Protection cap for my precious new compression drivers?

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TNT

TNT

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This is mostly self-invented facts that are not correct.

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JMFahey said:
Fact is you do :cool:
DSP is a digital way of *emulating* what a physical crossover does, Math comes from decades old Physics and Math, only done by software and processing, so be certain it IS emulating what capacitors do.
In fact it´s emulating ALL components in a passive crossover to get same frequency response (which is what you want it to do), including inductors, attenuators, etc., so you´ll "have as many (virtual) capacitors in the path as the design calls for"
Only special advantage is that you can simulate "perfect" components, such as zero ESR capacitors, zero resistance inductors, etc.
But slope,phase shift, etc. , will be same as in the original crossover you are emulating/simulating.

So what?

Drivers in principle expect some kind of crossover and are designed with that in mind.

Just imagine a third order (passive) crossover and what all those components do to amp damping :eek:

So if a driver is competently designed, it will stand anything between amp and voice coil, including attenuating resistors, very common in crossovers, and a humble cap must be well within acceptable prameters.
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weltersys

weltersys

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mpa said:
I've built dozens of actively driven speakers with compression drivers over the years and have never installed a protection cap and never had a problem. TBH most compression driver diaphragms are not massively expensive to replace but in this case the diaphragms would cost me more than I paid for the drivers and are quite difficult to get hold of!!
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Beryllium diaphragms do have some interesting properties/problems.
Just thought I'd share this old post:

Affects of bi-amping on passive crossovers

"Concerning blocking caps.
I tested and revealed a rarely discussed but quite logical phenomenon that is quite interesting. It started when we were "shattering" TAD 2001 1" drivers yet everything was in order. Proper protection, 8K x-over point and relatively low power going to them. And no matter what we did we were loosing 1"s. It was when I noticed after a show that we "shattered" some diaphragms on boxes that were not even plugged in, that I was able to isolate the problem.

Turns out the blocking caps were decoupling the low frequency damping of the amp, from the HF drivers. Low frequency energy from the other components in the array were "violently" moving the diaphragm and smashing it against the phase plug till it shattered.

We actually drilled a hole in the driver casing to mount an sm98 inside the back of a driver. We were able to see a reduction in LF signal on the mic, though slight, when we shorted out the terminals of the driver.

Another experiment was we hooked up the terminals of the 1" to the input of an RTA. Then we put LF tones and pink noise into the 15"s. We measured the signal generated by the 1" with and without the blocking cap. With no blocking cap the damping factor of the amp shorted out the voltage that the TADs were generating. With the blocking cap, there was considerable low frequency output being generated by the 1".

OK, so you are not using TAD's but think about it. The amps' damping loads down the diaphragm at low frequencies, therefore reducing the amount of motion. The blocking caps are a very high impedance, at low frequencies. Therefore blocking caps greatly reduce the ability of the amp to restrict diaphragm motion! The diaphragm, moving from the LF spends less time centered in the gap and is therefore less efficient. Also the diaphragm is moving with the LF signal and "blurring" the sound.

We eliminated the blocking caps and problem solved! The failure rate of our 1" dropped from 1 to 2 a show to 1 every 30 or so shows. Additionally, we all agreed that our system sounded noticeably clearer when we eliminated the blocking caps on the 2" as well.

One way to protect horn drivers with a passive circuit, without the decoupling issue, is to use a cap and a choke (coil). The choke would be directly across the terminals of the driver and therefore provide LF damping. The combo would give you the added protection of a 12 db per oct x-over and allow you to use a lower x-over point and have more protection. The downfall is of course cost and added labor."
-Dave Rat

Having also noticed my system sounded noticeably clearer when the blocking caps were eliminated, if worried about the "thump" problem I'd consider the last paragraph.
As far as the best capacitors and coils to use, I'll leave that to the "golden ears"...

Art
 
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ScottG

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krivium

krivium

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Very interesting indeed.
Art do you know if same thing happen with dome tweeters ( tweeters in general)?

For 'blockers' i use the 'high grade precision film caps' from

Ask Jan First ® ; electron tubes and more

( scroll down the page, after the 7 segment display and Nos Elektrika caps).

