Because of the dearth of units left in the States and my indifference towards engaging in a bidding war versus fellow Asian hobbyists, I patiently hunted them for 20+ years via other channels.
The 405A is a 4" 60-15,000 Hz wide range driver with a sensitivity rating of 92dB/4ft/1W. It's equipped with a massive Indox magnet that's almost the same diameter as its cone.
IMHO and experience, Altec cabinet plans always deliver sonically. Aside from a full understanding of the physics of sound, their engineers used their ears as the final arbiter in a design brief. To me, that trumps any design completely derived from a mathematical formula or computer simulation. So I asked my buddy @ Hommage Audio to fashion a Bonsai pair of Altec 614-style boxes based on the above dimensions.
Interior stuffed with Dacron
For sentimental reasons, I have a pair Realistic Minimus 8s on my test bench. I always thought they were above average, although not extraordinarily special. Same deal with the "Holey Frame" drivers I pulled out of a Sony TC500A RTR machine. To my ears, both FE103 derivatives have an upper midrange resonance, which require an EQ/contour network to make them more listenable.
As soon as I hooked them up to my near-field hifi system, I was pleasantly surprised that they play like their bigger brothers, albeit at a reduced scale.
It's physically impossible for the 4" cone of the 405A to extend much below 90 Hz, but the roll off is gentle and there's enough harmonics to suggest bass lines. I hear a slight trace of peakiness in the presence region. For my taste though, an EQ filter isn't necessary.
Although the Altec 405A can't replace the Altec 755C (much less the 755A) in my near-field set up, its midrange depth, micro dynamics, detail resolution and overall tonal balance makes it worthy of the Altec badge!👍😊
In my reality check article, I used the above chart to associate frequencies with the vocal range of humans and acoustic musical instruments. Please use it as a guide to the RTA traces and discussion of frequency ranges below.
Lou Donaldson on Snell Type JIIIs
The Snell Types E, J, and K have developed a reputation as single ended triode (SET) amp-friendly speakers. Arguably, my pair of Type JIIIs can be a good stop gap but I'll try to explain in the simplest terms as to why, in the final analysis, they don't meet my criteria for flea power amplifiers designed with "it's the first watt that counts" ideology.
Snell Type JIII specs
Since I couldn't find a late 80s to early 90s Vifa catalog, I based all the specs from the above information provided by Snell. The low(ish) nominalimpedance (Z) of 6 ohms is an advantage when driven by current source devices such as solid-state amplifiers, which can typically supply more power to a lower Z load. OTOH, vacuum tubes are inherently high impedance/voltage source devices, thus requiring output transformers to drive lower Z loads. However, any well-designed tube amp with an 8 ohm tap from the secondary of the output transformer shouldn't have problems driving the Type JIII.
Snell Type JIII
While the man cave is hardly anechoic, this RTA trace is smoother compared to anything I've taken from any of my Altecs. It pretty much tracks the manufacturer's specs.
Altec 753C
In spite of the fact that the Altec 753C's RTA isn't quite as smooth, it has a half octave greater extension in the low end. The top end also starts to roll off earlier, at around 13kHz. But as further discussed below, the performance of the Altec 802D compression driver + Altec 32C belies its 40s Western Electric roots.
The radiating area of the Altec 414A cone at 95 square inches is 2.5 times greater than the 8" Vifa M21's 38.5 square inches. Both use paper cones - the Altec cone is left bare and suspended by a treated accordion surround, while the Vifa uses high compliance foam and its cone is treated with some form of damping compound. The added cone mass from damping helps low frequency extension. Regrettably, it also reduces speaker sensitivity, among other things.
Altec 414A in wide range mode
In wide range mode, the 414A's 95 square inches of radiating area covers a frequency range of six and a half octaves, starting from around 40Hz-3500Hz. That's just a few notes shy of a piano's range at both extremes as well as the fundamental notes of most acoustic musical instruments and easily, the entire human vocal range. This driver sounds very natural to my ears and plays smoothly with no detectable glare or shout manifested when listening to music. I’m happy to report the tiny spike before 1kHz isn't audible to me. 😉
The Vifa M21's smaller radiating area of 38.5 square inches tasked to reproduce five and a half octaves from 49Hz all the way to its 2700Hz roll off point is a greater challenge.
