Note
I designed this speaker with a full 6dB of baffle compensation, which sounded great when
it was sitting in the middle of the computer room. But when I installed it in situ, it sounded a bit bloated.
So I don't recommend anybody build this design until I've had a chance to correct it.
Design Goals
This speaker is a temporary replacement for my mains,
which will have to be scavanged for parts to make my new mains.
I originally planned on using the Scan Speak 8513 tweeter, but
it did not have the efficiency to allow proper shaping when combined with
a pair of M16's in parallel.
Drivers
The woofer is the GR Research
M16, the tweeter a Morel MDT-30.
The M16 is capable of good, tight bass. It seems to not like being crossed higher than about 2500Hz, probably because of resonances above 3kHz.
The Morel MDT-30 is known as an excellent $50 tweeter, which is capable of high levels of output. Since the point of a 2.5-way design is output, it seemed a natural choice.
The M16 is capable of good, tight bass. It seems to not like being crossed higher than about 2500Hz, probably because of resonances above 3kHz.
The Morel MDT-30 is known as an excellent $50 tweeter, which is capable of high levels of output. Since the point of a 2.5-way design is output, it seemed a natural choice.
The Box
This is the exact same box as used in my M16/8513 project, so if you've built that
and want more output, you can simply cut a new driver hole and use the existing boxes.
The box is sealed (no port) and is 38 1/2" x 6 1/2" x 13 1/2" (HxWxD) and made from 3/4" MDF. There are three shelf braces, one between the woofer and tweeter, the second between the woofers, and the third about 12 inches below that. The box is fully stuffed with Poly-Fil. The target Q is 0.707.
Cut the holes in the braces however you're comfortable. I recommend cutting 3 rectangular holes, each 3"x3.25", like so...
NOTE: The box in the pictures is 37 1/2" high. I decided an extra inch was necessary to cut down on some baffle diffraction from the tweeter.
The drivers are centered on the baffle. The tweeter's center is 3 5/8" from the top and is flush mounted. The woofers' centers are 9 1/2" and 17 1/2" from the top, and are NOT flush mounted.
Here is a very large drawing of the box which shows both the 2-way and 2.5-way configurations.
TIP: To save you some cutting, you can use the 12" wide MDF shelves available at Home Depot for the sides, top, bottom, and braces. It should take five 12"x48" shelves and two 24"x48" sheets of MDF to make a pair of speakers.
The box is sealed (no port) and is 38 1/2" x 6 1/2" x 13 1/2" (HxWxD) and made from 3/4" MDF. There are three shelf braces, one between the woofer and tweeter, the second between the woofers, and the third about 12 inches below that. The box is fully stuffed with Poly-Fil. The target Q is 0.707.
Cut the holes in the braces however you're comfortable. I recommend cutting 3 rectangular holes, each 3"x3.25", like so...
NOTE: The box in the pictures is 37 1/2" high. I decided an extra inch was necessary to cut down on some baffle diffraction from the tweeter.
The drivers are centered on the baffle. The tweeter's center is 3 5/8" from the top and is flush mounted. The woofers' centers are 9 1/2" and 17 1/2" from the top, and are NOT flush mounted.
Here is a very large drawing of the box which shows both the 2-way and 2.5-way configurations.
TIP: To save you some cutting, you can use the 12" wide MDF shelves available at Home Depot for the sides, top, bottom, and braces. It should take five 12"x48" shelves and two 24"x48" sheets of MDF to make a pair of speakers.
The Crossover
To design the XO using lspCAD, I had to create 2 projects. The first had only the woofers in
a 2-way configuration. The combined simulated FR and impedance curves (with a 2.0mH coil)
were exported, and then imported into the second project. From there, the design process went as normal.
The XO is 4th-order acoustic LR at about 2.2kHz.
The XO is 4th-order acoustic LR at about 2.2kHz.
Conclusions
This is a pretty good speaker for the money. Using cheap XO components,
you can build a pair for under $300. Offhand, I don't know of anything else that will
match the output for that price and still deliver this level of sound quality. This speaker
is VERY dynamic. Listen to some old recordings from the 70's (before dynamic compression became commonplace),
and the thing really rocks. As far as back-to-buck ratio, this is probably
the best speaker I've designed to date (Oct 2002).
(I should give credit where credit is due. The high performance/price ratio is because of Danny Richie's excellent woofers.)
The only things that keep me from saying this speaker is excellent is a little twang in the lower treble on some music. There is a bit of a knee in the high-pass filter right at cutoff, and that's the culprit. Lowering the value of the tweeter cap will cut this a bit, but will also generate a hole in the response. Raising the value of the resistor may help compensate for this, but I've already bought the XO parts...
Measurements coming soon...
(I should give credit where credit is due. The high performance/price ratio is because of Danny Richie's excellent woofers.)
The only things that keep me from saying this speaker is excellent is a little twang in the lower treble on some music. There is a bit of a knee in the high-pass filter right at cutoff, and that's the culprit. Lowering the value of the tweeter cap will cut this a bit, but will also generate a hole in the response. Raising the value of the resistor may help compensate for this, but I've already bought the XO parts...
Measurements coming soon...