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Discussion Starter #1 (Edited)
I've been reading these boards for a few weeks now after stumbling upon them in my home theater endeavors and I can honestly say I'm very impressed at all the knowledge and really awesome ideas here (IB stuff, etc.)

Anyways, I have a moderate idea of how all this audio stuff works, I work in a music shop that does alot of A/V and home theater-esque stuff. Friend has a 15" Polk MM2154 (pdf for them is here.) He bought two of them for his truck and ended up not using them, so we want to put them into his home theater which is lacking a nice subwoofer(s). We want to get the lower end, rumbles you feel from these if its possible.

According to the PDF it only needs 42.5L air space in a box, and when I use the calculator on the site here, the box is alot smaller than I thought it would be. I'm not sure if I'm using it improperly or what. Would a box like 30"x20"x20 be too big? If you guys could give me some actual outside dimensions (using 3/4 mdf) and possibly why, because this is a learning process for me and I want to understand what I'm doing. Aside from the box itself I'm going to need an amp for it and a guy I know suggested one of the speakercraft powerbass amplifiers. I don't know if there would be a preferred amp I could use for one (or both if I made two boxes) of these?

Thanks!
 

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These are single coil 4 ohm correct?

According to the PDF it only needs 42.5L air space in a box,
That is for a car audio application where the cabin gain boost the low end tremendously. For HT the sub needs to be modeled to see what the best box size and tuning is for HT.
 

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We want to get the lower end, rumbles you feel from these if its possible.
It's possible as long as you don't mind a fair sized box for each sub. Each in 8 cu.ft tuned to 20 hz would be the best you could do. Input power is 200 watts with a rumble filter at 18 hz. Porting is two full length 4 inch flared ports. With room gain you can expect 112 db at 20 hz from one sub.

Polk.JPG
 

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Discussion Starter #5
I've heard from a few people you can very easily mess up porting a box and seeing as I've never built a ported box from scratch I'm kinda weary of doing it wrong. Would I lose alot if I kept it sealed? I don't wanna break the drivers lol
 

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The difference between building a sealed and building a ported is cutting 2 more holes and adding tubes, it's as simple as that. The only way you can mess up is installing the wrong length tubes or not using a rumble filter. With sealed you're giving up 7 db at 20 hz, that's a big difference due to the subs limited Xmax. And you would still need a rumble filter at 20 hz with 200 watts input.

Don't be scared of building a ported sub, we'll gladly walk you through it. It's the only way to get what you want from these subs.
 

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Discussion Starter #7
Sounds like a good plan. The rumble filter you're talking about, is that a physical thing put in the box? I'm lost on how to tune it to a certain hz (my guess would be in the shape of the box but I'm probably well off.) If I have dimensions and measurements on where to put the ports etc I'll be all set :)
 

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A rumble filter is a high pass filter, it's electronic and built into most subwoofer plate amps. The exception is Elemental Designs plate amps, they don't have it. Pro amps don't have a high pass filter so you need to use and add on unit like the Reckhorn B1 or the Elemental Designs e.Q2.

A good choice for a sub amp at the moment is the Parts Express 240 watt plate amp (non boost model). They are $109, you would need one for each sub.

Tuning a sub is determined by the port diameter and length for a given box volume. 8 cu.ft tuned to 20 hz would require two 4 inch diameter flared ports that are 17" long. Parts Express has them. Ports need to be one diameter (4 inches) away from any wall. Keeping that in mind, here is a box calculator that will help you design the proper sized box.

http://www.hometheatershack.com/forums/enclosure-volume-calculator/

Any questions, just ask.
 

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Discussion Starter #9 (Edited)
Would something like this speakercraft bass power 250 work better? Also what is the difference and cons I'm assuming of the same plate amp with the bass boost on it? the receiver I'm using has just one RCA plug for the sub out, I'm missing where I'd plug it in there because its stereo inputs (just plug it into the mono side?)

edit: I was also looking at the Behringer A500... If I understand this right I could use that to power the two of those subs because it can do 2 x 230 at 4ohms. I'd want to put them in the front and back, and its like 25 ish feet from front to back of the room... is that too far to run cable to them from the amplifier? I don't know how severe the loss would be if I ran that far.
 

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The Power 250 has a lower frequency response of 30 hz, not good when you're trying to reproduce a 20 hz signal.

An amp with boost is for a sub design that is lacking in the boost frequency range and would benefit from the boost. The sub also needs the ability to handle the increased cone excursion that the boost would produce. It's definitely not for this sub design.

To connect more then one amp to the single LFE output you would use a Y splitter.

The A500 would power both subs but you still need a high pass filter. A 25 foot run is not a problem.
 

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Discussion Starter #11
I think I'm going to go with the A500 for this, seems like the best thing to do for both. I'm really leaning towards going with a sealed enclosure even if I lose a little bit of performance, just because I have the most experience with those and the people I work with suggested that over it being ported; just because I have them physically here they can deal with it if it doesn't work properly. I had a little idea for this that may or may not work hence me presenting it here, this is the layout of his room,

He has 3 sets of front L/R speakers, one are really nice higher end speakers, there are older tower ones on the floor that do a good job on the lower end, and small ones on shelves that work well for the mids. Just one of them alone doesn't sound as good as when we use all 3. Right now the main receiver is on the highs, and a pre out is sent to an old receiver that uses speakers a/b for the other two. A center speaker is in between the two table units that hold the ps3, receivers etc. A dual 6" powered woofer unit is in a receded closet in the back, along with rears on the left and right.

I was thinking of putting both subs, in separate long boxes along the bottom of the front like so, (possibly like 4ft long x 20inches high x 20 inches deep)green is where the boxes would go, in place of the tables there now and I'd just build a shelf into the wall to hold everything.


Sound like an ok plan in any shape or form? also where can I find a good high pass filter?

Thanks again for all the help :)
 

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Discussion Starter #13
I guess my biggest and really only hurdle at this point is picking how much air to have in the box, making dimensions from that is pretty easy but I dont really know an easy way to get real optimal measurement for it. How much would the 8 cu. ft change if it was sealed? Like i said making measurements based on that is pretty easy aftwards.
 
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