Auto Lamps for Speaker Protection
Scott Dorsey
devices, sort of like crude PTC thermistors, but I haven't seen anyone
actually give reasonable rules on what lamp combinations give good results
with given drivers. I'm trying to systematically test some of these, but
first I want to know what lamps people have used with what drivers in the
past and had good results with, so I know where to start. Anybody got
some experiences they could give me?
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."
David Griffiths
electroncic crossovers with built in dc protection!! A lot better
Idea!!
Chris
--
All of the Smaller Yorkville Boxes still use the Lamps for protection.
Cheap and reliable...!
Chris Welsh
chris...@home.com
Ottawa Canada
André Huisman
Scott wrote:
> >Everybody talks about using automotive lamps for speaker protecting
> >devices, sort of like crude PTC thermistors, but I haven't seen anyone
> >actually give reasonable rules on what lamp combinations give good
results
> >with given drivers. I'm trying to systematically test some of these, but
> >first I want to know what lamps people have used with what drivers in the
> >past and had good results with, so I know where to start. Anybody got
> >some experiences they could give me?
> At one time we used 12volt back up lamps .. but then we got
> electroncic crossovers with built in dc protection!! A lot better
> Idea!!
I don't think there are much professional amps out there without DC
protection. I also don't think that there are designers who are ignorant
enough NOT to use DC blocking caps (I mean every self respecting active
X-over manuf. writes that in their manual using bold capitals) in active
systems (the only system where the HF driver _can_ be connected straight to
the output of the amp without any cap blocking that DC).
So now we have a problem. We both have an amp that won't put out any
substantial amount of DC without shutting off AND we have a speaker that,
even if the amp DID put out an enormous amount of DC, wouldn't see it
because of that nasty behavior a capacitor has. And please don't start with
"short term DC" for that's an oximoron. If it's DC, it's DC, the voice coil
will see it as DC, as will the amp's protection. If it's not DC, the voice
coil won't see it as DC and neither will the amp's protection.
As to the answer to "which" lightbulb. Me thinks it would require an amount
of trial and error that would mount to a much higher price than replacing
the odd diaphraghm (for most users). I also quite frankly hate the idea of
having such a nasty compression element in my signal chain (the speakers do
that enough already ;-). I also fail to see how one can use one lightbulb
(brakelight 21W was suggested just a while ago) and actually think this will
have a heat up constant equal to the driver it's protection, considering the
vast amount of totally different HF drivers out there.
But I HAVE seen it in use in commercial products (I still have to laugh
about the memory). I once saw a band use a Community speaker system (the
cabinet type with a lot of piezo shit and other crud). It too had a
lightbulb but it was on the mid section (go figure). Feature was that every
time the singer opened his mouth, the cabinet went from being a sound
cabinet to a lighting fixture. Yes, I'm serious and NO, I can't take such a
product serious.
The JBL control range also uses a lightbulb for tweeter protection and I
have to say it actually DOES work in that cabinet. Snag is that this is NOT
an "off the shelve" lightbulb, it's somekind of very small halogen bulb. I'm
quite sure that they had to blow a substantial amount of HF drivers to get
the right size bulb (but in that case it DOES work ;-).
If I wanted to protect a HF driver (which I BTW leave up to the speaker
processors) using somekind of passive protection, I'd probably go for a fuse
or a polyswitch. Both are (IMO) less intrusive to the signal path. Still a
fair amount of tweaking would be required. I'd start off with a rating at
some 50% of the _driver's_ continuous power handling and upsize it if it
blows a lot.
I, for the live of me, can't see how a 21W lightbulb is going to protect a
100W 2" (4" voice coil) driver (lamp would be far too small for that). I
also can't see how a 21W lightbulb is going to protect that fragile 10W
(38mm voice coil) ring radiator. I CAN see how a 3A fuse is going to protect
that 100W driver and a 0.8A fuse is going to protect that 10W driver (or
something in that neighboorhood).
--
André Huisman
New Line licht & geluid
hui...@new-line.nl
http://www.new-line.nl
--- pardon my French, I'm Dutch ---
Black River Media
Simcoe now, but skulk around with some music types.)
With car audio we'd use a GM dome light, the kind with 2 bullet end
terminals, wired in parallel with a wire wound 10W, 30 ohm resistor. That
pair would be put in a break in one of the speaker cables.
I can't give you parameters Scott. It was more a case of "If you're going to
keep coming back every Saturday morning with a blown driver, we better put
in some magic audio shock absorbers". The parts we use haven't changed in
over a decade. A bass player is trying it for his highs which are expensive
to replace. I'll ask how they're working.
Charlie
"Chris" <chris...@home.com> wrote in message
news:3B1EA84D...@home.com...
