Different loudspeaker topologies each produce characteristic on- and off-axis flaws.

Evidence

The original Quad ESL (Figure 1.3(c)) had a good on axis behavior, but the large radiating panels degraded off-axis performance, causing in-room performance to be compromised. The “dual-concentric” Tannoy (a) was an attractive concept, but it radiated annoyingly bright and colored high frequencies along with very boomy bass. The multi-driver large box Wharfedale (d) exhibited numerous resonances, and abundant acoustical interference. It was very colored and lacked sufficient low and high frequencies. — Toole, Floyd E, Sound reproduction- the acoustics and…, 75

Categorization

• XREF: The observation that ESL panels hurt off-axis response foreshadows the modern directivity-dispersion tradeoff discussion central to loudspeaker design.