Capacitor to protect compression drivers? |
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Griffin
Registered User Joined: 11 August 2009 Location: Cornwall Status: Offline Points: 57 |
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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
Registered User Joined: 20 November 2007 Location: Italy Status: Offline Points: 977 |
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someone told me to protect my cds with a car lighting bulb....
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mk2_ginger_biscuit69
Old Croc Joined: 03 November 2008 Location: Brighton Status: Offline Points: 7801 |
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LABEL it or wire it on 4core speakon with labeled ends/a patch panel. job done |
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''Remember that the object of a subwoofer is to enhance the output of your main speakers, not overpower it''
''Dubstep - an elongated electronic fart'' |
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Tony Wilkes
Old Croc Joined: 02 August 2004 Location: West Midlands Status: Offline Points: 4840 |
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http://forum.speakerplans.com/tweeter-comp-driver-protection_topic27008_post268351.html?KW=light+bulb+protection#268351 Tony |
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Conanski
Old Croc Joined: 26 January 2006 Location: Ottawa, Canada Status: Offline Points: 2515 |
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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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Griffin
Registered User Joined: 11 August 2009 Location: Cornwall Status: Offline Points: 57 |
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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
Registered User Joined: 20 November 2007 Location: Italy Status: Offline Points: 977 |
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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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markie
Old Croc Joined: 31 October 2005 Location: Sunny Liskeard. Status: Offline Points: 4570 |
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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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If it's got wheels or tits it's gonna cost a fortune
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Dom
Old Croc Joined: 25 February 2004 Location: United Kingdom Status: Offline Points: 1700 |
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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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"It sounded like a million fire engines chasing ten million ambulances through a war zone and it was played at a volume that made the empty chair beside me bleed."
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bitzo
Registered User Joined: 20 November 2007 Location: Italy Status: Offline Points: 977 |
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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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mk2_ginger_biscuit69
Old Croc Joined: 03 November 2008 Location: Brighton Status: Offline Points: 7801 |
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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!!
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''Remember that the object of a subwoofer is to enhance the output of your main speakers, not overpower it''
''Dubstep - an elongated electronic fart'' |
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bitzo
Registered User Joined: 20 November 2007 Location: Italy Status: Offline Points: 977 |
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ok but 80w is the rms wattage...is it the same of the electrical ones?
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