Explorations in Audio

Karsten Hein

Are you ready to Explore?

In 'Explorations in Audio' I aim to share some practical insights on setting up and optimising an affordable HiFi system. Although one would think that, really, all has been said about HiFi, some surprisingly simple questions still remain, e.g.: 'Is digital superior to analogue?' 'Do cables matter?' 'Can digital cables pick up interference?' 'Should speakers be placed on spikes?' 'Has evolution in HiFi made older gear obsolete?' 'Where should I place my sub?' 'Which room correction works best?' - On the other hand: 'Are these really the right questions?' - We shall see.

What's new in eiaudio?

While the entries in this blog are divided into the three distinct categories above, you will find a mixed listing of the most recent postings below. The most recent article is shown first. If this is not your first time visiting, the listing below is a good place to quickly check if anything is new.

Your input is more than welcome, as long as you follow the basic audiophile rule of ‘ear over mind’. This means that you do not comment based on what you think you know, but only on the basis of your own listening experience. Please feel free to suggest gear for testing as well as leave comments on the descriptions provided here.

  • Sony CDP-502ES

    Sony CDP-502ES

    16/01/2023

    Author: Karsten Hein

    Category: Gear & Review

    Tag(s): CD-Players

    [Test in progress. Full review coming up soon.]

    Specifications

    • Type: Compact Disk player
    • Laser principle: GaAlAs double hetero diode
    • Disk revolutions per minute: 500 ~ 200 (CLV)
    • Paying speed: 1.2 - 1.4 m/s
    • Error correction: Sony Super Strategy
    • DAC compound: 16-bit, straight line
    • Frequency range: 2 - 20,000 Hz (+/- 0.3 dB)
    • Harmonic distortion: < 0.0025% (1 kHz)
    • Dynamic range: < 96 dB
    • Wow and flutter: below measurable limits
    • Line output: 2 Volts
    • Headphone output: 28 mw (32 Ohms) 
    • Power consumption: 16 watts
    • Dimensions: (W) 430mm x (H) 80mm x (D) 335mm
    • Weight: 8.5 kg
    • Accessories: Wireless Remote, RM-D502
    • Country of manufacture: Japan
    • Year(s): 1984-1987

    Jörg Hegemann
  • Kenwood Basic M2 Sigma Drive

    Kenwood Basic M2 Sigma Drive

    14/01/2023

    Author: Karsten Hein

    Category: Gear & Review

    Tag(s): Power Amplifiers

    Having previously reviewed the Kenwood KR-9400 receiver of the mid 1970s, with its posh-looking brushed aluminum face plate, solid aluminium buttons and switches, all housed in a an assembled metal frame that had originally been flanked by wooden sides, the black box design of the Kenwood Basic M2 with its thin, bent metal enclosure of the mid 1980s was a bit of a let-down. The M2 shared this aesthetically reduced, light-weight design with most of the competing products of its time. Where, just ten years earlier, innovation had been in the machining and assembly of parts, this next phase was mostly about experimenting with the electronics inside, to eliminate the shortcomings of the earlier circuit designs.

    The 1980s were also a time of increased price competition. With more companies entering the market in the lower and mid-price segment with gear that fulfilled the basic demand of the average consumer, material and shipping costs needed to also come down on some of the established brands in the market. Kenwood was such an established brand, and the M2 Basic chassis offered 100 watts per channel more than the KR-9400 receiver and, proving the point, weighed five kilos less. Five kilos of net savings in materials and shipping weight would have made a considerable difference in the cost planning of a company that could sell thousands if not millions of iterations of each product.

    In terms of assessing vintage equipment, the modern mass-market approach often lead to the immediate depreciation of value, once the manufacturer’s warranty period had expired. However, this did not necessarily mean that the sound quality itself was compromised or that the inner circuitry similarly reflected the mass-market approach of the chassis. In fact, the 1980s were still a time of HiFi innovation, and the M2’s Sigma drive introduced an all-new solution to the age-old challenge of handling the dynamic back current running from the loudspeaker to the amplifier. Instead of simply offering ultra-low internal resistance and measuring signal damping at 1,000 Hz, Sigma drive took into account the real feedback of the loudspeakers, regardless of the frequency.

