Need Help!!

[christjared]

Hello,

I am looking for some help in the car subwoofer box building area. What I am working with for a vehicle is a 1991 Ford Escort, and in this little hatchback Escort I will be putting 4 15" Soundstream SPL subwoofers. I will be using 2000 watts rms to power all 4 subs. This set up will be competing in USACi comps and also local stereo shop competitions. What I am wondering is what type of box would I need for competing for SPL purposes. I know a ported box is the way to go when trying to do SPL, but I can not figure out port dimensions or how large the box should be. In the Soundstream owners manual for the 15's it says to use a vented enclosure that is anywhere from 2.0-4.0 cuft, tuned to 50hz-30hz for just a single woofer. I know that I could multiply all of these specs by number of drivers and get a nice fancy answer, but I know there are some experts out there that have done computerized box simulations. During the comps the prefered frequence range that we typically run is from 57-70. That usually takes too much time to set the desired frequency. Is there any help out there or pointers I should know before going into next season. Thank you very much for any input, it will come in useful.

Thanks again

JC

[michael hurd]

Send me the T/S parameters via here or email, and I will see what I can whip up on Win ISD. Might take a few days, as I have work to do as well.

[christjared]

Hey perfection takes time! I am just glad that you are able to help. Here are the T/S para. Thanks !

Frequency Response 25-500

Sensitivity 95db

Rated Program Power, Watts 400

Fs 23

Qts .360

Qms 9.22

Qes .380

EBP (Fs/Qes) 60.5

Vas (ft3) 9.82

Vas (liters) 278

Vas (m3) .278

Cms (um/N) 229

DCR (ohms) 1.60

Levc (mH)@1Khz 1.80

BL (Tesla m) 11.20

Sd (in2) 143

Sd (m2) .092

Sd (cm2) 924

Xmax;one way linear (mm) 7.6

Xmax; one way peak (mm) 30

Vd (linear cm3) 702

Vd (peak cm3) 2772

Vd (linear m3) .000702

Vd (peak m3) .002772

Mms (grams) 201

Magnet Assembly (oz) 238

Magnet Weight (oz) 100

Vf (volume of frame, in3) 320

Coil length 27.9

[michael hurd]

Looking at the specs, the BL^/RE is 78.4, pretty decent. Looking at the short coil, I would have to assume that this is an underhung motor on this woofer. 7.6 mm xmax is not much, compared to today's available drivers. Sensitivity is good, that may cut down on your power requirements.

What are the max dimentions you are restricted to? Is there a certain output level that you are looking at achieving? 145 db, 150 db??

[christjared]

Yes the xmax isnt the greatest but considering these drivers were made in the mid 90's I think its pretty good. The dimensions we are restriced to is 38" wide by 16" high and about 39-50" long. Those are the restrictions to the box. I am looking for output around 150+ from these four. We had 3 hooked up in a 86 Bronco II with a soundstream Rubi 1002 and did a 149.7 and on one of the subs the wire to the second voice coil fell of somehow. So we hoped to get 150+ or atlease 153. Batts and wire are still in the making, and I think we did settle on some amps. The new Hifonics Titan amps, cant remember the model number, but it should effectively give us around 400 if not more watts a sub, which is what they are "programed" to take. Then after the amps arive then it is mod city to the interior of the car, like sound deadening, expand'a'foam and other such materials. If you have any ideas on to deaden the interior of the car please let me know.

Thank you

JC

[michael hurd]

They will take a lot more than 400 watts before destruction, especially for burps. I have done some modelling, they look good in a big vented box, but not sure if we could fit 4 in the design, gimme a bit to see what I can whip up.

As far as good inexpensive class D amps goes, the Sundown Audio 1500 and 3000 are pretty damn good, from all I have read on them.

