Review: Dunlavy Audio Labs Dunlavy IVa crossover modification

Category: Speakers

Dunlavy crossover modifications starring Duelund Coherent Audio

This review has been a long time coming, and delayed because my speakers have been going through extensive modifications not originally planned. I’m writing this with great detail (which makes the review long) because I wanted anyone who is considering this project will have full insight into what is required. I apologies in advance for the length, but I strongly feel it is important to know what to expect.

This is written specifically about Dunlavy IVa speakers, but could be pertinent to other Dunlavy speakers. This project I have been considering for many years after hearing others claiming great improvement in their speaker’s performance. I finally got to the point where this project was NEEDED because of the incredible clarity I was receiving from my gold DIY interconnects. For the first time I became aware of the faults in my speakers, I was hearing the “graininess” often discussed with Dunlavy, and so I began researching.

For those of you who have read my writings, I often research every aspect I can before I delve into a project. Modifying my speakers scared the %$@& out of me, so I needed a lot of input before I could get comfortable with the idea of taking a hot soldering iron to my crossover. I read everything I could find about Dunlavy speaker modifications at many different Internet forums. I searched in vane for schematics that could help direct me, but I was told by many that no such thing was available, and in fact if it was, it would not have values listed because Dunlavy designed each crossover circuit to match the drivers it was associated with.

This meant the only way to determine the resistor, inductor and capacitor values was to actually pull out the crossover. (The crossover is easily accessed by removing the speaker cables and then the eight screws from the metal plate on the back of the speaker where the speaker cables attach. Then gently pull on the plate which is attached to circuit board. The circuit board slides in a set of groves that are used to support the board. This entire process is very simple, just be careful.) Once the board is pulled out you will find the values written on the components. Turns out this is not quite so simple, the resistors and capacitors were often bundles in groups of two or more running in “parallel” and glued together using silicon glue. In order to find the values of the components hidden by the ones on top I would need to de-solder the pieces and pull them apart. I was no where near comfortable enough with the project to do this yet, so I simply wrote down the manufacturer (Solen) the values I could see and pushed the crossover back into the speaker.

My next task was to research replacement capacitors, resistors and inductors. I wrote all my “friends” in the industry including Audiogon members, retailers, modifiers and some manufacturers to get input from those who know far more than me. One company was consistently recommended for capacitors. Mundorf MCaps, specifically MCap Supreme and MCap Supreme Silver/Oil were on the top of everyone’s list. This led me to research Mundorf’s capacitors as well as resistors and inductors.

Searching through Google for retailers that carried Mundorf I found myself at [url=http://www.partsconnexion.com/]Parts Connexion[/url], and consequently stumbled upon the best read I have seen in a very long time. THIS IS A MUST READ!!! [url=http://www.humblehomemadehifi.com/Cap.html]Humble Homemade hifi[/url] which is a capacitor shootout performed by Tony Gee who has posted a number of DIY projects (mostly speakers) as well as other great information. The capacitor test is an ongoing process as Tony continues to evaluate high end capacitors for both speakers and electronics. Tony found the Mundorf to be excellent products, but in April of 2006 he discovered what he now uses as his reference capacitor.
Tony’s new reference capacitors are made by [url=http://www.duelundaudio.com/]Duelund Coherent Audio[/url], and it turns out they also make resistors and inductors, but as is true with the capacitors these are not like anything I had seen before. Duelund Coherent Audio manufacturers components designed by Mr. Steen Duelund. (Sadly Mr. Duelund unexpectedly died last year, but his legacy and company are being carried on by the new owner Frederik Carøe.) These products are the result of Mr. Duelund’s lifetime's dedication to the design of audio components. His design philosophy includes an emphasis on phase coherence and the exclusive use of diamagnetic materials wherever possible.
This link is to an excellent review regarding crossover modifications done by [url=http://www.tnt-audio.com/accessories/duelund_xover_e.html]TNT-Audio[/url]. This next link is to a forum where the man posting, the owner of [url=www.bd-design.nl]BD-Design[/url] did a [url=http://www.bd-design.nl/forum/forum_entry.php?id=10753]comparison[/url] of a number of the Duelund capacitors.
Similarly to how I handled the information gathering process with my other short listed capacitors, including Mundorf, Amp Ohm, Clarity Cap, Audyn Cap, Sonic Craft, Multi-cap and Jensen capacitors, I wrote the manufacturer directly about my needs. Because Duelund had not yet established a dealership in the US, I was lucky enough to speak directly with the Duelund owner and consequently developed a good relationship with him. At the time Duelund’s products they were only handled in North America by Parts Connexion, Canada. The line has subsequently been picked up by [url=http://www.e-speakers.com/products/duelund.htm]E-Speaker[/url] and [url=www.electrumaudio.com]Electrum Audio[/url].

