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Old 12-21-2009, 10:12 PM   #1
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Default Home theatre cheap subwoofer SQ awesomeness

So I have had this subwoofer enclosure for awhile now. It is a 12" dia sonotube cabinet with a 4" port tuned to IIRC around 30 Hz. The enclosure is about 4 ft^3, a decent size. The speaker is a fantastic little MB Quart PWD-254 10" DVC (rated at 300W RMS 750W peak) I bought from Parts Express several years ago. I am powering it with a bridged Peavey CS400 a friend of mine gave me for free.

The sound was good, but a little boomy for my taste. I am more of a sealed enclosure guy in that I like tight clean musical bass, even at the cost of SPL. But for a home theater sub I want both SPL and SQ, since I use the system for movies and music. So I had considered doing something insane like building a huge 15" Shiva sealed enclosure with gobs of power. This would have meant spending more $$ on a new subwoofer, and more amperage (to make up for the non-ported enclosure).

But before I did that, I figured I would give the MB Quart and the Peavey one more try in a different configuration. Inspired by some of the TL projects I had seen on-line, I had been toying with the idea of building a 1/4-wavelength transmission line enclosures using sonotube, so I decided what the hell, time to give it a try. I do not have any pictures to post yet, but really there is not much to it. The enclosure is just a 12" dia sonotube, cut at about 9'6" (about 1/4 wavelength @ 30 Hz), open at one end, with the MB quart mounted on the other end, firing upward, magnet outside the enclosure. It looks a lot like this

More details here...
Steve's Compounded, Super-Duper Shiva/Sonotube(R) T-line Subwoofers
This is about as easy as a transmission line gets.

So I build the whole thing, put some polyfill in the tube (about 4 lbs, all I had) stand it up behind the TV, and give it a listen. The source music is a copy of Dark Side of the Moon on SACD, played on a PS3 connected to a good Yamaha amp via HDMI. DSOTM needs no introduction of course, but if you have not heard it on SACD with a good system, it sounds really, really good.

So the famous heart beat starts up, and begins to rattle the walls and windows, but with no distortion, just a solid, tight, THUMP thump, THUMP thump... So far so good, the SPL was still intact, but the SQ was already sounding better. There was none of the subtle coloration of the thump like the ported enclosure had.

Then Breathe starts...
Holy hell... tight, seamless bass guitar, even sound level and sound quality through all the bass notes. The kick drum is solid and clear. The Great Gig in the Sky, and Us and Them sounded amazing. It is hard to describe this stuff verbally, but basically it is solid, clean, clear strong bass, with enough power to fill my 16'x20' room (with an 11' Cathedral ceiling).

So if you want a cheap, easy DIY subwoofer that sounds great, and you have the room (it is big), and can get past the dreaded SAF (spouse approval factor) then go for it. It does not have to stand up on end from what I hear. I considered going for a lower tuning and laying it on the floor, but this will do nicely for now. I have designed it so I can put a longer tube on it in about 5 minutes.

Last edited by ZX-Tex; 12-21-2009 at 10:39 PM.
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Old 12-21-2009, 10:36 PM   #2
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Just snapped some pictures. Not pretty, but it sounds great.


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Old 12-21-2009, 10:41 PM   #3
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that is awesome, I need that. Lets get some recommendations on subs.
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Old 12-21-2009, 10:47 PM   #4
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That looks ghetto as ****, but if it works who cares. I'm waiting on my budget Polk PSW505 to get in. Should make enough bass for a 15' square room.
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Old 12-21-2009, 10:48 PM   #5
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If you are thinking about it, DO IT! It is awesome, and really easy to build.

