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Discussion Starter #1
Hello. This is my first post here although I have read posts for several years.

Although I'm not completely illiterate in terms of home theater, I am in relation to many of you! So, I ask your help with my upcoming build.
First off, this build is for my "work in progress" home theater. I currently am running a Marantz 7500 receiver with 7.1 inputs from a sony blue-ray that decodes the new Dolby Tue HD and DTS HD Master Audio. This powers a hodge podge of Klipsch, Polk, and Altec Lansing speakers making up a 7.1 system. My viewing comes from a Panasonic LCD projected onto a DIY 4x8 screen. Sound quality for my needs is now very good (my opinion here).

For my build... I have a Crest Audio VS 1500 rack amp capable of runniing a 2000 watt 2 ohm bridged load. PLENTY of power for anything I'd ever want to do. I have been looking for 4 - 12" subs to do a "couch riser sub box". This will be made with a 4x8 footprint and have a rear couch atop it. Internal volume will be pretty large obviously, at least 32 cubic feet (up to). Would likely build to have 4 seperate ported enclosures within the whole riser.

I can buy POLK psw505 12" high excursion drivers for only $60 apiece. That puts me at about $300 for the four including shipping. My hunch is that these would be just fine for me but I can't find any T/S parameters for them. I'd like to know if anyone can find them out and help me with a bass reflex design? The original polks are powered with a 300 watt rms amp and have a rear slot port in a rather small enclosure. Can I "size up" my volume and get some lower frequency response? Any and all build ideas would be greatly appreciated (but, I am a teacher with three small kids and money doesn't grow on any of my trees.)

p.s. I have a good workshop and can build anything I need to.
 

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Obtaining the T/S parameters will probably be difficult. There's zero chance that Polk would supply them. The PSW505 was not a stellar performer to begin with. The sub is tuned to 35 hz and ''falls short on the very deepest (below 30 Hz) material"" from a review I read. If you have $300 to spend I'm sure we can find something to fill your needs.
 

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Discussion Starter #3
Ok, it's a shame I can't get them... (the parameters)

What would you do if you were me and had this amp and riser to build?
 

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Discussion Starter #5
Hello,

The room is 12 x 20, basement, currently open to the stairway up but will be closed off with an exterior door eventually. Basically a typical 12x20 room with my screen on one of the 12 foot walls. At 8 feet from the screen I have 2 "recliners" that extend to about the 11 foot mark. After that there is a couch where one can get a pretty good view but I want to build a riser for it. My plan was to place four 12" subs along the front of the "rise" thus killing two birds with one stone. They would essentially fire into the base of the recliners in front of them.

$300 is just what I could get those subs for and they sounded like they might fit my bill. I thought that in some larger enclosures that I could get the full benefits of those high excursion designs and reach some lower frequencies than Polk did in those tiny enclosures.

I've considered 12's along the front of the riser or maybe 15's or 18's on the top of it (under the couch, firing up with ports out the front).

Ideas?
 

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A pair of upfiring 18's for $300 would be the ticket. The Mach 5 Audio MJ-18M is $155 each shipping included. They would give you the most output for the money. They work in 10 cu.ft. tuned to 18 hz. They are presently sold out, just waiting for word from the owner as to when they'll be back in stock.
 

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Discussion Starter #8
Thanks, that sounds like a very reasonable plan to me. Would you reccommend running only 2 with this amp (and have a bit extra power in reserve) or would you run 4 drivers at roughly 500 watts apiece? They say they are 700 watts rms rated. I wish there was a way to run three of them but I'm unaware of a safe wiring scheme for that (some convoluted series/parallel set-up perhaps, if at all!).

If you do suggest four, would it be wise to build another box elsewhere in the room or can I just place them all in the riser and still get great results. I'm definitely thinking all-in-one given the proximity to the viewers (right below some and directly behind the others). I'm thinking that I might have to bolt down that couch....:bigsmile:
 

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If he's willing to spend $600 on four 18's wouldn't he be better off to buy better speakers instead of more speakers?

I am planning on picking up a pair of maelestrom x or the soundsplinter rlp18 (probably end up with the rlp18's). Wouldn't he be better off getting a pair of these?
 

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Discussion Starter #11
My floor is cement with an area rug thrown down. I eventually plan to have a carpet installed with a good pad below.

By better speakers do you mean in terms of longevity/quality, spl, materials, etc??? I'm no expert but wouldn't 4 of these buggers at 500 watts apiece be more desirable than say two 18's at 1,000 each? Like I said, room is not the issue in terms of cubes so I can go with larger internal designs.

Thanks for any input or suggestions you guys have; I'm definately learning as much as I can!

Oh, the $600 would be about as far as I'm willing to go on the drivers - I just can't imagine wanting more than that will buy me. As it is, I'm concerned about there being too much bass and no one in the house being able to do anything other than feel my movies. I've never used a rack amp in this way before either (from receiver LFE to homemades) so that will be a learning process as well.
 

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Better subs means better performance. You don't have room for 4 Mj-18M's and aren't rquired if you are ""concerned about there being too much bass and no one in the house being able to do anything other than feel my movies."" A pair if IXL-18's will outperform the MJ-18M's, and are $530 shipped. They will outperform a single Malestrom-X and a RLp-18.

One thing I should mention is the MJ-18M's will require a sub sonic filter, an add on unit is about $100. The IXL-18's are tuned lower at 15 hz, and shouldn't require one. I'll do some modeling to show you a comparison of the two as soon as I get a moment.
 

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Discussion Starter #16
Hmmm..... I just typed all kinds of stuff but lost it. UGH.
Well, here we go again.
First, thanks for the great info. and for putting up the graphs for me, they were a big help! Right now I'm leaning towards the two IXL 18's. The website says they are 1,000 watts RMS and are dual 2 ohm voice coiled. Let me list some specs on my amp-

Power Specifications:
8Ω Stereo 400W
4 Ω Stereo 750W
2 Ω Stereo 1000W
8 Ω Bridged 1500W
4 Ω Bridged 2000W
1kHz, 1% THD+N

Is this the best way to wire them, each subs coils in series giving each sub a total resistance of 4 ohms? I found a great diagram at Crutchfield here if I'm correct in doing it this way http://akamaipix.crutchfield.com/ca/learningcenter/car/subwoofer_wiring/2DVC_2-ohm_2ch.jpg
That would give me a 4ohm load and deliver 750W per driver.

OR, can I somehow either get a 2ohm load in stereo or a 4ohm bridged configuration. I can't seem to figure that one out on my own right now (if it can be done?).

Thanks much!
John
 
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