My newest subwoofer project

[bemis23]

Yeah I can see that. My home computer is running Linux, so while WinISd works fine for easy simulations, the WinISD Pro doesn't play well with WINE. Unibox works well though, even in OpenOffice Calc.

Anyway, final results of the model:

1x 12" Dayton RSS315
4235 cu in box (4434 cu in usuable after port, suffing and bracing accounted for): dimensions: 17.5"x22"x11" - not optimum, but I have to compromise with the wife somwhere.
Port will be 31.2" long flared at both ends, with a 4" diameter.
Driver will unload at 400W (max power) at 17hz, Port airspeed becomes audible at 400W at 16hz. At 200W, the driver doesn't unload until 15hz and port airspeed is always inaudible. As a result i'm thinking 12dB/octave high pass filter at 19Hz?
Max SPL: 111dB
F3: 26Hz
F6: 20Hz

This seems like a winning design to me, given my box size limitations. Do you guys have any other suggestions?

[bemis23]

Vent questions

When planning for my subwoofer, I had planned on the vent, but failed to take into account just how much a 90 degree 4" elbow joint takes up.

Does the number of turns in a vent affect the sound?

How do you measure the linear length of the elbow?

What is the margin of error in tube length for a specific tune?

Edit: I also read a post where it was recommended to cut the 4" straight PVC at a 45 degree angle and then melt the ends together to make a 90 degree corner. Will the sharp corners cause any problems in this application? The port is designed for a 20hz tune.

[ThomasW]

Does the number of turns in a vent affect the sound?

Enough turns will change the tuning

How do you measure the linear length of the elbow?

Through the center

What is the margin of error in tube length for a specific tune?

10%

Edit: I also read a post where it was recommended to cut the 4" straight PVC at a 45 degree angle and then melt the ends together to make a 90 degree corner. Will the sharp corners cause any problems in this application? The port is designed for a 20hz tune.

Never said anything about melting anything together. I have recommended the use of 45 degree elbows.

[bemis23]

Okay, well it looks like the elbows I've got are about 5.5" through the center. Currently for the port there will be a total of 4 90 degree ports yielding a total length of 30.5 inches (0.7 short of the recommended 31.2" - well within the 10% tolerance). Is this enough to seriously affect the tuning? Is the tune-delta predictable?

The note about melting the 45 degree cuts together was in an old thread here:

http://www.htguide.com/forum/showpost.php4?p=424573&postcount=16

BTW: Thanks for merging the threads, Thomas.

[bemis23]

After going over all the models again I think I'm going to try using a square port. Is there any reason I can't use the walls of the cabinet for the outer edge of a port?

I was thinking that I could basically build a tunnel that would travel along the walls of the cabinet to the port exit point. This would let me preserve some of the clearance directly behind the driver and I could get away from the 5" diameter PVC elbow fittings. Vb changes by <50 in^3.

Any thoughts?

[ThomasW]

Those are known as slot ports.

http://www.htguide.com/forum/showpost.php4?p=336143&postcount=5

[bemis23]

Those are known as slot ports.
http://www.htguide.com/forum/showpos...43&postcount=5

Okat thanks for the links. I've worked out the port dimensions and I think it'll work. when I'm constructing the port itself, should I chamfer or roundover the internal corners? What about the external corners? Will the sharp edges create any problems inside the box?

[ThomasW]

Smoother corners can't hurt. Doing so increases the amount of work considerably because the smoothing can't decrease the size of the opening.

[JonMarsh]

Mongo doesn't like corners in ports... ports bound to have more turbulence with corners than with a straight shot.

[bemis23]

Smoother corners can't hurt. Doing so increases the amount of work considerably because the smoothing can't decrease the size of the opening.

I was thinking I would use a round over bit (1/4-1/2") on the innermost corner and on the opposite side include a piece of wood that has been shaped using a identically sized cove bit. The other option I thought of was to make the rounded over corner and use a 90 degree brace to form a mold cavity. I could line the wood with plastic wrap and fill the mold with bondo and get an exact match - but I'm not sure if the bondo would ever seperate from the plastic wrap.

Jon, I wish I had room to do a straight 4" round vent - but the box just won't allow it unless I do some crazy vent outside of the box.

