Jan 032018

I am absolutely thrilled to be able to announce the Duelund Coherent AudioStokowski Altec Project for 2018!

This exciting project will showcase the Duelund Coherent Audio tinned-copper components, and will be a world first for a crossover constructed of tinned-copper components.

As you know, I have been extremely impressed with the prototype tinned-copper capacitors and resistors Frederik Carøe has sent to me to try, and the thought of building an entire crossover with Duelund tinned-copper components makes me positively giddy!

Frederik is as excited as I am about the project, and says he’s really looking forward to making some tinned-copper inductors too, which will also be a world’s first!

Stokowski A7 Voice of the Theatre loudspeaker.

Let me refresh you about the history of my vintage Altec Voice of the Theatre loudspeakers that were once owned by the great conductor, Leopold Stokowski.

Leopold Stokowski at Carnegie Hall 1947 (public domain photo)

On November 11, 2015, my friend Ron and I embarked on an audio adventure that took us to the Emerald City of Seattle to look at and listen to a pair of vintage Altec Lansing Voice of the Theatre loudspeakers that were custom built for Leopold Stokowski (April 18, 1882 – September 13, 1977), while he lived in New York and was conducting the American Symphony Orchestra.

Upon arriving in Seattle, Ron and I met with a very nice gentleman and his wife, Jeff and Lynn, who had advertised their Altec Voice of the Theatre loudspeakers with the interesting history, as being for sale.

Jeff told us, “I bought these speakers in New York 40 years ago from a colleague of Leopold Stokowski’s at the American Symphony Orchestra. He told me that Stokowski gave them to him before he left New York permanently for London. He was a conducting student of Stokowski’s.”

After a brief listen I bought those historic Stokowski Altec’s, and Ron and I brought the big & heavy loudspeakers back to my place, where I’ve been very happily listening to them with the SPEC RSA-M3 EX Real Sound Amplifier from Yazaki-san.

A little more information about Leopold Stokowski:

Leopold Stokowski had moved from London to New York City in 1905. In addition to his conducting, Stokowski was very interested in the recording and reproduction of music, and experimented with it as early as 1933 with his assistant conductor, Alexander Smallens, using a 3-microphone placement, that Bob Fine would later perfect.

Stokowski became a member of the Audio Engineering Society, collaborated with Altec, and played music from recording sessions back over Altec Lansing Voice Of The Theatre loudspeakers, driven by low powered vacuum tube amplifiers.

Altec built the great conductor a pair of full-sized Altec Voice of the Theatre loudspeakers enclosed in large custom “evening dress” cabinets for listening to music at home in his New York Fifth Avenue apartment (above).

After a long career conducting in America, at age 90, Leopold Stokowski moved back to London in May of 1972 in order to further his recording career, and his Altec’s ended up in Jeff & Lynn’s hands, and eventually worked their way into my life!

I am thrilled to have the Stokowski Altec’s, first because I love Altec Voice of the Theatre loudspeakers in general, and secondly because this pair of Altec’s has such historic significance – that’s so cool!

So what makes up these custom Voice of the Theatre loudspeakers that Altec made for the great Maestro?

Stokowski Altec A7’s

The most obvious thing about the Stokowski Altec’s are that they are enclosed in huge custom wood cabinets, with burgundy grill cloth.

They’re built very solidly and professionally, and everything has been fitted perfectly together. These are vintage loudspeakers, and they’re quite old now, and their cabinets have accumulated a few scuffs and scrapes over the years, but still they were in very nice condition.

Altec 803B in my VOTT’s, which is an earlier version of the 416.

The bass-horn cabinets inside the external cabinet enclosures look similar to the 825, are very well made as well, and house some pristine Altec 803B low frequency drivers.

The 803B low frequency driver is described in the Altec literature as, “The Altec 803B is a 15-inch low frequency loudspeaker of professional quality, chosen to complement the finest broadcast and recording studio monitor systems (such as the A7 and A7-500) in addition to providing the critical listener with superb bass reproduction for all wide-range public address, sound reinforcement and theatre or auditorium systems.”

