The
purpose of this design was a dual-woofer loudspeaker with high
sensitivity, excellent on-axis and off-axis performance for under
$150/pr (exclusive of cabinet and finish.) Chosen were the Dayton 6 1/2"
woofer and 1 1/8" silk dome tweeter. The woofer was chosen for its
ability to produce very deep bass for a woofer of this size and because
it could do it in a reasonably small enclosure. The tweeter was chosen
because of its excellent performance at such a low price. The woofer
currently retails for $16.85 and the tweeter for $15.50. Given the low
cost of the drivers, the challenging aspect of this project was to
arrive at a set of loudspeakers that would introduce budget-conscience
speaker-builders to a system that provides performance that belies their
low-cost.
To reach
this objective, this design attempts provide flat on-axis and off-axis
response, clean midrange (within the capabilities of the woofer),
detailed high-frequency performance, and deep bass that does not "boom"
or sounded muddied. Deep bass often comes at the expense of high group
delay when using inexpensive speakers, due to the large box volume
necessary to achieve a low tuning frequency. In this case, the
enclosures are tuned to 36.75 Hz with an enclosure volume of just 31
liters. While these speakers do not sport the smallest footprint around,
they will almost certainly meets spousal approval when attentively
finished, especially when the spouse considers the excellent sound and
very lost cost.
One
comment you will hear on many message boards from those who seem to have
a definitive opinion on speaker design is that Dayton's inexpensive
woofers do not produce midrange of equal quality to some traditional
monitor-style two-way speakers costing roughly the same amount to build.
While this is true, other DIY speakers in this price range absolutely
require the addition of a subwoofer to produce response in the lowest
octaves. The advantage of such speakers, however, is that the
midrange performance is slightly better. Consider your desire for
deep bass and high efficiency versus a slight improvement in midrange
performance when selecting which design you want to build.... but
beware, the pundits full of free advice won't tell you how important
efficiency is. These speakers have an efficiency of about 89 db/1W
@ 1M. What this means is that at a distance of 1 meter, these
speakers will produce 89 decibels of sound pressure with a 1 watt input
signal. Traditional monitor-style two-ways (such as the Dayton 2
project) only produce about 83 decibels, under the same conditions.
To achieve the same listening volume with traditional monitor-style
two-way speakers, you need 4 times the amplifier power! And even
then, the single woofer will be experiencing much greater excursion (and
non-linear distortion) at equal listening levels. Lesson?
Two woofers are better than one.... and don't underestimate the
significance of a speaker's efficiency rating.
The Crossover
The D3 highpass
filter
The crossover's function in a loudspeaker is to "route"
certain frequencies to the individual drivers and to
"contour" the response of each driver to give
the speaker a smooth, balanced output across the
frequency spectrum. You don't want to send deep bass to a
tweeter and you don't want your woofer trying to
reproduce cymbal crashes. Accordingly, a properly design
crossover is the heart and soul of the loudspeaker. Using
various methods, the designer can use the crossover to
change most every aspect of how the speaker performs --
where the soundstage is located, how deep the bass
sounds, and many other things that all wrap-up into the
final system. A good crossover can make inexpensive
speakers sound great, while a poorly designed crossover
can make hundreds of dollars worth of exotic European
speakers sound like terrible.
To develop the most accurate and best sounding
crossover possible, the CLIO measurement system and
CALSOD loudspeaker design and simulation software package
were used to develop "baseline" values from
crossover components. Once an initial design was
obtained, final "tuning" was done by hours of
listening and by numerous, reliable ears. The final
crossover employed uses a first-order electrical lowpass
filter with impedance compensation and a "peak
filter" to smooth the midrange response of the
woofer. The highpass is a second order electrical filter
with a "tilting" attenuation network to provide
just enough tweeter padding to match the output of the
woofer and a slight rolloff of the high frequency
response to give the speakers a relaxed, yet detailed
sound. Both drivers are connected with normal polarity. The in-phase
crossover occurs at 2khz. All inductors are 18awg air
core except the .60mH series inductor in the woofer
crossover. That inductor is 14awg. The parasitic
resistance (DCR) of the inductors is accounted for in the
crossover design and helps shape the response of each
driver. Avoid the temptation to use lower gauge inductors
as some peaking the filter transfer functions will occur.
