Subwoofer Setup for SPL Competition

tinmanchris217 · Feb 19, 2009

Hi guys, latest project is a competition-grade system to compete in USACi and DB Drag events, where the goal is to get loud. Really loud. Either on music or test tones.

I opened the topic to collect knowledge from the forum as the project progresses.

Step 1 - pick the proper amplifier and subs for your class.

For USACi, popular in the southern US, the classes I'm in is 0-600w RMS @ 4 ohms. Subs are unrestricted, but I chose to keep in the lowest class for Street Beat/Bass Race competitions too. This restricts you to either 1-12" woofer, or 2-10" woofers.

For monetary reasons and the love of a challenge, I picked 2 Pioneer Premier Champion PRO series 10's. Their build quality is excellent and they can handle 800w RMS each.

The amplifer I picked is the Hifonics Brutus bxi1610d, which does
550w RMS @ 4 ohms
1100w RMS @ 2 ohms
1600w RMS @ 1 ohm

Real wattage is a little over 1500w RMS, if your electrical system can handle it. Hifonics is a great company that builds strong amps and doesn't cut corners. It's not a kicker, but close, for half the price.

- Chris

tinmanchris217 · Feb 19, 2009

Step 2 - Finding the RAV's resonance frequency

To successfully tune for SPL, you have to maximize the effects of
1) the amplifier
2) the subs
3) the box
4) the car interior

The effect of "cabin gain" or amplification due to the size of your interior. If you have chosen your amplifier and subs to work well together, and sized big enough for your vehicle, the issues left are BOX and CAR.

The two are related heavily, and the first step to optimizing, is finding where your car "peaks" at, or its resonance frequency. To do this, its recommended by professionals, to setup a sealed box, with Q = 0.7, usually a 1 cubic foot box for 1 10" subwoofer.

To make a 1 cube box, cut some 3/4" MDF into rectangles that will come together, to make a box with 1 cube of internal volume.

See pics.

Testing will probably happen this weekend. The idea is to find which frequencies are most amplified by the car, as compared to being in a big room/space.

Chris

otterpopjunkie · Feb 19, 2009

Hi Chris, got some good info there. What method do you use to measure the pressure levels in the car? Do you have a mic hooked to a computer or just a SPL meter? I've used a live FFT program in the past to check my car's resonance frequencies, you doing anything like that?

I've got a 15" HX2 in a sealed 3/4" mdf box to spec volume with a RF T3002 amp. I wasn't looking for competition just low cost bass. (15" is too big for the small rav4 anyway) The thing that drives me nuts is the distracting vibrations I get all over when I crank it up (heard both inside and out). I wasn't sure if matting would really help that or if you'd ever dealt with that in the rav4.

paradigmsk8er · Feb 19, 2009

skip the dynamat and go to lowes or home depot and look for "peel and seel" its a type of roof flashing. You can get large rolls or 12 foot by 1 foot sections for much much cheaper then dynamat and it does the same thing. Dynamat is simply an acoustic damping material that uses weight on body panels to reduce it. It does help. It will also help keep your vehicle cooler/warmer by acting as insulation. Use a blow dryer to heat it enough to soften (not to get gooey sticky) and apply with hands. As for the plastic panels vibrating you can add rubber, foam, etc to the insides to help but be weary of interference wiht other parts.

TINMAN-be weary of using cookie cutter box designs--the q can vary dramtically with the suspension system on particular drivers. I am going to guess the pioneers have a relatively high QMS and QTS so you might want to check that out-While bassboxpro is a good program I find it unneccessary for car audio really. The best results come from experimentation as I am sure you will see-I still use winisd to plot the ideal curves and figure port area and box volume..it is relatively accurate for a start especially for freeware. Even without a proper Q you should find the resonant frequency of your vehicle easily enough-its usually a 5-10 dB peak so its noticeable.

Also remember-your box tuning needs to work with the Res Freq of your car, not necessarily match it. The best way to find the best results is to make an adjustable slot port (info can be found online, its too lengthy to easily explain) so that you can adjust the length on the fly, while using meter time to figure uot what tuning works best with your vehicle.

