Re: Measurement of M40.1 in designer's listening room
OK, as a one-off I've set-up my M401s roughly in the normal place (I don't have an exact spot, the floor's not marked) and measured with the same omnidirectional reference mic at my usual listening position. To my surprise, following your method (which I still don't believe is appropriate for testing hi-fi speakers at home) of driving two speakers simultaneously, you'll see just how smooth the overall response is.
All rooms introduce a gentle lift at low frequencies as is shown here. Providing that it's gentle, it very much enhances the quality of the overall listening satisfaction. Maybe you've read here that I'm very much a supporter of the QUAD-type tilt controls. It makes no sense to me whatsoever to have removed tilt controls from amplifiers (a fad in the 80s that infuriatingly caught on) because a click or two on the tilt control and, if you chose, you can exactly compensate for the expected room gain in the lower frequencies. You might well prefer the lush, warmer uncorrected sound ( I do), but if a perfectly flat graph trace is what you want then you can easily have that. But be careful - my experience is that a ruler flat response, especially in the bass, just doesn't sound involving.
Peter Walker, QUAD's founder and a contemporary of our founder, Dudley Harwood knew exactly how speakers behave in real rooms and designed a solution. To quote the QUAD manual -
"The tilt control operates exactly as its name implies and produces a very gradual change in balance across the musical spectrum without changing the overall subjective level. This absence of sudden change means that there will be no 'colouration' added to the sound. The sound will remain entirely natural... If either the recording environment and the listening room are rather lush sounding, the -1 (or even -2) would be used to restore detail. In using this control the extreme bass and extreme treble should not unduly influence judgement because they are separately adjustable. The bass control serves two purposes. In the step mode the control acts as a step filter which removes the characteristic 'honk' caused by the excitation of the room's eigentones when the loudspeakers have to be placed in or near a corner."
As I said recently here, 'if Harbeth made an amp it would have a tilt control': I think I've fully justified my position on that. It's nothing short of a disgrace that tone controls do not appear on amplifiers - they are the perfect, inexpensive and logical way to optimise the room without resorting to lots of physical damping - although their use is really complimentary.
Now this unscheduled discussion has pinched a good deal of time from other work which I must now return to. I hope though that it's put you on the track to getting along with your room as is, or experimenting with options for improvement which may be electronic (like the QUAD-tilt or similar) or mechanical - like panel absorbers. Good luck.
Oh P.S. - remember - gradual tone-controls like the QUAD tilt control will only adjust general trends in the bass; they will not attack and remove 'hot' frequencies due to room nodes etc.. To do that you will have to use narrow-band correction, either digital or analogue. Perhaps borrow a system?
Alan A. Shaw
Harbeth Audio UK