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So when people say Sub woofer tuned at 20 Hz or 19Hz , What exactly do they mean? I am a beginner and I have read about sealed and ported subs, How do you tune a sub? :scratch:

Regards,
Dev
 

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Discussion Starter #48
ok guys, what is the easiest way to cut the hole for the driver, the opening for the amp and window brace?

also, what size/type of screws for 3/4 mdf? i thought about pre-drilling the mounting holes with a small bit to ensure the mdf doesn't split once assembly begins. thanks in advance...
 

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mlkmgr, any updates on your build? I just built this same box last weekend but haven't bought my sub or amp yet. I put my old Sony 12" sub powered by a 100w amp in it and it sounds 10 times better than the enclosure the Sony sub originally came in.
 

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ok guys, what is the easiest way to cut the hole for the driver, the opening for the amp and window brace?

also, what size/type of screws for 3/4 mdf? i thought about pre-drilling the mounting holes with a small bit to ensure the mdf doesn't split once assembly begins. thanks in advance...
I use sheetrock screws. You want to predrill for these or risk splitting. The drilling and screw situation can be more complicated than it appears, maybe it's overkill but I like to drill the outer board larger than the outside dia. of the threads of the screw, so it doesn't bind...then also countersink the head. There are tools that do this but the same can be accomplished with a set of regular drill bits.

A router and circle jig can make very nice cuts for the driver but if you aren't picky a jigsaw will work and may be more readily available and/or cheaper.

Careful working with that MDF, it makes a lot of nasty dust! Work outside and/or use a dust mask if possible, I prefer plywood but that comes down to personal choice.
 

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Discussion Starter #51
just an update, if you want to call it that, i have the mdf cut and am ready to assemble. however, i went and cut the diameter of the hole for the driver too large. i had to go pick up a new sheet of mdf--(thinking of a smaller sub for another room so will have some mdf for later). after looking at it and doing a pre-assembly before gluing or using screws, i realize where some design flaws have been made. nothing too major, but a cut here and there will make this assembly much easier. will post back hopefully tomorrow with some updates!!
 

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Discussion Starter #52
quick question before assembly begins. i just downloaded winisd "pro" and the slot port required is longer than the other winisd version i was using before. which version should i be modeling after.

the original version, with 6.35cu ft & 18Hz tune stated ~18.92" vent length while winisd pro states 24.22". this would be using a 1" x 21" vent opening.

which should i use? i would like to know now before i begin assembly as i do have the mdf on hand to make the longer vent if necessary. thanks to those that can help!!
 

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I don't use WinISD but I have Bass Box Pro and would be willing to do a reality check on the volume and port length for you. Did your outside dimensions end up being 22.5 x 25.5 x 26.5? Using 3/4" MDF? One Shiva Driver? How much bracing did you use? Just what is in the last diagram?

Mike
 

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I think this is also going to depend on how much fill you are planning to use. Are you planning to go minimal, typical or heavy fill? Just playing with this factor alone seems to change the necessary port length by about the differences you are looking at there.

Mike
 

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Discussion Starter #55
correct, outside dimensions 22.5 X 25.5 X26.5 and using 3/4" mdf. bracing was used as shown in "cut sheet". using the bracing calculator from this site, i calculated 3.678 L (224.438 cu in) for the bracing. the amp is 10X10X5 mounted to the back.

Thanks for your help Mike!
 

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Discussion Starter #56
i based my design off the "6.35 Cu Ft tuned to 18Hz with 50oz polyfill" on the shiva application pdf. http://www.diycable.com/main/pdf/shiva_app.pdf
i just did not want to use the "flared ports" in the design.

so just using the recommendations from the app pdf, i would say using 50 oz poly-fill. i don't know if you classify the fill as min, typ, or heavy? is one type classification better than another?
 

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Basically, the more fill you use (up to a point), the larger the enclosure looks to the woofer and the shorter your port has to be to achieve the same tuning frequency. For now, I'm going to call 50oz typical. Kevin may be able to tell us if it is considered typical or heavy fill for a cabinet of this size.

Mike
 

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Well, here is what I come up with...

Using the typical fill option, I get 22.92" as the necessary port length at 1" x 21" to tune to 18Hz.

Even considering the extra wood needed to make the port that length, I come up with a net internal cabinet volume of 6.8 cu.ft.


Using the heavy fill option, I get 20.26" as the necessary port length at 1" x 21" to tune to 18Hz.

Considering the extra wood needed to make the port that length, I come up with a net internal cabinet volume of 6.825 cu.ft.

This thing is going to rock! The attached graph shows FR without room gain. Once you factor in room gain, you should have some very usable output into the teens or lower!

Let me know if you need anything else.

Mike
 

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Discussion Starter #59
so is the 18Hz an ideal tune? would i be better off shooting for a lower tune? should i go lower? as i stated, i simply modeled the internal volume and what not after the shiva pdf.

i noticed in your graph it states 300Watts. i am using a 500Watt amp if that makes a difference?

with my fubarred calculation on box volume (i used the box calculator here on the site, but must have done something wrong!!), should i add some addtional bracing to the box to help stiffen it up? thanks again...
 

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Naw, the amount of power will not have an effect on FR, only output. To demonstrate this, I have attached another graph. I also attached a graph showing you will run out of excursion somewhere around 15Hz. You'll want a high pass filter on this baby so you don't trash your brand new woofer. :whew:

As Kevin has said many times (and I am paraphrasing) don't sweat the small stuff. Your design is good. The biggest thing I would be worried about is port noise but I think earlier in the thread Kevin said you were good with that so sweet deal!

If you tune this thing to 17Hz or 18Hz or 19Hz I don't think it really matters that much. If you want to go lower you can but the lower you go, the more of a problem port noise may become. Your bracing looks good to me. I really don't see any problems. :T

Mike
 

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