Hi, I've get my first pair of B&C 21SW152-8 and some questions were raised.
Firstly I've break-in them with shaped bursts of 12Hz sine, with cone travel ~2-2.5cm p-p, duration more than 50 hours for today.
1) After that, measured TSP and see that Cms is much lower than expected, this leads to Fs 41Hz and shift of all derivative parameters, like Vas=133, higher Qts. If I only substitute measured Cms with expected from datasheet, then derivative parameters excellently fit with datasheet. What should I do, continue break in, use measured TSP or datasheet TSP?
2) During break-in one driver started to making clicking noises in spider. Clicks happen when cone moves inward, clicks felt by fingers in spider, only on one side and near to outer of spider. Youtube what is might be and how to deal with it?
This noise prevents me from TH like designs 😕
Firstly I've break-in them with shaped bursts of 12Hz sine, with cone travel ~2-2.5cm p-p, duration more than 50 hours for today.
1) After that, measured TSP and see that Cms is much lower than expected, this leads to Fs 41Hz and shift of all derivative parameters, like Vas=133, higher Qts. If I only substitute measured Cms with expected from datasheet, then derivative parameters excellently fit with datasheet. What should I do, continue break in, use measured TSP or datasheet TSP?
2) During break-in one driver started to making clicking noises in spider. Clicks happen when cone moves inward, clicks felt by fingers in spider, only on one side and near to outer of spider. Youtube what is might be and how to deal with it?
This noise prevents me from TH like designs 😕
The driver will remember that. I know that some recommend brutalizing a bass driver like that to breal it in, but it will also break the spider as in the signal used will impose itself as a permanently remembered trait. Slow, steady, varying signal is what i do.
dave
The B&C 21SW152-8 has an Xmax of 15mm, 30mm peak to peak, Xlim of 60mm peak to peak. At 25 mm, the driver is not even reaching it's linear excursion, so is not broken in, and won't be broken by that excursion.
The driver suspension is probably not broken in yet, and after it is you still may need a higher test voltage than you used to measure near it's proper Fs of 32Hz. I'd use the datasheet TSP unless the driver is actually defective.
460 grams of moving weight cause a lot of shaking. The "woodpecker" sound in your video link sounded like the driver magnet structure hammering the table it was on- the entire driver appeared to be moving.
Do you hear any noise when you push the driver cone evenly by hand inward 15-30mm?
Art
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weltersys,
Thanks for Xlim value, I've missed it from datasheet and had doubts about maybe this noise coming from coil beating the magnet.
I'm sure there is no any interaction of driver and table because it happens even when I hold driver in hands. I've pushed driver cone inward as much as I can without standing on hands, cone moved ~15-20mm. Dead silence from driver.
planet10,
did you measure Fs during your process of break-in? Is it decreased to stable value over time?
Thanks for Xlim value, I've missed it from datasheet and had doubts about maybe this noise coming from coil beating the magnet.
I'm sure there is no any interaction of driver and table because it happens even when I hold driver in hands. I've pushed driver cone inward as much as I can without standing on hands, cone moved ~15-20mm. Dead silence from driver.
planet10,
did you measure Fs during your process of break-in? Is it decreased to stable value over time?
I always broke the drivers in first, 2-300 hrs min at low level with FM.
What we typically measure with the kit available to typical diyers, the numbers you generate will probably not be as useful as the factory numbers.
The kit we use collapes the T/S curves to scalars at a different place. I only ever used them for driver matching (except when i had nothing else to work with, those boxes i would like to make a but bigger, not a failure i have has with factory numbers).
dave
What we typically measure with the kit available to typical diyers, the numbers you generate will probably not be as useful as the factory numbers.
The kit we use collapes the T/S curves to scalars at a different place. I only ever used them for driver matching (except when i had nothing else to work with, those boxes i would like to make a but bigger, not a failure i have has with factory numbers).
dave
If only one driver has the noise, then it is defective.
That said, if you hear no noise pushing the cone by hand, I'd suspect the shaped bursts of 12Hz sine may have a square wave component, like the DC click you hear when using a battery to test polarity. Try using a normal sine wave.
You also said the clicks happen when cone moves inward, if you reverse the signal polarity and the clicks happen on the outward stroke, that also would confirm a problem with the signal.
That said, if you hear no noise pushing the cone by hand, I'd suspect the shaped bursts of 12Hz sine may have a square wave component, like the DC click you hear when using a battery to test polarity. Try using a normal sine wave.
You also said the clicks happen when cone moves inward, if you reverse the signal polarity and the clicks happen on the outward stroke, that also would confirm a problem with the signal.
Dave,
Pro subwoofers like the B&C 21SW152-8 are designed to be pushed past Xmax on the first use with no ill effects.
Professional users would not accept a product that would require 300 hours of break in, or a driver broken when used within it's rated parameters.