Altec 414A specs
The 414A goes lower than the Snell JIII but not quite solid down to the claimed 30Hz rated fundamental. With a 99dB/1W/4ft sensitivity, it has an 8dB advantage over the Snell Type JIII's 1.6 cubic foot (cf) ported box rating of 91dB/1W/1M. Housed in a 4 cf bass reflex cabinet, the 414A can definitely move a whole lot more air with minimal power input.
Reverse engineered Snell JIII crossover
The type JIII's crossover is a bit more complicated than my Altec 753C XO below. Encircled in red is a paralleled choke/resistor/capacitor EQ network for the Vifa woofer. This shapes and/or controls cone resonance in the midrange. Unfortunately, the EQ network also absorbs power.
Case in point, BBC engineers' extensive use of EQ in the LS3/5A crossover made it notoriously inefficient. But to their credit, whether it was the earlier 15 ohm or later 11 ohm version, it was a friendly load, especially to tube amplifiers.
Altec 753C crossover
Since the 414A has no serious peaks or dips, which I verified through years of listening and later confirmed via RTA, I chose to run it in wide range mode in which the woofer rolls off mechanically. This preserves the efficiency/sensitivity of the woofer and makes the crossover simpler since it only involves a 4 uf capacitor acting as a high pass filter. By using non-inductive resistors, the Altec 802D compression driver is attenuated to match the 414A's sensitivity. Then I adapted the high frequency EQ circuit from the Altec 30923 to tweak the shape of its top end response.
Left: Altec 802D + 20275 Right: Snell/Vifa D26
For the higher frequencies, Snell chose the Vifa D26 1.25" soft dome fabric diaphragm that has a radiating area of 1.23 square inches vs. the Altec's 2.25" diameter aluminum diaphragm with an equivalent 4 square inches of radiating area.
Snell employed a sharper 12dB/octave slope high pass filter for the dome tweeter to cut in @ 2700Hz while I blended the 802D compression driver/32C horn combo at a gentler 6dB/octave slope @ 3500Hz in the Altec 753C just where the 414A top end response starts to taper off.
Altec 802 + 32C horn
My old school high frequency horn loaded system uses the Altec 802D compression driver in conjunction with the 90° H x 60° V dispersion Altec 32C horn originally designed by Western Electric for their 753C monitor system. It's merely coasting along from 3500 Hz, generating the top most octaves and harmonic overtones compared to the hard-at-work direct radiating Vifa dome tweeter diaphragm of 1.23 square inches struggling to replicate the final octave of top end fundamentals from 2700Hz. Hence, the Altec horn system reproduces much faster and cleaner transients with ease, while also enhancing the already effortless presentation of micro and macro dynamics of the high efficiency 414A woofer.
I'm not set up to plot a reactance chart for the Altec 753C and Snell Type JIII but after using them with various amps in my collection, I guesstimate that both proffer a benign resistive load. However, the 16 ohm nominal impedance, simpler crossover of the Altec 753C and its greater efficiency are a godsend to low damping factor single ended directly heated triode amps.
Ever since I built my first pair of open baffles, evaluating drivers in wide range mode in order to gauge their ability to reproduce an accurate midrange has become routine. Listening to the Vifa M21 woofer in this manner wasn't a very pleasant experience because it sounded very dull. This is in stark contrast to the snappier midrange of the Altec 414A, which I've been using in wide range mode for many years. Likewise, the Vifa 8" was totally outclassed by a handful other woofers and wide range drivers in my collection including the 10" Altec 406Z and Altec 756B.
It's a no brainer that the long travel foam suspension + cone damping extended the low frequency response of the 8" Vifa. But to my ears, this was achieved to the detriment of midrange performance. Is bass extension really more important than midrange accuracy in the high-end audio era? Why is cone damping so prevalent in modern drivers? Western Electric, Jensen, Altec, and their contemporaries all used bare cones.
During the era of Western Electric and Altec, engineers used their ears, guided by cutting edge technology test equipment. This can be gleaned from contemporary ads and press releases. I can't help but wonder if the Vifa woofer was designed merely to satisfy test instrument requirements and laboratory standards without any ear testing involved. If that is the case, is that what we consider progress?
I chose the Altec 755C over the near mythical Altec 755A for this feature because IMHO, it is a worthy benchmark for an 8" wide range driver that is still quite accessible and affordable in the real world. Based on the above specs, by the time Altec introduced the 755C in the late 50s (or early 60s?), they had conceded to the spec wars triggered by the commercialization of stereophonic equipment. I've listened to the 755C loaded in an OB, 2cf box or the Silbatone cabinet but never heard a solid 40Hz low end, merely well defined harmonics of that fundamental.