If I bought another sub, I would probably get a Dayton Audio from Parts Express, like this one...
Parts-Express.comayton RSS315HO-4 12" Reference HO Subwoofer 4 Ohm | subwoofer rss315h0-4 12" subwoofer dayton reference rs sub dayton loudspeaker reference-22008
Something like that could shake the crap out of the house with a good, strong amp. It has a Fs of 32 Hz so if you put that on the end of a 10' long tube it should work great. I am assuming it will still have good SQ even though it is a little bigger than the 10"

Here is a legendary Sonotube transmission line project in care you want to go really nuts... This one holds within 3 dB from 17 Hz to 70 Hz. Some good technical info there as well.
http://thecarversite.com/yetanotherf...nstruction.pdf

Last edited by ZX-Tex; 12-21-2009 at 11:04 PM.
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Old 12-21-2009, 11:04 PM   #6
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I'm no audiophile or sub guy, could you explain to me exactly what the sonotube does for the sound? I don't quite understand as it is filled with acoustic foam.
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Old 12-21-2009, 11:12 PM   #7
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Sonotubes are basically thick wall cardboard pipes that come in a lot of different diameters, from 10" to 36" and up. Their real purpose is to act as a form for pouring concrete columns. Because it is a pipe it has inherent strength and rigidity. Thus one can build a stout subwoofer enclosure without resorting to heavy walls of MDF or the like. Stiff solid walls are very important for speakers, especially subwoofers.

So someone figured out a long time ago that sonotube is a cheap and easy route to building subwoofer cabinets. I bought a 12" dia x 12 foot length for $30 and I can carry it easily. If you build a boxed shaped cabinet from MDF of equivalent volume, it will be MUCH heavier, much more expensive, and a lot more work. Lots of people use sonotube, even high-end speaker builders. Google 'sonotube subwoofer' and you will see what I mean. Sealed enclosures, ported enclosures, band pass enclosures, and transmission lines are all built with it.

Just the reduced weight is nice. Most of the mass on a sonotube sub comes from the speaker itself. with an MDF enclosure it is the other way around. I'll bet mine above weighs around 30 lbs. Build that out of MDF and I am guessing it would weigh well over 100 lbs.

The sonotube I used is not the kind filled with foam. It is just a tube. I did fill it with polyfill (pillow stuffing) but that is ubiquitous practice for any speaker. Polyfill does good things like adding damping (to reduce ringing) plus it makes the enclosure act like it is 'bigger', up to 30% IIRC if it is used correctly.

So the sonotube is really great for a transmission line. Just cut it to the right length, stick a speaker on the end, tune with polyfill, done. One still has to get the right speaker and cut it to the right length of course because they need to be tuned like any other enclosure. Things get more complicated if it is a converging or diverging port transmission line.

Last edited by ZX-Tex; 12-21-2009 at 11:23 PM.
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Old 12-21-2009, 11:17 PM   #8
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I guess I understand that. So a larger enclosure = cleaner and deeper sounds?
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Old 12-21-2009, 11:39 PM   #9
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I was just looking around for a good cheap project, and happen to have four cabinets worth of speakers I don't mind tearing up.
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Old 12-22-2009, 01:34 AM   #10
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Quote:
Originally Posted by NA6C-Guy View Post
I guess I understand that. So a larger enclosure = cleaner and deeper sounds?
Not necessarily, but sometimes. It depends on the speaker type. With sealed enclosures usually the bigger the better, at least until it gets ridiculously big. Really though it all comes down to tuning. Whenever I am designing a speaker cabinet I use WinISD (great freeware speaker design software) and try out several kinds of speakers in different types of cabinets.

WinISD does not work for transmission lines, or it is not intended to anyway.

I just spend a couple of hours running a bunch of different kinds of music through it, including Fagen's "The Nightfly" and I am still pleased. It could maybe use a couple of more pounds of polyfill to smooth out some tiny peaks at the very low end, but then again it could just be standing waves in the room. Otherwise I am still really pleased. My wife hates it

"But honey, LISTEN TO IT! IT SOUNDS AMAZING"

BTW I know everyone has probably heard Dark Side of the Moon a million times in various states of mind. But if you have not heard it on SACD, and you have a system that will play one, like a PS3, get a copy of the SACD! It is like rediscovering DSOTM all over again. Just hearing how amazingly beautiful "Us and Them" is totally worth the purchase. It is basically a remastered recording, using 5.1 sound, with stunning audio quality.
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Old 12-22-2009, 02:03 AM   #11
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I have, or had the SACD version of DSOTM, but it got scratched to hell. I also don't have a PS3 anymore and I don't think my Blu-Ray supports SACD. I wonder if you can get SACD quality files onto a computer? Not sure if that would be supported. I could just listen to it through the receiver that way.
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Old 12-22-2009, 03:06 AM   #12
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OP, that is the worst design for a subwoofer enclosure I have ever seen. You obviously have no clue what you are doing.

