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Getting into SPL Competition, the beginners guide

So you’re interested in competitive car audio sound offs and SPL competitions ? Good for you ! SPL competition is a great way to spend an otherwise quiet Saturday afternoon. No matter what format you’re interested in (dB Drag Racing, MECA, IASCA, etc) this primer is a great way to start on the path to your new hobby.

Dont be intimidated, you dont need the best and most expensive equipment, or any expensive metering equipment to be competitive in SPL competition. DecibelCar.com has been created to show everyone out there that competitive car audio can be affordable and fun, and this guide is here to show you how to achieve the best you can with what you have available right now. All cars are separated in classes to ensure people with normal equipment dont compete against the guys with custom equipment, manufacturer sponsorships and interiors made out of solid concrete !

Lets delve a bit deeper into the fun and exciting sport ! With our help and a bit of your free time invested wisely, you should be well on your way to winning your first trophey and making new friends.

 

Equipment. What should I look for?

First thing to do is research. Visit our forums, other SPL forums, local forums, do some searching around and see what others are using. Check results from competitions and see what the winners are using. This gives you a good idea of whets getting the results. Use this info then look at what you can afford. Maybe you can’t afford the “Monstrous Edition Handmade by Monks in Tibet” equipment, but you afford a lower model from the same company (Eg. DD35xx series instead of 99xx).

Amplifiers: always get the most power you can for your dollar. Remember the power only comes from certain impedances so consider this when choosing an amp and sub combo. IE. Don’t get a DVC 4ohm woofer and amp that makes best power at 1ohm !

Subs: Good woofers last longer and can be reconed, extending their life, consider this when shopping for your new subs. Cheap subs usually aren’t worth the cost of reconing.
Look for subs that are well constructed and have a good power handling rating. Also make sure you get them in an impedance that will allow you to load the amplifier for maximum SPL

Battery: There are a lot of options. Optima and Odyssey are extremely popular, and also extremely expensive. Good results have also been had from cheaper Exide & Supercharge batteries with a high CCA and RC. Quantity depends on what class you will be running for dB Drag’s.

Cable: on the topic of power, power in is power out. Serious SPL competitors use multiple 0g cable runs for this reason. For a complete run down of how to correctly upgrade, refer here: http://www.caraudioaustralia.com/forums/in…howtopic=450791
Also note that some amps will burn out if the input power is too low. $100 worth of 0g cable won’t seem so expensive if you’re faced with a $700 amp repair bill.

Fuses: while not required by dB Drag rules, ARE required at most shop events. This is for your safety ! Most cars are daily driven and an electrical fire is not fun. Same goes for grommets on cables running thru holes in metal. Be sensible, your car or your life isn’t worth a number on a screen.

Headunit: For Street classes it is essential it has PAUSE, Remote Control, RCA pre-outs and good anti-skip. Alpine, Pioneer, Clarion & Blaupunkt have a good reputation with Street competitors.
For Podium (external headunit) classes Pause & RCA pre-outs is essential. A $100 Supercheap CD player does the job just as good as a $1000 Alpine.

Caps: A cap will not help SPL as proven many times in the past. Refer here: http://www.caraudioaustralia.com/forums/in…showtopic=42742

So I’ve got the equipment, what class am I in ?

Know the rules before you show up. If it’s your first comp the organizers will be pretty lenient and let things slide, or let you fix them before running. Don’t expect this the second time.

The hard & fast of dB Drag rules are:

Street:
Interior must be stock.
Engine off.
Limited batteries.
Limited capacitors.
Headunit in Factory location.
Battery in factory location.
No stereo component can interfere with normal driving/seating (back seats must fold, etc).
Subs/boxes/amps must remain in the cargo area (boot or hatch area).
Nothing above the Window Line.

Street MAX:
Interior must be stock in front of the B pillar (behind the front most opening door).
Engine off.
Limited batteries.
Limited capacitors.
Battery in factory location.
Walls (going above Window Line) OK.
No internal structural modifications (welded plates, etc).
No cutting of body structure.
Podiums OK.

Super Street No Walls:
Interior must be stock in front of the B pillar (behind the front most opening door).
Removing front seats OK.
Engine on.
Unlimited batteries.
Unlimited capacitors.
No cutting of body structure.
Podiums OK.

