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  #1  
Old 08-16-2013, 04:08 PM
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Another Cheap JBL 4430 Mod

So if you spend way too long researching the 4430, as I have, you will find scattered comments from renowned people such as Zilch and others, here and on LH, commenting that the (net 5 cubic foot) 4430 cabinet is tuned to around 34 Hz, and that it would sound better (smoother, with more bass extension) tuned to around 29 Hz, perhaps by lengthening the ports. (Going lower than 29 Hz, perhaps by blocking one port, could be really hard on the woofers.)

Rather than cutting down the ports, I started a thread here to explore ways of re-tuning the cabinets in a harmless, fully reversible way.

In the process, one kind responder pointed me to a tuning calculator here and I spend some time exploring (and discussing on that thread) various options.

After mulling it over for a long time, I first dramatically improved my bass response by hard-wiring the normally-switched crossover, as detailed in this thread here.

Then yesterday, I went to Wal-Mart and bought for $10 (in the Kitchen and Bath department), one black Mainstays "Double Sink Cushioned Kitchen Mat" (item no. MS41-051-150-86) which is about 3/8" thick soft pebbled black foam vinyl, with tapered edges.

After some experimentation I used a new box-cutter knife and a straight edge to cut four pieces, each about 9.5" long and 12" wide, and put one into each of the four port tubes, effectively reducing them from about 4 1/8" inches inner diameter to about 3 3/8" ID, and lengthening them to 9.5 inches. I got this number using the calculator above, for one straight edge and one flared edge on each port. With two straight edges I would have used a nine-inch port. With two flairs, ten inches.

Happily, the rubber mat I'm using has one smooth side and one pebbled side, so I can see which one is quieter (a moot issue, I'm finding), and it has rounded factory edges, so I can use that edge for a flared end (see my photo above) or cut a straight edge for a straight end. I can also cut a piece short and mate it with other length pieces, in the middle of the factory port, to test different lengths and/or put a flared or straight edge on either or both ends.

The result? The port liners make a huge difference, at least with test tones: Playing a 29 Hz test tone without the liners, the tone is almost completely inaudible. With the liners, it's clearly audible, and a dB meter shows about a 5 dB increase in output at that frequency, dropping below that and rising above. (I haven't used pink noise with an RTA - yet - to get a really clear picture.)

I may monkey around a bit more to optimize the length, but I think it's already damn close. Playing music, I go from hearing about 10% of a certain super-low set of notes that I use as a reference (Tosca's Dehli, disc 2, track 1, at around 2:20, which seems to hover around 25 Hz), to hearing about 70% of it.

For $10 and an hour or two of playing around, this seems to have been a very good experiment.

Edit: JBL's own tuning specs for the woofer (5.64 diameter 11" port in 5CF box = 30 Hz) seem to validate the applicability of the tuning calculator I used above, which yields virtually the same numbers; see http://www.lansingheritage.org/image...2235/page2.jpg. This sheet indicates an optimal tuning frequency of 30 Hz.

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File Type: jpg DSC_4859-001 (Medium).JPG (96.7 KB, 223 views)
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Last edited by Zonker92; 11-11-2014 at 04:51 PM.
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Old 08-16-2013, 05:59 PM
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Now if we can just invent a pair of undies to fit those cheeks we might get rich.

Great stuff Zonk, since I have no port tubes for my 4430 cabinet project yet, I will be interested in your final sizes to use on mine. I would like to try and get the tweeter to go a tad bit higher too, I think I can hear a touch above what they are rated at. After my ADS high wears off I'll be ready to polish those JBL cheeks of mine up, and get some 4430 action around here again.
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Old 08-16-2013, 06:05 PM
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Funny, I actually have a mental design for a grill cover for the cheeks. It would be a half-cylinder-shaped wire frame, covered with JBL blue Lycra, that simply lies over them, with a little tab at the top to engage and hang off the slot at the base of the horn baffle. But I have no plans to make it, as I like to leave my cheeks nekkid!