    In the tradition of decent High End power amplifiers, the Basic M2 used a separate power supply for each stereo channel. This was to lower the noise floor by eliminating cross-talk between the channels. The two heavy transformers were place to the left side of the amp, thus leading to an uneven distribution of weight within the unit. The main board holding the two large capacitors per channel was located in the centre of the unit, culminating in the power transistor section with one large heat sink and a large cooling fan to the right. In domestic operation, the cooling fan would not play much of a role, but for owners willing to drive their M2 at full capacity, the fan would provide a safety net for the survival of the transistors.

    The Basic M2 employed two pairs of transistor ICs: one set of DAT1521P / DAT1521N and one set of DAT1018P / DAT1018N, all of them fast switching 5-pin power MOSFETs made by Sanken. Especially the DAT1018P/N variety saw repeated supply shortages in recent years which would have made repairs of the amplifier section more difficult. The choice of fast switching ICs would have provided the Basic M2 with greater resistance to high frequency feedback which would otherwise have exceeded the slew rate of the amplifier. The new Sigma drive circuitry would have similarly benefitted from the choice of ICs.

    The Sigma drive was designed to integrate the physical behaviour of a dynamic driver and the resulting dynamically unpredictable back current within the circuitry of the amplifier by monitoring the resulting deviation right at the speaker terminal and converting it into a mere current variation. As amplifier output constituted a voltage surplus, the ability to maintain voltage deviation at zero, by means of adaptive damping, led to exceptionally low harmonic distortion of just 0.004% measured across all frequencies. Effective back current damping was rated at above 1000:1 beyond the audible spectrum. With the new Sigma drive feature on board, Kenwood introduced a new dimension in noise control that had the audio press of the 1980s interested for some time.

    Kenwood was not the only HiFi manufacturer attempting to improve back current handling. Yamaha introduced “RO Control” on their B-4 and A-9 amplifiers, Aurex called their version “Clean Drive”, and Fidelix referred to their concept as “Remote Sensing NFB”. However, none of these technologies went as far as that of Kenwood which included measuring the whole loudspeaker from the voice coils to the speaker cable. This would have given Kenwood the upper hand in achieving the most accurate readings, if it had not been for a few issues that involved the use of two strands of speaker wires which needed to be connected in a fashion that was somewhat counter intuitive.

    For the Sigma Drive circuitry to work its magic, two sets of wires needed to be connected between the amplifier and each speaker. Next to the common red and black binding posts per channel, there were two additional binding posts on the amplifier that were labelled as Sigma Sensor. Therefore the second set of wires ran from the Sensor posts, quite counter intuitively, to the same binding posts on the speakers. This feature was only available for the speakers A and not for the speakers B. This meant that owners of the amplifier hat to study their operating manuals carefully in order not to misconnect and destroy their amp. When connecting the amp for the first time, I therefore asked my wife to look over my shoulder and assure that all instructions in the manual were followed.

    When connected correctly, the rather power hungry Basic M2 offered a spacious and clean sound that was tonally rich and slightly dark in true Kenwood fashion. Hooked up between our Dynaco PAS-4 preamplifier and Martin Logan SL-3 electrostatic speakers, the music sounded soothing and voluptuous rather than exciting or sharp. This was an amplifier for easy entertainment rather than analytical listening. For an amplifier of this size and caliber I was surprised by the amount of control it held on the flow of the music and on the rhythm. Where the Kenwood receiver sounded overly eager to tell the whole story all at once, the Basic M2 seemed to hold back, occasionally to the point of stomping and drudging. This may have been the effect of transients being cut short, and it sometimes took the fluidity from music event.

    I was generally pleased with the Basic M2’s performance. Connected to a difficult load as the Martin Logan SL-3, the Kenwood could really show its back current handling abilities. In combination with the two sets of OFC multi-strand speaker cables that I had available to test the Sigma Drive, I would hesitate to brand it audiophile material. However, it was well possible that a different combination of wires and preamplifier would have led to a more revealing result. Tonally rich and dark, the Kenwood followed the preferred sound signature of American customers of the time and thus offered a welcome contrast to the established European brands.