After a number of conversations with Duelund’s owner, I learned a great deal about his company and more importantly I gained perspective on their incredible dedication to building the best products possible. These guys were special, and I became sold on working with them to re-build my crossover network.

The first issue of business was to determine what exact components and values my crossover had. This required me to de-solder a number of the cheap Solen sand wire wound resistors and the Solen capacitors to see what were underneath the top components. While trying to separate the sand resistors I cracked the sand casing down to the element on two of the resistors. Because the actual element was not damaged, I was told I could still use it, so I soldered them back in and emailed the values to Duelund.

I was not able to see a value posted on the existing inductors, so I needed de-solder them and measure the values myself. I emailed them to Duelund so they could know the required values on the midrange inductor (foil type) and the bass (toroid type) to replace the Solen wire coil inductors. Within a day I received an email with an attached schematic that was their interpretation of what I sent them. I then verified the information, and re-drew a schematic for them with the verified information along with some missing information regarding the bass design.

From this sketch, the Duelund engineers were able to determine the “critical” components that needed to be upgraded. The remaining components were of less importance, and because of my budget constraints we decided to only replace the critical capacitors, resistors and inductors.

It turned out the one (and only) capacitor and resistor on the positive circuit of the tweeter were to be replaced. The midrange required one capacitor, one resistor and one small inductor be replaced. Finally the inductor on the bass circuit was also identified to be upgraded. The price quote for two capacitors 826.00 Euro, or $1090.00, one pair 5.6 µF (tweeter) copper and one pair 10.0 µF (midrange) copper. The resistors at 1.65 ohm and 0.62 ohm were 60 Euro, or $79.20 and the two inductors, 4.42 mH (166), 0.082 mH (68) were 234 Euro, or $308.88.

The total of 1166 Euro, or $1539.12, including shipping is certainly not cheap, and might be considered insane for a speaker that can be bought for under $3000 at Audiogon. To further drive home the price disparity consider the Vifa tweeter used in the IVa sells for $25 each.

As I awaited the fabrication and delivery (within two weeks) I ordered Mundorf MOX (metal oxide) resistors from E-speaker for $3.50 each to replace the remaining wire wound sand resistors. When the package arrived from E-speaker I de-soldered the crossover board from the internal speaker wire. As I was doing this, I noticed the exposed copper from the internal wires were seriously corroded and actually bright green. I tried to determine how much of the wire was corroded by removing more of the wire jacket and found it was no more than a couple inches; but that is a good indication of the quality wire used in the Dunlavy speakers. It is clear the wire will require replacement too. This is a big project in itself, so I ignored the wire for now and proceeded to remove the crossover entirely from the speaker so I could work on it.

The installation of the Mundorf MOX resistors was quite simple; they ended up being just the same length as the original sand wire wound. I then reinstalled the crossover for a listen. Much cleaner, no change in tonality or pace, I just had an easier time seeing the instruments. Many people have recommended this affordable and easy modification, and I fully concur. At a very minimum, change the resistors. It will not affect any of the attributes that you love in your Dunlavy speakers; it will just make them cleaner and clearer.

Once the Duelund components arrived I again removed the crossovers. I then removed the tweeter and primary midrange capacitors and resistors but was asked by Duelund to wait with the inductors so I could see what each component was doing. The step of installing these new components was a bit trickier than the MOX resistors. The Duelund capacitors are rectangular, almost square in shape and look rather like an English cigarette pack or possibly a fancy dark chocolate bar. In fact my wife bit in to one, damn her, and of course I had to bury her after that. Oh what a waste.

Due to space limitations on the existing crossover board, the capacitors required installation on edge. I mounted them in a silicon glue and strapped them down using cable ties. In the perfect world an external crossover would be used with the components mounted flat where vibration would have less affect. The side mount is less than ideal, and inside the speaker means the capacitor must vibrate, but I have no idea how much this affects the sound. I was able to place one of the leads out of the capacitor directly into an existing hole on the circuit board. The other lead required a small piece of wire to connect it to the other hole.

The resistors are quite a bit longer than the original, but they come with long enough leads to run them along the outside of the resistor body and into the original mounting holes. I again mounted these in silicon glue. Once these components were mounted I reinstalled the crossover into the speaker and took a listen.