Then take that frequency, build a solid box with LOTS of bracing and heavy baffles, a good amount of port area, and go at it. Remember too that with a proper build your enclosure needs to workw ith the acoustic damping of the suspension to allow for the most power possible to be sent to the driver.

Sometimes unorthodox boxes work out great. I have built a 4.5 cubic foot, 35 hz tuned enclosure with gobs of port area for a single cheap pioneer IMPP 12 that actually rocked the house, and got immensely loud and allowed it to take a lot of power.

I have also built "spec" enclosures that sucked ass going off manufacturer recommendations. Playing around is the best way to get the best results.

Remember--if you can run 2 guage power and ground and go under your hood and rewire the big three wiring with 2 or 0 guage and you'll see a nice gain in efficiency and current.

Be careful because I remember whent he first brutus amps came out people were loving on them til abotu a year after the release when they started blowing up.

Good luck and have fun! you'll spend a lot of money on MDF and supplies but its fun aint it?

tinmanchris217 · Feb 19, 2009

Paradigm,
Thanks alot for the advice. I'm still in the learning phase for understanding Q's and tuning, but I understand the theory behind transfer functions, wave theory, suspension, etc. Lots of book knowledge, but not enough test time (yet :twisted: )

The pioneers have a Qts (?) of about 0.72, so they are plenty stiff enough to do a small sealed enclosure, but can be coerced into a big floppy ported setup, like your 4.5 cf w/ monster port. Thats almost identical to one of my proposed designs, besides tuning freq.

As far as Big 3,
Stinger 4 ga from alternator
0 ga ground from battery
2 runs of 4 ga back to the amp (I had an extra 30 feet laying around)
6" of 4 ga for amplifier ground (to main frame rail)

From my research 4 ga, can handle 80-120 amps depending on length, and 0 ga will do 200+.

OtterPop,
Since I am poor, I'll be testing with my Radioshack SPL meter. El Cheapo, but it works well enough to collect basic data (+- 1 dB up to ~130 dB)

A single 15" sub works well for getting deep, and moving alot of air. Good for quality and "showing off" but not for peak pressures. There are exceptions though.

otterpopjunkie · Feb 19, 2009

Yeah I'm too cheap to buy dynamat, I've looked at getting thermal insulation / peel 'n seal from McMaster-Carr in the past. Mainly I'd like to know if that would stop the rattling without deadening the sound outside or inside the car too much, I'd still like to be heard

The tough part is the rattle comes mostly from the plastic parts on the exterior of the car, like the rear door, I've stuffed foam in there before but I think to fix it permanently I need to put some bolts through or something...

Hey Tinman, are you still in school? Just curious what degree you were going for. There's a few programs you can test online for free that can do Fourier Transforms with a mic connected to your computer, if you were curious of the exact frequencies that you're hitting, works as an EQ feedback. I don't remember what I used but Spectrum Analyzer Pro, SigView and DSSF3 have trials.

Beyond that there's probably nothing I can add to this discussion so I'll butt out

paradigmsk8er · Feb 20, 2009

add peel and seel to the back of the plastic panels, and see about adding rubber to anywhere where the plastic rests on metal. that should seriously insulate any vibrations you have. MCM is good, but shipping adds up. Check locally first-I personally liked the foot wide rolls its much easier to work with and still cheap as chips.

Big enclosures have two drawbacks-poor transient response (not something you are worrieda bout) and lowering power handling. There are some advantages, one of which is being very efficient in a lot of circumstances. Other times they can completely ruin things. I got very lucky with our design.

Tuning is going to be your biggest issue. Once you have an idea of what tuning you want to use-build your test enclosure. I would suggest starting around 2.2 cubic feet per sub with a tuning close to but slightly under (By maybe 3-4 hz) your resonant frequency. Good amount of port area, with as few bends as possible. Then make it so you can do an adjustable port to adjust the frequency, and cut several 2x4s. (Make it a shared airspace enclosure, works better and is easier). Using the 2x4 segments, put them inside the enclosure to reduce or add airspace as needd until you find a good volume, then figure out your airspace by subtracting the volume of 2x4 from the actual airspace in the enclosure.

