Discovering How Amplifiers Dramatically Affect Loudspeaker Output

While reviewing the Bowers & Wilkins 801 D4 speakers, I had occasion to address a potentially consequential issue, namely the demands the 801 D4 makes on the amplification preceding it in the audio chain. During my first weeks with the 801s, I remained enthralled by the way they uncovered the basic nature of all stripes of music they encountered—but also began to sense a lack of control and “grip” with dynamic source material. I’m not just talking about grand opera and headbanger metal; a well-made solo piano recording could also alert me to the issue. My 60W Pass XA 60.8 monoblocks were clearly falling short; substituting the 200Wpc David Berning Quadrature Zs got better results, but I was still “leaning in” to fully engage with the music.

This isn’t a new observation, by any means. The 801s have long had a significant impedance drop from the upper bass to the middle midrange. Although Andy Kerr explained that the D4 version of the speaker was “somewhat kinder than the D3” in this regard, it still requires a lot of power, and the right kind of power, to perform at its best. I’m certainly not a measurement kind of audiophile—my skills are rudimentary, and my engineering background is nil—but I do have a Dayton Audio OmniMic V2 system that I use for taking measurements from the listening position to optimize subwoofer integration and to at least take a look at the in-room frequency response of the loudspeakers here for review. I connected it up, played sine wave sweeps and, with the Berning amplifiers, saw an 8-to-10dB depression between 200 and 1000Hz. The lower bass was messy, as well. Clearly, I needed to hear the 801s with more robust amplification.

The nearby dealer Doug White (The Voice That Is) loaned me the new Tidal Intra stereo amp that delivers 330Wpc into an eight-ohm load and 670 watts into four. The substitution of the Intra for the Quadrature Zs was transformative. The measured dip decreased to just 2-to-3dB, which can easily be room variation. Subjectively, there was an obvious improvement in immediacy and control. 

One certainly should not conclude that there are only a few amps out there that will do the job. Just a few days after I parted ways with the review pair, for example, I heard the new 801s at Capital Audio Fest played with a pair of McIntosh MC901s, the solid-state section driving the woofers and the tube section handling the upper drivers. The results were stunning. 

The fundamental point is that the way different amplifiers handle the varying impedances and current demands of real speakers is not a given. By a long shot.