Loudspeaker using MarkAudio "OM-MF4-MICA" - part 4 - Listening impression and measurement

First, I adjusted the 250 Hz peak when combined with the lower cabinet. However, I only had to add a little sound-absorbing material in the middle of the duct.

Since I did not have a proper sound absorbing material on hand, I substituted aquarium filter mat. The material was probably polypropylene, 8mm thick. The only place to put it in was at the first fold, and I just pushed it in from the duct entrance.

First, I compared each frequency response.　The results of the measurements with the "Audio Frequency Analyzer" are as follows (without sound absorbing material = upper figure, with sound absorbing material = lower figure).



As expected, the one with sound absorbing material was about 2dB lower at 250Hz. If the amount of sound-absorbing material is increased, it should decrease even more.
However, it might block the sound path, so I left this one piece alone.

I finally got around to listening.

Usually I play CDs that I have on hand and listen to them as I go along, but this time I had to hear how the different methods would change the sound.

I used a sample CD from the January 2011 issue of Stereo magazine.

This time, I chose classical and jazz from these recordings because I wanted to hear the difference especially in the low-frequency direction.

　12. Saint-Saëns: Symphony No.3 "Organ Symphony"
　13. Ornette Coleman: Bird Food/Trissonique

The left-right spacing was about 1 m, and the listening position was about 2 m away from the SPs. Sealed and both bass reflexes were performed with TAOC stands, and the acoustic maze was placed on the lower cabinet.





The sealed system is designed to be used on a desktop, with the ducts blocked by a board. For the bass reflex (upward-facing) system, the board was shifted so that the duct would be open.

The feeling of each method was as follows.

- Sealed box:


The timpani percussion was light, and it was difficult to hear the descending part of the organ scale. Although I could hear the pitch of the bass, the sound of the strings hitting the fingerboard seemed louder.

- Bass reflex (upward-facing):


The timpani percussion was rather audible. The organ scale was also not well resolved. The sound of the fingerboard still seemed to resonate.

- Bass reflex (downward-facing):


The timpani percussion became more prominent and the tutti was more powerful. The volume of the wood bass could be felt.

- Acoustic Maze:


The scale of the orchestra sounded a whole lot larger. I could hear the pitch of the organ. The bass guitar sounded more powerful.

Since this is just a subjective impression, I measured the frequency response of each piece.

I set up the iPhone at the listening position (1.8m, about 15° to the loudspeaker) with the left channel only, played a song, and checked the frequency response with peak hold.

Before that, I examined the characteristics of the music source itself with "Music Frequency Analyzer". This application can digitally analyze ripped music data. The following result is a peak-hold analysis of the frequency response of the entire music source.



"Organ Symphony" was nicely smooth over the entire frequency range.



"Bird Food" was recorded at a fairly high level in the 63-250 Hz range.

If the frequency response of this sound source could be reproduced well in a listening environment with speakers, it would be the reproduction of the original sound. However, in practice, I think it is quite tough.

The actual measurements for "Organ Symphony" were, from top to bottom, sealed box, bass reflex (upward facing), bass reflex (downward facing), and acoustic maze.



With the sealed box, 125-200 Hz had a reasonable sound level. With the bass reflex (upward), the same band seemed to be emphasized.

With the bass reflex (downward), the 160 and 200 Hz frequencies dropped slightly and the energy shifted to the 100 and 125 Hz frequencies.

In the acoustic maze, 100 Hz rose further and 80 Hz rose by 6 dB.

The same trend was observed with the "Bird Food." The 160 and 250 Hz frequencies in the bass reflex (upward) were at more stronger level.



# Ignore the frequencies of 20Hz and 31.5Hz as they are external noises such as automobile noise.
# A line was drawn later between 80Hz and 100Hz to make it easier to see.

I expected the acoustic maze system to improve down to about 63Hz, but as far as the characteristics are concerned, it came up a little short.

I was hoping for a little more at lower frequencies, given the combined system size of the top and bottom. I thought it was necessary to either extend the sound path further or switch to a double bass reflex system.

This time, I focused on how the low-frequency characteristics changed depending on the type of system.

I thought it was not necessary to emphasize bass so much for a desktop installation. I found that this unit has sufficient reproduction ability even with sealed or bass-reflex systems.

After that, this system should be flipped upside down or duct blocked depending on the sound preferences and the genre of music. For serious listening, the unit should be placed on the lower cabinet. It may be a little troublesome.
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Loudspeaker using MarkAudio "OM-MF4-MICA" - part 3

Custom speaker stands made for MarkAudio "OM-MF4-MICA" can be transformed into various SP systems depending on the setting with the main speakers.

