How to Hide a Sub in Plain Sight

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:

250w Plate Amplifier:

2 Ports:

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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20200924 163126

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