Looking through many, many specs, I dont seem to find any air temperature range specs.
In addition, I see many posts that seem to say that performance is related to air temperature. When a driver is spec'd out, does anyone know what the standard air temp is for that spec?
I had this failure on a 2" 4591...any thoughts? 50W 3500Hz...
Thanks for any help!
In addition, I see many posts that seem to say that performance is related to air temperature. When a driver is spec'd out, does anyone know what the standard air temp is for that spec?
I had this failure on a 2" 4591...any thoughts? 50W 3500Hz...
Thanks for any help!
An externally hosted image should be here but it was not working when we last tested it.
Air temperature for driver testing is generally considered to be "room temperature", around 70 F. The temperature within a driver will increase quite a bit over the ambient temperature if high power limited dynamic range program is used, but the BMS drivers are tested and rated using a signal with only 6 dB crest factor, much less than typical program material. The diaphragm itself would not have a problem from heat in any normal environment, the voice coil and former would burn first.
The failure you photographed appears to be excursion related, the voice coil shows no heat discoloration, perhaps your crossover was at 50 Hz rather than 500 Hz or some such error. I once lost a half dozen diaphragms due to a coil winding error causing the crossovers to be off by a couple octaves
.There is a possibility of defective material, but BMS has good quality control, so unlikely.
Did you examine the debris for any evidence of any foreign material, a metal fragment or such?
What does "50W 3500Hz..." have to do with the destroyed diaphragm?
Art
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Simply showing what was sent to the driver when it failed.
I didnt find anything but the pieces of plastic...
I am more concerned about operating air temperature. It can get below freezing and above 55C. Would that have an effect?
Yes, I have sent these images to BMS as well...
As far as quality control, I do have some issues...I have 30 of these drivers, and it looks like one of the threaders on the cnc machine was going bad, on almost all of them, one of the bolt holes for the feedhorn was badly threaded, and on 2 of them, the hole was not threaded at all.
Not sure if it matters, but the sealant job on the coil leaves a bit to be desired....(the sanded effect is a bit strange as well)
An externally hosted image should be here but it was not working when we last tested it.
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The freezing end would be a concern, condensation inside the driver could lead to a layer of ice on the diaphragm and a stuck voice coil that could cause tearing if a large signal was applied. The weight added by ice would also change the diaphragm resonance, so a midband chirp might be "just right" to kill it, even if the coil was not frozen. A friend of mine that provides outdoor sound in winter conditions leaves low level pink noise on at night to avoid the "frozen driver syndrome".
One time in Minnesota, running late for a set up, the frozen drivers did not have a chance to warm up before sound was run through them, it sounded like the JBL 2420 HF drivers were shot until they freed up.
Do you know the temperature of the driver when the damage occurred?
Any of the 30 other diaphragms show problems?
Have you conducted an impedance sweep of the driver on the horn you use?
Thanks for all of the replies..still working with BMS on this....they say the drivers can work to -40F.
I really dont think it got that cold out, but I need to be prepared for that eventuality. The low level signal, pink noise, all great advice.
Really odd failure...
EDIT: If anyone wants any measurements of the insides, let me know...
I really dont think it got that cold out, but I need to be prepared for that eventuality. The low level signal, pink noise, all great advice.
Really odd failure...
EDIT: If anyone wants any measurements of the insides, let me know...
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