Oh my God, this was very clean and very clear. I likened it to a computer monitor where the resolution had been set at 800 x 600 dpi and it was increased to a stunning 1600 x 1200 dpi. Everything had such incredible refinement. Not more detailed or etched, it just was so much clearer in focus. This was a new experience for me in audio. The new components did not make any more information appear, everything I was used to hearing remained, but so much more refined. This alone would be worth the effort, but the most striking thing was how smooth the treble sounded. It was literally silky smooth, liquid and effortlessly flowing. I was mighty impressed, and feel this was a major step forward in performance of my system. The problem I encountered however was with the clarity of my interconnects added to the modified speaker I sensed I was very much hearing the flaws of a $25 tweeter.

This led me on another search, this time ending at [url=www.madisound.com]Madisound Speaker Components, Inc[/url] for a premium tweeter. They were able to spec a very closely matched tweeter made by Seas, a Norwegian speaker manufacturer. I ordered two at about $200 each and while I was waiting, I installed the inductors. This however was not quite that simple. The toroid bass inductor was smaller than the original wire coil type. Originally there was a small .22µF capacitor installed in the center donut of the wire coil inductor. In order to mount the tighter smaller toroid inductor I needed to relocate the small cap. It turned out there were unused holes in the circuit board that were usable to install the small capacitor off to the side of the new inductor.

Once the inductors were installed the bass seemed tighter and better defined. The soundstage was definitely deeper with much stronger imaging. But there was a real issue, the treble was glaring, edgy and way to up front. In that the inductors had nothing to do with the tweeter, and I still had the original tweeter installed, I figured the issue was at the crossover point of the midrange. Perhaps it was cutting off the midrange at a higher frequency than originally designed, thus accentuation the highs??? I wrote Duelund and within an hour I had a reply. (Now remember they are seven or so hours different than me, and it was clearly after hours. This type of service was consistently what I received. Duelund quite possibly has the best service and communication of anyone in the industry, at least in this case.) I was told to re-install the existing inductors and verify what I heard. Before I did so, I measured both the existing and the new inductors once again. I then returned the original inductors to the crossover. I was now very aware of the added grain in the original inductors. I had not been aware of this graininess prior to swapping inductors, but it was quite noticeable now.

As I said, before I installed the original inductors back into the crossover, I measured the value once again. The original inductors measurements did not match the new inductors; in fact they did not match the value that they were built to. The only explanation is the hand held meter I was using was out of calibration, and by a sizable amount of about 0.008 mH at the lowest value parameters, or in the case of the midrange inductor this is about ten percent. The crossover design accepts 5%, this clearly put the smaller inductor out of design parameters.

For the bass inductor this was within 2%, so we concluded it should be acceptable and within the design limits. Duelund wanted to verify that we had the right value before they build another pair of inductors for the midrange, so they put together a few wire wound inductors in different values. They sent them to me within a week and had me solder them in. We finally settled on a value, and they built a new set of foil type inductors. I soldered them in, and the treble settled down for the most part.

Now if you have been paying attention, and you’re not sound asleep yet, you may recall I ordered new tweeters. Before I tested the various wire coil inductors I installed the new tweeters. This was not so easy however, I was requires to cut a notch at the hole where the tweeter slid in. This was not a huge deal, but certainly outside the expected project parameters. I used a small Xacto saw that I use for building ship models. This turned out to be a perfect saw. Once the new tweeter was mounted I sat back and listened. This was a very significant improvement. The first most startling thing is if I put my ear right next to the tweeter it is crystal clear. The existing tweeter (and midrange) has a sharp, even painful noise at that distance. As a result even more graininess was gone. The highs sparkle in a very smooth and silky fashion. Now the extreme highs were effortless, and so much more open and transparent.

It has been a couple months now, and any burn in needed is over. I looked into replacing the midrange drivers but it is tough to find a match. Besides given the fact that still today I am not sure I quite have the tweeter sounding as balanced as the original design, so altering the midrange drives might be a huge mistake. Yes the speakers sound much clearer, cleaner, more liquid, soooooo smoooooth and the resolution is incredible. But clearly just replacing speakers does not quite resolve everything. Changing midrange drivers without a better understanding of how to tune a crossover would be too dangerous. The woofers it turns out were upgraded to premium cones when the speaker went from the model IV to the IVa, so there is nothing to gain in replacing them.