    Specifications

    • Type: Stereo Power Amplifier
    • Special features: High-damping, Sigma Drive
    • Power output (8 Ohms): 2x 220 WPC
    • Power output (4 Ohms): 2x 324 WPC
    • Frequency response: 1Hz to 200kHz (-3 dB)
    • Total harmonic distortion: < 0.004%
    • Dynamic headroom: 1.5 dB (8 Ohms)
    • Damping factor: 1000:1
    • Transistor-ICs: Sanken DAT1521P/N, DAT1018P/N
    • Transistor type: Power MOSFET (5-pin)
    • Rise time: 1.8 uS
    • Slew Rate: 100 V / uS
    • Input sensitivity: 1.0 V / 47 kOhms
    • Signal to noise ratio: > 120dB
    • Speaker load impedance: 4 to 16 Ohms
    • Power consumption (max.): 1.350 watts
    • Dimensions: (W) 440mm x (H) 158mm x (D) 373mm
    • Weight: 15.5 kg
    • Country of manufacture: Japan
    • Year(s): 1983-1985

    crossXculture Business Language Training
  • Robert Grodinsky Research RGR Model 4

    Robert Grodinsky Research RGR Model 4

    14/01/2023

    Author: Karsten Hein

    Category: Gear & Review

    Tag(s): Pre-Amplifiers

    The Model 4 was the successor of the Model 3 preamplifier and was built by the American audio engineer and former Audio Research (ARC) developer Robert Grodinsky in his newly founded company. The Robert Grodinsky Research (RGR) was based in Lincolnwood, Illinois, and built a select range of High-End audio equipment that included its own brand pre and power amplifiers, as well as processors for other companies, e.g., Audio Research, Koss, and Pioneer). Robert Grodinsky himself also offered tuning and upgrade solutions to owners of Audio Research equipment.

    The Model 4 came in various sub-versions that mostly differed in the design and functions of the phono stage. The basic model came with two phono inputs on which the capacitance could be independently adjusted in three steps: 30, 130, 360 pF. It was designed in the early 1980s, when phono was still the most likely source for High-End audio listening. Having two adjustable inputs would have made the Model 4 a welcome feature for vinyl heads of the time. Early versions offered moving magnet (MM) inputs, whereas the revised Model 4-1HG featured inputs for MM and moving coil (MC) cartridges.

    The renowned HiFi magazine The Absolute Sound made Robert Grodinsky Research famous by discussing the merits and shortcomings of the Model 4 at length. While the soundstage was deep and wide with an open and holographic representation of music, the Model 4 was also a departure from the slightly darker and fuller American sound. As such, the Model 4 was more similar to the High End sound familiar from Germany and Japan. The phono stage was described as outstanding in the given price range. As Robert Grodinsky continued to make adjustments to the Model 4 design throughout its 2-year history, it will be difficult to find two preamps that sound identical.

    At 6.5 kg, the Model 4 was of surprisingly heavy build for a preamplifier. All controls were made of metal with the knobs being L-shaped. Volume was set via stepped attenuator. The active signal source was indicated via warm-glowing LED light. There were two buttons to set the tape dubbing direction and two buttons to activate the tape monitors which could also be used as pass-through to other components. A versatile Mode-selector allowed the user to play the left or right channel signal independently, to reverse channels, or to down-mix the output signal to mono. For those working with HiFi or PA equipment professionally, features like these could come in very handy, e.g., when trying to identify and correct an electronic or acoustic issue.

    The RGR Model 4 also included knobs to adjust bass, treble, and balance to the room, as well as a subsonic filter for eliminating rumble and feedback that would typically come from playing records. It was surely a concession to the High-End purist and not the PA user that the tone controls could be fully discharged from the signal path at the touch of a button. All buttons and switches gave great haptic feedback, except for the small switches at the back of the unit that were used to adjust phono capacitance and that were sometimes described as imprecise and below expectations. Another such quirk from today’s perspective was the unusually narrow gab between the cinch/RCA sockets that allowed for standard diameter cinch/RCA plugs only. However, with the cinch terminal being bolted in with studs and the internal free wiring, it would be an easy task to upgrade the terminal to the modern standard. 

    The Model 4 also featured an external processor loop, a field that Robert Grodinsky was an expert in. A look inside of the unit revealed a large motherboard on which smaller modules were vertically stacked. These modules functioned as discrete operating amps and were used to produce signal gain. Perhaps it is this particular design that led to the Model 4’s non-fatiguing and airy sound that provides good sound-staging, imaging and bass. There was also a Model 5 power amplifier to accompany the preamplifier which has meanwhile become quite rare on the market. While the early Model 4 was sometimes criticised for its build quality, particularly the quality of its soldering, the Model 5 amplifier was seemed to have been under better supervision right from the start. 

