The SE-10842 Loud Speakers
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I’m audibly oriented. Because I was born with less than normal eyesight, I missed many of the visual sites the norm could see. As a consequence, I developed a greater audible sense. One of these senses is hearing sound reproduced from recorded media. Over my 70 year life span, I’ve heard a lot of reproduced sound. I could easily hear the subtle nuances from many systems including their short comings. I didn’t look for perfection, just something that was within tolerability – what many would describe as a subjective term. Since Y2K, our visually oriented society has been hell-bent on achieving perfection in video – 720, 1080, 4K, 8K, 3D, etc. Prior to this, we were satisfied with 220 lines of blurry resolution on a CRT from VHS tape – a standard that has been … since 1954. It was during this time when we were concerned with accurate reproduction of sound. But then, CDs & MP3s – and audio went to hell. If speakers didn’t kick your ass, they weren’t worth consideration. I on the other hand feel differently. I love natural sound, not synthetic, loud, blasting, fuzzy, repetitive distortion. There are still many others like me – mostly overseas though – a few are here. I wanted this clean sound but I didn’t know how… Then, I met one who knew the methods. From him, I eventually learned. That was in 1980. Since then, I’ve heard and I understood. It was in 1989 when I decided it was time to construct a set of not so expensive speakers that would rival something like what was said about the Altec Lansing A7 or Tannoy Arden speakers of the late 1950s in so far as midrange clarity was concerned. I realized available 12 to 15 inch drivers were fraught with complications and distortions so I had to seek alternatives. It was while riding in a colleague’s car he would enter into car audio competitions where I heard a sound that intrigued me. In one of his attempts at boosting his mid-range, he installed a set of expensive 4-inch titanium domed mid-range speakers along with their companion titanium tweeters. After a bit of fiddling with the knobs, I was able to hear a jazz legend singing clearly through these speakers. I was quite impressed at their up-front clarity. Several days later, he offered to sell me these titanium speakers.
JBL T030 / 095TI 4” Titanium Domed Midrange Specifications:
JBL T06 1” Titanium Domed Tweeter/Neodymium Specifications:
The above speakers were designed for automotive use. JBL did build a hideously expensive speaker system with similar 4 inch drivers. However, the raw drivers themselves were never available. Note. The JBL T030 Midrange and T06 Tweeter are no longer available.
Subwoofers
The next issue was the problems associated with subwoofer technology including sealed vs ported enclosures. Over the years of listening, I realized that, though ported speakers did have a greater bass response, they were subject to considerable distortion and inaccuracies. Also, to reduce upper frequency harshness and boost the lower frequency response, sub-woofers were designed to have a heavier moving mass. In so far as low frequency response in sealed enclosures is concerned, a heavier moving mass driver also seemed to be a requirement. I however decided on a smaller sealed box with a light moving mass 10-inch driver coupled with a passive radiator. At the same time, the speaker needed to be able to handle enough power to produce adequate bass with a servo amp. Based upon the specs, I purchased four Rockford Fosgate SPP-104 10-inch speakers. To hopefully increase the bass, I planned to mount two of them in a 2-sectioned enclosure. This was 2 speakers per channel, each in their own 1 cubic foot space. However after some tests, I realized the SPP-104s would only work in a ported enclosure. The pliable foam surround would breakdown under compression, not to mention, the lack of rigidity of the cone causing it to be subject to dishpan warping. It would be in 2002 when I discovered a rare 10-inch speaker that had the characteristics I was looking for.
10" Thruster Woofer, Dayton Loudspeaker Specifications:
The Dayton subwoofer has a relatively light moving mass that would allow it to be used with a servo controlled amplifier. Its rubber surround is narrow, made of rigid rubber and will not breakdown under pressure. Also, its dust cap serves as bracing to reduce cone distortion. The cap itself is shaped such as to eliminate harmonics that a normal dome of that size would have. The reason for the 10 inch size requirement is this speaker is a balance of moving mass, cone rigidity, ample excursion and surface area for good air movement. Note. The Dayton 295-165 10" Thruster Woofer is no longer available.