All resistors are 10W, non-inductive wirewound. All caps are Dayton
polypropylene with the exception of the 47uF cap in the lowpass -- use a
47uF non-polar electrolytic cap bypassed with a 0.47uF film and foil
bypass cap. A complete suggested parts list is shown at the end of this
page.
Shown below are both the original crossover for this project and a
revised version of the crossover (bottom) with modified component values
to account for changes in the Dayton tweeter (relevant to units
purchased between July, 2001 and May, 2002.) Please note that the currently
available parts list is for the original crossover. If you
are uncertain as to which tweeter you have, use the original crossover.
Also, a wiring diagram and schematic showing the placement of optional
"bypass" capacitors is included in the left-hand column of this page.
Click to enlarge the images below.
The D3 Crossover
(only use this crossover if you purchased
your Dayton Tweeter between July. 2001 and May 2002)
The Enclosure
The enclosure for this design was optimized for the
deepest bass response possible without sacrificing detail.
The result was a 1.17 Cu. Ft (33L gross internal volume)
ported cabinet tuned to 36.75 Hz. The final tuning
frequency was slightly lower than my original design
target of 39hz due to reduced driver dampening by using a
14awg inductor in the final crossover design. The sides
are supported with a vertical brace that also supports
the inner end of the 3"x8" rear-firing vent.
Vent openings should be slightly flared to smooth the
airflow.
Construction of the enclosure is quite
easy and should take less than a day to cut and assemble
the cabinets and baffles. All drivers are flush mounted.
The vertical brace, not clearly shown in
the diagram, is 8"x8" with a hole in the center
to support the vent (see a picture of the inside of the enclosure in the
column on the left). Speaker wire binding posts should be
placed near the vent and the crossovers mounted on the
rear baffle. Acoustic dampening foam should line the top,
bottom, and sides of the enclosure. No foam is used on
the rear baffle, but approximately 4 oz. of "AcoustaStuf"
should be teased and placed in the rear half of each
enclosure to slightly dampen the back wave of the woofer.
To help you cut the baffles, I recommend
the "Jasper Circle Jig" and the following
dimensions:
Woofer Cutout: 5 3/4"
Tweeter Cutout: 3 3/8"
Flush Mounting Recesses:
Woofer: 3/8" Radius rabbet, 3/8" depth
Tweeter: 1/2" Radius rabbet, 3/16" depth
Final Comments
& Performance Data
This
project has been exciting and challenging. The true test of an engineer
is not how good he can build something, but how well he can use the
available means to arrive at a product that exceeds the value of the sum
of its' parts. In this case, the final speaker sounds great, images well
and provides an acceptable soundstage. Combining this with the fact that
all the drivers and crossover components cost under $150, I believe that
this project has been successful. I know that I'll be enjoying my set
for years to come and it will sit proudly among speakers in which a
single tweeter costs as much as this whole pair.
Listening
Critique (Originally Posted 4/6/01)
When it comes right down to it,
however, music is art and speaker design is the
integration of art and science to reproduce the music in
the most pleasing manner possible. Does this mean that
accuracy, flat response, etc. are sacrificed? No, of
course not... but these are all factors that get weighed
as part of the final equation... and that final equation
simply determines whether the sum of what goes in is
equal to what comes out. In this case, I'm am very
pleased with the results and believe that for the $150 in
parts these speakers cost, what comes out is worth
significantly more than the sum of its parts.
After final assembly last night, I
"auditioned" these speakers with a variety of
music against my Altec Lansing reference speakers (A TMWW
costing about $2000 in 1988.) The Altec's are not the
pinnacle of speaker technology, but the drivers are
excellent, the crossover appear well designed, and they
have (to me) always sounded wonderful -- I feel they
provided a good basis for comparison to learn the
strengths and weaknesses of the D3. So how do these
inexpensive MTM's stack up? Very well!