ZZZ...@whiskey-creek.net
<see_pos...@il.ok> wrote:
> And please don't start with
>"short term DC" for that's an oximoron. If it's DC, it's DC, the voice coil
>will see it as DC, as will the amp's protection. If it's not DC, the voice
>coil won't see it as DC and neither will the amp's protection.
>
gospel, I can't comply with your plea.
AC, by definition, is in a continous state of change. DC, by
definition, is static at some point of time. The amount of time is
not necessarily relevant.
There are most Certainly power amps with DC protection circuits that
will see high-level, low frequency information as "DC" and go into
protect, even though technically the signal is Not DC.
Additionally, the longer a voice coil is held out of the gap, the
quicker it will heat up, and the greater the likelyhood will be that
it will fail. Again, high-level, low frequency information, while not
technically DC, is fully capable of causing this to happen.
In both cases, the result is the same as if DC had been applied,
although in reality it's AC that's changing state so slowly it's
treated by the equipment as though it were DC. If one were to slow
the waveform down enough, it could literally be measured as DC by a
DVM. So therefor, yes, there is such a beast as "short term DC", as
it simply depends upon the time-base of measurement whether it can be
construed as DC or AC. Personally, though, I don't care for that
term, as it isn't particularly accurate, but the result is the same.
Mark
The truth as I perceive it to be.
Your perception may be different.
Triple Z is spam control.
Brad
pair of SoundTech monitors that use light bulbs for HF protection as
well... Interesting thing too. The Woofers have red surrounds and
when the bulbs light, the enire red surround lights up hell of bright!
~the end
GK
"André Huisman" <see_pos...@il.ok> wrote
> The JBL control range also uses a lightbulb for tweeter protection and I
> have to say it actually DOES work in that cabinet. Snag is that this is
NOT
> an "off the shelve" lightbulb, it's somekind of very small halogen bulb.
I'm
> quite sure that they had to blow a substantial amount of HF drivers to get
> the right size bulb (but in that case it DOES work ;-).
The 400W Motorola piezo drivers have some small special looking lamp and a
PTC!
>I CAN see how a 3A fuse is going to protect
> that 100W driver and a 0.8A fuse is going to protect that 10W driver (or
> something in that neighboorhood).
Much more realistic approach. I have also seen self resetting thermal
circuit breakers used in home stereo speakers that work well.
GK
--
http://www.ancientharmony.com
"Noise proves nothing. Often a hen who merely lays an egg cackles as if she
laid an asteroid."
Jay Levitt
> I haven't seen anyone
> actually give reasonable rules on what lamp combinations give good results
> with given drivers.
Then let me be the first to go there...
Halogen bulbs will give you a brighter, crisper, warmer sound.
Fluorescent bulbs will, of course, give you that tube sound.
Heat lamps will give you sizzle.
Broken bulbs add "air".
Grow-lites make the sound muddy.
Frosted bulbs smear the sound.
Christmas bulbs add coloration.
Clear bulbs are, uh, very transparent.
OK, I'm out.
--
Jay Levitt | This is not the start of World War III
Wellesley, MA | No political ploys
j...@jay.fm | I think both your constitutions are
http://www.jay.fm | terrific, so now you know - be good boys.
Kendall
> Then let me be the first to go there...
>
OK, I'll play...
I thought grow-lites were supposed to give the sound a certain "bloom".
And I've heard that flood lamps will wash out the sound.
Of course, that means that spotlights give you a tightly focused sound.
Auto headlamps are best used for that "driving" sound.
And I just know that neon will do something to it, but I'm too tired to
think of it... Anyone?
Kendall
--
Remove "123" from e-mail
address to reply
Karsten Krambs
>PTC!
André Huisman
> > And please don't start with
> >"short term DC" for that's an oximoron. If it's DC, it's DC, the voice
coil
> >will see it as DC, as will the amp's protection. If it's not DC, the
voice
> >coil won't see it as DC and neither will the amp's protection.
> Sorry, Andre', for the sake of those who may read your words as
> gospel, I can't comply with your plea.
Gospel??? Me??? People taking the words of an atheist as the gospel?
<grinning>
Anyway. What I was refering to was that some people suggest the flattening
of the tops results in DC (because it's flat, it looks like DC for that
period of time so it must be DC). This notion is, of course, a wrong notion.
That and ONLY that is what I was addressing.
> AC, by definition, is in a continous state of change. DC, by
> definition, is static at some point of time.
Do you see the duality in the sentence above? A 1kHz square wave would, by
the definition above, be very much DC for 0.5msec in time (and then again DC
for another 0.5msec etc. etc.).
> The amount of time is not necessarily relevant.
See duality reference.
> There are most Certainly power amps with DC protection circuits that
> will see high-level, low frequency information as "DC" and go into
> protect, even though technically the signal is Not DC.
The added benefit from this approach is a simple (and not always effective)
subsonic protection.
> Additionally, the longer a voice coil is held out of the gap, the
> quicker it will heat up, and the greater the likelyhood will be that
> it will fail.