Passive Radiator
Dayton Audio NS310-PR 12” Cast Frame Passive Radiator I needed an adjustable Passive Radiator – one which I could add or remove weight. Originally I planned on making one using a rubber mold and a heavy rigid surface such as a piece of particle board – something with minimal harmonics. Then this thing came along. And yes, I could easily tune it.
In the end, I ended up using two washers in the 1 cubic foot enclosure. These washers are large heavy disks with a center hole. I epoxied them in their place in the back center of the cone – where the voice coil would normally be.
I also adhered a circular sheet of rubber to the front face for additional high harmonic dampening. This radiator has a flat front. The cone has some sort of honeycomb webbing between the cone and the face. As for the servo’s positive feedback, the feedback rolls off below 40 Hz, so it’s not adversely affected by the radiator. The negative feedback or dampening still works well over the whole range.
This NS310-PR passive radiator is interesting in that Dayton Audio used their LS12-44 Subwoofer without a magnet, voice coil and connectors and added a center piece that holds the weights. It makes a good passive radiator, but a not so good subwoofer – which has a whopping moving mass of 166g. Note. The NS310-PR Passive Radiator is no longer available.
The Amps
The next issue was the amplifier. I wished for the clarity of class A architecture, but those huge amps were hideously expensive. They were also not conducive for servo control. I had looked at a number of less expensive A-B amps including Adcom. But their design made it difficult for these amps to be retrofitted with the addition of servo circuitry. It was while reading an obscure hi-fi publication when I stumbled across an article about a company called Velleman which was located in Gavere in East Flanders, Belgian. They sold kit amplifiers, one of which was the K4010 150 watt RMS mono block amplifier that would do class A up to 25 watts.
In 1993, I enticed an esoteric hi fi dealer into going to Dayton, Ohio and purchasing four K4010 amps with two unlabeled metal enclosures with no punched holes for knobs, switched, etc.. He then traded me these for a pair of slightly rusty 1955 A-116 Bud-Box McIntosh 30 watt tube amps.
Prior to getting the amps, Velleman had published the schematic and it was clear to see that the four final mosfets were directly coupled to the output. The way they negated the possibility of DC on the speaker outputs was the same as most high end amps do by including a DC sensing circuit and cut-out relay. In the K4010, this is over half the amplifier’s components. Basically, the actual amplifier itself is a simplistic design and was easy to reverse engineer and modify.
The K4020 Mosfet Amplifier Specifications:
Each of my speakers has one of these integrated onboard two channel amplifiers. One channel is for the subwoofer and the other for the mid-bass, midrange and tweeter. These speakers are considered active powered speakers. Note. The Velleman K4010 and K4020 Mosfet Amplifier kits are no longer available.
The Line Level Input CrossoverSince I planned having duel amplification for each speaker, I needed a way of splitting the input audio into 2 component frequency ranges (the first channel, the subwoofer, and the second channel, the main three speakers. Again, I looked at various options including the pro-audio scene. But to my surprise, pro-audio didn’t have as high of standards I thought they would have had. Even companies like Rane had – or rather didn’t have that good of specs. Besides, most of these crossovers were large 19-inch rack mounted boxes. Then there were bunches on eBay and Amazon which were designed for car audio. I guess head-bangers didn’t really care all that much about audiophile grade high fidelity. I did find one audiophile alternative, but it was hideously expensive and was still in a large box. Then I found the following on eBay.
This crossover was designed by KMTech Design in the UK. It uses the Texas Instruments SoundPlus OPA2134 dual audio-grade op-amp. The crossover is based on 2nd order filters, with a roll-off of 12dB / octave. Technical specifications:
The 8 ceramic capacitors (C1-C8) set the crossover frequency which is determined by the following calculation: Capacitor value in nanofarads = 1 / (0.000138 x crossover frequency in Hz).
