What's a DRSC?
It's a new type of speaker where front and back sound radiations of the drivers are utilized.
For multiple reasons:
DRSC vs traditional monopole speakers
- Less or even no room modes excitation
A room is an acoustical element. The shape, position of the speakers and listener, furniture, walls, carpet, curtains... everything modify the sound. Some elements absorb the sound and others reflect it. Reflections change the frequency and time response of the system. The frequency response can be corrected with and equalizer, but the time response (phase distortion and reverberations) need a bit more power to be solved.
To understand how a room affects the sound, sound technicians use the Impulse Response of a room. To simplify, the IR is the equivalent noise heard in a room after a gun shoot, balloon explosion or even a clap, a very short and powerful noise.
- Room 1
- Room 2
- Room 3
- Room 4
- Room 5
- Room 6
- Room 7
Monopole impulse response.
Looking at the graph from left to right the first spike is the direct sound (clap,gun shoot etc) after there are some early reflections and finally the reverberation (sound reflected more than once)
Dipole impulse response.
On the other hand, in the dipole impulse response graph it's clear that there is "less room". The effect of the room is minimized compared with the direct sound.
Room frequency response.
This is the frequency response of one of the rooms listed above. The frequency response measures how direct sound behaves, but we already know more...
Room waterfall plot.
In a waterfall plot all the information is visible: how the frequency response is modified over the time. Those crests are room resonances or room modes and are caused by the reflections of the sound inside the room. Note the slope of the crests are different because the energy/absorption (quality factor of the resonance) is not the same at all frequencies.
Looks ugly, eh? All the music played inside a room is modified mixed and blurred with all those resonances.
Some examples of rooms with horrible acoustics:
- Normal music
- Room 1
- Room 2
The "clap trick" is very useful measuring the room acoustics: just clap inside different rooms and try to recognize the differences between them. The last test will be to clap outside in the middle of a forest with no sound reflections, that's how a dipole sound.
All sound waves travel at the speed of sound. Depending on the frequency, the waves have different wavelength. When the wavelength is similar to the dimensions of the box (0.5,1,1.5 ... times the wavelength) a resonance (or standing wave) occur, modifying the normal response of the speaker. Normally there are a lot of resonances inside the cabinets because of the wide bandwidth of the speakers.
First (half wave), second (full wave) and third (3/2 waves) harmonic standing waves (of speed; pressure are 90º shifted) inside a enclosure.
To reduce this problem, traditional speakers are filled with fibers.
Dipoles have no real box and they don't suffer of this type of resonances. The design was carefully made to push the "open pipe" resonances away in the spectrum.
Traditional speakers compress air inside the box and this process is not completely linear. To be linear the process must be as much isothermic (filled with fibers) as possible or work in an infinite baffle, but the real data shows that the process stays between adiabatic and isothermic. It is only linear in small signal response. At large signal response the distortion is clear:
Gamma = 1.4
To reduce the power demanding the Thielle Small parameters of the speaker and box volume are set to give some resonance at the low end of the spectrum. Resonance means energy storage. Energy needs to be provided to start moving and needs to be released to stop moving. The cone of the speaker moves a bit out of control. The system has no real control of the movement. It is an open loop.
Dipoles have a total lack of these problems.
As dipoles don't compress air, the movement of the cone is easier. The mass of the cone can be lighter too because there is no mechanical stress as in the traditional speakers. Speakers are extremely inefficient devices (around 1% of efficiency) because the mass of the cone is way bigger than the air moved. The cone of the dipole speakers can be lighter offering a superior efficiency.
Polar diagram of a DRSC
The sound is directed in the listener. This is extremely useful and efficient, all the power goes in one direction: in the direction you need it to be.
Traditional monopole speakers radiates in circles exciting all the resonances of the room. Is very difficult to localize a monopole bass speaker. The sound comes from everywhere. In a dipole the sound comes only from one direction. Playing bass instruments and even voices are incredible, how easy is to localize them.
Easy acoustic isolation (EAI®)
Looking again at the polar diagram of a DRSC two lobes are visible and represent the front and back radiation waves of the speaker amplified by the wave-guide (box). The amount of cancellation between the front and back waves is directly dependent of the speed of sound. When those out of phase waves hit a wall, the material changed and the speed of sound too:
The speed of sound is 10 times higher on average on normal home materials, allowing the walls of the room to act as an acoustic short circuit, minimizing the isolation needed and keeping the sound inside the room.
Traditional closed box speakers suffer from an increase in the frequency of resonance of the baffle because of the compliance of the air inside. The bandwidth of the bass drivers is normally compromised with closed boxes. Vented boxes offer better bass extension but very bad temporal response and suffer from acoustic short circuit below Fb (resonant frequency of the box).
The roll of bass frequency of a dipole is normally selected only on the SPL (Sound pressure level) needed. They can go really low as the cut off slope is only 6dB/octave. If a dipole can generate 30Hz @ 100dB it will have no problems with 15Hz @ 94dB (now the problem is if your ear is sensitive enough). With some correction the frequency response can be flat again and extended to the deeper region.
Panel resonances are a real problem in monopole speakers. If the stiffness and absorption of the walls of the cabinet are not enough, very unpleasant resonances will appear. Dipoles can generate the same SPL with fewer forces affecting the box. The box can be lighter and still resonate less.
Other speakers need exotic material to work properly and price is increased dramatically. The Freedom Speaker with the revolutionary DRSC offers an ultra high-end quality and performance at a very low price.
To overcome the acoustical short circuit, The Freedom Speaker has two very powerful 15" woofers. For the rest of the spectrum, two 4" full range drivers.