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Quad 8" subs for my office

anotherhobby

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NOTE: this started with dual subs, then I built two more here. Here is the total set of 4 custom subs:

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I just finished up a pair of subs for my office, and thought I'd share my project. I’ve been making a lot of audio upgrades in my office recently, and the most recent was a quest to get better bass response. My wife's office is across the hall from mine, with a bathroom in between that we both share a wall with. She works all day like me, so I needed to keep that in mind. My office is just 910 cubic feet (around 11’x10’x8’), so I knew I didn’t need anything epic to pressurize the room, but I still wanted nice smooth bass with good extension. I’ve also never really designed/built/finished speakers of any sort before. However, I do have a good table saw, router, jig saw, lots of clamps, and everything else I needed.

With all this in mind, and very little research, I designed an 8-inch sealed sub enclosure for the Dayton Ultimax UM8-22. I know the of the larger Ultimax’s reputation and capabilities in Home Theater use, so figured/hoped the miniature version would perform well for it’s size. I followed their recommended volume of .35 cubic feet. For enclosure dimensions, I made the sub's baffle as small as technically possible when using 3/4" MDF, and then added the needed depth to accomplish the correct volume with bracing and the driver inside it. No magic here. I designed it in SketchUp:


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And so I began making a giant mess in my basement. After cutting up the MDF, I worked thru gluing the enclosures together.

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The last part of the getting enclosure together was building the baffle. Because the face plate was so close to the driver size, I had to counter sink the mounting nuts because they’d end up getting sandwiched between the face and the enclosure, and I also had to grind the inside edges or the hit the driver.

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From there I was able to mount the driver for a test ride to see how it would sound. I hooked them up to a Crown XLS1500 that I got used for cheap off ebay (525 watts per channel into 4 ohms). I was able to test them different heights, and they actually measured best about 6” off the floor. That's great because I wanted the subs up on legs for several reasons. They would lift them up out of the toe stubbing zone, it’d make them easier to move when vacuuming the floors, and I thought it’d look cool and unique. I was really happy that it measured well too!

IMG_9221.jpg


For the finish, I wanted them very dark and glossy with a high quality finish, but knew that painting was way out of my skillset. I saw a DIY speaker job somewhere that used Wilsonart Masonite, and I thought it looked great. I ordered a sheet, ran several edge and finishing tests with my router, and became confident I could get a good finish. I went to work.

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Once they were laminated and finished (that was a lot of work to get right), I attached the legs, installed the speaker connectors, added some polyfill, and finished them off by mounting the drivers.

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And here they are:

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This is where they now live!

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Next up was dialing them in as best I could with REW, a UMIK-1, a 70 Hz crossover, and a parametric EQ app on my Mac. I have a new miniDSP Flex on order, so when that gets here I’ll have a lot more tools to dial them in. That said, I’m very impressed with how well I was able to get them set up so far. I am getting a pretty flat frequency response with extension down to 10 Hz. I can play a little over 95 dB average volume at my seated position before the subs run out of steam and make bad noises. They absolutely rock and sound way bigger than they are, and I'm incredibly happy with them.

In this graph, the aqua line is my current room response just using these, a 70 Hz low pass dialed in on the sub, and EQ on the Mac compared to the purple line which is just my speakers alone (Revel M105s) with no filters and with zero EQ. The point with this is that you see zero issues at the crossover point and those filters work just fine. The 50 Hz null is from the room and can only be dialed out with a 3rd sub.

comparison.png
 
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Glen20

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Nice work.
They look fantastic!!
Do you happen recall the name of the legs you used ,or even have a link.
Thanks G
 

Eetu

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Nice! I've been thinking doing something similar for my office but with 2x Dayton Reference 8" (since they are a lot cheaper where I live). Something I'm also considering is mounting the drivers (and connectors) on the backside firing into the wall. So that the subs have a clean look and the drivers are protected. A quick google didn't reveal any obvious drawbacks. Thanks for sharing!
 

D!sco

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Very nice, clean build.

How does a single eight compare to the DOS 6.5" SVS PB3000 Micro you have sitting there?
 
OP
anotherhobby

anotherhobby

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Very nice, clean build.

How does a single eight compare to the DOS 6.5" SVS PB3000 Micro you have sitting there?

Thanks! The little sub in the picture a Kanto sub6. I did look at the SVS SB3000 Micro before I decided I was going to build, but two of them were more than I wanted to spend. Performance wise, like most rooms in domestic homes, my room needs multiple subs to get a good response.
 

