Intact Audio Speaker Autoformer + Lycan3R WP12024 Horn

I ordered the Intact Audio speaker autoformer with a -6dB to -15.5 dB/0.5dB attenuation range based on the fact that my Altec 802 drivers are about 12dB more sensitive than my 99 dB/1W/1M Altec 414A woofers. Other than that, I went into this project hoping that Google would be my friend, only to find out it wasn't!😉

Since I use external crossovers for my Altec 753C, disconnecting (and reconnecting for comparison purposes) the Altec 32C/802 horn/compression driver is a breeze. The 753C-style cabinets essentially serve as bass bins in which the 414A woofers operating in wide range mode (unfiltered) + the 20275 diaphragmed 802 compression drivers mounted on the Lycan3R WP12024 horns are perched on top!

Lycan3R WP12024 Horn

A couple of months after I blogged about the 3D printed prototype of the WP12024 horn, Trieu sent a pair of these beautifully finished cast aluminum production versions. Included in the package was a set of parts for a horn stand patterned after the Western Electric original I've only seen in Stereo Sound Tube Kingdom.

Altec 756B + 32C + 806 + 23744 = mini 757

The WE756A is the middle child in the Western Electric series of wide range drivers introduced in the late 40s.

I've seen and heard a couple of WE/Altec 728Bs + a dozen or so pairs of 755As, but I've never heard a WE756A and have only seen one in the metal at a radio show many years ago. Although still quite scarce, its Altec 756B brother isn't quite as elusive.

Back: Blonde + Mahogany Altec Melodist 700A
Front L-R : WE728B, Altec 755A/pr. + Altec 756B

The few Altec 756Bs I've encountered all came out of the Altec Melodist 700A. It's a compact bass reflex speaker system loaded with the 756B, supplemented on top by a 3000A horn tweeter via an N3000B crossover. The 700A belonged to the Melodist monaural hifi system line, which Altec targeted at apartment dwellers in big cities of midcentury America.

 Subsequently, the 756B was replaced by an 8" Altec 401A and was re-designated as the Melodist 700B. With the introduction of stereo for the mainstream market in 1958, the Altec Melodist line quietly faded into oblivion.

 If found in good condition, the Altec Melodist 700A is a fine looking midcentury modern artifact! Unfortunately, the < 1.5 cf ported box doesn't allow the 756B to shine sonically, IMHO. Since it shares similar proportions to its more successful contemporaries like the Acoustic Research AR-1 and the Jensen Duette, the cabinet design may have been dictated by market positioning rather than sound engineering.

My once-in-a-lifetime lucky find 700A above has lived a hard life. The lower front edge of the cabinet was missing while the sweet and airy but very fragile 3000A horn tweeter element had been replaced by a tiny ferrite magnet dome tweeter.😏 A "mod" that has been circulating in the internet, so watch out.  

 

Fortunately, the 756B is very well preserved. If memory serves me right, the WE756A frame is more substantial than the Altec 756B. That’s probably the reason why the back handles were omitted in the Altec. The 756B has an 8 ohm voice coil, while the WE756A is 4 ohms.

J-Rob's Altec 756B at 
Capital Audio Fest 2016

Joe Roberts has already done a great job of describing the sonic qualities and proper implementation of the Altec 756B in his (Geekstar) "My big ten inch --Altec 756B" post at the Altec User's Board. He also gave insight on the shifting Asian market for vintage Western Electric and Altec gear. A guaranteed fun and informative read!

Since I don't have Joe's networking skills, I resigned myself to the reality that my Altec 756B will be the main speaker of my monophonic hi-fi set up, just as Altec intended.

Click for a videoclip

Meanwhile, I repurposed (sealed) a Heathkit AS10 (almost 2 cf) cabinet to familiarize myself with the 756B. I listened to it as a wide range driver with and without top end assistance from either a 32A/802/34852 + an XO based on this schematic or 3000H with an L-Pad + 0.5 uf - 1 uf paper in oil cap. The simplest XO I used was a 0.22uf paper in oil cap in series with the + terminal of the 3000H, no L-pad needed. That also sounded good, albeit, with slightly less sparkle.   