*SE System uses 82 nf
Note. The above calculation is specific to this crossover.
The Second Channel Speaker CrossoverI set about to design the speaker crossovers using high grade metal film caps and copper foil chokes.
Crossover Frequencies: 800 and 5000 Hz
In testing the JBL T030 4-inch titanium domed midrange speaker, I found that there was a harsh peak at 1,565 Hz. I then designed a notch filter to flatten this harmonic out.
I took a piece of acrylic, a piece of aluminum L stock, mounted the components on the acrylic board and mounted everything to the back of the 4-inch speaker.
Parts ListSo far, the list of components I was able to obtain included two each of the following
After acquiring the above components – well it would be another five years (2004 age 54, the year I was married for the first time) before I would actually construct the cabinets.
The Boxes |
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The interior of the 10-inch box is 1 cubic foot. The 10-inch box has a 12-inch heavily weighted passive radiator mounted directly on back of the 10-inch sub-woofer box. The interior dimensions of the 8-inch driver box are modeled after the Mackie HR824. The 8-inch is the same speaker used in the first generation HR824. This driver only needed to work down to 80 Hz and therefore didn’t need the passive radiator which is normally on the back of the HR824 underneath the amplifier. There is 6 3/8 inches below the bottom of the amplifier inset to accommodate plugs and such. There is a half-inch venire of plywood around the outside sides of the pressed board speaker boxes. The front of the cabinet has a full coverage bow-front grill cloth cover. The back of the cabinets is just the painted particleboard of the 10” speaker as well as the amplifier inset area of the 8-inch, 4-inch & 2-inch speakers. Located in this area behind the amp is an opening to access the cross over network. ½ to ¾ inch pressed board is used because of its non-resonant sound absorption qualities. The speakers pictured at the top of this page are sitting atop two optional boxes I made to lift them up to a nice listening level.
The ServoThe definition of a servo is a methodology of controlling a motor such that it runs exactly at the desired speed with the appropriate torque. When applying servo technology to a speaker motor (a voice coil and Magnet), the servo circuit addresses several parameters, velocity (frequency) and amplitude. The physical characteristics to consider are moving mass (Mms) and the ability of the motor to move that mass (Bi). Also to be considered is the free air response (Fs) and the amount of air behind the speaker. The total moving mass is the Mms plus the volume of air. The lighter the mass and the stronger the motor means the more efficient the servo system. This means the speaker has to be mounted in as small of a box as possible while allowing enough volume to create the lower frequencies. This increased pressure in the box means the rolled surround must be very stiff yet be free to not impede the speaker cone movement. Also, to get lower responses a longer movement or excursion (Xmax) of the cone is needed. Because of the servo, all of these tight factors go contrary to speaker building methodology. Speaker builders seek to have a very low free air response, a large box, a heavy moving mass, and a short excursion. The detector circuit of the motion feedback servo detects the movement of the speaker through what is called back-EMF or electro motive force generated by the movement of the speaker. To explain: when the speaker is not moving, the power to get it moving is greater than when it is moving. When it is moving or oscillating, the power it takes to keep it moving is less than when it is not moving and it needs to move. If the signal is removed from the speaker, there will be a current generated by the movement of the speaker as its amplitude diminishes. These movements and power requirements can be detected and, through a servo circuit, it can tell the amplifier to vary the amplitude so that the speaker closely produces the sound that is being sent via the preamp. It is the function of the servo circuit to tell the amplifier to increase or decrease the amplitude depending upon the action of the speaker. There may also be times when an inverse amplitude may have to be applied when the speaker is moving too much. The servo circuit will add or subtract current based on the movement of the speaker with respect to the point of the wave being produced. In music terminologies, the terms are called notes (frequency), attack (start), sustain (continuation), and diminish (stop). Attack is the necessity for the mass of a speaker to immediately start at the beginning of the tone. Sustain is the necessity for a speaker to produce the correct tone or note and not a harmonic. And diminish is the necessity for a speaker to stop at the same rate as the end of the tone. Notes or frequency is the capability of the speaker to produce the range of notes at the same amplitude at the required scale.
