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A new project

Dentman

Dentman

Well-Known Member
I've been wanting to upgrade my downstairs family room audio system for a while now. This room is also open to my kitchen. Currently we have a cheap,($89.00) Insignia bluetooth sound bar in place.
We very seldom sit in this room or watch TV, in fact the sound bar isn't even hooked up to the TV. I use it for both podcasts and music while cooking or cleaning, that's about it.

After some talks with Franklin about me wanting to upgrade the X-overs and drivers in my little Minimus 7's and pair them with a vintage Pioneer receiver I have laying around, he talked me out of it. He suggested he build me something. I told him about my very limited budget and he still managed to come up with what looks like a very good solution. He will be charging me a very reasonable fee for his services as well. Still this will come in at a great price for the complete project. Here's a copy of his latest email to concerning the design.

"Jack -

Attached is a drawing of the plans for the 2.1 speaker system we are working on.

The width of the sub module is 22 inches.
The width of the satellite speaker is 6.75 inches
The combines width when placed against one another is 35.5 inches
All enclosures are 5 inches height without feet. We will put the tallest feet which will fit into the cavity to get the most clearance for the sub's down-firing driver.

The amp in this design is mounted on the rear left of the subwoofer. We could easily flip it over and put it on the rear right, so look at where you are placing it and consider which side you'd prefer to put it on before we glue-up the enclosure.

The port for the sub is on the rear right in the drawing. (note that the two front to back blocks of wood inside the sub enclosure will be braces with lots of holes cut in them to let air pass through freely)

The satellites are simple sealed boxes, so nothing fancy there."

rps20190421_124841.jpg
 
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This will be a fun little project.

The drivers are small... 3" fullrange speakers in the satellite cabinets and a 5.25" subwoofer in the amp/bass module. The size falls sonewhere between a portable bluetooth speaker and a mid to large sound bar.

I think it'll sound pretty great.
 
Dentman and I went back and forth on this system being in a single larger enclosure sitting on a shelf similarly to a sound bar versus making it a three piece system - essentially a powered 2.1 system. Ultimately, we decided the future potential of putting the satellite "cubes" in more ideal locations for stereo listening with the subwoofer located more ideally for bass reproduction outweighed the convenience and aesthetics of a single box on the current shelf install.
 
I have been working on a different small subwoofer project and since I needed to setup a stacked dado blade on my table saw for that project and since this system for Dentman also calls for some dados, I chose to kill two birds with one stone.

I quickly cut the pieces for this project's enclosures and then setup the dado and made those cuts.

I then dry-fit the pieces for the subwoofer section to ensure they all fit:

Cabinet_DryFit_20190423_115307.jpg

The two middle panels will be cutout to be used as braces, and the array of panels on the right make up a folded rectangular vent.

This should be a nice little subwoofer.
 
As I was straightening up after my day in the shop I noticed a box on my door. It was the drivers ad amplifier Dentman ordered for this system.

I took them out of their boxes to confirm no visible damage, and everything looks fine. Excited, I am!

DriversA_20190423_165411.jpg

DriversA20190423_165403.jpg
 
It has been raining all day, so I had to keep the garage door almost entirely closed while I worked on the enclosures for this system today.

All of the MDF panels and braces are cut and ready for assembly, so I did a dry fit of the woofer module and the satellites:


DryFitSat_20190424_140210.jpg
Satellite without the front baffle in place

DryFitSat_20190424_140221.jpg
Satellite with the front baffle in place

DryFitSub_20190424_135456.jpg
Woofer module with the front and rear panels removed. Note the folded vent at the left of the enclosure in this photo.


DryFitSub_20190424_135505.jpg
Opposite side of the woofer module, you can see how the vent will work.

Worth paying attention to is my placement of the full-range driver on the front of the satellite baffle is offset in both directions by a prime number - 2/5ths on the long dimension and 3/7ths on the short dimension. While this won't make a historically huge improvement to the sound, it will provide improvement and make long listening sessions more enjoyable and the music @Dentman loves sound more slightly natural.

Also of note is that I glued a 3/4" ring of MDF to the baffle where the subwoofer will be mounted allowing me to countersink the sub-driver far enough that the huge roll surround suspension is not forward of the baffle. Since the baffle will be facing downward with feet raising the enclosure above the shelf, I want to ensure as much free air-flow from the woofer as possible with no restriction. The enclosure is 5 inches tall and the space between the two shelves where @Dentman intends to install this system is 6 inches, so that gives me up to just under 1 inch of clearance below the woofer cabinet for sound to propagate into the room. I have a creative method for ensuring Dentman can get the most clearance possible without running out of space, but I'll share that later on if he chooses to go that route.
 
Here's a photo of the subwoofer module being glued up. I am mainly posting it to show the MDF ring I glued to the rear of the baffle behind the cutout for the subwoofer driver.

SubGlueUp_20190424_143654.jpg

To do that, I took an old cutout leftover from a larger speaker build which fit between the two braces and simply glued it in place. I had to cut the rabbets on the panel with the table saw before I glued on the disc. Since the disc already had a center guide hole drilled in it for the router circle jig, once the glue dried I merely drilled it out again and continued on through the new panel under the disc. Then I used my router with the circle jig to cut the hole for the subwoofer. It was quite simple, in the end and only took a little more time than would be necessary to cut the speaker hole without the backing.

Once this glue is dry, all I have to do is glue and clamp the front and rear panels on before I start the sanding and rounding over process.
 
I spent most of the morning fine-tuning the crossover settings on a separate speaker project I am working in parallel with this one for @Dentman, so while I was auditioning what I hope is the final configuration, I decided to knock out the soldering and wiring of the speakers in this project in the same room.

Driver_Soldering_20190425_110044.jpg

Since these are mostly small drivers and we are trying to keep costs down, I chose to solder the wire directly to the speakers' terminals rather than use crimp-on removable connectors. This is the most reliable method, and it saves about 21 cents per connection. It also eliminates protrusions to the side and makes inserting and mounting the speakers, especially the tiny ones, much easier. The opposite ends have crimp terminations for the input cups and the sub connects via a Euro-Block terminator on the back of the amp. I bent the exposed wires at a 90 degree angle and tinned them to prevent stray strands from shorting something out.

When it comes to the electrical parts, I am now in a position that as soon as the enclosures are ready I can assemble this system and test.
 
So what's the circuit block in the middle? Is that some sort of general crossover? Or is that an amp? Or dsp? or... ?
 
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