New box for my Maelstrom-X? - Home Theater Forum and Systems -

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post #1 of 48 Old 03-03-10, 01:35 AM Thread Starter
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New box for my Maelstrom-X?

I changed the place of where my sub is currently sitting, and it opened up some options for a larger box
I talked a few things over with Mike P. (he's a huge) help.) about port dimmensions for a 16 cu.ft. box, and he came up with this for me. I wanted to be able to change the tuning by blocking/plugging up some ports. That way I can have the best for music, and for movies.
He came up with eight 4x5 inch ports at 45 inches long for a 23hz tuning, plug up five of those ports, and it lowers the tuning down to 14hz. Port velocity for the movie tuning is 23m/s at 13.60hz, so that will be fine. That's with a 14hz HPF. The port resonance is 150.42hz, so that is kinda close to the optimum 190hz resonance. Keep in mind that I can block more ports to lower the tuning even more, but high port velocity starts to kick in.

Here's a WinISD graph showing the improvements over my current box.

I should expect a 4dB gain from 17hz down. At 14hz, I should be up by about 6.5dB with the new box. With a few ports clogged up, at 10hz, I will be up ~8dB up from the old box, although I don't really care about 10hz output.

I'm working on drawing something up on Paint to hopefully let you guys see my design. I would use Sketchup, but I don't have it installed at the moment. And Paint is easier for me because I haven't experimented with Sketchup much yet.

I also have the thought for two-four 18" passives from Kevin in my mind. So, I might end up going down the PR route instead lol. It just looks much easier to build, and I can keep the box slightly smaller due to not having extra port volume.

Hopefully I can get this second build started sometime soon, but I'm currently busy with my racing, and school. So its kinda on the back burner for a while. But, I will get this new box built sometime soon! lol.

Last edited by sub_junkie; 03-03-10 at 01:42 AM. Reason: Added more information
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post #2 of 48 Old 03-03-10, 12:08 PM
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Re: New box for my Maelstrom-X?

o wow FUN!
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post #3 of 48 Old 03-03-10, 07:09 PM Thread Starter
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Re: New box for my Maelstrom-X?

What is the cut off air velocity for an 8 inch round port?
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post #4 of 48 Old 03-04-10, 01:47 AM Thread Starter
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Re: New box for my Maelstrom-X?

One quick question. I recently saw a box that was ported for movies, but had multiple smaller ports in the box also. They were just sealed up when the movie porting was wanted. What I'm getting at is, will the ports that are blocked off still function somewhat unless they are completely clogged up? Like not just sealed off at the tip of the port so no air could get by, but would that affect performance any if you didn't have the whole port sealed off so air couldn't go half way up the port?
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post #5 of 48 Old 03-04-10, 09:18 AM
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Re: New box for my Maelstrom-X?

The whole port doesn't need to be plugged, SVS uses this technique also.
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post #6 of 48 Old 03-07-10, 02:56 AM Thread Starter
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Re: New box for my Maelstrom-X?

Now that I've gone back through a few designs, I will be able to fit a 22 cu.ft box into the wanted space. It will be tuned to 14.32hz. <Outer> Dimmensions for the box will be 20.75 inches deep (countersinking driver; add .75" for second panel), 48 inches tall, and 56 inches wide.

I wish I could get this built right away! But, patience is a virtue...
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post #7 of 48 Old 03-07-10, 03:18 AM
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Re: New box for my Maelstrom-X?


That size for a sub would yield 32 cu ft before port, bracing and wood etc.... This leaves about 25 cu ft. A single maelstrom could still take 1500 watts before max excursion and you would need a 10" port to keep port velocity down. 1st port resonance is 189hz and tuned to 14hz would give you some crazy bad bass mate. No hpf on my pic but you probably woudn't need one. I have not found the need for one yet.

Here's what I come up with. Defo a 2 man job to build it though.


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New box for my Maelstrom-X?-dylans-sub.jpg  

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post #8 of 48 Old 03-07-10, 08:47 AM
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Re: New box for my Maelstrom-X?

I'm for you using those discounted PR's they have and then using the additional space for an even bigger internal size.
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post #9 of 48 Old 03-07-10, 09:13 AM
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Re: New box for my Maelstrom-X?

With an SVS sub you have to change the sub sonic filter setting when ever you change the number of ports. Would you have to include that adjustment in a diy build?
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post #10 of 48 Old 03-07-10, 11:29 AM
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Re: New box for my Maelstrom-X?

I don't want to sound negative, but I want to play devil's advocate here before you possibly do something you regret.

Changing tunes by plugging ports is not a sound concept in my opinion. When you lower the tune, you need more cross sectional area, not less. Also, using 8 ports not only makes the build harder, but it increases the turbulent flow in each port as compared to using a single larger port.

What are you hoping to achieve with music with a 23hz tune that you can't achieve with a 14hz tune? If there isn't much below 30hz in the majority of all music to begin with, getting extra extension doesn't help or hurt anything, as it isn't being used. Since the enclosure volume stays the same, excursion above 30hz will stay almost exactly the same above 30hz as well, so the bass won't be noticably cleaner. There may be a minimal headroom advantage above 30hz, but I doubt you'd be able to get everything out a Maelstrom 18" in that range to begin with, even sealed.

All you would really be accomplishing is degrading your transient response with the higher tune, as can be seen from measurements of SVS subs with this concept.
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