Simple 46 amp (1250mWpc) > Altec 755C in Silbatone enclosures
Granted the 755C can go a bit lower, subjectively, its low frequency extension isn't significantly greater than the 755A. I'm glad though that Altec was able to retain much of that captivating midrange + dynamics even if it's not quite as realistic as its older Western Electric-designed 755A sibling.
Altec 755C in the Silbatone box
The Silbatone + 755C combo loses about an octave at the frequency extremes vis a vis the Snell JIII but has a 5dB advantage in sensitivity. Despite the spikes and dips in its RTA trace, I much prefer listening to the Silbatone 755Cs. Maybe the dips and spikes = musical?🤔
Snell JIII = 1.6 cf vs. Silbatone 755C = 1 cf
Whether driven by my SET amps, Dynakit ST35 or Nobsound/JLH 1969 clone, the Snell Type JIII sounded veiled and anemic compared to the Altec 753C and Silbatone 755C. With the Snells, I have to turn up the volume a couple of notches to be engaged musically but with the Altec 753C or Silbatone 755C driven by my weakest 750mW per channel SE71A amp, I already hear subtle details even at background sound pressure levels (SPLs). Understandably, the JIII could not compete with the Altec 753C at the loudest end of the spectrum since it doesn't have the physical size to move as much air. But considering Snell's reputation, I expected better resolution and nuances at low to medium SPLs.
Music Reference RM9 amp > Snell JIIIs
The most convincing full range sound I got from the Snells was when they were driven by the Music Reference RM9 amp, a push-pull parallel/triode connected EL34 stereo amplifier producing 35 watts per channel with the negative feedback set at minimum. Alas, with this combination, the irresistible charm of the single ended directly heated triode amp is lost...I can't have my cake and eat it, too.😔
Altec 755C in Silbatone cabinet + 3000H super tweeter Truth be told, lately, I find the use of a super tweeter redundant
Through the years, I’ve tested a few vintage and contemporary 8” wide range speakers but haven't found any which could closely approximate the 755C’s sound quality. The design isn’t rocket science and if Great Plains Audio still has the original tooling, I don’t see any reason why the humble 755C PA speaker can’t be reproduced at a reasonable price. That would be a great boon to single ended directly heated triode amp aficionados, especially those who have limited space in their listening room.😊
Contrary to current trends in speaker cabinet design, the wider front baffle area of the Altec 753C cabinet (and to a lesser extent, even the Snell Type JIII), enhances projection by acting as an acoustic soundboard. Western Electric and Altec speaker systems were usually fitted with wings in theater installations, which is the main reason I've been an advocate of the wide open baffle. In principle, this is practically no different to the fully open lid of a grand piano during a performance in a concert hall.
Altec 753C + mini tour of the man cave
The Snell Type JIIIs can give a glimpse of what directly heated single ended triode amplifiers can do. But these are definitely not end game speaker systems for those who want to indulge in the delights of flea powered single ended directly heated triode amps. As competent as the Snells are and given their already above average sensitivity (compared to typical high end audio speakers), they could never spook me into believing musicians come alive in my man cave the way my Altecs can at times. For some organic reason, I can also listen to my Altecs for extended periods without listening fatigue creeping in. Keep in mind though that the empirical and subjective observations embodied in this article only reflect my musical aesthetics and priorities. YMMV.
I hope I was able to illustrate that there's no myth or magic to a fine sounding and efficient speaker system. All it takes is a basic understanding of the physics of sound and learning how to compromise.
Re-foaming the 8" woofer found in various incarnations of the Type E, J and K Snell speakers is a very contentious issue exacerbated by their cult-like status amongst audiophile admirers.
Vifa M21WN-07-04 woofer Left = $25/pr. foam (yellowish tint), Right = $40/pr. Euro foam
In this day and age of marketing hype, spending $100 or so to import a pair of alleged original foam from European sources is, IMHO, not justifiable. How does one determine which retailer is being truthful?
Given that I wanted to give this project my best shot, when I noticed that Simply Speakers* added a Euro version to their website for $40 a pair/shipped, I placed an order. This is just one of the many reasons why this installment has been delayed.
*No affiliation, just a satisfied customer!
WARNING!
In Part 1, I re-foamed my pair of Vifa M21WN-07-04 woofers using the $25 foam kit. I specifically mentioned that the dust cap and cone are just one piece.
I've seen discussions in audio forums suggesting the removal of the dust cap to center the voice coil. I have to reiterate that the removal of the dust cap = a DESTROYED woofer!