[bemis23]

Okay, I believe I've finally hit upon a vent design that will work. It's a slot vent with the terminus at the bottom of the left side of the box. The port length will run across the entire bottom of the box and then up the right sidewall ~12". After thinking about a couple different dimensions it occurred to me that I could use the entire bottom of the box and then between the slot and the bottom/side of the box insert a strip of MDf to create two rectangular slots (each measuring 5"x2.5"x26"). I realized I could brace the opposing two sides of the box against the centerline MDF port-seperator/brace as long as I avoid the woofer. The total slot construction including the brace will be exactly 11" wide which will help brace the front and back baffles as well.

I do lose ~1.5-2dB @ 20 hz and about .5dB @ 30hz, but I realized with the port rotated 90 degrees around the vertical axis they will gain quite a bit due to boundary loading (along the fireplace)and floor effects (from the tile hearth). The schematic is looking pretty complicated right now, but I've got some good ideas on how to tackle the woodworking side.

If you guys see any immediate problems let me know. Otherwise I'm gonna try to prototype the wall and vent construction tonight.

[ThomasW]

Using the slot construction to act as box bracing is a standard practice.

You'll get boundary loading from the wall/fireplace regardless of where the port is placed, since we're talking LONG wavelengths here...

[bemis23]

Using the slot construction to act as box bracing is a standard practice.

Hmmph - and here I thought I was being all clever.

[---k---]

I can't think without pictures and my brain is fried right now.

Just for reference, make sure you've seen NeoDan's Easy Button Tables, with a slot port. May help: http://www.avsforum.com/avs-vb/showt...ht=easy+button

[bemis23]

I have seen many of the EasyButton build threads. I would like to eventually build one, but that will be for another room that's not as important.

[Jim85IROC]

Mongo doesn't like corners in ports... ports bound to have more turbulence with corners than with a straight shot.

Yup. I built a slot-ported enclosure for my car for a pair of Tangband 8s... I can't remember the calculation but I think my ports were the equivalent of 3" ports, but I still got some port noise at high volumes, presumably due to the tight turns. I did round-over all of the inside turns of the slot port, but that's still a lot of bending for the air to go through.

All in all though, those 8" subs pounded pretty hard.

Here's a drawing of the enclosure I built:


It's 0.5 cubic feet and tuned to 35hz. The center chamber was just a spot where the amplifier was mounted.

One neat thing about this design is that it gave me the ability to change the port tuning frequency simply by changing that top piece of wood.

Slot porting may not always be ideal, but in a lot of cases it provides you with some useful packaging options.

[bemis23]

i've attached a very rough, not to scale drawing to post the vent configuration.

[bemis23]

well, after dealing with some tooling issues I'm going to cut all the wood tonight and route the driver holes and recesses to have everything ready for glue up tomorrow. Acoustically will it make any difference if the vents face each other or should they face the same direction? I assume not given that the ports are tuned for 20hz, but I wanted to check with the acoustics wizards on here before I glue on baffles.

[ThomasW]

It should be thought of as one vent not two....

[bemis23]

I apologize my question wasn't very clear. The vent on each sub is rotated 90 degrees around the vertical axis from the front baffle. I'd like to rotate the vents in opposite directions (clockwise on one sub and counter-clockwise on the other) so that when the system is placed in the room the vents are aimed at each other, aprroximately 5' apart, and horizontally perpindicular to the woofer output. My assumption is that there won't be any acoustical issues with this placement, but I'm not yet educated enough to say so definitively.

[bemis23]

This thread seems to be pretty much dead, but for anyone that cares I've scrapped the idea to use the subwoofers as stands. My wife has agreed to let me place two smallish tower enclosures flanking the mains for subs. Each one will house a RSS315HF-4. Basic specs below if you're interested:

Dimensions: 13x13x35 internal (15.25x14.5x36.5 external)
Box volume: ~3.7 ft^3 after bracing, driver, ports, and stuffing
Vents: 2 - 3" ports each about 20"
Maximum A/S: 35m/s @ 350watts @ 17hz
Maximum safe excursion limit: 18hz @ 350watts
SPL @ 350 watts: 110db
F3: 19.6Hz

This also opens up my choices for L/C/R since i'm no longer putting such strict placement/size requirements on the design.

