Speakers
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| MBL 101 X-treme $ 199,000.- (a pair) |
Probably the only topic where the audiophile community agrees upon: of all components used, speakers have the biggest impact on sound quality. You might try different cables, different device drivers, tweak the buffer settings, etc., etc., nothing will affect sound quality as much as a pair of speakers.
One of the few sources of objective testing (measuring) is the Soundstage AV website.
It uses the methods as developed by Canada’s National Research Council (NRC).
http://www.soundstageav.com/speakermeasurements.html
Sean Olive is Director of Acoustic Research for Harman International.
He runs a blog containing articles about subjective speaker measurement: http://seanolive.blogspot.com/
How to position speakers.
Give them some air, against the wall or in a corner is not a good idea.
I use solo piano recordings to position them. If the arms of the pianist are too short, they are too wide apart.
A more useful advice can be found here: Audio physics.
Passive
Almost all speakers targeting the audiophile are passive.
One amp is driving multiple drivers. A crossover is needed to split the signal into frequency bands the drivers are build for. The crossover is in the power part, so only passive components can be used. This put constrains on the steepness of the filtering resulting in a substantial overlap between the drivers.
Active
The pro-world is dominated by active speakers, often 2 way systems where each speaker is directly driven by its own amplifier.
Slowly active systems targeting the home are entering the market.
The crossover is done before the signal enters the amp. This allows the implementation of better and steeper filters because now active components can be used instead of passive components only.
It also allows for correction of differences in phase.
Having an amplifier driving a single speaker maximizes the damping.
This will improve the transient response of the driver.
A very common active crossover is the 4th order Linkwitz-Riley.
The benefits are:
- Absolutely flat amplitude response throughout the passband with a steep 24 dB/octave rolloff rate after the crossover point.
- The acoustic sum of the two driver responses is unity at crossover. (Amplitude response of each is -6 dB at crossover, i.e., there is no peaking in the summed acoustic output.)
- Zero phase difference between drivers at crossover. (Lobing error equals zero, i.e., no tilt to the polar radiation pattern.) In addition, the phase difference of zero degrees through crossover places the lobe of the summed acoustic output on axis at all frequencies.
- The low pass and high pass outputs are everywhere in phase. (This guarantees symmetry of the polar response about the crossover point.)
Source: Rane Corporation
Butterworth all-pass crossover stage-audience relationship
Linkwitz-Riley crossover stage-audience relationship
Linkwitz-Riley is probably the summit of analogue crossover design.
At the same time it might be its swan song too as today all this and much more can be done using DSP.
Passive speakers can be turned in to active ones by replacing the crossover by an active one.
- Stereo 2- or 3-Way, or Mono 4- or 5-Way
- Linkwitz-Riley Alignment with 24 dB per Octave Slopes
- Adjustable Driver Alignment Delays
- Infrasonic, Ultrasonic and RFI Filters
- Low & Mid Output Muting (3-Way)
- Mono Sub Output Option
- Constant-Directivity Horn EQ Option
- Input & Output Level Controls
- Fully Active Balanced XLR Inputs & Outputs
- Internal Universal Power Supply (100-240 VAC)
DSP
Audiophiles are focused on a perfect reproduction of the recordings. In case of digital audio, a bit perfect rendering of the recoding is the holy grail. This is very much using a digital source as if it is a turntable, getting an as perfect reproduction of the source as possible.
As the signal is digital, it can be processed. Use a processor to do the crossover, correct phase differences by delaying part of the signal, correct frequency response, impulse responses in other words: bit imperfect as possible to improve the sound. That is the using the power of digital audio.
Digital in
You can do the processing on the output of the pre-amp but today an audio source is digital most of the time. A logical step is to take the digital out of the source and do the processing in the digital domain before it is send to the amp.
This can be done on a PC as well, a multi-channel sound card and software to control the channels.
The Loudspeaker Frequency Allocator is a 4-way, stereo DSP loudspeaker crossover that works with ASIO compatible multichannel sound card. Layout of each crossover leg is consistent with the way professional loudspeaker design software packages work. User is not limited to pre-canned filter algorithms such as B3 or LR4 that are so prevalent in the available hardware and software crossovers on the market today. Instead, we provide a series of flexible processing blocks that can be individually optimized to deliver the best match for the loudspeaker drivers used. Textbook filter settings are of course possible (either through direct input or by recalling factory patches), as are a vast range of other settings.
A brief list of features:
- fully integrated Phase Arbitrator section for transient-perfect reproduction.
- each DSP crossover leg adjustable from 6dB/oct to 42dB/oct on Low Pass and High Pass side.
- 4- band fully parametric equalizer in each leg.
- low and high shelving filters in each leg- both switchable between 6dB/oct and 12dB/oct (with q adjustment).
- up to 50msec delay in each leg- adjustable in 0.01msec steps (3.4mm resolution).
- output polarity switch in each leg.
- filter response display.
- frequency response data (.frd text file) for each loudspeaker driver can be imported and merged with filter's response.
- three zoom levels for viewing of the graphs.
- fully skinnable- GUI clearly laid out in an xml-like file.
- comes with two premade skins.
- 64bit processing throughout. SSE2 instructions utilized.
Source: Thuneau
A tweaker's heaven and the most advanced way to blow your tweeters.
But the concept it perfect, compensate for all deficiencies of your drivers by compensating for it in the digital domain. As a forum user put it:
Phase correction and room correction are slightly different animals. Both use forward reverse processing, i.e., they "pre-muck" the signal in the opposite way the system is *about* to muck things. Then, the pre-mucked signal coming into the system (crossover, room, whatever) is mucked according to the following vastly oversimplified formula:
opposite_pre_muck + muck = muckless
Presto
A bit more about speakers in the Reference section.