Two thoughts:
The BMS 18N862 - while being very good drivers - have a comparable light cone. Its rather built for closed or ported enclosures. It provides a lot of xmax, but I am not sure if the cone strenght is suited for higher compression ratios. Its not a typical "horn suited driver".. But I haven´t tried it in this enclosure, so its just a thought...
When listening to your video, the sound is a very hard clicking. Sounds coming from the cabinet usually have a more soft thumbing like sound (wood on wood), this sounds more like metal to metal... A cone slapping onto wood also sounds different,,,
I can only guess without having the drivers in my hand, but it sounds a little like something is loose in the motor of the driver...
Could you try the following: Place the driver upside down on a flat, rugged surface. The concrete floor of a basement for example.. Make sure, the surround gives enough high to allow the cone some mm of movement, so the cone won´t hit the floor when moving forward. If in doubt, place a spacer ring under it.
Now apply some sine noise of 10Hz and increase the volume Slowly while pressing the driver down on the floor. The air tighter the whole "chamber" under the cone is - the better.... How does it sound? Don`t go full power, it will stress the cone too much..
Another test: Hold the woofer freeair - now you can turn up the volume much higher, there is almost no resistance on the cone and you can achieve more travel distance.. Do the 10 Hz thingy...
The BMS 18N862 - while being very good drivers - have a comparable light cone. Its rather built for closed or ported enclosures. It provides a lot of xmax, but I am not sure if the cone strenght is suited for higher compression ratios. Its not a typical "horn suited driver".. But I haven´t tried it in this enclosure, so its just a thought...
When listening to your video, the sound is a very hard clicking. Sounds coming from the cabinet usually have a more soft thumbing like sound (wood on wood), this sounds more like metal to metal... A cone slapping onto wood also sounds different,,,
I can only guess without having the drivers in my hand, but it sounds a little like something is loose in the motor of the driver...
Could you try the following: Place the driver upside down on a flat, rugged surface. The concrete floor of a basement for example.. Make sure, the surround gives enough high to allow the cone some mm of movement, so the cone won´t hit the floor when moving forward. If in doubt, place a spacer ring under it.
Now apply some sine noise of 10Hz and increase the volume Slowly while pressing the driver down on the floor. The air tighter the whole "chamber" under the cone is - the better.... How does it sound? Don`t go full power, it will stress the cone too much..
Another test: Hold the woofer freeair - now you can turn up the volume much higher, there is almost no resistance on the cone and you can achieve more travel distance.. Do the 10 Hz thingy...
Hey Sabbelbacke,
Thanks for the reply, i appreciate it!
I know exactly what you mean by sounding metallic and both me and my dad can't understand exactly what's going on here! But i did use a 5hz sine wave for around 30 seconds already and the excursion was pretty much to Xmax and there was not one peep from the motor, at all. it was actually quite beautiful to see lol
I also did the free air test as well and absolutely no noise from the motor, as far as i could hear. This is why I'm so baffled as to what the problem is.
I think I'll do the tests again in free air and really make sure I'm not hearing anything from the motor and I may have to buy another driver to at least test the cab but I really don't wanna spend anything at this point, to be honest!
Just to add, i have 2 of these drivers and cabs and they both have the exact same problem. I know both drivers can be damaged but I just don't see how as i haven't used them much over the last 2yrs and the max power i've given them is around 2kw and nowhere near xmax.
Thanks for the reply, i appreciate it!
I know exactly what you mean by sounding metallic and both me and my dad can't understand exactly what's going on here! But i did use a 5hz sine wave for around 30 seconds already and the excursion was pretty much to Xmax and there was not one peep from the motor, at all. it was actually quite beautiful to see lol
I also did the free air test as well and absolutely no noise from the motor, as far as i could hear. This is why I'm so baffled as to what the problem is.
I think I'll do the tests again in free air and really make sure I'm not hearing anything from the motor and I may have to buy another driver to at least test the cab but I really don't wanna spend anything at this point, to be honest!
Just to add, i have 2 of these drivers and cabs and they both have the exact same problem. I know both drivers can be damaged but I just don't see how as i haven't used them much over the last 2yrs and the max power i've given them is around 2kw and nowhere near xmax.
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If you create a situation where the noise is present - can you pinpoint the location of the origin in the cab by listening/moving your head to the source ?
nah it's impossible to figure it out. I did try that but it just sounds the same everywhere. I remember that i did try and put pressure with my fingers on various parts of the cone while testing and it did change the noise somewhat. I'll try and get a video done tonight of that test!
