Altec speaker cabinet builders manual

The most common finish is a utility gray with no grill over the front of the woofer box, and with the large Hz tweeter horn exposed atop the cabinet. As woodworking goes, it would be relatively straightforward to build a shell around each speaker with two sides, a top, and a grill, turning them into furniture.

My wing-man Stephaen tells me that I exaggerate the ease with which tasks can be accomplished. The A7 Speakers In Small Rooms: There is a prevailing myth that the A7 speakers do not work in small rooms and that the listener s need to be far away from the speakers in order for the woofer and tweeter to blend.

Do not believe it. I have my pair set up with 9. I enjoyed them at the movies when I was young. A friend had a beautiful pair with furniture finish and grills when I was in my twenties. But for many reasons it never occurred to me to try a pair. The Stokowski A7 speakers are gorgeous, and look deceptively small in the small room Jeff uses them in.

Jeff is the third owner. Even in the small room, and even with the stock crossover units which leave much to be desired I could hear the promise of these speakers. Jeff also has a pair of A5 units, which use different components than the A7. The woofers of the A5 use more massive magnets than the woofers of the A7.

The A5 tweeter uses cellular horns an array of many small exponential horns , versus the sectoral horns of the A7 tweeters. The tweeter compression drivers of the A5 are more massive than the compression drivers of the A7. With a Hiraga network in place, and some fine tuning, Jeff has his A5 units sounding mighty wonderful. I would compare the A5 and A7 speakers using the Hiraga crossover circuit and top performance capacitors to chocolate.

The A5 would be very dark chocolate. The A7 would be medium dark chocolate. Although the A5 components are more expensive than the A7 components, I somehow prefer the A7. Jeff doesn't have to worry about that. He has both. The Sound of the A7: So how will I describe the A7 speakers as set up in my Garden of Earthly Delights listening room: full bodied, rich, directly engaging, punchy, present, immediate,smooth, sweet, musical, articulate, and nuanced, with a big sound stage, pin point localization of instruments, and lots of space.

The sound stage lies well behind the loudspeakers. That is what I hear. I can't speak for others. However my wing man, Stephaen, who does not often throw bouquets at audio systems, said quietly the other day as we were listening "those are good loudspeakers, Petie.

I can't tell you much more, as the set up of the two systems is so different as to defy comparison. I will say that I have not yet heard the Wilson system provide some of the more subtle musical qualities provided by the Altec system, nor have I heard the Altec system do the "slam" provided by the Wilson system. One needs to know what one wants. We have not yet heard big power Audio Research amplifiers on the Altec speakers.

My modest 30 wpc triode wired push-pull amps do not sound as good as the 15 wpc ultralinear Heathkit UA2 amplifiers driving the Altec speakers. Sound Pressure Measurements: Gary Ford, a very competent sound systems professional living out our way , is good at speaker measurements. Gary dropped by recently and did a measurement of the Altec A7 speakers in the Garden of Earthly Delights. I knew that these speakers sounded good, but did not know how they might measure.

From the listening position they measured very well indeed, with and without the giant horn subwoofer in operation. The frequency response was from the low forties to about 12 kHz without the subwoofer.

The drivers for this measurement are the B 8 Ohm alnico magnet woofer, the D 8 Ohm alnico magnet compression driver, and a pair of Altec biflex drivers for the subwoofer horn. Why use a wide range driver for a subwoofer? It was what we had on hand when the woofer was built. The measured system frequency response with the woofer engaged is from the 20 to 12 kHz with the subwoofer. From about 50 Hz to 12 kHz the response drops in an almost straight line on a log-log frequency response graph the so called Bode diagram we audiophiles see so often , falling about 1.

The L-pad setting for the tweeter is the one that makes the speaker sound best. I asked Gary about the gradually falling response. He advised that a smoothly falling response makes for good listenable sound and is targeted by some sound reinforcement professionals. My experience has also been that a smoothly falling response, or at least a wide band reduction of frequencies centered on about 3 or 4 kHz, makes a system sound lovely. By wide band, I mean the output might start falling at Hz, reaching a trough of maybe 4 dB at 3.

Every effort I have made at flat loudspeaker response equalization has ended in disaster. Gary's measurements were another learning experience for me, reinforcing observations I had made before about the desirability of having the system response fall with increasing frequency , but about which I was tentative.

