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Underbody braces, turbos and more!

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PostPosted: Mon Sep 20, 2004 10:33 pm 
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King of Pompous
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Joined: Sat Aug 25, 2001 4:22 pm
Posts: 5596
Location: Ottawa ONT.
Been a while since I've had something to add to the FAQ section but ran across this post on another forum I'm on. It was written by Loyd Lowry who is responsible for the FAQ on building the wall in his car with the 18 8" subwoofers. The thread can be found at the Sound Illusions forum. As a note..the car was not made to compete but actualy did quite well this year...here are the stats:

2004 Competition Results
March 28th Krazy Walts MECA Show M3 151.1 db 1st place
April 25th Krazy Walts MECA Show MR3 149.1 db DB3 122.3 db 1st place x 2
May 2nd D&J MECA Show MR3 147.9 db (with music) 1st place
May 23rd Krazy Walts MECA Show M3 152.9db MR3 150.1db DB3 122.5 db 1st place x 3
Current MECA WV MR3 Record Holder

Here are some things that you can try to do when looking for that extra tidbit of SPL. The end result of this trial and error day netted +2db of output and cost all of $5 US!! If some of you guys are competing next year you will definetly want to read this.

Here goes:

Loyd Lowry wrote:
hey guys, Nick and I just finished up working on an install today.. guy wanted to see how much louder we could get his new install... he's running:

Vehicle: 1995 Jeep Cherokee 4 door

Subs: 2 RE SX 15's dual 2's

Box: 6.6 cuft ported w/ 99 sq inches of ported 12.5" long

Amp: Hifonics Brutus 1500d

all db testing was performed using a Termlab USB SPL meter.. (sensor)
mic was placed on the passeger side, in the kick, which conforms to the rules in MECA's stock SPL classes. I'd like to mention, that this is posted as a general idea on what can / can't work for SPL.. it won't have the same effect in every vehicle.. so please don't use this as an iron rule

First thing we did was pull the vehicle up, and found his resonant frequency... turned out it was 46hz

first full power burp the vehicle did a 146.4 db, with the vehicle at 900 rpm

first thing we did, was have him was scoot the passenger seat all the was forward..

gained .5 db 146.9 db

we then made him lean towards the passenger side, from his seat..

gained .1 db 147.0 db

now we had him rev the motor to 2000 rpm, and burp again

gained .3 db 147.3db

next up, open up the glove box...

lost .1 db back to a 147.2 db

we then lowered his back seat, usually a gain in most installs..

not this time.. lost another .1 db 147.1 db and left it down due to laziness

he shut the jeep off for 5 minutes, to rest the alternator (stock)

next, we unhooked his 2.4 farad power ASScoustik cap from the system..

gained .2 db, back to a 147.3 (wow... a cap hurt his score.. imagine that)

now the big surprise for us.. we unhooked his battcap model 400
now with the battcap unhooked too.. another burp

gained .1db!!!!!!!!!!!! up to a 147.4 db


next, we had him scoot his driver side seat forward as far as he'd fit.. hehe

gained another .1 db 147.5 db

next burp, I went over and pushed in on the passenger side door..

gained .1db again 147.6 db

we let the jeep take another 3 min break.. then moved the box back 3 inches from where it was (appx 8" from the rear gate)

gained .2 db 147.8 db

we then tried proping the woofer end of the box up slightly

dropped .1db 147.7 so we took that back out

just to check we moved the box back 2 more inches, and didn't show a change, still a 147.8 db

another rest stop, then I held the tailgate of the jeep

dropped .5 db 147.3 db (OUCH) so we didn't do that anymore hehe

now since the box was firing rearward, we decided to try different paths.. so we put the woofers firing up, towards the roof..

lost 1 full db 146.7 db

now we fired the woofers forward...

lost 2 full db 145.7 db

screw that.. rear firing rules

put the box back where we started back to a 147.8 db

now the screwy stuff :

Duct tape was put around the subs gasket to completely seal off the box

GAINED .2 DB!!!!!!!!!!! 148.0 db

who said ductape isn't loud eh?

now some love for the port.. I busted out some 40 grit sandpaper, and sanded the rear of the port, down to a nice U shape.. and added some ductape over it..

gained .2 db 148.2 db

now I sanded the leading edges of the port, on all 4 sides.. and ductaped themnother burp... nother gain.. .1 db 148.3 db

so after 2.5 hours of testing, and 5 bucks spent on ductape, and sandpaper....

started with a 146.4 db
ended with a 148.3 db

a gain of 2.0 db (yah, not 1.9.. cause we would have gained .1 if we would have put the back seat back up.. remember it was left down for the remainder of testing there buddy )

and finally.. since there seems to be alot of interest in what the 1500d actually does.. we benched it...

at 12.0 volts, into a 2.57 actual ohm load (1 ohm nominal) we got a whoopy doo 931 watts of power....

so Im not exactly thrilled with it...

anybody with questions.. fire away... hope you all take something from this

Loyd L.


So as you guys can see experimentation definetly can get you somewhere! In this case they gained a HUGE 2db increase. You can barely heart that but in an SPL competition that is a huge improvement. Hope some of you guys can walk away with this and apply it to your own systems and increase your scores.

Have fun

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