The Robin-HT5 is based on HiVi M5a midwoofer. Initially, I was concerned that such a small 9 liters box will boost the midbass too much, making it into a boom box. Fortunately, JBL tuned their box to 50Hz, so there isn’t any mid-bass peak.
HiVi M5a in JBL HT5
Fig 1 – Frequency Response of M5a in HT5 box. Mic at 1 meter, tweeter axis. Impulse Window = 5ms. No Smoothing.
The RAW response of the M5a in the HT5 box is pretty scary (Fig 1-Black plot). There’s an upward climb from 500Hz due to baffle step. It took me a while to get the response that I wanted but I eventually got it (Blue plot).
HiVi M5a with JBL HT5 Horn
Fig 2 – Frequency Response of M5a with Low Pass filter and HT5 horn with High Pass filter
Fig 2 is the Frequency Responses of the HiVi M5a with a low pass filter and the HT5 horn tweeter with a high pass. Acoustically, the crossover is at 2.5kHz.
Robin-HT5 Frequency Response
Fig 3 – Summed Response of M5a and HT5 bi-radial horn.
Fig 3 is the Frequency Response of the Robin-HT5. The M5a and the JBL Bi-radial horn sum well. There are not cancellations in the crossover region.
Robin-HT5 Cumulative Spectral Decay
Fig 4 – Robin-HT5 Waterfall plot. Window = 1.3ms (769Hz), Time Range = 1.0ms, Rise Time = 0.1ms
I was pleasantly surprised by the Robin-HT5 Waterfall plot (Fig 4). The HiVi M5a doesn’t appear to have much decay from 1kHz onwards. There’s no mistake with this plot. The Waterfall Time Range is indeed 1.0ms, meaning this is a highly magnified view. I don’t believe I’ve seen anything so clean before.
Robin-HT5 Toneburst Energy Storage
Fig 5 – Robin-HT5 Toneburst Energy Storage. Impulse Window = 5ms.
The Toneburst Energy Storage in Fig 5 reaffirms the Waterfall plot. There’s no excess energy between 1kHz to 2kHz. There is a very tiny amount in the crossover region from 2kHz to 3kHz. Nothing to worry about.
Fig 6 – Robin-HT5 Spectrogram. Impulse Window = 5ms
The Robin-HT5 Spectrogram shows virtually no time smearing at 2kHz. The plots in Fig 4,5 and 6 all indicate that the HiVi M5a is an exceptionally well controlled midwoofer.
the sound of Swift HT5
I was apprehensive whether this clean reproduction will end up sounding clinical and lifeless. Alas, my fears were unfounded.
I threw whatever I could at the Robin-HT5. From Another One Bites the Dust (Queen) to Stronger Woman (Jewel), even Infernal Dance (Stravinsky-The Firebird Suite) , the Robin-HT5 did not disappoint. No subwoofer needed. And that is in 4pi placement.
The Robin-HT5 is very musical. If you are starting from scratch, I suggest you use HiVi M5a over the Zaph ZA-14. I thought the Swift-HT5 is good. Well, the Robin-HT5 is better.
If you’re interested in this modification, kindly send me a mail for the crossover. You agree to undertake this modification at your own risk. I am not responsible for any damage to your speakers.
March 30, 2018Projects