I know for a fact that my hearing ends around 14-14.5K, so I don't miss the sonics above 16K on the horns. (I love my iPhone / iPad frequency generator apps for exploring this sort of issue, and for trouble-shooting sperkers.)

I may not adjust these sleeves any further for some time, since I don't have good enough test equipment to dial in the length perfectly. I may slightly bevel the edges where they meet, though. But basically, a 12" wide x 9.5" deep rectangle seems about right with one flared end. (With two, I would go 10 inches. With straight edges I would go 9 inches.)
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Last edited by Zonker92; 08-20-2013 at 04:11 PM.
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Old 08-16-2013, 06:13 PM
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I probably not the only person that considers those woofers to be some of the best ever, I really liked their sound and could live with how low they go but there is nothing wrong with improving them.
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Old 08-16-2013, 06:14 PM
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Yeah, they're pretty great either way.
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Old 08-17-2013, 04:46 PM
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Nice, be interesting to try with the 4435 too, or even with the L300, similar woofer.
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Old 08-17-2013, 04:58 PM
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WOW - VERY impressive work! Thanks for sharing the measurements
and the measurements!
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Old 08-17-2013, 06:12 PM
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Quote:
Originally Posted by mech986 View Post
Nice, be interesting to try with the 4435 too, or even with the L300, similar woofer.
I'm interested in the effect this might have on the L300's, I was just reading about how Nelson Pass stuffs the port with Dacron to reduce the 50hz bass bump. Wondering the sound difference between stuffing vs. lining? Both options are certainly cheap enough to experiment with and see. Thanks for posting this idea!
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Old 08-17-2013, 06:26 PM
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Old 08-17-2013, 06:35 PM
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So glad I'm not the only one who enjoys this stuff! I should emphasize how crude my measurements were (iPad dB meter apps and the internal mic, plus my ears), but with some better equipment I think this basic approach could be dialed in quite well.

Edit: JBL's own tuning specs for the woofer (5.64 diameter 11" port in 5CF box = 30 Hz) seem to validate the applicability of the tuning calculator I used above, which yields virtually the same numbers; see http://www.lansingheritage.org/image...2235/page2.jpg. This sheet indicates an optimal tuning frequency of 30 Hz. The dotted line shows my port tuning in my five cubic-foot cabinet, using a single port virtually equivalent to my double ports:

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File Type: jpg BL 2235 Data Sheet - Port Tuning.jpg (45.0 KB, 140 views)
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Last edited by Zonker92; 08-18-2013 at 04:02 PM.
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Old 08-17-2013, 08:13 PM
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Just remember that reducing the diameter of your port will affect things differently than shortening it... not saying one way is worse than the other in this situation, just reminding you that the two alterations can give slightly different outcomes. I doubt your changing it enough to cause any negative port noise, though.
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Old 08-17-2013, 08:15 PM
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Yup; I had the same concern, but even up close with loud test tones I'm not hearing any port noise.
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Last edited by Zonker92; 08-18-2013 at 04:00 PM.
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Old 08-20-2013, 03:12 PM
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Quote:
Originally Posted by janikphoto View Post
Just remember that reducing the diameter of your port will affect things differently than shortening it... just reminding you that the two alterations can give slightly different outcomes.
Opposite. Opposite outcomes.
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Old 08-20-2013, 05:34 PM
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The 2nd paragraph is right, and explains what's wrong about the first .
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Old 08-20-2013, 05:36 PM
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Ah, sorry, I deleted my last post because I was confusing myself.

But to restate it (correctly this time maybe?): As I narrowed the ports' diameter and lengthened them, I tuned them lower, right? So (I think) making them longer lowers the frequency, as does making them narrower.

Right?

Honestly, I just used the online calculator lined above, which seems to reach the same the results JBL that published, above, for this cabinet.
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Last edited by Zonker92; 08-20-2013 at 05:56 PM.
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