[mhennessy]

The Roberts R707.

This is another set with a strong reputation for sound quality. And it does extremely well in these tests, happily. But with one important caveat: be careful with the tone controls! You can make this set sound horrible. There is too much range with both, and the amplifier/speaker combination doesn't cope well. This set - like the RP72 - uses Baxandall tone controls, but really needs padding resistors at the ends of the pots to restrict the range to something sensible...

This measurement was complicated by the loudness contour on the volume control. I set the volume to the mechanic centre, so we're seeing the effect of that on the measurements. The tone controls don't have a pointer, so to put those in their mechanical centre, I used stickers as temporary pointers.

The black trace - helped by the loudness tap - is really not bad. A very gentle tweak of the bass and treble controls ends up with a surprisingly flat response. These ended up being somewhere between 2 and 3 o'clock on their rotation - as mentioned, you have to be careful with these. Now, these sets roll away at HF a bit early, and the bass is a bit "bumpy" (high Q driver), but ignoring the harmless 1.6kHz dip, this set can be flat +/-4dB from between 70Hz and 11kHz.

Unfortunately, things change when the volume control is advanced past the mechanical centre, as the loudness tap reduces its influence on the response. For brevity, I didn't investigate this today, but could do in the future.

So, a good result!