GRS PT6816-8 Dipole Planar Tweeter Review

GRS PT6816-8 Dipole Planar Tweeter

I bought this planar tweeter in May of 2023 but never got down to testing her. This 2 year hiatus came about because of important family matters that required my personal attention.This is compounded by health issues which is only getting worse. After setting up another lab in my new home, I am looking forward to continuing my journey in audio.

For this review, the PT6816 is mounted in dipole fashion. In dipoles, the rear of the tweeter is “open” back”, that is it is not enclosed. Sound radiates from the front as per normal but it also radiates from the back. The front sound is in-phase whereas the rear is out of phase. There are advantages and disadvantages in using dipoles but I will leave that for another day. The main reason I’m using a dipole to test this tweeter is simply because it’s the fastest and most convenient way. If it doesn’t work out, I will resort to a rear chamber.

Fig 1 – GRS PT6816-8 RAW Frequency Response (Dipole)

Fig 1 is the RAW frequency response of the dipole PT6816. For this measurement, the bass is removed from the test sweep. This is important otherwise the tweeter will be damaged as no capacitors are used.

From the plot, we can see the tweeter goes as low as 400Hz, after which she dies off quite rapidly. To protect the tweeter, I’m inclined to cross her at 700Hz. At this frequency, the tweeter will be more robust. Furthermore, I will avoid the notch at 500Hz.

Fig 2 – GRS PT6816 crossed at 700Hz High Pass (24dB/oct)

Fig 2 is the plot with my active crossover set at 700Hz (24dB/oct). Just as I had hoped, the roll-off is smoother. This is something I can live with.

Fig 3 – GRS PT6816 Toneburst Energy Storage

I like to use the Toneburst  plot because it offers me a quick analysis of the artifacts. The PT6816 is surprisingly free of artifacts (Fig 3) till about 10kHz where she experienced a burst of energy. Frankly, I’m not concerned with what happens at 10kHz. I will deal with it if necessary. It is the lower treble that interests me. From 1kHz~5kHz, there are no artifacts. Incredible. 

Fig 4 – GRS PT6816 Waterfall

Fig 4 is the Waterfall plot of this planar tweeter. All the artifacts are concentrated at 10kHz. Even then, they will not interfere with the music as they dissipate very quickly.

Fig 5 – GRS PT6816 Wavelet

The Wavelet in Fig 5 is something I’ve never seen before. There is a similar pattern of the main wavelet at 6kHz. Though the intensity is less, it looks exactly the same.

Fig 6 – GRS PT6816 Spectrogram

I thought perhaps OmniMic was recording a false plot. I switched over to REW (Fig 6) and the result is the same. At 6ms, a plot is recorded that looks similar to the main spectrogram.

It took me a few days to digest the meaning of these Wavelet and Spectrogram. It then occurred to me that the secondary plot is a reflection of the sweep from the back wall. Don’t forget, this is a dipole. The sweep is also emitting from the rear of the planar.

Summary

So far, the measurements are pretty impressive. The next step is to marry the PT6816 with a woofer to ascertain how she performs in a typical 2-way. More to come.

Unless otherwise stated, all measurements were made in Full Space (4pi). Mic at 36 ins, tweeter axis. Impulse Window=5ms. No smoothing applied.