The SE-10842 Servo
Servo Motion Feedback I designed these speakers not to blast sound, rather to accurately reproduce music. These are not meant to get “LOUD!”, rather to be enjoyed at a comfortable listening level. Most high end audiophile speakers are rather large. This is because the oversizing of drivers is needed to reproduce ample sound which is normally in the lower-middle range of a speaker’s capabilities – where distortion is still at a minimum. But, with that in mind, good and accurate bass response is also necessary. This is where 90% of speakers fall short. This includes $35,000 systems. What they lack is some type of servo to control their bass speakers. Many high-end amplifiers do have some kind of dampening or negative feedback to stop speaker movement after the bass has stopped. But what they lack is what is called attack or an instantaneous start of bass notes. A kick-drum heard through most speakers lacks the real thump; rather what is heard is a momentary subdued tone. The same is true for the plucking of a bass fiddle or cello. What is needed is some kind of positive feedback where the amplifier sends out enough current to instantly start and stop the speaker. Basically, the amplifier needs to know what the speaker is doing in a similar way as a hard drive controller knows where its heads are on a disc. There are two ways a servo speaker can tell an amp what it’s doing. The first is a less common methodology which includes an accelerometer. This is a special device built into a speaker that acts as a variable capacitor, varying its capacitance proportionally to the movement of the speaker. The second is to return or send the back-EMF of a speaker back to the amplifier. An accelerometer is a little more accurate and the attack is a tiny bit quicker because there is no hysteresis with a capacitor. However, this methodology requires special speakers with built-in accelerometers – which, because of their intricacies as well as their specialized use, are quite pricy and rare. Back-EMF requires no special additions to a speaker other than the speaker should have a light moving mass and a rigid supported cone. Mackie decided on this approach when they designed their HR824 studio monitors. Also, a servo circuit design is easier to implement.
Not So Common ComponentsAbout the above notes on availability of the various key components: the reason Velleman K4010 amplifiers are no longer available is their cost. 90% of people seeking stereo power amplifiers had a large variety of types available for half to 1/3rd the cost. Also, the K4010 mono and K4020 stereo amplifier was available in kit form only. Also, the reason the aforementioned speaker drivers are no longer available is there was not enough of a demand for these to allow their production to be profitable. These components were designed during a time when there were enough US amateur audiophile speaker builders who were still designing and building systems to accurately reproduce sound. Most of these speakers were purchased by buyers who didn’t understand their purpose. As a consequence, they were disappointed in their performance. They thought they were buying drivers that were similar to other drivers and as such mounted them in inappropriate enclosures. Meaning, they didn’t kick ass.
Is There BetterVery few people have actually heard an electrostatic speaker system. During the years when I could hear nearly 18 kHz, I had the opportunity to hear a set of Quad ES speakers. The sound was unbelievably accurate. The orchestra was as if it were live in the space I was listening to it in.
The reason for this is an electrostatic capacitance speaker lacks an anomaly known as hysteresis. Magnetic hysteresis occurs when an external magnetic field is applied to a ferromagnetic metal such as steel and the atomic dipoles align themselves with the field. After the magnetic field is removed, part of the alignment will be retained: the material has momentarily become magnetized. Once magnetized, the steel will stay magnetized for some period of time. To magnetize it in the reverse direction requires a magnetic field of equal force in the opposite direction. The hysteresis curve shows this anomaly with the y axis being the forward and reverse magnetic fields and the x axis being time. What the curve shows is the time it takes for the speaker to start responding to a frequency. Though a servo does help with lower frequencies, the midrange and tweeters do lag a bit. Though this may not really be noticeable, when listening to an electrostatic speaker, this becomes readily apparent to the finicky experienced ear – such as a musician who plays in an orchestra.
