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I decided that after the fun I had with my DIY front speaker project, I thought it'd be more fun to design a "timbre-matched" pair of rear speakers based off my DIY front speakers. I've been down the 3-way road with my college speaker project, and thought it would be fun to try a 2.5-way speaker, now dubbed The Sun Ones. For the Sun Twos, I went with a more conventional TM design, where the tweeter is situated on top, and then 1 midwoofer underneath (the photo up above shows what I'm describing). The midwoofer is used for handle the bass/midrange up to the crossover frequency with the tweeter, and it runs all the way through its frequency response. There is a bit of baffle step compensation built into the crossover, around 4.5dB. This pads the tweeter down where the baffle step loss starts to dissipate as the rest of the frequency spectrum becomes more directional and radiates in 2pi space - in front of its baffle (front panel). Conventional TM speakers require the tweeter's output to be shelved down so that the baffle step loss is minimized, but this means the overall speaker efficiency drops by 3dB to 6dB depending on where the speakers are placed in a room. This means adding in some baffle step compensation in the crossover network. Click here for more details on the baffle step diffraction loss and compensation.
I wanted to say "Thanks" to the following folks for all the help and guidance they gave through the process. All were extremely patient with my questions and pushed me to get me to this point.
I decided I wanted a maximum height of 18" for the speakers (I settled for 17" in height). This I decided on 10" for the width of the front baffle. This would allow me to use the Peerless HDS439's and apply a 3/4" roundover without much hassle. The depth of the enclosure was totally dependent on the needs for the internal volume for the 2 midwoofers. As it turns out, the depth of the enclosure was 12". This was due to tuning the enclosure to around 48Hz with a 2.25" wide port 5" long for internal volume around 16 liters (0.565 ft^3) because that's what was required by the Peerless HDS439 driver.
The final box dimensions are 17"x10"x12".
You'll notice that my front baffle has the drivers located off the vertical center line. This was determined by using Paul V's Baffle Diffraction Simulation spreadsheet. After playing around with driver placement scenario, I decided on the one I used since it gave me the best results (minimal diffraction reflections for the tweeter). I wound up with the following offsets:
I picked up parts for the crossover, ports, and drivers from both Audio Lab of Georgia, Madisound, and Zalytron. I got the MDF, glue, and screws from Home Depot. A friend of mine - Jeff has a nice workshop with a table saw and helped me make all the MDF panel cuts.
I ordered a 3/4" roundover bit, and Jeff was nice enough to let me use his big ol' Porter router that accepts 1/2" shank size. The front baffle has been rounded over on all 4 edges with the 3/4" roundover bit to help with baffle diffraction. Paul V's spreadsheet led me to do the roundover on the front baffle.
Here's the frequency response of the tweeter measured on a LAud setup on the front baffle:
Here's the impedance/phase response of the tweeter measured on a LAud setup o the front baffle:
Here's the frequency response of the midwoofer measured on a LAud setup on the front baffle:
Here's the impedance/phase response of the midwoofer measured on a LAud setup o the front baffle:
Though I have a big subwoofer which I can use to fill in the low end, I still wanted these speakers to play nice and tight bass. With the enclosure tuned to around 50Hz, my F3 was also near there.
Initially, to test the overall frequency response of these speakers, I took on-axis measurements from 1m away. I didn't have fancy measurement software and microphones yet. Please bear in mind that I was using a BassZone Test CD from Stryke and a digital Radio Shack SPL meter, which doesn't measure too well above 10KHz, so I ignored SPL readings over 10KHz for now.
This was my current overall response for the speakers (as of 7/1/01 last year):
3 meter frequency response graph
But this was a pretty inexact way of doing things, and in 2001 I bored people to tears with my incremental changes and repeated manual measurements of their effects on the speaker's frequency response. So I'm scrapping all of those graphs, and will be showing up what a good measurement system (LMS) and crossover optimization program can do to speed up the crossover design process.
I met RobC at the 2001 Atlanta DIY speaker meet in the fall, and found out that we lived close by each other. RobC was nice enough to help me out with a revamp of my crossover design. Rob had the LMS measurement system and the LEAP crossover optimization software.
