Altec 2-way XO Redux

This is an update on crossovers I use for the Altec 2-way speakers.

JEL N1600 Crossover

JEL N1600C + HF EQ
optimized for the 802 driver fitted with the original
16 ohm 20275 diaphragm

Altec 2-way horn system redux

Truth be told, I was never fully satisfied with the performance of the Altec 2-way which is why I never uploaded the old article in the Arkiv.

Altec 753C

Radio Shack

In February of 2015, Radio Shack filed for Chapter 11.

So I was delighted to see this Radio Shack store announcing a comeback in midtown Manhattan during a visit in the summer of 2016.

When I was a student in NYC in the 80s, a neighborhood Radio Shack store was just around the block if I needed a resistor or capacitor for a project on a Sunday afternoon. By 2008, I was in the suburbs and Radio Shack was in a strip mall just a mile and a half away. Now I have to drive 35 miles to the next town ;(

In the early 90s, many SE amp DIYers started their foray into efficient speakers inspired by this book by David B. Weems. The speaker projects used various raw drivers from the Radio Shack catalog.

40-1354A

Radio Shack no longer had 2A3 triode tubes on their shelves when Sound Practices started publishing in 1992,  but one could still buy this 5 1/4" full range driver listing for less than $10, IIRC. This speaker was efficient enough to be driven by an SE2A3 amp to satisfying levels.

I used this driver in a compact bass reflex box...

from David B. Weems book

...as well as in a Tapered Quarter Wave Tube (TQWT)

Not quite in the same league of sophistication and refinement as the Altec 2-way, but lots of fun since they can boogie on a couple of triode watts ;)

Time Warp

During a recent "let's see where the wheel takes us" expedition, my wife and I spotted this in Pennsylvania. 

40-1310

As I browsed around the store, a pair of 40-1310 super tweeters bearing their original sticker price immediately caught my eye. I told my wife about them and she insisted that I get this pair of NOS Chinese-made plastic version for $60 + tax, so I can time travel.

These drivers developed quite a following in the 90s because the original all-aluminum units embossed Realistic were allegedly OEM'd in Japan by Fostex. The graphs above and below should corroborate this speculation. Later versions with a plastic pod and horn were subcontracted in South Korea and then China.

Fostex FT17H

I didn't join that 90s bandwagon. Instead, I bought a pair of the equivalent Fostex FT17Hs sans pod from Madisound for $70. I used them as super tweeters for Altec 755Cs and 755Es until they were superseded by a pair of superior Altec 3000Hs.

 Brand new Fostex FT17Hs are now made in China and can be had for a little less than $100/pair. I still believe they are excellent value for the money. Perhaps the early Japanese all-aluminum 40-1310s can command a slight premium, but beware of unscrupulous eBay flippers asking ridiculous amounts for the plastic version.

Subtlety

Before inserting the 40-1310 into the Altec 2-way, I bypassed the built-in electrolytic cap/choke crossover components. For the past 20 years, I've been using smooth and natural sounding paper in oil caps in the signal path of my preamp, amp and crossover, nothing else.

Altec 2-way + 40-1310

Altec 2-way sans 40-1310

In this application, the 40-1310's positive terminal is protected by a 1uf PIO cap and then connected to the high-pass section of the crossover. The effect of the super tweeter is subtle...just a touch more air.

As I was about to sit back to reminisce the 90s with the 40-1310, an internet friend informed me that Radio Shack just filed for another bankruptcy claim ;(

This prompted me to visit my favorite branch...

...fingers crossed. ;(

Altec 2-way XO update

The Altec N1600C series crossover has been a significant constituent in the evolution of my Altec 2-way horn speaker system. C. G. McProud's 1947 article on page 101 of Audio Anthology, Volume 1, was my first encounter with series crossovers although Western Electric was already using the topology in the 1930s. As an aside, my knowledge of electronics is basic. I don't even own a circuit simulation program and rely on my collection of audio electronic textbooks, old magazines plus what my ears tell me as reliable internet sources for "techie stuff."

Reality Check: Musical Instrument Frequency Chart + A Tidbit of Wisdom from Radiotron 3rd Edition

Musical Instrument Frequency Chart

This musical instrument frequency chart should serve as a reality check for those who obsess about metrics. During the triode era and up until cycles per second (cps) was replaced by kilohertz (kHz), a bandwidth specification of + or - 1dB from 30-15,000 cps was considered state of the art. That old standard actually made more sense if we look at the bandwidth of acoustic instruments in the chart above.

The chart is also a practical reference for all of my speaker/driver/horn articles past, present and future. Likewise, it is a handy visual aid to interpolate the pink noise + iPhone Real Time Analyzer (RTA) app traces even if in most cases they don't correlate to what we hear.😆  

In a couple of instances, an RTA trace has agreed with what I heard. In reality though, pink noise and other waveforms used for audio testing have nothing in common with musical notes and harmonies. Audio measurement is very far removed from the dynamic nature of music. To me, the RTA, audio generator and oscilloscope are tools that can be helpful if used with discretion.