If a voice coil leaves the gap, the driving force is _gone_ (B*L). The
suspension force, wanting to pull it back into the airgap however is NOT
gone. So there you have it, a state which is impossible in real life.
Besides: If a voice coil is driven outside the air gap (or even close to
that) then that's a sign of a speaker which is being abused instead of used.
This thread however was about HF drivers. Every HF driver has a voice coil
which is actually shorter than the air gap it's placed in. So for HF drivers
it's actually impossible to get the voice coil out of the air gap.
> Again, high-level, low frequency information, while not
> technically DC, is fully capable of causing this to happen.
In which case the design of the filter prior to the HF driver is inadequate.
> In both cases, the result is the same as if DC had been applied,
> although in reality it's AC that's changing state so slowly it's
> treated by the equipment as though it were DC. If one were to slow
> the waveform down enough, it could literally be measured as DC by a
> DVM. So therefor, yes, there is such a beast as "short term DC", as
> it simply depends upon the time-base of measurement whether it can be
> construed as DC or AC. Personally, though, I don't care for that
> term, as it isn't particularly accurate, but the result is the same.
Agreed. Probably the best way to describe the different states is:
1. A signal the driver can handle OR
2. A signal the driver can't handle.
;-)
Mike Tulley
>Everybody talks about using automotive lamps for speaker protecting
>devices, sort of like crude PTC thermistors, but I haven't seen anyone
>actually give reasonable rules on what lamp combinations give good results
>with given drivers. I'm trying to systematically test some of these, but
>first I want to know what lamps people have used with what drivers in the
>past and had good results with, so I know where to start. Anybody got
>some experiences they could give me?
Scott,
Most of the Yorkville Elite series speakers use automotive light bulbs
for HF driver protection. The bulb size varies, depending on the power
rating of the driver. Their smallest crossovers, rated at 160W, used
to use a hard-to-find 6V tail light bulb. Larger units rated at 500W
use headlight bulbs. Those speaker ratings, by the way, are not RMS.
They rate their speakers in terms of the appropriate size amplifier,
so the number is roughly twice the RMS rating that most pro speaker
manufacturers use.
As a very rough guess, it appears that the wattage rating of the 12V
bulb is similar to that of the HF driver that it protects. An auto
headlight bulb will be rated at around 60 to 80W.
I use several models in the Yorkville Elite line. If it would be
useful to you, I could look up the automotive part numbers for the
bulbs. I've only blown a bulb once, and it was available at the
nearest all-night truck stop.
Mike T. in Edmonton, AB., Canada
Paul 'Max' Murray
> >
> > Grow-lites make the sound muddy.
>
> OK, I'll play...
>
> I thought grow-lites were supposed to give the sound a certain "bloom".
>
.....grow-lights should only be used by *budding* engineers. ;-)
Mike Borkhuis
> think of it... Anyone?
Neon adds that annoying buzz.....
Mike Borkhuis
Worship Technology
wors...@rochester.rr.com
Scott Dorsey
Scott Dorsey
>
>The favourites for tweeter or HF driver protection seem to be the
>small tubular lamps used in automobiles for licence plate, side, and
>interior lights. They are available for 12 and 24 volt systems in 5
>and 10 watt ratings; obviously each type has a different resistance /
>temperature characteristic.
These are mostly 211s for the 12V ones. I have seen the 1141 in frequent
use, too. There are some other types, though, and I want to know what
the numbers on them are.
>Selection depends on application; sometimes they are in series with
>the driver, sometimes in parallel with a resistor or other crossover
>element. Some experimentation is required, as they must be properly
>integrated into the system design if they are to work properly.
Yup. I'm running I/V curves on a few lamps right now to see what they
look like.
>Manufacturers who have used this technique include respected names
>such as JBL (some of the Control series) and Turbosound (some of the
>smaller TCS cabinets). There was, of course, also the infamous Bose PA
>cabinet which when driven hard in a darkened room made an effective
>Son et Lumiere display........
Right, but this doesn't answer my question. Which lamps are they using
with which drivers? I wouldn't mind seeing full crossover schematics
(since the lamp will affect the driver impedance that the crossover sees
even when it's cold, so it will alter the crossover design), but that
would be gravy.
Reese Thomas
>manufacturers use.
>As a very rough guess, it appears that the wattage rating of the 12V
>bulb is similar to that of the HF driver that it protects. An auto
>headlight bulb will be rated at around 60 to 80W.
Hmmmm..... Never seen a headlite bulb as a HF protect. So for the average
50 watt driver?????? During High SPL sets, could we maybe double as spots
on the front man? (grin)
>I use several models in the Yorkville Elite line. If it would be
>useful to you, I could look up the automotive part numbers for the
>bulbs. I've only blown a bulb once, and it was available at the
>nearest all-night truck stop.