Then go ahead and build your final enclosure. It will probably still take some tweaking but its always good to have flexibility so you dont have ot build 20 boxes, only 3 or 4

JonRav4 · Feb 20, 2009

Check out www.SecondSkinAudio.com for insulation ideas.

rscotta831 · Feb 20, 2009

I love Dynamat, but it's too expensive.

I did LOTS of research & shopping before I settled on RAAMmat:

http://www.raamaudio.com/cgi-bin/index.cgi?p=pr

The owner, Rick, was as good at customer service as advertised all around the net.

I had a shop apply it on the interior roof + the entire rear of the vehicle. I was very concerned about it falling off the roof in the Summer since I live in the South. Rick guaranteed me via email that if it ever fell, he'd pay to have it put back up. After 2 Summers thus far, it's still holding strong. And 2007's Summer was BRUTAL...near 100 degrees 3 weeks straight.

I also bought some of his Ensolite 1/8" foam to go underneath the door panels + rear door panel.

tinmanchris217 · Feb 21, 2009

Update, did a basic SPL test to get resonance frequency. Turned off crossovers, and kept my old Lanzar amp at 2/3 of normal gain (~200w), and same for head unit, to ensure no clipping effects or nonlinearities.

I tested the SPL at the top of the dash, drivers side, with all doors closed. Then tested with all doors open for a free-air comparison, from the trunk.

Data:
Freq Front Rear
30 107 109
35 110 109
40 112 110
45 114 109
50 115 111
55 114 112
60 112 113
65 105 114
70 104 115
75 102 116
80 100 115
85 114

You guys can see that between 40-60 Hz, the sub performs pretty linearly, but peaks at about 50 Hz. I tested it down further, and found

The RAV4.1's cabin resonance frequency peak is about 50-52 Hz.

For those setting up vented systems, that means you should tune your ports to 46-50 Hz for max SPL(loud bass), or between 32-40 for maximum frequency extension (deep bass).

Chris

paradigmsk8er · Feb 22, 2009

my personal suggestion:

start with a 4.5 cubic foot box, 48 square inches of port area (4x12) tuned to 47 hz. Give it a 1.5" mdf front baffle, brace relatively heavy, and run the wires out the port instead of using a terminal.

apply power, and see how it works. With a relatively low cabin gain like that you should still have reasonable response on most rap and music, and can adjust your eq if itll go that low for a reasonable boost low to mellow the peak out so it is SLIGHTLY musical.

Since you aren't running an all out SPL burp machine (3 or 4 drivers and thousands of watts) there is no need for a 55-65 hz tune like a lot of them end up being..which is nice

tinmanchris217 · Feb 22, 2009

So this is what I came up with for my box. I used Google Sketchup to draw them. All engineers and technical people should try Google Sketchup, its WAY easier than solidworks and much faster for a basic 3d model.

Its about 4 cf per sub, and tuned to 48 Hz. According to BassBox, it should do pretty well and has plenty of port area.

From my reading, more port is always better, right?

Any suggestions for improvement would be welcome. Thanks guys.

paradigmsk8er · Feb 23, 2009

4 per sub? thats a lot but if you throw power at them it will probably work...though I'm not sure they have the excursion to use all the airspace/port area to theyre advantage. it looks good, I have a feeling you find yourself working with less volume in the end but its a good starting point. let me know how it works.

tinmanchris217 · Feb 23, 2009

Well, according to bassbox, the SPL peak at resonance frequency goes up with the size of the box. So, I figured why not give them my whole trunk, a la CRX box. That way, the subs could have a clear shot at the mic, and there would be MORE than enough port area (140 sq in).

Your words makes alot of sense though, because if there is too MUCH air compliance behind the speaker, it won't have enough "push" to move all that air at its maximum pressure. I'll have 700-800 w RMS on each sub. Figured that would be enough, but I am putting it in 3 times the recommended enclosure size. From my reading, SPL subs prefer either:

- 25-50% more than recommended box size
- very small boxes (one note wonders)

Might rework the design for ~2 cubes per sub. The max recommended is 1.2 cubes, which is a little small, but makes sense for the Pioneers with a Q > 0.7 and xmax of about 9 mm. 1.8 - 2 cubes (each) seems appropriate from my reading and experience (minimal).

