JL 8w7 built in cabinet

[GO-NAD!]

Yes, Granteed, that helps some. However, I have a big issue that might have been missed due to the length of time I let this discussion sit quiet. What I'm trying to accomplish is to construct a subwoofer that can hide behind a solid wood cabinet. There won't be any speaker pointing out into the room from behind a grill. I was originally asking if I could build something inside the cabinet, and basically point the sub's speaker down and out the toe kick area. However, what I'm coming to realize is that the vent is for relieving pressure inside a box where the speaker is pointing out of the box, and the pressure is due to the motion from the backside of the cone. So the vent isn't meant to be the source of the speaker's sound, but just something to enhance the speaker's performance. I think this added to my confusion.

Does that make sense, and is there a solution? Or is it staring me in the face?

The purpose of the vent is not to relieve pressure - it is there to tune the subwoofer to the desired performance envelope. If you want a visual aid to help understand how that works, you can download WinISD from here:

http://www.linearteam.dk/default.aspx?pageid=winisd

It's free software for designing speakers. Just pick your driver (or any driver, for that matter) from the database, choose a "vented" box and you can see what happens when you change the enclosure volume and/or the vent dimensions. You will see the line on the graph change as you manipulate dimensions. I think you'll have one of those "aaaah, I understand now!" moments.

As for the sketch that GranteedEV linked, all you would need to do is tip that box forward 90 degrees and voila - the driver and vent both point down and the solid top becomes the front.

All that said, those electrical outlets could present a problem. If the electrical code is the same as it is where I live, you cannot cover any junction box with a permanent structure, i.e. it must be accessible. If you can mount the subwoofer so that it doesn't interfere with access to the outlets, you'll be OK. From your photo, there may be enough room to mount it on the fireplace or the dividing wall side to accommodate it.

 

[GranteedEV]

I was originally asking if I could build something inside the cabinet, and basically point the sub's speaker down and out the toe kick area.

It depends on how much clearance you give it. There's definitely examples of downfiring subs.

 

[Bushka]

OK guys, between the pics you posted and the WinISD program I finally get it!

Of course that now leads to more questions:

1. In this thread I was given specs found on Dr. Mark's website. He recommends a 1.463 Vb and and Fb of 26.56 Hz, so I entered that info into WinISD so I could play around with box dimensions which were not listed by Dr. Mark. I will also try to use his port dimensions but I assume the WinISD port dimensions will be just as good if his don't work with my box configuration. The question is whether his V(total) of 1.898 takes into account the internal port so that I should really be using V(total) to dimension the box.

2. Does Boxnotes basically do the same thing as WinISD? I have both programs.

3. The vent does complicate things a bit and according to WinISD it is a toss up for this particular driver for vented/closed. I would still like the best product I can make. Is venting really worth it?

4. I'm going to mount the speaker facing down toward the floor and will probably have it about 4 inches off the floor. There will only be one exit for the sound - out the front of the cabinet at the floor so I hope this won't create some kind of interference/vibration pattern. I would like to mock up a drawing and post it here if someone wouldn't mind commenting on it.

5. How do you measure the length of the vent? If I need say 38.85 inches long, is it measured along the centerline of the vent or what? In other words, the outside of the vent running along the box is longer than the inside dimension as it makes bends inside the box.

6. The speaker and amp will take up some room inside the box. Do I need to adjust the box volume for this?

I think I can get a pretty close box design made if I can answer these things, then I can finalize things and finish up with a couple of final questions. Oh, and it looks like the wall outlets won't interfere with the box.

Regards.

 

[annunaki]

I would recommend doing some additional research. There is actually some good information here JL Audio tutorials

1. V(total) should be used to dimension the enclosure

2. WinIsd Pro Alpha is probably similar to box notes

3. Proper venting is well worth it!

4. What is the total surface area of the opening at the bottom of the cabinet?

5. The center line of the vent is the way to measure (see my link above as well)

6. Yes

 

[TLS Guy]

Can we help this guy model a sub for a built in cabinet? Its in THIS THREAD

Thanks y'all....

