Distortion in the frequency response of small speakers and deep bass

Every radio amateur who at least once independently built acoustic systems knows that even the exact execution of the project, the recommendations of the authors of the design, does not always lead to the desired result. With all the complexity or simply impossibility of assessing the quality of home-made acoustic systems at home, except “by ear”, the authors of designs often do not provide either methods for evaluating their projects, or recommendations for their use (placement and connection of acoustics).

It happens that after the repetition of the next “masterpiece”, when the joy of finishing work on it passes, a period of painful assessments and conclusions begins. Enthusiasm and momentary euphoria often give way to almost disappointment. Indeed, it is difficult to look for the reasons for unsatisfactory work already in the finished structure, when “everything was done as it should”. Or maybe the design is good, but the amplifier is “not like that” or something else … Sound familiar?

Look in the amateur radio magazines of yesteryear for articles on loudspeaker design. Dear authors created their versions almost blindly, without taking into account the physics of electromechanical transformations and acoustics as such. Undoubtedly, a number of designs of home-made acoustic systems, techniques for modifying industrial acoustic systems and dynamic heads are successful and deserve attention.

Many designs have become a good “school” for lovers of high-quality sound reproduction in the endless cyclical process of creating or reworking a speaker system according to the principle: “It will just get really good …”.

But, note that the authors compared their developments (maximum) with industrial samples of acoustic systems from factories of the former USSR. They would try to compare their projects with the products of such companies as BOSE or JBL …

The objection to the purchase of an imported speaker system of the lower and middle price category is as follows: “Who told you that such acoustics in your living room will sound and not emit sweet-voiced sounds?” Motives like: “Don’t do it anyway” do not convince.

Of course, there are samples of branded acoustics that are incomparable in their design and sound, but their cost (as well as all the know-how) is very high.

Even now, when there is a real opportunity to use high-quality modern speaker drivers, descriptions of home-made acoustic systems (already on a new element base) that inherit design errors from previous years continue to be encountered. It seems that in the current variety of choice of source material, we can calculate and competently build only the speaker cabinet (box).

In fact, it is not only the volume of an acoustic system that is a determining indicator of quality. Sometimes the case, correctly calculated from the point of view of a uniform frequency response, does not sound. With the reduction of the main disadvantage of the existing dynamic heads – a significant unevenness of the frequency response in the mid-high frequency range, they will be little inferior to a good third of the imported ones and they can be used to build an acoustic system that will satisfy the discerning listener.

The beauty of building your own speaker system lies in the freedom to choose a design and get the desired result regardless (or almost independently) of the cost, which cannot be achieved in mass production. So, there was and still is the point to try to replenish your knowledge and start over. Despite the fact that in this material the specific design of the speaker system is not given, some aspects of the low-frequency section of the speaker system are presented from a practical point of view and are available for repetition or self-analysis with sufficient accuracy.

First. The acoustics of the room, or, more simply, the living room, is far from perfect. If you cannot improve the acoustics of the room according to all the rules (the proportions of the “golden ratio of 0.618: 1: 1.618”, the judicious use of sound-absorbing materials, the choice of the location of the acoustic system, the choice of the listening point, etc.), then you really should look mini-complex and calm down. Otherwise, let’s move on.

On the one hand, every room sounds different, even after making all reasonable adjustments to the setting. On the other hand, each of us knows the peculiarities of his home, we are accustomed to the “home” color of sounds. Our brain subconsciously begins to transform what we hear to its original color. So what really needs to be done in the room is to minimize standing waves, adjust the reverberation to an acceptable level, remove or damp resonant objects (surfaces), and organize the correct listening area.

Second. The emergence of new sound sources based on digital technologies, such as Hi-Fi video (with FM sound recording) tape recorders, PC (MPEG), compact and mini-discs, imposes new requirements on the speaker system: increased uniformity of phase-frequency and amplitude -Frequency response, wide dynamic range, minimal intermodulation distortion.

The nature of distortion in the speaker is due to the physics of the sound reproduction process and is so multifaceted that all types of distortion can hardly be eliminated in practice. However, some of them are well studied in the amateur radio world, and therefore lend themselves to control during the design process. The main rule should be this: each type of distortion is reduced individually and carefully.

Third. Cost of work. In any case, the cost of materials and components spent on the manufacture of a good “home” speaker will be incommensurably less than the cost of the speaker that you would have purchased if you had such an opportunity. This means that it is very profitable to invest your knowledge into the construction, which is called “for yourself”.

Last thing. When buying a branded speaker, no one, except the manufacturer, will give you recommendations for its placement and correct “tuning” for a specific situation. Neither the sellers nor the Internet have this information – only the subjective opinions of “experts” from the same stores. With the exception of some speaker models, to which printouts of the measured frequency response and harmonic distortion in the operating frequency band are attached, we have to buy practically any branded acoustics on the “pig in a poke” principle.

We start by choosing the speaker drivers. This will determine the type of speaker, namely two-way or three-way design. From experience I can say that it is very difficult to build a three-way speaker at home. Research and experimentation costs are double that of a 2-way speaker. Try to select dynamic heads for a two-way loudspeaker based on their acoustic powers (nominal power taking into account sensitivity) LF-MF to MF-HF as 1.5 … 3.0 to 1.0.

The overlap of the frequency ranges of the heads must be at least 2 octaves (4 times), otherwise it will not be possible to ensure accurate matching and smooth transitions of the phase-frequency …