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A few years ago, I posted a project on a speaker build based on a design by Joe Rasmussen on DIYAudio.com, the Elsinore Mk6. Many of you have had the opportunity to visit and listen to those speakers in my system. They are a really nice design, consisting of four identical mid-bass drivers (SB Acoustics SB17MFC35-8) and one softdome tweeter (Scan-Speak Discovery D2608) installed in a custom waveguide. The upper two mid-bass drivers act as midrange as well as bass, the bottom are bass drivers (2.5 way design). The speaker is efficient (92 dB/1W-m) and have a ruler flat impedance curve at 6 ohms over the entire range. So a very easy drive for tube amps, particularly my Class A2 211 SET amplifiers which turned out to be a very nice pairing.

Since I built my original Elsinore speakers, Joe Rasmussen developed a cost-no-object version keeping the original tweeter/waveguide, but using the state-of-the-art Purifi PTT6.5W08-NFA-01 mid-bass drivers. These are very expensive (300 Euro each shipped from Denmark), but are very low distortion and very well controlled (fast). Joe also implemented some upgrades to the crossover recommendations (particularly the tweeter cap) that improves performance at the top. I decided to splurge on the expense of the drivers to move forward to something that for me would be more-or-less an endgame speaker that works great with my stable of 20W+ tube amplifiers, both SE and PP.

I will be following up with several pictures and discussion on my enclosure construction, but first a picture of my system with the new speakers and a subwoofer to better support the bottom octave. More to follow.

With the high quality drivers, I decided to approach my cabinet build using more advanced materials than the MDF used in my first Elsinore build. I originally considered using Baltic plywood, but due to the Russian embargo, the price is much higher, and it is more challenging to find it in the thickness needed (1"). I ran across some discussion that the ideal panel material is bamboo plywood. It has much higher tensile strength (equivalent to mild steel), a higher modulus of elasticity, at about the same material density as BB plywood (MDF is slightly heavier). This means the panels are stiffer and resonate at a higher frequency where there is lower excitation and can be more easily damped. However, it turns out to be more expensive and harder to get than BB plywood, and most suppliers deal in wholesale for interior construction projects and do not cater to someone buying a couple of sheets, and the shipping cost can be as much as the material cost. However, 1" thick bamboo plywood is available as finished work surfaces (table tops) that can be ordered and shipped at no cost for pickup (or delivery in the case of Amazon). The size is also much easier to handle (32"x72") rather than full sheet (4'x8'). The baffles do use 3/4" material, this is available from a couple of sources as bamboo plywood shelving in 12" x 48" size that are inexpensive to ship. For interior cabinet bracing I used BB plywood or BB ply+MDF composite.

Since bamboo plywood is prone to chip-out, and is tough on tools, I used this project as an excuse to upgrade my tools, picking up a Makita cordless plunge/track saw along with parallel guide rails for repeatable rips, and a snap on track square. I was able to get a level of precision in my cuts that is difficult to achieve on my portable tablesaw without having to worry about infeed/outfeed issues, and a properly aligned crosscut sled. The tracksaw cut thru the bamboo plywood leaving clean, straight cuts with no splintering or chipout. A very worthwhile investment.

Two questions, why not Baltic Birch plywood, and if you are going all out why not an active crossover?

Bamboo plywood is superior in material properties over Baltic Birch plywood, and has a distinctive and (to some) attractive look, particularily the edge grain. With BB ply, there is also the issue of edge grain, which can be a "feature", though I was considering using a similar (maple) or contrasting (oak/walnut) solid wood on the edges that could be chamfered. The downside of BB plywood is that it does not stain well (blotchy) and therefore the best course is keeping it natural in color, paint, or veneer. I was seriously considering BB plywood, though, and my decision for bamboo plywood was made once I found sources for the material I needed. I do have to say that I had more problems with chip/tearout with BB ply than bamboo plywood, I do not think the quality is a good as it used to be, and this is a complaint I have read from other builders who have been moving over to Appleply and bamboo plywood. I knew I did not want to use MDF and deal with all the dust.

