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DIY Lightweight Composite Cab Build

#341
Crockettnj said:
For it's introduction, you'd have to scroll through to post # 725!

http://www.talkbass.com/forum/showthread.php?t=368003&page=37
Click to expand...

Ugh! Thanks for the shortcut.

I gave up on the Carvin idea quite a while ago. I've got four Yamaha AS312 cabs. They're really hi-fi. They are three-way, sealed. The specs say they go into the 40 Hz range for F3. So, of course, they're really inefficient.

They're nice for PA and they sound really good. I don't know that I'd want to take them as a bass rig on a gig. They'd probably do the job, but that's a lot more cab than I want to carry. If I ever get my dream gig as a percussionist/utility player I might consider it.

Thanks again for getting me into the ballpark (page 37) of the Carvin thread for the good part of the discussion.

KO
 
#350
zac2944 said:
A few more logo ideas. Thanks to those who posted/PM'ed suggestions.


Here's a different font and more subtle color scheme. A little less Nascar. ;)
zaclitelogoplate13.gif


IMG_1076zaclite2.gif


Here's a different logo.
c3logo10.gif


IMG_1076C3logo.gif
Click to expand...



Hmm... I like both. Use the C3 as a series badge, just make it say 'C3 Cabinets' or something, like how Ampeg uses their logo, then have the SVT badge on the cab, it'd look really professional then. I am in love with this cab. If I had the money, I'd be begging you to build me a nice 8x10 or something.

That would be a dream, right? :D
 
#351
Last night I finally got around to checking the tuning of the cab. I wired a large resistor (~50ohm 20W) in series with the drivers and then took voltage readings in parallel with the drivers while sweeping a sine wave signal from 35-70Hz. The voltage drops to a low point right at the tuning frequency of the box. I kept narrowing the signal range until I located the minimum.

Here's my test rig in the back-bedroom laboratory. ;)
IMG_1096.gif


As built I had a tuning frequency of 48Hz. My design frequency was 50Hz. I was able to dial it in by trimming about an inch of the length of the ports and then retesting. I actually built the ports an inch too long so that I could trim them down later, so my WinISD calcs were very accurate.

Once the cab was tuned I used some black silicon caulk to seal the ports and the piezo array to the cab.

I'll be bringing the cab to a rehearsal to night for some testing.
 
#352
zac2944 said:
A few more logo ideas. Thanks to those who posted/PM'ed suggestions.


Here's a different font and more subtle color scheme. A little less Nascar. ;)
zaclitelogoplate13.gif


IMG_1076zaclite2.gif
Click to expand...

I like this color scheme and font; but you may be a bit modest - how about making the ZacLite in the larger font, putting the "composite bass cabinets" in smaller type under the TB210. Do you have room for a hyphen or space between the B and the 2? It seems a little crowded to me.
 
#355
BartmanPDX said:
There's no telling how much I'd be willing to pay if it were possible to make a clone of a Berg NV610 using these materials. :ninja:
Click to expand...

A 610 would be pretty straight forward. Getting the same tone as the NV610 would be another story.

I've got a lot of engineering experience and have a good handle on the structural design and building aspect of cab design, but nailing a certain tone or voicing is something I'm pretty new at. I'm sure guys like Jim Bergantino, Don Oatman at LDS, etc. can do this very easily with all their years of experience. I've still got a lot to learn in that department.
 
#358
ehque said:
Am i right to say that if none of your speaker panels are flexing, the performance of your speaker will very closely match WinISD predictions? I'd love to see some real world measurements of sensitivity in an anechoic chamber.
Click to expand...


That is something I'm trying to understand better. What happens on paper (or on Winisd) and what happens in the real world are two different things. I believe that my port calculation were accurate because the nature of the physics behind those calculations is fairly straight forward. Frequency response is whole other ball of wax. WinISD assumes your signal is a perfect sine wave. Your bass produces a much more complex signal.

For now I'm limited to testing with only a SPL meter and sine wave signal generator. I'm looking into getting an test mic and running RTA software for more accurate analysis. I doubt I'll ever have access to an anechoic chamber, but the backyard will work for now. The neighbors give me the strangest looks when I'm sweeping text tones. I live in a very dense city neighborhood just outside of Boston. I just hope they spare me so I don't have to explain.
 
#359
If you make music in an anechoic chamber, those measurements are useful. Otherwise, the factory (Eminence) measurements are just fine for predicting the upper end response above a few hundred Hz. WinISD and all the other T/S prediction programs aren't really very useful above 100 Hz. That is where the factory response charts come into play.

RTA done outdoors with a standard technique, such as groundplane, 2w/2m, or 100w/10m is a more realistic measurement of real world performance. Both values produce a chart directly comparable with 1w/1m. The 100w plot shows the effects of the onset of power compression.

Be prepared for results that look pretty anemic. There is a big difference between real world RTA, and manufacturers' B.S. numbers. Outdoors at 10m is also where most direct radiator cabs gets their butts kicked by the bass horn crowd.
 
#360
ehque said:
Am i right to say that if none of your speaker panels are flexing, the performance of your speaker will very closely match WinISD predictions?
Click to expand...

You also have to consider other losses in the system - leakage through cone, port friction, damping from internal insulation, etc which all lower the total Q of the system:

"An equation for enclosure
losses is:

1/QB = 1/QL + 1/QA + 1/QP (1)

where QB refers to total box energy losses
QL refers to energy losses due to leakage
QA refers to energy losses due to
absorption
QP refers to energy losses due to port
friction

I say "refers to" because any actual energy loss is
expressed in an inverse way. Our convention of expressing
energy losses inversely, as "Q", is what makes the subject
difficult to grasp intuitively."

(Courtesy of Andy Lewis @ Acme)

Alex
 

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