“Utilizing heavy Alnico V permanent magnets (2.4 lbs.), rugged, die-cast frames, edge-wound copper ribbon voice coils of the largest practical diameter (3″), and exceptionally compliant cone suspension, these LF transducers combine the advantages of long-term operation with unparalleled response throughout the entire audible bass frequency range (20-1,600 cycles).”

The Altec 803B low frequency driver has a continuous power rating of 30W, a frequency response of 20-1,600Hz, a sensitivity of 99dB (SPL at 4″ from 1W), and 114dB (SPL at 4″ from 30W).

The Altec 803 low frequency driver has an impedance of 16 Ohms, the cone resonance is 25 Hz, the Alnico V magnet flux density is 12,000 Gauss, the frame (basket) is structurally-reinforced cast aluminum, the cone is molded fiber, the cone suspension is a high-compliance cloth surround with mechanical resistance, the voice coil is edge-wound copper ribbon, the diameter is 15 1/8 inches (7″ deep), and the weight is 17.5 pounds.

Altec 804A compression driver

Up top are Altec 804A 16-Ohm compression drivers mated to Altec 511-B horns.

The Altec 804A and Altec 802D compression drivers are essentially the same design, and are shown together in Altec literature.

The Altec 804A / 802D both use large diameter (1.75″) aluminum ribbon edge-wound voice coils coupled to a large (2.25″) aluminum diaphragm having tangential compliance. Both have a mechanical phasing plug with two exponential acoustic slots, which provides the proper phase relationship from sound emanating from the center & outer edges of the diaphragm and voice coil assembly, to give maximum high-frequency reproduction and a smooth overall response.

Like the 803B low frequency drivers, both the Altec 804A / 802D are rated for 30W. The Altec 804A / 802D frequency response is 500Hz to 22,000Hz, voice coil diameter is 1.75″, impedance is 16 Ohms, and diameter is 4.5″.

Altec 804A compression driver on 511B horn.

The primary difference is their magnets, as the 802D uses a 1.2 lbs., 15,250 Gauss magnet, and the 804A uses a 13 oz. 13,000 Gauss magnet, which reflects their intended use as compression drivers for sound reinforcement in large spaces with high ambient noise levels (802D), or smaller spaces, like home listening rooms or smaller recording studios with moderate ambient noise levels (804A).

The Altec 804A compression driver is optimized for loudspeakers, “… located in non-reverberant space having moderate ambient noise levels, the Altec 804A driver proves a perfect match (Such conditions would be analogous to the average listening room or smaller broadcast and recording studio)”, and pressure sensitivity is rated at 109.5dB at 1W and 124.2dB at 30W.

Altec 804A compression driver on 511B horn.

The Altec 511B sectoral horn is intended to be crossed over at 500Hz.

Full back view of the drivers and sectoral 511B horn.

Here’s the N-500-D crossover network …

As I mentioned earlier, Leopold Stokowski was a member of the Audio Engineering Society, collaborated with Altec, and played music from recording sessions back over Altec Lansing Voice Of The Theatre loudspeakers, driven by low powered vacuum tube amplifiers.

Presumably, the audio engineers at Altec optimized the component choices & cabinet construction for this custom pair of Altec loudspeakers to best match Leopold Stokowski’s personal playback tastes.


I’ll leave the N-500-D crossovers in place but disconnected, to preserve the historical configuration of the loudspeakers, and the Altec N-500-D crossovers will replaced with the Duelund Coherent Audio tinned-copper crossovers that are the subject of this project – exciting stuff!

Hiraga A5 16 Ohm crossover design courtesy of Sound Practices.

The Duelund crossovers will be based on the Hiraga 16 Ohm crossover design (above) and will consist of the following parts, and of course Duelund DCA tinned-copper wiring:

C1: 2 x 18uF
C2: 2 x 10uF
C3: 2 x 0.82uF

R2: 2 x 140 Ohm 10W
R3: 2 x 24 Ohm 50W
R4: 2 x 100 Ohm 10W
R5: 2 x 10 Ohm 20W

L1: 2 x 6.6mH
L2: 2 x 6.6mH
L3: 2 x 6.6mH

We’ll use an L-pad on the HF output to help dial in the balance between the low and high frequency drivers.

