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Discussion Starter #1
I need a sub. I started looking around, and came to the conclusion that an eD A2-300 would fit the bill. However, since I live in Canada, the cost went from $350 USD to $515 CDN (after shipping etc.). The same went for other subs (HSU, SVS, BIC). I did not like the idea of paying 150-200% of the US price, so I started looking into DIY kits.

I know nothing about this, I've never done anything similar before, and I'm not exactly "handy" so treat me like a total newbie.

With $400 CDN, can I get a kit (or parts) that will outperform (or be on-par with) the A2-300?
Size is not an issue, and looks are not an issue. The only issues are cost and performance. The primary use will be movies/tv followed by music, about a 70-30 split.

I've looked at the following:
Quartet10 - $365 shipped + materials + labour/time
Quartet12 - $474 shipped + materials + labour/time
MJ-18M, 2 4" flared ports, and BASH300 - $491 shipped + materials + labour/time

I'd only consider the ones going over my budget if they are *better* than an A2-300. I've looked at graphs, and they seem better, but like I said, I am a newbie. Given that this would be my first DIY project, and my requirements above, what parts/kits would you recommend? I'm not "married" to any option I have right now, so I'm considering everything. The only thing is, IB = not an option.

I'd appreciate any suggestions, advice, and recommendations.
 

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Do you have any wood working experience? Do you have the tools to make accurate cuts in MDF? If building a box isn't a problem for you then $450 would get you an excellent sub for the money.

The MJ-18M in 12 cu.ft. net volume tuned to 20 hz with three 4" flared ports and a Bash 300 watt amp would out perform a A2-300 without question. The sub is $175 shipping included and get the amp and ports from CSS.

mj18m.JPG
 

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Discussion Starter #3
Thanks for your reply.

You're right, it is actually cheaper than I calculated. I don't have experience in cutting MDF, but I can get help there. I'm not too worried about that. Would you say the Mach5 option is the best one, at least from the ones I listed?
 

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Discussion Starter #5
Sounds great, thanks for your help.

Is there a set building/construction plan for the MJ-18M that I should follow?
 

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Discussion Starter #7
Whoa... nice. Thanks.

I still don't know where/how to start though. Should my volume be 13 cu. ft? That's one of the specs listed on the MJ-18M page. Do I just figure out what volume I want, and then try making a box the appropriate size? What about the braces? And ports? If I just order 3 4" ports from creativesound, won't I have to worry about their lengths?
 

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The net volume should be 12 cu. ft. To that you add the dispacement of the ports, sub and bracing to get the total internal volume. 12 .cu. ft. tuned to 20 hz means you use the three 4" ports as they are, which is a 17" length. No cutting or adding on for a simple build. Bracing will depend on what the cabinet dimensions are, post what your dimensions are and we'll figure out what you need.
 

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Discussion Starter #9
Thanks for still guiding me along, heh.

Before I get my dimensions, the 4" ports on creativesound are 12" long, or at least that is what the page says. That means I should email them to see if they have 17" ports first, right? Or was your 17" length referring to something else?
 

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Discussion Starter #14
Thanks for the replies.

Still waiting for an answer from CSS.

If I was to cut PVC pipe, would I need to make the flared ends?

I've been playing with WinISD. These are the settings I used:

Driver = 1 Mach 5 Audio MJ-18M, normal placement
box type = vented
alignment = QB3
box volume = 12
vents = 3, 4" diamater, 17" length
signal = 300W

Given the above, my tuning frequency ends up @ 20.57Hz. If I understand correctly, altering the diameter/length of flare ports, and the box size, affects my tuning frequency. I can go backwards and change the tuning frequency, which would adjust the ports and box size. Do I understand that correctly?

Now, can I just tune for something like 14Hz? or 30Hz? What does tuning mean exactly? Is it roughly the point at which the graph would level out? So at the tuning frequency, and up, the SPL would be almost constant (relatively speaking) compared to the frequencies below the tuning frequency?
 

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If I understand correctly, altering the diameter/length of flare ports, and the box size, affects my tuning frequency.
Yes. Changing the diameter of the ports also affects the port air speed.

I can go backwards and change the tuning frequency, which would adjust the ports and box size. Do I understand that correctly?
Changing the tuning frequency changes the port length, not the box size.
Now, can I just tune for something like 14Hz? or 30Hz?
With the right sub for a specific application, yes.

What does tuning mean exactly?
Tuning a sub gets the most output for a specific application. The MJ-18M tuned to 20 hz in 12 cu.ft with 300 watts would give you the most low end output for HT.

So at the tuning frequency, and up, the SPL would be almost constant (relatively speaking) compared to the frequencies below the tuning frequency?
At 20 hz and below the effects of room gain come into play which WinISD does not account for. An average is 6 db depending on the size of the room. There is the possibility of a flat response (relatively speaking) down to 15 hz or lower. Modeling results and real world results are 2 different things. This can be seen in the subs builds posted here where the design was done with a modeling program and the subs in room response was measured with REW.
 

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Discussion Starter #16 (Edited)
Thanks.

How do I get started with the calculator on this site?
If I start with the box dimensions, I don't have the volume of the bracing. If I start with the bracing, I don't know how big it should be because I don't have box dimensions. I can get the volume of the ports, but not the subwoofer driver.

EDIT: Yet another question - is there any advantage to trying to build a sonotube over a box? I never even considered tubes, but maybe I should have. Aside from shape, I don't know what the main differences are.
 

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Start with box dimensions that have an internal volume of 13 cu.ft. Subtract the bracing, port and sub to see how close you are. You can make adjustments from there. It doesn't need to be exact, as long as it's close.

Tubes are easy to build if you have a router to cut the circles with. Aside from shape, there are no differences in performance.
 

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Discussion Starter #18
Thanks again.

Would I need different parts for a sonotube? I mean, the MJ-18M driver and only 1 port? What would you recommend for a first-timer, sonotube or box?
 

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A tube would be easier as it's just a tube with endcaps, no bracing to worry about. It can be built with one port which would be a 8" diameter sonotube, which is big enough to allow you to upgrade the amp in the future and not have to worry about port noise. The legs can be 1" diameter dowels. To give you an idea, here are the dimensions you would need for a 24" diameter sonotube.

sonotube.JPG
 

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Discussion Starter #20
Heh, thanks for your continued help and quick replies!

Could I use the same driver? Are some drivers better suited to tubes, while others are to boxes? Or does it not matter?

Just downloaded that program, trying it now.
 
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