My problem is the 5hz and freeair tests i did, completely contradict the theory of the driver being at fault here?
My problem is the 5hz and freeair tests i did, completely contradict the theory of the driver being at fault here?
Using a cardioid mic and headphones make listening to a specific areas of the cabinet much easier, and at a far lower volume than putting your head inside it. You could cut the LF on the mic to make the problem easier to hear whether you have plywood delamination slap or cone/voice coil flap.
The BMS 18N862 Xmax is 19mm, 38mm (1.5") peak to peak, the video did not seem to approach that much excursion.
As Sabbleback mentioned, the light cone may not be up to the stress.
it may start rocking at less than Xmax due to uneven stresses, if it is the driver a deep narrow cut at one specific frequency may calm it down.
The BMS 18N862 Xmax is 19mm, 38mm (1.5") peak to peak, the video did not seem to approach that much excursion.
As Sabbleback mentioned, the light cone may not be up to the stress.
it may start rocking at less than Xmax due to uneven stresses, if it is the driver a deep narrow cut at one specific frequency may calm it down.
What is the compression ratio of your design?
What is the nominal compression ratio where that driver was used?
As most of the people here than know their stuff pointed out , is possible that the cone is not strong enough to withstand the compression ratios.
You said you are on your third cabinet and looks like the 1st one sound ok?
What if you remove the driver from the 1st "good" cab and stick it on the third.
If it sound ok ...is your other drivers
If slaps it means something wrong on your latest build.
Dimensions or something.
My 2 cents.
Max.
Guys, im not sure why i didn't discover this on my last free air test but it's the drivers! both doing exactly the same....bad batch maybe?
Now, the sound is worse at around 60hz but if i do 30-40hz the sound disappears. This says to me it could be loose tinsel leads on the inside of the dustcap?? on the outside the leads are rock solid and tried to put some foam between the outside tinsel leads and the cone and didn't make a difference. Also, If i put my finger just slightly on the cone while the noise is appearing, it seems to dampen the noise. if i press slightly harder, it goes away. for me this points to something loose rather than a broken motor.
What'd you reckon?
Any suggestions on getting the dust cap off?
Now, the sound is worse at around 60hz but if i do 30-40hz the sound disappears. This says to me it could be loose tinsel leads on the inside of the dustcap?? on the outside the leads are rock solid and tried to put some foam between the outside tinsel leads and the cone and didn't make a difference. Also, If i put my finger just slightly on the cone while the noise is appearing, it seems to dampen the noise. if i press slightly harder, it goes away. for me this points to something loose rather than a broken motor.
What'd you reckon?
Any suggestions on getting the dust cap off?
looks like you got a bad batch , maybe those 2, cause the 1st cabinet sound ok ?
do you have warranty ?
is BMS lowering their QC ?
do you have warranty ?
is BMS lowering their QC ?
yeah the first cab was definitely fine. no warranty im afraid.
Ha, who knows man, but i'm just hoping it is that cos i'm not paying £1600 to replace 2 drivers!
Ha, who knows man, but i'm just hoping it is that cos i'm not paying £1600 to replace 2 drivers!
well i've taken the cap off and everything looks absolutely fine! the leads are fully secured and glued in with no movement whatsoever! everything else is rock solid and well built. not sure what else it can be! Will probably speak to BMS tomorrow and see what they suggest.
Attachments
just waiting for an email back from their tech guy. i do feel like i'm gonna have to change them!
I was wondering the same thing.
You want to be under 3 to 1. Similar to BR and BP ports being no smaller than 33% of Sd.
24" = 8" port.
21" = 7" port.
18" = 6" port.
15" = 5" port.
12" = 4" port.
8" & 10" = 3" port.
6.5" = 2" port.
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I think BMS have some of the stronger motors in 12" and 15" ,18" not so sure but BMS is top 5 worldwide brand,.
18sound , Beyma , B&C , RCF , Ciare, Eminence , Radian. Just to say some good names.
i wish i can tell you the ratio but i have no idea. all i can say is it's the exact same designs as XOC but using the BMS drivers.
I got the response from BMS this morning. This is what he said.
on a side note, these cabs are not used very often and were not used during covid for almost 2yrs.
I've never got these close the xmax so it seems that this has happened during them just sitting there not doing anything for almost 2yrs! A recone it is then.
I got the response from BMS this morning. This is what he said.
on a side note, these cabs are not used very often and were not used during covid for almost 2yrs.
I've never got these close the xmax so it seems that this has happened during them just sitting there not doing anything for almost 2yrs! A recone it is then.