MarkAudio "OM-MF519" Speaker assembly Part 7 - frequency characteristics


After painting, I played a lot of music with this speaker for sound aging.

My personal impression is that the bass sound is very loud despite the 8cm full range. This is probably due to the bass enhancement effect of the double bass reflex.

# frequency characteristics (distance 1m, Pink noise, measurement by RTA app "Audio Frequency Analyzer")

However, looking at the frequency characteristics measurement above, it seems that the elasticity and tightness are retreating compared to a general bass reflex type, probably because 125-200Hz is slightly depressed. In a sense, 100Hz or less is too high.

Next, I adjusted the length of the second duct and examined how the frequency characteristics changed.

# Original duct (15cm)


I prepared a paper pipe with a slightly smaller diameter and measured it in units of 2cm.

The level of 100Hz decreased in the duct +2cm. It may be the effect that the duct area is slightly reduced.

# Duct +2cm


After that, the length of the duct was increased by 2cm, but no significant change was observed. It is also possible to pick up ambient noise.

# Duct +4cm


# Duct +6cm


# Duct +8cm


# Duct +10cm


# Duct +12cm


As a trial, I changed the length of the upper and lower ducts extremely. But, it did not be much different from closing the duct.

# Duct +2cm, +10cm


These results was not clear, so I have to try several times with different dates. I try listening with a duct length of + 4cm for a while.
posted by toons at 03:20 | Audio


MarkAudio "OM-MF519" Speaker assembly Part 6 - external painting


As usual, the back and top plates were painted with black spray. To change the taste a little, I started to paint blue to the side plates, but the gas ran out during spraying on both sides.


I gave up and overlaid with black from above. After all, it doesn't look good in the surrounding black.

And then I found the remains of the cork sheet!


If the front baffle is cork-lined, I expect a retro feel. The baffle surface is where the woodworking bond is diluted and bonded, and the surface is coated with a thin aqueous varnish to increase strength.
The baffle edge was not able to be processed well and it floated a little around the middle.

It was made by cutting out round to fit the unit.
The sound absorbing material was inserted with the weight of the left and right channels matched.



Finally, the speaker was completed by tightening the duct screws!

posted by toons at 00:17 | Audio


MarkAudio "OM-MF519" Speaker assembly Part 5

MarkAudio OM-MF519 Double bass reflex speaker is almost completed.


However, the entire box is still under consideration for external painting.


For trial, I painted only the duct part of back side.

posted by toons at 01:50 | Audio


MarkAudio "OM-MF519" Speaker frequency characteristics, part 3

MarkAudio OM-MF519 Double bass reflex speaker is being adjusted.

The characteristic (1) was the result of adjusting the sound absorbing material to match my listening preference.

This was a measurement result at 1m above the unit axis (tilt about 15 degrees to the front of the baffle). The peak at 250Hz dropped, and the characteristics seemed to shift to 200Hz or below.

The characteristics of the second duct seemed to be concentrated around 60-100Hz. Then this area may not change unless the duct length is changed.

(1) Frequency characteristic of adjusting the sound absorbing material

Incidentally, the characteristic (2) was measured on the front axis of the unit. The peak of 12k-16kHz which is the high frequency characteristic of this unit was appeared.

(2) Frequency characteristic on the front axis of the unit

The characteristic (3) was the result of distance from the baffle to 2m.
Although a peak was seen at 100Hz, I thought that it was possible to get around 50Hz as a low frequency characteristic.

(3) Frequency characteristic from the baffle to 2m

As for my impression, I could hear the profound feeling of the bass and strings with the feeling of adding a subwoofer.

However, the feeling of tightness in the low frequency area will be reduced, so the rhythm may be lighter in jazz and pop music. I don't know if this is a characteristic of the box, or if the work accuracy or adjustment is insufficient.

