Note: These plans can be purchased here.
In this blog post I test and review the Markaudio CHR120 fullrange driver. This is a 12cm driver featuring a magnesium cone and dust cap.
This driver is slightly larger than a typical 6.5" driver, with and SD of 147 cm^2 which is about the same as the Fostex FF165WK driver which has an SD of 132 cm^2.
Using a 1 cu ft (28 liters) enclosure I tuned the cabinet to 40Hz with two ports measuring 45mm diameter x 100mm long each.
The frequency response exhibits breakup starting at 3kHz which shows up as stored energy (resonance) in the burst decay and CSD plot. This is to be expected for a magnesium drive in this size category.
All of the resonances end rather quickly at 12 cycles using a -35dB vertical scale noise floor. Only the resonance at 18kHz continues to ring past 30 periods (cycles).
The CSD shows the same result but with depth axis changed to time in milliseconds.
Harmonic Distortion 85dB
K2 remains below 0.10% along with K3, a good result.
Harmonic Distortion 95dB
H2 and H3 remain low even at the elevated output SPL.
Playing a multitone test signal (12 band per octave) at 85dB test signal (1m) produces the following IMD. Distortion is at -60dB (2kHz) in the midrange and -67dB in the upper treble (10kHz)
Lowering the sampling rate from 44.1kHz to 22kHz reveals more detail in the test results for bass. Distortion in the bass region (100Hz) is -52dB. A good result.
Increasing the test SPL to 95dB is revealed below. Midrange and treble distortion reduces to -50dB. Bass distortion at 100Hz remains low at -50dB. This is an excellent result especially considering the driver's size.
Changing the sampling rate back to 44.1kHz reveals distortion artifacts in the treble.
Isolating the results to the 10kHz - 20kHz portion of the bandwidth reveals an interesting distortion profile (see below). The bass frequencies have modulated into the treble frequencies in the form of tapered bases at the bottom of each test tone. This is likely not very audible considering their proximity to the harmonic tones. What is important is the noise artifacts between the test tones, in which case it is shown to be -70dB below the test tones, which is an excellent result.
I produced an off-axis colored polar map in the horizontal axis. The driver is flush mounted into the baffle. The baffle has no round-overs and is 23cm wide.
The polar map shows some gradual narrowing starting at 2kHz. Coverage at 10kHz is about 44 degrees which is quite good for a driver of this size. The coverage remains constant even up to 16kHz.
Baffle Step Compensation
After some adjustment I decided on the baffle step circuit below.
The Baffle Step Compensation (BSC) is comprised of the 10ohm and 2.5mH components. The 6ohm and 0.47mH is the high frequency contour circuit which adjusts for the peak in the response starting at 7kHz.
The affect of the high frequency contour circuit is shown below with red being the raw response of the driver, and black is with the contour circuit in place. The circuit has the most affect on the 7.5kHz region providing a -3dB attenuation.
Adding in the Baffle Step Compensation (BSC) is shown below. The BSC comes into affect at around 600Hz and provides -4.5dB of attenuation.
The final result is shown below.
After making the necessary adjustments mentioned above, I was able to critically evaluate the sound quality.
Below is a ranking for my subjective impressions on the sound quality...
Soundstage Depth --- 9/10
Soundstage Width --- 7/10
Smoothness --- 8/10
Coherence between midrange and treble --- 9/10
Coherence between mid-bass and midrange --- 8/10
Vocal Clarity Male --- 8/10
Vocal Clarity Female --- 7/10
Accurate Musical Instrument timbre --- 8/10
Sense of Dynamic Range: --- 6/10
Overall the Markaudio CHR120 provides a pleasurable listening experience.