«8 ohm compatible» is not «8 ohms»: Wharfedale Diamond 12.1 on a Marantz PM6007
Wharfedale claims no nominal impedance at all, only a 4.0 Ω minimum. That lands exactly on the Marantz’s 4 Ω limit: safe, with nothing to spare. 45 W give 104.5 dB at 2 m.
Safe, exactly at the limit.
The Diamond 12.1 datasheet does not state a nominal impedance. The line reads «8 ohm compatible», with a separate minimum of 4.0 Ω. The wording is deliberate and worth translating: it says the speaker will not upset an amplifier’s 8 Ω tap, not that it presents 8 Ω. The 4.0 Ω is the figure to design around, and it lands exactly on the PM6007’s 4 Ω limit — safe by the comparison, with nothing left over.
Where the Marantz keeps its requirement. Not in the specification table, which has no impedance line at all, but on the connection page: 4–16 Ω on Speakers A or on Speakers B, and 8–16 Ω when both pairs are driven together. Bi-wiring a single pair from A+B stays at 4–16 Ω, because that is one load, not two. Anyone who reads only the spec sheet will never see any of this, and the A+B case is precisely where a speaker sitting at 4.0 Ω stops being fine.
Level, and the limit that is not the amplifier. 45 W into 8 Ω at 0.08 % THD, 20 Hz–20 kHz, both channels driven; sensitivity 88 dB at 2.83 V / 1 m, a genuine one-watt figure at 8 Ω nominal. At 2 m that gives 104.5 dB, 6.5 dB below the 105 dB reference peak, 1.5 % cable loss on 16 AWG, damping factor 47. But Wharfedale prints a peak SPL of only 96 dB beside that sensitivity — the pair of numbers says the cone runs out of excursion before the amplifier runs out of watts. The 104.5 dB is what this amplifier could deliver into this sensitivity, not what the speaker will produce cleanly.
What to take from it. Marantz also lists 60 W into 4 Ω but without stating bandwidth or distortion for that figure, so the catalogue carries only the 8 Ω rating; damping factor is quoted as 100 at 8 Ω, 40 Hz–20 kHz. If you want more level from this pair, the honest lever is distance, not the volume control: at 2 m you are already close to what the cabinet does cleanly, and a second pair on the B terminals would take the load below what Marantz allows.