2022/09/27

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)
01.バスレフ(下)_1.JPG

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.

01.特性バスレフ(下).PNG

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)
02.バスレフ(上)_1.JPG

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.

02.特性バスレフ(上).PNG

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)
03.BH_1.JPG

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

03.特性BH(1).PNG

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
04.密閉(1)_1.JPG

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)
04.密閉(2)_2.JPG

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

04.特性密閉(1).PNG

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.
.s
posted by toons at 02:36 | Audio