Here is the model for this driver, which has been on my website for some time.

 

[Bushka]

4. What is the total surface area of the opening at the bottom of the cabinet?

The space that the cabinet fits into is 45.5" wide by 20" deep. There may need to be a support brace down the center of the cabinet touching the floor, but my cabinet builder can probably work around that if he needs to (maybe just a post in the middle or something).

If you are asking about what the opening itself will be, I imagine something like a toe kick area without the toe kick. Again, I'll have to ask the cabinet maker, but probably close to 4" high by 44" wide. So the speaker will point down to the floor, which will be about 4" away. I could position the speaker near the front edge of the cabinet if that helps. Do you think this will be a problem?

 

[Bushka]

Here is the model for this driver, which has been on my website for some time.

Yes, I used that information to plug into WinISD so I could get box dimensions. I didn't realize it came from you, or who Dr. Mark is, but it seems people hold him in high regard.

Thanks again!

 

[annunaki]

The space that the cabinet fits into is 45.5" wide by 20" deep. There may need to be a support brace down the center of the cabinet touching the floor, but my cabinet builder can probably work around that if he needs to (maybe just a post in the middle or something).

If you are asking about what the opening itself will be, I imagine something like a toe kick area without the toe kick. Again, I'll have to ask the cabinet maker, but probably close to 4" high by 44" wide. So the speaker will point down to the floor, which will be about 4" away. I could position the speaker near the front edge of the cabinet if that helps. Do you think this will be a problem?

You will be fine to down fire through an opening of that size. It should not restrict output too much to cause any real noticeable affects.

 

[Bushka]

You will be fine to down fire through an opening of that size. It should not restrict output too much to cause any real noticeable affects.

I don't know if it will be necessary, but would I still be OK if the cabinet maker puts a support brace down the center of the cabinet base? In that case, the floor area will be about 22" wide by 20" deep. Then the toe kick opening area would be about 22" wide by 4" high. Still OK?

I'd like to mock up a drawing of everything. It would be great if you guys could take a look and point out any problem areas before we start building anything.

Thanks!

 

[annunaki]

I don't know if it will be necessary, but would I still be OK if the cabinet maker puts a support brace down the center of the cabinet base? In that case, the floor area will be about 22" wide by 20" deep. Then the toe kick opening area would be about 22" wide by 4" high. Still OK?

I'd like to mock up a drawing of everything. It would be great if you guys could take a look and point out any problem areas before we start building anything.

Thanks!

If he is a credible carpenter there is a way to add the brace without sealing off both areas.

I would not recommend shrinking it down further, as it will begin to act similar to a 6th order bandpass making your response much less linear.

 

[Bushka]

If he is a credible carpenter there is a way to add the brace without sealing off both areas.

I would not recommend shrinking it down further, as it will begin to act similar to a 6th order bandpass making your response much less linear.

OK, thanks. I'll post back with a drawing and prolly 100 more questions.

 

[Bushka]

Attached is a first round mock up of the subwoofer box and location. I used the data provided by TLC Guy at:

http://www.drmarksays.com/wp-content/uploads/2008/07/jl-audio-8w7-3pro.pdf

I used a VTotal of 1.898 and a 2.5x6" vent that is 37.74" long (measured at the centerline).

The box has the speaker firing down as indicated. The blue dotted line on the side of the box is the OBash amplifier. The red part, of course, is the vent. It is open to the floor at the back next to the speaker, and it wraps around inside and vents downward above the speaker. I have quite a few questions so lemme list the first ones that come to mind.

1. Do I have the right general idea or am I missing something big?

2. I'm not sure what VTotal is or why I'm using it. Vb is the net volume inside the box, which is 1.463, and it seems like I should be using that figure. I would add the volume of the vent plywood itself, an estimate of the amp volume inside the box, and the volume of the speaker. That would be the VTotal I should shoot for, no?

