In this blog post I would like to feature the Markaudio CHR70A fullrange driver. This driver was sent to me by my customer. The drivers are relatively affordable at only $26 USD each.
We get started with a frequency response measurement. The driver fits in my 1630 speaker so this is representative of a narrow baffle result.
We see that the response is somewhat flat through the midrange. At 10kHz there is a +5dB peak which continues to +7.5dB at 13kHz. This is the mechanical breakup for the diaphragm which is to be expected with an aluminum driver of this size.
Below is Markaudio's own published data which looks extremely flat by comparison. To me, my results still look respectable for a fullrange driver. I'm not sure why Markaudio continues to embellish their test results in such an extreme way. The vertical scale actually goes into the negative digits. This is very silly.
Looking at the off-axis I was able to produce the following polar map. Keep in mind however I did not flush mount the driver. So this result could be improved somewhat. We have a reasonably wide listening window with 8kHz having an 80 degree listening window which narrows down to 40 degrees by 13kHz.
The directivity pattern is generally what we see with other drivers of this size.
Producing an overlay of 0,15,and 30 degrees is shown below. This tells us that moving 15 degrees off-axis will help mitigate the breakup peak and help balance the sound somewhat.
If we look at time domain performance we see some respectable results. We see that the dip at1.8kHz is in fact a mild resonance. But these are minor quibbles on a very good result.
The CDS is good as well. Markaudio has made some effort to quell the breakup energy, so ringing is kept a bay.
This can be shown in the impedance sweep where we don't see much happening in the upper treble.
Nonlinear Behavior
We first look at harmonic distortion at 80dB 1m. The driver does admirably across the spectrum.
Increasing to 85dB sees things rise pretty quickly in the lower midband, but still reasonably low distortion. We do see a mild bump at the 1.6kHz region with H2.
Using a 12 band per octave multitone signal at 75dB produces at noise floor -55dB down through the mid-band with the exception of the bump at 1.6kHz which reduces to -40dB. Distortion in the upper treble is -50dB. Personally I would like to see better performance here. 
Increasing the test signal to 80dB we see the 1.6kHz region reduce to only -36dB. The upper treble isn't doing much better. This is about as much as we'd want to push this driver if attempting to reproduce bass frequencies.
If we high pass filter the driver at 250Hz we see things dramatically cleaned up across the spectrum.(75dB test SPL). We now see distortion drop to only -60dB!
Increasing the test to 80dB is shown below, but we see that pesky 10kHz breakup mode coming up through the noise floor, but still -60dB down. However at 5kHz we are actually -63dB, which is compression driver territory for low distortion.
Increasing still to 85dB and we see a linear increase in distortion, however still nicely low. This driver really responds well to high pass filtering in terms of cleaner midrange and treble.
Suitable Application
Considering the test data it would seem that this driver would do well in a bass limited application where bass and mid-bass was supported by other drivers. Alternatively this driver would do well on simple music. I don't think it's reasonable to put a passive high pass filter on the driver, however a good solution may be an active setup with a 250Hz crossover point. I would suggest doing this the analogue route with something like the Xkitz 2-way crossover.
If you want to go a more simply route, another option is to let the Markaudio run with no filter and simply augment it with bass. I attempted to do this with Speaker System No.1630 which has dual 5" Scanspeak woofers in a separate enclosure. The sensitivity matched perfectly and so the Markaudio did not require any padding to bring it's level down. Below is the resulting overlay. I placed a single 8mH inductor on the scanspeak drivers to provide the necessary low pass filter. The Markaudio was left unfiltered. The below result does not take into account room boundary reinforcement which would extend the bass response.
Subjective Listening Impressions
With my main listening room taken over by woodworking, I have been focusing on smaller speaker setups for smaller rooms, at least for the time being. My room measures 12’ wide x 16’ deep with the speakers setup on the narrow wall, although I may change the setup to the broad wall.
I ran the CHR70’s with bass reinforcement from the lower dual 5” ScanSpeak woofers. This added scale, weight, and fullness to the sound. Otherwise the bass was far too gentle and light.
Overall I enjoyed the sound quality from the CHR70A. Firstly, what immediately jumps out at me is the treble sharpness. There is a razor sharp treble detail that also includes great soundstage depth and low level detail retrieval. Soundstage width seems tightly focused to the physical spacing of the speakers and does not listen extend to the side walls of my room.
Dynamics are decent and better than most driver of this size, but not near the dynamics of a good horn and compression driver.
I found that the sweet spot was in the 60-70dB SPL listening level which is a normal listening level for most.
I listened to the speakers at 15 degrees off-axis. If I listened on-axis the timbral balance shifted and it was too bright.
Cymbals came through with great clarity, however they didn’t sound real in terms of what it would sound like live, however it was still enjoyable. Cymbals sounded like they were miniature. 
Overall it’s a complete bargain that these drivers cost so little and are able to reproduce such admirable sound. Limited only by dynamics and soundstage width, these drivers deliver all the resolution you could want from midrange to treble. These drivers are a prime candidate for “B” systems or desktop solutions.