Altec 755A in an Open Baffle

My adventure into high-efficiency speakers started with a pair of Altec 755Cs (and later, 755As) mounted on this very same open baffle. It was easy for me to appreciate the lack of boxy coloration, having lived with Quad ESLs for a couple of years.

Altec 755A in Open Baffle

Most open baffle detractors complain about the lack of bass response. However, the above trace doesn't pale too much in comparison to the Altec 755A + Dr. Bae/Silbatone box and Altec 755A + 618 below, even if it does look ugly!🤣

Maybe the suck out between 250-1kHz is what I hear as the absence of cabinet coloration or the "lack of snap" J-Rob heard?

Dr. Bae/Silbatone Box + Altec 755A

Despite being very compact, this empirically designed box exploits the fullest potential of the 755A driver. 

Altec 755A in Silbatone Box

This trace looks better than the 755A + OB above but not as nice as the Altec 755A + 618 trace below.

Altec 755A + Altec 618

[2 cubic foot sealed box]

A pair of Altec 618 cabinets

The Altec 618 is the classic 2 cubic foot sealed box for the 755. It has to be rigidly braced to minimize upper bass/lower midrange coloration, although some listeners may prefer that "warm" bloom.

Altec 755A in the 618 box

This trace is the flattest of all three. But subjectively, the Dr. Bae/Silbatone box + 755A sounds more neutral and tonally more accurate. I don't hear the sudden rise from 1 kHz and peaks at 1.5 and 2 kHz. 

The Altec 618 box is now loaded with 755Cs and has great synergy with the JLH 1969 clone amp.

Altec 753C

 My exposure to the Western Electric WE757A and WE753C in the late 90s inspired the Altec 2-way project. The sound of those two classic speaker systems was already familiar. They sounded very similar to the 755A with more extension in the low end + airier highs. But what really sent me on a quest to emulate them were: greater efficiency so that I can enjoy my flea powered SE-DHT amps and less congestion (more layering and instrument separation) at higher SPLs. The Altec 753C is the final destination of that journey. 

Along the way, the Altec 755A was my loyal guide for midrange accuracy and coherence, which is why I discussed the driver in its various guises above.

Altec 414A in the ported 753C cabinet

The Altec 414A woofer running in full-range mode covers at least six octaves, from 45 Hz until it starts rolling off in the 3 kHz region. Unlike most drivers of this size and type, this is very smooth-sounding and delivers a great midrange without nasty cone break up modes up to its natural roll off point.

Prior to using the 414A, I had a pair of Altec 419A Bi-flex. I also seriously considered a pair of Altec 416A but both drivers exhibited nasty peaks starting from 1-3 kHz. Now I wonder if those peaks would've been visible using pink noise + my iPhone RTA app? 

I could've studied how to filter the peaks using EQ. However, all these extra crossover circuit complications would've adversely affected the efficiency of the speaker system, which I wanted to avoid. In the end, I stuck with my original plan of keeping it simple.

Altec 414A

Fundamental frequencies below 45 Hz may look rolled off in the trace but the harmonic overtone series (hence, harmonics or harmonic overtones) of the frequencies below the roll off point reinforce the [weak] fundamental in making those lower frequencies audible in actual musical reproduction. The BBC LS3/5A is a good example of a small speaker that "reproduces" low frequencies via harmonic overtones. 

My straightforward explanation: A:27.5 Hz played on an upright piano will produce less intensity as a fundamental note compared to that from a nine-foot concert grand because the instrument is physically smaller and the length of string, shorter. However, that upright piano's A:27.5 Hz is still perceived as A:27.5 Hz by the human ear, albeit less visceral, because of the harmonic overtones produced. 

Due to the 414A's sharp roll off past 3 kHz, the upper frequencies need reinforcement. 

Altec 32C horn + 802D + 20275 diaphragm
XO below

For many years, I struggled to make the Altec 811 horn work in this context. I started crossing it at around 900Hz @ 6dB/octave slope. Then, I cloned the Altec N1600C crossover, which effectively raised the crossover point an octave higher with a sharper 12dB/octave slope. 

None of these crossovers could blend the 414A and the 811/802D coherently to mimic my favorite full-range driver, the 755A. The "shouty distortion" was always present even with a simple 2 uf paper in oil cap + variable L-pad.

Altec 32C + 802D

After several years of frustration to the point I almost gave up, a fortuitous meeting with the Altec 32C horn opened a whole new world for the better.😄 It turned out that the objectionable "shout" I was hearing emanated from the Altec 811 horn.

The Altec 32C horn + 802D driver combo fill in the last 2 octaves of fundamentals + another 2 octaves of harmonic overtones using the high-pass crossover below. 

Sound Practices

I've learned so much from getting to know the Altec 755A, 755C, 414A, 802D and 32C intimately as well as from the other components that I ultimately rejected. 

The countless hours I spent assessing and listening to these transducers individually is a sound practice I highly recommend to audio DIYers!

Simple Crossover

Ever since I discovered the sonic delights of paper in oil as coupling capacitors in the signal path of preamp and amp circuits, I've also adapted their use in crossovers. 

