Dual RL-P18 LLT for my 2000 cu ft HT soon - Page 5 - Home Theater Forum and Systems - HomeTheaterShack.com

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post #41 of 183 Old 06-01-07, 04:50 PM Thread Starter
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Re: Dual RL-P18 LLT for my 2000 cu ft HT soon

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aceinc wrote: View Post
My suggestion on the bracing is if you are going to brace in the middle of the cabinet with 1"x4" or similar instead of placing the braces parallel to the walls of the cabinet put them at an angle.
What's the benefit of putting them at an angle?
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post #42 of 183 Old 06-01-07, 08:54 PM
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Re: Dual RL-P18 LLT for my 2000 cu ft HT soon

My thoughts are that if braces are needed to reinforce the cabinet and increase the frequency at which the cabinet resonates (as well as reduce the tendency to resonate) placing them as non-symmetrically located as possible and oriented so that they break the cabinet into a number of non rectilinear sections may be beneficial. I can see at least 3 benefits;

1) oddly shaped spaces will discourage standing waves.

2) panels whose braces are assymetrical and oriented "randomly" will tend to have fewer reinforced resonances. In other words if there are multiple panels with the same geometry and bracing they will tend to resonate at the same frequency, reinforcing (amplifying) the resonated sound.

3) reflecting high frequencies at an angle will increase the amount of travel before they will go through the speaker cone, (as opposed to hitting a flat piece of wood and bouncing right back) decreasing their amplitude, and increasing the amount of polyfill they will travel through, reducing their amplitude futher.

These are my ideas, I do not have test data, or other empirical evidence to substantiate them. Perhaps some heavyweights can weigh in on these concepts.

I would not expect a large difference, but with a little effort you may get some benefit.

Paul
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post #43 of 183 Old 06-02-07, 02:19 AM Thread Starter
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Re: Dual RL-P18 LLT for my 2000 cu ft HT soon

Paul,

Your thoughts seem very logical... And anyway I think that if the benefits are only minimal, there is no drawback!!
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post #44 of 183 Old 06-02-07, 04:43 AM
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Re: Dual RL-P18 LLT for my 2000 cu ft HT soon

Regarding standing waves, I have a set of Atlantic Technology speakers (System 8200) where the cabinets have sloped backs that is suppose to help with standing waves.

Would the same design benefit subwoofers?? Any guesses how much slope would be correct??
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post #45 of 183 Old 06-02-07, 05:06 AM Thread Starter
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Re: Dual RL-P18 LLT for my 2000 cu ft HT soon

Of course this would help for subs also. I applied such a shape for my car's, but for the monsters I will be building I have to keep the rectangular shape for better utilization of volume and save some space.

I do not think the slope is so critical....remember that all these are hepling factors but not basics IMO...

B Rgds
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post #46 of 183 Old 06-02-07, 11:56 AM
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Re: Dual RL-P18 LLT for my 2000 cu ft HT soon

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for what it is worth is I like MDF
I on the other hand, would follow the advice of the cabinet maker, and build the box out of plywood. You want it to be void free (ie Baltic Birch or ApplePly).

Hopefully, without starting a holy-war, i will state my opinion, that MDF is one of the worst materials for building speaker enclosures. I'll put an exclaimation on that by saying that we get MDF for free, yet still go out and buy BB for making boxes.

For a subwoofer this is even more the case. Even staunch defenders of MDF will admit that the extra stiffness of plywood makes it better for subs. Probably the most important characteristic of a sub box is that it not act like a balloon. (another little realized problem with MDF is that it is not air-tight)

The box needs to be braced (and please do not be tempted to put them dead centre -- that is the worst place for them)

The need for stuffing in a sub is debatable, but the rational was covered pretty well in an earlier post. Do take into consideration that it will change the apparent volume of the box, and thus its impact on the box tuning needs to be considered.

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post #47 of 183 Old 06-02-07, 11:58 AM
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Re: Dual RL-P18 LLT for my 2000 cu ft HT soon

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Regarding standing waves, I have a set of Atlantic Technology speakers (System 8200) where the cabinets have sloped backs that is suppose to help with standing waves.
If you do the math, given the size of even a large sub box, and the frequencies at which it will operate, standing waves are not an issue.

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post #48 of 183 Old 06-02-07, 12:25 PM
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Re: Dual RL-P18 LLT for my 2000 cu ft HT soon

Some of the cabinets that are built based on the LLT design defined elsewhere on this site can have dimensions exceeding 5'. Wouldn't this start causing problems around 113hz? Not out of the range of some subs.

Cost is one reason for some of us to be involved in this "hobby" and the difference between 13 ply, void-free BB and MDF can make or break a project.

Regarding MDF being airtight, I use what I believe to be a simple, effective, and low cost option to resolve this;

After the cabinet is built, but before finishing the outside I slop a thick coat or two of latex paint on the inside of the cabinet. To maximize my funds, I only buy "oops" paint from the local Home Depot/Lowes at $5.00 per gallon. I try to get semi-gloss, as this tends to be quite rubbery when dry, my current cabinets that I am building using a design from planet10's Frugal-horn.com web site, have a rather garish purple interior.

Paul
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post #49 of 183 Old 06-02-07, 12:30 PM
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Re: Dual RL-P18 LLT for my 2000 cu ft HT soon

Quote:
but before finishing the outside I slop a thick coat or two of latex paint on the inside of the cabinet
Doesn't latex breath though? I wonder if an oil based varnish or the like would be better? Don't really know.

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post #50 of 183 Old 06-02-07, 02:41 PM Thread Starter
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Re: Dual RL-P18 LLT for my 2000 cu ft HT soon

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planet10 wrote: View Post
The box needs to be braced (and please do not be tempted to put them dead centre -- that is the worst place for them)
Thank you for your post , I just need some clarifications pls
What do you mean by dead center?
Quote:
The need for stuffing in a sub is debatable.
How? Pls elaborate, Do you mean that not stuffing would be acceptable?
Quote:
Do take into consideration that it will change the apparent volume of the box, and thus its impact on the box tuning needs to be considered.
dave
According to the modelling softwares, lining the walls does not change the tune but slightly the FR...Anything wrong with it?
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