3. The cabinet itself (only part is shown, in blue line) will be 3/4" plywood. Can this serve as the side, back and bottom of the box, or should I build a box inside the cabinet and screw/glue it to the cabinet wall?

4. The speaker is over 17 lbs and will face the floor. Do I only need one layer of plywood to mount the speaker on? Will the speaker even fit in the hole if I doubled up on the plywood? Also, if I ever have to remove the speaker, I'll need a short screwdriver so I can reach through the toe kick opening and unscrew it from the bottom. This doesn't appear to be a fun job so hopefully it will last a long time.

5. Will I need any internal bracing to strengthen the box? It is pretty small so I'm hoping that isn't necessary. For now it is 12.5 x 17.5 x 20.

6. I've shown the toe kick area in blue highlight. There will be another identical cabinet on the left side of the fireplace and I thought it would look funny if the right cabinet had an open gap at the bottom and the left one was solid baseboard. I thought I could put posts and a small decorative trim on both cabinets. The left cabinet would have solid wood recessed behind the trim, whereas the speaker side would be open. Anyway, hard to explain but my kitchen sink cabinet was done like that.

7. Oh, one last thing on the vent - "Vent ends = one flared" Does this mean that one end of the vent should be routed to a curved exit and the other end doesn't matter? Or, is telling me that there is one vent and it should be flared (rounded over) on both ends. It's a little confusing.

OK, that's enough questions for now. I realize if I bought a book I wouldn't have to ask all this, but this forum has been so helpful and it's better feedback than a book.

(I should also mention that the jl-8w7-3pro speaker has been discontinued so I imagine there is something similar made by JL Audio).

Regards,
Dan

 

[TLS Guy]

Attached is a first round mock up of the subwoofer box and location. I used the data provided by TLC Guy at:

http://www.drmarksays.com/wp-content/uploads/2008/07/jl-audio-8w7-3pro.pdf

I used a VTotal of 1.898 and a 2.5x6" vent that is 37.74" long (measured at the centerline).

The box has the speaker firing down as indicated. The blue dotted line on the side of the box is the OBash amplifier. The red part, of course, is the vent. It is open to the floor at the back next to the speaker, and it wraps around inside and vents downward above the speaker. I have quite a few questions so lemme list the first ones that come to mind.

1. Do I have the right general idea or am I missing something big?

2. I'm not sure what VTotal is or why I'm using it. Vb is the net volume inside the box, which is 1.463, and it seems like I should be using that figure. I would add the volume of the vent plywood itself, an estimate of the amp volume inside the box, and the volume of the speaker. That would be the VTotal I should shoot for, no?

3. The cabinet itself (only part is shown, in blue line) will be 3/4" plywood. Can this serve as the side, back and bottom of the box, or should I build a box inside the cabinet and screw/glue it to the cabinet wall?

4. The speaker is over 17 lbs and will face the floor. Do I only need one layer of plywood to mount the speaker on? Will the speaker even fit in the hole if I doubled up on the plywood? Also, if I ever have to remove the speaker, I'll need a short screwdriver so I can reach through the toe kick opening and unscrew it from the bottom. This doesn't appear to be a fun job so hopefully it will last a long time.

5. Will I need any internal bracing to strengthen the box? It is pretty small so I'm hoping that isn't necessary. For now it is 12.5 x 17.5 x 20.

6. I've shown the toe kick area in blue highlight. There will be another identical cabinet on the left side of the fireplace and I thought it would look funny if the right cabinet had an open gap at the bottom and the left one was solid baseboard. I thought I could put posts and a small decorative trim on both cabinets. The left cabinet would have solid wood recessed behind the trim, whereas the speaker side would be open. Anyway, hard to explain but my kitchen sink cabinet was done like that.

7. Oh, one last thing on the vent - "Vent ends = one flared" Does this mean that one end of the vent should be routed to a curved exit and the other end doesn't matter? Or, is telling me that there is one vent and it should be flared (rounded over) on both ends. It's a little confusing.

