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doober View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote doober Quote  Post ReplyReply Direct Link To This Post Posted: 24 June 2020 at 9:37pm
BMS drivers have a distinctive rear cover. These are the 4538 I'm using, not the same as the Eminence, and has a ferrite magnet, but has a certain similarity




I made a bit more progress today, did another 2 bungs on the Mad Max Lathe. It works quite well, the grinder has around 3:1 reduction ratio which helps keep the speed constant as I gouge away. It's definitely one of my more refined home made tools, some of my contraptions have been way more ghetto and often quite scary to use.

I cut the baffle slots into the bungs using a bearing router.




I assembled the driver/baffle/bowl and did some plots, then took it apart again and did a bit of fettling to take the edges off on the driver side.




This made no noticeable difference to the response before the fettling. I was going to remove more MDF but I got distracted and had a mojito instead.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Bams Quote  Post ReplyReply Direct Link To This Post Posted: 24 June 2020 at 10:13pm
Now i’m wondering how your cocktailshaker looks like.... on a serious note.. wow! So nice to see real Diy..
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Post Options Post Options   Thanks (0) Thanks(0)   Quote tomr_29 Quote  Post ReplyReply Direct Link To This Post Posted: 25 June 2020 at 12:15am
Sorry to be off-topic on the main thread but isn’t the ‘similar to BMS’ due to their patent on their annular diaphragm comp design having expired? Therefore any manufacturer is now free to use the same concept for compression drivers. 

I love the Heath Robinson homemade tooling btw. Really enjoyed following this thread and seeing your progress. Makes me feel like getting the tools out to do something fun instead of DIY for once!

Tom



Edited by tomr_29 - 25 June 2020 at 12:15am
Proper capitalisation is the difference between helping your Uncle Jack off a horse and helping your uncle jack off a horse.
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doober View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote doober Quote  Post ReplyReply Direct Link To This Post Posted: 30 June 2020 at 5:57pm
A bit more experimenting...


Some more rounding on the MDF bung/ring





Then a bit more





The measurements of all 4 on the same graph





Not much difference really.


Here's a the graph with the plasticine version added for comparison





I'm not sure what's going on here. The latest mdf version is very similar in shape to the plasticine one, much neater though. The mdf one is slightly taller in the centre bung area, so I guess the nest stage is to take some off this area and see what happens.
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doober View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote doober Quote  Post ReplyReply Direct Link To This Post Posted: 16 August 2020 at 4:38pm
I've done some more work on this, I really wasn't happy with the mid response. After a few other attempts I came up with a horn split into 16 sections rather than 4, still using the same flare dimensions though. I made 2 new mini horn bits from silicone, and attempted to GRP the first 2 bits with limited success, they are way too small to get the mat to lay properly. I decided to add some colloidal silica to resin to make a thick grease like consistency and brush/spread it on after a layer of gelcoat. This was repeated for the rest of the 16 channels.

Driver side of baffle with bung




Slightly messy looking horn. When I make more I might cover the whole outside with fibreglass mat to add more strength. Maybe smooth it out with an abrasive wheel on the grinder first though.





I added some bits of ply to make a 90 degree horn





Measured with no EQ or filters





This looks quite a bit better to me! The next step is to tidy the GRP bit up and make a silicon mold of all 16 channels in one. Then I can move onto making a new box, double the height of the first version, with 4 mid and 4 HF and a curve in the vertical plane. I also need to work out how to fit 4 of the 10" low mid in too.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote LjudLahger Quote  Post ReplyReply Direct Link To This Post Posted: 16 August 2020 at 10:09pm
Hi, nice project!
I was thinking of this dip at around 800hz, have you done a measurement with only the bowl, a closed box without the horn?
Because I was wondering if this is the middriver or the horn doing thisSmile

Keep up the good workThumbs UpThumbs Up
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doober View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote doober Quote  Post ReplyReply Direct Link To This Post Posted: 18 August 2020 at 8:16pm
Looking at all the plots I have done using this driver there is always a small dip around 800Hz, it varies in frequency a bit depending on whether the horn is attached, but is always there. In the latest horn it is around 700Hz. Half wavelength of 700Hz is fairly close to the slot (and therefore horn) height, and length of the ply horn. This dip could be a mouth reflection, or a reflection between the top and bottom horn walls. Or something completely unrelated caused by the rear chamber...

The next version will not have parallel top and bottom walls, and a better mouth termination. It will be interesting to see how things change.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote KidCreole Quote  Post ReplyReply Direct Link To This Post Posted: 19 August 2020 at 5:55pm
Originally posted by doober doober wrote:

I put the other drivers in today. It was a bit tricky getting the lower compression driver bolts in.



Hopefully next week I'll get some more measurements done.
Why clamshell straight onto a 90 degree bend?
Mykey Wattco
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Post Options Post Options   Thanks (0) Thanks(0)   Quote KidCreole Quote  Post ReplyReply Direct Link To This Post Posted: 19 August 2020 at 6:10pm
A far easier build and hardly any losses
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Post Options Post Options   Thanks (0) Thanks(0)   Quote BP1Fanatic Quote  Post ReplyReply Direct Link To This Post Posted: 19 August 2020 at 6:44pm
AWESOME thread!
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doober View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote doober Quote  Post ReplyReply Direct Link To This Post Posted: 20 August 2020 at 9:32pm
Originally posted by KidCreole KidCreole wrote:

A far easier build and hardly any losses


That would definitely be easier to build, but would either lose some horn length or make the box a lot longer with more empty space inside.

I did consider facing the drivers more towards the rear corners to remove the initial 90 degree bend and reduce the angle of the second bend, but there would be no way to get the drivers in- they have to go in through the back of the box.
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doober View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote doober Quote  Post ReplyReply Direct Link To This Post Posted: 16 September 2020 at 9:37pm
I tried the mid section with the new HF (from my other thread), I added a bit of EQ, more can be done though. As usual the test wasn't done in ideal conditions







Looks like it's getting somewhere, although the next stage might change everything....

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