3 Power Acoustik MOFO 12's

I'm looking at a picture of a 99 Grand Cherokee on line and it looks like I'm OK, and the port can go there but confirm it anyway please.

The wheel well looks like it might block just an inch or two, but thats OK

Oh, one more thing, the speakers do need to face toward the rear of the truck, not up.

 

Low frequency waves are long and the more room they have to fully develope the better off we are. By bouncing the sound off the rear hatch, I have the additional length that I need.

I'll post the dimensions after church tomorrow.

 

Then make sure the port is on the driver side. Originately I was tune to 36 Hz, but if we need to impress a meter, I will need to tune it just a bit higher.


OK, the box will need to be 40-inches wide, by 15-inches tall by 21-inches deep.

The port will be 13-1/2-inches tall by 4-inches wide. The port length will be around 16-inches long. This will get our tuning around 35-36Hz

If we want it louder then we need to adjust our tuning to around 38 to 40 Hz. This means the port length will be around 13-inches long.

I'm gonna run my program one more time (wifes birthday today) when I get a chance and post the result. It will probably be late tomorrow. I will have plenty of time tomorrow

 

My wife doesnt get home for about 10 more minutes.

At 40Hz we have a huge gain, but the graph is not that smooth. OK for competition only, but I'm gonna assume you want to listen to it also. If we drop tuning to 38 Hz we lose alot of gain, the graph is smoother and we still have 3dB of gain.

In both cases the f3 points (how low it hits) are the same, so changing from 40 to 38 doesnt effect how low it hits. So lets stay with 13-1/2-inches to 14-inches.

 

Predicting SPL numbers is difficult with a non-competition system.

I say non-competition because my design methodology is completely different for a competition system.
1. First I need to know the length of the vehicle, from the right front corner to the left rear corner.
2. I need less woofers, two would be more than enough. The less paths to the mic the better

The speed of sound (in inches per second) divided by vehicle length equals resonant frequency of the vehicle. Unless you have a Suburban, you'll end up with frequencies around 120Hz or more, much more. Thats OK, Divide by 2, because an octave lower is OK.

Now lets say we end up with a resonant of around 55Hz, we need a box that peaks at that frequency. We adjust size and tuning so our box peaks at the vehicle resonant frequency. Now we have one really loud box. Using this technique, I've reached 144dB with a single 10 and 500-watts.

Anyway, your box is peaking around 40 to 45 Hz, way too low for serious competition. But don't get me wrong, its still loud.

Measure your vehicle, just for curiousity and let me know what it is. I may play with a competition box, this week. I'm a teacher so I'm off this week. I also need a few more things, Re, Le and Sd are not listed on the website. I need those specs for more accurate simulations

 

The specs that are missing on the web site are Le (in milliHenries) Re (in ohms) and Sd ( which I can estimate if necessary). But I need Le and Re to run a more accurate analysis.

But that box will perform well. Normally I like to tune near 40Hz or more, but not with your woofer. The red line is a 40Hz tuning, the yellow is a 38Hz. If we tune to 36 we lose alot of gain.

The port needs to be 13-1/2 to 14-inches. This woofer is picky. Stay between these lengths.

 

Yes, just like the picture on Post #20 and make the port closer to 13-1/2, I would much rather be too short than too long. In fact, shoot for 13-3/4-inches. This way we will end up good regardless

 

Something like this, I added braces because I can.

This picture was made on the Promethean Board I use in my classroom.

 

I like the Promethean Board

 

promethean.....any relation to pythagoras? LOL!

 

I go back to school on Tuesday, I teach Algebra and Math Models.

And definately post pictures and a full report. Use complete sentences:lol: