What would happen if the woofer didn't bottom out?
"My personal opinion here is to design a bookshelf speaker that won’t bottom out as easily, allowing it to be played at louder SPL levels, but ultimately producing less low end bass extension. The user can than bass manage the speakers and mate them with a good subwoofer or two to get the full range sound without stressing the system's woofers, thus preserving dynamic range and vocal clarity."
This implies that if the speaker with its bass extension is similarly combined with a subwoofer, that full range sound without stressing the woofers cannot similarly be achieved, and that dynamic range and vocal clarity cannot similarly be achieved. This does not make a whit of sense to me.
It seems to me that with a small speaker of this size and its itty-bitty woofer, that it is manifest that there will be consequences if it extends down below a couple hundred Hz. My intuitive expectation is that the woofer will either bottom out or else exhibit very high levels of harmonic distortion starting at SPL much lower than the level at which the woofer bottoms out. The question becomes whether you design the speaker so that its natural response curve rolls off before it gets into deep bass, vs. design it so that it will extend into deep bass at low levels but exhibit high levels of distortion when played at moderate levels, or design it so that it will extend into deep bass at low levels and assume that owners that want to turn it up to eleven are familiar with the operation of the bass control on the amplifier or the receiver. Evidently, Gene has issues with tone controls, and feels that rather than make it necessary for him to turn down the bass when he wants to crank it up to eleven, the manufacturer of the speaker should design it so that the response curve rolls before it gets into deep bass, even when played at low and moderate SPL.
Basically, it was turned up way high, and instead of exhibiting a steady increase in harmonic distortion, it continued to behave in a linear manner up until it bottomed out, and this is as bad thing?? Perhaps the reason why it is looked at this way, by the person having this complaint, is partly that they don't actually bother to take measurements of distortion and study how those measurements interact with other factors.
Many speakers do not bottom out no matter how high they are played, but you have to ask why this is so. If the force applied to the voice coil increases linearly, should not the displacement of the coil increase linearly as well? If it does not, then doesn't this imply non-linear distortion? In most speakers, one or both of two things will happen to prevent the coil from reaching the hard limit of its travel. In the ideal, the surround and the spider behave as ideal springs (and dampers), which means that there is a linear relationship between displacement and force. In reality, as they are stretched to their limits, the ratio of force to displacement increases, i.e., doubling the force no longer doubles the displacement. Additionally, and contrary to what I often read, overhung voice coils do not ever actually overhang the gap, because of all the stray flux. This is especially true when the magnet assembly is joined to a basket made of stamped ferromagnetic steel. The strength of the magnetic field experienced by the voice coil diminishes as it moves away from the midpoint of the gap, and as it does, the ratio of force to displacement changes. The electromagnetic force weakens as the coil displacement increases, the effect of which is equivalent to the opposing force (due to the surround and spider) increasing in a non-linear manner as the displacement increases.
These non-linear effects conspire. The net effect is that instead of the driver hitting a hard bottom, it hits a soft bottom, and it starts to do this long before the hard bottom would otherwise be felt. In practice, it is these distortion-inducing effects, and not the intentional application of high-pass filtering, that prevents most speakers from bottoming out. The reason they do not bottom out, in other words, is because they are designed in a way such that the distortion increases gradually from a moderate SPL and increases more rapidly than the SPL. It is analogous to "soft-clipping" circuits, which some people like. You can design an amplifier so that it will exhibit "soft clipping", but the price paid is invariably that the level of non-linear distortion will increase dramatically and before the hard clipping level would otherwise be reached. It is a dumb idea, and a better idea is to put idiot lights on the front of the amp so that audiophiles who actually are deaf because they always play stuff too loud can tell when the amp is clipping. By analogy, it makes sense to think of the woofer bottoming as an idiot light of a similar sort. The alternative would be to alter the driver so that it is inherently inferior and so that instead of bottoming out, it exhibits distortion that a good many audiophiles are evidently incapable of hearing. A loudspeaker review that does not at least attempt to measure flatness of frequency response and non-linear distortion is about as useful as human excrement, and the reason, for the lack of meaningful insight into the reported behavior of this woofer, is due in no small measure to the fact that no meaningful testing of any sort was done with this speaker. All they actually did was open it up and take some pictures, and offer some purely subjective and inherently worthless opinions on the quality of its sound. Well, given that they are selling these speakers and that they represent themselves as providing a greater service (which they do), I suppose that's the least they could do for us.
