to make a bipolar, as I had them.

Cheers
GCT

[GCT]

Thanks for the actual JBL cap values -1 octave below electronic crossover.