After using both these foam kits, I can confirm that the voice coil on this particular Vifa woofer is self-centering. If you encounter voice coil problems, it's either the foam you used is suspect or you seriously deviated from the instructions.
RTA Traces
$25 foam vs. $40 Euro foam
Only one Vifa M21WN-07-04 was fitted with the Euro foam so I could compare them.
Die-hard Snell aficionados and "specialist" retailers contend that "generic foam" will kill the bass response of the Vifa M21 woofer. Given the RTA traces below, which foam is generic?
If we split hairs, this $40 Euro foam trace looks just a touch more ragged.
Euro foam serial number
FWIW, unlike the $25 foam, the Euro foam has a serial number. Does that give it more credibility?
Listening to Foam
$25 foam vs. $40 Euro foam
Evaluations were conducted in full dimensional mono!
The sonic dissimilarity was very subtle. It only became obvious in A/B comparisons in which I was consciously listening for a difference. Also, as usual in audio, better metrics don't necessarily = better sound because audio tests (in this case, pink noise) are static while music is very dynamic!
Listening to Billie, Ella, Julie, Frank, Tony and Johnny H, it was relatively easy to discern better midrange presence from the unit fitted with the Euro foam. When I pulled out my Ray Brown, Curtis Counce, Charlie Haden and Mingus CDs and LPs, I heard more tuneful and articulate bass lines from the Euro foamed woofer. The woofer with the $25 foam had a tendency to sound boomy while the midrange was just a touch veiled.
That said, if your Vifa M21s are already fitted with the $25 foam replacement and you're not very DIY savvy, it's nothing to lose sleep over. IMHO, you're still listening to a pair of very decent classic speakers. However, if you're a seasoned DIYer restoring an unmolested pair of Type Js or Es with rotten Vifa foams, go for the $40 Euro foam!
I wish I could travel back to the early 90s to find the honest-to-goodness truth.
Instead of worrying about matters beyond my control, I'm going to replace the $25 foam on the other Vifa M21 with Euro foam so I can listen in full dimensional stereo!
As I mentioned in my reply to a reader's query in Snell Type J III, Part 1, I'm the temporary caretaker of a pair of 15 ohm Rogers LS3/5As while my buddy Jose's basement is getting sorted.
ca. '93
Long time readers know that I was aBBC LS3/5A user. A pair of 15 ohm Rogers replaced my Magnepan SMGas in '86. As a partner in a company that distributed Spendor speakers in the Philippines in the early 90s, I also owned a pair of 11 ohm bi-wireable Spendors.
ca. '94
In the preceding two pictures, my pair of DIY PP2A3 monoblocks struggled to drive the Spendors in my tiny apartment. Despite that, the BBC near field monitor opened my ears to the virtues of directly heated triodes. Alas, they were superseded by Altec 755s because I needed more efficient speakers to pursue flea-powered single ended directly heated triode (SE DHT) amps.
The Bextrene cone KEF B110 5" woofer + the complex crossover/EQ network = 82 dB/1W/1M, very inefficient! But kudos to BBC engineers, IME, the speaker is still a relatively easy load for low-powered tube amplifiers because of its high(ish) impedance across the audio band.
Just as I remembered, the LS3/5As are very capable of portraying the midrange magic of an SE300B or even an SE2A3 at near field distances. However, to get some boogie factor out of them, they need the power output of at least a Dyna ST35. But as good as the ST35 amp is, a catch-22 situation ensues because it sounds veiled compared to the aforementioned SE DHT amps.
Snell Type J III + Rogers LS3/5A
I was viewing the past through rose-tinted glasses when I posted (#3) in HiFi Haven - mea culpa! There's a greater similarity in tonal character between the Rogers LS3/5A and Snell Type J III. The Altec sound is another entity altogether!
Given my post SE amp/High Efficiency transducer expectations, the Altec 755As in Dr. Bae/Silbatone cabinets are tonally more lifelike across the audio band, offers better resolution, has more low frequency extension, greater micro and macro dynamics and plays at higher SPLs in a package that's not significantly larger.
