Notacop

Ok so I got tired of my current subs pretty fast.


I currently have 2 old Kicker Impulse 15's in a sealed box that is about 2.5 cubes sealed after speaker displacement.


I do not like the lack of punch it has. I listen to all variety of music from classic rock (zepplin, doors, pink floyd) to newer music (DMB, Weezer, blues traveller) to rap (all the new stuff). So I wanted a box that would be a good all around performer. Sealed boxes usually fit the bill but with these sloppy subs there was no hope.

I got a deal on a different forum on 3 RE8's and while I am waiting for them to arrive I am trying to decide what I want to do with them.


I have come up with 4 options in order of simplest to most complex and I present them to you for your viewing pleasure. Feel free to point out any errors I may have made or provide constructive criticism.

My goal is to get something much more musical than what I have now and to keep as much output as possible in the process.

I will be using the same amp (mtx 2150x) to run any of these setups.

These will be going in the back of my 2005 Scion xB as a false floor in the back where the cargo storage and spare tire used to reside.

Here are pictures of what it currently looks like with a 38"x20"x9" box in the back.

Left side:


Right Side:


Front edge:


View from a few steps back:



Oooh check out that pimpin dual exhaust:



Wait!!! how did that pic get in there ;) Actually you can see my plates which correspond to my forum name but that does not make much sense on this car. When you see the plates on my last car you will understand:

http://www.cardomain.com/id/notacop

It was fun.



I do not want the new setup to be any larger than that. As you can see 38" puts it right up against the shock towers on the sides, and 20" puts it very tight against the back of the seat. Any more than 9" tall and I can't get away with it being a false floor after carpeting it.

All of these drawings were done in MS Excel and the grid lines are at 1" increments.

Option one is the simplest and most space efficient. All 3 RE8's that I purchased in a simple sealed box:



external dimensions are 30"x16"x6" for an internal volume of about 1 cube after speaker displacement.

I believe this enclosure would give me the sound I am looking for but I am afraid the output will not be there.

Option two solves the output issue with a little hit to the punchiness (is that a word?) of the box. I present 3 RE8's in 1.3 cubes (after port and woofer displacement) with 15 square inches of port area (2 ports 1.5"x5") each port 30.25" after end correction. External box dimensions are 38"x20"x6.5" Tuned 30 hz:



Ok well that is a good option but I have worked with ABC boxes in the past and thought I could probably get the same output as 3 sealed with 2 in an ABC box. So I whipped together an ABC box for 2 RE8's. External dimensions on this one are 33.75"x20"x6.5". The ports are 1"x5" and they are 28.25" long with end correction. I am a little concerned with only 10 square inches of port area for 2 8's. I do not have my final numbers in front of me as to the exact internal volumes and tuning frequencies. If I remember right they are 0.7 cube for the large chamber and 0.37 for the smaller chamber. These gave tuning frequencies of about 23 and 33 hz.




That solves the quality and output but why only use 2 subs if I am going to have 3 available? So I went to town trying to cram 3 8's in an ABC box in the space I had available. PVC ports were not an option because a pair of 2" is not really enough port area and a pair of 3" would have to be 25"+ which just does not fit in the size and shape I am working with. External dimensions are the same as what I have back there currently; 38"x20"x9". Ports are 1.5"x7.5" for a total of 22.5 square inches of port area. The ports are 40" long after end correction. Overall Volume is 1.61 cubes after port and woofer displacement. 1.08 In the larger chamber with the subs and 0.53 in the smaller chamber. These tune to about 25 and 35 hz. This should play low and loud and be very musical.




I was hoping to be able to slim down the size of my box to under 7" overall height, but it is very tempting to keep the 9" height and squeeze 3 8's into an abc box in the back.


Let me know your opinions

BLACKICE

Well, I used to run 8 RE 8's in my Xa so I know how to make them sing. First off, have to be careful in putting 3 in your enclosure, depending upon the type you build, could cause cancellation big time internally.

General rule of thumb, .5cft for each RE 8. If you want incredible resonant bass (I used to play 10 cycle tones as a demo with 2" of excursion on those babies!), then it's the wave phase alignment you need to worry about, assuming you don't go sealed or straight ported. I used modified snail shells to do mine and it worked great, but I pounded all 8 with a Tru SH-1 just for fun.

Those RE8's can play low, we showed that for sure, but it's all in the enclosure and the geometry of your vehicle. Concentrate on that and you will have a system that meets your goals for sure.

Kind Regards,
Matt

Notacop

hmm how can you figure out cancellation? For now I slapped em in a quick 1 cube box for all 3 of em. The box is 20x16.5x8.5 outside dimensions. The speakers are in a triangle on one of the 20x16.5 faces. They do pretty good on my mtx 2150x wired to 6 ohm. not super loud good enough. I have only listened for about 10 minutes since I put it all together so far.

BLACKICE

Well, if you are running a sealed enclosure, obviously there is no cancellation. If you are running a basic ported box, generally you are safe as well.

Running 3 subs together in a common chamber is always a tricky setup, because it's the third sub that usually is the problem. There are ways around it but it will depend entirely upon the type of enclosure you are going with. For example, if you used a basic snail shell enclosure then the trick would be to use the right size aeroport on the slant board between the second and third sub. Another option is to have each sub in it's own separate chamber.

If you are using 1cft gross for all 3 then you don't have enough volume to do what you want. I would stick with .5cft net for each sub ported, 20% less if you run common chamber. I do alot of advanced mathematical enclosures (modded t-lines, folded horns, snail shells, etc.) and I can tell you that it takes alot of teting to get those just right, and they differ from vehicle to vehicle, sub to sub.

What you might try first is to build your enclosure as 3 separated ported enclosures, each about .5cft. That way each sub has the correct volume, ported will ensure that you have little chance for error on the enclosure, and let you see generally what you will get out of those subs in your xB. You can them go from there using that as a baseline. You can also then put your common 3 sub enclosure back in and see the difference. Also, you might want to watch the movement of all 3 subs to see what's happening with them. If your enclosure has near perfect acoustical resonance then of course the subs will move very little, or perhaps servo, but it one appears to be moving wildly out of control, then you know.

As for cancellation, I always meter ever single change and track it. Move the enclosure 1" forward, I meter it. Change the angle of the seat back, I meter it. You would be surprised at what might give you a big gain. Also, another "eyeball" test we use for wave phase is to meter with the door open and close. But you have to know your vehicle and it's geometry of course.

In an xB I would have the ports and subs either both firing backwards, loading off the hatch, or both firing up. Usually the best positions.

Well, I said alot, not sure if I answered your questions though. Let me know if I didn't.
Kind Regards,
Matt

Lonely_Raven

Dude, awesome box design. I'm a big fan of both sealed and
bandpass and sometimes transmission line.

I like your last design the best.

Whatever you choose, please share the measurements,
because I think I'd like to build one too! I'm realizing my
current bandpass whistles too much with more modern music
but is fine with rock. I want the same flexability as you.

J_A_Trevino

yeah keep us updated on your progress, looking good though.