Goal: Bass!

I am making two 15" subwoofers to fit under my front projection screen on either side of the center channel. They cannot be very deep, maybe 15" deep. Screen begins 29" above floor.

Current plan is:
Two 15" Dayton RS High Fidelity RSS390HF woofers.
Two 195 liter boxes 29" tall, 40" wide, 15" deep, made of 1" mdf. Heavily braced.
Each tuned to, ~16.5hz with a 6" tube 32" long. (Not enough room available for LLT... maybe a "medium", low, tuned... any thoughts on tuning?)

Box will be heavily braced, and padded. Port will be radiused 3/4".
Painted black as the woofers are immediately below the screen.
Power will be by a pro amp: I currently have a QSC USA 370: 185 wpc into 4 ohms. I am considering upgrading to a QSC RMX 1450 or 2450. (Any thoughts?)

http://www.partsexpress.com/images/295-468m.jpg

---Click this link to see a sketch of the vented subwoofer box.--- (http://web.mac.com/jamesmiyake/iWeb/Site/Library_files/Sub-design-2.jpg)

I would like to hear any comments, or suggestions.

Sounds good to me!

Looks fine to me. When you only have so much room, you only have so much room.

You might want to look at bumping up to 17hz, for a higher port resonance. Any higher and you get a hill a 30hz.

The USA 370 should be plenty. If you feel the need to go bigger on the amp, you will definitely need a highpass. ;)

Hmm, how wide is your screen? Any chance you can bump each sub up to maybe 225 effective liters? That levels the FR out a bit more and should mesh a little better with room gain. 250 watts a piece should do it. Ultimately this driver would like to see a lot more volume, but you're tight on space - just make sure you squeeze out every last liter available, it will help.

Hope it goes well!
James

Looks fine to me. When you only have so much room, you only have so much room.

True, true

You might want to look at bumping up to 17hz, for a higher port resonance. Any higher and you get a hill a 30hz.

So you think we should shorten the port abit, I'll look into that.


The USA 370 should be plenty. If you feel the need to go bigger on the amp, you will definitely need a highpass.

I think I read somewhere that the QSC amps have a 5hz highpass build in.

Thanks,
James

Hi Steve, thanks for your comments:

Hmm, how wide is your screen?
96" wide screen = 13 inches for the center, leaves just over 40" for each sub.

Any chance you can bump each sub up to maybe 225 effective liters?
Well not my first choice. I'll have to think about it.

That levels the FR out a bit more and should mesh a little better with room gain. 250 watts a piece should do it. Ultimately this driver would like to see a lot more volume, but you're tight on space - just make sure you squeeze out every last liter available, it will help.

I'll look into it. Can you explain what is to be gained by the small addition of volume in this instance?

The FR seems pretty flat with a gentle rolloff of -4 at ~22hz. The tuning is quite low around 16.5 hz, so pretty close to an LLT, just not enough room for a true LLT. So are we gaining any advantages by the low tuning, and what are we not gaining by using a medium size box?


Thanks,
James

96" wide screen = 13 inches for the center, leaves just over 40" for each sub
You mentioned the usbs will be 29" tall max - couldn't the center speaker go on top of the subs? Or are you using a vertical center?

I'll look into it. Can you explain what is to be gained by the small addition of volume in this instance?

The FR seems pretty flat with a gentle rolloff of -4 at ~22hz. The tuning is quite low around 16.5 hz, so pretty close to an LLT, just not enough room for a true LLT. So are we gaining any advantages by the low tuning, and what are we not gaining by using a medium size box?

Well tuning low is only part of the equation - another significant part is having enough enclosure volume to go with that low tune. Ideally this driver would like ~325 effective liters and a ~14.5hz tune - that would be more like an LLT design for the HiFi15. If you overlay the two designs to compare them at the same time, one with 195 liters and 16.5hz tune and the other with 225 liters and a 16.5hz tune, and you look at FR, you'll see the larger one is a bit flatter and has a better rolloff.

Hi Steve,
You mentioned the usbs will be 29" tall max - couldn't the center speaker go on top of the subs? Or are you using a vertical center?
Center is tower configuation that fits just under screen.

Well tuning low is only part of the equation - another significant part is having enough enclosure volume to go with that low tune.
I know you advocate:
1) Low tuning to lower the distortion below occurring below the tuning frequency below the audible frequency.
2) Enlarging the box allow the slope to match the room rise.