JE Labs mini 757
inspired by the Western Electric 757A

After extensive listening in wide range mode, I determined that a mono hifi set up will benefit from a wider baffle + the dispersion pattern of the Western Electric-derived 32 horn. So I sketched a slant front ~ 2.5 cf infinite baffle that has a provision for an Altec 32C horn + 802 driver and sent it to John Piro of Hommage Audio.

728B vs. 756B

As expected, the 756B is more extended at the top end than the 728B with almost, but not quite, equal bass extension. However, music through the 728B held my attention appreciably longer without my reaching for a clip-lead to fill in the top octaves with the 32/802 horn/driver for more harmonic overtones above 5 kHz. 

RTA = Altec 756B in a ~ 2.5 cf infinite baffle 

I confirmed this during one of my shop talks with J-Rob, who also found it more rewarding to listen to 728Bs in wide range mode than to his 756Bs. It makes me wonder if the 756B and its WE756A brother were designed with a middle-child syndrome gene in their sonic DNA.🤔

After many years of collecting Altec 1" compression drivers, I've only landed a single Altec 23744 "light" aluminum diaphragm, which was fitted to an 806 motor that was used in the Altec 9849 monitor speaker.

Things started to crystalize when my friend Dave V. aka Salectric,🙏 sent me his spare .085 mH choke. It was a proprietary part found in the EQ circuit of the Altec 9849 crossover, which is an 8 ohm speaker system. This EQ circuit shapes and boosts the response of the 32/806 horn/driver combo. Incidentally, Dave's "Last PAS" articles written for The Audio Amateur contributed to my 80s Dynaco hacking activities.

RTA = Altec 32C + 806 + 23744

 The 4 uf paper in oil capacitor serves as a first order high pass filter hinged around 5 kHz with a gentle 6dB/octave slope, while the variable 8 ohm L-pad shapes and controls upper frequency overtones to taste. 

inside the mini 757

John P did a great job of building a very rigid cabinet, which saved me the time and trouble of having to experiment with damping. I just lined the interior panels with Kimpak and I was ready to listen.

RTA = JE Labs mini 757

This project transpired as an opportune moment to assemble all the singleton Altecs from my collection - 756B + 32C + 806 + 23744 - into a formidable monaural hifi speaker system.😊

JE Labs mini 757

My ears hear close to half an octave of bass extension from the mini 757 compared to the 755A in a Silbatone or 618 cabinet. Due to its greater efficiency, it plays louder while dynamics at micro and macro levels are less compressed. The larger cone area of the 756B + wide baffle + 90° horizontal x 60° vertical dispersion of the 32C horn, portray a bigger sense of scale. All of these were achieved without compromising the midrange realism I enjoy from my beloved 755A. 

However, the Altec 753C is perceptibly more efficient, offers at least an octave lower of extension with more authority. It also produces higher SPLs. 

Alas, we can't defy the physics of sound...

JE Labs monophonic hifi

...so I focused on the aesthetics by spicing it up with a touch of Charles Eames and Dieter Rams! 😉

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

The above crossover circuit, as discussed in this previous post, was optimized for my cherished pair of green Hammertone Altec 802Ds fitted with the original aluminum 20275 diaphragm, which has an aluminum wound voice coil. To my ears, this diaphragm has a more prominent midrange response which necessitates rolling off the upper midrange/lower high frequencies of the 414A woofer for flatter response.

JEL Universal Altec 2-way XO

For the Altec 802 driver equipped with the 34852 (16 ohm) or 34647 (8 ohm) diaphragms, which have copper wound voice coils, I recommend the 6dB/octave crossover circuit below which is hinged at around 2500 Hz + high frequency EQ boost. This aluminum diaphragm has less energy in the upper midrange giving a tonal balance that sounds more extended in the high frequencies compared to its 20275 predecessor. In this implementation the Altec 414A woofer is connected as a full-range driver inspired by Joe Roberts. 

JEL Universal Altec 2-way XO with HF EQ circuit

Altec 414A + 32A/802/GPA 34852
+
JEL Universal Altec 2-way XO

I've also used this crossover successfully with the Altec 802 driver fitted with the Symbiotik diaphragm, Emilar EA/EC175 and Renkus-Heinz SSD1800/1400. Please take note of the different capacitor values for 16 or 8 ohm drivers.