[ThomasW]

This thread seems to be pretty much dead,

It's your thread, so it's alive as long as you keep it so.....

Dimensions: 13x13x35 internal (15.25x14.5x36.5 external)
Box volume: ~3.7 ft^3 after bracing, driver, ports, and stuffing
Vents: 2 - 3" ports each about 20"
Maximum A/S: 35m/s @ 350watts @ 17hz
Maximum safe excursion limit: 18hz @ 350watts
SPL @ 350 watts: 110db
F3: 19.6Hz

IMO it's too tall. Tweeters are best placed at ear level or slightly above. Anything placed on top of these will have the tweeters way too high

But it appears you've changed your mind again given your post on Tech Talk

[bemis23]

It's your thread, so it's alive as long as you keep it so.....
IMO it's too tall. Tweeters are best placed at ear level or slightly above. Anything placed on top of these will have the tweeters way too high

But it appears you've changed your mind again given your post on Tech Talk

Yeah I forgot to include that tidbit. This is the design for the box that I seperated from the mains as I mentioned in the PE forum. These two boxes will flank the main L/R speakers. Funny, managing tweeter height was one of the driving factors for me seperating the boxes to start with. :T

[bemis23]

Well, the wood is cut and the first glue joint is drying in clamps as I type this. I'll post more pictures as I get further along.

[bemis23]

The skeleton for box #1 is done and the double front baffle is in clamps. While that's curing overnight I'll construct the PVC ports. Tomorrow it'll be time to route the driver and port holes.

If everything goes well tomorrow I might have this box done on Sunday. I'll work the basic box construction for sub #2 during the week and it should be done next weekend.

A note about the picture....I clearly do not have enough clamps because this is every clamp I own. FWIW the clamps are a mixture of Craftsman and Bessey tradesman clamps. The construction and materials looks to be almost identical, so I will be keeping my eye on the Sear's ads for clamps on sale.

All in all, good progress today - aside from one stupid mistake that was fortunately easily remedied with a little sanding.

[bemis23]

Well, nothing ever goes according to plan. i got the driver hole routed in the baffle only to find out that I'd made the recess lip a touch to small. After some creative patchwork I started working on the port holes and then things got really screwed. Not having the small hole Jasper around I decided to to just borrow a friend's jigsaw. so after careful planning and measurements I started my cut. When I got done I realized that at the end of the cut the saw and gotten out of square (I was probably not paying attention to the boot/surface contact and mitered the cut is probably what happened). So while I had a serviceable 3" hole in the front of the baffle the rear was nearly 4" and irregularly shaped. Time to start a new baffle.

Fortunately I have enough MDF around that I can continue without needing another wood run, but it's frustrating to be set back another 48 hours after working so diligently all weekend.

Oh well - patience is key. I'd rather wait another 48 hours and have the work be done right rather than try another dubiously-useful patch and live with the internal nagging that would result from knowing I didn't do it right.

[chasw98]

Been there, done that. Sometimes I have had to do it 3 or 4 times cause I just didn't get it. At least it is a cheap mistake!

[---k---]

I swear I've had to use sandpaper and/or a dremel tool to enlarge every single driver hole I've ever cut. (probably about 1/2of the holes) They are always about 1/16" too small. And, I have a lot that are too deep. At least they are easy fixes.

[bemis23]

Ok got the new baffle driver hole routed. I measured everything with calipers before and during the process and it came out about as perfect as I've seen. The recess lip may be 1/64th of an inch too large if it's off at all - the driver's lip has no play in the hole at all and sits perfectly flush with the face of the baffle.

Now I have question though....

I made two 5"x5"x3/4" braces for the tip of the PVC that will glue to the rear of the front baffle to keep the port in place, but I'm not sure what kind of filler/glue to secure and seal the PVC in the brace. Can I just glue it in with Titebond? I thought about mixing some sawdust and Titebond to create a thick tacky filler for sealing up around the jigsaw cut as well. What say you, great speaker-gods?

Edit: Now with 100% more pictures!

Also: I assume that whatever I use to affix the PVC to the wood bracing will work for attaching the two PVC straight pipes to the elbow?

[---k---]

I don't think Tightbond will bond to PVC. Really not sure, but don't think so.

