4' wide, 3' tall, 15" deep for HT sub

[warnerwh]

We're going to go with 2 drivers in a box 48 wide/ 36 tall/ 20 deep. This should end up being about 17cuft. I'll try to model this myself but will appreciate confirmation that I'm correct. I'd like to see this sub get down to an F3 of 15hz, I'd be very happy. I'm still planning on using two RL-P 15's unless some recommends something better.

This is a gift for my best friend who in the last 35 years has always been there to help me and deserves the best and that's exactly what I am trying to do.

Btw, how low of information are on DVD's these days?

Thank You

[ThomasW]

We're going to go with 2 drivers in a box 48 wide/ 36 tall/ 20 deep

Properly built those are going to weigh a TON

Btw, how low of information are on DVD's these days?

Depends on the movie. There are Foley stage effects as low as 3Hz-5Hz on action adventure flicks like Batman Returns, WotW, Blackhawk Down, etc. This is a trend that only going to increase.

[warnerwh]

Here's what I came up with using a 27" long and 8" diameter tube. I tried numerous combinations of various diameters and lengths but could do no better:



If I change the series resistance to 4.0 I got this:




That second graph looks pretty good to me. I suspect I still didn't do everything correctly. What do you guys think? Thanks

[---k---]

Properly built those are going to weigh a TON

Mine is near that size and the box weighs 190lbs and the drivers add 60lbs for a 250lbs total. That is a far cry from a 2000lbs TON. Stop scaring people.

:rofl:

[warnerwh]

Ryan: I have informed Earl I estimate a weight of at least 250-300 pounds and suggested I build two boxes and set them side by side. No go, he wants one box. He's a general contractor and has alot of young guys to move it around for him but getting it into his truck with just us may be a bit of a challenge. :E

I'll print out the thread on your sub and read it again. Now that I'm getting to the nitty gritty part I need to think more about construction technique. I will use BB to help keep weight down. Then at least add one thickness of MDF on the baffle.

I believe I'm going to have to get a crossover to make it easier to adjust volume and I don't know what kind of crossover is available in his Yamaha HT receiver. I will be at 8 ohms total impedance actually, not 4. It appears the 8 ohm curve is better:



Btw, what is "end correction"?

Thank You

[ThomasW]

Btw, what is "end correction"?

That's whether the ports have flared ends.

Mine is near that size and the box weighs 190lbs and the drivers add 60lbs for a 250lbs total. That is a far cry from a 2000lbs TON. Stop scaring people.

:rofl:

Oh you take all the fun out of this...

[warnerwh]

First I'll go ahead and build the box most likely this week. For flared ends I'm thinking of using a bowl for a mold and using fiberglass and resin. This will be very strong, I just have to figure out what to put on the bowl so the fiberglass doesn't stick to it. If anybody has a better idea please let me know. I figure I can just glue the fiberglass to the pvc with epoxy.

How does the flared part of the tube effect length? Was that part of the calculation for the 26.5" port length or added to it?

Chances are good what I came up with is wrong but I know that two drivers will work in that large of a box. The port diameter and length though are critical to get right and I'm far from confident in my model.

Pictures will be posted as I do box construction. With this kind of woofer power I'm not sure what will be needed for structural rigidity. Obviously building it way over kill structurally will add more weight which in this case needs to be kept down as much as possible.

[---k---]

For flared ends I'm thinking of using a bowl for a mold and using fiberglass and resin. This will be very strong, I just have to figure out what to put on the bowl so the fiberglass doesn't stick to it. If anybody has a better idea please let me know. I figure I can just glue the fiberglass to the pvc with epoxy.

That is another good way. You can probably experiment with WD40 or other oils as a form release.
See http://www.users.bigpond.com/bcolliso/test-ports.htm for some other ideas.

How does the flared part of the tube effect length? Was that part of the calculation for the 26.5" port length or added to it?

I believe that the port length is from end of flare to end of flare.

Chances are good what I came up with is wrong but I know that two drivers will work in that large of a box. The port diameter and length though are critical to get right and I'm far from confident in my model.

I'm not sure I'm following your models. And what you mean by needing a cross-over and that you'll be at 4 ohms. I'm not an expert, and I'm not claiming I do everything correct.

Box size, box tune, port length and port size are all interrelated. Changes in one affects the others.

