Markaudio CHP-70-P Gen2 with Audax TW010E1

why the Audax TW010E1

Because this is one of the few tweeters I have that works superbly with a 1st order filter. The other is my Morel CAT 378 which is an overkill for the CHP-70. Not all drivers will work well with 1st order networks but I believe the CHP-70 with the TW010E1 will sound fabulous. 

Fig 1 – CHP-70 Baffle Width = 6-1/2″ |  Sealed Box 1.7 liters  |  No Smoothing

Fig 1 shows the response of the two drivers with their associated 1st order filters. The Red plot is of the Audax TW010E1. The Blue plot is the CHP-70.  Disregard the deep notch at 150Hz. That’s cause by a floor bounce in my setup. Judging from the plot, it looks like the CHP-70 rolls of at about 100Hz in a sealed box.

Fig 2 – 3-way response overlay

Fig 2 shows the summed response (Black plot) of my 3-way system. The bass is from my 8″ Silver Flute bandpass subwoofer. It extends to 200Hz where the CHP-70 takes over. This plot was made with an electronic crossover set at 250Hz (24dB/oct) to cross the bandpass to the CHP-70 satellite.

Fig 3 – 3-way Frequency Response

For clarity, Fig 3 is the final frequency response with my Toucan-SF, an 8″ Silver Flute bandpass sub. The response below 200Hz is a bit peaky because the microphone is picking up reflections of my room. Nonetheless, it is a good indication of how a speaker behaves in real situations. 

In this exercise, I’ve not made any attempts to correct the baffle step. There is almost a +6dB rise due to the narrow 6-1/2″ baffle width. I can correct that later. Right now, it’s still at an exploratory stage. If the speaker doesn’t sound right, there’s no point going further.

Fig 4 – CHP-70 with TW010E1 wired in Reversed Phase

To check on the crossover phase, I rewired the tweeter in reversed phase (Fig 4). A broad notch appeared from 3kHz~6kHz. It may not look very pretty but for a 1st order network, it is quite extraordinary. With some fine tuning, the notch will look smoother and more symmetrical. Notice that below 200Hz, the CHP-70  rolls off sharply. That’s due to my electronic crossover 250Hz high pass filter.

Fig 5 – Step response of CHP-70 with TW010E1

The beautiful Step Response in Fig 5 is of the CHP-70 with the TW010E1 using only 1st order passive networks. The transient is faster and cleaner than using the Elite VRT18. It won’t be difficult to align the two drivers. The acoustic centers of the the two drivers are already very close.

Fig 6 – Waterfall of CHP-70 with TW010E1

The Waterfall plot in Fig 6 shows some artifacts at 3kHz and 7kHz. The 3kHz indicates some ringing from the CHP-70 whereas the ones at 7kHz are from the Audax tweeter. 

Fig 7 – Toneburst Energy Storage

The Toneburst Energy Storage in Fig 7 shows excess energy at 3kHz and 7kHz. This reaffirms the artifacts recorded in the Waterfall plot in Fig 6. 

Fig 8 – Spectrogram of CHP-70 with TW010E1

The Spectrogram in Fig 8 shows another facet of the speaker behavior. Both the Waterfall and the Toneburst points to ringing in the treble but the Spectrogram shows otherwise. When the frequency is plotted against time, the problem areas are from 1kHz~3kHz. Yes, there’s some ringing at 7kHz but they last for only 1 msec. The ringing from 1kHz~3kHz, on the other hand, last up to 6 msec. This can flare up as shrillness in female voices.  

Fig 9 – Harmonic Distortion of CHP-70 with TW010E1

This is where the Audax TW010E1 beats the Elite VRT18 hands down. The 2nd (Red plot) and 3rd (Violet plot) harmonics in Fig 9  flatline at -30dB. That’s a good -50dB down from 80dB. The Elite VRT18, on the other hand, exhibits high distortion from 5kHz upwards (Fig 10).

Fig 10 – Harmonic Distortion of CHP-70 with VRT18

is the TW010E1 better than the VRT18

Definitely. It not only measures better but it sounds smoother too. Somehow, the speaker sounds more natural. Perhaps it’s from the 1st order network. Whatever it is, the music is extremely relaxing.

As the ultimate test, I played Teresa Teng (邓丽君 dèng lìjūn). Her songs are one of the most demanding. If the treble is not right, she’ll be very difficult to listen to. That’s because in the Mandarin language, there are much more sibilant fricatives than in English.

In What do you have to say (你怎么说 nǐ zěnme shuō), her rendition is one of pain from being cheated by someone she loves. Yet, she maintains her dignity. There’s not a hint of anger nor hatred. Just sadness. Throughout the entire song, the sibilant fricatives are well controlled and precise in their definition.

Fig 9 – Impedance plot of CHP-70 with TW010E1

Even the impedance plot looks better. With the Elite VRT18 ribbon, it dips to 5Ω at 20kHz whereas with the Audax TW010E1, it is about 7.5Ω. Apart from that, the rest of the plot looks similar.

Part 1 – CHP-70 with Audax TW010E1
Part 2 – Time Alignment
Part 3 – Correcting Baffle Step

Enclosure used is 1.7 liters Sealed Box stuffed with Polyfill.
Crossover is available on request. Free for DIY. Not for Commercial use.
Unless otherwise stated, all measurements were made with the mic at 36 ins, tweeter axis. Impulse Window=5ms. No smoothing applied.