Next step for my project was to use a couple of smaller Mundorf silver in oil capacitors to bypass a big 82 µF Capacitor in the midrange. It is not feasible to replace this big capacitor with something vastly better. Mundorf does make an 82 µF capacitor, but it would not necessarily be any better than the Solen. I added a .56 µF and a .01 µF bypass capacitors, these seem to tame the treble just a bit further. These also seem to clean the midrange slightly, maybe a bit smoother.

So if I was to conclude the entire experience thus far, I would say that there is a great deal to be gained by modifying these speakers. Simply replacing all the resistors will have a significant impact on the sound. Replacing the capacitors made a significant improvement, so much so that I felt I was hearing the flaws of the cheap tweeter used in the IVa. This was not acceptable, and I could hardly go back, so I needed to replace the tweeter. Replacing the tweeter probably changed the value I should use for the capacitor and resistor. This is an assumption on my part, and something way beyond my knowledge and ability. Changing speaker cones is in affect re-designing the speaker and should not have been done by me without some better understanding of how crossovers work. The inductors proved to me I should have taken them to a technician to do the measurements just to avoid the problems I had, but once I found the right value, the inductors made a huge difference. The soundstage is real, deep and defined in a very three dimensional fashion.

Would I do this again? Yes, and I would probably make the same mistakes. If I knew more about speaker design and the way crossovers work I might have had a better result in the treble, but even now I refuse to take the time to read and learn. I am not big on reading technical dry papers. I would rather jump in way over my head and hope I can swim.

I should state that I am not quite complete. I intend to replace the remaining capacitors with Mundorf MCap Supremes. I will also be bypassing all the capacitors with Vishay Roederstein MKP 1837 as recommended in the Humble Homemade HiFi capacitor shootout. I also expect to replace the internal wiring, but that is not as easy as it sounds because I must remove all the drivers. I have just received Eichmann binding posts to get rid of the poor sounding brass posts that are standard on the speakers. I will post the results of these projects as they unfold.

jd

I want to add one final word on Duelund Coherent Audio. I have had the opportunity through my reviews to get to know a number of manufacturers in this hobby. I have further developed relationships with all sorts of “professionals” in audio, and I can easily say Duelund, and specifically the owner, Frederik Carøe is as enjoyable a person to work with as I have found. Beyond that, his personal attention and service was beyond reproach.

Add to the great service the wonderful sounding components and I have a hard time imagining using any other company for a project of this type with a health budget. I am most pleased. Below I have pasted a description of there components as described at the suppliers web sites.

Frederik Carøe
Owner
Duelund Coherent Audio
Tel. +45 28 27 52 40
www.duelundaudio.com
info@duelundaudio.com
Copenhagen
Denmark

The Duelund Coherent Audio Virtual Stack Foil Capacitor
A capacitor made specially for loudspeaker crossovers.
This new capacitor is the realization of a lifelong ambition. It consists either of pure aluminum foil, pure copper foil or pure silver foil and high-density paper, soaked in pure mineral wax, treated with special lacquers made from natural materials and wrapped in natural paper.
Unlike all other audio capacitors available no form of unnatural sound degrading materials are used. No metallization and plastics such as polypropylene are employed in the construction of these capacitors as the ensuing negative influence on the signal is unacceptable.
The stack-foil design ensures very low inductance, forming a solid block resulting in a form free of internal resonances. While the technical background may sound humdrum, the sonic splendor these capacitors make possible is anything but. The capacitors are made by hand in order to ensure the strictest tolerances possible.

Resistors

Designed by DUELUND Coherent Audio of Denmark for Loudspeaker Cross-Over these 10 to 15 watt non-inductive (they are purely resistive, since they are a solid element and have no electrical characteristics of a coil) resistors utilizing graphite as the resistive element, and pure silver wire for the lead out material. A phenolic cylinder is used to protect the resistive element itself.

The special characteristic about this resistor is that it displays a negative temperature coefficient. For example, when the voice coil of a speaker heats up, its impedance rises. The DUELUND Graphite Resistor counteracts this by means of a decreasing impedance. The results are greatly improved dynamics from the driver.

TOROID INDUCTORS
With a core made from special materials our aim has been to target hysteresis and saturation in ways that has not been done before. These coils will transform your speakers if used in conjunction with your speakers' midrange- or bass drivers.
Furthermore, the inductors can be placed adjacent to each other without degrading their performance.

Associated gear
Sony SCD-1 with all avalible modifications by Richard Kern, run off a Shunyata Research original Hydra. Aesthetix Calypso pre-amp, Plinius SA-102. Jade Audio 99.99% pure solid gold interconnects, Kubala-Sosna Emotion speaker cables and power cords, many tweaks.