Altec 753C crossover using paper in oil capacitors + Mills
non-inductive resistors
schematic

I've found the RTA to be helpful in adjusting crossover points with the help of a crossover calculator. A simple example: if the sound is harsh, move the crossover point higher. If you need more bite or presence, go lower.

Altec 414A + 32C horn + 802D compression driver  +
JP 753C ported cabinet = Altec 753C

If I were to summarize, the Altec 753C sounds lush and romantic!

Altec 753C 

Driven by 3500 milliwatts per channel of SE-DHT power, these speakers allow me to enjoy Mahler symphonies in my man cave with nuanced macro and micro dynamic contrasts. It gives a middle of the hall presentation which is my preferred perspective. The midrange is warm and coherent with a nice three dimensional quality.

Even if the extreme lows are curtailed, the harmonic overtones produced in this frequency region have enough foundation for big orchestral works. There's a wispy ribbon-like airiness in the extreme top which, to my ears, no longer need help from my pair of Altec 3000H super tweeters.

I probably could've gotten another half octave of bass extension if I chose the 15" Altec 416A woofer, but then I would've run into problems blending it with the 32C/802D horn/driver using a simple crossover. Even if I succeeded in EQ'ing out the peaks of the 416A, efficiency and midrange coherence would've suffered.

Everything is a compromise and I believe I've chosen wisely.

Wanted: smooth sounding 12"-15" wide range driver + horn + compression driver

Although Great Plains Audio is still manufacturing the 414 and 802 drivers with alnico magnets, IMHO, the listed prices are too steep to even attract the attention of the DIY community or smaller boutique manufacturers. 

I've used and highly recommend their replacement aluminum diaphragms for 1" format compression drivers. I've been told that the GPA 414 doesn't sound like the classic 414A/Z/8B/16B and is 3dB less efficient. However, I don't have hands-on experience with the GPA drivers to confirm any of those claims.

GPA is our only direct connection to the past when transducers were designed using human ears aided by measurement tools. For that alone, I want them to succeed!

Radiotron, 3rd Edition Redux

Let's (re)visit a topic that has served the interest of the entire audio industry, except the bottom-line of this hobby - the enjoyment of music!

Sad to say, no one has heeded D. Massa's advice. 

Besides, the test tones used for distortion analysis have no bearing whatsoever to the highly dynamic and complex harmonies contained in the simplest musical score.

Yup, this was 80 some years ago and there still are self-proclaimed audio pontiffs who insist on this metric!🙄

Azzolina Audio KS12024

Western Electric KS12024

Western Electric KS12024
Note: ~ 140° throat bend

The Western Electric KS12024 is a 2-piece cast aluminum 4-cell sectoral high frequency (800-1000Hz cut-off) horn with a 50°H x 40°V dispersion pattern. It was implemented in the Western Electric L-8  and L-9 speaker systems.

Western Electric L-8
from the Silbatone Collection

SETUP 2024

Single Ended Triode Users of the Philippines 2024

At the dawn of the 21st century, I uploaded hifi systems owned by audio buddies who had been inspired by the Sound Practices ethos. These were the guys who originally coined SETUP. After a couple of decades, the number of Filipinos who indulge in this hobby has increased exponentially.

Here's what I saw and heard during my recent visit.😊

Harana Audio Workshop

Altec 311-60 horns + 288 drivers with Fostex super tweets on top of a pair of Harana V-Vent bass bins with partial horn loading

SRPP SE2A3 Circuit Redux

Back in the late 90s, I dismissed the hi-mu/low-gm SRPP input/driver because I found that the circuit had a tendency to sound tiring over extended listening. However, my memorable encounter with the Morikawa SE2A3 amp owned by my buddy Jose was haunting. I had to revisit this circuit just to make sure I left no stones unturned. 

Earlier this year, Steve of Angela Instruments shipped me the "shop mule" SRPP SE2A3 amp for a check up. After replacing the leaky coupling caps, the amp was as good as when I delivered it to the shop over two decades ago.  

My hotter operating point = slightly more power compared to Prof. Morikawa's SRPP 2A3 amp.

!!!WARNING!!! 

The voltages in this circuit are potentially lethal! Build at your own risk!

Click here if you'd like to try the SRPP 45 triode circuit.

Use a Hammond 302AX power transformer instead of T1 + T2 A&B

Click here to see the "cleaner" 10kHz square wave from the Morikawa SE2A3 amp

In spite of the 10 kHz square wave spike from the budget Hammond 125ESE output transformers, it was a very refreshing musical reunion with the Angela SRPP 2A3 amp. 

During its residency in the man cave, the amp powered my back up Altec 2-way system above, Altec 755As and Altec 755Cs in Silbatone cabs below. It was totally devoid of the listener fatigue I previously ascribed to the circuit. Even with the brightest and harshest software and/or hardware thrown into the listening chain, I couldn't induce the unpleasant quality which bothered me in the past. 

Then it dawned on me that I started doubting the SRPP's musical abilities when my Altec 2-way project commenced. Sorry SRPP, it wasn't your fault...😟

YMMV!😉