Couple Random Sub Design Questions - Home Theater Forum and Systems - HomeTheaterShack.com

 
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post #1 of 5 Old 08-05-12, 06:46 PM Thread Starter
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Couple Random Sub Design Questions

So I am soon going to be building my first DIY subs and had a couple questions...

I plan to basically make some interchangeable sonotube endcaps so I can do several different types of subs using common end-caps which I will clamp onto different lengths of sonotube to allow me to figure out what I like without building 50 different cabinets (I'm a gluten for punishment ). Depending how things work out, I may finish up the sonotube to be final or build a cabinet based on what I learn...

So on to the design questions...

1) Ported driver question - Due to the size of the test design, I will need to lie the sonotube on it's side as opposed to the normal vertical design...as a result, the driver will be in the corner of the room with the port near the middle of the front wall. What impact does this have? I am guessing the port will not get the same boundary gain that the driver gets, so the shelf will be down several DB...is this correct? If so, then could I reverse (so the driver is in the middle) and let the difference in gain help raise the shelf (relative to the driver)? Of course doing so would come at an overall SPL cost since the driver loses the gain but if that works, it would allow the boundary difference to help flatten the shelf.

2a) Sealed - I think I am pretty good on my plans for testing a single sealed driver, but I also want to test a sealed dual opposed driver setup. Based on looking at commercial opposed cabinet dimensions, they seem to keep the drivers pretty close...is there any guideline on how close/far apart the drivers should be? I would have thought if too close, the magnetic fields would interact...

2b) Also, I saw some generic comments about mechanically bonding the opposed drivers to better absorb the mechanical vibrations but I could not find any good examples where people discussed doing this in their design or how they did - does anybody have any pointers on this (or opinions how important it is)?

Thanks

- Mike
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post #2 of 5 Old 08-07-12, 09:10 AM
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Re: Couple Random Sub Design Questions

I am not sure what mechanically bonded means. If your building a dual opposed sealed sub then mechanical vibrations cancel each other so I am not sure what else you would need other than a good solid box.

Why were you laying the box on its side? Is it because of ceiling height or another reason?

Will the subwoofers have pole vents or not?

If not then I think placing them close would be just fine. Lots of people do it on IB builds and the magnets are as close as possible and they are just fine.

"Music is the space between the notes"
[T]o talk well and eloquently is a very great art, but that an equally great one is to know the right moment to stop.
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post #3 of 5 Old 08-07-12, 06:03 PM Thread Starter
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Re: Couple Random Sub Design Questions

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chrapladm wrote: View Post
I am not sure what mechanically bonded means.
I presume they meant mechanically connected to help further absorb the mechanical vibrations - I've seen the comment in several threads but nobody ever discussed details...(I found several the other day and now my searches bring up nothing... )

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chrapladm wrote: View Post
Why were you laying the box on its side? Is it because of ceiling height or another reason?
I have a front projection screen - anything over 40" tall would block part of the screen - taking out 5" for legs, this only leaves 35" of height...
Once I figure out which design I like, I will consider building a box if necessary to work around dimension problems if I need to...but these initial tests are to allow me to quickly compare the different designs...

Quote:
chrapladm wrote: View Post
Will the subwoofers have pole vents or not?

If not then I think placing them close would be just fine. Lots of people do it on IB builds and the magnets are as close as possible and they are just fine.
Now that you ask, I think they are (testing with a pair of TC Sounds LMS-R 15s) - so I guess some space to breathe is in order...
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post #4 of 5 Old 08-07-12, 10:37 PM
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Re: Couple Random Sub Design Questions

I made a dual opposed sono that was for dual 15's and the height was only 30" tall. I used a 20" sonotube. Ended up around 95liters.

Testing different designs is always a good thing so you can hear the difference instead of just looking at simulations all day. I myself would go with four sealed 15's in dual opposed cabinets if I was you. And if you need more just add another four. But most people dont want more than four 15's. This will be the smallest setup.

The ported would be very nice also if you used four 15's but would be a big pair of cabinets.

The only thing I have seen where others try to bond any of the subwoofers was for cooling. I have seen builders modify the pole vents to make an external cooling method. How I dont know.

So when are you getting started on testing?

Have you checked out the data-bass.com website? It is very helpful for us DIY folks.

"Music is the space between the notes"
[T]o talk well and eloquently is a very great art, but that an equally great one is to know the right moment to stop.
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post #5 of 5 Old 08-08-12, 07:39 AM Thread Starter
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Re: Couple Random Sub Design Questions

Quote:
chrapladm wrote: View Post
I made a dual opposed sono that was for dual 15's and the height was only 30" tall. I used a 20" sonotube. Ended up around 95liters.

Testing different designs is always a good thing so you can hear the difference instead of just looking at simulations all day. I myself would go with four sealed 15's in dual opposed cabinets if I was you. And if you need more just add another four. But most people dont want more than four 15's. This will be the smallest setup.
Ya - ironglen in another thread was suggesting 2 dual-opposed subs (4 drivers total) so I do plan to test that out.

Based on different models (mfr vs WinISD vs Unibox recommandations) I have ranges of 90 to 180l for my dual opposed test. Interesting to note that your box almost lines up with the Unibox model...part of the point of the tests is also to see which models line up with what I hear & like


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chrapladm wrote: View Post
The ported would be very nice also if you used four 15's but would be a big pair of cabinets.
Ouch - a 4 driver ported would be huge! My 1-driver ported models are 220-280L....even though I do not have a WAF to contend with, 1000L for subs is a lot of space

Quote:
chrapladm wrote: View Post
So when are you getting started on testing?
Hope to get a single sealed together this weekend & use the results from that to tweak the follow-up designs...issue is I have no way to baseline (or is that bass-line ) my room gain...once I have a feel for how this one compares to the models, I'll tweak the other designs...

Quote:
chrapladm wrote: View Post
Have you checked out the data-bass.com website? It is very helpful for us DIY folks.
Yep - I have made use of that site...but thanks for suggesting it



If you are curious, here is the draft test plan:

Drivers are LMS-R 15s to be driven by a spare channel on my Cinepro 3k6-mk3 ([email protected], [email protected] approx). Final config will likely get a dedicated amp...
I have a balanced MiniDSP on order to provide for EQ/HPF/etc.

Tube 1: 2' long 18" sonotube to be tested with 1 driver (approx WinISD design) and 2 drivers (approx Unibox design)

Tube 2: 5'8" long 18" sonotube to be tested with 1 driver and 2 different port lengths (8" sonotube x 50" and 34" - approx 16 and 20hz tunes)

To avoid dealing with feet for testing, all will be tested horizontally. Final builds may be vertical if under 40" overall height.



Time to go find your threads and see what you posted on your build
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