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Custom DIY 2x15 cab build

#281
kraigo said:
Bad math. Area = pi * r^2 where r is the radius

One 4 in diameter port = 12.57 in^2. Two gives you 25.13 in^2.

For contrast, one 6 in diameter port gives you 28.26 in^2.

Playing around last night, with six 4" diameter ports, top, middle, bottom on each side, you could feed power in until you run into the excursion limits (~730 watts according to WinISD) and your port air velocity would still be about 62 ft/sec. That's a little above the recommended 5% of the speed of sound (~55 ft/sec), but pretty reasonable.
Click to expand...

The port area on our Super Fifteen is about 70 in^2. BIG!
 
#282
In my 2x1x15 cabs using the Kappalite 3015 (86 liter each) I used 21.2 in^2 per cab (42.4 in^2 per 2 cabs), shelf ports with flared divider on the inside, flush on the outside

I calculated them to be "just enough for 750W / 2 cabs". If I was to design the boxes again I'd probably increase area a bit to avoid chuffing / losses up to considerably higher power (what I'd do if I moved to a high power power-amp).

I am using now a TC electronic RH750, so I am very far from power levels / deep lows showing any problems with port area. By the way, this is another case of "SVT sound matching well with a 2x3015 cab", overall sound is really good, tight and loud.
 
#283
Interesting sidebar discussion going on here. John's built the cab he wants that operates within the parameters he's set, and he's done a great cosmetic job.

Me, I started out wanting to design cabs that would meet extreme use to the top of what the drivers are capable of, so I tend toward more bracing and large unconstricted ports that won't wander in tuning as the night progresses, or chuff - even if one is driving the motors to the very top of what they are capable of. I also favor slightly larger boxes as I feel that improves the character and venue-friendliness of the low frequency output, and balances it better with the all-important mid-range. That's a big aid in making ported designs sound their best. But all these factors add a few pounds and make things a little larger, while so many people are really into smaller and lower weight. So something always has to give.

All is compromise. Making informed compromises, knowingly, John's got a good box.
 
#284
greenboy said:
Interesting sidebar discussion going on here. John's built the cab he wants that operates within the parameters he's set, and he's done a great cosmetic job.

Me, I started out wanting to design cabs that would meet extreme use to the top of what the drivers are capable of, so I tend toward more bracing and large unconstricted ports that won't wander in tuning as the night progresses, or chuff - even if one is driving the motors to the very top of what they are capable of. I also favor slightly larger boxes as I feel that improves the character and venue-friendliness of the low frequency output, and balances it better with the all-important mid-range. That's a big aid in making ported designs sound their best. But all these factors add a few pounds and make things a little larger, while so many people are really into smaller and lower weight. So something always has to give.

All is compromise. Making informed compromises, knowingly, John's got a good box.
Click to expand...

+1 the Starliner 215 is awesome.

And on the sidebar ~

If a port is two small there is chuffing and possible driver damage at high power levels - what happens if the port is two big? Also, does WinISD tell which port size is best for extreme use with two 3015 - and if not, how do we know?
 
#285
thanks GB.
i agree. everything's a compromise, and i'm extremely happy with the size, weight, tone and output capability of the cab. i got the aluminum dust caps and installed just one of them on the top driver so i could place my ear up to each speaker and while playing at somewhat reasonably soft but loud enough to 'get it going' level to compare the high end. IMO, the aluminum one is definitely a bit brighter and sweeter (much more JBL-ish) on the top end with both the STM900 and the SVT.

2x15cab-18.jpg


2x15cab-19.jpg


i just ordered a 1/2" padded cover for it today since i'm going to use it on my next gig to test it in a 'real world' environment.
 
#287
As the port area increases, everything else being equal, the tuning frequency of the box rises (it's somewhat counter-intuitive). So to get the same tuning, you have to increase the depth as well as the cross sectional area. You then have to make the total volume of the box larger to compensate for the volume lost to the port.

Not a huge deal, but it's one more thing to balance in the design. It's the only downside that I know of for increasing the cross-sectional area of the port.