>Mike T. in Edmonton, AB., Canada
Also how are the bulbs hooked up? Series or parrellel with a resistor, and
if so, what value ? THanks
Brad
are about 1000 miles from me down at school.. I was just suggesting
this because you might be able to find a pair that the owner would let
you open up.
Curt Wells
rat's ass if my drivers are blowing up!
Just kidding.
I've noticed many clubs around the US save money on Hi-Freq drivers by
simply never repairing them! when pointed out, the ex-Guitar
center-soundguy says something like... 'Huh? Guess I'll try that lightbulb
trick the guy at Mars talked about.'
Offering no solution as usual. Curt.
steve
Steve
Robert S Ely
creek.net says...
> On Wed, 6 Jun 2001 23:42:37 +0200, "André Huisman"
> <see_pos...@il.ok> wrote:
> > And please don't start with
> >"short term DC" for that's an oximoron. If it's DC, it's DC, the voice coil
> >will see it as DC, as will the amp's protection. If it's not DC, the voice
> >coil won't see it as DC and neither will the amp's protection.
> >
for explanation... as long as it is changing value. You get the same
results, but the definition of AC and fluctuating DC are different.
Fixed DC (constant value of voltage say -52.7VDC is bad for speakers.
since it isn't changing, meaning the voice coil is NOT moving and has
current applied. This is where the heat comes from. Straight EI=W=heat.
If the voltage and/or current is changing the voice coil heats and cools
and since it moves due to the magnetic field, it has air movement
removing heat from it.
> Sorry, Andre', for the sake of those who may read your words as
> gospel, I can't comply with your plea.
>
> AC, by definition, is in a continous state of change. DC, by
> definition, is static at some point of time. The amount of time is
> not necessarily relevant.
Actually that is incorrect. AC is a changing voltage/current that
changes POLARITY. You can have, what LOOKS like AC, but is it does NOT
change polarity it is fluctuating DC. It is just more or less of a value
of the positive or negative. Like changing from +5vdc to +12vdc to +3vdc
(or negative likewise).
+ |
| -----
|-----\ -----/
| ------/
0V|-----------------------------
|
|
- |
This is fluctuating DC NOT AC
+ |
|
| -----
0V|-----\ -----/
| ------/
|
- |
This is AC
>
> There are most Certainly power amps with DC protection circuits that
> will see high-level, low frequency information as "DC" and go into
> protect, even though technically the signal is Not DC.
You can have AC and DC in the same signal.
If the amp goes into hard clipping long enough it would interpret that
signal as DC, if it stays to one side of 0V.
>
> Additionally, the longer a voice coil is held out of the gap, the
> quicker it will heat up, and the greater the likelyhood will be that
> it will fail. Again, high-level, low frequency information, while not
> technically DC, is fully capable of causing this to happen.
The longer is is held in one position with power applied it will heat
and could fail. Voice coils depend on the motion (due to changing
current flow (usually AC) to keep cool.
Keep in mind Transistors are basically complicated diodes and only work
on DC gating current flow. Ther seem to be like variable resistors, but
if you look at transistor circuits, they usually have isolation
capacitors between stages.
>
> In both cases, the result is the same as if DC had been applied,
> although in reality it's AC that's changing state so slowly it's
> treated by the equipment as though it were DC. If one were to slow
> the waveform down enough, it could literally be measured as DC by a
> DVM. So therefor, yes, there is such a beast as "short term DC", as
> it simply depends upon the time-base of measurement whether it can be
> construed as DC or AC. Personally, though, I don't care for that
> term, as it isn't particularly accurate, but the result is the same.
AC at 0Hz is considered DC since there is no change of polarity.
Internally DVMs can only measure DC. There is circuitry that
simulates/converts the AC to DC so it can be measured.
>
> Mark
>
> The truth as I perceive it to be.
> Your perception may be different.
>
> Triple Z is spam control.
>
>
--
--
Robert S Ely - aka - Eli-the-Iceman
rse...@optonline.net
rs...@dhs.state.nj.us
rse...@hotmail.com
hsr...@vm.state.nj.us
ICQ#: 33390750
AOL-IM: Eliice1954
Peter Larsen
Hi Andre,
"André Huisman" wrote:
> Scott wrote:
> > >Everybody talks about using automotive lamps for speaker protecting
> > >devices, sort of like crude PTC thermistors, but I haven't seen anyone
> > >actually give reasonable rules on what lamp combinations give good
> > >results with given drivers.
A necessarily trial and error based quest that is not to be recommended.
It could cost more in blown drivers to find out than the amount of
drivers burned in sensible use.
> > >I'm trying to systematically test some of these, but
> > >first I want to know what lamps people have used with what drivers in the
> > >past and had good results with, so I know where to start. Anybody got
> > >some experiences they could give me?
No. But I plain do not think adding lightbulbs in series with a
loudspeaker does anything good to the sound quality.
