Hej!
Linkwitz har tagit fram basmoduler till sin Pluto-högtalare. Eftersom Pluto är en aktiv högtalare med diverse aktiva filter så är ddet inte lämpligt att dela med ett vanligt 24/12-filter.
Från Linkwitz hemsida.. (Pluto är själva högtalaren och Pluto+ är basmodulen)
The PLUTO+ subwoofer is an addition to the 2-way PLUTO and was designed to reduce the low frequency demands on its relatively small woofer driver which limits output volume and low frequency response. The small driver was chosen to obtain omni-directional response into the transition region to the tweeter. The design goal for PLUTO+ was to leave PLUTO unchanged and not to require circuit or component changes. Something similar was done with the addition of THOR to ORION. In order to accomplish this, some of the low frequency content of the input signal must be shifted away from PLUTO so that it is reproduced by the subwoofer instead. This task is not as straight forward as it may seem, because PLUTO's acoustic low frequency response is that of a 2nd order highpass filter with -3 dB corner at 60 Hz. Cascading this filter with any standard 100 Hz electrical crossover filter highpass section will not result in a 100 Hz acoustic crossover. PLUTO's response determines the missing electrical filter response, that when added leads to the desired LR4 acoustic crossover response. The block diagram of the w-ASP shows the necessary circuit elements
To obtain the desired 100 Hz LR4 acoustic crossover behavior for the subwoofer it is merely necessary to cascade an electrical LR4 lowpass filter (U4) with the biquad equalizer (U5B). The LR4 acoustic highpass filter for PLUTO, though, requires more effort since that speaker's low frequency response has a 2nd order roll off below 60 Hz. This must be equalized - again with a biquad (U2A) - to become an acoustic highpass with fp = 100 Hz and Qp = 0.7 to form one of the two LR4 crossover highpass filter stages. The other stage (U1B) then uses the standard electrical LR4 filter topology.
För att åstadkomma det här har Linkwitz tagit fram ett aktivt filter.
På www.linkwitzlab.com besriver Linkwitz hur filtret är konstruerat, både i text och bilder. Så här står det i texten:
-ASP circuit description
The input signal which comes from a preamplifier is buffered and then divides into a branch for the midrange and a branch for the woofer. In the midrange branch is a highpass filter section, a biquad and an allpass. The woofer branch has two lowpass stages, a gain control, a shelving lowpass, a biquad and two opposite polarity output buffers.
| Concept & design | Subwoofer-ASP | Supplies | PLUTO |
Woofer - Analog Signal Processor
A new circuit board has been designed to simplify the construction of a woofer to midrange crossover or the addition of a subwoofer to an existing loudspeaker such as PLUTO or ORION. Previously it took one MT1 and two WM1 printed circuit boards, now the same task is accomplished with two w-ASP circuit boards, one for each channel, and additional capability is provided.
The w-ASP topology allows for a wide range of applications, but is geared towards sealed boxes and dipole woofers. The circuit description below gives an indication of how the board can be used.
The pcb itself is of the same high grade construction as all the other pcb that I offer, with 2 layers of 1 ounce copper on 0.062" FR4, tinned pads and plated through holes, copper fill and silk screened legend on top, solder mask top and bottom. The dimensions are 6.75" x 6.0".
w-ASP circuit description
The input signal which comes from a preamplifier is buffered and then divides into a branch for the midrange and a branch for the woofer. In the midrange branch is a highpass filter section, a biquad and an allpass. The woofer branch has two lowpass stages, a gain control, a shelving lowpass, a biquad and two opposite polarity output buffers.
J1 - The input signal goes through a dc-blocking capacitor and RFI filter.
U1A - Buffer stage and also configurable as shelving highpass.
U1B - Highpass filter section
U2A - Biquad, popularly known as Linkwitz Transform in this particular topology. Used to shape the acoustic highpass behavior of the midrange so that together with U1B a LR4 acoustic highpass is formed.
U2B - Allpass filter for delay of the midrange.
S1-S2 - Toggle switch to apply the unfiltered input from J1 to the midrange and turn the woofer off, or to turn on midrange and woofer equalization.
U3A, U3B - Two notch filters for room or dipole equalization.
U4A, U4B - Two lowpass filter sections in the woofer channel for crossover to the midrange.
U5A - Adjustable gain for the woofer and inverting amplifier that can be configured as shelving lowpass for dipole 6 dB/oct equalization. The Sum junction allows to sum in the other channel if a single woofer is used.
U5B - Linkwitz Transform to extend the low frequency response of the woofer.
U6A, U6B - Output buffer stages of opposite polarity for driving two power amplifiers in bridge configuration. When U6 is not needed, then Jumper-out allows connection to J3. The notch filters of U3 can be wired to Notch junction for equalization.
DC supply filter - Post filtering of the external power supply and power on LED.
U7A, U7B - Not shown in the schematic but at the top of the pcb are two powered amplifier sections that can be wired as necessary. Multiple solder pads for each lead, ground and floating pads are provided. It is a convenient circuit board section for experimentation with opamps.
Ovanstående finns på:
http://www.linkwitzlab.com/Pluto/woofer-asp.htm
Här finns även bilder
Frågan är nu - går det åstadkomma det här med ett Behringer DCX2496?
Själv begriper jag ingentig av hur Linkwitz filter är konstruerat, men det vore kanon om det gick anvädna ett DCX2496 istället.
Någon som har några synpunkter?
