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.
posted by toons at 02:36 | Audio


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.
posted by toons at 19:22 | Audio


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.



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.
posted by toons at 21:29 | Audio


"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.
posted by toons at 20:49 | Audio


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.
posted by toons at 22:15 | Audio