Super Street:
Interior must be stock in front of the B pillar (behind the front most opening door).
Removing front seats OK.
Engine on.
Unlimited batteries.
Unlimited capacitors.
Podiums OK.

Extreme:
Subs can not come in front of the B pillar (behind the front most opening door).
Full rebuilt interior OK.
Engine on.
Unlimited batteries.
Unlimited capacitors.
Podiums OK.

Monster:
ANYTHING GOES.

For the complete and UP TO DATE rules, refer here: http://www.termpro.com/dbdrag/rules/

Am I ready to compete now ? No, you need to prepare.

If you want to be competitive, you need to prepare !

First, get a copy of a Test Tones CD. DecibelCar.com is pleased to supply a free downloadable Test Tone’s CD right here with sine wave frequencies between 15hz & 80hz.
Or download our updated MP3 Tones for Memory Sticks test tones!

Secondly, you need meter time. You’re options are:

– Visit your local car audio shop and see if they have one (most do), and ask how much to rent some meter time.
– Borrow one from a friend. All serious competitors own a meter, so nows a good time to make friends with one.
– Go to a test & tune day. CAA has meet days where you can test & tune, usually for free or a small donation for the meter owners time.
– Buy your own.

TermLAB is the official SPL meter for almost every SPL comp on the planet, so is the best for you to buy. Available online from www.termpro.com or used on various online forums.

Thirdly, get a battery charger. Around $25 buys you a nice little 2 amp charger and it’s worth every cent. When you’re at a comp next, pay attention to what the winners doing between runs. (Hint: they sit their cars on the charger !)

Once you have access to a meter, your tones disk and charger its time to find your “note”. Due to box tuning, woofer movement and cabin gain, there will be one frequency that is louder than them all. This is why we use test tones spaced in 1 Hz increments !

Testing procedure:

1. Use lowered volume, say 1/2 volume, during your test.
2. Install the microphone/sensor box in the dB Drag position. This is on the passenger’s side, 13″ across and 4″ up the windscreen.
3. Turn off LOUD, BBE, flatten the equalizers and any other bass boosters. They can cause the amp to clip and subs to be damaged.
4. Start at a reasonably high note, around 45 Hz. With the meter running, play the tone for 3 seconds then pause.
5. Turn off the headunit, connect the charger and start charging.
6. Wait 5 minutes, during this time write down the result (Eg. 135.6dB @ 45 Hz).
7. After the 5 minute cool down, reset the meter, turn the headunit back on, check that the volume is the same as last time, go up 1 Hz and do it again.

Repeat Steps 4 thru 7. You will notice that SPL will go up with the note, then start dropping. The frequency you played loudest is the “note”. This is the track you will play at the SPL comp.

Finding the Resonant Frequency

Resonant Frequency is where the sympathetic vibration of the cabin is at its loudest. You can tune the enclosure to peak at this frequency, giving a boost to your SPL.
To find it, use a sealed box and follow the same steps as outlined above.
Then, remove the sealed box from the car and place it in an open air area. With the mic/sensor 1m away from the speaker’s cone repeat the test process.

Minus the out of car response from the in car response, which ever frequency is the highest dB is your resonant frequency.

Loudest setting ?
First off, gains aren’t a volume control. Winding the gains “flat” won’t increase your score, it will hurt it and may cause damage to the equipment. Around the 10 o’clock setting is good for most amps fed with 4 Volt precuts. If you’ve already had your gains set, leave them.
To find out how to correctly set gains, refer here: http://www.caraudioaustralia.com/forums/in…showtopic=36002

Once they’re set, you can test to find you loudest volume setting:

1. Use the note you found earlier.
2. Install the microphone/sensor box in the dB Drag position. This is on the passenger’s side, 13″ across and 4″ up the windscreen.
3. Turn off LOUD, BBE, flatten the equalizers and any other bass boosters. They can cause the amp to clip and subs to be damaged.
4. Start at a reasonably low volume, around 1/2. With the meter running, play the tone for 3 seconds then pause.
5. Turn off the headunit, connect the charger and start charging.
6. Wait 5 minutes, during this time write down the result (Eg. 135.6dB @ Volume 20).
7. After the 5 minute cool down, reset the meter, turn the headunit back on, reset the track to start at 0 seconds, go up 1 “notch” in volume then do it again.

