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Capacitor to protect compression drivers?

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Griffin View Drop Down
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    Posted: 26 October 2009 at 1:28pm
Hello everyone,
 
I have a 4 way reflex system for the local beach party scene down here in Cornwall.  The top end is two PSD2002s.  They are crossed over at 1.5K by an Ultradrive and each one gets a theoretical 250 watts from a Prosound 1600 (I know, I KNOW! Never again!). 
 
The thing is, since converting the rig to all active crossovers, I have been having nightmares about someone accidentally connecting a comp driver to the output of the mid section, or worse the subs.  Clearly it would all be over pretty quickly if that was to happen.  They are in cabs with 10" mids and all the connectors are the same, so it would be easily done!
 
A while back someone mentioned that it was possible to protect HF drivers with a capacitor wired inside the cab - how would I go about doing this?  I presume it would be wired in series to act as a high pass filter, but what type of capacitor would I need, and how many volts and Farads?
 
Thanks in advance for any help!
 
 
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bitzo View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote bitzo Quote  Post ReplyReply Direct Link To This Post Posted: 26 October 2009 at 2:25pm
someone told me to protect my cds with a car lighting bulb....
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Post Options Post Options   Thanks (0) Thanks(0)   Quote mk2_ginger_biscuit69 Quote  Post ReplyReply Direct Link To This Post Posted: 26 October 2009 at 2:41pm

LABEL it or wire it on 4core speakon with labeled ends/a patch panel. job done

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Tony Wilkes View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Tony Wilkes Quote  Post ReplyReply Direct Link To This Post Posted: 26 October 2009 at 2:49pm
Originally posted by bitzo bitzo wrote:

someone told me to protect my cds with a car lighting bulb....


http://forum.speakerplans.com/tweeter-comp-driver-protection_topic27008_post268351.html?KW=light+bulb+protection#268351

Tony
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Conanski Quote  Post ReplyReply Direct Link To This Post Posted: 26 October 2009 at 2:49pm
Both methods are widely used but the light bulb will require some adjustment in levels the harder the system is driven because it soaks up more power at higher voltage levels.. that's just the nature of a resistive load. The other downside to the bulb is it provides no low freq protection. Use an online calculator to figure out what value capacitor to use, it's tied to the driver impedance so you need to know that, and select a frequency an octave below the crossover like 800hz or so. That comes out to 25uF for an 8ohm driver for example, use a 200v nonpolarised cap and if you cannot find a single cap of that value you can parallel 2 or more to achieve it, like a 15uf and a 10uf.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Griffin Quote  Post ReplyReply Direct Link To This Post Posted: 26 October 2009 at 4:07pm
Thanks everyone.  Yeah I've already labelled them, thanks Mr Ginger!
 
Part 2 of this question, then:  Does a capacitor bring about a phase change in the output?
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bitzo View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote bitzo Quote  Post ReplyReply Direct Link To This Post Posted: 27 October 2009 at 9:15am
so these protections, light bulb, L-pad, capacitor have to be calculated in relation with the amp that I use, and with the number of cds....I mean...if I have to add some cds or...changing amp...I have to change the resistance values, or the capacitor values too... am I right?
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Post Options Post Options   Thanks (0) Thanks(0)   Quote markie Quote  Post ReplyReply Direct Link To This Post Posted: 27 October 2009 at 10:13am

Bitzo. You seem slightly confused about the purpose of each item.

 
1) The light bulb provides protection from over-powering the HF driver. At normal levels the signal passes through unimpeded. When the power increases the bulb starts to glow and gets brighter with more power, in effect "using the power before it gets to the HF. Eventually the bulb will blow, hopefully before the diaphragm (bulbs are cheaper). It does NOT provide any protection against lower frequencies than the HF driver can cope with.
 
2). An L-Pad is used to balance the HF  to the bass driver (HF drivers are usually much higher sensitivity, but only appropriate when a passive crossover is used. On an active system the relative balance is achieved with the crossover or amp gain controls. The resistor values are dependant on the driver impedence. Online calculator here
 
3). Capacitors are used along with inductors, in passive crossovers to achieve the separation. The cap value is dependant on the respective driver impedences and the required separation frequency. An online calculator can be found here:-
It's also possible to use a simple capacitor as "backup" in an active system. Again the cap value will depend on the driver impedence and required minimum frequency.
 
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Dom Quote  Post ReplyReply Direct Link To This Post Posted: 27 October 2009 at 10:33am

Wire all your cabs to 8 way speakons. 1=sub, 2=bass, 3=mid, 4=hi.... 

Then you can just run 1 cable to the stack and it doesn't matter how you link the cabs together everything will work just fine....
 
It also means you can let any idiot wire things up for you....
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bitzo View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote bitzo Quote  Post ReplyReply Direct Link To This Post Posted: 27 October 2009 at 12:28pm
Many thaks markie very clear!
so... I guess for a 80w comp I have to use a 12v car bulb with a 4 A limit or a 24v bulb with 2 A limit...
correct?
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Post Options Post Options   Thanks (0) Thanks(0)   Quote mk2_ginger_biscuit69 Quote  Post ReplyReply Direct Link To This Post Posted: 27 October 2009 at 12:52pm

Watts / Voltage = Current (A)

80w / 12v = 6.67 A (2DP)
80w / 24v = 3.34 A (2DP)
 
not sure what the effects of this would be in terms of compression or sound quality. I dont really see much need. Just make sure its you rigging, and turn up amp gains slowly to make sure its right, say starting on the mids.
 
if this rig is intended for use by others, wiring up on 4core/8core with patch panels, and anti tamper rig setting is a must. A newbie at the controls could blow the lot, hardware protected or not!!
''Remember that the object of a subwoofer is to enhance the output of your main speakers, not overpower it''

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bitzo View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote bitzo Quote  Post ReplyReply Direct Link To This Post Posted: 27 October 2009 at 1:00pm
ok but 80w is the rms wattage...is it the same of the electrical ones?
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