I would probably use this:

I've used it for various things. It a very thick adhesive and will bond to almost anything. I think that is what you're looking for. It is like $3.50 a tube at Lowes/HD.

[brent_s]

Ok got the new baffle driver hole routed. I measured everything with calipers before and during the process and it came out about as perfect as I've seen. The recess lip may be 1/64th of an inch too large if it's off at all - the driver's lip has no play in the hole at all and sits perfectly flush with the face of the baffle.

Now I have question though....

I made two 5"x5"x3/4" braces for the tip of the PVC that will glue to the rear of the front baffle to keep the port in place, but I'm not sure what kind of filler/glue to secure and seal the PVC in the brace. Can I just glue it in with Titebond? I thought about mixing some sawdust and Titebond to create a thick tacky filler for sealing up around the jigsaw cut as well. What say you, great speaker-gods?

Edit: Now with 100% more pictures!

Also: I assume that whatever I use to affix the PVC to the wood bracing will work for attaching the two PVC straight pipes to the elbow?

PVC to MDF...Goop seems to work well.

For PVC to PVC, you'll want to get the appropiate primer and glue...should be near the plumbing section where you bought the PVC. I have read where someone used this to join PVC to MDF as well, but I'm not sure I'd trust it since the "glue" creates a weld more than adhesion to join PVC.

-Brent

[bemis23]

Well I made good progress today:

1) Internal sections of the port are welded together - once the front section of PVC has had time to cure to the front baffle I'll weld that together
2) PVC face is attached to the front baffle and guide holes drilled in the baffle and ready for routing flush, to be followed by a 3/4" roundover for the flare
3) All of the box bracing has been cut and the horizontal bracing is glued in

I dry clamped the front baffle when I was fitting the bracing to make sure I had enough clearance to not block the internal port holes and had enough room for the driver. It also gave me a good chance to see how well the box is going to come together.....and the verdict is that I'll have a fair amount of sanding to get all of the edges flush (I didn't go the oversized baffle/flush trim route method because it was just easier to get Lowe's to make the major cuts for me since I don't have a vehicle to transport large sheet goods and have no side/outfeed support to handle that stuff easily on my little tablesaw). Regardless, the box is level and pretty dang square.

Pictures below. If I don't work too much overtime I might be able to get this box ready before the weekend, so I can start on it's twin.

[bemis23]

Well I got the port holes flush routed and rounded over. I did have the bit set a little too deep to I got a touch of a lip on the roundover, but a little wood putty smoothed it out and after sanding it will be unnoticeable. The rear baffle got the binding posts installed and wired - and then the rear baffle got glued up. With the rest of the internal port construction finished The front baffle has been completed. I dry clamped the front baffle and added most of the box stuffing. I loosened the clamps and the front baffle is now in final glue and clamp.

Tomorrow will be the final test when I install the driver and gasket. If it sounds good a little flush routing and sanding will get this box to it's final form until the mains are built and tested so that I can decide on a finish that will match across the entire set.


Note: The third picture is a dry fit without clamps - the clamps will remain in place overnight as the glue cures.

[bemis23]

Well yesterday I installed the driver and gasketing. I hooked up everything and took the new sub for a test drive - played some rock, jazz, and funk, followed by some watching some select scenes out of 300, Pearl Harbor, and playing a couple rounds of Call of Duty online.

First impressions? It sounds much better than I had hoped for. I have some room issues that I'll have to deal with, but I'm hoping that adding the 2nd sub will help mitigate some of the room effects. Output isn't quite what I expected, but I think that the subwoofer has significantly more headroom than my amp. My little EP1500 just isn't providing the kind of power that I expected, and the clip limiter is kicking in if I turn it up loud at all. My next electronics purchase will likely be an Emotiva XPA-1 to run this bad boy and it's twin which should give me more than enough amp to power these subs cleanly. On the other hand when paired with the small commercial satellites that I'm currently running for mains it has more than enough output.

I am extremely happy with the set up thus far. I'll post a picture of it in my living room once I find my camera.

It still needs to be sanded and have the edges rounded over, but it was very satisfying to hear it finally sing.

[---k---]

Well, we tried to talk you into a 15" sub.