Time for a story.

Left to right: Ron Barbee, Andy Moore, and Pete Riggle.

Pete Riggle had stopped by for some audio fun & games right after I got the Stokowski Altec’s and listened to them with the SPEC M3 amplifier streaming jazz from Jazz24 in Seattle.

Pete liked what he heard so much from my Altec’s he went home and bought a pair of Altec A7’s, and has been having a ball experimenting with them, and they sound really, really, good in Pete’s Garden of Earthly Delights listening room (above).

In fact, Pete’s superb results with his A7’s are what inspired me to do the crossover project for my Stokowski Altec’s.

The Altec’s are capable of an incredibly high-level of performance if you take time to get them dialed in right with some good crossovers.

Custom silver Duelund CAST caps. Note the coffee cup for scale.

In the spirit of the Duelund-WRSE Project, Frederik and I are embarking on the exciting Duelund-Stokowski Altec Project!

The beautiful Duelund CAST components as used in the Duelund-Westminster project.

Frederik said he would be starting on building up the tinned-copper components for this project in the next couple of weeks, which I’m really excited about.

I would like to thank Frederik Carøe for his support of the Duelund-Stokowski Altec Project, as I quite literally couldn’t do it without him. A huge thank you to Frederik!

Well, 2018 is entering in like a lion, roaring with excitement, and kicking off the new year (and my retirement!) with the Duelund-Stokowski Altec Project is a dream come true!

Stay tuned, I’ll be reporting every step of the way about this exciting project, and as always, thanks for stopping by, and may the tone be with you!

 Posted by at 9:50 am

  28 Responses to “Announcing the Duelund Coherent Audio & Stokowski Altec Project for 2018!”

  1. What a great story and context for these awesome speakers – congratulations 🙂 Do you know of their exact (40+ years) age, and are the drivers in your estimate still in “tip-top” shape?

    • Hi Mikael,

      These Altec A7’s really are amazing loudspeakers, and I sure do like them. They’re playing jazz in the background right now as I write this, and are sounding fantastic.

      I don’t know their exact age, but I suppose I could come pretty close by finding out exactly when the drivers were manufactured.

      I saw the Altec 803B drivers advertised in the March 1959 issue of High Fidelity magazine as the “New Altec 803B”, but I don’t know exactly when they started production.

      Leopold Stokowski moved back to London in 1972 at age 90, so using those two dates as the bounding dates, they could be between 45 and 59 years old.

      All of the drivers are in perfect shape and still sound fantastic!

      Kind regards,


      • Hi Mikael,

        I have found out the production dates for Altec 804A/802D compression drivers.

        The 804A compression drivers were produced from 1961 to 1964 (the 802D compression drivers were produced from 1957 to 1972), so assuming the Stokowski Altec’s were built during the production dates of the 803B bass drivers and the 804A compression drivers, the Stokowski Altec’s were built sometime between 1961 and 1964 (57 to 54 years old).

        That raises the interesting observation that they were built before the A7 or A7-800 loudspeakers were introduced by Altec by a couple of years, in 1966, so I guess the Stokowski loudspeakers are not related to A7’s after all, but were rather predecessors to them.

        Kind regards,


  2. Hi Jeff
    Standing by to make ready to assist most any time.

  3. Hi Jeff,

    What a wonderful project! It will be so very interesting to hear the Stokowski heritage A7-500 speakers with the Hiraga circuit network using the fabulous Dueland components.

    When I heard the Stokowski A7-500 speakers in your small front parlor, I heard a directness, honesty, and immediacy I’d not been aware of as a possibility for small or medium sized listening rooms. So I put a bee in friend Harry’s ear, and Harry delivered, finding a pair of A7-500 speakers available here in the Northwest, that had been hanging in a church in Montana.

