5 Attachment(s)
Acoustic (Air) Suspension
It's been a very long time since I've worked with or listened to small closed-box speakers, a design approach pioneered by "East Coast Sound" proponents of the '60's - AR, Advent, KLH, etc.. Building DIY Minis recently led me to trying that approach with JBL drivers, with good result.
A little research in Dickason's Loudspeaker Design Cookbook serves as a refresher on the essentials:
1) A good starting DIY project - easy to build and easy to succeed; the alignments are not critical.
2) Excellent extended bass, as the rolloff is just 12 dB/octave.
3) Driver parameters:EBP = Fs/Qes < 50
Qts > .3
Low Fs
High Xmax
High MMS
High Vas
4) Box size - for true air suspension, < 1/3 Vas.
5) Easy to measure (test) and understand.
There's not many JBL drivers that qualify, but BB6P EBP meter identifies these potential candidates:
116A, H, H-1
123A
125A
127A, H
2145A
2213
Another group, more intermediate between closed and vented designs includes:
2245
508G
LE10A
LE8T-8
Sub1500
[Lists subject to change without notice.... ;) ]
I have been using a $15 yard sale pair of AR4x as test boxes (18.45 l, 0.652 cuft gross internal volume,) but recently discovered that the OASR "Dr. Seuss" horn would just fit. Ut-oh:
3" hole saw and small Sawzall make the "clover-leaf" cutout for the OASR horn with 2407H neodymium tweeter.
708G-1 8" woofer fits perfectly. I'm trying others, too.
Control 128W crossover (2.5 kHz) plus notch filter on the woofer and L-pad + compensation cap on the tweeter gives immediately satisfying results, bottom.
Off to critical listening tests, soon.... :thmbsup:
watch the stuffing near the port!
Quote:
Originally Posted by SETriode
Stuck some poly fill inside my l100 cabinet today after installing my 104hs and I wasn't too impressed. Perhaps I'll have to start experimenting later, but in this application (where the woofer half of the midrange) i think you've got to pick either blocking the port or stuffin the box with insulation. Polyfill was just too much and all i had left was HF and upper MF, so for right now I'm gonna leave em be and enjoy my new amplifier and midranges. Which if you have an l100 i strongly advise and upgrade to 104h's
If you're trying to run it as a ported system, you have to make sure the airflow through the port on the inside of the cabinet is unrestricted. Allow 3"-4" minimum clear space all 'round the inside end of the port. Same goes for getting up against any of the moving parts of the woofer, including the tinsel leads. Use cheescloth stapled back as appropriate to hold the insulation.
Also, try fiberglass inside of polyfill. It just plain works better. And use only long-strand fiberglass -the short stuff can get into places it shouldn't, like the voice-coil gap-
Filling or stuffing the box adds virtual volume -up to 30-40%, which will tame the peak and lower the cabinet tuning -which helps in either case, ported or A-S.
3 Attachment(s)
L88 Damping, Box Fill. Closed Port.
R21 is high-density fiberglass insulation, 6" thick. It's what I had on hand here, purportedly better than normal density for this. Added benefit is I now have two densities in the box, each presumably optimal over a different frequency range.
Impedance, phase, and nearfield (~1/4") frequency response, before and after installation of fill augmentation.
Black cone 123A woofer:
L46s in an HT environment- benefit from a port plug?
Hi Zilch- not sure if there's enough info available to you to simulate this situation & come up with any opinion, but I've got six L46s slated for my 5.1 surround setup, and since I was at the Depot yesterday purchasing plugs for my L100s, I picked up two 2" plugs as well that would fit a test pair of my L46s.
My thought was that, in an HT environment (where there's some serious dynamics, but a dedicated sub for 80Hz & under), the L46s might have a happier, longer life (suspended animation :D ?) with the ports plugged.
Driver is a 117H-1, not sure of the interior volume of the cab, I'll poke around or take some rough measurements if this intrigues you in the least.
Thanks in advance,
je
Interesting to hear that.
Quote:
Originally Posted by
Zilch
What's stunning is the difference in behavior of the cone. It's loose and floppy with the port open. Once you plug the port, the effect of the enclosed air "cushion" is immediately apparent in the stiffness of the suspension.
The 122-A in my L166 seems stiff even with the port open. Did JBL try to eliminate some of the loose boom with this woofer? Dare I plug the horizon?
Also, the 044 tweeter, has a higher extension than that in the l100, before I go ahead and re-cap this thing, should I think about giving it a new crossover?
1 Attachment(s)
LE15A, 5.5 cubic ft., port vs closed box
Quote:
Originally Posted by
speakerdave
The LE15A was initially presented by JBL as a sealed box driver. Does anyone have any experience with it in that type of enclosure? I've read quite a lot about disappointing bass from this driver in bass reflex enclosures, but no one seems to look at the more gradual roll off of low bass in a sealed box which results sometimes in actual greater extension. That coupled with careful use of room rise might get a good result with this driver in a livingroom sized space. Since this driver was first offered for either closed box or bass reflex, I should think it would be an option to try sealed. I would think also that the big magnet would be an advantage for that.
I think the real price of going sealed over bass reflex with that driver (and others) would be either remembering to stay within the decibel level it can produce safely that way (not a problem most of the time) or adding more cone area. The added cone area dictates a low crossover point for me. I find that even crossing over in the mid-hundreds there is definitely a sense of multiple sources that I don't care for (at my listening distance--10-12 feet). Even drivers side-by-side, following the most conservative view on when acoustic coupling occurs (acoustic centers a quarter wave length apart), pairs of 15 inch drivers must be crossed over at under 200 Hz.
David
Here you go - old fashioned data from a real oscillator (port tuned to 31-32 Hz):
"old fashioned" test gear
Nothing fancy, the response includes the room etc. Gear was an old HP 200 CD oscillator (recently refurbished) and the engineering standard, RadioShack sound level meter :blink: a couple feet back. Tried to stay close to minimize the room effects - not to engineering test standards - but surely shows the Helmholtz effect. Speakers are 30 years old! Owner is much older. MM