    Robert Grodinsky Research closed its doors in the early eighties only to resurface under the name RG Dynamics shortly after. It is said that Robert Grodinsky was also the driving force behind a later company by the name of State Technology Research.

    Specifications

    • Type: Solid state stereo preamplifier
    • Version: Mark I (without MC connectivity)
    • Phono inputs: 2x moving magnet (MM)
    • Phono adjustments: 30, 130, 360 pF capacitance
    • Phono equalisation: RIAA +/= 0.1 dB
    • Line inputs: 2x Auxiliary, 2x Monitor
    • Tape record outputs: 2x cinch/RCA
    • Rated output voltage: > 2.0 V
    • Harmonic distortion (1 kHz): < 0.005%
    • Intermodulation noise: 0.006%
    • Power bandwidth: 0.5 Hz to 300 kHz
    • Frequency response: 20 Hz to 20 kHz (+/- 0.05 dB)
    • Signal-to-noise ratio: Phono MM/MC: > 80 dB
    • Signal outputs to amplifier: 4x line/RCA
    • Tone controls: Bass (20 Hz) +/-12 dB, Treble (15 kHz) +/-12 dB
    • Dimensions: (W) 484mm x (H) 95mm x (D) 300mm
    • Weight: 6.5 kilograms
    • Country of manufacture: USA
    • Year(s): 1980-1982

    80s night
  • Shure 701 Pro Master for Modern PA?

    Shure 701 Pro Master for Modern PA?

    13/12/2022

    Author: Karsten Hein

    Category: Explorations

    Tag(s): Loudspeakers

    When I first carried our freshly acquired Shure 701 Pro Master series speakers from their private seller near Marburg to our car, I remember thinking how unfair it was to be dragging these public address classics from one private household to another. Being in excellent condition, they well deserved to delight audiences at public venues. Back at our house in Frankfurt, I ran some tests and found that they actually had some audiophile potential, at least in the upgraded way they were presented to me, with a new crossover installed and their horn decoupled from the back wall of the speaker cabinet. And so, I proceeded with the construction of two solid wooden stands for them and enjoyed listening to them for a while. This was in June 2022, and I am happy to report that Mark Knopfler’s guitars had never sounded so good at our house.

    When my brother approached me shortly before Christmas that year, asking me if I had an idea of which speakers he might recommend to solve the sound issues at the organisation he worked for, I remembered the Shures with their 102 dB of decibel output at just one watt and thought this might just be their chance to play a public venue once again. On the other hand, I did not want to sell my brother an audio solution that was not also in the interest of his employer. Frankfurt’s Gallus Zentrum was a publicly funded youth organisation that did media projects with school children and young adults. They were looking for speakers that would serve as the main sound source at video events with kids and also with the general public. Thus far, they had used a pair of smallish Canton bookshelves for this purpose, of which one had recently died and been replaced with a small JBL Control 1 Pro. Neither of the speakers was ideal for the purpose.

    We decided that I would bring the speakers to the Zentrum for auditioning. My brother was kind enough to help my carry them down the many flights of stairs in our building and into the car with me. After all, twenty-six clunky kilos per speaker was an unpleasant load to be carrying alone. I had not been to the Gallus Zentrum for a long time and was happy to find it in the same industrial style design as I had last seen it. The main listening room was almost 14 meters in depth, seven meters in width, and 3,30 meters in height. There was a slightly elevated wooden stage at the front with creaking floor boards and a photo canvas perched along one side wall. The room was almost completely unfurnished, and even the few chairs present were of simple wood and without cushions. There was nothing to prevent the sound from bouncing back from the walls, floor, and ceiling, and I could see that this would lead to some issues.

    We first listened to the existing loudspeakers that were driven by an Apart Audio Champ 2 amplifier. I knew this amplifier well and could see that its 200 WPC into 8 Ohms were able to provide enough power for a venue of this size. The Canton speakers had been attached near the ceiling in each of the two corners of the front wall. Jörg played a movie that had been created with the Zentrum’s young customers, and we both had trouble to understand the words that were being spoken. A combination of factors lead to this phenomenon: The source material was a non-professional recording made with non-professional actors. The bookshelf speakers did not give the sound direction. Instead, the sound waves were emitted at a wide angle and consequently bounced around the room. The Cantons being full-range speakers, the corner placement made them sound overly boomy and resonant in the room.

