- Written by John E. Johnson, Jr.
- Published on 26 April 2010
- Earthquake Sound SWAT 2.4 Wireless Transceiver
- Page 2: Design of the Earthquake Sound SWAT 2.4 Transceiver
- Page 3: The Earthquake Sound SWAT 2.4 Transceiver In Use
- Page 4: The Earthquake Sound SWAT 2.4 Transceiver On the Bench
- Page 5: Conclusions About the Earthquake Sound SWAT 2.4 Transceiver
- All Pages
On the Bench
The SWAT 2.4 does have more noise than you would encounter with a direct wire connection, but that is to be expected. Here is a 1 kHz sine wave spectrum. The receiver output clipped at about 1.2 volts output, and the output varies with the input to the transmitter (which varies as you change the volume control on your receiver). I did not hear any noticeable clipping in use, so the output voltage of the receiver obviously stayed below 1 volt. I could hear a hiss only if I turned the volume up nearly to full output (with no music playing).
The frequency response of the SWAT 2.4 was flat from 20 Hz to 20 kHz. It was down 2 dB at 10 Hz, which might affect some subwoofers, but this is correctable with the Auto EQ functions that are present on most receivers these days.
For transceiver 3, which had the receiver under the couch, I used two Bryston PowerPro 120 monoblocks, shown with the transceiver in the photo below. To test the limits of the system, I used an extra receiver paired to transmitter 3 and ran the left channel output of receiver 3a to one monoblock and the right channel output of receiver 3b to the other monoblock. It worked without any problem. Under normal conditions, you would only need the one receiver since it has stereo outputs.
I thought it appropriate to give some performance spectra for the Bryston PowerPro 120 monoblocks here.
THD+N vs. Power Output is shown below. It delivered 160 watts rms into 8 ohms and 240 watts into 4 ohms before rising rapidly to clipping (1% THD+N).
I measured THD+N vs. Frequency in a different way this time. Instead of the usual power resistor as a load, I used one of my Carver Amazing Mark IV ribbon speakers, because impedance changes with frequency, and this affects amplifier performance. I use planar speakers for the rear channels, so I wanted to see how the Bryston would perform into an actual planar speaker load. First, here is the Impedance/Phase graph for the speaker.
Now, THD+N vs. Frequency for the Bryston PowerPro 120, with 10 volts output into the Carver speaker. For comparison, I also tested my reference McIntosh MC1201 monoblock at 10 volts into the Carver speaker. You can see that the Bryston, with no load, had a steady 0.002% THD+N from 10 Hz to 50 kHz, while the McIntosh was at 0.0007%. At 10 volts output, the Bryston maintained a distortion level in the 0.005% to 0.009% range. The McIntosh had about 0.02% distortion in the low frequencies, but then dropped to 0.001%. Both amplifiers had a distortion peak at 8 kHz, which in the speaker impedance/phase graph, corresponds to a low impedance and - 600 phase (difficult region to drive).