In December, 2001, I stopped by with my speakers, and he took some measurements of the drivers while installed in the speaker baffles, and used the measurements to come up with a preliminary crossover design. Rob noticed a problematic resonance peak at the knee of the break frequency for the tweeter with my other tweeter filter, so he revamped the crossover for me. I built it, and listened to it for a few months.
Our schedules never quite meshed until late March of 2002, but I finally brought my speakers back for re-evaluating with the new crossover design in place. I had thought the tweeter was bit too loud, and needed some padding. After listening to the speakers, and then measuring them, my ears proved me correct. Here is one of the graphs showing a pronounced upswing in the tweeter output:
Graph 1 : As you can see I needed around 3dB of padding on the tweeter. We took all of the measurements in his garage. At this particular position, the F3 for the bass shows up to be around 60Hz. Later, next month, the bass response looks worse, but it was because we measured it from a different spot in his garage.
A week later, after I make some tweeter padding changes, I take the speakers back to be re-measured at Rob's place.
Graph 2 : Here's a graph of the 2 main crossover region from the midwoofer output, and the tweeter output. These graphs are pretty bumpy since they are 1/10 octaved smoothed. Most graphs you see are 1/3 octave smoothed, and smooth they are. I've increased the tweeter padding from -2.5dB to -5.5dB to get the levels in line with the midwoofer output. It appears to be the right amount of padding.
Here is the graph of the frequency response of the final crossover design. It's pretty close
to +/- 2dB from 50Hz to 20KHz. The bass response is closer to how it looks like Graph 1.
The initial crossover design (LR=Linkwitz-Riley):
From that initial design, I used Rob's tweeter filter (to get rid of resonance peak from the old filter) and adjusted the tweeter padding (changing l-pad resistor values) and used an old midwoofer filter:
This is the final crossover. (last updated 5/20/02):
Hint: For faster navigation, when you click on your first picture link, don't close that 2nd window, but resize this window and position it so you can see both windows concurrently. I've designed it so that you can leave that 2nd (photo) window open, and you can click to your heart's content in this first window, and the images will only show up in that 2nd other window. This should also speed up your visit here. If you want separate windows, then right click of the photo links and select the "open in new window" option.
Here we go:
Day 1 (Saturday 6/9/01)
The raw materials - wood panels:
Photo 1 : Here's the cut up MDF, plywood, and bracing. I also had the front baffle rounded over with a 3/4" roundover bit.
Photo 2 : I mark a border around the 1/4" thick plywood layer, which I will glue to the backside of the front baffle. This is to give the T-nuts (for the drivers) something to sink their teeth into when I pound them into the plywood later. Here is a shot of the glue that I applied to the backside.
Photo 3 : Got clamps? Just applying some clamping pressure to the plywood being glued to the backside of the front panel.
Photo 4 : Here I spend some time marking front baffles for the driver holes, and the flushmouting perimeter. Fred tried to give me the "paws-up"sign (I'm sure that's what he's thinking). I re-use the same driver placement as I did with the SunOnes. The tweeter center is located 3" of the top, and 3/4" off the center line. The midwoofer center is located 9.5" from the top, and 1/2" off the center line. The front baffle is 10" wide and 17" tall.
Photo 5 : Based on lessons learned on my previous attempts at flushmounting drivers, I decided to be a little smarter with the flush mounting of the drivers. So here you not only see the front baffles with the tweeter holes cut out, but you see a test piece I used to vertify the flushmount diameter, and the tweeter hole diameter. And somehow I still made one of the 2 flushmount diameters too wide - will need to slap some woof filler or caulk in the gap. Doh!
Photo 6 : Since the midwoofers have that funky truncated edges to them, I carefully route in the straight edges for them on the baffles. My router has a straight edge side to its base, so I just used a scrap MDF clamped on top of the baffle to give me a "fence" to guide the straight edge routing.
Photo 7 : Here's a shot of the router doing its thing. Currently it's doing the flushmounting of the midwoofer hole. That's my trusty Sears Router Guide that I use as a circle jig.
