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Phil Starr

Easy 12" cab build

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Hi Vince, the Beyma will still be 350W and just as loud in the smaller cab, in fact with the SM212 power handling is increased at some frequencies. You will lose some bass as described.

For my own use I am contemplating building a cab of 35-40litres, I decided in pub venues the 50l cabs are just too powerful in the deep bass region, and I quite like the coloured response of the 30l cab but just a little extra bottom end would be great for me. I also want two cabs the same size a 50 and 30 together does look odd.

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Hi Phill

I have one more question. When i make a simulation with Winisd, with 2 ports of 64 mm diameter and Fb = 50 Hz and Vb = 30L, Winisd calculates 21 cm for the length of the ports. Winisd calculates 16 cm for the length if Vb = 37L, the external volume of the box .

So ? How did you calculate 16 cm for the length of the 2 ports ?

Thanks

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I made the box slightly bigger than 30l for the intrusions into the box, the ports the speaker and the battens. Then I fiddled with the tuning frequency to get the best I could in terms of response, cone excursion and port velocity. The aim with this one wasn't to get a flat response but to get something usable in acoustically difficult spaces. I didn't test it out live until the week after the bass bash but I'm happy enough with it so I haven't gone on to see what improvements other tunings might do. I can't remember what frequency I arrived at but you could put the dimensions of the ports into WinIsd and it will calculate the tuning frequency for you. 

All I can say at this distance in time is that it works for me in the country pubs I usually play in.

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I seem to recall that I measured your cab, Phil, and found the tuning spot-on.

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14 hours ago, stevie said:

I seem to recall that I measured your cab, Phil, and found the tuning spot-on.

That was certainly the case with the 50l cab Stevie, I think it was the first time we met. I felt a warm glow of smugness, then when I got home I realised I'd fitted the wrong ports 🤔. I'd been experimenting with different tunings the night before. I can't remember if we tested the 30l cab.

For anyone following this computer modelling gets you quite close but there are things it doesn't take into account. The cab itself has an influence QL and the speaker manufacturers specs can be out, the speakers also have a manufacturing spread, they aren't all quite identical. Even the amp you use and the impedance of the speaker leads have a small effect. If you can it's best to test which Stevie does. The BassChat designs have all been tested. They have all gone through extensive listening tests, have been gigged and most of them went through Stevie's measurements.

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Hi

did you check the tuning by mesuaring impedance or with rice on the cone ? And finally, what was the tuning ?The ports lentgh were calculated to have a tuning about 50 Hz.

thanks

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We measured the impedance. If you haven't got that facility, the rice-on-the-cone method works too. The tuning was meant to be 50Hz.

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Hi everyone

 

Is there someone who remembers what is the width of Female Disconnect Crimp Terminal to plug wire to Beyma SM 212? Impossible to get this information ...

Thanks !

Vinceom

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I don't have the SM212 but I have another 12" Beyma driver. It looks like they all take the same spade terminals, which are 6.3mm. You could always get your ruler out to check.

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If I already had the driver, i could check with a ruler ... I'm ordering this week all I need for my cab and i don't know this information.

Vinceom

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Posted (edited)

Hi

and here is my cab. Thank you very much for the advices. The events aren’t made for the moment (because of the covid, my 80 mm cylindar saw is in my other house).

Some informations : Okoumé plywood 15 mm,  bracket and bracing 20x20mm. The driver is a Beyma SM212.
external dimensions : H430xW500xD360
internal dimensions: H400xW470xD300

The amp head is TC electronics BH250.

I will try tomorrow morning the sealed version.

Thanks to all of you guys !

Vinceom
 

 

 

F2EC2EBD-A73D-452A-A1CA-1074773D76CD.jpeg

80F1FC02-2366-4BCE-93DE-D7D8EB5F2B72.jpeg

41311C2F-E18E-4CC9-8628-013403F94123.jpeg

F936BBF4-0993-4A7F-ACF1-A33DB4BC4B38.jpeg

833E9800-E956-42A2-960F-B7869B232760.jpeg

59DA29D3-B959-4575-808B-BB55E153F53A.jpeg

Edited by vinceom
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If you screw and glue the panels together, let the glue dry, then remove the screws, drill out the holes slightly, put a drop of glue in each, hammer in dowels and smooth them. That way, you won't destroy your router bit amid a shower of sparks when the time comes to round the cabinet edges.

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1 hour ago, Dan Dare said:

If you screw and glue the panels together, let the glue dry, then remove the screws, drill out the holes slightly, put a drop of glue in each, hammer in dowels and smooth them. That way, you won't destroy your router bit amid a shower of sparks when the time comes to round the cabinet edges.

I've got a fantastic little plastic jig for dowelling, I just use that straight off, no screws, when I work plywood these days.

Used them to make this box:

Finished.JPG

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On 19/04/2020 at 22:56, Stub Mandrel said:

I've got a fantastic little plastic jig for dowelling, I just use that straight off, no screws, when I work plywood these days.

That sounds handy. Any chance of a link to where it can be bought? Thanks.

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On 19/04/2020 at 20:41, Dan Dare said:

If you screw and glue the panels together, let the glue dry, then remove the screws, drill out the holes slightly, put a drop of glue in each, hammer in dowels and smooth them. That way, you won't destroy your router bit amid a shower of sparks when the time comes to round the cabinet edges.

If you use this method with the battens you can leave the screws in, they aren't anywhere near the edge of the panels.

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On 18/04/2020 at 10:23, Phil Starr said:

coming along nicely :)

It is such a simple construction technique isn't it?

Hi everyone

building the cab is very easy. But I had some problems with the ports. I can’t measure impedance to check whether tuning frequency is ok so I tried with rice on the cone. It didn’t work very well. So I trusted Winisd and cut the pipe to the right sound. And sound’s pretty good !

One more thing : is it a problem if the cab is not 100% air proof ? 
Thanks!

Vinceom

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1 hour ago, vinceom said:

One more thing : is it a problem if the cab is not 100% air proof ? 

It nibbles away at efficiency, its good practice to plug leaks.

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10 hours ago, Stub Mandrel said:

It nibbles away at efficiency, its good practice to plug leaks.

Yep. A spot of silicone bathroom sealant usually does the trick.

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On 21/04/2020 at 23:16, Phil Starr said:

If you use this method with the battens you can leave the screws in, they aren't anywhere near the edge of the panels.

True, but it offends my OCD...

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