This design is based on a carefully designed passive crossover that incorporates corrections for frequency, phase and impedance to make the system work as a whole. The design has evolved over the course of close to 20 years by Joe Rasmussen. It has a flat 6 ohm impedance curve, uses 1st order crossovers with corrections for phase coherence, and most importantly, is driven by a single amplifier without any additional correction in the digital domain. I have a very high quality and purist digital and analog path (Chord DAVE + MScalar, with the DAVE used as a digital preamp), and inserting any digital correction would comprimise the sound quality. It makes no sense to have a near state of the art digital to analog converter, only to send the signal through an inferior A2D stage and then reconvert back to analog thru a lesser DAC in a digital crossover. An active crossover would mean additional analog processing (more devices, caps, cables, etc.) and use of multiple amps, each having their own characteristic sonic signature. As currently configured, the output of the DAC directly feeds the amp driving the speaker, on the analog side, switch in a high quality passive ladder attenuator, the output feeding the amp. I use the absolute minimum number of gain stage, and use of a single amplifier means a coherent sonic signature.

David

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Walt

I think that the system has been in development for 20 years explains a lot. 20 years ago you were not going to do a active dsp/crossover for the best quality. If Joe Rasmussen were starting over today what would he do? In the past few years DAC's have greatly improved and come down in price -

https://www.audiosciencereview.com/foru ... dsp.30804/

and if you want to go the route of having your computer do the dsp and have a usb DAC there is -

https://www.audiosciencereview.com/foru ... iew.35661/

and it sounds like HAL is in love with his Danville Signal dspNexus dsp/crossover.

When is comes to speakers when I have to downsize these are the ones I would consider -

https://www.audiosciencereview.com/foru ... tor.28039/

When is comes to wood you may want to check out "The Woodworkers Club" in Rockville -

https://woodworkersclub.com/

Also I don't know how you are equipped but you are welcome to use the woodworking shop in my basement (table saw, band saw, panel saw, stationary belt sander, planner, radial arm drill press, and router table).

Brombo,

Thanks for the offer to use your shop, though I doubt I will be undertaking a speaker project anytime soon. I do have a Bosch portable table saw that I recently rebuilt the motor on, used an extended fence, infeed support and flat outfeed for a few cuts on some rips that I used, but found that the Makita plunge track saw was much easier to manage because the work was stationary, and the TSC parallel guide system ensured precision and repeatability. With a shop vac hose attachment on the saw, there was virtually no dust. Of course I cannot say that about routing...that was a big mess and took alot of time. I needed to take some of that outside, the dust was so bad. I have a Jasper circle template, a 1/4" solid carbide straight bit, and took cuts 1/16" depth per pass to avoid any tearout issues. So did just fine with the tools I had, planning in advance for each operation to ensure no mistakes. I think it is important to know one's tools, what they can do, and adjust to their limitations. Where there is a chance that that something could go awry, rethink how to do it, test it first, and then proceed with care and confidence.

I know Woodwookers Club (Woodcraft), I was back and forth a few times over the course of this project, picking up tools, clamps, and the BB plywood for the interior of the cabinets.

Regarding digital crossovers and DSP, this may work fine if your source is digital, but when you also have a commitment to high performance analog as I do, using an ADC in the loop is a step backwards in sound quality. I do not want to comprimize here. I experimented with this using a handful of different ADC units, up to 192/24 resolution, but although the result was fairly satisfactorily, it still did not have the same magical quality of an all analog reproduction path. So keeping everything in the analog domain (past the DAC) was the only way for me, and I think, many others who are committed to analog. Similarly, I have little interest in pursuing Class D amplification, I enjoy designing and building tube amplification, and building (not designing) Class A solid state amps. So perfectly happy with keeping with "old school" solutions.

Now, if all I used were digital sources, I would rethink this. I have to admit, at the last CAF, I really liked the ADC active monitors I heard and could easily live with them.

David

David

I have found that the DeWalt routers have the best dust collection. In routing mdf or plywood I use solid carbid upcut and downcut spiral bits. The Woodworkers Club has for hire a large NC router (fill their shop with the dust).

https://www.dewalt.com/product/dw621/2- ... nge-router

I am told that Festool routers have better dust collection but they cost a lot more. The next time you are routing and if you want to try the DeWalt let me know.