We create not only our own speaker systems, but also do restoration, repair, tuning of speakers from other manufacturers.
Yes, they sometimes break, lose their appearance, need prevention, and so on. But the main thing – over time, the speakers may be a little bored with their not very good sound that they laid the manufacturer. Of course, the sound quality is not lost over time if the speakers are in good condition, the main thing is lost – interest in music if the sound of the speaker is not properly tuned by the developer. It’s no secret that the sound of the speaker is not all (even well-known) brands are close to ideal, and probably every experienced music lover or audiophile has encountered this.So, we return the attractive appearance and most importantly – life in the sound of the speaker!
Revel Performa M20 – shelf speakers of a well-known American manufacturer.
Reconstruction
Cabinet. Well made, massive, with stiffening ribs in the right places, almost deaf – ideal design for a classic shelf speaker. The cabinet has been restored, re-coated with black matte paint, and the decorative frames have also been restored and covered with new acoustic fabric. The bass reflex port is adjusted to a tuning frequency 1/3 octave higher for even better alignment with the bass speaker.
Drivers. Revel branded midbass drivers have undergone thorough diagnostics and minor repairs. Great drivers with good performance and incredible overload capability. Unfortunately, one of Revel’s tweeters could not be restored to the required parameters, so the branded tweeters were replaced by no less branded Seas, model H1147. They are also tweeters with a dome metal diaphragm and an additional rear camera.
Crossovers.
Completely new circuit, high and low frequency attenuators are disabled, impedance compensation circuit is added.
New tuning of crossovers, new sound.
Technical details of crossover settings:
1st order low-pass driver filter with a notch circuit tuned to 7.5 kHz. The filter starts the frequency correction from the frequency of 200 Hz, gradually tilting the characteristic to 2 kHz by minus 7 dB. The notch circuit removes the harmful “hump” frequency response of the midbass speaker. The 3rd order high-pass filter was also selected based on the high-frequency driver’s own frequency response. The low-frequency and high-frequency drivers are electrically connected in opposite phases. The frequency characteristics of the filters are “mirror” to the frequency characteristics of the drivers, so the overall frequency response of the speaker system with the new filters is as close as possible to linear. The uniformity of the frequency response is +/- 3 dB in the range of 60 Hz… 25 kHz, and in the most important mid-frequency range is in the range of +/- 1.5 dB. The impedance compensation circuit equalizes the resistance of the speaker system in the frequency range 125 Hz… 25 kHz to the value of 5 Ohms (+/- 0.7). This circuit is designed for correct operation of tube amplifiers with “non-zero” output resistance.
Transfer functions of crossovers 
Frequency response of loudspeakers 
Impedance 
Schematic and assembly diagrams of crossovers
Details of filters.
Traditionally, inductors of Ukrainian production Vajd Audio. Capacitors from the German manufacturer of audio components Monacor.
Anticipating the rather frequent questions about the use of inductors on ferrite cores and electrolytic capacitors: inductors are selected in such a way as to reduce the effect of their active resistance on the characteristics of the filters and at the same time “fit” within reasonable limits of overall dimensions.Electrolytic non-polar capacitors (or polar capacitors of double capacity with opposite serial inclusion) are used in circuits operating in the frequency range up to 2… 3 kHz. In this case, the electrolytic capacitors are only in the impedance compensation circuit. Large sizes of film or metal-paper capacitors of the required denominations can be replaced by small electrolytic capacitors without negatively affecting the sound in compliance with the requirements of the frequency range and accuracy of their denominations.
And finally, a few photos of crossovers that I made by accident, but they seemed interesting to me, reminiscent of the night city)