You're model shows effective 17cuft, so I think you're talking about increasing the size from the original? Remember you need to subtract from the total box volume the volume of the port, drivers, and bracing. I think I calculated ~70L in port, driver, and bracing for my sub.

Make sure you look at your port velocity in those models. I used a 9 1/2" port with mine. If you have high port velocity, you could get chuffing noise. I'm not sure if there is a specific velocity that chuffing starts at. A lot of people say to keep it under 25 m/s. I went up to 30m/s at full power. I think you're at 45m/s, but this is at a real low frequency, so probably doesn't matter, but is is easy to get rid of with a bigger port.

Reducing the box volume, and keeping the port size and length the same will result in the first resonance of the air inside the port lowering. Best to keep this above 200hz. I'm pushing it at ~180hz.

I use the standard crossover in my receiver and then the volume control on the amp.

so those are somethings to think about and consider.

[ThomasW]

It's a real pain to make DIY flairs.

If you're running 6" or smaller just buy premade flares. If you end up using large diameter ports, just mount the port behind several layers of the baffle material, and use a router with a monster roundover bit.

If you do a forum search you'll find threads dedicated to this topic

[warnerwh]

Ryan: The box size is now 3'x4'x20". This is about 19cuft with nothing in there. I guessed that I will lose 2 feet with drivers, bracing and port. Using a Behringer crossover will make life easier as it is more flexible and easier to use. The 4 ohm model is incorrect. Using to RL-P 15D2 wired in series will total 8 ohms, I should have made sure of what I was doing, this isn't differential equations. :lol: I sure don't understand why changing the impedance changes the model so much.

Thomas: Thanks so much. Flaring using a roundover will be much easier.

As far as chuffing goes I'll not worry about it as I've read a few times that this is easy to damp if it is an issue. Right now figuring port velocity isn't something I know how to do. When I go to HD tomorrow I'll measure what diameters I have to work with and do the model again.

Looks like the port will take 2.5cuft, if this is wrong for an 8"dia. and 26.5" long port please let me know. If someone knows how much volume the back of the RL-P 15's use up I'd appreciate it.

Thanks

[Mr. Lamb Fries]

If someone knows how much volume the back of the RL-P 15's use up I'd appreciate it.


According to their website, it takes up .21 ft3, or 5.9 liters, or 360 in3

[ThomasW]

.21 cu ft is 5.9L, and that's the number we've been using since we started designing with the RL-p15"

[warnerwh]

Where do you guys get tubes 8" in diameter? I can't find anything that large at Home Depot. Do the concrete places have them that small by any chance? Thanks

[---k---]

Both Lowes and Menards here carries 8" tube. Hummmm....

Look in the phone book under Construction Supply companies.

[warnerwh]

Thanks, I'll go out to Lowes tomorrow. I'm about ready to put this box together. Will have drivers Friday. I'll post pics and we'll confirm exact port length and where I should position it.

[warnerwh]

Now I'd really appreciate some help. Here's the box and port


Tube:



Now I need to confirm port length and where would be the best place for it. Actual inside dimensions are 46.5"w x 34.5" h x 19"d. I thought I read WinISD Pro accounted for the box thickness but want to make sure as this leaves room for error depending on how you construct the box. If someone can tell me how much volume a tube 8" diameter and 27" long uses I"d appreciate it. Drivers are .42 total and the shelf braces will be .35 just guessing.

I also read that you're supposed to keep the rear of the port it's diameter away from the walls and the rear of the drivers. Looks like I don't have that option.

Before I put in the shelf braces I want to put in the holes for the port to help mount it. I hope I can go through the side but if I have to have the port facing upwards it will just get done that way. Any help is greatly appreciated.

Thanks

[warnerwh]

I end up with a volume of 14.25 cubic feet. Port length of 24.99" for an 8" diameter tube here:



Please let me know if this is correct. Volume of the port is 5,000 cubic inches or 2.9 cubic feet. This seems like alot but I double checked, still doesn't mean it's correct. It's tuned to 17.5hz.

My plan is a double thickness for the baffle and three shelf braces. Any other recommendations let me know.

As soon as someone confirms design and where to put the port I'll finish the box and Kyle said I will have drivers by Saturday or Monday.

[---k---]

I don't think you subtracted the volume of the port from your total volume. I got the same 420cuft gross volume. When I subtract out the port, driver, and bracing I get 365L or 12.9cuft.