Adaboy4z

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I had plans to transform my man cave like that, BUT the wifes job(case manager) was moved home permanently due to Covid last year. Now she has the biggest desk with dual monitors... sharing sucks
.
 

Colonel7

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That said, I’m very impressed with how well I was able to get them set up so far. I am getting a pretty flat frequency response with extension down to 10 Hz
Nice build and nice output. Are you using a bass boost to get down that low in room? Amazing performance for a pair of small sealed subs
 
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anotherhobby

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Nice build and nice output. Are you using a bass boost to get down that low in room? Amazing performance for a pair of small sealed subs

Thanks! I was pretty surprised by how low they went when I first hooked them up. The small room with a closed door (only 115 sq/ft) helps a lot since they are small subs. Also, sealed subs roll off smoothly and can be EQ'd to dig deep (which is what I did), but I gave up a ton of headroom to do it. This system doesn't go super loud, but it doesn't need to since I sit 3' away, and it sounds fantastic.

The graph below shows the measured in room response of the subs + mains with and without EQ. I've also added a pic of all the EQ bands that I set to get that response. All but 4 bands are in the bass region. I probably could have spent more time getting it even better in the EQ app, but I have a miniDSP Flex on the way so I'm going to spend my time on that when it gets here.



EQ-compare.png

Screen Shot 2022-01-18 at 10.23.46 PM.png
 

Wolf

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I built a 0.5ft^3 sealed with a 200W Yung amp on it. Yes, they are power hungry. Yes, they are quite capable. Yes, they do make erratic noises sooner than you'd like in the power scale.

On the UM-8-22, Xmech = Xmax, so there is no grace period. The cone can smack the frame. I also find that 200W is right about where the power needs to be, as i can clip it easily. 300W would be about right. I also find that 80Hz is all the higher i want it to go.

Did you stuff it at all? I added a bit.
Looks great! Thanks for the legs link....
 
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anotherhobby

anotherhobby

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I built a 0.5ft^3 sealed with a 200W Yung amp on it. Yes, they are power hungry. Yes, they are quite capable. Yes, they do make erratic noises sooner than you'd like in the power scale.

On the UM-8-22, Xmech = Xmax, so there is no grace period. The cone can smack the frame. I also find that 200W is right about where the power needs to be, as i can clip it easily. 300W would be about right. I also find that 80Hz is all the higher i want it to go.

Did you stuff it at all? I added a bit.
Looks great! Thanks for the legs link....

All of your observations pretty much perfectly align with mine.

The Crown amp is a bit more power than they need, and yes, over driving these subs makes some nasty noises, and as you say there is zero grace period. Luckily I don't drive them hard 99% of the time. Once my miniDSP Flex gets here, I'm hoping to dial in the levels on the Crown to reduce the odds of bottoming out.

As it is now, I've only bottomed out when I was intentionally pushing them to see where the cutoff was, and using very bass heavy material obviously. I'm thinking it also might help to roll off the deep bass a bit more with the miniDSP. I don't need 10 Hz frequency extension for music... that's just what they do in my little room. And, it's not like they are doing something impressive at 10 Hz other than really pumping back and forth. I'm thinking if I start rolling them off at 30 or 25, they'll be less apt to get bottomed out, but I won't know any of that until I get to playing and testing.

Yes, I did stuff them with poly fill. Not packed, but not loose either.
 

juliangst

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I might be a bit late to this thread but those absorption panels really drew my attention.

What material are those and do they actually help?

I have a really similar desk setup and I only have space for the kind of panels you have there.
 
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anotherhobby

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I might be a bit late to this thread but those absorption panels really drew my attention.

What material are those and do they actually help?

I have a really similar desk setup and I only have space for the kind of panels you have there.
I made the absorbtion panels myself using 2" thick OC703 fiberglass panels covered with FR701 fabric, which I ordered from Acoustimac. The wood frames I made from MDF that I had on hand. I've added some additional room treatments since these, but I'm still using the ones above in the exact same spot. They make a huge difference.
 