[christjared]

Yea I think for burps I have heard of people doing 1500 watts to a sub for that purpose, but yet this needs to last us awhile, I dont want to be replacing subs all the time, and if we move up in watts we will be up a class also. So we need to keep the watts low, but clean. I have heard of the Sundown Audio amps before, but I did find some Hifonics amps, they are the Titan series. Havent be able to find alot on them but I havent looked that hard. On the box design we were thinking two facing up towards the back window in the hatch, and then two facing forward towards the front windsheild. USACi says that the back seats can be removed from the car, so thats why im thinking two facing forward two facing up, and also having the ports facing up, bouncing off the rear hatch. Right now we have a single SPL 15 in there with an old Rockford Fosgate 200 DSM. The sub is facing the rear window and the port is facing up and all the way back towards the tail lights (the port is on the same face that the sub is mounted on) and it is bouncing off the hatch. That is pretty loud right now so thats why I wanted to model the box after the single one right now. Alright now off to work on a house!!

Thanks

JC

[michael hurd]

If you use single 3/4 construction with bracing inside, we could do a box for 4, within the 16 cu ft you have to work with. Height may possibly be an issue though. What you want is a box that has peak output in your range, and a vented 3.0 cu ft net box ( for one SPL 15 ) tuned to 50 hz will be 3db more output in the same region as a sealed box of 1.7 cu ft. For this reason alone, I would suggest a higher tuned vented box, to maximize output in that region. Also, you have less excursion for the same power input.

As far as port area try to stuff as much as you can, I would suggest 4 8" ports if this is common box ( shared airspace ) as each port will be 9.42" long. My calculations come up with 16 cu ft gross, , 1.86 cu ft used up by 4 8" diameter ports and the driver displacement. This leaves 14.13 cu ft. for the net airspace.

With 400 w per driver, my calculations assume 139 db without any gain from the cabin at 65 hz with 10 mm excursion from each driver. With cabin gain, you may be as high as 159 at that frequency. As you add bracing and keep the port length the same, the tuning shifts downward in frequency. For this reason, you may have to remove the ports and trim some length off each one to retune the box. I would make the panel with the ports removable for this reason.

The drivers have 30 mm peak excursion capability, so keep that in mind, you can certainly throw more power at them without having the coil slap the t-yoke and get misaligned. I assumed that the box would fill the entire area you posted, taking into account the 3/4" thickness.

[michael hurd]

As far as deadening, it is less important in an SPL vehicle. Some tips I could give you are to reinforce, reinforce, reinforce. Plan carefully before you start. I assume this is NOT a daily driver car, and this will be purpose built.

Pressure will leak out of any opening, this is counter-intuitive. Seal up the heater box/ cowl area, and the body vents. ( these allow the doors to shut without slamming hard, they have a rubber flap ) Most vents are located in cars in the trunk area behind the bumper cover, or sometimes in the front doors.

What other modifications are you allowed? Run the largest wire you can afford, check around for 3/0 gauge and get the largest alternator that will fit in the brackets.

[christjared]

This will be just an SPL vehicle. Thanks for the advice so far!! We have begun on bracing of the vehicle, starting out wiht alot of expand 'a' foam in hollow areas and areas that have holes started in them. We havent decided on what other types of reinforcing we shall use yet, but we havent purchased amps or batts right now, but we are thinking of Kinetik batts (cant remember the model numbers), and we are still trying to find some amps. I thought we had some picked out but I think we are still working on other decisions. We are going to gut the carpet up to the B pillers in the car because thats whats allowed, and there is going to be alot of spray on sound deadner. I was thinking of just going with 1/0 back from the stock batt, to the other two( or single) batt, and then up the alternator to atleast a 105 amp. We have to take the dash off and do alot more sealing up under there, I just hope it all can be be done before next season.

World Finals!

JC

[michael hurd]

You definately need more than 105 amps. I have a large alternator stock on my car, and on transients, the voltage will sag down to below 12 volts on the factory volt meter in the dash. Keep in mind you have some hungry amps to feed. Even at 80 % efficiency, a 2 kw amp will consume around 2.4 kw input. 2.4 kw @ 14 volts = 171 amps. You still have not run the ignition system or anything else on the vehicle. If the voltage sags below say 12.5 volts, 2.4 kw = 192 amps.

