Real speakers in real rooms - what to expect especially in the lower frequencies
When loudspeakers are being developed, they are usually designed and optimised (and subjectively evaluated e.g. critically listened to by the designer) under conditions whereby the listening environment plays as small a part in their performance as possible. Taken to a ridiculous (and subjectively ill-advised) extreme, a loudspeaker could even be entirely designed and approved in an anechoic chamber thereby completely removing the listening environment from the design equation.
Loudspeakers tend to radiate sound in all directions at the lowest frequencies and as frequency increases they generally become more beamy - i.e. they concentrate their sound in an ever narrower sonic pencil beam and logically, there is less sound spraying sideways. That's deemed to be a 'good thing', because with less sound sploshing around the listening room away from the essential axis to the listener's ears, the contribution of the room to the overall subjective experience should diminish. At least, that's the working hypothesis.
From time to time, with real-world speakers in real-world rooms there will be an unfortunate coincidence of dimensions, distances and surface absorption such that no matter how much effort is expended on stands, cables, pucks, spikes and the like the lower registers are unnatural. Rarely do listeners comment about excessive leanness in the bass even though the test equipment can readily reveal it. The problems that draw attention are due to subjectively excessive bass. Now some common sense. To be able to detect a difference in loudness, the human ear needs to detect a marked increase or decrease in sound pressure. That difference is measured generally in decibels, and as an approximation we can say that 2 or 3dB is barely detectable under optimum conditions in the middle frequencies where are ear is at its most sensitive. At lower frequencies, where our ears have poor sensitivity, perhaps ±6dB or even ±10dB is barely audible. That's a really good thing because it allows us to use real-world speakers in real-world home listening rooms and not be excessively concerned by the lumpiness in the bass register. It also means that, if we are honest, the introduction of gizmos and gadgets that make, if best, 0.01dB measurable difference to the sound simply cannot make the improvement they are claimed to make. Any benefit they could have is swamped by the lumps and bumps in the room's response.
So, is it likely that if you have a room issue at low frequencies that this can be solved with fancy cable? No. Not unless the amplifier is so poorly designed that its feedback control can't adjust to whatever cable load is connected to it and no audiophile should use such an amplifier for fear of damaging his speakers. How about different types of stands? Many say this can make a difference. Or what about isolating disks or the like between speaker and stands? Again, some swear by it and as it's unlikely do do any harm, why not have a flutter with them.
What are we left with as remedies if we discount these first, inexpensive and reversible steps? This is where we have to draw a dividing line between subjective DIY tweaks and acoustic science, a line none of use are really qualified in experience or resources to tackle to a perfect solution. Whatever we dream up has to strike a balance between what's practicable - and cosmetically acceptable. This is where we have to accept in our hearts that real speakers in real rooms cannot ever fully reproduce the concert hall experience. That's because the concert hall or recording studio is a box with its own acoustic character (esp. in the low frequencies which are difficult to treat), replayed over a loudspeaker (another box, same issues) in the listening room - yet another box. And if the recorded musical instrument itself is a box (cello, guitar etc.) then that's yet another box with its own acoustic character. So, recording a cello and replaying it at home is a box recorded in a box replayed through a box in a box room. And the only 'box' we have any influence over is, of course, the listening room itself, unless we want to delve inside the speakers and redesign them.
So what acoustic issues can we encounter when we put real-world speaker (like Harbeths) in a real world typical listening room at home? Continued ....
Alan A. Shaw
Harbeth Audio UK