Competition Newbie build help

[Loud(ish)_Geo]

I'm planning an overhaul of my 93 storms system to compete in the Meca spl modified m1 class. The build is planned to consist of an American Bass xd1522 (running off my current pioneer gmd9701 amp at 1200w@1ohm) I plan to build a (round about) 4cu ft ported box that will go where my back seat is currently, and it'll be tuned to 30hz through a pair of 3" aero ports aimed between the front seats. I'm mostly just looking for advice to any changes to the box as well as what to do to get my power under control and any other tips and tricks for competition. I don't know if I should try to mount a bigger alt or if a big three and suplementary battery would be enough to handle my bass amp + my 200w rms x4 4channel. Also as a disclaimer the car will not only be for competition so I'm not willing to give up bandwidth to gain peak dbs

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[THATpurpleKUSH 5,000+ posts]

30hz is too low for spl, you want the ports tuned to around your vehicle's resonant frequency which is the note that you will burp. A geo metro will prob peak in the upper 40s to low 50s.

Ports need a hard surface to load off, fire the ports to the side or rear

Multiple small ports are less efficient than a single port.

If you are serious about competing then use a single 6 or 8 inch port.

Lastly, buy an SPL meter if you dont already own one.

You need to do lots of testing, without owning a meter you are pretty much dead in the water.

 

[THATpurpleKUSH 5,000+ posts]

I am a supporter of competitions and I've been to MECA events, so in the interest of helping you and participation in the organization along with having a normal day off for once in a very long time, I had a few minutes to model your design to give you and idea of where you are starting at.

Keep in mind models are not the end all be all of performance, this is simply a guideline and its for an XD15-44, the main difference is going to be the impedance plot because of the different coils, I didn't have a 2 ohm version XD in my database. I am including some quick screen shots as well as the pdf with all plots. Note that your design is very bottom heavy and some adjustments will need to be made, starting with ditching the severely undersized ports and stepping up to a proper size.

The plus side to this design is that it will handle rated power down to about 27hz before xmax is reached and it begins to unload but it will be pretty boomy sounding at that point.

 

[Loud(ish)_Geo]

I am a supporter of competitions and I've been to MECA events, so in the interest of helping you and participation in the organization along with having a normal day off for once in a very long time, I had a few minutes to model your design to give you and idea of where you are starting at.

Keep in mind models are not the end all be all of performance, this is simply a guideline and its for an XD15-44, the main difference is going to be the impedance plot because of the different coils, I didn't have a 2 ohm version XD in my database. I am including some quick screen shots as well as the pdf with all plots. Note that your design is very bottom heavy and some adjustments will need to be made, starting with ditching the severely undersized ports and stepping up to a proper size.

The plus side to this design is that it will handle rated power down to about 27hz before xmax is reached and it begins to unload but it will be pretty boomy sounding at that point.

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Thank you for all the help man I'll definitely take all that into consideration

 

[Popwarhomie 5,000+ posts]

What he said. Get a meter. Do a sweep to find your cabin peak hz. Go from there.

 

[Loud(ish)_Geo]

Just took a look at my car, and it seems the best placenta for the port would be aimed straight up at the massive rear hatch window, would it be a bad idea to do that

 

[Loud(ish)_Geo]

Just took a look at my car, and it seems the best placenta for the port would be aimed straight up at the massive rear hatch window, would it be a bad idea to do that

Placement not placenta

 

[Buck 5,000+ posts]

What's the space you have and what is the car? I'm not sure if I missed it, is it a Camaro or a Geo? lol

 

[Loud(ish)_Geo]

What's the space you have and what is the car? I'm not sure if I missed it, is it a Camaro or a Geo? lol

It's a Geo Storm "mini Camaro" and in terms of space I have very little, the box is gonna take up where the back seat is and into a bit of the trunk, and I plan for it to not go above the window line

 

[Buck 5,000+ posts]

I'd have to see the box orientation to understand I think.

 

[Loud(ish)_Geo]

I'd have to see the box orientation to understand I think.

This should give you the general idea, the green would be the baffle

 

[hispls 5,000+ posts]

This should give you the general idea, the green would be the baffle

That would most likely be a colossal failure. If you're not going to do a proper flat wall you should consider staying in the trunk. What you have illustrated may well put you into a wall build class too which will have you in the lanes with guys who have you beat by 20dB.
First and foremost you should figure out which organization has shows local to you and read their rule book to figure out what class you're going to be in and consider the limitations. Next buy an SPL meter. You definitely will never be competitive if you do not own one or have easy access to one. Best yet would be to find a local team or crew who competes a lot that you could join and share ideas and resources.

 

[Loud(ish)_Geo]

That would most likely be a colossal failure. If you're not going to do a proper flat wall you should consider staying in the trunk. What you have illustrated may well put you into a wall build class too which will have you in the lanes with guys who have you beat by 20dB.
First and foremost you should figure out which organization has shows local to you and read their rule book to figure out what class you're going to be in and consider the limitations. Next buy an SPL meter. You definitely will never be competitive if you do not own one or have easy access to one. Best yet would be to find a local team or crew who competes a lot that you could join and share ideas and resources.

I'll definitely have to get a meter but as I said in the start of the thread I plan to compete in Meca sol's modified m1 division (I would've preferred to compete in the street modified division but I don't think that I'll be able to meet their "enclosure must be 1ft from the headliner rule for that class"), but either way I'll be in the 1500 pressure class which a 1200w 15 should put me at the edge of so that + the very small cabin of my car should give me a slight advantage as well. Lastly (as I also said at the very beginning of the thread) it's not gonna be a pure competition build so I'd be perfectly happy to lose a couple db to bandwidth or style gain. I'm not really planning to build something that'll come first in every event, I just want something competitive enough that I could have fun with

 

[hispls 5,000+ posts]

I'll be in the 1500 pressure class

1500W measured how? Clamp, rated power? Are there """cheater amps""" for that org?
Mounting a sub central in a vehicle is a recipe for failure every time both for good flat response and max SPL.

 

[THATpurpleKUSH 5,000+ posts]

I'll definitely have to get a meter but as I said in the start of the thread I plan to compete in Meca sol's modified m1 division (I would've preferred to compete in the street modified division but I don't think that I'll be able to meet their "enclosure must be 1ft from the headliner rule for that class"), but either way I'll be in the 1500 pressure class which a 1200w 15 should put me at the edge of so that + the very small cabin of my car should give me a slight advantage as well. Lastly (as I also said at the very beginning of the thread) it's not gonna be a pure competition build so I'd be perfectly happy to lose a couple db to bandwidth or style gain. I'm not really planning to build something that'll come first in every event, I just want something competitive enough that I could have fun with

Meca clamps actual power and combines that with the cone area in sq inches to determine pressure class. A 15 on a 1200w amp should be in the lowest possible pressure class. If its a true 1500 class, you will be seriously outgunned because the impedance rise puts you at roughly half of the amps rated power which is about 600 +176 sq in of cone area so that puts you at 767 which is half of what is allowable. It would be like bringing a safety box cutter to an AR15 shooting match.