Will post the Sketchup of the revised design. And commentary, as always, is appreciated.

tinmanchris217 · Feb 23, 2009

So, updated model

~2 cf per sub, tuned at 48 Hz, with 2 slot ports, 4.5" x 10" = 90 sq in. port area.

Everything fits snugly, but works JUST right. Woofers will be somewhat separated, but still will act as a single chamber to pressurize, with 2 outlets.

Best of all, I don't have to go buy more wood, since this design uses almost everything left over from the test box. Probably will make it on Wednesday, if all goes according to plan. Comments?

paradigmsk8er · Feb 23, 2009

two ports isn't ideal for your setup. Your drivers have a lot less linear excursion then I thought at 9mm, but you wont see any gains from two ports and will probabl yonly see disadvantages--higher velocity air exiting and longer ports. Remember turbulence=lost SPL. I would go back to a single slot port, rough 3.5-4x12 ish in area...probably do 2.2-2.5 per sub in airspace and see ho that models up.

Remember--almost every driver models up best in extraordinarily large boxes...9 times out of 10 I would look at the plot then go with my gut instinct

tinmanchris217 · Feb 25, 2009

So I simplified things a little and need to decide between the following choices.

All have similar tuning of 48 Hz, 60 sq in of port area, and between 2.2-2.3 cubic feet per woofer.

My final issue is alignment, which one do you guys like?

paradigmsk8er · Feb 26, 2009

I think you will find ports and drivers firing the same direction to be a much better alignment--a much lower risk of cancellation.

FWIW I have seen some good competition setups in which both port and driver fire towards the roof..and some that fire rearward. test that too

otterpopjunkie · Feb 26, 2009

Is there a divider between the port and the speaker? I know very little about box building but it seems that would make the box do very little (without a divider), because part of it's job is not only to tune to freq you want but also provide some (albeit little for ported enclosures) backpressure to prevent overextending of the speaker under high load.

Also, I'm not sure if others have read anything about this but I recall last year while doing some research that for the strongest resonance at a given frequency, a sound wave much have at least (or around) 1/4 length to resonate the strongest, which I took to mean you'd want enough room from the speaker/port to the wall/roof of your car for 1/4 wavelength or more. This allows for constructive interfence of the pressure waves as they travel back to the sub. For 50Hz this makes a problem in the rav4, because if I remember correectly that's around 2.5-3 feet for 1/4 wavelength. It was a long time ago I last considered this but I was wondering if you've all considered it (or if it's even valid).

tinmanchris217 · Feb 26, 2009

@ Paradigm,

I totally agree. After I posted, I went back and tested everything in bassbox, and it says that at resonance, the back wave will be 180 degrees from its original phase, ie, in phase with the woofer. That means having them the same distance from the mic, is optimal.

This was my supporting argument for the upward woofer/upward port design. So they can be in phase. The reason for choosing the size that I did, was to make sure that the box can fire either upward or to the rear. Since you had good success with the rear-firing, I definitely want to try it out.

@ Otter Pop,

Your theory is less than elegant, but quite correct. 1/4 wavelength is ideal. The reason that a 50 Hz signal, or 22.5 ft. wavelength works, is because the path isn't direct. 1/4 * 22.5 = 5.5 ft.

If you think about the wave travelling on the path of least resistance, it will go up the trunk, along the roof area, and down the windshield. It will also diffuse heavily down into the cabin, but you can tell that a "straight shot" of 3 ft, becomes between 5-6 ft when it travels in an arc.

2 conclusions come from this:
- many people fire their subs to the rear... so the sound will resonate a bit lower, giving them stronger "low bass".
- filling your trunk with a box will cause your resonance frequency to go up.

Btw, there is no divider, its just a slot (rectangular prism) that runs along the interior of the box. like dis

As always, thanks for the commentary and help.

Subwoofer Setup for SPL Competition

tinmanchris217

tinmanchris217

otterpopjunkie

paradigmsk8er

tinmanchris217

otterpopjunkie

paradigmsk8er

JonRav4

rscotta831

tinmanchris217

paradigmsk8er

tinmanchris217

paradigmsk8er

tinmanchris217

tinmanchris217

paradigmsk8er

tinmanchris217

paradigmsk8er

otterpopjunkie

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