box tunning for spl comp

[mel80]

so im going to my first comp this weekend in a very very long time , right now i have 3x 12's in just under 6cft tuned to 28hz it sounds great for daily driving and music and gets plenty loud but i know if i tune the port higher it will get a good bit louder , class im entering is a trunk class that has to score from 53hz down , pre breakin fs on the subs was 50hz and 43hz after breakin im thinking about cutting a port tuned to 44hz for the comp. i also gain a good bit of volume back in the box with the higher tuned port  the port is a 10 inch round port.

 

unfortunately i dont have access to a meter i can use for testing before the comp so i just gota make a good guess and run with it 

 

thoughts / suggestions ?

Edited April 25, 2023 by mel80

[Joe X]

 

 

If you are going to a burp type of competition you may want to get a cheap $20 SPL meter just to find out your vehicle's resonant frequency, you will have to setup your ported box to peak at that frequency to be loudest.

 

The following link tells you how to get your resonant frequency, they use expensive tools but you should be able to figure out how to do it in a cheaper manner:

 

https://audiojudgement.com/resonant-frequency-car/

 

The other thing is the port, many times is used firing driver's side for comps in a setup like yours, next is port area, if your resonant frequency turns out to be high, you need more port area, you will want port airspeed to be low, below 20 m/s at least, lastly flared ports perform much better, lastly is best to have a variable length port, you tune to below your theoretical frequency and start reducing the length until you hit the peak, you go past it a bit and then back down for the optimal setting. Hopefully some of it will be helpful.

 

[mel80]

unfortunatly i dont have time with my work schedule to do any real testing this was a last minute thing for me heck the day i leave for the comp im working a 12 hour shift and then heading directly to las vegas for the comp basically going to be work 12 hours make the 3 hour drive get to the hotel sleep for a few hours and im off to the comp. im hoping to have enough time in the morning tomorrow to get my lithium bank in the car  . i took a guess and cut a port tuned for 40 hz i can swap the ports on the fly and i do get reruns so i can experiment a lil there . my current port is tuned way low so im sure the 40hz tune will pick up some db but ill know for sure this weekend 

 

both classes im going to enter allow for music or tones, both are trunk classes one is upto 5k max power rating and the other is 5k clamped 

 

either way be nice to get some as is numbers and see were i end up as the summer goes on and i have time to do more work on it 

[Joe X]

Yes the resonant frequency of most vehicles very rarely gets down to upper 20s, usually will be somewhere from mid 30s to mid 60s so 40Hz has better chances than 28.

 

So have a fun and learning weekend and review what I posted above later on when you have the time. It will be nice to get some numbers so that you have some data to compare as you tune up/improve your system over time.

[mel80]

yeah i actually have an rta setup just the lack of time to do anything right now , but its something ill deff do before i hit my next comp so i know for sure right were i should tune the box to 

[mel80]

so when i got to the comp i ende dup running some low power sweeps to see were i was peaking at and it was around 40 hz . so what i ende dup doing was pulling my port and cutting it down which i ende dup doing a few times my very last run i went a lil short and ended up losing about 3 db ( 50hz port tunning ) , my biggest peak was when the port was at 44 hz so i know my sweet spot is between 42-46 hz for next time 

[Joe X]

You may want to try a pro port with flares and adjustable length, I think it was a 10" diameter you were using so this:

 

https://www.bigass-ports.com/category-s/183.htm

[mel80]

 

 

yeah i was going to get one from big ass ports im going to make some box changes i think im going to drop down to 2 of the 12's dbl the power and put the port on the speaker side or i may leave all 3 subs in and fire the port out the back of the box instead of the side so i can either run it with subs into the cabin along with port , or subs/port back , or the other config would be subs into cabin port back , or subs back port into cabin 

[Joe X]

Already changing it? Awesome, with many trunk cars you will want to do subs forward port forward sealed off, that actually excludes the trunk volume increasing cabin gain.

[mel80]

15 hours ago, Joe X said:

Already changing it? Awesome, with many trunk cars you will want to do subs forward port forward sealed off, that actually excludes the trunk volume increasing cabin gain.

im not 100% sure what ill do yet i do wanna hity one more comp with my current setup and id like to run the subs back and see what it does , to my ear it deff seems to pick up some db with the subs pointed back i just didnt try it at the comp cause witht he subs facing into the cabin the port was easy to get in and out to try different tunings so i never turned the box around .

i do know this the box is so big that theres not alot of space for the sound waves from the port to get around the box into the cabin , and with the 3x 12's theres no way to get the port on the same side as the subs 

 

worst case is i buy 3 more subs and build a wall lmao 

 

im actually going to buy my own spl meter here soon so i can do some testing at home with various configs and see where i can pick up a few db