Changing your volume looks like it gives up a very very little bit between tuning and 20hz. and it also lowers your first port resonance point down to like 200hz. So, I think you're fine.

Though, Unibox is showing me for that volume and tuning of 17.5, the port should be 28.9" long.

[warnerwh]

The actual internal volume measuring inside dimensions is 17.6 cubic feet. Subtract 2.9 for the port and .42 for the back of the drivers you get about 14.25. This is what I modeled in WinIsd. Tuning frequency is set to 17.5hz but Winisd shows 24.99. Outside of the box will measure 20.5"d x 36"h x 48" wide.

I read that the TS parameters in WinIsd are incorrect. Could that have something to do with our different port lengths? Also did you use 2 drivers? Thank You for modeling it for me and double checking.

[---k---]

The actual internal volume measuring inside dimensions is 17.6 cubic feet. Subtract 2.9 for the port and .42 for the back of the drivers you get about 14.25. This is what I modeled in WinIsd. Tuning frequency is set to 17.5hz but Winisd shows 24.99.

I read that the TS parameters in WinIsd are incorrect. Could that have something to do with our different port lengths? Also did you use 2 drivers? Thank You for modeling it for me and double checking.

Oops, you gave inside dims. give me a second.

You should get the T/S correct.

For the port:
Lv = (23562.5*Dv^2*Np/(Fb^2*Vb))-(k*Dv)

where,

Dv = port diameter (cm)
Fb = tuning frequency (Hz)
Vb = net volume (litres)
Lv = length of each port (cm)
Np = number of ports
k = end correction (normally 0.732)

So it has more to do with the volume and slightly due to the absorption and end corrections.

[---k---]

Okay, fixing the volume, I get the same 24.36".

[warnerwh]

Thanks Ryan. Now I can go ahead and put the port in. Where would you put it?

[---k---]

It doesn't really matter. Just try and keep it like 4"-8" away from the walls and end.

I'm not sure how you plan to arrange everything, but I think looking at your box I would put the drivers on the 19"x35" ends so they oppose each other and cancel the vibrations. Then I would put the port sticking out the top with a grill over it (still need to make that for mine, ooops). Or put the port sticking out the bottom and put some legs on this thing.

And don't go cutting until tomorrow morning after Thomas has had a chance to proof everything I say.

[warnerwh]

"And don't go cutting until tomorrow morning after Thomas has had a chance to proof everything I say. "

Thanks, I will finish the box as soon as I get an ok. I'm not sure I can put the woofers firing outward. I'll ask my friend who I'm building this for. That does seem like the best idea. We need to finish this so I can do another sealed sub for my stereo.

[ThomasW]

The location of the drivers and port depend on furniture or other obstructions on the ends of the sofa.

[warnerwh]

I will place the port at 6" from the outside edges of the rear corner. The other end will be at the center of the cabinet between the drivers and below them.

I"m wondering if I really need a flare for this port. It's so large I can't imagine any chuffing sounds but if it's a problem let me know and I'll learn how to use a round over bit.

Thanks

[ThomasW]

If you already have a roundover bit, go ahead and use it on the front opening of the port

[warnerwh]

Thanks Thomas. I'll go buy a set of bits. It appears this router can be a useful tool.

I'll get the shelf braces installed as well as the port and you guys can tell me if you recommend more bracing or anything else. Pics later.

[warnerwh]

Here's where I'm at now. If you think I should add some mdf to the rear panel I will as I have to get some for the front baffle anyway. This thing seems pretty light right now. Any other suggestions please let me know.





For the flare I used a 1/2" round over bit. I also rounded some of the interior bracing. The quality consistency of my flare is far from perfect but should work better than sharp edges.

Thank You

[ThomasW]

The spacing of the braces is a bit odd. If they're not fixed in place move the front and rear brace further toward the middle

Also I'd remove more material from the middle and rear braces.

[warnerwh]

Thomas: The spacing of the braces from the center is 18". I figured I needed to leave room so the brace and fiberglass wasn't near the drivers. The drivers will be facing forward on the large panel not yet installed. If I should still place them closer please let me know. They're not permanent yet. Thank You.

I'll remove more meat from the middle and rear brace.

[ThomasW]

If the drivers go on the open side there should be a horizontal brace between the drivers to support that large section. It would be best if that brace tied in with the other braces

Fiberglass doesn't hurt the drivers. The interior surface of all the walls should be covered with glass.