It will break in overtime and give you a little more output. Give it a few days of regular use.. Also, make sure you didn't overstuff it when you lined the walls with insulation or whatever. Make sure the port isn't blocked by fill.

Check your wiring and how you have it hooked up to the amp? Are you using the middle set of binding posts and running the amp bridged? Make sure the switches are set correctly.

Also, you could be clipping the input of the amp. You might try turning down the sub channel output of your receiver and turn up the amp. You might also want to try the reverse.

[bemis23]

I tried your suggestions with the amp, but to no avail. I'm also getting a ground loop that I haven't been able to isolate yet.

I'm going to be working on the next box tomorrow and pulling the driver out of the completed sub to finish sanding and routing so I'll play with pulling out some stuffing and see if that helps.

[Paul W]

Did you buy 8 ohm or 4 ohm 315's?

[bemis23]

4 ohm

[Paul W]

You may want to ask Emotiva about your intended use of the XPA-1 with two 4 ohm loads. The XPA-1 is rated for 500 watts @ 8 ohms (your drivers in series), though it is "stable below 4 ohms", it isn't rated for 2 ohms (your drivers in parallel).

The XPA-2 is rated for 2 X 500 watts @ 4 ohms and may make a better match for your subs...and it is $100 less. I use an XPA-2 for a sub amp & it doesn't break a sweat.

[bemis23]

Good point Paul. I forgot about checking for 2-ohm stability.

[bemis23]

Well I managed to finish construction of the 2nd box yesterday. Got it hooked up for sound test and it seems to be operating well - although this box has a couple leaks that need to be fixed - not a big deal. The bigger PITA is that one of t-nuts came loose and is free spinning. Since I glued to front baffles on (something I will not do again) it's going to require a hacksaw to cut the bolt head off and remove the driver for finishing. I think the real problem is that I was trying to rush to finish the box.

Are there any good alternatives to T-nuts? I really like the black socket head cap look, but the T-nuts are a serious pain to use. Another question, relating to baffle construction: how do you guys seal a removable front baffle? I didn't think it would be a big deal, but now that I have some issues that I need to correct, I really wish I'd opted to go for a removable baffle.

The second subwoofer has definitely solved most of the room issues I was having this weekend, but not all of them. Fortunately the only serious room modes remaining are not in the listening area (mostly concentrated in the kitchen and dining room) so I'm not too worried about them. I am very suprised by how different the sound changes on the vertical axis. Very low bass (<40hz) is much stronger and more pronouned when sitting, rather than standing. Any ideas?

[---k---]

I just use drywall screws with my drivers after having similar t-nut issues. Thomas usually recommends glueing a piece of plywood backup to the mdf to use as a better base for the t-nuts. I've glued my t-nuts in place with some epoxy.

I would probably use thick neoprene weatherstripping. I like the "Automotive/Marine" grade stuff from HomeDepot. Has really good adhesive.

If you need more power (which I'm not convinced that you do), I would say get a tried and true EP2500 for subs.

[bemis23]

Yeah I tried using just some Titebond on the T-nuts hoping nto for bond, but to hardent eh wood surroudning the T-nut to make it hold. I might not have given it enough time to cure (~2 hrs) but it didn't work all that great for me.

My buddy that has been helping me also recommended epoxy - but I resist on the grounds that epoxy is messy and a pain to use. It seems to be that there has to be a better way.

I just found an older thread here about the T-nut/H-nut issue, so maybe just some more research is required.

As for sealing a removable baffle, where is the weather stripping placed?are youlining the leading edge of the skeleton frame, or adhereing the stripping to the baffle and just placing it the appropriate distance (e.g. 3/4") from the edge? Seems like this would be a less than ideal seal?

[bemis23]

Ok, well I just put the subs through the Sheffield labs drum improv, and a few more test tracks, followed by some music.

I've played with the amp some more, and while it's providing a little more output, it is clear that these subs just have way more headroom than this amp can really utilize. That being said, I can't imagine that I really need any more output. I'm shaking windows, pictures, and internal organs and when my wife gets back from out of town she's going to be really pissed that one of our wine glasses rattled over and broke!

I'm simply stunned at the quality of bass that two 12" woofers can give. Needless to say, I'm clearly going to have to build some new (large) mains that can keep up!!!!!!