Opening Statement

I went to the woods because I wished to live deliberately, to front only the essential facts of life, and see if I could not learn what it had to teach
~Henry David Thoreau, Walden

Saturday, June 8, 2024

Ziv II Speakers -- Kit from Madisound, aka Ziv Two Speakers


Ziv II Build Notes:

I wanted to build some speakers that would meet several criteria that are challenging to find together in a commercial speaker:
  • Very clean, detailed sound -- characteristic of “audiophile” speakers
  • Ability to reproduce frequencies at least down to 60 Hz, so a subwoofer isn’t essential for music
  • Metal grill to survive or discourage cats, toddlers, and teenagers
  • Small form factor to fit into a bedroom or even mount on a wall
I want to enjoy having kids around, and not worry too much that my speakers might get damaged by a nerf ball being thrown around, or a pet getting interested in the grills.  In other words, I love good music, but in the end I wanted “dad speakers” as much as I wanted to build audiophile speakers.

The Ziv II speakers, which Madisound carries as a “kit,” seemed like a good starting point.
After building them, the Ziv II speakers impressed me in three ways:
  • Detailed resolution:  These speakers reproduce music in nearly all the detail present in the original recording.  Vocals are clear and natural, the attack of a drum or cymbal is well defined, the subtle sustain of softer notes is clear, and the instruments are well separated from each other.  Almost eerily, the quiet is quieter than I'm used to.  Notes begin and end crisply, so you get moments of silence that are very well defined, something that didn’t occur to me until listening to these speakers.
  • Uncolored tone:  Everything sounds very natural.  I notice this most in classical,  jazz, and vocals where my ears might be best attuned to what the live sound would be.  These speakers aren't "warm," which is a common, yet vague, term to describe certain types of distortion that many sound systems produce.  
  • Authoritative, crisp bass:  The F3 is probably somewhere near 55 Hz.  You get almost all the bass fundamentals in the music even without a sub.  I listen to music in my car and on earbuds a lot, and I’ve been reminded of how much of the low end is lost in those contexts.  There is a richness that surprised me in these little speakers.  Many smaller speakers have an F3 of around 80 Hz or even higher, so these are much richer than most small speakers, but don’t have the bass of good quality tower speakers.  More on this later.
People talk about speakers being “non-fatiguing,” and perhaps that’s the same idea as being forgiving of irritating recording anomalies.  These speakers don’t accentuate the static in older recordings, or the sonic artifacts of older microphones.  In that sense they aren’t as detailed and precise as some speakers, or maybe it’s some subtle engineering choice that Morel made.  In any case it’s very enjoyable to listen to older recordings as well as new material.  Yes, you can still hear microphone distortions on older recordings, and be irritated by the sound quality of garage recordings, but I find myself happy listening to almost anything professionally produced.

Some things worth noting:
  • Limited volume:  These speakers play at a good listening volume, but not dance-party loud.  You can reproduce jazz and classical music beautifully, but not at the volume of a live performance.  I would pair them with a receiver capable of clean sound at 80W at 6 ohms.  They sound great, but they definitely have a top end on volume.  These are great for a modest living room or large bedroom.  Not really suitable for larger rooms.
  • Limited low-end:   In terms of fundamentals, not much is happening between 30 and 60 hertz:  there is the bottom end of the kick drum, part of the kettle drum, a few cello notes, and the lowest piano and pipe organ notes that are hardly ever played.  So what are you missing?  It’s the resonances that reach down into the lower frequencies.  My current home theater speakers have an F3 around 40, and I have a sub for really low frequencies.  For some music you will notice this difference in a side-by-side comparison … but it’s not such an issue that you will necessarily care.  For home theater applications, you lose the low end of environmental noise:  ocean waves, the rumble of thunder, hoof beats, traffic noises, crashes and explosions.  So you might want a sub, but I prefer to leave it off personally.  
With rated power handling of 150W on the woofer you might think these could play really loud, but be realistic.  A normal 6.5 inch woofer can’t play below 60Hz at high volumes without distortion or exceeding it’s mechanical limits.  Physics gets in your way.  In a large room, a teenager might well “turn up the music” enough to wreck these speakers without a volume limiter on the receiver, so that’s something to consider when pairing these with a receiver.

Based on my previous experience I wanted to use a proven, engineered design.  I studied available “kits” and discovered the Ziv II at Madisound.  These speakers were designed by Russell Kauffman when he was Technical Director and Head of Acoustic Design at Morel, which is an Israeli company that makes high-end drivers.  Translated from the Hebrew, “Ziv” means "radiance, brilliance, or light of God," so I think that gives you an idea of the quality that he was going for with this design.  Mr. Kauffman designed the famous “Fat Lady” speaker, and the Ziv II uses the same 6.5” driver as that speaker.

Speaker “kits” are not like typical kits you might buy.  You get a box of components and a wiring diagram for the crossovers.  No instructions or further advice.  The drivers and crossovers with some miscellaneous parts cost me around $1,800, purchased from Madisound in 2024.  The components are definitely of a quality favored by audiophiles and the kit price is quite reasonable for what you get.

Madisound publishes the crossover design if you want to wire your own.  I had mine made by Madisound as part of the kit, opting for the upgrade of the tweeter capacitor to the Mundorf Supreme EVO Oil capacitor.  This capacitor is supposed to give the speakers even more detail in the high end than the standard capacitor.

The drivers are the Morel SCW-636 6.5” carbon fiber woofer and the Morel ST1048 supreme tweeters.  These drivers are characterized by very flat frequency response when crossed over at around 2,300 Hz.  The crossovers are relatively simple in design due to the linearity of these drivers.  Both drivers are very attractive and worth showcasing as examples of industrial design.