Since the internal adjustment is over, I will consider finishing the box surface.
posted by toons at 02:54 | Audio


MarkAudio "OM-MF519" Speaker frequency characteristics, part 2


I tried putting the sound absorbing material into the first and second cabinets. It was shifted to the low side, 40/50Hz level up, dipped occurs at 160Hz.

And I reduced them for the first cabinet a little more. Adjustment was troublesome. Although it got more sense of volume in my hearing, the sound response was declining.

I will try to make a sound with this for a while.
posted by toons at 09:29 | Audio


MarkAudio "OM-MF519" Speaker frequency characteristics, part 1

Attached the MarkAudio "OM-MF519" unit to the double bass reflex speaker box, so I made sound test.

I measured the frequency characteristics at the begining of playback and after aging for 1 hour. It was tested by the RTA app "Audio Frequency Analyzer" with pink noise.

# Begining of playback

At the start of playback, there was a dip at 125Hz, but the level increased a little in about an hour.

# After aging for 1 hour

The original high frequency peak of 12-16kHz has disappeared. This is probably because the baffle is slanted and the measurement point is about 15 degrees off the unit front axis.

In addition, when blocking to tape one duct as a test, the 63/80Hz sound level was dropped. The second cabinet duct was seemed to have worked well.

# Blocking one duct

It wasn't the final sound because there was no sound absorbing material yet in the box, but the sound resolution was very good. The bass range did not drop to the lowest sound, but it had enough low-pitched feeling unlike a simple bass reflex.
posted by toons at 00:12 | Audio


MarkAudio "OM-MF519" Speaker assembly Part 4


I scraped off the gap between the baffle and the side plate. I found that it had a little off, but I'll try sanding again even before final painting.

The duct plate was temporarily fixed. I'll measure the frequency characteristics with no sound absorbing material by attaching the speaker unit once.
posted by toons at 01:15 | Audio


MarkAudio "OM-MF519" Speaker assembly Part 3


I attached a terminal plate and routed the wire through the first duct. The surplus plate was reinforced by adhering it appropriately to the large area plate.

When attaching the remaining side plates, it felt a little floating, so I made a fine adjustment by sanding the protruding part.


I glued the side plates and waited about half a day with a weight on top.

The inside of the speaker is only accessible from the speaker unit hole and the back plate duct. It can be the adjustment of the duct length and the addition of sound absorbing material.

I will make the appearance better by shaving the protruding part with a file when the adhesive is dry.
posted by toons at 00:21 | Audio


MarkAudio "OM-MF519" Speaker assembly Part 2

First of all, I filled up the shortage of the duct back plate with a 23mm plate from the bottom plate.


And the duct back plate was assembled. The duct is a 150 mm long paper pipe.


The top plate and upper back plate were bonded.


I assembled the part that would become the first cabinet, but there was a slight gap.


The first cabinet was glued to the baffle plate and fixed with a surplus plate sandwiched so that the duct width was 12mm.


This completes the assembly of the main components. And the parts were fixed to the side plate.


It seemed that the reinforcing material of each corner and the bond were attached too much.
Before attaching the side plate on one side, it is necessary to route the terminal plate and wiring cord.
posted by toons at 01:55 | Audio


MarkAudio "OM-MF519" Speaker assembly Part 1

MarkAudio OM-MF519 Double bass reflex speaker is under assembly.

At 9am, the temperature was already over 30°C and I have to work it while taking a break.
I carefully cut it with a circular saw, but after 15 minutes, I couldn't stand it and interrupted.


The cutting error is 1-2mm, but the inner cabinet is not visible, so even if it was allowed to some extent.

My troublesome work is increased, so the outer box has to make sanding after assembly,


After opening the unit hole and duct hole, i found that the size of the back plate duct was small.

It was too stupid to notice after opening the duct hole. I regretted that I should not divided the backboard.

It may be cut off the excess board and re-drilled, or it may be stepped with a larger reinforcement.
posted by toons at 03:23 | Audio