> > At one time we used 12volt back up lamps .. but then we got
> > electroncic crossovers with built in dc protection!! A lot better
> > Idea!!
Amplifiers that accept to have a DC offset on their output terminals
have no place on the road. Also, except for the possibility of amplifier
failure it almost only could be caused by severe clipping which should
not have happened in the first place.
> I don't think there are much professional amps out there without DC
> protection. I also don't think that there are designers who are ignorant
> enough NOT to use DC blocking caps (I mean every self respecting active
> X-over manuf. writes that in their manual using bold capitals) in active
> systems (the only system where the HF driver _can_ be connected straight to
> the output of the amp without any cap blocking that DC).
After a listening test CSR decided NOT to use blocking caps on neither
midrange nor treble drivers, not exactly my recommendation but the owner
would rather take the gamble and have a better sounding system. A very
british and very ingenious protection setup was also ripped out of
Martin "shavers" and 215 bass bins with a remarkable sonic improvement
as the result. No increase in premature loudspeaker deaths was observed.
This does NOT constitute a general recommendation of removing protective
contraptions, it appears to be a much better choice to include a first
order passive highpass filter on all drive units in the cross-over math.
> So now we have a problem. We both have an amp that won't put out any
> substantial amount of DC without shutting off AND we have a speaker that,
> even if the amp DID put out an enormous amount of DC, wouldn't see it
> because of that nasty behavior a capacitor has. And please don't start with
> "short term DC" for that's an oximoron. If it's DC, it's DC, the voice coil
> will see it as DC, as will the amp's protection. If it's not DC, the voice
> coil won't see it as DC and neither will the amp's protection.
There can indeed not be any such thing as "short term DC", strictly
speaking defining DC as DC is only possibly valid if the universe can be
shown to have an infinite lifespan in both directions of the timeline.
The present asumption is that it has a beginning, consequently DC does
not exist, only approximations thereof ... O;-)
This does not negate that "DC drift" is a valid technical term, however
unless an amplifier is faulty it should not happen unless it is badly
clipped, and even then the amplifier would be misbehaving so badly that
it should assume itself faulty and shut down.
> As to the answer to "which" lightbulb. Me thinks it would require an amount
> of trial and error that would mount to a much higher price than replacing
> the odd diaphraghm (for most users). I also quite frankly hate the idea of
> having such a nasty compression element in my signal chain (the speakers do
> that enough already ;-). I also fail to see how one can use one lightbulb
> (brakelight 21W was suggested just a while ago) and actually think this will
> have a heat up constant equal to the driver it's protection, considering the
> vast amount of totally different HF drivers out there.
André ... some day you might end up implementing it in some context, not
because of its sonic merits, but in spite of its demerits, because it
can be a practical way to implement some protection and the only way you
can implement in the few final hours before a tour starts. Do not say
"never" on this one - with an instrument amp + speaker combination it
might even distort just right.
> If I wanted to protect a HF driver (which I BTW leave up to the speaker
> processors) using somekind of passive protection, I'd probably go for a fuse
> or a polyswitch. Both are (IMO) less intrusive to the signal path. Still a
> fair amount of tweaking would be required. I'd start off with a rating at
> some 50% of the _driver's_ continuous power handling and upsize it if it
> blows a lot.
This is non-simple, because of the time constant issue. A fuse - or
lightbulb - rating that is A OK for a cold driver could be likely to
allow a hot driver protect it by frying first. 20 percent of rated
continuous power and slower-blo seems more sensible and it might well be
that you would be unable to ever blow that fuse without clipping the amp
supplying the music signal.
> André Huisman
Kind regards
Peter Larsen
Scott Dorsey
>
>I don't think there are much professional amps out there without DC
>protection. I also don't think that there are designers who are ignorant
>enough NOT to use DC blocking caps (I mean every self respecting active
>X-over manuf. writes that in their manual using bold capitals) in active
>systems (the only system where the HF driver _can_ be connected straight to
>the output of the amp without any cap blocking that DC).
The lamps do nothing for DC protection, and DC isn't an issue for the
tweeters anyway.
The whole notion of using the lamps is that they are effectively PTO
thermistors; they have a low resistance when cold, but as voltage is
applied, their resistance increases. If you plot the I/V curve, it's
extremely nonlinear. This can be used to limit the current through
any load.
The notion here is that if it's sized properly, it can prevent clipping
and other abuse from damaging a tweeter, while having little sonic effect
at reasonable levels since at those reasonable levels it's cold enough
to be linear.
>As to the answer to "which" lightbulb. Me thinks it would require an amount
>of trial and error that would mount to a much higher price than replacing
>the odd diaphraghm (for most users). I also quite frankly hate the idea of
>having such a nasty compression element in my signal chain (the speakers do
>that enough already ;-). I also fail to see how one can use one lightbulb
>(brakelight 21W was suggested just a while ago) and actually think this will
>have a heat up constant equal to the driver it's protection, considering the
>vast amount of totally different HF drivers out there.