The recommended internal box size was 10.8 liters with a 6.5” long 2” diameter rear port to reach an F3 of around 55.  An F3 of 55 means that the decibel volume of the bass is at 50% of normal at 55 Hz.  This is remarkable bass extension for a speaker this small, and relatively close to the much larger JBL L100’s, which use a 12” woofer.  With a subwoofer crossed in at 60 Hz, the subwoofer contribution would be modest, so I consider a subwoofer optional for most purposes.  

Factoring in the displacement of the port, the drivers, and the crossovers, I needed about an enclosure with a total internal volume of 12 liters.  Using ¾” Baltic Birch as the material, the outside dimensions of the box are 15” tall, 9.25” wide, by 8.5” deep, not including the grill in front.  I used Baltic Birch over MDF primarily because I like working with Baltic Birch, and at the small box size I thought that there wouldn’t be much of an issue with resonance.  This turned out to be wrong however, and I ended up sinking twelve #12 x 4” screws into each box as a modification to cut the unexpected vibration.  

For this small of a speaker, no fancy joinery is necessary.  I used butt joints stiffened with WeldBond and connected with countersunk #6 and #8 screws.  Weldbond has a long open time, so I could assemble the boxes completely without rushing.  In retrospect, I should have used longer screws and more of them to cut the resonance further.

Space is at a premium on the front baffle, so given the size and length of the port I decided to offset the tweeter from the centerline, and on the back, the port is also offset to separate the end of the port from the tweeter.  

Two speakers can be cut out of ½ of a 4’ x 8’ sheet of Baltic Birch, so I made all my box pieces out of half the sheet of plywood with some left over.  Machining the wood was straightforward.  I used a circle jig and router to create the mortised openings for the tweeter and woofer.  I used 6-32 t-nuts for the woofer, tweeter, and terminal plate.  They don’t take much time to install, but I’m not sure that I would use them again.  The main advantages are that you can test fit everything, and later you can get the drivers really tight against the baffle.  However, it’s necessary to use thread locker at some point or there is a chance that the screws can loosen over time.

For the grill I used 16 gauge high-flow steel perforated sheet with a hexagonal hole pattern and 79% open area.  I got mine from McMaster Carr.  Metal grills are undoubtedly less acoustically “transparent” than thin, lightweight grill fabric, but they are much more pet and toddler proof, and it gives us a chance to see the beautiful Morel drivers.  Since the steel mesh doesn't stop UV light, speakers with this style of grill should not be placed in the direct sun.  Steel takes primer and spray paint quite well, and usually holds up in an interior location without rust if painted properly.  The grill material that I got was ductile and easy to work with.  I did not try aluminum, which is also available.  Stainless steel is available, but it does not take paint very well.  I’d like to try it another time though without paint.

After using a 3” abrasive cutoff wheel to cut the grill to size, I used a bench grinder and abrasive deburring wheel to cut off and lightly polish the nibs.  I found this less time consuming and easier than it sounds.  I also tried cutting the 16 gauge sheet with tin snips, which did not work well, and diagonal cutters, which did cut it quite easily one wire at a time.  I notched each corner and bent the edges with a bending brake so that the grill would be ¾” off the front baffle.  Careful work with a rawhide mallet would also work I think.  To affix the grill to the front baffle, I used ⅝” x ⅝” x 3/64” angle anodized aluminum, with the grill affixed to the angle aluminum using JB Weld “original” formula epoxy, applied with a static mixing syringe, which is probably the only way to get a good bead.  If I was doing this again, I would use ½” x ¾” x 1/16” angle anodized aluminum to give more room for the 8-32 screws that I used to affix the angle aluminum to the front baffle.  The ⅝” works, but the clearance is tight.  The 8-32 screws went into zinc-plated steel threaded inserts, threaded into the front baffle.  This is pretty easy to do, but the ¾” inch angle would provide more distance from the edge.

I wanted the main finish to be slightly off-white, but not in a beige direction.  Rustoleum has a Pearl White in their Universal Spray Paint line that I decided to try.  I primed the grill with with Rustoleum’s self-etching automotive primer.  The wood was prepped with a regular all-purpose wood primer applied with a foam roller and foam brush.  Then it’s just a matter of carefully applying the pearl white layer.  Just as a side note, Rustoleum makes an automotive lacquer in Pearl White as well, but the lacquer has aggressive solvents and can’t be applied directly over the self-etching primer, so I went with the regular spray paint.  The lacquer would be worth trying as well and it’s supposed to be more durable than the regular paint.

Things I might do differently next time:
  • It would be good to provide explicitly for wall mounting, including installing threaded inserts to accommodate that easily, maybe in a Vesa 100 pattern.  The speakers weigh about 18 pounds, so wall mounting requires a heavy-duty bracket.
  • I would add more long, heavy screws to cut the box resonance and vibration further.
  • The binding posts take up a lot of room on the back.  I would try to use a less space-intensive set of posts so there is more room on the back for a wall mount.
  • As mentioned before, I’d use ½” x ¾” x 1/16” anodized aluminum angle to hold the grill.
My brother Andrew was an audiophile and got me interested in high-end audio.  I also have a couple of friends who are audiophiles with the gear to prove it.  I love the way that their systems sound, but I’m not interested in that kind of investment and space commitment.

Earlier I built speakers using a HiVi F10 as the woofer and loved the sound, but they can’t handle a lot of volume.  Then I built some 3-way tower speakers and a 3-way center channel using Morel’s mid-level drivers and custom crossovers from Solen.  The tower speakers sound very good, but I had to use the equalizer built into my Onkyo receiver to fine-tune the sound.

These experiences convinced me to go with a design so that the speakers can just be plugged in and will sound great without a lot of adjustments.