In the Wren-BC, the Markaudio CHP-70 now has a companion, a Peerless BC25SC08-04 tweeter for the treble. That will elevate this full range to a higher level. The first order of the day is to tame the frequency response of the CHP-70.
Fig 1 – CHP70 Frequency Response
The Black plot in Fig 1 is the RAW response of the CHP-70. That is the response when used as a full range. The Blue plot is with my network. Note the cone breakup peak at 5kHz. It disappeared in the Blue plot.
Fig 2 – CHP70 Low Pass and BC25SC08 High Pass
The Red plot in Fig 2 is the Peerless BC25SC08-04 tweeter. I adjusted the filter to match the asymptote of the CHP70. For this plot, I spliced in a Nearfield response at 400Hz.
Fig 3 – Summing at Crossover Passband
The Black plot is the summed response of the two drivers. No cancellations are observed in the crossover passband, which is good. It indicates the crossover is working properly.
Fig 4 – Wren-BC Frequency Response
Fig 4 is the final frequency response of the Wren-BC. As can be seen, it is not flat throughout. There are dips at 650Hz, 1.5kHz and a chunk from 4.5kHz~5.5kHz. Higher up, there is a +5dB peak at 10kHz.
Fig 5 – Wren-BC Step Response
What is lacking in the frequency response is more than made up for in the Step in Fig 5. This is what the Wren-BC is all about. A beautiful, vertical transient. No breaks, one straight line. It is not Time and Phase Coherent yet but it’s close. All I need to do is use a step or slant the baffle but I’ll leave that for the time being. What I want to do is to listen to the Wren-BC first.
Fig 6 – Wren-BC Waterfall
Fig 7 – Wren-BC Toneburst Energy Storage
The Waterfall (Fig 6) and Toneburst (Fig 7) plots show some minor artifacts at 4kHz and 10kHz. I seriously we can hear any smearing. What is of more concern are the blue slices at 1.5kHz.
Fig 8 – Wren-BC Spectrogram
As I expected, there is a streak in the Spectrogram at 1.5kHz. There’s another one lower down at 1.1kHz as well. These are not from the Peerless tweeter because it has been rolled off already. They look like some ringing from the CHP-70. I don’t think they’ll smear the midrange. They dissipated after 10ms.
Auditioning the Wren-BC
What a difference a tweeter makes. Now, the treble sounds right. The extensions in the high frequencies are audible. Without a tweeter, the CHP-70 treble sounds dull.
The midrange still display the clarity and transparency that are the outstanding features of the CHP-70. Vocals and instruments are clearly heard.
As for the bass, I can’t complain. An F3 of 70Hz may seem high but it’s a small sacrifice to pay for a 4″. As it stands, having a bandwidth of 70Hz~20kHz is already an achievement.
The Wren-BC is most suitable for users where space is a premium. It’s a fairly compact 7 liters bookshelf design. Doesn’t take up much space. And if the user is not a bass head but loves vocals instead, then it’s a perfect match.
Can I live with the Wren-BC? Most certainly. It has a very “clean” sound. By that, I mean listening to it doesn’t stress me. Maybe I’m more sensitive to distortion than most people. There are some drivers that I just cannot listen to. The CHP-70-P Gen2 is not one of them.
Crossover is available on request. Free for DIY. Not for Commercial use.
April 28, 2020Projects