    When Jörg turned on a second set of speakers that was connected to another amplifier and mounted on the side walls in the second half of the room, there was a small delay between the sound sources that further muffled the sound. I suggested that we try a different source material, and we switched to Simply Red’s 2005 “Cuba!” concert on YouTube. However, the sound only improved slightly and remained largely unattractive. The big question was, if the Shure 701 Pro Master would be able to improve what seemed to be a hopeless situation. To be honest, I did not know myself, because I had never before set up loudspeakers for public venues. And, considering the width of the speakers, I also understood that our options for placing them in the room were somewhat limited. After all, we did not want the Shures to get in the way of the large video projection area that required most of the front wall surface to remain empty.

    My brother operated the audio/video equipment from an elevated control room that oversaw the stage area and could be reached via an old iron ladder. For the Shures to be connected to the Apart Audio amplifier, we had to run a new set of wires from the speakers to the amp. I think we were both more than a little surprised to find that our 2x 25 meter rolls would just be long enough for a permanent installation. We started our sound explorations by placing the Shure speakers at some distance to the front and side walls. They were parallel with the walls, and the resulting sound was less boomy, and high frequency reflections were similarly reduced. When sitting down on the stools in the audience, however, we both noticed that we were only able to listen to one speaker at a time with no trace of stereo-effect. There was also a slight lack of bass in many positions of the room.

    When we turned the projector on, the Shures blocked part of the screen area, and we began moving them towards the side corners. Bass performance improved without being boomy or accentuated. And toeing the speakers in towards the center of the room further minimised side wall reflections. There was an unnatural squeakiness to the sound that had been even more prominent with the Cantons that was most likely the result of the bare floor, ceiling and walls, but overall, the resulting sound was much more enjoyable than before. I could now see myself attending an event at this location and reporting positively on the sound. The latter had been quite unthinkable before. And, to our surprise, adding the second pair of speakers to the equation further enhanced the sound in the room. The time delay had disappeared. Adding substance to substance, the large room was now naturally alive with music.

    My brother and I ended the evening by putting the speaker cables into the available ducts along the walls and left the scene looking sophisticated and tidy. Following the weekend, Jörg showed his colleagues the resulting sound and discussed the size and usability of the speakers. Everyone agreed that this improvement to sound would raise to appreciation of the film events to a new level with students and the general public. And so it happened that my newly founded eiaudio company officially sold its first set of speakers. I was very proud of having been a part of this improvement of sound quality and also enjoy knowing that the Shures have found a new home in which they naturally belong and can perform at their best.

    From the experience, I learned that loudspeakers for public address offered bass response that took into account the characteristics of large rooms and did not so easily lead to an overly bass-heavy sound. Proper PA speakers sounded at their best when driven at higher than living room volumes, simply because the materials used were more difficult to excite and more difficult to break. Horn loudspeakers were designed to minimise room reflections by channeling the sound towards the listener without this bouncing off the side walls on the way. The Shures were quality PA loudspeakers, even after all these years, that served the purpose of the Gallus Zentrum well. I wish Jörg and his team lots of success in their projects next year. May the Shures be with them.

    < Watts, Sound Pressure, Decibel | Shure 701 Pro Master Review >


    Digitising Records
  • 29. Room Mode Calculations

    29. Room Mode Calculations

    11/12/2022

    Author: Karsten Hein

    Category: High Fidelity

    I first heard the term ‘room mode’ mentioned when a friend of mine came by our house to audition our newly acquired Martin Logan SL-3 electrostatic loudspeakers with me. Jens, who had spent some years composing music and collecting analogue modules, was not immediately taken in by the large sound canvas of the Martin Logans and instead pointed out that there was an obvious lack of bass-slam from such large speakers. He went on to suggest that this lack might be attributed to room modes and that proper alignment of the speakers and the listening position might fix it. However, as I did not understand what he was talking about, I rather believed the speakers themselves to be at fault. I wondered, if the crossovers had been tampered with, if they needed to be recapped, if perhaps the amp was too weak, or if the Mylar diaphragm had somehow lost its magnetisation. When Jens left later that night, I was therefore feeling quite shattered.

