Let’s talk about acoustics
Have you ever wondered what happens to the front panel of a speaker when the woofer cone is pushed forward?
That’s right, at this point the entire panel is moving backwards, including the midrange and the tweeters mounted on it. Consequently, the sources of mid and high frequencies move away from the listener at the moments of the compression wave of the woofer along the front. Also, the movable front panel itself is a source of radiation, as you understand, not intended for this at all. And finally, the amplitude of the woofer itself is partially damped due to the opposite offset of the panel. Of course, the main harm is that the panel that bends under load is a source of radiation of various parasitic resonant frequencies.
Various means are used to combat this phenomenon and body resonances. They simply reinforce the front panel, use composite materials, multi-layer construction, elastic damping when placing the speaker. There are even more effective methods: the use of struts from the inside, the use of two independent front panels, one of which, the internal, is a carrier, a woofer is fixed on it, the external has an independent support and almost no radiates sound into space. The loudspeaker is also used to mount the loudspeaker in a special open inner box, mechanically connected only to the rear wall, while the front only has a cutout along the loudspeaker profile.
Good loudspeakers should have the most rigid and inert enclosure, and they should be solid or rigidly fixed. The high rigidity of the structure itself, while saving material, is obtained through the use of non-parallel walls, this practically completely eliminates standing waves inside the box, which generate unnecessary overtones and prolonged bass, although this it does not solve the problems of vibration the walls themselves. An inexpensive solution is spacers. Rigid or weight mounting is required due to offset of all speakers with strong woofer cone offset, especially noticeable at lower frequencies. Bill Gates has solved this problem at home by installing the speakers themselves on the wall, the so-called “wall of sound”, this is also an ergonomic solution.
The mutual influence of the LF and MF-HF channels is not only mechanical. If the amplifier does not have the lowest output impedance, then the powerful background EMF pulses arising in the LF speaker winding through the LF filter go to the AC common input terminals, and from them to the MF channel. , experiencing a time delay. Along the way and at the edge of the band division, this signal can be strong enough to degrade the sound. It uses solutions like bi-amping and bi-wiring. The first is to feed different bands with different amplifiers, each of which operates in its own frequency band, transmitting the signal to the corresponding speaker through its own cable. Advantages: total absence of mutual influence of bands, no need for passive filters between the amplifier and the loudspeaker, the ability to use more effective active filters at the crossovers up to the creation of completely mirror characteristics at the limits of the band sections, higher overall efficiency, more stable operation of the amplifier-speaker system due to narrow band. Cons: the need for two amplifiers and a crossover filter. Bi-wiring is a much less efficient solution when using a single amplifier and separate pairs of wires go to the speakers for different bands. The back-EMF signal is bypassed at the amplifier’s output terminals, first passing through one pair of wires and returning through the other to another frequency channel. It makes sense to use at least pure oxygen-free copper (b / c) as the wires for the speakers, preferably a thin single-core wire for the HF channel and relatively thick, it is already possible to have multiple cores in the LF.
The signal that has passed through the integrator circuits of the amplifier and the AC filters, as well as delayed by the more inertial moving system of the woofer, undergoes time shifts, that is, greater delays in the low frequency region compared with discharge. -frequency one. To compensate for the phase shift, the speakers of the multi-directional system can be positioned so that the tweeter is further forward of the listener. I implemented it this way: on the front panel, in which all the speakers were initially located (in the same plane), I made a hole in the form of a small mini speaker, I made an additional panel with a slot for the tweeter, it You placed it inside, attaching it to the front panel from the inside, and you already placed the speaker on it.
