Fantastic cabinet work!
Can you please explain the carbon fibre finish? - material, application, finishing, polishing etc. I may try, too.
Can you please explain the carbon fibre finish? - material, application, finishing, polishing etc. I may try, too.
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I'm not sure what needs explaining. It is 5HS carbon fiber fabric laminated over the MDF. After it cured, I removed the peel ply and painted on a layer of epoxy to fill the peel ply texture. Then sanded and sprayed with 2k urethane clear coat.
The speaker in the photos is effectively still a prototype, and I don't think I'll do carbon the same way for the final speaker. I'm still weighing my options as other projects are taking priority right now. Either I'll make thin composite CLD panels, or I'll be boring and do MDF with gloss black finish.
Can anyone give some insight into my distortion measurements here? I'm looking at the 3rd order distortion from my "woofer". The woofer has higher distortion than the subs, although I believe it is all inaudible. It just doesn't look that nice in measurements, so I'd like to understand it.
The woofer is the new B&C 12TBX100. Of my two measurements below, the lower SPL level test had relatively high 3rd order distortion. But when I increased the SPL by ~10dB, the 2nd order distortion increased to roughly match the 3rd order.
My theories--is this caused by relatively small sealed cabinets? Or is this relative change of 3rd order distortion related to the demodulation rings becoming more effective with the higher SPL measurement?
When I model the drivers, they don't seem to care what size cabinet they are in.
I know the 12TBX100 has demodulation rings. I first ordered the 12PS100 since it modeled nearly identically, and I had not yet realized why the 12TBX100 was slightly more expensive. But then I realized the 12PS100 is missing the demodulation rings. So I sent them back and exchanged for the 12TBX100s. I'm not sure if the demodulation rings actually make a difference between 60hz and 500hz, but I've read they don't do anything below 100hz...
The woofer is the new B&C 12TBX100. Of my two measurements below, the lower SPL level test had relatively high 3rd order distortion. But when I increased the SPL by ~10dB, the 2nd order distortion increased to roughly match the 3rd order.
My theories--is this caused by relatively small sealed cabinets? Or is this relative change of 3rd order distortion related to the demodulation rings becoming more effective with the higher SPL measurement?
When I model the drivers, they don't seem to care what size cabinet they are in.
I know the 12TBX100 has demodulation rings. I first ordered the 12PS100 since it modeled nearly identically, and I had not yet realized why the 12TBX100 was slightly more expensive. But then I realized the 12PS100 is missing the demodulation rings. So I sent them back and exchanged for the 12TBX100s. I'm not sure if the demodulation rings actually make a difference between 60hz and 500hz, but I've read they don't do anything below 100hz...
Yes - I regularly get these results with PA drivers! Like the well known 18Sound 8NMB420 - has very high THD at low levels.
It's just not very well spread knowledge ...
I ASSUME it has to do something with the spider/surround/??? - some "limiting" of the movement at smaller levels. But could be completely wrong cause other, similar build drivers don't have this limitations.
SB Acoustics 10" woofer drivers also show similar behaviour at midrange frequencies (not at low frequencies) - high H3 which stays more or less the same when level rises. Very unusual for THD.
My solution - test all drivers by myself before using and comparing a bunch for a serious project. Don't select from datasheets ... doesn't work for top notch projects.
That sounds expensive! There are not many drivers that can do what I am asking this one to do, so I probably have to stick with it.
But I'm curious if enclosure volume has any affect on the distortion? I think it is odd that I'm seeing this 3rd order distortion.
A proper development is expensive. Throwing chassis together and knit a network is less expensive. It depends on your goal ;-)
But there is a reason why most bigger studio speaker manufacturers use PHL driver for low frequencies. They also have modern high power 12" drivers - I would start there.
I would bet it's not the closed volume. Build a test volume and measure to be sure.
I understand. I have atleast $100k invested in my carbon fiber knee pad project, which is a simple object. It's actually designing all the molds and testing materails that is expensive and time consuming. I am now on the verge of being ready to sell something! I should be working on that right now, but I'm letting myself be distracted.
This speaker thing is just a hobby.... And I believe what I'm looking at is not audible...just for the record.
This afternoon I remembered the initial up close measurement of these drivers was really good, so I repeated that again. Up close, at the center of the driver, it is nearly flawless to my eye. I measured at the surround, and still good. I took successive measurements as I moved the mic back, and everything looked good.
At the listening position, the distortion was simlar to what I typically measure. I did increase the SPL for each test, so it makes sense that there would be somewhat more distortion.
But with the completely unfiltered response, I still have a clear "hump" in distortion. I was starting to think it is room related, but then, the up close measurement hints at the same pattern of distortion.
I think my next step is to bite the bullet and do some outdoor testing. When temps warm up.
Up close, woofer center. (There is a low shelf and high shelf filter applied.)
Listening position:
Listening position, no crossover, no filtering:
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