[warnerwh]

Thomas: The box will be sitting on the 4' width. The braces will be vertical to the floor. Are you saying I need to run braces going the other direction also? If so can I use cross bracing like closet dowel? I guess I could put mdf shelf bracing going the other way too.

The drivers will be 1" more toward the middle of the cabinet than perfectly centered. The front baffle will have two large pieces of mdf mounted to the back of the plywood. Then I will cut out holes in mdf large enough to fit around the outer frame of the drivers so the driver is set back from the front so in effect the front baffle will be 3 layers or 2.25".

Thank You

Here's the braces with more meat removed, not pretty but I think structurally it's ok:

[ThomasW]

That's fine for those braces, But you need shelf bracing that's perpendicular to those.

[warnerwh]

Thanks Thomas. I'll get some mdf and place it above and below the back of the drivers. I'll make shelf braces that fit all the way around and will be connected to the existing braces as well as the front and rear panels.

Would there be any advantage to mounting the drivers a couple inches lower than center of the cabinet for room gain? Thanks

[ThomasW]

No benefit other than a lower center of gravity

[warnerwh]

Hopefully the cross bracing here is adequate. They all fit tightly and all braces are tied to each other. Everything has been glued with Titebond II then an hour later I went and put hot glue around the edges. I can pick up the cabinet with any of the braces. :



I will sand things down to fit perfectly unless you think I should do more. Being as I've read that this ply is adequate with one thickness I'll not worry about the rear panel. It seems like I should glue mdf to the large sections that are 18"x34.5" though. Edit: I went ahead and glued mdf to the rear panel, now I feel better.

Thanks again.

[warnerwh]

I will be glueing mdf to the top and bottom and cross braces from the top to the bottom as well as from one side to the other. Please let me know if that's enough. This thing is starting to get pretty heavy. With drivers I'm estimating well over 200 pounds. I've decided I will go three layers of the 13 ply for the baffle rather than sandwiching the ply with mdf to help keep weight down. Otherwise it will take 4 guys to move it. Any help is appreciated. Thanks

[ThomasW]

Being as I've read that this ply is adequate with one thickness I'll not worry about the rear panel. It seems like I should glue mdf to the large sections that are 18"x34.5" though. Edit: I went ahead and glued mdf to the rear panel, now I feel better

3/4" ply needs to be properly braced. The "rear" panel in particular needs some kind of reinforcement between the existing braces. That's too large an area to go unsupported.

This is my idea of an adequately braced box with 1.5" thick walls...... :W

[warnerwh]

Thanks Thomas. I'm on my way to Home depot. I will go up and see if I can figure out how to build shelf braces that will fit. If I have to I can remove the cross braces in the large areas.

It says on the SS website mounting depth is 21cm. This is 8.3" if I'm correct. My concern is position of the shelf braces. I can go above and below on the left side as you face it but the other side has the port. Would it do any good to put a shelf brace below the port tube? Thanks

[warnerwh]

How about if I add two more braces facing the same way as the others and then adding braces going the other way? I can put them closer toward the center but the distance between the center brace to the side brace I'm unsure of.

If I places both drivers say 4" outside edge to outside edge how much distance is safe for the extra side braces to be?

I'll go up and make two more braces like the existing now but won't put them in until I get your recommendation on distance Thomas. Thank You

[warnerwh]

I have braces just set in there now:



I'm wondering if I could center them like that and just cut out around the drivers. Or should I move them out away from the center. I have plenty of mdf to do anything necessary. I think it should still make it under 300 when done. Please let me know.

Then we'll figure out how to put the shelf bracing going the other way. I just figured being as I have the mdf I may as well add two more shelf braces going the same way as the others, especially after you posted that pic. Thank You

[ThomasW]

As long as the new braces don't obstruct the vent holes on the back of the magnet you're good to go..

[warnerwh]

Thank You very much Thomas. I'll have the drivers so I can see exactly what I'm dealing with tomorrow.

With the extra braces do we still need braces going the other direction from brace to brace?

[warnerwh]

Here's the cabinet with one of the two extra braces installed. I rounded all the cutouts. There will be a good 3" behind the heat vent.

Do you recommend I add any more bracing anywhere? Your help is greatly appreciated Thomas. I probably appear not too bright sometimes I'm sure but still want to do a good job. Thank You