Above 10 kHz the Hiraga network provides a rising drive signal to the tweeter, which might add a little extension to the tweeter output at these frequencies. Looking at the smoothed frequency response plot below, and noticing the shelving of frequencies above the Hz. It certainly would provide a flatter measurement.

However the system sounds best with the tweeter set where it is. If one were a hound for bright high frequencies, it might make sense to turn the tweeter up just a little. On a different point, the rising output of the subwoofer at very low frequencies helps deal a blow to the Fletcher-Munson effect without exciting boom frequencies in the 50 Hz range. The A7 response curve immediately below is taken at the listening sweet spot with a pair of A7 speakers in the Garden of Earthly Delights with the big horn subwoofer playing.

The factory provided area of square inches for the bass box port of the A5 and A7 speakers is too large for best results. With the large area the bass was boomy and poorly defined. An article on the A5 by John Stronczer suggested that it might be desirable to reduce the port area. This left two 34 square inch vents, one on each side of the plywood board.

The board was friction fit into place using card stock shims as required. This gave a very nice bass response with which I was quite satisfied for an extended period. A timeworn methodology for adjusting vent area is to do woofer-in-box electrical impedance sweeps, adjusting the port area to achieve two roughly equal impedance bumps. This was done for me by Gary Ford, mentioned above. With the vent at either the original square inches or at 64 square inches we found only one impedance bump.

Reducing the port area of the A7 speaker to 34 square inches resulted in two roughly equal impedance bumps. My initial impression on selected pieces of music was that 34 square inches of port in each box was preferable to 68 square inches. More recently I happened to be playing a succession of pieces, all with a lot of very low bass material.

What I heard was disturbing. Even with the big horn subwoofer turned off, I was hearing some of what I can only call grotesque bass undertones. Upon opening up the port area to the previous value of 64 square inches, the bass returned to a very pleasant presentation on all the material that I played.

So we are back at 64 square inches, and very pleased. With good crossovers and the right setup, the A speakers are really wonderful. They are completely non-clinical, with a big full rich bottom end, lots of nuance and inner detail, good localization of performers, big space, and a really musical presentation.

The article was published in Positive Feedback some years ago. John set up a version of the A5 based on communication with Jean Hiraga. Jean Hiraga , son of a Japanese father and a French mother, was in a unique position to bridge the European and Japanese world of audio, speaking both languages fluently, and with a deeply felt attachment to the art and craft of high-fidelity sound.

He was exposed to Japanese triode culture in the mid-Sixties - twenty-five years before the American triode revival in the early Nineties - and brought it back to Europe. Without Mr.

Fortunately for music lovers everywhere, events took a different course. John also shows a crossover for A5 speakers with 16 ohm drivers.

Neither of these schematics shows an L-pad for the tweeter, which has turned out to be a necessity for my A7 speakers and for Jeff's A5 speakers. When faced with the need for improved crossovers it occurred to me that the notch filter Hiraga included in his A5 crossover would possibly be a welcome addition to many 2 way speaker systems, which often are too hot in the Hz to 9 kHz range addressed by the notch filter.

So I decided to try the Hiraga's circuit for the A5 speakers A7 speakers using component values specified by Hiraga. Here is the circuit for 8 Ohm speakers, with the L-pad included.

The image may be difficult to read, so here are the values: In the low and high pass branch the inductors are 3. The capacitor in the low pass circuit is 36 uF 40 uF works equally well. The capacitor in the high pass circuit is 19 uF 20 uF works equally well. The notch filter inductor is 3. The notch filter capacitor is 1. The notch filter resistor is 12 Ohms. The resistors to ground are 70 Ohms and 5 Ohms. The L-pad is 8 ohms. This circuit, typical of second order crossovers, connects the tweeter out of phase with the woofer.

Note that the amplifier positive terminal is connected to L-pad terminal 3. The compression driver negative terminal goes to L-pad terminal 2. The amplifier negative terminal is connected to the crossover ground bus which is connected to L-pad terminal 1 and the compression driver positive terminal.