- Main SP (Bass reflex port on the underside)


First, I measured the frequency response of a small bass reflex with only an upper cabinet.
To keep the same conditions as much as possible, a gap duct was secured by sandwiching a single board over the lower cabinet.



The 100-160Hz frequency response is higher than that of the TAOC cast iron speaker stand, but this may be due to aging. I think the frequency response is not so bad.

- Main SP (above the bass reflex port)


Next, the upper cabinet is turned upside down. Due to the central placement of the unit, the front view was almost the same. The ducts were now on the top panel side and about 5 cm longer.



The frequency response has shifted from a peak of 100-160Hz to 160-200Hz.
The calculation was about fd=240Hz. If it is placed on a desktop, it may be swapped up or down depending on the music.

・Main SP + SP stand (BH)


Finally, the upper cabinet was connected to the lower cabinet to see how low frequencies could be reproduced.



Oops, a peak was measured at 250 Hz in 1/3 oct-band response.
A wave of 234.5 Hz was output, which was the calculated resonant frequency of the lower duct. It was indeed functioning as a resonance tube.

In advance, I was thinking that it would not work as a horn because the upper cavity volume is large for a back-loaded horn, and the throat area is also quite large and the aperture is small.

Compared to the bass reflex system, the 100-160Hz level is about the same, and the 40-63Hz level is slightly higher, possibly due to the quarter-wave effect.

I will work on the 250Hz peak later, but this time I turned the lower cabinet upside down.

- Lower cabinet flipped upside down


The bottom panel did not have duct connection holes, but it had a reinforcing plate the same size as the top panel to allow the upper cabinet to be placed on it. When the upper cabinet was placed on top, it was also perfectly merged.

- Main SP (sealed type)


This changed the upper cabinet from a bass reflex operation to a sealed system.



The frequency response was not a steep drop in the low-frequency part like a bass reflex, but a gradual drop below 100 Hz. The f0c calculated as sealed was 137.5Hz.

I have measured the frequency response of each of the four ways of use. I thought I had approximately the behavior and characteristics I had in mind for each method.

I was concerned about air (sound) leakage from the connection point between the two cabinets, but the measurement results did not seem to indicate any significant leakage.

In the next issue, I would like to report on the audition and consider the countermeasure for the 250Hz peak.
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Loudspeaker using MarkAudio "OM-MF4-MICA" - part 2

I have prepared a custom speaker stand specifically matched to the MarkAudio OM-MF4-MICA speakers!

This speaker stand has a height of 462mm. When the main cabinet is placed on it, the front height is 662mm (562mm to the center of the unit).



There is a hole on the top surface. You can also see a hole on the lower back side.



Now let's place the main unit with the unit attached. It fits perfectly.



Actually, this speaker stand has a horn structure.



Even though it is a horn structure, the sound path is not that long.
The lower cabinet alone is about 1400 mm long.　Thus, it has characteristics intermediate between CW horns, resonance tubes and acoustic labyrinths.

When combined with the upper cabinet, the　structure is as shown in the following picture, and the sound path together with the duct in the upper cabinet is 1450 mm long in total.



If think of a resonance duct as [speed of sound / length of sound path], I get

340 m/s ÷ 1.45 m = 234.5 Hz.

For your reference, here is a photo of a board-cutter.



This also only needs to be laminated to the side panels in the order of the sound path, so the production time is about 3 hours. It is important to note that the spacing of the boards dividing the interior must be matched.

In the next issue, I would like to introduce the amazing features of this SP system along with the measurement results.
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Loudspeaker using MarkAudio "OM-MF4-MICA" - part 1

MarkAudio "OM-MF4-MICA" is a 6cm unit, so I decided to make a small bass-reflex system.

To make it small enough to be placed on a desk, I designed it to be 12 cm wide, 15 cm deep, and 20 cm high.



The small number of boards made cutting easy, and production was not difficult since the boards are laminated to the side panels one after the other.



At the time of temporary assembly, the duct direction was toward the unit, but I wanted to increase the duct length a little more, so I changed the direction to face the back plate.



The bottom plate had a 12 mm gap to allow the bottom duct to exit to the back plate side.



The bottom plate had a 12mm gap and the content area is about 1.9L. The duct frequency (fd) calculation assumed about 170 Hz.

A little sound-absorbing material was added to the top board side, and the side panels were attached to complete the project.