No, it won't, because it's got a much higher resistance (when hot) than
the driver. Don't think about it as sinking power, think of it as a voltage
divider with one side constant and one side adjustable.
Trial and error is NOT the right way to figure out how to do this, partly
because lamps are going to vary from unit to unit so you need to have good
data on variations as well as full I/V curves for each lamp before you
design this sort of thing.
The reason I am asking is because I am curious what is being used out there
before I even think about plotting curves.
>The JBL control range also uses a lightbulb for tweeter protection and I
>have to say it actually DOES work in that cabinet. Snag is that this is NOT
>an "off the shelve" lightbulb, it's somekind of very small halogen bulb. I'm
>quite sure that they had to blow a substantial amount of HF drivers to get
>the right size bulb (but in that case it DOES work ;-).
It is an off the shelf lamp, but it's selected for a particular curve.
It's not a halogen device even though it's a tubular lamp.
>I, for the live of me, can't see how a 21W lightbulb is going to protect a
>100W 2" (4" voice coil) driver (lamp would be far too small for that). I
>also can't see how a 21W lightbulb is going to protect that fragile 10W
>(38mm voice coil) ring radiator. I CAN see how a 3A fuse is going to protect
>that 100W driver and a 0.8A fuse is going to protect that 10W driver (or
>something in that neighboorhood).
The notion is that cold the lamp has about .2 ohms, and hot it has around
50 ohms. So, it's like throwing a 50 ohm resistor in series with your
8 ohm voice coil on peaks. This gives you around a sixth of the current
that you'd have without it.
Phil Allison
news:9g56mn$cgh$1...@panix3.panix.com...
Scott,
you are on the right track but some facts are slightly off.
All bulb lamps use pure tungsten wire filaments so the VI curves are all the
same shape. From cold to bright (0 to 13 volts) the increase in resistance
is 12 to 16 times, the higher figure is for halogen bulbs which get hotter.
The current reduction will help greatly with DC protection where horns are
driven direct off power amps - some people actually do this in active x-over
systems. It would be possible to size the bulbs so one will blow open if the
amp ever goes DC.
Bulbs may cause some compression of very loud sounds but their attack and
decay times are so slow that there is no distortion produced.
I have seen 12 volt bulbs of 10 to 30 watts rating used in series strings of
two to four depending on the horn power and impedance ratings and max amp
output voltage.
BTW I know of one speaker that uses a bulb to protect the woofer, well, it
only has the one driver. The Bose 101.
Regards, Phil
dougb...@hotmail.com
<soun...@uswest.net> wrote:
>At one time we used 12volt back up lamps .. but then we got
>electroncic crossovers with built in dc protection!! A lot better
>Idea!!
The only prob with this approach, is that the x-over comes BEFORE the
amplifier, and it is amp clipping that is the real culprit. There are
some great X-Os with hard limiters, and these, if used intelligently,
would be a nice alternative.
However, the bottom line is that all of these solutions attempt to
introduce some kind of dynamic limiting, and the BEST kind is the kind
that comes from the brain of the engineer, who knows what the limits
of his/her system is.
-dB
dougb...@hotmail.com
<blackri...@home.com> wrote:
>With car audio we'd use a GM dome light, the kind with 2 bullet end
>terminals, wired in parallel with a wire wound 10W, 30 ohm resistor. That
>pair would be put in a break in one of the speaker cables.
>I can't give you parameters Scott. It was more a case of "If you're going to
>keep coming back every Saturday morning with a blown driver, we better put
>in some magic audio shock absorbers". The parts we use haven't changed in
>over a decade. A bass player is trying it for his highs which are expensive
>to replace. I'll ask how they're working.
>Charlie
The only thing I don't like about this approach is that power is being
consumed at all times. Consider a circuit with zener diodes, relay,
etc., that only introduces these limiting elements when the voltage
level approaches the danger point.
-dB
Bob Quintal
> 222 51358 <3b643d6c...@news.swbell.net> article retrieved - body follows
bulb, which I used for years is about 1/4 ohm cold. Music peaks won't
warm it sufficiently until the power becomes excessive. and it protects
much more transparently than your relay and zeners.
> -dB
>
ChuxGarage
>>electroncic crossovers with built in dc protection!!
A cheap fix to idiot proof your stuff is a #1156 12 volt lamp wired in parallel
with a 10 ohm 25 watt (or larger) resistor. At normal levels, the insertion
loss is neglegible. If somebody really floggs the system, the light goes on
and its resistance increased dramatically as the filament heats up. Unlike
using just a bulb, (which makes all the highs go away when the lamp lights up)
this arrangement keeps audio on, just at a lower level. I've never plotted the
actual resistance, but it seems to do the trick most of the time.