Photo 8 : After about 3.5 hours under a tree, but still managed to get my arms and feet burnt, I finish the driver hole routing. Here's a shot of the drivers in the holes on one baffle, and a non-occupied baffle. I wish I were faster getting these holes routed, but I tended to over-check the routing measurements so I don't have to re-do the baffles. I'm sure some people can do this in 1/3 of the time I took.
Day 2 (Monday 6/18/01)
Photo 9 : Now I drill in the holes for the drivers.
Photo 10 : Here's a shot of all the screws in their new homes.
Photo 11 : I widen the screw holes on the backside of the baffle. To ensure that the screws will fit into the t-nuts, I screw in the screws and make sure the teeth bite into the plywood so I'll know where the t-nuts need to be tapped in.
Photo 12 : I tap in the t-nuts carefully to keep the same alignment so I won't have any problems with screwing into the t-nuts. Sometimes the t-nuts don't line up correctly, so I'm trying to avoid that situation.
Photo 13 : Glue is applied to the t-nuts to add a little more adhesive permanance to the t-nuts.
Photo 14 : Here a shot of both front baffles and the holes and t-nuts installation for the midbass drivers.
Photo 15 : I start the holes for the tweeter drivers.
Photo 16 : The screws are test for fit in the newly drilled holes for the tweeter.
Photo 17 : I tap in the t-nuts and apply glue over them.
Photo 18 : I finish up both of the tweeter t-nut installation, and show both baffles being done.
That's it for tonight, it's getting too dark for anymore work since I will have to do some routing next.
Day 3 (Tuesday 6/19/01)
Photo 19 : These are pieces for the tweeter compartment backside. I draw lines for the height of these pieces, and will cut them down to size.
Photo 20 : This is the mid-brace, I've drawn the circle that will be routed, and the 2 corners that will have 2"x2" bracing installed for the box's rear panel.
Photo 21 : I route in the circles and the 2 corners for each mid-brace. Also, I cut in the corners for the tweeter back panel - top of the photo.
Photo 22 : Since I have to wire up the tweeter through the tweeter back panel, I drill in a hole wide enough to fit the speaker wire through it.
Photo 23 : Here the mid-brace and the tweeter back panel is glued together.
Day 4 (Thursday 6/21/01)
Photo 24 : It's time to start glueing the panels together to form a box. I apply some glue to the edges of the sidepanels. I will clamp the box in a 2-step process to improve the fit of all the panels. So I will glue one side panel and the top and bottom panels together in step 1.
Photo 25 : I clamp up the sides (I use the front baffle on the bottom as a guide for proper alignment of the panels).
Photo 26 : Once those 3 panels are glued, I move to glueing the midbrace into place, and did apply glue for the other side panel.
Photo 27 : The final clamping of the box occurs here. You can see how the midbrace fits inside the box now. I "punch" out and remove the front baffle (on the bottom) so that the excess glue doesn't wind up glueing the front baffle before I'm ready to glue it into place.
Photo 28 : Once the panels are all glued together, I use my orbital sander to smooth out any glue excess, and panel irregularies (not much since I was careful to get the panels clamped in the proper alignment).
Photo 29 : I do some caulking of the seams, some of it is overkill, but I was on a roll.
Photo 30 : Now it's time to glue the front baffle to the rest of the box. I apply glue to all of the edges that will mate with the baffle.
Photo 31 : After applying some pressure on the baffle, glue oozes out, of course.
Photo 32 : I wipe up all the glue around the perimeter.
Photo 33 : In order to apply more pressure while the glue dries, I place another piece of MDF and plop a bag of sand on top of it. I let the glue dry overnight.
Day 5 (Friday 6/22/01)
Photo 34 : More caulking of the seams, especially for the front baffle.
Photo 35 : I test fit the 2"x2" bracing. I had to do minimal sanding of the ends of the block to make everything fit just right.
Photo 36 : More test fitting the back panel with the bracing installed. The nail is just used so I can remove the back panel easier.
Photo 37 : Time to install the bracing, here's a piece with plenty of glue on it.
Photo 38 : Here's one more shot of the glued bracing along the height of the box.
Photo 39 : Finally all the pieces are glued/caulked/installed into the box.