I waited a day for the adhesive to dry and measured the characteristics. The measurement location changed from before, so I made a comparison with my standard FOSTEX FE83N SP system.



With pink noise playing, amp volume at the same position, and measurement 100 cm on the iPhone axis,
The frequency response measured by the "Audio Frequency Analyzer" app was shown below.

・OM-MF4-MICA


・FOSTEX FE83N


The mid-high frequency characteristics of the OM-MF4-MICA were wonderfully flat, and above 16 kHz was the character of Mark Audio.

That would be expected to be flat with a frequency response at a 30 degree angle.

The duct frequency was probably around 160Hz based on this characteristic, and it looked 100Hz-12.5kHz flat.

The FE83N system seemed to have a slightly higher level at 1k-2kHz.

My impression of the OM-MF4-MICA system was that it did not have the typical papery sound. The high frequencies of cymbals and flutes were nicely diffused, and the graininess of the piano was also apparent.

However, the fundamental sound of the double bass and orchestral tutti reproduction were tough. If the speakers were installed closer to the wall, a little more low end extension might be expected.

So, I guess the only work left to be done is painting.

To be continued in the next article.
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"Special Selected Speaker Units 2022 MarkAudio Edition" - OM-MF4-MICA

I recently obtained Stereo magazine's ONTOMO MOOK, "Special Selected Speaker Units 2022 MarkAudio Edition".



The loudspeaker unit in this issue is the Mark Audio "OM-MF4-MICA" 6cm full range.

The "OM-MF4-MICA" unit looks from the outside as if the metal diaphragm of the previous "OM-MF4" unit has been replaced with paper one to simply make it lighter, but in fact many improvements have been made to the unit.

- OM-MF4-MICA T/S parameter
　Re = 6.8Ω
　Fs = 106.69Hz
　Vas = 1.17L
　Qts = 0.55
　Sd = 23cm2
　Mmd = 1.33g
　Mms = 1.39g
　Spl = 85.23dB/m
　Max Power = 7W(Nom)
　XMax = 4.0mm(1way)

- OM-MF4 T/S parameter
　Revc = 8Ω
　Fs = 97.5Hz
　Vas = 1.15L
　Qts = 0.64
　Sd = 24cm2
　Mmd = 1.63g
　Mms = 1.69g
　Spl = 83.41dB
　Max Power = 7W(Nom)
　XMax = 4.0mm(1way)

The moving mass (Mmd) of the mechanical system is 0.3 g lighter. It has a higher Fs and a higher sound pressure level.
And the Qts is lower, so it may to sound better in the duct with a slightly higher load.



Two years ago, I built a loudspeaker using "OM-MF4" unit with an unusual appearance theme, and it is now in use as a desktop audio system.

I'm going to try a simple bass reflex this time, or not... So see next time.
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Bill Evans - Time Remembered

Today is the anniversary of Bill Evans' death.

I have always been fascinated by the jazz piano of Bill Evans. Even though 42 years have passed since his death in 1980, his music continues to attract people's attention.

It has been a while since I watched the film "Time Remembered: Life & Music of Bill Evans".
The documentary depicted his tumultuous life, and I was reminded of the magnificence of his way of life. It is a valuable record because it includes interviews with musicians who were associated with him and his real voice.

Unfortunately, I never had the opportunity to hear his live performance, but I have been to a place where Bill Evans visited.

It was jazz club "Lady Day" that I used to frequent in the old days, where live sessions were held every night.

There was a handwritten signature of Bill Evans among many other musicians on the plaster wall of the club. He probably had come here on his Japan tour in 1978. I remember always drinking bourbon at the counter where Bill Evans sat.

That store has already closed and I can no longer ask the story of the signature. It is a shame that when the club closed I did not get that plaster wall with my signature on it.
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Sound quality measurements for Amazon Echo Dot 4th generation.

I got "Amazon Echo Dot 4th Generation" on summer sale!



I bought a bundle of "Amazon Echo Dot 4th generation" and "Amazon Smart Plug" due to the super special price. Actually, I just wanted the Smart Plug.



It is almost the same 10 cm in diameter as "Amzon Echo Dot with Clock 3rd generation" introduced the year before last, but the 4th generation looks much larger because of its spherical shape.



The overall design is stylish, but the top button design is a bit clunky.



The 3rd generation is more well-designed. I regret a little that I should have chosen the 4th generation with a clock as well, because it is very convenient to be able to display not only the time but also the volume level settings.

