Hand crafted SP with ONKYO "OM-OF101" vol.6 - finale


I put into action the addition of a tweeter to increase the high frequency energy of this loudspeaker.


First, I checked the 30-degree characteristic of the OM-OF101 unit alone again, and found that it gently dropped from above 4KHz.

- Frequency response of OM-OF101 full range (30 degrees)

If the OM-OF101 unit was to be connected to a tweeter, I felt that an 8k-12kHz crossover was appropriate.

The additional tweeter was an Olasonic super tweeter included in DigiFi No.20 magazine.
I got it about a year ago at a bargain price, and it had been forgotten in a corner of my bookcase, so let's have it sing this time.

First, I tested the frequency response of the super tweeter only, using different capacitors that I have.

There were four types of capacitor capacitance: 0.22μF, 1.0μF, 1.5μF, and 3.3μF. The manufacturers varied, and included some that had been used quite some time ago. I didn't take a picture of them because they looked bad with butyl rubber stains and such.

To match the 30 degree response of the OM-OF101, I measured the frequency response at a 30 degree angle from the front axis of the Olasonic tweeter.

- Frequency response of Olasonic tweeter alone (30 degrees, 0.22μF)

- Frequency response of Olasonic tweeter alone (30 degrees, 1.0μF)

- Frequency response of Olasonic tweeter alone (30 degrees, 1.5μF)

- Frequency response of Olasonic tweeter alone (30 degrees, 3.3μF)

The 0.22μF capacitance had a low high frequency level. The 1.0μF capacitance extended to 16kHz. The 1.5μF capacitance had a lower level above 10kHz due to the phase. I thought that the 1.0μF capacitance was the safest choice.

Next, I measured the frequency response on the axis. I retreated from the baffle surface by 0 mm / 15 mm / 20 mm.

- Frequency response of OM-OF101+Olasonic tweeter (on axis, 00mm)

- Frequency response of OM-OF101+Olasonic tweeter (on axis, -15mm)

- Frequency response of OM-OF101+Olasonic tweeter (on axis, -20mm)

The offset of 20mm was quite low from 10kHz onwards. In the case of the 00mm offset, which is the same as the baffle surface, it seemed to go down gradually from 4kHz.

The offset of 15mm showed an increase in the high frequency range. This was because the voice coil position of the OM-OF101 unit was around 12-15mm, so I guessed it was standard practice to match the voice coil position. After that, I decided to fine-tune the position while listening.

I could also try changing the polarity, but I decided to play a few songs in this state (C=1.0μF, 15mm from the baffle surface, normal phase) to check the sound.

At first listen, the reproduced sound was clear and crisp in the high frequency range and the center position was clear. Because of the super tweeter, the connection between the mid and high frequencies was natural.

The female vocalist sang without any sense of clutter. The bass line in the low range also seemed to have changed to a tighter direction. This might have been an effect of aging the unit.

Finally, I compared the characteristics with those of the ScanSpeak 10F/8422-03 10cm full-range unit, which was included in the August 2012 issue of Stereo magazine.


I designed this box with a 3.7L capacity and bass reflex rear duct fd=108Hz. The box is designed to be installed horizontally, so I felt it would be a bit uncomfortable if it was installed vertically.

- Frequency response of ScanSpeak 10F/8422-03

- Frequency response of ONKYO OM-OF101

Their sound pressure levels seemed to be comparable, but this box had a significant drop below 100Hz. There was a 9 year difference between the two boxes, so it was hard to compare them under the same conditions.
posted by toons at 03:03 | Audio