    The next person to visit us was my audiophile companion Luigi. He listened to the Martin Logans, was not especially pleased with their ‘tall stage’ impression which resulted from their sheer height, and started moving them around the room with me. He suggested that greater distance to the front wall would improve imaging and stage depth, and I tentatively agreed with him. We found a position about 1.10 meters into our 5.60 meters deep room that worked well, and we both left our session in a mental state of unsettled turmoil. The Martin Logans were not so easily placed because of their dipole nature. Even one centimetre of deviation in wall distance could mess up imaging, tonality, rhythm, phase coherence and speed impression. It then took me another four weeks to determine the exact position for the SL-3 to finally lock in with our listening room. 

    I spent the next months upgrading the amplifier and improving the wiring. I also found a CD player that sounded more analogue and a phono cartridge with improved tonality. I sorted out grounding issues, eliminated trailing edge transformers from the proximity of the system and could hear gradual improvements with each step. Upgrading to solid-core silver cinch/RCA interconnects offered superior dynamics, and symmetrical power cords served to bring about the finishing touches. The system had become revealing and tonally rich. The sound stage was impressive, even if a little taller, as Luigi was quick to point out. The position of the speakers had been found by ear over the course of many months. I could hear that 1.12 meters distance worked well, but I did not know why this was. In fact, I was feeling uneasy about swapping speakers to run new tests for eiaudio. Luigi joked that he had some friends who were so scared to lose what they had accomplished that they set their systems up for life. That prospect did sound pretty sad.

    I did not want to be that kind of audiophile. Instead, I preferred to stay true to my mission of exploration that is proposed by the title of this blog. I needed to find a solution of how to set up speakers quicker with more assurance of having found the best position. Then, one day, as I was standing at the shack of my favourite audio technician, I heard him speaking to one of his customers inside. I did not want to interrupt, but as I was listening, I noticed that his customer was speaking very soberly about some basic issues in HiFi that had also troubled me for some time. I could feel that we were kindred spirits and decided to step inside. We were quickly introduced and started speaking about the subject of cables, interference, and grounding, carefully checking each other out, because some people can be quite stubborn insisting that their current state of knowledge should be the end of everyone’s explorations. We were both relieved to find that this did not seem to be the case. At the end of our talk, I gave Peter Englisch my eiaudio.de business card and invited him to join the blog discussion. He said that he would have a look, and we went separate ways. 

    Some weeks later, I gave Peter a call, and he seemed happy to hear from me. As it turned out, he had read all my articles in the High Fidelity section and was somewhat pleased with the contents he found. He pointed out that, in some of the articles, although my description was accurate, it was also apparent that my grasp of the subject did not yet allow me to present the issue in a nutshell or state the single cause of an issue. I agreed that this was most likely the case, because I had not first studied the subject but instead worked my way towards a solution while moving from the practical application towards the theory. I felt proud of the progress I had made in just over two years, and he offered to help me take it a little further. Peter informed me that he had written a number of Excel sheets that allowed him to enter room dimensions to derive from them the best possible speaker positions. He offered to send me his spread sheets and promptly did so later that day. I confess that it took me a few weeks do get over the shock of seeing so many numbers and graphs on each page. With some time, however, the initial panic subsided and allowed me to work with the sheets.

    I took our laser length meter and measured the inner dimensions of our main listening room to be 5.58 meters in depth, 4.78 meters in width, and 2.78 meters in height. The walls had some furnishings which would have some impact on sound, and I considered the resulting alternative measurements where the furniture affected room dimensions at ear level. Most prominently, there was one Ikea Besta cupboard that narrowed the left side wall by 0.43 meters at the listening position, resulting in 4.35 meters width. Upon entering the results of my measurements in the Excel sheet, I saw that each of the three dimensions (h, d, w) was treated separately without apparent effect on the others. The Excel sheet also did not care if the height and the width value were swapped: The results looked the identical, although one would probably notice the mistake in entry when setting up the speakers in this way. I found that a greater wall-to-wall distance always led to lower resonance frequencies, of which there were three: the first room mode, the second, and the third.