Largest wire you can fit / afford, and as many batteries as you are allowed. If you are on a budget, and weight is not an issue, consider 4d or 8d batteries. ( think industrial ) They will put out insane amounts of amperage for a lot less than fancy gas-recombinant types. Welding shops are good suppliers of wire, for a LOT less than fancy esoteric stereo shops.

[christjared]

I see what you are saying, and yes this is some what of a slow budget build. Weight and appearance is not an issue, just where can you pick up those batteries at? We will most likely go with welding cable because it is cheaper, and provides the same purpose as the fancy wire does. I really don't know where to get a 200 amp alt. at or who around my area that will build one to those specs, or how expensive they are, so if you know anyone who would like to donate one that would fit on a 1991 Ford Escort please let me know Talked to my team mate and he found Cadence TXA- 1000D amps that will produce 1000 watts at 1 ohm. So that should be 500 watts rms a sub, should be plenty for what its doing. Thanks again man!

JC

[michael hurd]

Here is an example of an 8D battery. http://www.dcbattery.com/rolls.html Pretty much any industrial equipment supply house can get you this type of battery inexpensively. Here in Canada we pay about $ 180 for one. Our Komatsu wheel loader has 2 of them in it. They are heavy, but have thick plates, and a lot of electrolyte in them, making them a long-life investment.

[DrWho]

One thing you might consider would be two dual side firing enclosures

made outta sonotube...it's crazy, but the shape of the sonotube doesn't

require any bracing at all....well, except for the baffles that the

drivers sit on. Running threaded rod through both baffles and

tightening down with lockbolts, lockwashers, and loctite should get it

braced up enough. Also, the dual side firing offsets the mechanical

motion of the drivers - in the end, you end up with a very very solid

enclosure that also doesn't weigh or cost that much. The amount of bracing you need for normal wooden enclosures is insane.

As far as ports....just keep in mind that ports have a maximum SPL

related to air velocity. Your cone excursion is at a minimum at the

tuning point so what you want to do is crank the output of the driver

right at that frequency - cramming all the volume out of the port. In

order to keep the air velocity low, you need to make sure the diameter

is huge. A single port is also more effective than multiple smaller

ports. If your goal is 150+ dB then I would start by calculating the

minimum port diameter that won't have air velocities that are too

restrictive.

If I had more time I would be willing to help out since these kinds of things are always fun, but alas school is really cracking the whip. I will mention though that I helped a friend build a sub just this last summer for a competition and my predictions came within 2dB of the actual max output - how's that for fudge factoring the non-linears? [H] (I predicted 138dB for his single 12" with a 200W amp and he ended up cranking 140dB).

[christjared]

I am not for sure that sono-tube would work in our case, but it does sound like a sound idea that I would like to try later on. In the box that we will make I was thinking of doing alot of port area, but havent decided on round vs. square. I know that round would be easier for quick changes in the tuning frequency, and square, well I havent really thought alot about how im going to make a ginormous square port that is removeable. As you have stated Dr. Who school is cracking the whip!! Well I know I have part of this weekend to draw up a box and try to get all the math part done so that we can build one quickly. I know its going to take alot of bracing, but we have alot of scrap wood laying around, and nothing too big to restrict air flow. I can recall the wonder box my friend made that was for two 12's. It had chopped off broom sticks in side the box runing from all the sides of the cambers. The box also had house shingles lined on the inside of the box. No matter what subs you put in that box it rocked, and it was solid. I really dont know how we are going to finish the inside of the spl box. I was thinking alot of resin to add strength and smooth things out. Is there any certain way a port should be located in a box. I know where we want it to produce maximum spl's in side the vehicle but does it matter on placement in the box itself? Well I am off to bed thanks for all the great input so far, and I will give updates as we build and when we are done!

Thanks Alot!!

JC