    With the stock N500-8A crossover the sound was a bit grainy. I had no idea how much potential the speakers really had until I built a crossover with very good components. I chose to try the Hiraga circuit (designed for his A5 speakers with the 1503 multicell horn) in the hopes that it might work well with the 511B horns. It does. I did Spice program modeling of Hiraga’s circuit, and found that it produces an electrical output with a dip of about 4 dB at 3500 Hz. The entry to the dip is around the crossover frequency with a gradual swale bottoming at about 3500 Hz. After the bottom of the swale the electrical output gradually increases to the baseline (or should I say bass line) level at about 10 kHz, and continues to rise above 10 kHz to assist the horn at the frequencies above 10 kHz. The Hiraga specified resistor in the notch filter is 12 ohms for the 8 ohm crossover, and 24 ohms for the 16 ohm crossover. If that resistor is changed to 60% of the Hiraga specified value, the notch in the electrical response is eliminated. My crossovers are set up with a switch so that I can have the notch or eliminate it. Depending on the equipment in the system, the program material, and the preferences of the listeners, I sometimes have the switch set to get the notch, and sometimes set to avoid the notch. I have also modeled with the Spice program a version of the Hiraga circuit that works for the 811 horn with an 800 Hz crossover.

    I must say that I love the results provided by the Altec A7-500 speakers with the HIraga circuit using high quality crossover components. Very direct, musical, dynamic, sweet, and smooth, with no trace of horn honk detectable by my ears. I have some big 3 way horns (the Po Boys) in the Garden of Earthly Delights listening room that have been neglected because I am enjoying the A7s so much.

    If you wish I can provide you with the results of my electrical modeling of the Hiraga circuit if that might be useful for the blog of your adventure. I look forward the coming adventure with great enthusiasm.

    Best Regards,


    • Hi Pete,

      Thanks for the great comment, appreciated!

      The Altec A7 and A7-500 were both released in 1966, and the version built for Stokowski appears to blend components from these two models.

      For example, according to Altec literature, the A7 was spec’d with 804A compression drivers and 803B low frequency drivers, the same as the Stokowski loudspeakers.

      Where the Stokowski speakers differ from typical A7’s of the period is that they are equipped with 511B HF sectoral horns instead of the normal A7’s 811B horns, like the A7-500’s, which of course necessitates its N500D crossovers. The bass horn cabinet for the A7 was the 825.

      The A7-500 was spec’d with the 802D compression drivers and either 803B or 416A (later) low frequency drivers, the 511B HF sectoral horn, the 825 or 856 bass horn cabinet, and an N500D, N500E, or N500G crossover.

      Note: It is my understanding that the 803B and 416A are nearly same low frequency driver, but as time went on Altec changed the name of the 803B to 416A after making a few changes to its design. The 803B was released in 1959, and the name was changed to 416A in the early 1970s.

      That means that the Stokowski speakers were built between 1959 and sometime before 1972, when he returned to London.

      The A7 and A7-500 spec’s above are for 16 Ohm loudspeakers as listed in the Altec literature of 1972.

      The Altec A7-8 (an 8 Ohm loudspeaker) was typically spec’d with 806-8A (or sometimes 807-8A) compression drivers and 416-8A low frequency drivers, an 811B sectoral horn, an 825B bass horn cabinet, and a N801-8A crossover.

      No doubt there were later A7 variants that used differing component mixes as well.

      Anyways, these lovely old Altec’s are sure a lot of fun, and I am greatly looking forward to our upcoming Duelund-A7 crossover adventure!

      I think I’ve already posted the electrical modeling you did of the Hiraga crossover circuit, but I’ll have to double check to be sure.

      Kind regards,


      • Hi Jeff,

        I use Werner Jagush (aka mast_mutter) crossovers for my Altec 604. It is a way better than original crossovers.
        The main idea of this crossovers to use autotransformer for horn level adjustment (instead of resistor).


        • Hi Alex,

          I have a pair of Werner’s 16 Ohm crossovers for the A7/A5, but I didn’t like them as well as the Hiraga crossovers I built, so I haven’t really used them much.

          While I like the idea of autoformers (my WRSE uses autoformers, for example), I didn’t think they performed as well with Werner’s crossovers as did the Hiraga crossover with really good Lefson resistors.



