| I first worked on the M5a in 2010. The tweeter I used then was a Vifa D25AG35-06 1″ Aluminum tweeter. Unfortunately, this fine tweeter is no longer in production.
In this new version, the Robin-DX sports the latest Peerless DX20BF00-04 fabric dome tweeter. Though it is a 3/4″, I’m confident that it will integrate well with the M5a. As in the first Robin, cabinet volume remains at 13 liters for the Robin-DX.
HiVi M5a RAW Frequency Response
Fig 1 – RAW frequency response of HiVi M5a in 13 liter box. Measurements below 400Hz are Nearfield.
The Black plot in Fig 1 is the RAW response of the M5a. Baffle width of the box is 8.5 inches. Due to the narrow baffle, the effects of baffle step come into play. We can see clearly a +3dB gain in the response starting from about 500Hz. To prevent the Robin-DX from sounding bright, I incorporated baffle step compensation into the network.
HiVi M5a Response with BSC and Low Pass Filter
 Fig 2 – Mic at 1 meter, tweeter axis, 1/12th octave smoothing
The Blue plot in Fig 2 is of the M5a with two networks, a baffle step compensation (BSC) and a low pass filter. The BSC filter effectively tames the rising response after which the low pass rolls off the highs.
Crossing HiVi M5a with the Peerless DX20BF00-04
 Fig 3 – Response of HiVi M5a with Low Pass filter and Peerless DX20BF00-04 with High Pass filter
The Peerless DX20BF00-04 tweeter crosses beautifully with the M5a (Fig 3). Acoustically, they meet at about 3kHz. What is important is the nature of the slopes after they meet. Note their symmetry before and after the crossover frequency.
Robin-DX Frequency Response
 Fig 4 – Summed Response of HiVi M5a and Peerless DX20BF00-04
The Black plot in Fig 4 is the response of the Robin-DX. The M5a and the DX20 integrate well. Though the ultra high frequencies are tapering off above 10kHz, I honestly do not find it objectionable. I can add an eq network but that will increase the crossover cost.
the Robin-DX in play
This speaker is very likable. The all important mid-bass is not muddy and the overall bass is not boomy. Equally important is the bass doesn’t bleed into the mid-range. This excellent separation contributes to a clear and transparent vocal presentation.
Due to the baffle step compensation network, voices do not shout at you. The positioning of vocals is slightly in front of the band. There are no harshness in the sibilance and the treble doesn’t exhibit any brittleness.
This new development in the Robin-DX paid off with the Peerless DX20BF00-04. The DX20 cost only about $12, yet performs like a tweeter costing twice as much. This is in line with my philosophy of designing speakers with the best performance at the lowest cost. |
