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Crow-II It was in 2018 that I designed the Crow with the Silver Flute W17RC38-08. Though it sounded good, the sensitivity was rather low. The Crow-II addresses this deficiency by leveraging on another woofer, a 7″ aluminum cone Dayton DA175-8
Fig 1 is the bandpass modelling of the Dayton DA175-8 in a 25 liters box that is used in the earlier Crow. The Violet plot is the optimum response recommended by Box-Port. The Black plot is with the DA175-8 tuned to Fb=65Hz. This is the flattest response with the best sensitivity.
The RAW response of the Crow-II is in Fig 2. It’s really close to the modelling in Fig 1. It goes to show the importance of accurate Thiele & Small parameters. The -3dB bandwidth is about 40Hz~125Hz. Note that at 700Hz onwards, the midrange and treble are bleeding out of the port. Even though their SPL are -20dB below the fundamental, it is prudent to remove them to avoid contaminating the midrange.
Fig 3 is a family of plots using my 24dB/oct electronic crossover with frequencies from 500Hz~90Hz. They show the midrange is completely eliminated even when my crossover is set as high as 500Hz (Black plot).
Fig 4 shows the recommended crossover frequencies for the Crow-II. The Blue plot is at 250Hz, Violet at 125Hz and Brown at 90Hz. For the flattest passband, the frequency is 125Hz.
The Crow-II box dimensions is in Fig 5. The upper chamber is lined with R-13 fiberglass insulation. This helps to reduce the spikes in the midrange and treble that emit from the port (Fig 2). The bottom ported chamber is left bare, no insulation is used. Note the Red terminal wire is soldered to the “Minus” tab on the woofer. In doing so, the output of the Crow-II will be in absolute phase. Crow-II with Sparrow-TAThe Crow-II is designed to replace a speaker stand. A small 2-way bookshelf speaker can be placed on top of the Crow-II and the tweeter height will be about ear level when one is seated. This is exactly what I did when testing the Crow-II with the Sparrow-TA in full space (4 pi steradians). For best results, I recommend bi-amping. This will require an external active crossover and an additional amplifier. Set it at 125Hz and adjust the volume of the 2-way to match. For those that have Home Theater receivers, there is normally a subwoofer output with a 125Hz low pass filter in place. You can use that for the Crow-II. Sound Quality of the Crow-IIThe bass of the Crow-II has excellent attack and is well defined. It is huge improvement over using the DA175-8 in a closed box or bass reflex. |
September 17, 2020HIFI DRIVERS, Projects
Fig 1 – Crow-II Bandpass Model
Fig 2 – Crow-II RAW Response.
Fig 3 – Frequency Response plots at 500Hz, 250Hz, 150Hz, 125Hz and 90Hz
Fig 4 – Recommended Crossover Frequencies
Fig 5 – Crow-II Dimensions