First off, anyone who builds these is
now required by law (my law, not a real one) to go out
and get Dire Straits' Brothers In Arms CD. This CD is
very well recorded and produced and will allow you to
discern the capabilities of various speakers. It has
excellent dynamic range and some beautifully subtle
timbres in the voices and instruments. Oh, and it's got
great music too! (Don't you get annoyed when you read
about the stuff allot of audiophile geeks recommend you
listen to? I'm an engineer at heart, not an audiophile,
so I say that if it ain't good music who cares how good
it sounds?! <g>).
Second, in about 4 hours of "critical"
listening (as opposed to just sitting there without
putting my fingers in my ears) we learned that the
soundstaging and imaging of these speakers is excellent,
provided you sit in the farfield of the speakers -- about
1.5-2 meters minimum. Also, the optimum placement for the
speakers is at least 2 meters apart with no toe-in (that
means they need to be point straight ahead.) Other than
that, you would need to hear them for yourself. In
comparison to the Altecs, the imaging was equally good,
although the soundstage was slightly forward. Also, the
Altecs have a soundstage that seems to encompass the room
from wall to wall... the soundstage of the D3 was more
than acceptably wide and seemed to start well outside of
the speakers. Also, we found that the D3's did a much
better disappearing act than the Altecs -- when the D3
played, the image was very well centered and moved around
effortlessly. The sound never seemed to emanate from the
speakers themselves. As well, the transition between
drivers in the crossover region was exceptional -- these
crossovers are almost inaudible.
Sonically, the characteristics of the
drivers themselves are, as you might expect given their
price, the only limitation we could identify. Although
the D3's always sounded superb, when we compared tracks
with the Altecs, we could definitely hear things through
the very expensive carbon-fiber impregnated cones that AL
uses that we could not hear through the D3's. One area
which exemplifies this is the sound of Mark Knoplfer's
Mesa Boogie. I have played guitar for many years and used
to own a Mesa Boogie amp for my Gibson Les Paul Special
guitar. I know the depth and warmth that this amp
provides from having spent many hours with it up close
and personal. Hearing Mark Knopfler make his guitar sing
through one is a near-religious experience to many
guitarists. The reproduction through the D3's was good,
warm, accurate and pleasing. Through the more expensive
AL's, there was a bit more detail and openness. Given
that speakers of similar quality would cost about $4000
today, it's hard to imagine that they sounded $3850 more
open, though. Given that the D3's had much more
authoritative bass (although not as crisp as that of the
sealed-enclosure AL's), my wife was of the opinion that
the D3's were more "fun" to listen to... and
for the difference in price there was no question which
was an overall better value.
Dayton MTM Parts Express Parts List
The following list contains all the crossover components you will need to build this project. Also included are a list of optional components and building materials you can obtain from PE for your project. Please see the project description for further information.
|
Required Crossover Parts |
|
PE Part # |
Description |
Qty |
|
295-305 |
6.5" woofer |
4 |
|
275-070 |
1-1/8" Silk Dome Tweeter |
2 |
|
266-330 |
.60mH, 14awg Air Core Inductor |
2 |
|
266-806 |
.20mH, 18awg Air Core Inductor |
2 |
|
266-814 |
.40mH, 18awg Air Core Inductor |
2 |
|
027-416 |
2.7uF PP capacitor |
2 |
|
027-424 |
6.8uF PP capacitor |
2 |
|
027-410 |
1.0uF PP capacitor |
2 |
|
027-426 |
8.2uF PP capacitor |
2 |
|
027-352 |
47uF non-polar electrolytic capacitor |
2 |
|
027-458 |
.47uF film and foil bypass capacitor |
2 |
|
004-4 |
4 ohm non-inductive resistor |
2 |
|
004-8 |
8 ohm non-inductive resistor |
2 |
|
004-20 |
20 ohm non-inductive resistor |
2 |
|
|
|
Optional Components and Misc.
|
|
PE Part # |
Description |
Qty |
|
027-452 |
.10uF film and foil bypass capacitor |
4 |
|
260-302 |
Binding Post Terminal |
2 |
|
260-316 |
Acoustic Foam |
2 |
|
260-317 |
Acousta Stuf |
1 |