          • Hi Jaff,

            Thank you for reply.
            Werner use vintage oil capacitors in his crossovers. These capacitors are good but not on the same level as Duelund Cast Copper.
            I’m planning to try Duelund bypass capacitors in high frequency part of Werner’s crossover.
            What do you think, which one will be better for this project Tinned Copper Foil or Silver Foil?


          • Hi Alex,

            The choice of bypass caps will depend on what direction you want your system to go in. The Duelund tinned-copper foil bypass caps will open up the sound and provide a more textured presentation, whereas the Duelund silver foil are a little more laid back and smooth sounding. Either is a good choice depending on what you are trying to do.

            Having said that, while bypass caps can work nicely (the Duelund Sn-Cu bypass caps were stunning in my Altec A5 Voice of Theatre crossovers), I think the best sound comes from using the Duelund CAST caps stand alone in the circuit.

            For example, a Duelund bypass cap on any given capacitor in a circuit will sound good, but it doesn’t sound nearly as good as using a Duelund CAST cap to replace a given cap in a circuit. At least that’s my experience.

            Good luck, and let me know how your project turns out!

            Kind regards,


  4. Any recommendations for the best inductors for crossover use?

    • Hi Paul,

      I’ve been very impressed with the Duelund CAST inductors in my Westminster’s.

      For this project Frederik is going to build tinned-copper inductors, so that should be really fascinating!

      Stay tuned!

      Kind regards,


  5. Hi Jeff, I have followed your Altec adventure with great interest. I have both Werner Jagush and Hiraga inspired crossovers for my A5 VOTTs with 1505 horns. I could probably live with both, but currently prefer the Autoformer crossovers from W.J. W.J. modified the filters I used on my Altec 604-8g so I can now use and adjust them them for both speakers.
    Best regards

    • Hi Kjartan,

      Thank you for sharing your impressions of your Hiraga-style crossovers for your A5’s versus the autoformer based WJ crossovers.

      Compared to the modified Hiraga-style crossovers I built, my WJ crossovers didn’t even come close. As we audio writers like to say, “The difference was not subtle.”

      I’m not opposed to an autoformer based design at all, and in fact my WRSE’s use autoformers to excellent effect in the HF circuit.

      While I thought the WJ autoformer based crossovers sounded ok and were nicely laid out, I thought they sounded kind of bleached and sterile from a musicality standpoint in comparison to the considerable musicality of my modified Hiraga-style crossovers, so the design certainly isn’t something I would consider using for my Duelund-A7 project.

      But everyone’s system needs and tastes are unique, so if the WJ crossover works well for you I would stick with it.

      Kind regards,


      • Hi Jeff,

        I think it is difficult to judge WJ circuit, because parts make huge difference in such circuits like crossovers.
        I haven’t play a lot with crossovers parts, but I have some experience in signal capacitors in amplifiers and pre-amplifiers. I did some capacitor rolling in my Croft Preamp, McIntosh MC30, EAR 834 phonostage and my current DIV 300B amplifiers using 6sn7-6f6-300 tubes and James Audio output transformers.
        I like musicality of Sprague “Black Beauty” capacitors. But Audio Note Copper where much better in everything with great musicality too. Last summer I changed AN Copper/Mular to Duelund Cast Copper between input and driver tubes and driver and output tubes. Duelund are much more expensive but the difference was huge – soundstage, transparency, frequency extremes. Duelund midrange even beats a famous AN sweet midrange.
        I thing to compare vintage capacitors from WJ crossover to Duelund Cast Copper, it is like to compare “Black Beauty” to Duelund Cast Copper in amplifiers.


        • Hi Alex,

          Thank you for sharing your impressions, I find them valuable, and I know many others reading this will too.

          I too liked the Black Beauty caps in my MX110Z for their vintage charm, but the Duelund CAST tinned-copper were a huge step forward for me.

          I think it will be fascinating to hear the Hiraga-style A7/A5 crossover built with Duelund tinned-copper components, and I am excited about the project.

          I am happy for those that are pleased with their results with the WJ crossover, but for me it’s not really a consideration anymore. After building and optimizing my A5 crossovers with a modified Hiraga circuit, my A5 crossovers performed so much better that the WJ has just been gathering dust.

