How to prevent Horn Drivers from blowing...

[li_gangyi]

As above...My school has 2 pairs of these on the stage monitors and facing the audience...but sometimes...when we are not around...or a total noob comes into the control room..he/she usually clips the amps really badly and blow the drivers in there...and they don't come cheap...so I would like a few suggestions on how to prevent that...short of education..can we have a "hard-ware" type of approach that can help to prevent blow ups again??

[SkinnyBoy]

polyswitches

[GM]

Posted on the HE forum:

GM

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Re: Light bulb limiters - picking and using proper bulbs?


Posted by djk on May 11, 2001 at 01:56:58
In Reply to: Light bulb limiters - picking and using proper bulbs? posted by freddyi on May 10, 2001 at 18:03:24:


Reply To: (#7084) Re: Fusing speakers
Author: dennis kleitsch
Date: Sunday, 16 May 1999, at 6:16 p.m.
: dk: A little known fact is that
: fast-blow(AGC,3-AG)type fuses actually take
: longer to blow for values less than 1
: amp.Thus a 3/4 amp fuse offers less
: protection than a 1 amp fuse for
: tweeters.AGX fast acting instrumentation
: types could be employed but use non-standard
: fuse holders(and are expensive).A 1 amp fuse
: is about perfect for most tweeters with
: 1" coils anyway.A more sophisticated
: protection scheme would be to buy a .5 amp
: Raychem RXE050 PolySwitch and wire it in series
: with the tweeter.In parallel with this wire
: a 561 lightbulb(automotive dome light)with a
: 2.2 ohm 2 watt resistor in series with the
: light.Drill a small hole in the front baffel
: and put a red LED in it.When the PolySwitch
: opens the current will now flow through the
: bulb/resistor combo.This will act as a
: dynamic limiter due to the positive nature
: of the resistance of the lightbulb
: fillament(it is less than .5 ohm cold and
: close to 15 ohms hot).The 2.2 ohm resistor
: is needed to insure most of the current
: flows thru the poly switch when the lamp is
: cold.When playing too loud the bulb will
: give off enough light to be visible thru the
: lens of the LED(the LED is not connected to
: anything,it is just a colored lens in this
: application).Clipping produces odd harmonics
: making the music sound 'bright' or
: 'harsh'.The dynamic nature of this limiter
: tames this too.The cost is no more than a
: couple of boxes of fuses.No nuisance fuse
: blowing(or running out),better sonics,and
: visual indication of overdrive. djk:
For most people the bulb in series is good enough.
While the PolySwitch shorts out the bulb at low volume
levels its DC resistance is no lower than the bulb by itself.
A 211-2 bulb is the same as a #561 but has end caps that solder easier.
If you want to get real fancy the EV STR tweeter protector and the B&W APOC
used a relay instead of the PolySwitch.Try the naked bulb first.
For 1.5"~2" 8 ohm coils use an #1156 tail lamp(optional components 1.5 ohms 5 watts
+ RXE110).For 16 ohms use #1141 with 3.3 ohms 10 watt in series paralleled with a RXE075,
these are NOT optional.The RXEs should not be used with amps that put out over 400
watts unless there is a pad on the driver(the usual situation).
Legal Notice:If you are trying to win the Darwin award pretend you didn't
read this(not responsible for people that kill themselves).

[PeteMcK]

From memory I think Rod Elliot's web site (Elliot Sound Products)has circuit for a simple limiter which can be built into the amp, not as simple as GM's solution though
Pete McK

[li_gangyi]

Where can I get the polyswitch easily in Singapore?? I understand RS has a range of poly-switches...but I'm not so sure which ones to get...and I wouldn't want to just get a light in series with the tweeter...not that assuring that it will actually limit the clips fast enough...and the horn is actually quite big...and the speaker handles about 300W in total...so are you sure the 561 automotive bulb is adequate...maybe I would like to get a more "solid" approach...what elese to offer???

[Centauri]

Forget the polyswitches - they are far too slow. I did a test and was able to feed twice the rated power into a load for 10 seconds before the poyswitch tripped - by this time the driver would have well and truley been stuffed.

I have used ordinary 12V automotive light bubs quite successfully, and the size of bulbs depends on the driver to be protected. Being drivers in wedges, I would assume they are probably quite small. A guide is:

HF Power Impedance Bulbs
-------------------------------------------------------
18W 8 ohms 3x 18W in series
36W 16 ohms as above

22W 8 ohms 6x 10W (2 parallel groups of 3 in series)
45W 16 ohms as above

16W 4 ohms 3x 25W in series
32W 8 ohms as above
64W 16 ohms as above

25W 4 ohms 9x 10W (3 parallel groups of 3 in series)
50W 8 ohms as above
100W 16 ohms as above

36W 4 ohms 6x 18W (2 parallel groups of 3 in series)
72W 8 ohms as above
144W 16 ohms as above

Just wire the bulb pack in series with the driver.

Cheers

[phase_accurate]

I once used a relay-based circuit for an Audax ring radiator that could withstand 18 Watts continuous and which was driven by a 100 Watt amp.

The time-constant was 100 ms and nobody ever managed to kill a tweeter.

The disadvantage of the circuit is that it may add distortion since it is fed by the driving signal.

If you are interested I can draw it wit a CAD program and post it here.

Regards

Charles

[JOE DIRT®]

Bulbs are often used in pro gear for tweeter protection and are better than a fuse but it comes down to common sense if you overdriving a speaker usually the amp is clipping and you run the chance of ruining both the speaker and the amp

DIRT®

[li_gangyi]

Yeah...but sometimes it's those noobs hat are operating the equipment..maybe I should just install a switch on the speakers...to turn off the tweeters..so only "pros" know the switch is there...

[Elso Kwak]

Hi ,
For tweeter protection we had good experiences with zenerdiodes mounted across the tweeters like in the Klipsch AA crossover for the Klipschorn.
This protected the tweeters very well in the Hersy loudspeakers.
The Heresy's were used in a pub and they blew the tweeters repeatedly. After the zenerdiodes were installed they keeped working. We used two about 5.5V 5 Watt zenerdiodes in series back to head across each tweeter.