• The move to the new server is done. There are some software and database maintenance updates in process. This has us passing the hat around to help out. We appreciate any donations. Seriously, even a dollar helps. The payment page may be found here - https://www.audiokarma.org/support.html

Light bulb in a crossover??????

jameselmer66

jameselmer66

Active Member
Okay, I have been an audio geek going on 30+ years. Don't even come close to knowing everything about audio. But I have gained some considerable experience over the years. I just acquired a pair of Mach 2 speakers. I don't remember ever having these or the Mach 1's in the past. So I promptly take them apart to see what they are made out of. Not bad, braced cabinet, decent components and then I get to the crossover. Looks like a quality built crossover but I notice that where one of fuses are supposed to be is an appliance light bulb. First time for me. At first I thought it was a hack job by a previous owner but after coming across a online Radio Shack inventory parts list I seen a comment line under the Mach 2 heading stating that 27 watt light bulbs could be used in place of fuses. Was this a common practice in the 70's and 80's for crossover building? Any comments would be appreciated.
 
Register to hide this ad
Common, eh, not so sure about that, but yes there are a number of designs that used them.

The resistance of the filament goes up as it gets hotter, which happens as you dump more power into the speaker, thereby serving to act as a power limiter.
 
EV used them as well. My Interface D's have the bulb. If I recall correctly, it's not much more than a 12v automotive type bulb.

I don't know if the speaker prefers a brakelight or blinker bulb...:scratch2:
 
Yeah, my old Bose 501's had a #211 12 volt "fuse style" bulb in the crossovers. I think they served to protect the tweeters.
 
Before a house fire took them away, I had a set of little Optimus speakers with Linaeum tweeters- they had light bulbs inside. I knew I should turn the volume down when they would light up bright! I could see the glow coming out of the port in the front.
 
Thanks

Thanks guys for all the comments. Really interesting though, I would have thought that over the last 30 years I would have seen this by now. Goes to show you learn something new everyday. And you all are right it is a 12 volt bulb. A yellow turn signal bulb at that. :D
 
I have some HH Scott speakers from the 70's that have a 12V GM dome light bulb in them. Kind of surprised me too.
 
The old UREI 813 crossovers for the Altec 604s used them as well -- and right up front for all the world to see. I think some Mastering Labs crossovers did too.
 
Some of the lower-end JBL Pro speakers use them as power limiters for the horns...TR series, for one. If you see the ports glowing on these speakers, turn it down! :D

je
 
We used a lot of these in car component speaker crossovers. Used to call them "optical compressors", lol...

John
 
I will never forget my first exposure to the light bulb xover. I was sitting around in a dark room listening to a set of EV Interface D's (I think it was) and really slaming them hard- through the port tube I kept seeing a glow appear on the transients- I instantly got worried that I was heating up the inductors into a state of glowing red hotness! Later after I went back to the store I bought them (second hand) I told them of my experience and they had a real good laugh on me and them told me about the light bulb current limiter. I felt like an idiot after that, then laughed at myself as well!
DC
 
Coytee said:
It's pretty darn loud when a pair of D's is lighting off
Click to expand...

Damn skippy on that one!! EV's were the only speaker I could push to the wall and watch the bicks shatter........and have enough light left over to read by!!
DC
 
audiomagnate said:
The original HP product was an audio oscillator that used a light bulb to minimize frequency variations.
Click to expand...

The HP 200A lamp is used in a feedback divider circuit, to stabilize output amplitude against changes from numerous causes, one of which is oscillator gain variation at different frequency settings. This takes advantage of the same property of lamp filaments that's useful in speaker systems, but for a different purpose. Modern polymer PTC (positive temperature coefficient) thermistors are used for speaker protection in precisely the same way as lamp filaments.
 
I can understand why the manufactures put the bulbs in (as this thread explains in detail) but I have removed my Light bulb from my Mach II's to hear much improved sound from the midrange unit.

I guess its like using really cheap thin wire if they put a bulb in there.

The signal will go from 79 strand > 15/25/40 strand multicore from the binding posts to the xover > copper board and componants of the highest quality > tiny thin bulb wire > 20/40 strand to the driver unit.

The extra detail I can hear without the blub is very noticable
 
Last edited:
You must log in or register to reply here.
Back
Top Bottom