Does the advantage of (1) apply even without performing step (2)?
If not why not? Your tuning of 14hz and my tuning of 16.5hz are not that far apart.

one with 195 liters and 16.5hz tune and the other with 225 liters and a 16.5hz tune, and you look at FR, you'll see the larger one is a bit flatter and has a better rolloff.
Well yes, but they don't vary more than like 1 decibel at any point in the curve.

Ideally this driver would like ~325 effective liters
325 x 2= 23 cubic feet out of my house! TWENTY-THREE! I don't think that will work!

Interesting stuff,
James

Anybody know anything about these?

Center is tower configuation that fits just under screen.
Ok, same here :)

Does the advantage of (1) apply even without performing step (2)?
If not why not? Your tuning of 14hz and my tuning of 16.5hz are not that far apart
You will still get the benefits of #1, but without the increased enclosure volume to go along with a low tune, you're limiting some of the potential of the sub. You lose some low end sensitivity, you don't get as much leeway with large ports, and your in room FR won't be as good. The two areas that I believe bass sound quality comes down to are in room FR and distortion.

The lower tune was only suggested with a larger enclosure, ~325 liters. But to that point, while 2-3hz doesn't seem like a big difference overall, when you get into the lower frequencies, octaves are much smaller, so the difference between say a 30hz and 27hz tuning, relatively speaking, isn't as large as the difference between a 16hz and 13hz tuning.

Well yes, but they don't vary more than like 1 decibel at any point in the curve.
That can get to be a slippery slope if you're not careful, as the same could be said for using a 175 effective liter enclosure. Then compared to that, same with 155 liters. Don't get me wrong though, if you can't go any bigger, the 195 liters with a 16.5hz tune will still be good - anymore volume you can potentially use would only help though.

Anybody know anything about these?
jmiyake,
regarding that port. I'd stick with your typical cylandrical port. If you insist on this enclosure staying the size you mention go with a side firing port, making sure it is at least its own diameter away from any walls inside of the box to be safe. The QSC Usa 370 looks good for this allignment as far as output and excursion go.

Bumping the volume up to 225 liters helps move the port resonance into a higher frequency range and brings the F3 down a bit. This is a good thing, but at the cost of getting a little closer to your maximum available Xmax right before the tuning point.

Your f3 will be measurably lower in-room than any of these graphs suggest, and port resonance which Unibox calculated to be around 182hz with the 195 liter enclosure will probably not be a problem. It is a matter of deciding whether or not you can accomodate the added ft^1 of volume per enclosure.

IMO, nothing you should lose sleep over ;)

You will still get the benefits of #1, but without the increased enclosure volume to go along with a low tune, you're limiting some of the potential of the sub. You lose some low end sensitivity, you don't get as much leeway with large ports, and your in room FR won't be as good. The two areas that I believe bass sound quality comes down to are in room FR and distortion.

Thanks for thise explaination! Makes sense.


The lower tune was only suggested with a larger enclosure, ~325 liters. But to that point, while 2-3hz doesn't seem like a big difference overall, when you get into the lower frequencies, octaves are much smaller, so the difference between say a 30hz and 27hz tuning, relatively speaking, isn't as large as the difference between a 16hz and 13hz tuning.

Interesting point... never thought if that.

That can get to be a slippery slope if you're not careful, as the same could be said for using a 175 effective liter enclosure. Then compared to that, same with 155 liters. Don't get me wrong though, if you can't go any bigger, the 195 liters with a 16.5hz tune will still be good - anymore volume you can potentially use would only help though.

True. I'll carefully see if I can't add more volume. But it won't be easy...

Thanks,
James

I'm kinda diggin' the original 195L/16.5Hz with a 6" port. Not an EBS, but looks like a nice middle ground between depth and excursion headroom just above Fb. I find air a very inefficient medium through which to trasmit very-low tactile frequencies into my couch/floor, so I'd rather combine this alignment with a Buttkicker or two than use up headroom trying for a few more Hz down low.

And they are really beautiful!
Heavy! About 30lbs. Pretty impressive. Time to buy lumber, work out cut plans.

I have decided to go with the 195 liter, and tuning of 16.5 hz. Due to space constraints and assurances from the forum that it would be a good compromise.

Thanks to all for your opinions and feedback. It has been really valuable. It's great to have this forum as a resource!

I'll post progress reports and images here.

