Do you have a link to exactly this statement from SL?One of the reasons Linkwitz didnt like the sound of boxed full range speakers was because of the delayed sound coming through the cone and giving coloration to the sound .
One of the reasons Linkwitz didnt like the sound of boxed full range speakers was because of the delayed sound coming through the cone and giving coloration to the sound .
"...some in the process of flexing the cabinet walls. Much of it reappears outside the box, because the thin cone presents a weak sound barrier. Just how much is difficult to measure, but it is a contributor to the frequency response. I am of the opinion that the effect is most notable in the low hundreds of Hz region, where stuffing materials are ineffective and the internal dimensions not small enough for the internal air volume to act as a pure compliance. Consequently, enclosures should be either very small (less than 1/16th of a wavelength) or extremely large, both of which are not very practical for different reasons. ”
Okay so I understand everything correctly, let's go through two closed box examples. A midrange with 0.2m cabinet depth and a woofer with cabinet depth 0.5m.
The phase inverted sound of the cone back side is radiated and passes through the damping material, is reflected and inverted at the rear wall of the cabinet, passes again through the damping material and penetrates through the woofer cone with a time delay to the outside - so far simple to understand and logical.
The time delay for the two examples is therefore about 1.2ms and 2.9ms respectively. If we assume that the damping material "slows down" the speed of sound a bit, we might add another 10-20% delay (1.4ms / 3.5ms). The delays are of course correspondingly lower with lower cabinet depths.
The assumption or estimation is now that this time-delayed sound is radiated through the driver cone with only -20dB attenuation and supposedly "smears" the reproduction precision.
Now let's compare this with a concept that is supposed to be clearly superior (has already been mentioned here and was also the choice of S. Linkwitz) - open baffle speaker.
There are no reflections that are reflected back to the driver cone and radiate, with a time delay, through the cone.
But of course it is with open baffle speaker so that the backward radiated, phase-inverted pressure fluctuations, take the detour around the baffle and are radiated to the front with a time delay.
In this case, we can use simulation to determine fairly accurately how high the SPL of the sound directly from the woofer cone is compared to the SPL of the backwards radiated sound on the reference axis of the speaker. The time delay (or phase shift) of the rear radiated sound depends of course on the dimensions of the baffle used. Should be roughly comparable to those of the CB speaker or slightly less.
I recently simulated an open baffle speaker for the ""Analysis" of cardioid speaker radiation via lateral slots - like D&D 8c" thread and reuse the results here. The speaker baffle looks a little unusual, but for our purposes it will do. The time delay would be in this case about 0.3m --> 0.9ms.
Here are front and rear views of the OB speaker and crucially the simulation of front and rear radiation and the resulting overall frequency response all measured on axis:
We now have our first data points. At 400Hz the rear sound is attenuated by -7dB compared to the sound from the front of the woofer, at 700Hz by -15dB.
So if the time-delayed sound coming through the cone of a sealed speaker with about -20dB of attenuation has an audible effect on the main signal, then an OB speaker would have to sound downright awful, since the attenuation of the time-delayed sound in the midrange is just -7 to -15dB.
Unless you argue that the time delay of an OB speaker compared to a CB speaker is on average smaller and therefore less important (1ms delay okay, 2ms delay very bad) - but I don't know of any study on this off the top of my head.