How to determine the positive terminal of an driver? Mark it with some red tape or paint. On the Lansing Heritage Site one of the forum members, jimd, has the following advice: " In the case of Altec cone drivers marked with terminals marked 1 and 2, 1 is hot as the magnet is behind the cone. In the case of the and other "inside out" type HF drivers, where the builders routed the sound output through the magnetic assembly, the magnet is in front of the diaphragm instead of behind it like conventional drivers.

Therefore, to get positive pressure at the exit of the Altec HF driver, one must apply positive voltage to terminal 2. The Hiraga Circuit as Modified by Pete Riggle: The circuit shown below, based on Hiraga's 8 Ohm crossover circuit, includes the tweeter L-pad, not included in Hiraga's original circuit diagram, and two switches not included in Hiraga's original circuit diagram.

With both switches open the notch filter resistance is 12 ohms the sum of 6 ohms, 3 ohms, and 3 ohms. This provides a 4 dB deep Hiraga notch, which starts somewhere around 1 kHz, deepens to a maximum at 3. If one of the switches is closed, the notch filter resistance becomes 9 ohms, which provides a 2 dB deep Hiraga notch. If both switches are closed the notch filter resistance becomes 6 ohms, which eliminates the Hiraga notch.

For the past few years this figure has had an error in the L-pad connections. These results were calculated using the Spice electrical circuit analysis program.

Pure resistance, inductance and capacitance were assumed. Response curves were also calculated adding parasitic inductance to the crossover resistance values and adding measured speaker driver inductance values to the load resistance values. The difference between the response curves with and without the inductance corrections was small.

These are the speaker response curves we would expect for perfect speakers when driven by the Hiraga circuit through a perfect power amplifier. What is the point of all this? We want to know the contribution to frequency response attributable to the crossover network.

Good capacitors are the key to good crossover networks. To get wonderful sound the capacitors need to deliver wonderful sound. They need to sound musical. Capacitors are often the weakest link in an audio component. On the basis of listening tests of capacitors using my Altec A7 speakers in the Garden of Earthly Delights, I have laid in a stock of high performance capacitors oil capacitors which I sell as Pete Riggle Personally Selected Loudspeaker Crossover Capacitors active link.

Don't be afraid to round up or down a little as needed to obtain capacitors to do the job. I will mention here that for the notch filter capacitors in his Altec A5 speakers Jeff Day has tried Dueland Cast capacitors with tin plated copper plates. Jeff is quite pleased with the resulting sound.

These capacitors are very expensive, and out of range for most of us. Not to worry. I must say that I am more than happy with the oil capacitors that I use and sell. Low Pass Crossover Inductors: For inductors for the low pass branch of the crossovers I suggest the lowest DC resistance air core inductors you can afford. What was of concern was the metal HF horns rang like a bell when tapped, so either they needed to be damped or replaced with something else.

Inside the main cabinet, however, all was pristine, likewise the HF drivers themselves are in excellent condition internally, outwardly the paint was a bit worn. No matter as they worked just fine! The JBL tweeter was a concern until I realised that it had been connected up wrongly and was barely making a sound. Something that needs to be mentioned is that the Altec A5, A6 and A7 use the same main cabinets, the The difference between A5 and A7 is the HF horn: the former uses one of the multi cells, the latter the sectoral type horn.

By definition, then, the one on the left is an A7 type. Fostex made these cabinets and the only difference that I have been able to find is that their design is mm smaller front to back. Otherwise they are identical to the Altec plans. Because of the corrosion of the metal horns, plus the ringing problem, I decided to have wooden multi cells made up. For those that decide to do the same, I used a simple exponential curve with a mouth of 10 mm square and tapering out to mm square.

There are different ways to make these, my woodworking chap made each side of the individual horns from solid wood and then glued and screwed them together. This was a very difficult way of making the multi-cell horns but, as each small horn consistes of four solid bits of wood, the end result is without resonances and quite heavy. The wood used is Jacaranda and finishes to light golden colour. Each horn mounts in a panel which is the width of the A7 cabinet.

The Fostex HF compression drivers have a manifold and the manifold connects to the wooden horn. There are many ways of building horns if, like me, you like DIY. Failing that in Europe or the States second hand ones are often advertised and can be damped externally.

