Get Your SPL Related Questions Answered Here!

[oldschool4me 10+ year member]

what define the classes in a comp these days? i havent been to one since the early 90s. are they still 1-100, 101-250, 251-500, 501 and up??? reason im wondering is that i am planning a new project for the spring and am wanting to be in the 100 w class. i have the sub amps that i plan to use. 2 crossfire 15hc amps rated at 15w x2. so thats 60watts, but they put out 370 underated watts at 1/2 ohm each. doubtful i can find an amp rated at 10w x 4ch for highs. so im going to probably go with another 15hc, punch 40, promos 12, us usa25, or something similar. anyone know or a 4ch thats rated at 40w let me know please. not sure of the vehicle yet have to see what i end up with. figureing crx, astro van, bronco, full size ext cab truck. and the vehicle will determin the subs and quantity of subs.

 

[Van man 10+ year member]

umm...i have a 1991 GMC Safari van...it was a cargo van everything was stripped...there are 2 bubble circle windows in the back and the front windsheild and the driver and passanger windows and thats it...has 2 front seats and the person that owned it b4 me...covered it in hard plastic panels and rivited it...i have 2 10s in it right now powered by a lightning audio 750 and im impressed about how it hits...but i have 2 12" kicker comp VRs and im throwing them in a slanted ported box...im hoping that it sounds twice as loud but yea...lol any input would be nice

 

[99durango5.9L 10+ year member]

heres my question.....it's a while away but im stoked there is a competition near my home i'm going to enter....its going to be my first one....unless something comes up before then....but i wanted to know it if makes a difference where you box sits in my truck?....right now its pushed all the way in the back, would moving it up closer to the front make any difference? //content.invisioncic.com/y282845/emoticons/confused.gif.e820e0216602db4765798ac39d28caa9.gif

 

[Ed Lester 10+ year member]

quote

99durango5.9L

heres my question.....it's a while away but im stoked there is a competition near my home i'm going to enter....its going to be my first one....unless something comes up before then....but i wanted to know it if makes a difference where you box sits in my truck?....right now its pushed all the way in the back, would moving it up closer to the front make any difference?

quote

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It does make a difference. If its in a durango one of the best setups is subs up, ports back and have the ports about 6-12 inches from the hatch. If subs are firing back then the same 6-12 inches would work. I suggest testing and testing. Try 6 inches one time and 12 another.

 

[Ed Lester 10+ year member]

Just looked at your pics, flip your box around and you'll gain at least 3 dB

 

[99durango5.9L 10+ year member]

Just looked at your pics, flip your box around and you'll gain at least 3 dB

really why is that?....

 

[99durango5.9L 10+ year member]

can someone tell me....why tho i would get more if i faced the port towards the back?....just the way the air moves?

 

[btdickey99 5,000+ posts]

Just looked at your pics, flip your box around and you'll gain at least 3 dB

man thats a bold statement

 

[99durango5.9L 10+ year member]

man thats a bold statement

what do you think?....would i score better with them towards the back?

 

[Ed Lester 10+ year member]

Bold statement maybe but it comes with 14 years experience in SPL.

Its all about wave alignment. In SUVs and hatch cars, you usually have a lower cabin resonance than trunk cars. Having the subs face up or back will allow the source wave to fill the entire length of the vehicle. If the are facing forward from the back of the car then the source wave will hit the windshield with a resonant frequency higher than what the cabin resonance is. Then the the reflected wave from windshield to the back will have to travel further and have a lower resonant frequency. So basically you are creating a harmonic resonance in which the peak frequency of the source wave does not match the reflected wave. You want them both to match as much as possible to create higher SPL.

Walled vehicles and trunk cars with the trunk sealed off dont really have any airspace behind the source (subs) so they can have the same resonance on the source wave and the reflected wave.

The theories are here for your reference, you can try it if you want and see if the theory is correct. I always suggest test and tune as much as possible. Cant hurt to just try.

 

[Supergumby5000 5,000+ posts]

I got a question, but i dont know how SPL related it is.

anyways, i have a chevy avalanche, with the sub box in the bed of the truck (blowing into the rear seats). There is about a 1/4" gap on each side of the box, giving room for air to blow into the bed of the truck.

I've been contemplating foaming/siliconing/something the gaps on my next instal this summer. Should i expect to see improvements or will this be a waste of time?

 

[Ed Lester 10+ year member]

1/4 inch gap is not big enough for low frequency waves to fit in, but sealing it will help with building pressure in the cabin. So basically it can raise SPL if your numbers are already high but wont help much if they arent too high.

The main thing it will help with is SQ. It could sound better when all sealed up.

 

[99durango5.9L 10+ year member]

Bold statement maybe but it comes with 14 years experience in SPL.
Its all about wave alignment. In SUVs and hatch cars, you usually have a lower cabin resonance than trunk cars. Having the subs face up or back will allow the source wave to fill the entire length of the vehicle. If the are facing forward from the back of the car then the source wave will hit the windshield with a resonant frequency higher than what the cabin resonance is. Then the the reflected wave from windshield to the back will have to travel further and have a lower resonant frequency. So basically you are creating a harmonic resonance in which the peak frequency of the source wave does not match the reflected wave. You want them both to match as much as possible to create higher SPL.

Walled vehicles and trunk cars with the trunk sealed off dont really have any airspace behind the source (subs) so they can have the same resonance on the source wave and the reflected wave.

The theories are here for your reference, you can try it if you want and see if the theory is correct. I always suggest test and tune as much as possible. Cant hurt to just try.

i wasn't doubting you....just asking why....sounds good, just standing the subs upright i noticed a difference....

 

[expo5.0 10+ year member]

for a competition outside of any of the ruling bodies-

what do you guys think is the fairest/most fun for the most people so far as-

1. sensor location

2. engine running or not

3. music/tone selection (i'm thinking leave it open to the competitor)

4. car sealed up or not (can they crack a window if they choose?)

5. any other things you foresee becoming questions?

 

[Ed Lester 10+ year member]

I say leave the sensor on the windshield but you dont have to be exact with measurement.

Engine running for all classes but limit them to rev to 2000-3000 RPM for safety.

Let them play whatever they want. Tones/music, CDs. IPODs, whatever.

Cars sealed because if they dont fully understand SPL, Opening windows and doors can hurt SPL and/or damage subs.

Clssification, define wall classes. If the enclosure is too high is it a wall? dB Drag's limit is the window line. NSPL is very relaxed and common sense says if its only a few inches above the window line, its not a wall.

Amp limits, you dont want a 40,000 watt system going against a 1,000 watt system.

Sub limit. 1-2 subs shouldnt go against 8-12 subs