Repeat Steps 4 thru 7. You will notice that SPL will go up with the volume, then start dropping. The volume you played loudest is the just before clipping starts. This is the volume to play at the SPL comp.

Advanced Meter Tuning & Testing

Stage 1: Enclosure Volume.
For this stage, use a test port that’s 13″ deep, and around the Summed SD in area (as explained above).

The way to test the enclosure volume is to make a big box (prolly bigger than ideal) and slowly reduce the space inside the box whilst blowing tones.. Use bricks or blocks of solid timber, phonebooks won’t work they’re not dense enough, and reduce the volume 1/2 a cubic foot each time. If the numbers are going down, then the box is prolly ideal (or could stand to be bigger). If the numbers slowly go up, then the box is too big, keep reducing space until the numbers start to drop, now you can work out the ideal enclosure volume (internal volume of your enclosure minus the volume of bricks).

Stage 2: Port Face Area.
For this stage, keep the ports 13″ long.

Try say 3 different sized ports. 4″, 6″ and 2x 6″ if you can.

Just chuck the ports in and blow tones, see what happens. Once you have an idea of around about what size is best, you can start adjusting around that size (IE. try a slightly larger and slight smaller port against the initial test size, etc until you find the ideal size. Ideal = loudest)

Stage 3: Port tune.

This is the easiest part. Now you’ve got your enclosure volume to port area to cone area ratio (IE. You know what volume + what port area + your subs is best), you just need to adjust down the port length to get the tune spot on. Make two new ports, same size as the one you decided was best in Stage 2, but make one about 18″ deep (or however deep you can fit), make the other 8″ deep. Again, run tones to find which the better length is, then make some more testers around that length.

The trick and what takes the time is finding the ideal box size & port size for your configuration. You’ll notice I made no mention of WinISD, Enclosure Calc, and the 1/4 wave tuning frequency method or anything else.. Those are the theoretical ways of doing all this. This is the hands on way of doing the tuning, and it seems to work the best, and as we know not everything works in practice.

Stage 4: Cabin tuning

There’s no real hard and fast rule for this. Move the seats around, fiddle with vent settings, etc. some gain, some loose. You can find a dB or two just from this.

Now I’m ready to hit the lanes ?

Yep you sure are. You’ve got a nicely tuned enclosure, you know the correct settings for the headunit, you’ve got your note and you know what frequency to play.
Burping in the lanes is the same as burping in a test. Wait for the meter to start running, hit it for 3 seconds and then wait for the timer to finish.

 

Here are some tips for events:

– Don’t crank your stereo between runs or when you arrive. It’ll heat up the gear, flatten the battery and hurt your score.
– Don’t play music. Music always costs SPL, burp tones.
– Disconnect any full range speakers. They don’t add any SPL, so why thrash them or waste valuable power ?
– Charge between runs.
– Don’t build drama by waiting for the timer to get near the end. If something goes wrong (miscued track, remote wont work, etc) you’ll need that time to get it working ! Burp as soon as the 30 seconds start, better safe than sorry.
– Only burp once during the run. After the first hit, the coils will be hot, the battery drained and it’ll only get quieter.
– Don’t use sweeps. They strain the equipment and waste power !
– Drive safely and slowly to and from the lanes. There are lots of crowds at these and you don’t want to hit someone.
– Keep your eyes open and brain in gear, don’t walk behind moving cars or in front.

Here are some tips for the social side of things:

– Be respectful. Competitors are competitive, but they’re also friendly and will treat you with respect if you show them respect. No one likes a loud mouth or people who talk trash.
– Don’t be afraid to ask for help. Most competitors are happy to lend a hand, give advice or go over your system. By the same token, don’t waste their time by ignoring their advice. If you have no intention of listening, don’t ask.
– Know your stuff, read up on all the rules for your class and dB Drag in general.
– Have FUN ! That’s why we do it after all.
– Congratulate the guy you’re running against. Win or Lose !

Good Luck ! We hope you can be successful at your first event 🙂

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