    The first room mode was the strongest and the result of the speed of sound of around 340 m/s interacting with the space between the room walls. The other two were harmonic resonances that occurred at double and tripple the frequency of the first room mode. Since sound waves peaked along the room walls where they were reflected backward, the nulls were spread across the room. For the first room mode, the null was at half the room depth (at 2.79 meters in the case of our room example). I learned that sound waves were different from electrical waves, as the floor of a listening room folded the bottom half of the potential sine wave upwards, thus placing the first resonance frequency at half the calculated resonance. The resulting calculation for the room depth resonance was: 

    340m/s (speed of sound) ÷  5.58m (room depth) = 60.93 Hz (sine wave)

    60.93 Hz (sine wave) ÷ 2 = 30,47 Hz (1st Resonance)

    The second depth resonance was at 60.93 Hz and produced three peaks in the room. Next to the natural peaks at the walls, the third peak was in the room center. The resulting two nulls were at the center of each room half, as if there was a wall between the halves where they could also accumulate. The third resonance was at 91,40 Hz and acoustically divided the room in three. The graph looked as if two separating walls were separating the three parts producing a null in each center and a peak at each imaginary wall. This created three nulls and four peaks over the total room depth.

    Since resonances could accumulate or cancel each other out, the best positions for setting up speakers and for the listening position were those in which the specific room resonances produced a natural balance in the relevant frequencies. In his descriptions, Peter referred to these locations as preferential positions. And although their factors remained the same for normal rooms, the resulting value would change with the dimensions of each listening room. The factors for the calculation of the preferential positions were:

    Factors: (+3) 0.125 — (+2) 0.2 — (+1) 0.45 — (-1) 0.55 — (-2) 0.8 — (-3) 0.875

    Results: (+3) 0.70 m — (+2) 1.12 m — (+1) 2.51 m — (-1) 3.07 m — (-2) 4.46 m — (-3) 4.88 m

    The distances provided in meters underneath each factor show the preferential positions for our room depth of 5.58 meters with all distances being relative to the front wall. The factors with negative numbers are actually mirror images of the first three factors and could more easily be measured from the back wall using the first three values. The mirror axis being at 0.5, which is half the room’s depth. I could see that the room dimensions had an effect on the first resonance frequency and the two harmonic counterparts, with larger rooms having lower resonance frequencies. The lower the frequency, the easier it was to place speakers in the room without interfering with our ear’s most critical frequencies, which are commonly around the spectrum of the human voice.

    Doing the calculations for our upstairs listening room produced far lower resonances than our main listening room. The upstairs room, which also served as our office, measured 15 meters in depth and 11 meters in width. There were no parallel walls, and also the ceiling elements were of various heights. The room depth resonance frequencies were 11.3 Hz, 22.67 Hz, and 34 Hz correspondingly. The resulting preferential positions were:

    Factors: (+3) 0.125 — (+2) 0.2 — (+1) 0.45 — (-1) 0.55 — (-2) 0.8 — (-3) 0.875

    Results: (+3) 1.88 m — (+2) 3.0 m — (+1) 6.75 m — (-1) 8.25 m — (-2) 12 m — (-3) 13.13 m

    When looking for the preferential positions for loudspeakers with respect to the width of the room, placing the speakers in mirrored positions along the room’s center axis would have produced a null in the listening position, because the latter was then located in the center of the room to form an isosceles (if not equilateral) triangle with the speakers. To avoid this effect, positions of varying wall distances had to be preferred. For our smaller 4.78 meters wide room, this could for example be a combination of factor 0.125 = 0.60 m and factor 0.2 = 0.96 m. The width distances were measured from each speaker’s center axis to the wall, whereas the depth distances was measured from the woofer’s voice coil to the front wall.

    In larger listening rooms, the highest order resonances were quite frequently produced by the limited ceiling height of the room. In our 2.78 meters high room, the resonances were 61.15 Hz, 122,30 Hz and 183,45 Hz. Preferential positions were calculated to be at factor 0.125 = 35 cm and factor 0.2 = 56 cm. The vertical distances were measured from the central axis from the largest woofer to the floor of the room and had to be identical for both speakers.

    The main listening position ought to form an isosceles triangle with the speakers. If the result was an equilateral triangle, this was even better. For the tonal balance, however, it was of far greater importance that the listening position corresponded with one of the preferential positions in the room. Once we began positioning the speakers and ourselves according to these factors, the first outcome was already quite acceptable. And it was from this assurance the we were able to begin with the fine tuning of the speakers to the wall materials, carpeting, and various furniture by moving the them a few centimetres or moving the listening position slightly in order to compensate for unwanted room accents. I found Peter’s method highly useful and will keep it in my toolbox for any upcoming adjustments.



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