Along the line I acquired a pair of NOS 15" Goodmans Audiom speakers and decided that, while one set of A7's is good, two must be better; so I commissioned another pair of cabinets. The idea came from the picture below left and is of an early Altec A6 stacked pair. One change I will make is to set the HF horn between the A7 cabinets and that will be Part 2 of this article. The above shows the second set of A7 cabinets, the center sketch is only for interest as the actual plans are here: Lansing Heritage, A7 plans.

These date to and I have made certain modifications to the build and not to the actual design. For the Imperial or Metric challanged The cabinet walls and horn have been increased in thickness to 32 mm and the support ribs behind the horns have been increased from 3 to 5. The horn sections were formed from three 10 mm layers of Supawood or medium density MDF with a 4 mm layer of veneered board. This is the only part of the cabinet build that takes any real skill. Note how the driver is partially covered by the horn - this is very important as it mass loads the front of the driver.

All Altec designs rely on this feature. Mounting the driver back in the cabinet also helps time align the HF driver which, mounted on whatever horn used, is fairly long.

Variations of this type of cabinet include one where the port size is increased to allow mounting the HF horn inside the cabinet so as to make the speaker assembly smaller. Shown at left the bracing for the horn flare. The cavities behind the horn to be packed with fibreglass wool. I have tried modern materials and always end up going back to fibregless.

The Voice Of The Theater range started in one year before me! The cabinet on the right is inverted, the port removed and the HF horn mounted in the cabinet. WAF even then perhaps? Down now to the nitty gritty of drivers. The Fostex clones were fitted with 16" L Laboratory series units and the extra set of cabinets with 15" Godmans Audiom Both have a resonant frequency of 25 Hz, but from there everything is different.

The Fostex weighs in at just over 8 kg, the Goodmans over 10 kg. Voice coils Aluminium, mm for the Fostex and 75 mm for the Goodmans. The HF compression drivers are Fostex D and are quite heavy at 3. One inch or Anyone wanting to embark on a project like this can pick and choose from many modern compression drivers or source old types as they choose.

Altec, JBL and even Westrex drivers are advertised on the net, at a price. The possibilities are endless. As in everything, it's up to your ears and pocket!

The only reason I have used these Fostex units is that they came with the A7 clones I bought. After six months of listening to the Fostex A7 cabinets leaving the HF section aside for now I was very impressed with the clarity, dynamics and punch delivered so, when the time came to send those away for cladding in Imbuia and replacing them with the new Goodmans clones, I was a bit worried.

To my joy, if anything, the new cabinets performed as well, but with a touch more bass and that left me a bit bemused. That is until my woodworking chappie rang me with a problem.

The Fostex cabinets were mm or 4" less front to back than the Goodmans versions, which were built to Altec plans. This is not serious as they will no doubt blend together in the final stack version, but it seemed odd that Fostex deviated from the Altec original.

Both types, however, work essentially the same with almost no visable cone movement, even at very high levels with thumping bass. The dynamic response from this type of cabinet can not be overstated, it is enough to cause visitors to actually jump when there is a drum strike.

Sitting back six meters from the wall, almost seven meters diagonally from the cabinet, there is a beat against the body and the heavilly upholstered chair shakes. I am certain this is a function of the cabinet design and have no doubt any reasonably sensitive driver will work equally well. Power needed for even very loud listening is minimal and my Stereo 20 Leak copes runs with the same drive from the preamp as do the 12" Goodmans Axioms in rear horn loaded cabinets. Except the end result is much higher volume in the A7 clones!

The picture of the final Goodmans A7 clone with multi cell at right. The reason for the rectangular panel actually a box around the multi cell is to provide a resting place when the Fostec A7 clone is mounted, inverted, on the top. The tweeter will stay more or less in the same position height wise in the horn mouth of the second cabinet.

The Fostex A7 clone is being clad with Imbui finish, the walls thickned to just over 32 mm, likewise the horn flares, the flares being reinforced with extra ribs at the same time. Shown at left is the back of the multi cell horn, with the Fostex D compression driver and manifold.

The Fostex three way crossover and the control panel for that which mounts in the side of the multi cell enclosure. Controls are for HF and Treble gain. For interest, the crossover measures mm X mm. Final connections for the two main drivers have still to be finalised when the second set of cabinets are installed.

When the other cabinets are in there should be a 3 dB increase in bass sensitivity. This construction may seem like violent overkill, visually it is at just under 1.

Finished with the two A7 cabinets and multi cell it will be 2.