Usually our rental customers blow the bulb and/or resistor. Occasioanlly they
take out the bulb, the resistor and the driver, but the driver failures are
much lower than with no protection. The renters alway say they weren't running
it very loud when they blow all that stuff up.
Hmmm?
They usually are also the same guys who bring speakers back with woofers that
have literally caught on fire and burned the cone, not just the voice coil.
Of course, they weren't running them very loud at all...
Chuck Conrad
Crossroads Audio, Inc.
André Huisman
> > The only thing I don't like about this approach is that power is being
> > consumed at all times. Consider a circuit with zener diodes, relay,
> > etc., that only introduces these limiting elements when the voltage
> > level approaches the danger point.
> The impedance of a lamp bulb is very low until it gets hot. A # 1157
> bulb, which I used for years is about 1/4 ohm cold. Music peaks won't
> warm it sufficiently until the power becomes excessive. and it protects
> much more transparently than your relay and zeners.
So the TC of the fillament isn't constant? And it's heat-up time is long? It
protect more transparently than a relay? Are you sure about all this.
IMO/IME The TC of the fillament is pretty constant. This means the
resistance increases quite lineair with temperature (and power). The heat-up
constant of the bulb is pretty short (otherwise it just wouldn't protect).
Due to this, it WILL have a compressor effect. It certainly is NOT more
transparant than a relay or a fuse. The latter only kicks in when triggered
and is dorment when not triggered. There's one thing that speaks for the
lightbulb: It's cheap. SO you can probably find it in cabinet in a price
range comparable to the lightbulb: Cheap!
The nice thing about using a fuse is that when a user screws up, it becomes
obvious to everyone (highs are gone). Another option is the use of a
polyswitch. This is a type of fuse that will be pretty (very) low impedance
as long as current rating isn't exceeded. It'll temporarily go high
impedance once the current rating IS exceeded. It's self resetting AND quite
transparant as long as you don't trigger it.
If you want to use a lightbulb then you'd best make DARN sure to incorporate
it's behavior into the design of the filter. Doing so requires a lot of
knowledge on speaker design. Once you have aquired such an amount of
knowledge, you'd probably end up NOT using the lightbulb (since you will
then have found out that the interaction between filter/speaker/lightbulb is
degrading the performance of your speaker) and you'll probably go for the
polyswitch. It's just that manuf. take a long time to find out new stuff to
put in their boxes (and if they can save a buck here and there, they WILL).
Yes, in some cases, the lightbulb/speaker/filter interaction might actually
be beneficiary DUE to it's NON transparant nature. As to which size/type
lightbulb for which speaker... That requires probably destructive tests to
beyond the budget of the average DIY'er AND/OR incorporates a substantial
amount of ASCII in the mathematical department.
Find the behavior of the polyswitch offensive (it turns off temporarily once
triggered)? Incorporate it into a seperate pad so it doesn't temporarily
switch off the driver but pads it by say 6dB. Add another polyswitch and you
can make a double staged pad. Etc. etc. etc.
Nice thing about polyswitches and protection other than a lightbulb: It
doesn't turn your speaker into a lighting effect. I've seen the lightbulb
used in JBL Control-5 speakers. That's exactly the type of speakers where
IMO they should be used in: Speakers of low budget and non important use
(wallpaper music). I've also seen them in some big Community speakers. I
just had to laugh (no matter how much others may like this brand)! Every
time the singer opened his mouth, the speaker cabinet went from acoustic
mode to incandescent mode. I just had to laugh!
--
André Huisman
New-Line licht & geluid
Phil Allison
André Huisman <see_pos...@il.ok> wrote in message
news:DZ897.339546$u5.67...@zwoll1.home.nl...
Aristotle would love you, Andre, your ability to do thought experiments and
draw conclusions is second to none.
Compared to doing real experiments it saves so much time too.
Regards, Phil
André Huisman
> Aristotle would love you, Andre, your ability to do thought experiments
and
> draw conclusions is second to none.
Thanks (I think?).
> Compared to doing real experiments it saves so much time too.
Well, actually I DID do some experiments on some car lightbulbs I had lying
around (when this discussion took place the last time (a month or two
ago?)). I measured them "cold", hot and 4 positions in between. That simple
measurement DID reveal that normal fillament bulbs have a pretty constant TC
(and the difference between cold and hot is about a factor of 10; give or
take). With halogen bulbs, the difference was roughly a factor of 12 (higher
operating temp probably).
I occasionally actually design speaker cabinets. Have done so for about 15+
years or so. And YES, it requires both thinking (even thought experiments)
as WELL as actual experiments. And NO, I'm not fond of the lightbulb. Manuf.
are taking efforts to reduce power compression to below 3dB and here we go
slamming a lightbulb on it (totally voiding the effort all together).