Listening to the LS3/5As was like seeing a former flame. The familiarity is there but the chemistry and fireworks are gone. (◞‸◟)ﾉ
In the late 80s, I could have gotten a Snell Type E or J after unloading my Magnepan SMGas. But I loved the sound of EMI and Decca recordings, for which I give credit to BBC-trained sound engineers, so I invested in a pair of Quad ESL57s and Rogers LS3/5As instead. I was such an Anglophile that I even became a partner in a company that imported Art Audio Amplifiers and Spendor Speakers to the Philippines. Unfortunately, we didn't make money...but that's another story.🤣
During a moment of nostalgia, I chanced upon this pair of Snell JIIIs online. I messaged the seller expressing interest. After two weeks of silence, I made a polite follow-up and was surprised to receive a reply that they were still available. According to the seller, he's had several offers from tire-kicking flippers but he chose to sell to me because I sounded like an enthusiast who'd give them a good home.😄
Typical of speakers from this era, the foam surrounds have disintegrated. Other than that, this is a very clean pair with consecutive serial numbers just like when they were sold in high-end audio salons in the late 80s to early 90s.
While waiting for the replacement foam surrounds, I thoroughly cleaned all vestiges of old foam from the cone and speaker frame. This was the most tedious and time consuming step in the re-foaming process but essential for a successful result!
Meanwhile, I also took advantage of the down time to analyze what makes this speaker system tick.
Deconstruction
Peter Snell was a very gifted speaker designer. Due to his untimely demise at age 38 in 1984, speaker models that were manufactured during his lifetime have developed a following. Peter Qvortrop of Audio Note UK was a big fan of the 2-way Type E, J and K models and continues their legacy in the Audio Note E, J and K using custom drivers and boutique parts.
The Snell E and J had front mounted reflex ports while the K was a sealed box/acoustic suspension design, which employed a different woofer. A rear firing 3/4" dome tweeter was added to the EII model, while the reflex port was moved to the back of the cabinet in both the EII and JII.
Vifa D26TG-05-006
The EIII, JIII and KII designation denotes the switch from a Tonegen 1" doped silk dome tweeter to the Vifa D26TG-05-006 6 ohm 1" dome pictured above. A tweeter level control was also added on all models.
Even if the JIII was manufactured posthumously, it retains the cabinet dimensions and proportions of the original model. After many years of experimenting with open baffles, Altec 614 and 618 and cabinets, I'm a firm believer in the acoustic superiority of Rubenesque front baffles over Victoria's Secret slim waifs.😆
Was the use of plywood (top, bottom and sides) + chipboard (front baffle and back panel) chosen for acoustic reasons? Regardless, the cabinet is of pretty high quality construction with particular attention placed on rigidity - see the brace from the front baffle to the back panel in the picture below.
Good quality air core inductors, electrolytic and film capacitors or a combination of both + an L-pad for tweeter level adjustment were used in the crossover network.
The high-pass is a straightforward 12 dB/octave 2nd order slope hinged at 2.7kHz, as previously mentioned. On the other unit, there was an additional electrolytic cap in the high-pass section with a higher total capacitance reading. This confirms Snell's claim of matching their units to within +/- 0.2dB based on a reference model in their factory.
Likewise, the low-pass section is also a 2nd order slope + an EQ/contour network for the Vifa woofer (see the LCR combo highlighted in red above). Explaining how this EQ works is beyond my technical ability. My empirical mind just knows that it "shapes" the woofer's frequency response. A similar, albeit more complex, crossover + EQ can be found in the BBC LS3/5A.
Since all the capacitors measured close to their indicated values, there was no rationale to change or upgrade. Besides, I want to hear these speakers as close to how they were originally designed.
Vifa 8" M21WN-07-04
AFAIK, the Vifa 8" M21WN-07-04 was the only woofer used in the J, JII and JIII. Based on the 49Hz-20kHz +/- frequency response specified in the JIII brochure, and cross-referenced to my Musical Instrument Frequency Chart, this drive unit/cabinet combo was tasked to cover six and a half octaves of musical information starting from the bass frequencies up to midrange fundamentals.
Re-Foam
After judiciously sifting through audio sites on the net, I chose the $25/pr. foam surrounds from Simply Speakers because they were recommended by audio hobbyists who exhibited good ears and common sense. Check their re-foaming video for a straightforward and confidence-inspiring tutorial.
The Vifa M21 voice coil is essentially self-centering. So don't even consider cutting or removing the dust-cap to shim the voice coil. It'll be ruined because the cone + dust cap is one whole piece.
Not bad for a first attempt in replacing foam surrounds, huh? 😉
Since time immemorial, I've been evaluating drivers bare naked (or mounted in a simple baffle) to hear their potential. After 25 years of enjoying Altecs, these drivers sound very different...🤔
