How does a 40uf capacity protect a compression driver?

[RKLee]

I need some help here. What is the technical reasoning for using a (40uf) non-polarized capacitor from Charge Coupled Networks (http://www.audioheritage.org/vbulletin/showthread.php?t=43) Ian Mackenzie 4-23-2003, 02:59 AM


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I assume you are bi amping, so remember to use a hefty series non polarised capacitor to protect your compression drive(40uf)
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.Does the capacitor block out low freqency energy?

I have a bi-amp speakers, and I don't have this capacitor wired into my system.

How do I wire this into my driver? I will be trying to protect an Altec 806 and EV T350.

[Robh3606]

With the 4430/35 crossover it's not just a protection capacitor in this case. That capacitor is actually part of the crossover. It's one of the poles and you really need it to get the correct voltage drive to the compression driver. It's 2 40UF caps in series not just one if you go charge coupled.

In any biamp set-up it is good practice to have a capacitor in series to keep any DC from turn on thumps out of the compression drivers. If you look at the JBL 5234 and 5235 crossover manuals there are recommended values depending on your crossover frequency and impedance

Rob:)

[louped garouv]

altec also has this handy dandy chart in the TLs

[RKLee]

Robh3606: Thanks that was the explanation that I needed.


altec also has this handy dandy chart in the TLsThis is exactly what I needed. So I would just wire the capacitor in series with one of the speakers leads?

I will be using the crossover points of 800Hz for my Altec 12" 414s to Altec 806/811 compression driver/horn, and 7KHz for the 806/811 to EV T350.

[louped garouv]

I believe it is supposed to go on the red side....

but maybe wait for confirmation ;)

[RKLee]

?

[SMKSoundPro]

Dear All,

Thank you VERY MUCH for this refresher course thread!!!

I have many things bi or triamped here, and this protective cap thing may have gotten missed on some compression drivers!!!

As always, some of you are a font of information!

Thank you again.

Scott.

[yggdrasil]

The capacitor can go on any lead.

And yes - It is (almost allways) drawn in series with the positive lead.

[RKLee]

altec also has this handy dandy chart in the TLsAltec should've include this little chart in their publication Al-6030-1 LOUDSPEAKER ENCLOSURES: Their Design and Use (http://www.lansingheritage.org/html/altec/plans/1974-enc-manual.htm). This publication was my bible when I built my Altec 12" 414, 806/811, EV T350 20 years ago. I would've included it as part of my project.

[Thom]

In series is in series it doesn't matter where you put it any more than it matters where you put the switch for your room lights. I guess whether you really should have known that depends on what kind of work you do how "techie" you try to get etc. As far as having bi-amped and tri-amped without it, it's done all the time. You only need it if something goes wrong. Boy do you need it if something goes wrong.

[subwoof]

The size of the capacitor needs to be large enough to be " not in play " at the crossover frequency. The formula for this is posted in jbl's technotes and elsewhere and interestingly this is less of an issue than it was back in the old days.

Any newer design amplifier that has a delayed turn-on relay or similar DC protection circuit should prevent any DC ( or AC below 10hz ) from reaching the diaphram during startup and operation.

One of the BIGGEST issues that is not often discussed is when the amplifiers AC mains voltage drops considerably when the system is driven hard or is supplied from a poor source. This is rarely a problem with a home system but is a MAJOR factor of transducer failure on portable systems big and small due to the long distanced the power is sometimes connected to.

Think of it this way. You are a tiny rowboat paddling away on the ocean. A very large wave can go under you and while you rise and fall with it, it does not affect your rowing ability. If you looked at this in mathmetical terms, the paddling is fairly fast repetiton ( high frequency ) but the large wave is a very low frequency.

It's the lows that KILL the diaphrams and this is what you need to keep away from them. Like those stupid commercials on tv and in the MTV videos - if you can see the woofer flop it is a PROBLEM because you cannot *see* movement above 40hz or so.

The florescent lights in your office turn on and off 60 times a second! Do you notice?? And when you DO see them flickering it's because one side of a long bulb has a burnt filament and it is now turning off at 1/2 of that....30Hz...!

Think about it....it's basic physics.

sub

[RKLee]

In series is in series it doesn't matter where you put it any more than it matters where you put the switch for your room lights. I guess whether you really should have known that depends on what kind of work you do how "techie" you try to get etc. As far as having bi-amped and tri-amped without it, it's done all the time. You only need it if something goes wrong. Boy do you need it if something goes wrong.My 414s, 806/811, EVT350 are tri-amped. I assembled a 200W Tigersarus Power Amp kit from Southwest Tech Prods. Corp(SWTP) they were really know for their computers than amps, Ft Worth TX; and one failed. There was smoke all over my parent's living room(it took a few hours for the acrid smell of burnt circuit board to disspate at my parent's house), and it wiped out the my dual 414s. I had to have them reconed because it litterally ripped the voice coil right off the form. I reconed them with real Altec cones at $40 each in 1978. Last of the big spenders. At that time it was a princely sum because the woofers were $80 each. I had .25amp fast blow automotive fuses in series with the woofers, but they just weren't fast enough. $10 for some capacitors is good cheap insurance to protect $100+ diaphrams.