I'm sure it works wonderfully in POS cabinets! I just like to aim a bit
higher than designing POS cabinets. In my smaller cabinets (passive full
range 12"/1") a simple set of resistors pads the signal to the HF driver.
With about 100 cabinets out there (some in my possession, most in the
possession of users), NO-ONE has blown an HF driver _yet_ (1" compression
driver, 44.4mm diaphraghm, system design is roughly 6 years old) and only
one has blown the series resistor. On the bigger cabinets the protection is
covered by the speaker processor. Some 32 cabinets are out there and only
one HF driver was blown (in my rig, somewhat my own fault, due to shortage
on proper equipment, this system went out on a rental take-away with a
Super-X 2300 in it (yes, I know, shouldn't have done that BUT it was one of
those "5 minutes to curtains" kind of things)).
André Huisman
Hello Phil,
I read an article that might actually offer a sollution to both of us (I was
actually quite taken with the idea). It uses a polyswitch, rated at about
50% of what one would normally use (I'd use it a tad higher ;-), bypassed
with a lightbulb of correct size.
Probably a "best of both worlds"? It offers the transparancy of the
polyswitch (up to a point), including not touching the signal purity. Once
the polyswitch's rating is exceeded, the lightbulb takes over with it's
compressor action.
http://www.electrosound.com/articles/safesound.html
Any suggestions as to what to start off with for a 16 Ohm 1" compression
driver, used from 2kHz and up with a continuous power rating of 40W (above
1kHz) / 60W (above 2kHz)?
I was kind of thinking about a 1.5A polyswitch with 2-3 brakelights (21W
each) in series, parallel to this polyswitch.
BTW: The 20+ Ohm series resistance between amp and 4th order passive filter
WILL have some strange side effects on said filter's transfer function.
Didn't even have to fire up Aristotle for that ;-) But then again, if you're
trigering the lightbulbs in the above scheme, you're already pushing things
beyond intended use.
Phil Allison
André Huisman <see_pos...@il.ok> wrote in message
Andre,
I think you are on to something practical with auto lamps and a parallel
polyswitch to delay the action of the lamps.
First measure the DC resistance of the horn diaphragm, if it is around 12
ohms thats fine.
Experience tells me to use slightly lower values for the polyswitch and the
bulbs, say 1.35 amps trip and 3 x 15 watt lamps. A 16 ohm horn will heat
twice as much at a given current as an 8 ohm, for this type of cct you must
think in current.
The thing to determin is the average horn current at the highest levels
still considered normal, I suspect about 1 amp rms for your 16 ohm.
Remember, the high frequency peak to average ratio is much bigger than for a
full range signal.
I think you should now do a real experiment and damn Aristotle.
Regards, Phil
Bob Quintal
> 222 51415 <DZ897.339546$u5.67...@zwoll1.home.nl> article retrieved - body follows
> "Bob Quintal" <bqui...@generation.net> wrote:
> > The impedance of a lamp bulb is very low until it gets hot. A # 1157
> > bulb, which I used for years is about 1/4 ohm cold. Music peaks won't
> > warm it sufficiently until the power becomes excessive. and it protects
> > much more transparently than your relay and zeners.
>
> So the TC of the fillament isn't constant? And it's heat-up time is long? It
The Temperature Coefficient of a tungsten filament is closer to
exponential and even if linear, the increase of temperature is in the
order of several decades. Don't forget that the average dissipation is
what generates the temperature rise in the filament. The Effective
resistance at normal conditions (12VRMS) is about 1 Amp. for a 1157
lamp. When the music has only bursts of HF sound like a cymbal hit, the
average power isn't enough to cause the lamp to glow, but if the HF
content goes up, then the lamp does not cool enough between bursts and
its resistance rises. This divides the power between the lamp and the
driver. this can be a gradual effect over a fraction of a second to
several seconds.
> protect more transparently than a relay? Are you sure about all this.
the relay will change the level in a step fashion when it switches.
The difference is like compression vs limiting.
>
> IMO/IME The TC of the fillament is pretty constant. This means the
> resistance increases quite lineair with temperature (and power). The heat-up
> constant of the bulb is pretty short (otherwise it just wouldn't protect).
> Due to this, it WILL have a compressor effect. It certainly is NOT more
> transparant than a relay or a fuse. The latter only kicks in when triggered
> and is dorment when not triggered. There's one thing that speaks for
And the transition between dormant and activated is pretty grating to my
ears. The variation in output from a lamp is much more palatable.
Several compresssors from the early years used a lamp and two Light
dependent resistors in a t network.
the
> lightbulb: It's cheap. SO you can probably find it in cabinet in a price
> range comparable to the lightbulb: Cheap!
>
> The nice thing about using a fuse is that when a user screws up, it becomes
> obvious to everyone (highs are gone).
That's fine if your customers will live with the absence of highs for
half a set.