A SINGER STANDING RIGHT IN FRONT OF YOU
Extended full range, vented loudspeakers
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Gianluca G., Italy 2019
Markaudio Pluvia Eleven Generation 1 Vintage Gold - 16 cm full range driver with metal cone. The rubber surround is invers. Resonance frequency is very low (39Hz) and impedance is 8 ohm
Stuffing in the middle of the cabinet cavity with polyfill did the most efficient job of attenuating standing waves, un-veiling mids and flattening the response
I am and remain a big fan of the full-range single-driver systems: the naturalness and the acoustic image they provide is superior to any multidirectional system with crossover filters. The music played by a fullrange loudspeaker appears very natural, easy to listen to, with effortless details and realistic timbre along with a solid image of the soundstage.
Pluvia Eleven is a great speaker and offers excellent bass extention. I mounted it into a bass reflex box with a resonance frequency of only 38 Hz (FB), tuned just below the natural resonance of the driver in air (FS=39 Hz).
But, this is my opinion, it has limitations, at least in my original cabinet: it is very sensitive to the quantity and positioning of the damping material inside the cabinet, it is very directional, it sounds a bit dark and has some brightness peaks here and there. In short, it should be "slightly" helped (or corrected) in some way at the mid-high frequencies.
At first, I was just thinking of putting a rear-firing ambience tweeter simply connected in parallel through a serial R-C network, which helps a lot to correct the medium-high frequencies, thus allowing PLUVIA11 to continue covering the entire sound spectrum, without any LP low pass filter in series. Unfortunately, this led to an imbalance in the total electrical impedance and, even if the rear tweeter greatly expands the soundstage on one side, it compromises the sharpness and clarity on the other, resulting in a slightly tired and artificial long-term effect.
The Haas effect, which is basically the main cause of ambient tweeters' good job, makes the brain work too much: artifacts are being created into the acoustic scene that originally did not exist in the digital recording.
The second alternative (which I then adopted) is to go on an almost traditional two-ways speaker, trying to limit the phase distortions as much as possible, in order to don't jeopardize the advantages of Pluvia Eleven, that is focus and naturalness of the acoustic scene.
Therefore, my original single driver loudspeaker became an "enhanced full-range multibox system" based on a minimal first-order filter with a new additional tweeter-box tilted back and angled slightly toward the listener in order to optimize its time-domain relationship with the Pluvia 11 speaker below.
To build a loudspeaker cabinet and calibrate the crossover network I first need a good simulation program, a real in-ambient measurement, but in general everything has to be tuned by ear during several long comparative listening sessions with varied musical genres. This design methodology is circular and adapts constantly, until you find the best trade-off, according to your personal tastes.
"Boxsim" is a good program to learn how loudspeakers behave and to make both physical (for the cabinet) and electrical (for the filter) simulations. My experience leads me to say that software, such as Boxsim, should be used for the cabinet project and for the initial approach of the filter design, then a microphone should be used to refine the result and, in the end, always the ears. The software is very useful to accelerate the design phase, but the ear is what tells us if a good job has been done. In my experience, I can say that flat response curves are not always the ones which are most pleasing to the ear; see for example the response of some full range speakers that are not the best on the chart, but still sound very nice.
To produce a better mechanical time alignment and minimise phase shifts, the SICA tweeter has been tilted downwards firing towards the listener and put slight backwards, while the fullrange speaker Pluvia Eleven remains mounted in a straight line to the front of the cabinet. This improves the tonal balance and the focus image around the frequency change at the crossing points when the drivers produce the same frequency.
Simulation software here can only help if you have in your hands the numerical data of the frequency response, the acoustic phase, the electrical phase, the impedance history and the exact position of the acoustic centers of both speakers: hence, the best angle and the relative off-set distance will be determined by hearing test in the room and only once the filter has been built.
Schematic of the 2-way filter crossover: note that the SICA tweeter has reversed polarity.
It has been about thirty years since in the TOP AUDIO in Milan, by chance, when passing through a demonstration hall, I was suddenly astonished and amazed by the sound of the monstrous Dynaudio's Consequence. This made me literary approach the Danish house trying to snatch the secrets of such musicality and neutrality, which I discovered were common to all its loudspeakers in production. Surely there were two factors: the primarily use of first-order crossover filters with very low cuts thanks to the use of low resonance tweeters and extended band woofers, and, then, the unusual reversed vertical array of drive units (tweeter below) that allowed to time-align the drivers naturally without having to set back the speakers.
