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How to Make a Subwoofer End Table  

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123Toid
(@123toid)
Illustrious Member Admin
Joined: 3 years ago
Posts: 1071
01/10/2020 12:52 am  

Let's be honest with Audio there is typically a certain amount of WAF (wife acceptance factor) that needs to be considered.  And typically subwoofers are the least accepted component of a home theater or stereo.  They are just ugly boxes that sit in the corner and make loud booms aka bass.  But what if we could take that same subwoofer and make it not only a central part of your home theater, but also a central part of your home décor?  That is exactly, what I choose to do.  But if you are going to do this, you might as well go with an even bigger subwoofer?  So why not use a 15" that can easily be hidden?  While we're at it, we'' pick up a few ports and a 250w plate amplifier.  It might not sound like much, power but this plate amplifier can actually power two of these 15" subwoofers way past reference level (more on why that is a little later).  In fact, for the components to build two 15" end table subs, it would cost around $500. Just want one, you could do it for around $350.

Parts Used: 

15" woofer: https://bit.ly/pn395-8

250w Plate Amplifier: http://bit.ly/30UimHx

2 Ports: http://bit.ly/4inport

 

Why Use PA Woofers:

Did you know the movie theater you go to, is using PA drivers.  So why aren't you? Most people aren't used to using PA woofers, instead they are used to what is commonly referred to as home theater subwoofers.  Let's talk a little bit about why these are commonly used.  These typically have high excursion, very low sensitivity and can be ported fairly low. The main advantage though, is it's box size.  This is due to Hoffman's Law.  Without going into too much detail, Hoffman's law states that a drivers sensitivity, low bass extension and small box size are directly related.  And you can only have two of these.  Since many people don't want huge ugly boxes, they choose a low sensitivity driver (ie needs more power to push it) and a small box.  Since, we are hiding this in plain sight, we can choose a high sensitivity driver (ie need a lot less power to push it), but have a larger box, which helps us still get low bass extension.  With that in mind, let's take a look at the design.

 

Design Process:

When I got these woofers in for a PA, build, one of them was damaged,  No issues though, PE sent me a replacement.  But while I waited, I decided to see what this could do as a subwoofer.  I was really surprised at how well it modeled with an EBS alignment. 

An EBS alignment stands for Extended Bass Alignment.  For this I choose a -3 EBS in about a 4 cubic foot enclosure.  In WinISD, this extends your bass response down to it's lowest frequency of it's F3.  Most people are used to seeing a ChevyChev alignment, which is flat.  The EBS response has a slight downward slope to it's F3 of about 32hz (with low pass). Take a look at the graph, with a 100hz high pass (4th order) with only 1 watt of power using a typical 1 meter response. 

spl 1 db

By tuning it this way, we do loose a little sensitivity, but with a high efficiency driver like this, it doesn't really matter.  You will still should be able to fill your room with bass.  As you can see 1 meter away we are getting over 120dB with only 120w.  This is important, as this is an 8ohm woofer, so that is max the 250w amplifier will give that woofer.  It's not until you get to 4 meters away that it hits 100db on 120w. 

spl 120w

 Port noise at 120w stays within 17 m/s which is exactly what we want.

port noise

Another important thing to look at is cone excursion.  At first, it looks like it will be an issue, but with the 20hz high pass that is built into the amplifier, you have no issues there. 

SPL cone excursion

 

Design Flaws:

No subwoofer build is without it's flaws.  SO let's talk about what these might be.  Since this is an EBS alignment, you may end up crossing your subwoofer over a little sooner in order to maintain a flat response in the crossover region.  Without that, it might raise that area up a few dB.  For most this won't be an issue, but it is worth mentioning. So if you typically cross your subwoofer over at 120hz, you may end up crossing this over at 100hz.

Some might not thing 32hz F3 is low enough.  They may want to get to that magical 20hz.  Which I completely understand.  Keep in mind that if you are used to commercial subwoofer, this is probably pretty similar tuning to a lot of commercial subwoofer.  With this in mind, let's talk about my real world performance.

Real World Performance: 

This is my performance, I cannot tell you how your room will or will not respond to the subwoofer. In room, it is really hard to say what type of response you will get. For me, in room, I got an F3 of 22hz. Or course that is with decent room placement and the cheap DSP-LF to help get the most out of my sub. Which I would recommend for any subwoofer.  It helps fine tune your subwoofer to your specific room.

This thing is pretty awesome though.  It can shake the entire house.  It is a pretty cool feeling having your couch shake 15' away from the subwoofer.  It is also a very clean response, without much motor noise.  It also doesn't need much excursion, which helps keep down the distortion.