          I do think that an autoformer used like an L-pad can be useful in balancing the HF & LF of loudspeakers, and there are some very interesting products being made by Intact Audio.

          Keep me posted on your adventures!

          Kind regards,


          • Hi Jeff,

            Thank you for the link to Intact Audio.

            I will try to do some upgrades for WJ crossover and report about results.


          • Hi Jeff,

            I added bypass 0.1uF Audio Note copper capacitor to WJ crossover HF signal capacitor.
            The difference is significant. Sound much more transparent, dynamic and colorful.
            I took these capacitors in storage box. So it was free update.
            My experience in amplifier capacitor rolling, shows that Duelund Cast Cu have huge advantage in high frequency resolution compared to Audio Note copper capacitors.

            I’m thinking to purchase Duelund Tinned Copper Foil capacitors.


          • That’s great, Alex, and your result is much like I experienced when putting bypass caps on my Altec A5 crossovers.

            My results so far suggest that the Duelund CAST tinned-copper caps are in a league of their own, and I really like what I’m hearing from them, and am really looking forward to building some crossovers for my Altec A7’s with them.

            Keep me posted on your adventures!


  6. Hello Jeff myself and others are shocked,you have had the Duelund a Jam caps at least several for many months
    And No feedback ,even Frederik said he is surprised that there is so little information out there ,even 6 months later.
    I just put the 3.3uf in blindly How many hours needed to break these in ? I only have 100 hours , thst is not even enough
    For standard caps these are big over 3 inch around and long. Jeff I would appreciate if you could drop me an email
    Another thing several have asked me ,I said I would ask you since you know Duelund so well
    These Jam caps are also a Tinned Copper ,paper in oil like the Cast caps , but they donot have the resin paper casing .
    Sonicly will these still be almost as warm as the paper cases, these being a Aluminum case . The extension is better then the RS
    Model the Tinned Copperfor sure ads detail and air . Please help us out with your observations .
    Thanks much ,Paul.

    • Hi Paul,

      I think I addressed your comments in my previous response, but let me reiterate.

      With the Duelund CAST caps I have tried, I would say they start to get pretty well run-in around the 100 hour mark (90% or so), but they continue to improve for a long time, probably 500 hours plus.

      I don’t have any Duelund JAM caps yet to try, so can’t say much about them. If I remember correctly, I think Frederik told me he thought the JAM caps offered about 80% of the performance of the tinned-copper CAST caps.

      Kind regards,


  7. Hi Jeff,

    Do you recommend to use multiple bypass capacitors AN 0.1uF + Duelund CAST tinned-copper 0.01uF?
    This part of Altec 604E crossover works from 1.5KHz and up.


    • Hi Alex,

      I did try using multiple bypass caps on my Altec A5 crossovers and it worked nicely to voice them.

      However, what I really recommend is using the Duelund CAST (or JAM) tinned-copper caps full-range, which I thought provided remarkable performance when I tried the Duelund CAST tinned-copper prototype caps in my A5 crossovers.

      Kind regards,


      • Hi Jeff,

        I need two ~7uF capacitors. Duelund CAST are way out of my budget.
        It is possible to use 2 JAM in parallel. But it is steel too expansive for me. WJ crossovers costed me less.
        I can allow only Duelund bypass capacitors.
        I know that sometimes bypass capacitors divide sound by frequences. I want to minimise this effect to make sound more whole.


        • Hi Alex,

          I understand completely.

          If you try decide to try the Duelund bypass caps be sure you let me know how you like them.

          Kind regards,


  8. It would be interesting to compare the Duelund XO to a high end active loudspeaker management system.
    There are a few things an active XO can do, which are not or very difficult to realize with a passive XO,
    One of the more obvious features, which is very convenient, specifically with horn loaded loudspeakers, is “EQ on-the-fly”.

    • Hi Dominic,

      Sorry to put a damper on your suggestion, but that’s never going to happen. Sorry about that.

      The reason is I’ve listened to a DEQX used as a crossover on horn loudspeakers owned by a friend and it didn’t impress me at all, either musically or sonically, so it is about as low on my personal interest list as things get.

      Kind regards,


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