Art
After they are broken in. When they aren’t extreme ecursions will leave a memory in the spider. Slow & steady ramp-up is recommened for best performance
dave
dave
Hello Dave, what wave file and how many watts for how long to correctly break in a driver .
Same for car drivers ? Vs PA
Same for car drivers ? Vs PA
I also have two 21SW152-8 since 2017 and the only nasty sound I ever heard was from an amp that couldn't deliver enough power. I never bothered to break them in and I'm more than happy with the infrasonics they produce 😉 Currently they're in separate 540L LLT enclosures but I'll soon build smaller boxes as I don't really need single digit frequency response.
Examine the glue joint where the tinsel leads enter the cone.
I suspect you will find that the adhesive surrounding this wire, while completely surrounded, may not be adhered entirely all the way around to the lead. When the lead vibrates, it ticks against this part that is close to the wire.
you can CAREFULLY trim this off. Tick gone.
I suspect you will find that the adhesive surrounding this wire, while completely surrounded, may not be adhered entirely all the way around to the lead. When the lead vibrates, it ticks against this part that is close to the wire.
you can CAREFULLY trim this off. Tick gone.
Attachments
I have never heard of this. What is the memory mechanism and its effect? Data please.
Further, why are we not recommended a break-in schedule by B&C or warnings about doing it incorrectly?
No idea.
Spider is coated with stuff you need to “break”. If you do it with emphasis you will break it in such a way that the spider remembers.
dave
Spider is coated with stuff you need to “break”. If you do it with emphasis you will break it in such a way that the spider remembers.
dave
Measure tsp after "breaking in". Repeat one day later. Your result will vary. Get confused. If close to factory values, use that. In most cases you do not know how the TSP was measured and the factory did better than you. A few % difference may be production tollerance, too. If you got two or more, measure all of them, it may give you an idea how much they vary.
TSP can give different resulis, depending on voltage used. A lot of people prefer a higher input signal that really moves the suspension, instead of just some millivolt. This also reduces background noise. Be sure to have some space around the chassis. Avoid measuring on hard surfaces, at least put some foam under it. Be sure driver and room temperature are close to 20°Celsius.
Do not measure a driver that has heated up from breaking in, leave it to cool down for an hour. You want compareable results.
I use to measure in a large room, the chassis clamped at the magnet on a stand 1m high. I use a thin rope fixed at the ceiling, securing the driver, as it happens the clamp slips from vibration. Do not ignore this! Otherwise you may need a new driver...
Some drivers do not change tsp from breaking in at all, like soft HIFI woofer. Some do return to initial values after a few hours. Some change permanently, usualy the "hard" boys.
TSP can give different resulis, depending on voltage used. A lot of people prefer a higher input signal that really moves the suspension, instead of just some millivolt. This also reduces background noise. Be sure to have some space around the chassis. Avoid measuring on hard surfaces, at least put some foam under it. Be sure driver and room temperature are close to 20°Celsius.
Do not measure a driver that has heated up from breaking in, leave it to cool down for an hour. You want compareable results.
I use to measure in a large room, the chassis clamped at the magnet on a stand 1m high. I use a thin rope fixed at the ceiling, securing the driver, as it happens the clamp slips from vibration. Do not ignore this! Otherwise you may need a new driver...
Some drivers do not change tsp from breaking in at all, like soft HIFI woofer. Some do return to initial values after a few hours. Some change permanently, usualy the "hard" boys.
Since measured T/S depends on the “weather”, so to compare properly the DUTs need to be measured at teh same time.
You would need a pressure/temperature/humisity constant room to test over mutiple days.
dave
This is what I wanted to point out, too. TSP are not constant. The variations do make for a few % of difference, even on minor changes in humidity, temperature and pressure. So if you get near the factory specs, if these are measured correctly and recently, you are fine.
.
A lot of Chinese chassis I know, and a lot of good drivers come from balloon country, are advertised with up to 20 year old measurement sheets. Usually nothing is the same, if such a driver from a fresh production is measured today. Expect magnet material, cone, spider and tolerances in most important areas to be very different. I think it is essential to make your own measurements. Anyone who is in speaker building should be able to spent 1$ to buy the wire and single resistor needed to do these..
.
A lot of Chinese chassis I know, and a lot of good drivers come from balloon country, are advertised with up to 20 year old measurement sheets. Usually nothing is the same, if such a driver from a fresh production is measured today. Expect magnet material, cone, spider and tolerances in most important areas to be very different. I think it is essential to make your own measurements. Anyone who is in speaker building should be able to spent 1$ to buy the wire and single resistor needed to do these..
@MrKlinky
Fibers etc in the whole suspension do have the 'memory'. when the force is applied on the fibers, they will soften. And those fibers will not heal by themselves. The change from measuring after break in and measuring again the next day would have to do more with temperature.
Fibers etc in the whole suspension do have the 'memory'. when the force is applied on the fibers, they will soften. And those fibers will not heal by themselves. The change from measuring after break in and measuring again the next day would have to do more with temperature.