What have People Thought about it?

My mom, said she really loved my new end table.  Should I tell her the secrets it hides?

My sister said there is no need for a back massage anymore.  She will just come over and watch a movie.

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123Toid
(@123toid)
Illustrious Member Admin
Joined: 3 years ago
Posts: 1071
01/10/2020 12:52 am  

Build Plans

 

Parts Used:

15" woofer: https://bit.ly/pn395-8

250w Plate Amplifier: http://bit.ly/30UimHx

2 Ports: http://bit.ly/4inport

1/4" T Nuts and bolts: https://bit.ly/33vD181

 

Box Dimensions:

This box uses 3/4" material. The dimensions can change a little to fit your space, but make sure you can fit everything.  Here are the dimensions I used. This is for the box only, not counting top or feet.

Height: 17.5"

Width 21"

Depth 25"

Box

 

Cut List:

This a sample cut list from a piece of 4' x 8' stock.

(2) Top and Bottom: 25"x21"

(2) Front and Rear: 21"x16"

(2) Sides: 16"x21.5"

Cut List

 

Ports:

For this I am using two 4" precision ports for each subwoofer built. The ports come as 5 different pieces.  One long piece, two flared ends and two connecting pieces.  Take the long piece and cut it down to 10" on each port.  You you will want to glue to ports together.  You will probably need to do this in the enclosure.  The pieces may not fit through your port opening, so it is best to glue them in the port hole. For this, I use CA glue or gorilla glue.  I love the CA glue, because it is so fast (if using the activator). Just make sure your parts are lined up before hand, as you only get one shot if you use that activator.  You will need to screw these in.  You will need four #6 screws.  You can pick up a pack at PE or just buy what you need at your local hardware store.  I like to go to Ace Hardware, as you can buy individual screws.

 

Top:

The top can be anything you want. But you will typically want it to stick over the edge at least 3/4" to 1" on each side - personal choice.  You can also make it the top of your box if you want it to be shorter.  Just make sure you account for this in your dimensions.  I used 3/4" Oak that I picked up from my local lumber store. I bought 1 piece of 1x12.  Lumber bought is typically bought at common size and not actual size.  The actual size of this lumber was 3/4" x 11.25".  This meant I did not have to cut the width down.  Glued together, was 22.5" which left 3/4" overhang on each side. I just need to cut the board into two 26.5" in length.  Then glued these together. 

 

Feet:

The feet can be any shape you want.  I just made a simple design and cut it out on the cnc.  But you could easily use a wooden dowel or even buy legs at your local hardware store.  Mine are approximately 3" tall.  If you wanted to shorten your feet you should be able to.  The max excursion of that woofer is only about 1/4" and the woofer sits out 3/4".  So you could possibly shrink it to about 2" although I have never tried it, so you would be taking a risk.

 

Braces:

Yes you should brace the box.  The best thing to do is get the ports installed and then cut some scarp 3/4" straight pieces and install them in places that will not get in the want of the ports, sub or amplifier.  You can also use a 3/4" wooden dowel if you want.  Just place these both horizontally and vertically where you can.  Make sure to leave enough room for 

 

Dampening Material:

This should always be used in a subwoofer.  You can buy some from PE or just go to your local Walmart and pick up an foam topper for a mattress.  Just line the walls with it and use staples or spray glue to keep it in place. 

 

External Design:

This is also personal choice.  I went ahead and just used a 2' x 4' piece of 1/4" material and cut the pieces to size on each side.  The width I cut to 3.5".  Keep in mind, if you do this, that once you add the ones to the sides or front, you will be gaining 1/2" which will need to be accounted for.  So if you do what I did, cut all the sides or front. and glue and nail them on. Then cut the sides  or front, whatever is left.  

 

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shrub0
(@shrub0)
Eminent Member Registered
Joined: 1 year ago
Posts: 46
04/10/2020 2:12 am  

I enjoyed the video. Can you share the inputs to Winisd so I can run a simulation? Thanks.


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123Toid
(@123toid)
Illustrious Member Admin
Joined: 3 years ago
Posts: 1071
04/10/2020 1:13 pm  

@shrub0

I just put it up above.  Hopefully this helps.  If not, let me know what you would like. 


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kanaaudio
(@kanaaudio)
Trusted Member Registered
Joined: 4 months ago
Posts: 71
04/10/2020 6:26 pm  

What a great idea, wow! Thanks for sharing!


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