OK, that's enough questions for now. I realize if I bought a book I wouldn't have to ask all this, but this forum has been so helpful and it's better feedback than a book.

(I should also mention that the jl-8w7-3pro speaker has been discontinued so I imagine there is something similar made by JL Audio).

Regards,
Dan

You have the right general idea.

To get VT, your add to Vb anything that displaces air inside the box.

So you add the volume of the duct, which is 0.35 cu.ft. You need to add the volume of the wood, in the duct that displaces are inside the box.

You add the volume of the driver, which is 0.06 cu.ft for this driver.

You do need to brace the cabinet well. Dado inter leaved vertical and horizontal boards, with large holes on the panels. This is called figure of eight bracing. 2 x 4s nailed in as bracing are virtually useless. You need to add the volume of air displaced by the braces to Vb also.

You need to add the volume displaced by the plate amp.

You do not add the thickness of the walls of the enclosure, as it is the inside volume we are interested in.

You do not need to add the volume of the damping material.

About 50% of the enclosure walls should be covered. Mineral wool is best behind the driver to minimize reflections and polyfill can be used for the rest.

Make sure all joints are well sealed with carpenters glue.

Dado joints are to be preferred over butt joints.

For the duct just taper the output edge of the duct with a rasp or preferably a router to bevel out the edges to minimize air turbulence.

Mount the driver flush with a router. I usually use double the thickness for the driver panel, by bonding two pieces together. The large hole for the driver causes too much weakness of the speaker panel otherwise.

You need to design this system so the sub can easily be moved out, to replace the driver or more likely a plate amp if you use one. Using a pro amp is to be preferred if the budget will allow. Making anything not easily accessible is something you will live to regret. I promise you that.

That pretty well covers it.

 

[Bushka]

TLS Guy: Thanks for the info.

I'm starting to think construction of this box is beyond the scope of what I would ask my cabinet maker to do. I have the equipment to do it myself, and have helped my father make speaker enclosures years ago, so I'm not too afraid of it.

(1) Given that, I would have to make the box and then set it inside of the cabinet, which will have openings in the bottom for the speaker and vent. I know some in this forum advise against that, and say I should construct the box as part of the cabinet. How about if I make the cabinet out of MDF and then glue and screw the right side, back, and bottom to the cabinet (see drawing in my post above). I would probably have to bring the completed box to the cabinet maker and have him mount it in his shop.

(2) Would it be acceptable for me to run some PVC outside of the box and along the floor as the vent instead of building the 2.5x6" vent inside? It would greatly simplify construction and size of the box. I would do something like run a 3" PVC pipe down from the box to the floor, then put a 90 elbow so the pipe runs on the floor in the 45.5" direction along the back near the wall. I don't know if 4" pipe will fit as the cabinet maker hasn't done the dimensions yet. I have lots of room down there and it won't be seen. What do you think?

(3) As far as accessibility, the plate amp will be easily reached just by opening the cabinet door. The speaker will be a little harder to reach, but I don't see any alternative unless the box was removable. I think I could reach the screws OK by reaching underneath, though.

 

[TLS Guy]

TLS Guy: Thanks for the info.

I'm starting to think construction of this box is beyond the scope of what I would ask my cabinet maker to do. I have the equipment to do it myself, and have helped my father make speaker enclosures years ago, so I'm not too afraid of it.

(1) Given that, I would have to make the box and then set it inside of the cabinet, which will have openings in the bottom for the speaker and vent. I know some in this forum advise against that, and say I should construct the box as part of the cabinet. How about if I make the cabinet out of MDF and then glue and screw the right side, back, and bottom to the cabinet (see drawing in my post above). I would probably have to bring the completed box to the cabinet maker and have him mount it in his shop.

(2) Would it be acceptable for me to run some PVC outside of the box and along the floor as the vent instead of building the 2.5x6" vent inside? It would greatly simplify construction and size of the box. I would do something like run a 3" PVC pipe down from the box to the floor, then put a 90 elbow so the pipe runs on the floor in the 45.5" direction along the back near the wall. I don't know if 4" pipe will fit as the cabinet maker hasn't done the dimensions yet. I have lots of room down there and it won't be seen. What do you think?