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anotherhobby

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UPDATE: I'm still very satisfied with these subs almost a year in, so now I am planning to add two more. I won't be able to start building them for a week or two due to to a pulled muscle in my back, but I have the plans all worked up. With 2 more of these subs put in the corners behind me, I'm expecting to be able to fill in all the dips you can see below, especially from above 35Hz to almost 60Hz with the nasty deep null at 50Hz. Other expected benefits are more headroom and lower distortion.

bass.png

The space constraints for corner placement are different, so I designed a new pair that are taller and triangular with attractive rounded corners. Standing on three of the same 6" tall furniture legs I used on the first subs, these will be 24" tall overall, but quite shallow. From the back corner of the sub to the center of the front face is just 8.5" and the extend out of the corner only 10" to each side.

mini-subs-corner.jpg


Each sub will can be cut from a single 2x4 sheet of 3/4" MDF as seen below. It'll take 18 kerf cuts on my table saw to make each corner radius bend. All vertical faces will actually be one continuous wrap around sheet, glued back to itself where the ends meet in the corner. It's only 6 total pieces of wood including the internal bracing. I did a test today on the Wilsonart laminate finish with my heat gun, and I was able to get a nice permanent bend that will wrap nicely around the round corners, so I'm confident on getting a nice finish again.

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Below you can see how they will tuck back into the corners. One will fit behind the chair, and in the other corner one will fit tightly enough to not make contact with the closet door when it opens. And yes, this is almost exactly what my office currently looks like. :)

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Below is from the side (window wall removed), and you can see there is plenty of space between the corner chair and the sub. The chair is obviously not for listening to music and is mostly for when people come in to chat with me. I don't know how long these will take me to build, but I'd love to get them finished sometime in January.

office-side.jpg
 
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anotherhobby

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Today I had some time to run a bunch of tests to validate whether building two more subs is worth my effort. The answer ended up being a very convincing yes.

I plan on setting up the 4 subs in pairs, with each front sub paired with the back sub that's on the same side, and then balancing each pair of subs independently using MSO and miniDSP 2x4HD. The pic below shows the plan, after which, I'd run Dirac calibration.

quad-subs.jpg


To get an idea of how well this would work, I took REW measurements of the subs for each side by physically moving one of the two subs I already have to the back position for each channel measurement. The graph below is single vs dual subs for the L channel, and I see an excellent improvement in native response! In addition to over 6 dB gained from below 20Hz thru 55Hz, the two deep nulls at 50Hz and 74Hz are also gone.

left-sub-dual-compare.png


Next up is the right channel. The graph below is single vs dual subs for the R channel, and again I'm getting the same increase in SPL, as well as a substantially smoother response! This looks great to me!

right-sub-dual-compare.png


Below are 2 graphs that just combine the above response curves together differently for a final comparison. The first one has both channels in the dual sub setup I run now. The second one shows the same for the quad sub setup. I see a dramatic improvement in overall room response, and will definitely be proceeding as planned.

both-channels-dual-subs.png


both-channels-quad-subs.png
 

Colonel7

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Today I had some time to run a bunch of tests to validate whether building two more subs is worth my effort. The answer ended up being a very convincing yes.

I plan on setting up the 4 subs in pairs, with each front sub paired with the back sub that's on the same side, and then balancing each pair of subs independently using MSO and miniDSP 2x4HD. The pic below shows the plan, after which, I'd run Dirac calibration.

View attachment 250202

To get an idea of how well this would work, I took REW measurements of the subs for each side by physically moving one of the two subs I already have to the back position for each channel measurement. The graph below is single vs dual subs for the L channel, and I see an excellent improvement in native response! In addition to over 6 dB gained from below 20Hz thru 55Hz, the two deep nulls at 50Hz and 74Hz are also gone.

View attachment 250221

Next up is the right channel. The graph below is single vs dual subs for the R channel, and again I'm getting the same increase in SPL, as well as a substantially smoother response! This looks great to me!

View attachment 250222

Below are 2 graphs that just combine the above response curves together differently for a final comparison. The first one has both channels in the dual sub setup I run now. The second one shows the same for the quad sub setup. I see a dramatic improvement in overall room response, and will definitely be proceeding as planned.

View attachment 250223

View attachment 250224
When I see your subs I keep thinking they’ll walk away with those legs. Kind of like this
1671141247447.jpeg
 

My adventures in stereo

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Interesting project
Quad sub is the way to go, I am only 3/4 there ;)

Like the way you measured the subs in different positions, so that you can recreate what a quad dub response will be
 
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anotherhobby

anotherhobby

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When I see your subs I keep thinking they’ll walk away with those legs.
Ha! Yeah, I think the first two I built look like little piglets. :D
Very cool. I've used laminate a few times on speakers. It's a slick way to get a nice finish. Legs look great with the glossy finish.
I'm really happy wit the laminate finish. Doing it was intimidating to me though, knowing how one screw up could botch the whole job. I'm shocked I didn't screw up either one.
 
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