Photo 40 : One last test fit of the back panel with the bracing installed permanently.
Day 6 (Saturday 6/23/01)
Photo 41 : It's time to work on the rear panel. Here I mark out the holes I need for the dual-input terminal cup and the port. I was able to situate the port in the area behind the tweeter compartment. It fits like a glove.
Photo 42 : Time to do some free-hand routing (because the holes don't have to be perfect and will hidden from view).
Photo 43 : After lots of sawdust, the holes are completed.
Photo 44 : I pop in the holes for the terminal cup.
Photo 45 : I screw in the screws for the terminal cup.
Photo 46 : I screw on the nuts for the screws.
Photo 47 : Here's a shot of the terminal cup and ports installed on the rear panels.
Photo 48 : I mark off the holes for the rear panel screws.
Photo 49 : I drill in the holes for the wood screws on the rear panel, I use a suitable bit with the right diameter.
Photo 50 : Then I place the rear panel into the box, and use a drill bit that is small enough in diameter to drill in holes that allow the wood screw to screw into the bracing. I practiced on a scrap piece before drill in all the holes.
Photo 51 : To countersink the wood screws, I get a drill bit that's as wide as the screw head, and then I run the drill IN REVERSE. By applying some pressure, you can produce the countersink holes in this manner. I also used a slightly smaller drill bit to give the countersink hole a little more depth.
Photo 52 : I test screw all the holes.
Photo 53 : I finally finish test screwing in all the screws for both boxes.
Photo 54 : Here's the first shot of the boxes sans drivers.
Photo 55 : Proud papa could not resist taking more than just 1 photo of the new boxes.
Photo 56 : Here's a shot of the rear panels with the screws installed.
Photo 57 : I finish caulking the rest of the seams now that the rear panel bracing is installed.
Photo 58 : Here I apply highly compressible weatherstripping on the perimeter of the rear panel bracing, and also inside where the crossover panel will sit on the bottom of the box.
Photo 59 : To compress the weatherstripping, I put a panel of MDF with a bag of sand on top of the rear panel of the box. I let this sit over night.
Photo 60 : For the rest of the evening, I work on constructing the crossover (XO) boards for the speakers. Here's a shot of both XO boards. The 1st one always takes a while to put together, but the 2nd one took hardly any time at all to put together. I am getting better with the physical connection of the components with each XO board I do.
Day 7 (Sunday 6/24/01)
I remove the sand bag from the 1st box, and put it on the 2nd box while I work on the XO installation for the 1st box.
Photo 61 : Here's just tweeter connector being crimped. I put in male/female spade connectors for the tweeter so I can remove the XO board without much hassle since the tweeter connection is impossible to get to with its own rear panel in place. (The connector for the midbass is easily disconnected.)
Photo 62 : Here's one of the tweeters with connectors in place.
Photo 63 : I carefully screw in the screws for the tweeter (I can't show my other hand protecting the dome while taking the photo).
Photo 64 : The midbass driver is screwed into place. It's easier to lay the box on its backside to keep the driver from falling out while screwing in the screws.
Photo 65 : After making the connections from the XO board to the tweeter and midbass, it's time to put the rear panel in place. Notice the compartment opening for the port.
Photo 66 : Here I screw in all the screws, notice that the previous night of compressing the weatherstripping pays off as the rear panel is flush and nice and tight when you screw in the screws.
Photo 67 : Just for completeness sake, here's the other speaker, and a closer look at the wires and connection to the drivers.
Photo 68 : Here's a corner shot of the speakers fully constructed (sans finish).
Photo 69 : One more shot showing the depths of the speakers.
Photo 70 : And finally a shot of both speakers' front baffles with drivers installed.
Yay! I'm preliminarily done! Once I finalize the crossover, I'll be veneering the sides, and painting the front baffle, and rear panel in the near future.
Here's a shot of the speakers set up temporarily in my home theater (photo coming soon).
I finally put a finish on the speakers:
Here's a webpage that details the process to get this look for the speakers.
 My home theater web page was a featured home theater for October 1999! |
Thanks for stopping by! Now go watch some DVDs and listen to some music!