Simplest Crossover

If you want the simplest crossover, my buddy Joe Roberts listens to his Altec 414A/802/32 set-up with the woofer in full-range mode + a 1.5uf paper in oil cap for the compression driver, no L-pad or HF peaking EQ circuit. See his Audiokarma post for more details.

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.

Let's recap how the 2-way horn system evolved...

The project was conceived in mid 1998 because I needed a monitor system that was more efficient than the OB/755 so I could listen to SE amps with 2 watts output and below.

I commissioned my cabinet maker neighbor to build 614 bass reflex cabinets and loaded them with Altec 419A 12" drivers + 811 horns (early version/heavy sand cast) and 804A compression drivers gathered from hamfests and radio shows. Crossover was a textbook 1st order/6dB/octave hinged at 900 hz and the horn padded down to match the sensitivity of the low frequency driver.

Altec 614 cabinet plan

Eventually I acquired proper 12" woofers - Altec 414As, which lack the upper midrange nasties of the 419As. The 414As have great midrange quality even if they lack the bass end of their larger 416/515 brethren.

Note damping is applied only
on two sides and the back.

802D compression drivers replaced the smaller magnet 804As

Altec 802D

+ super tweets...

Altec 3000H 

Series crossover

While exploring proper monophonic playback, I discovered the N1600C crossover which came with a single 605B Duplex I acquired. When I inserted it into my Altec 2-way, it sounded significantly better than the textbook parallel 1st order/6dB per octave crossover I had been using.

N1600C clone

Using paper in oil caps and low DCR air core chokes, I cloned the N1600C and thought it was as good as it gets with my Altec components...

ca. 2006

Lessons learned over the past 15 years

1. Choose a woofer with excellent midrange characteristics.
2. In hindsight, the 804A/811 was a much easier combination to tame than the 802D/811. Perhaps this is due to the smaller magnet on the 804A which makes it 3dB less efficient. Note: the 806A is similar in specs to the 804A but some sources say they are built differently.
3. Horns sound better crossed over at least one octave above its rated cut off.  I'd go as high as possible if my woofer can play well into the upper midrange.
4. Don't be afraid to pad down the compression driver which is at least 10dB more efficient than the woofer.
5. Try series type crossovers like the Altec N1600C above or N1500A which have lower insertion loss due to the 1st order/6dB/octave low pass filter. Note: the high pass section =  2nd order 12dB/octave 
6. I only use paper in oil caps in my crossover. 

811>32C

Through the years that I had been attending radio shows and hamfests, I got to know people who opened rare opportunities for me to hear the Western Electric 753C, Western Electric 757A and Altec 1505 horns with Western Electric 555 field coil drivers on top of 825 cabinets loaded with 515s. Most memorable was a single Western Electric 15A horn  + WE555 field coil compression driver driven by a pocket FM radio my buddy Ding and I heard at Scott Stilwell's shop in Philadelphia. The huge horn produced mid bass and rolled off like a 755C or 755E. Thus, "shouty," honky or harsh is not something I associate with good horn speakers.

Altec 32C/802D + Altec 3000
trial ca. 2009

A pair of Altec 32C horns I got in trade back in 2009 had been languishing in my storage bin despite realizing its potential after an initial test run. Given the 32C's pedigree - a direct descendant of the metal Western Electric 32A horn found inside a Western Electric 753C monitor speaker - I had an inkling that it would be better than the 811. But a busy schedule and other life matters got in the way. ;)

Replacing the 811 horns with the 32Cs transformed the 2-way horn system. The 32C/802D blended with the 414A/614 without any crossover alteration. If the 811 projects an in your face/front row seat perspective, the 32C is more like sitting at the middle to back row seat wherein instruments and/or vocals have been given enough time to reverberate in the concert hall. Exactly the kind of sound perspective I prefer!

Despite its polite and refined presentation, the 32C retains the transient speed, dynamic ability and top end extension expected from a horn such that I found the use of 3000H horn super tweeters redundant. In fact extreme high frequencies from 32C/802D sounded airier than the 811/802D + 3000H combo. I have a feeling that most detractors of the 90° bent horn design never heard an original Western Electric 753C, Western Electric 757A or even the more recent Altec 9849 monitor speaker.

Although there's another tweak I am experimenting with at the moment, this horn is here to stay. As Johnny Hartmann sings, "...it's wonderful..."

HAPPY NEW YEAR!