Now, as for it's sound quality as a smart speaker, well...
It still had the sound tendencies that disappointed me in the 3rd generation. So I measured its frequency response.

- Amazon Echo Dot 4th Generation


- Amzon Echo Dot with Clock 3rd Generation


Connecting to iPad via Bluetooth and playing pink noise, I measured the frequency response with the "Audio Frequency Analyzer" app.
The 4th and 3rd generation were played back under identical conditions, with a measurement distance of 100 cm, 1/3 octave band, and peak hold.

The 4th generation has a rather straightforward frequency response, having improved the don-shari tendency and the significant drop in the mid-range that was a problem of the 3rd generation.

It is still a dull bass, as the single full-range unit forces the low frequencies up too much. However, the unnaturalness of the human voice, as in the third generation, is much improved.

As an audiophile, I am not likely to enjoy music much with this sound quality. I guess I will have to adjust it with the equalizer and use it for specific music genres. Well, I have unfortunately decided to have this product work in my bedroom as an Alexa voice assistant.
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Goodbye, ONKYO!

Yesterday, ONKYO Home Entertainment went bankrupt. It is very unfortunate.

ONKYO is a famous Japanese audio manufacturer founded in 1946. The ONKYO brand will be deeply remembered by us audiophiles as a manufacturer that made a great contribution to the world of pure audio.

Thank you for all these years, ONKYO!
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Replaced the insulator of YAMAHA analog record player GT-2000L.

Yamaha Analog Record Player GT-2000L.

This is a great piece of audio equipment in the golden age of audio that I continue to use with great care.

The weight of GT-2000L is quite heavy, about 28kg, and the genuine insulator was screaming under the weight of years of use.

The genuine insulators were made of rubber and spring composite structure, and they were strong enough to withstand more than 12kg of weight per insulator, even if they were replaced with 18kg gunmetal turntable "YGT-1".

Now, it's in such a mess!



Two of the four insulators were damaged, especially one where the rubber adhesive had completely peeled off and the enclosed spring had popped out.



YAMAHA didn't have any spare parts in stock, which is not surprising since the product was almost 40 years old.

I've been looking for it on the Internet auctions, but I couldn't find any genuine insulators, so I had no choice but to use other insulators.

Last year, I found interesting parts among all the junk, such as audio cables and radios, in an item called "Audio Junk Set" on online auction.

I decided to bid on it at a very low price, and when I checked what I received...



This was a set of four genuine insulators for GT-2000. This was truly a grab bag!

They were in very good condition with very little apparent deterioration, and had probably been installed in GT-2000 for a short period of time.



After disinfecting and cleaning with alcohol, it caused a blooming phenomenon of the rubber. So I applied a little bit of KURE rubber protectant, and it returned to its original black tint.



As a test, I tried to find out how much difference there was in the degree of shock absorption between the old insulator and the new insulator.
I put my iPhone SE2 on the turntable and used the vibration analysis app "Vibroscope" to measure the difference.

- Measurement result of vibration absorption at OLD insulator


- Measurement result of vibration absorption at NEW insulator


This measurement was made when the GT-2000L was placed on the YAMAHA GT-rack "GTR-1W" and the rack shelf was hit hard by hand intermittently. The results show that the new insulator dampens external vibrations better than the old one. I tried to apply the same force as much as possible, but it is difficult to apply exactly the same kind of vibration, so this was just for reference.

Now I can enjoy original sound of the GT-2000L for the first time in over a decade. I'm sure it will be fine for another 10 years or so.
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Paco de Lucía

Today was the birthday of the great guitarist Paco de Lucía (Birth of December 21, 1947).

A genius who transcended the boundaries of flamenco and opened up new horizons in guitar music.

Whenever he came to Japan, I went to listen to his live concerts.

Speaking of live concerts, the super guitar trio with John McLaughlin and Al DiMeola in "Friday Night in San Francisco - Live" (1981) is famous, but I would like to mention "Live Under the Sky" (July 25, 1981, Denen Coliseum, Tokyo). I was particularly impressed by his performance with Chick Corea at this live. It was an unprecedented outdoor live performance in heavy rain.

When I received the sad news that he passed away on February 25, 2014 during a live tour in Mexico, I cried at his loss.

In his later years, he was playing guitar with the superb technique like his younger days, but I had admired his ever-evolving attitude and musicality.

The album entitled "Fuente y caudal" (1973) was the starting point of Paco's music for me. It was the beginning of Paco's creation of new music in the tradition of flamenco. If you have a chance, please listen to it.
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