(3) As far as accessibility, the plate amp will be easily reached just by opening the cabinet door. The speaker will be a little harder to reach, but I don't see any alternative unless the box was removable. I think I could reach the screws OK by reaching underneath, though.

If you use a PVC pipe ebven a 4" pipe 29.5" long gives a vent air velocity of 25 m/sec. This is too high for a sub.

Any how the vent and cone need to reinforce each other. You need to be aware that between 50 and 25 Hz most of the output will be from the port and not the speaker cone. So the speaker and port opening should be on the same face.

If you think you can replace the driver OK, go ahead with your original plan.

 

[Bushka]

Any how the vent and cone need to reinforce each other. You need to be aware that between 50 and 25 Hz most of the output will be from the port and not the speaker cone. So the speaker and port opening should be on the same face.

That's interesting. Not really looking forward to building that internal vent, but still interesting...

If anyone can comment, I have one real outstanding issue, and that is about how I build this thing into the cabinet. Please see my post above. Can it be attached to the cabinet as I mention? Essentially if I do this then the back, side and bottom will be double thick while the top and side with the plate amp will be 3/4" MDF.

 

[TLS Guy]

That's interesting. Not really looking forward to building that internal vent, but still interesting...

If anyone can comment, I have one real outstanding issue, and that is about how I build this thing into the cabinet. Please see my post above. Can it be attached to the cabinet as I mention? Essentially if I do this then the back, side and bottom will be double thick while the top and side with the plate amp will be 3/4" MDF.

As long as the enclosure is well braced there will be no problem with the above plan.

There will be sound transmitted through the walls of the enclosure to the cabinet, so you need to make sure your cabinet is strong and free of rattles.

That is a powerful sub and will find anything that can vibrate and make a noise.

 

[GO-NAD!]

That's interesting. Not really looking forward to building that internal vent, but still interesting...

If anyone can comment, I have one real outstanding issue, and that is about how I build this thing into the cabinet. Please see my post above. Can it be attached to the cabinet as I mention? Essentially if I do this then the back, side and bottom will be double thick while the top and side with the plate amp will be 3/4" MDF.

Personally, I would build the sub enclosure separately and slide it into the cabinet, above the opening in the cabinet bottom. As for securing it in place, my take would be that if the sub enclosure is touching any other surface, it needs to be securely fastened to it in order to avoid rattling between the two surfaces. That said, it looks like the only possible surfaces that you can attach, are the sub bottom and the cabinet bottom. Even then, the 4" space you have to work with under the cabinet won't make that easy.

So, here's what I would do in your circumstances:

1) When finalizing the cabinet and sub dimensions, ensure the sub it will fit in the cabinet without touching the back or side walls.
2) Glue some carpet underlay (or other resilient material) around the perimeter of the opening in the cabinet bottom. Then position the sub enclosure on top of the material.

That's how I installed my in-ceiling subs and it worked well for me.

 

[Bushka]

In ceiling? Did you say "in ceiling"? I don't remember if that came up before, I'd have to look at the old thread. How does an in ceiling sub work? Do you need the same box parameters to do that?

 

[GO-NAD!]

In ceiling? Did you say "in ceiling"? I don't remember if that came up before, I'd have to look at the old thread. How does an in ceiling sub work? Do you need the same box parameters to do that?

It works the same as any other. The box parameters stay the same; you just modify the shape to suit the installation. If you take a look at the photos in this thread, you'll see the brackets that transfer the enclosure weight to the joists. Between the brackets and the joists, are strips of foam which are there to dampen any vibration. Also, around the perimeter of the baffle opening in the ceiling are strips of foam (which you can't see, of course), so there is no direct sub/ceiling contact. I also applied a bead of acoustiseal caulk to ensure there are no drafts through the opening. Your installation would be much simpler than mine.

http://forums.audioholics.com/forums/showthread.php?t=63454