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Old 26th October 2008, 03:18 AM   #1
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Default Porting a JBL 2123 for midbass duties

I have a pair of 10" JBL 2123H that I would like to use for midbass duties. These are high efficiency (101 db), low xmax (2.5mm) pro audio drivers. They drivers are very similar to the 8" JBL 2118 (97 db) which have been used with great success in some high profile SQ cars back in the 90's. Such as Mark Eldridge's 1987 Toyota 4-runner. Typically that application was sealed or AP.

My current plan is to use a .5 cu/ft cabinet tuned to 83 Hz. I will use an 18db electronic crossover at 90 Hz; the crossover point is not adjustable. My current plan is a .5 cu/ft cabinet tuned to 83 Hz.

My questions are:
-Is the placement of the port critical? My current plan was to place the port adjacent to the driver.

This thread was originally started in the Loudspeaker section:
porting a midbass
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Old 26th October 2008, 04:07 AM   #2
infinia is offline infinia  United States
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what's the make for the car, and any general location of the boxes.
source's
amps?
EQ?
Bass woofer?
treble horn?

What sound/levels and music are you going for?
Any other info that might be useful or different?
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Old 26th October 2008, 05:43 AM   #3
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Objective: There is no particular SPL level I am trying to achieve. Just clean dynamic sound in a noisy environment. In particular I am seeking very dynamic mid bass. In 1986 I got into a truck to listen to the sound system. The music wasn’t playing very loud; the sound was clean and crisp. Nothing exceptional, just very clean sound. But on some drum and bass guitar notes my shirt moved. You could feel the impact. It was veseral. And yet the music wasn’t loud, but when the midbass was needed, it was there. That is what I am going for.

Car – 20002 RSX, basically a Civic hatch back coup.

Tweeters – LPG 26NA, metal dome tweeters, Described as airy sound. XO @ 6.1K,
http://www.madisound.com/catalog/pro...roducts_id=543
Location - Flush mounted in A-pillars firing at each other, 2 inches above mids.
Amp - Soundstream D100II (1991), 100 w/channel

Mids – Peerless 3” Wide Range; Described as transparent .xo @ 250 Hz and 6.1K Hz,
http://www.madisound.com/catalog/PDF/830986.pdf
Location – A pillars firing between driver and passenger
Amp - Soundstream D200II (1991), 200 w/channel

Midbass – JBL 2123, xo @ 250 Hz and 90 Hz,
http://www.jblpro.com/pub/obsolete/2123.pdf
Amp - Orion 280GX (1988), High Current, 40w/ch into 8 ohms
Location – Below rear window in .a sealed .6 cu/ft box

Sub – DIYMA12, Describe as transparent. xo @ 90 Hz, sub sonic at 29 Hz,
Amp - Orion 280GX (1988). High current. 360 w mono.
Location – Hatch in stealth box firing across the car right to left.85 cu/ft tuned to 31 Hz
DIYMA12. Specs
Fs: 25.21 Hz
Qms: 4.748
Vas: 41.71 L
Cms: 121.9 um/N
Mms: 326.8 g
Rms: 10.91 mohms
Xmax: 23 mm
Xmec: 32 mm
Dia: 25 cm
Sd: 491 sq. cm.
Vd: 1.129 L
Qes: 0.383
Re: 3.6 ohms
Le: 1.319 mH
Z: 4 ohms
BL: 22.07 N/A / Tm
Pe: 1000w (up to)
Qts: 0.354
no: 0.169
SPL: 84.3 1W/1m


HU-Pioneer PRS880 – Crossover and EQ
http://www.pioneerelectronics.com/pi...tionManual.pdf
Built in auto EQ (with microphone) and adjustable crossovers at 250, 1.25k, 1.6k, 2K, 2.5, 3.1, 4k, 5k, 6.3, 8k, 10k, 12.5k @ 12, 18, and 24 db.
This HU is only capable of running a three way so I will cross the sub/midbass at the HU at 250 Hz and send the signal to a Audio Control 2XS to split the signal for the sub and midbass..

Audio control 2XS crossover - This will split the sub out put from the HU into separate sub and midbass signals .This crossover is set at 90 Hz with a chip. This particular crossover was chosen for two reasons:
-Orion GX amps can not be bridged without an Orion 400BDG bridging module, the Audio control 2XS unit has that capabilities built in.
-18 db subsonic filter @ 29 Hz.

At one point I was going to use a Coustic XM7 4 way Electronic Crossover and 5 band parametric eq but decided not to because it wouldn’t mono my sub amp and did not have a subsonic filter.
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Old 26th October 2008, 06:29 AM   #4
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2-D200II's and 2-280GX's. Nice.

Quote:
crossover is set at 90 Hz with a chip
Do you have additional chips to play with?
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Old 26th October 2008, 12:50 PM   #5
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Hey TS, I just have one D100 and one D200. One nice thing about the all four of these amps and the AC 2XS is that they all fit under my front seats.

I could get a 106 Hz chip. I had forgotten about that. I should buy that now so I have that option later incase I need it.
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Old 26th October 2008, 01:45 PM   #6
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Hi
Alot of info to digest at the moment.

1) Any and all info (freq options) on the Xover "chips" schematics, etc. we could use!
Thinking we could design the mid BR box/ports to adapt to the Xover or a combination there of.

2) At some higher frequency the sound from the midbass ports would sound funky. Seems at 100 Hz you getting close?


3) Whats the plan for final EQ adjustments?
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Old 26th October 2008, 02:18 PM   #7
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1) For the crossover from midbass to sub for the AC 2XS, I can get 72 Hz, 90 Hz (current chip), 106 Hz, 129, and 153 Hz. No schematics are avaliable. For the rest of the croosover handled by the headunit are programmed.

2) At some higher frequency the sound from the midbass ports would sound funky. Seems at 100 Hz you getting close?

I was going to use the auto eq funtion as a starting point and tunig from there. I understand that the are harmonics of the midbass attack in the upper ranges that might need to eq'd.

BTW, the HU also has time alighnment.

Thank you for your time.
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Old 26th October 2008, 02:31 PM   #8
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Quote:
Originally posted by mitchyz250f
Thank you for your time.

Your welcome. Good luck with your car.


edit> You can handle it from here?
PS You can add the 90Hz HP filter response to Unibox.
And after all, if the mid starts to distort due to port unloading, you can just turn the volume down.
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Old 26th October 2008, 02:43 PM   #9
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Can you make recommendations for the crossovers for the midbass? I was thinking based on your comments I could tune the box to 83 Hz and crossover at 106 for some added protection. Does this make sense?

Can you elaborate on 'Thinking we could design the mid BR box/ports to adapt to the Xover or a combination there of.'

Did you want schematics of my system or the chips?
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Old 26th October 2008, 02:47 PM   #10
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Quote:
Originally posted by mitchyz250f
Can you make recommendations for the crossovers for the midbass? I was thinking based on your comments I could tuned the box to 83 Hz and crossover at 106 for some aded protection. Does this make sense?

Can you elaborate on 'Thinking we could design the mid BR box/ports to adapt to the Xover or a combination there of.'

Did you want schematics of my system or the chips?
Re>filter schematics for modeling.
I wanted to get a better idea of the actual filter response since it's so close to the port tuning?
edit>Normally with sealed wideband drivers you don't care too much about close in as long as the HP&LP are balanced and operate away from driver resonances. but not the case here.
We are talking about hopefully getting 6-10 dB of out band rejection by fine tuning your port and box alignment to the HP filter corner.
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