Since then, I have always built speakers with first-order filters with very satisfactory results before switching to the full-range sound, the latter being the only one that allowed greater tonal neutrality.
The filter was originally designed with first order attenuation (-6dB/octave slope): that because this type of filter is 'transient perfect', meaning it passes both amplitude and phase unchanged across the whole spectrum. The benefit of a first-order crossover is that they are electrically coherent in phase, that is, all signals at all frequencies are 90 ° out of phase. From here, the electrical and acoustical relationship coincide only if the acoustic centers of the speakers are in exact alignment in the vertical plane.
A driver used with a first-order crossover has to exhibit extremely good performance in the response, I would say extended two octaves and half beyond the specified crossover point.
This led to search and purchase for my original loudspeakers of a tweeter with very low resonant frequency, power at least equal to Pluvia Eleven (nominal 45W / max 90W), equal electrical impedance (8 ohm) and a with sensitivity +3/+6dB higher (>>88dB), letting me able to tune the tweeter filter with only two components but including a series resistor; if the tweeter had the same sensitivity, the resistance could not have been included, greatly limiting the very important and foundamental session of filter calibration by ear.
In addition, the cost and quality had to be comparable to those of Pluvia Eleven.
It was not an easy choice, especially from catalog. Thus, I discovered an Italian company, undeservedly little known, that builds excellent speakers with high efficiency: this is SICA, LP 90.28/N92TW, 8 ohm, 94.4dB, 50W nominal power, 1.1-inch dome and with a resonant frequency of only 600Hz!
The very low frequency resonance of the tweeter (SICA) and the upper extended bandwidth of the full range (Pluvia Eleven) can handle this type of filter without increased distortion across the crossover frequency.
Subsequently, after many listening sessions and with the help of Boxsim software, the filter was improved by adding R-C networks to the drivers. Becoming the load seen by the amplifier more resistive, the parallel resistors flatten the loudspeaker impedance, while the capacitors damp unwanted peaking at medium-high output frequencies: these peaks in the response are maily due to the breakup behaviour of the fullrange cone, over all in 8kHz-10kHz area, which can translate into annoying audible "hiss" in the singer voice, expecially those female.
The upper driver LP 90.28/N92 (8 ohm), by SICA Altoparlanti s.r.l. (Italy), is a treated silk dome tweeter which exhibits extremely low resonance (600Hz) and distortion across its extended frequency spectrum
Boxsim freeware simulator is one of the most powerful and user friendly software programs available for simulating HiFi loudspeakers. It is aimed at ambitious amateur loudspeaker builders who have already experience of calculating loudspeakers but it is also suitable for beginners who wish to use this program to acquire those skills. In contrast to many other loudspeaker simulation programs, Boxsim also includes its own algorithm for simulating edge diffraction from the baffle (baffle step). As a result, Boxsim is able to simulate a loudspeaker of virtually any proportions based on measurements in a standard environment. Launched by UweG, Visaton.de, now version 2.0, Boxsim is free-of-charge to the user (freeware).
At home, in-room measurement of one loudspeaker, using SONY PCM-M10 omnidirectional stereo microphones (@ 2.83V, 2.1 meters distance, 85 cm above floor at mid point between tweeter and full range, average and calibrated L&R mic): 1/3 octave band frequency sweep, pink noise (at 1/3 octave and one octave band shifted -50dB), including white noise comparison. Curves are relatively similar to each other and closely resemble what has been simulated with Boxsim software. Fluctuations of 1/3 octave curves are limited within ±6 dB from 50Hz up to 20KHz.
Two-tone intermodulation distortion (IMD%), using two prime tones at 167Hz and 2447Hz frequency, both played at -10dB level.
In-room measurements of the total harmonic distortion (THD%) of the loudspeaker at the various frequencies: 50Hz, 100Hz, 1KHz, 2.5KHz, 5kHZ, 10kHz tones (@ 2.83V, 2.1 meters, 85cm from floor, average L&R mic). Less than -30 dB (3%) at low frequency and less than -40 dB (1%) at mid-high frequencies is normally considered to be good. Harmonic distortion of "The 2020 Anniversary Ed." is below 1.5% starting from 50Hz, with the 2nd harmonic being dominant: an audio system with high levels of second order harmonic distortion usually sound quite pleasant and warm.