$400 CDN to spend, what do you recommend? - Page 2 - Home Theater Forum and Systems - HomeTheaterShack.com

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post #11 of 26 Old 01-12-10, 02:37 PM
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Re: $400 CDN to spend, what do you recommend?

If that box size is to large for your room the Dayton 12" RF driver is another good choice.
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post #12 of 26 Old 01-12-10, 02:37 PM
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Re: $400 CDN to spend, what do you recommend?

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My mistake, I though the ports were 17" long which they need to be for your sub. Contact CSS to see if they sell port extensions.
He could also use 4" PVC pipe from a hardware store. Cut 36" in half and you got 2 ports.
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post #13 of 26 Old 01-12-10, 07:31 PM
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Re: $400 CDN to spend, what do you recommend?

That would work, he'd need enough for three 17" ports.




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post #14 of 26 Old 01-12-10, 08:45 PM Thread Starter
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Re: $400 CDN to spend, what do you recommend?

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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post #15 of 26 Old 01-12-10, 09:22 PM
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Re: $400 CDN to spend, what do you recommend?

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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.

Quote:
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.
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Now, can I just tune for something like 14Hz? or 30Hz?
With the right sub for a specific application, yes.

Quote:
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.

Quote:
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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post #16 of 26 Old 01-13-10, 06:14 PM Thread Starter
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Re: $400 CDN to spend, what do you recommend?

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.

Last edited by dfn; 01-13-10 at 08:10 PM.
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post #17 of 26 Old 01-13-10, 09:09 PM
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Re: $400 CDN to spend, what do you recommend?

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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post #18 of 26 Old 01-13-10, 10:55 PM Thread Starter
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Re: $400 CDN to spend, what do you recommend?

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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post #19 of 26 Old 01-13-10, 11:53 PM
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Re: $400 CDN to spend, what do you recommend?

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.

0 CDN to spend, what do you recommend?-sonotube.jpg




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post #20 of 26 Old 01-14-10, 12:43 AM Thread Starter
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Re: $400 CDN to spend, what do you recommend?

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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