Martin-Logan Electrostatic Speaker Element Design |
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The ES speaker does not have a problem with hysteresis because it is electro static energy that moves a thin membrane between two electrodes. Note. An electrostatic speaker is rather inefficient because the energy it takes to move its membrane is thousands of volts, which requires a higher wattage amplifier to get sufficient amplitude. The problem most head-bangers of 2019 find with electrostatic speakers is dynamic range. They don’t get loud enough. This was also true for audiophiles even as late as 15 years ago. Today the two or three remaining manufactures that build ES speakers have, with significant improvements in the diaphragm membrane material, designed these speakers to have a reasonable dynamic range. When I decided to build my speakers, these electrostatic speakers were extremely pricy especially on my yearly income of $35,000. Today one can get a pair of ESL 8s on Amazon for $2,500 which is about the same price they asked for a set in 1998. But, back then 2.5k was $4,000 in today’s dollars. Today's would-be coveted system is made by a company called Martin-Logan. Not only are they exceedingly accurate and clear, but the sound emanates from one source. This is called the sound envelope. Envelope, in musical sound is the attack, sustain, and decay of a sound. Attack transients consist of changes occurring before the sound reaches its steady-state intensity. Sustain refers to the steady state of a sound at its maximum intensity, and decay is the rate at which it fades to silence. This envelope also contains all of the frequencies. In a normal speaker, the various ranges are divided up and played through different speakers. This can cause cancellations and distortions when the sound is recombined. In electrostatic speakers, all the sound emanate from one source. Martin-Logan has also solved another issue with their speakers and that is dispersion. This is sound that is dispersed in a wider angle allowing the listener to be in different places and still clearly hear the music without having to be in what is called the sweet spot. When I designed my speakers, I used the JBL titanium speakers not only because of their clarity, but also because in the frequency range they were to be used, both the midrange and tweeter had a wider field of dispersion than the norm. Admittedly, the ideal symphony listening experience would be with either 192 kHz at a 24 bit sampling rate digital, or a clean LP – this with a $4,000 set of Martin-Logan ESL Xs and a class A amp between. However, because I could only afford to build my own speakers, with titanium mid-ranges, they sound almost as good. Plus mine can kick some butt. Also, Martin-Logan woofer drivers are not servo controlled.
Regrets?It may seem by the list of components and parts listed above that I may have spent thousands on the SE-10842 speakers. However, the materials used for the enclosures were left over from various projects such as pressed board from kitchen countertops, plywood from cabinets, and the front grill-cloth I had for years. The Vifa 8-inch speakers came from BG Micro where I got 4 of them for around $35.00 each. The 10-inch speakers were on closeout for $40.00 each. The amplifiers came from swapping a guy two old rusty mac amps that were in my cousin’s family for – I don’t know how long. I did get the titanium speakers at a significant – well loss for my colleague because he had used them for a short time. I think it was $150.00. The passive radiators were a Hamvention find at $25.00 each. I was damn lucky to find those. They had been previously closed out. The only real expensive things were the components for the speaker crossovers. Because they were high-end capacitors and coils, I think I paid over $300.00 for all that stuff. Also, I lost $200.00 on the 4 Rockford Fosgate speakers when I sold them. This was way before eBay. All-in-all, I’m pleased. They’ve been in use for over 14 years. I did replace the mosfet finals last year. Over the years, I also went through two or three iterations of preamps until I settled on a class A preamp from China that seems to be working really well. No noise. No hiss, perfectly flat, 0.00003% THD, etc.
Class A LME4972HA Preamplifier
Left out of the above preamp image is a modification of the addition of a set of 600-600 nickel core unbalanced to balanced transformers. This was added because the integrated amplifiers in the speakers are fed by lengthy audio cables – balanced cables eliminate line noise. So, am I pleased? Yes. Life is good. The music is good – or rather, excellent. Stephen - April 2, 2019
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