KO

Joe Louvar said:
+1 the Starliner 215 is awesome.

And on the sidebar ~

If a port is two small there is chuffing and possible driver damage at high power levels - what happens if the port is two big? Also, does WinISD tell which port size is best for extreme use with two 3015 - and if not, how do we know?
Click to expand...
 
#288
kraigo said:
As the port area increases, everything else being equal, the tuning frequency of the box rises (it's somewhat counter-intuitive). So to get the same tuning, you have to increase the depth as well as the cross sectional area. You then have to make the total volume of the box larger to compensate for the volume lost to the port.

Not a huge deal, but it's one more thing to balance in the design. It's the only downside that I know of for increasing the cross-sectional area of the port.

KO
Click to expand...

Yep.

The larger area port needs to be longer to reach the same tuning. Taken to the extreme, you can reach a point where the box needs to be too large/heavy to be practical or meet your design goals. There is also a point of no return when trying to tune a small box very low with a large enough port to prevent chuffing. The volume occupied by the port must be subtracted from the overall net volume the driver has to work in. You simply can't make the port long enough to reach the tuning without making the box bigger.

It's all balances/tradeoff's.
 
#289
BTW, i was just playing thru the cab at stage volume and beyond (way louder than i would at a gig) and the aluminum caps really brought out the high end of the 3015's, and actually quite a bit more than they did on th 2512 II's. maybe it's my imagination, but they seem to have quite a bit better off-axis mids and highs as well with them, since i moved from being in front of the cab to standing 45 degrees off to the side and the tone didn't seem to get much, if any, darker, whereas i could easily notice it being darker off-axis before.
 
#290
I was having a good time with this thread until you metioned that it might be brighter / sound better to saw the duct cover off an expensive speaker!
Think I might practice on something a little less pricey before going this alum. dust cap route.
With a steady hand and the right tools, how hard is it to remove the cover without nicking the cone?
 
#291
This video demonstrates the method, in general terms; the speaker being given a replacement cap is an EV15. As best I can tell, the trick is correctly mating the OD of the cap with the ID of the cone (once the old cap is removed).

This is from Simply Speakers. Orange County Speaker's site has less animated instructions.

Speaker Repair EV Dust Cap Replacement by Simply Speakers - YouTube
 
#292
Jim C said:
I was having a good time with this thread until you metioned that it might be brighter / sound better to saw the duct cover off an expensive speaker!
Think I might practice on something a little less pricey before going this alum. dust cap route.
With a steady hand and the right tools, how hard is it to remove the cover without nicking the cone?
Click to expand...

the cab sounds great with the stock speaker, but it's easy to replace the dust cap if you have a steady hand.
a brand new #11 blade cuts thru it easily. you just cut it at a slightly shallower angle than the main cone so you can't poke a hole in the cone. i leave about 1/32" of the paper cap on it as a guide for the glue bead and for centering the new aluminum one.
 
#298
dhsierra1 said:
I was referring to the aluminum cone mods as a side by side w/the JBLs. If you feel the verbal description captures the difference I'll take your word for it :D
Click to expand...

i need to put a new neutrik speaker connector on one of my JBL K140 cabs (my vox beatle has an xlr on it right now and i can't find it's dedicated cable) and the Neutrik's arriving tomorrow. i rearranged/relocated some of my cabs in my storage room yesterday and both of the ones with the 1/4" connectors are buried in there).

the beatle cab will probably be the closest sounding one to the 3015 cab since it's also ported so that's the one that i'll use for the K140/3015 aluminum cap comparison clips.
 
#299
this is really appreciated because there's a lot of us out here (besides me) interested in viable JBL alternatives.

Doesn't have to be 100% spot on soundwise because if you add the deeper bass and higher power handling capabilities of the modern KappaLites then I think you've just done a great service beyond your great cabinet design here. Sorta like what happened w/Leo Fender evolving the P Bass concept at Music Man, then later still w/G and L. Evolution through intelligent design, but still keeping all that was good about the original idea :bassist:

And if you still prefer the original version of the P (or the JBL) you can always just buy that :cool:

Thanks very much :D
 

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