Those Ft caps exist up to 100uf and are not far from modern german 'boutique' caps ( in technology used) without the high price tag. But they are huge.
 
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weltersys

weltersys

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Joined 2008
krivium said:
Very interesting indeed.
Art do you know if same thing happen with dome tweeters?
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The problem Dave Rat had with the undamped (capacitor coupled) Beryllium diaphragms shattering in very high SPL situations was because the diaphragm was hammering the phase plug, less than 1mm excursion required for contact. A dome tweeter would not have that clearance issue, and would have less impedance transformation, not having a horn "funneling" a large surface area to a smaller one.

Beryllium diaphragm's impedance curve, stiffness and brittleness can be problematic under certain conditions.

Art
 
Y

YSDR

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Joined 2013
JMFahey said:
I am not talking about that one but the "equivalent/emulated" ones inside the DSP crossover :)
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A DSP still not emulates (fortunately) a capacitor between the amp and the driver. It's not even possible because the DSP is before the amp and the capacitor is after the amp and the latter is modify the load impedance, the amp's damping factor and brings other undesired things to the table.

Edit: ohh I get it, you mean it emulates line level components? They are still not the same, because the components are rather physical devices and the DSP is more likely logical.
 
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AllenB

AllenB

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zeagan said:
Going to be doing active crossover but was worried a cap would affect those numbers. Or do you just hook it up with the cap and then measure and set the active after the fact?
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Don't forget the passive element is buffered here. It's just a nice self-contained unit helping the cause. If you measure with the cap, you can use your arsenal of other filters to align with your target response.
seanny said:
Adding a cap will significantly degrade your amp damping factor.
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Yes, no. This one is a bit of a myth, or maybe misrepresentation. The amp/crossover/driver do work together toward the result, whether that is better or not depends on the goal.
YSDR said:
changes the impedance what the amp sees and a DSP solution is not.
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I assume you're using Voltage amps.. why should it matter?
 
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daqvin_carter

Member
Joined 2007
I would think two octaves below cutoff would be safe for startup transients and avoid altering the crossover.
I have seen live systems with a specific startup sequence of breakers. Hurts to watch the drivers die when line power is going off and on due to either lightning or some other fault.
 
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plasnu

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Joined 2011
mpa said:
A couple of weeks ago I go a good deal on some 18Sound ND4015be 1.5" throat 4" Beryllium diaphragm compression drivers and now have them installed in some JBL 2384 horns driven by Aleph J in a Bi-Amp active setup. Beautiful sound! BUT, Aleph J has a noticeable switch off thump and although I have a mute switch on the amp when I power it down I am concerned that a power outage or an error could send this thump to my Be diaphragms :eek:
So I guess a protection capacitor is needed? Crossover is 630Hz so if I go an octave below that I'm going to need quite a large capacitor!
Any suggestions as to a good cap for this job? They sound so good I don't really want a capacitor in the signal path to affect anything :D
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I have a very similar setup. I had been driving JBL 2 way (total 4 woofers) with 6ch Aleph J amps. It is true that AJ thump was annoying, so I used speaker protection relays on tweeters instead of extra capacitors, and they were working just fine for years.

Currently, tweeter is driven by much smaller SE SIT amp, and it has 80uF x2 (160uF) motor run cap bypassed with Mundorf. SE SIT amp requires output cap anyway. ;)
 
M

mpa

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Joined 2010
plasnu said:
I have a very similar setup. I had been driving JBL 2 way (total 4 woofers) with 6ch Aleph J amps. It is true that AJ thump was annoying, so I used speaker protection relays on tweeters instead of extra capacitors, and they were working just fine for years.

Currently, tweeter is driven by much smaller SE SIT amp, and it has 80uF x2 (160uF) motor run cap bypassed with Mundorf. SE SIT amp requires output cap anyway. ;)
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Wow. I bet 6ch's Aleph J gets fun in the summer!

How do you find the SIT in comparison?

I tried the DIYA speaker protect relay boards and the SSR boards from a group buy but neither of them could catch the switch off thump.

I'm loving these big JBL's though!
 
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