Unquestionably, the "D3" is the most popular project I've published. I think that's for a good reason -- these are excellent speakers for very little money. The D3 has incredible bass and clear highs for about $150 in parts.

Overview

The Dayton III is a 2-way, dual woofer loudspeaker using the Dayton 6-1/2" paper cone woofer and 1-1/8" silk dome tweeter. These drivers have been the subject of a lot of discussion on the Parts Express Tech Talk board because they are among the "best bang for the buck" in low price loudspeaker drivers. This woofer is able to produce exceptionally low bass for a given box size and the tweeter produces clean, clear highs. When you hear these speakers you won't believe that the total cost for drivers and crossover components is under $150/PAIR!

I decided to design a dual woofer speaker in an MTM configuration using these drivers because there have been a lot of requests from people to use my earlier designs with the Dayton speakers in this manner. For those of you new to building your own speakers, MTM refers to the front baffle configuration where you have the speakers arrangement comprising "midwoofer - tweeter - midwoofer". This type of arrangement is widely accepted as having significant improvements over single woofer designs, at the expense of the larger cabinet size and (of course) the extra speakers.

By using the Dayton drivers, this speaker has all of the advantages of a dual woofer design at a fraction of the cost of many high-end systems, but certainly provides an "introductory level" of audiophile quality sound.

Design Objective

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 an "introductory level" of audiophile performance.

By "introductory level", what I mean is that these speakers provide flat on-axis and off-axis response, clean midrange, 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.

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 designed 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 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. All the parts are shown in the parts list here.  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 beginning in July, 2001.)  Please note that the currently available parts list is for the original crossover.

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. 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 Recessions:

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.

On-Axis Frequency Response (Normal & Reverse Phase)

Impedance (50% Fill, no crossover)

System Impedance

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.

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.

This project was designed and constructed by Wayne Jaeschke of SpeakerBuilder.net

Used with permission. Parts Express 2001 All Rights Reserved