>^..^<
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Old 12-22-2009, 03:14 AM   #13
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Ahhhhh hAHAHAHA! Catman symbol. I get it now. Funny! Catman, what a douche
His doucheness is so big, it would not fit in a 24" dia sonotube of any length.
He is such a big douche, that he frequently volunteers at the local zoo to help give female elephants that fresh feeling. I hear he can treat several in the same day.
He once drained an entire fresh water lake while refilling himself. Shipping in the Great Lakes region has not been the same since.

Maybe if I bought a Nak source unit and a McIntosh amp, I would be Catman worthy.

Last edited by ZX-Tex; 12-22-2009 at 03:25 AM.
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Old 12-22-2009, 03:46 AM   #14
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Maybe, but no guarantees lol. Much respect goes to you for actually being able to do this. I have wanted to for quite some time, but never ever would get approval. What you can do is paint it black and allow pictures and decorations to be hung on the tube.

While you are at it, you may want to look into building some bass traps to control your room reverberations for proper tuning (if you get SAF qualified):

Canuck Audio Mart &bull; View topic - DIY: 2d QRD (Skyline) Diffusor Build

Actually, while you're at it, it couldn't hurt to mock up some skyline diffusers as well.
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Old 12-22-2009, 04:10 AM   #15
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Looks sweet, i might do this style sub for my 20x20 room hehe

If you have extra left over paint from when ever you painted your living room you should paint the sonotube, That is if the looks bother you.
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Old 12-22-2009, 08:35 AM   #16
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The diffusor effect can also be achieved by bookshelves, plants etc.

I do strongly recommend bass traps. People (other than you :P) spend a lot of money on speakers and components but don't put effort into tuning the room. Bass traps can make a shitty square room sound pretty decent. You have a nice big room though and a cathedral ceiling is superior for acoustics.

One thing about the design-- wouldn't a long port design like that hit 30hz and the harmonics really well but not necessarily the other notes? I'd bet that frequency response would be all over the place.
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Old 12-22-2009, 09:28 AM   #17
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I have a powered 12" subwoofer, I simply put it where I sit on my couch and crawled around the floor until it sounded best and placed it there....I guess I'm doing it wrong.
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Old 12-22-2009, 10:52 AM   #18
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Quote:
Originally Posted by Braineack View Post
I have a powered 12" subwoofer, I simply put it where I sit on my couch and crawled around the floor until it sounded best and placed it there....I guess I'm doing it wrong.
Nope. Did I tell you to do that?

Tex, check these guys out. Auralex Acoustics - World-Class acoustic foam sound control products at real-world prices!
You want a subdude under there. Trust me.
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Old 12-22-2009, 10:55 AM   #19
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no, i read it somewhere online when i first setup my shitty home theater setup years back.
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Old 12-22-2009, 11:12 AM   #20
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Yep I am going to work on the room next. I need some bass traps and the like, as well as some soundproofing. My wife keeps complaining it is too loud I plan on hanging some curtains beside and behind the front stage (TV, front speakers, sub) so the TL will end up being hidden from view. The room is a little too live right now so I want to try adding some damping with the curtains. I may build some bass traps too.

Feaflora the response sounds to be really flat. That is a big deal for me since I hate peaky subwoofers. BTDT. I have a buddy that has a nice analyzer I need to borrow to check it out some more but it sounds flat to me. Last night I listened to some jazz recordings with stand up bass playing walking bass lines and did not hear any peakiness. All the notes were the same volume.
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