And don't forget that proper positioning, room treatments, and eq (in that order) will have a more profound effect on in-room performance/accuracy than marginal changes in alignments, or even choice of driver.

The goal again to have high quality bass to match my line arrays:
One pair of subwoofers to fit under the front projection screen. 40" wide x 29" high x 15" deep.

The plan:
http://home.earthlink.net/~jmiyake/sitebuildercontent/sitebuilderpictures/subdrawing.gif

Pretty standard ported subwoofer design. One little twist, to increase the port length a couple of inches I am going to an exhaust nozzle extending a couple of inches out the side of the speaker.

The 1" MDF has been purchased and mostly cut to size.

Purchased 6" thin-walled sewer pipe. The pipe is huge! I suddenly got a sense of the enormity of this project, notice the t-square for scale. It was only available in 10' lengths.

http://home.earthlink.net/~jmiyake/sitebuildercontent/sitebuilderpictures/sewerpipe.jpg

Drawing First Dust!
http://home.earthlink.net/~jmiyake/sitebuildercontent/sitebuilderpictures/router.jpg
The 15" hole looks awfully small on the front plate! The jig is a big circle cutting jig.

Before the first fitting test.

http://home.earthlink.net/~jmiyake/sitebuildercontent/sitebuilderpictures/spkhole.jpg
The Dayton RS HiFi 15". The speakers are gorgeous! They have black aluminum drivers, huge magnets and surrounds. They have these even proportions, that make them look like a giant five or six inch driver. Kinda weird.

Perfect fit!
The subwoofers are recessed and flush mounted.
http://home.earthlink.net/~jmiyake/sitebuildercontent/sitebuilderpictures/resessed.jpg

Actually, the rim hole was just a bit undersized, and I had to sand it a bit with a dremel to fit.

More to come...

Looking good ;)

Looks great so far. I look forward to your impressions of the finished subs and more pictures.

Thank you Willd and exocer for your encouragement. Hope this project turns out well.

James

Here are the horizontal braces.
http://home.earthlink.net/~jmiyake/sitebuildercontent/sitebuilderpictures/horzbracingopt.jpg
The upper braces have the driver cutouts. The lower braces have a large opening to allow airflow to the port exit.

Each pair of cutouts is a different dimension to spread out the resonance killing hard points.

Cut-outs are rather rough since it is just internal bracing.

If this were for a regular speaker I would router all edges with a 3/8" round-over bit, but since it is a sub, I can't even pretend to come up with a reason to go to the effort to do so.

All for now. Geez, I figured I'd be much further along by now.

James

Excellent job! Wow, look at that detail. :cool:

Niiiice bracing dude.

I predict some intense bass in your future. :D

I'd be damn proud to call those braces my own.

Thanks for the nice comment on the braces...
I got a lot of family stuff going on during the week. Hopefully I can steal away some time to work on the subs some more.

I miss bass! Haven't had any real bass for several months.
So I am very motivated to get this done.

James

Progress has been slow but steady.

All the cutting has been done but the port exit hole, and related pieces.

The gluing has been completed except for the back cover which is to go last, and the aforementioned port bits.

http://gallery.avsforum.com/data/507/Bracing-overall.jpg

1" mdf throughout. A network of shelf braces. The largest unbraced area is about 13"x14"

http://gallery.avsforum.com/data/507/BracingAngled.jpg

Notice that I ended up rounding over all the internal braces anyway with a 3/8" roundover bit. I just couldn't help myself.

http://gallery.avsforum.com/data/507/portarea.jpg

Sewer pipes have been cut to size. I still need router out the port opening.

http://gallery.avsforum.com/data/507/faceToScale.jpg

Here is a front view. Notice the yardstick for scale.

More Pics!!!

Very interesting thread. I had a similar space constraint problem and was planning an isobaric design using the same drivers. This halved the box volume from the optimal 309 liters to just 154 liters and reduced the port requirement to two 18" long 4" diameter ports . . . . and provides output that is down just 1 db at 20 Hz.

I didn't follow through with that design though. I got the Audyssey MultEQ system and found I had enough room gain to not need flat response down to 20 hz so am building a pair of 85 liter sealed boxes for the RSS390HF drivers (again, isobaric to keep the box size down and for the other advantages of isobaric). The result is nearly flat in-room response down to about 16 Hz and no problems with Xmax should any spurious content come through at 10 Hz.

Anyway, very useful thread. Thanks to all.