B&W Matrix 800 Series Variable Bass Alignment Filter & Equalizer
B&W Bass Alignment Filter. enlarge. This free website's biggest source of support is when you use these links, especially this link directly to this equalizer at eBay (rare), and this link to all B&W Matrix speakers (see How to Win at eBay) when you get anything, regardless of the country in which you live. Thanks! Ken.
Bowers and Wilkins' Matrix 800 series of speakers from the late 1980s through the mid-1990s were designed directly to John Bower's vision as part of a system incorporating an active, dedicated low-level filter in the preamplifier signal path to optimize the bass performance, not only in frequency, but also in the time and phase domains.
This dedicated bass equalizer, also called a variable high-pass alignment filter, was often included with the speakers since its frequency response is an integral part of the systems' sixth-order design, however, some speakers were purchased without it, necessitating finding one of these filters on eBay today, as this one was acquired for $110 in 2011.
Without this equalizer, the naked B&W Matrix speakers are a vented fourth-order design, specifically in a Bessel alignment. "Fourth-order" is an engineering term that refers to all vented and passive-radiator speakers; sealed boxes are "second order."
In this discussion, "alignment" has nothing to do with physical placement of components, drivers or anything; in this case, alignment refers to the poles and zeros of the abstract (imaginary) mathematical transforms that are used by speaker designers to predict the exact frequency responses of speakers before they are built. Speakers are designed by modeling the low-frequency performance as an electrical filter, for which engineers have many tools to simulate. Once simulated, the drivers, vents and boxes can be designed and then built just once exactly without having to build numerous samples to see what happens.
For the Matrix series, a Bessel alignment (type of frequency response curve) was chosen for the physical speaker because the Bessel alignment just happens to have uniform group-delay, meaning all frequencies leave the speaker at the same time, so nothing gets time-smeared.
The Bessel alignment also has the advantage that adding a very simple second-order electrical filter (this equalizer) allows one to create a completely different kind of alignment, a sixth-order Butterworth alignment, whose frequency response is also flat, and extends and extra half-octave deeper in the bass. The high-pass nature of this filter also ensures that extreme low-frequencies below the speaker's range are removed, preventing the woofer cone from flopping all over due to recording-venue noise (or turntable rumble for you old-timers).
This bass-alignment filter (BAF) is so integral to the design of the Matrix 800 series that even the shipping boxes say "SIXTH-ORDER" in great big letters, and this equalizer provides two of those six orders. B&W speaker specifications were listed "like this,*" and the "*" said "when used with the active alignment filter. Without the filter, the response is much worse.
"Filter" and "equalizer" mean the same thing here. Engineers call this a "filter," while to most people, "equalizer" means more. This "filter" very precisely boosts the bass, as well as removing subsonic frequencies that cause distortion.
The circuitry is all discrete, using a few transistors instead of an integrated circuit operational amplifier.
Low-frequency loudspeaker design is usually at mercy of your box volume.
Box volume ultimately determines the limits of overall sensitivity and bass extension.
For any give box volume, the sensitivity and bass cutoff frequency are interrelated. To get more bass extension, you have to lose sensitivity throughout the entire audio band, or to get more sensitivity, you have to give up bass extension,
— unless —
you use a dedicated active equalizer designed to correct exactly the low frequency response, in which case, you can get the equivalent of a much larger box' improved low-end response, or more sensitivity, or a combination of both.
This little equalizer is the brilliant little addition designed as part of this series of speakers to allow much deeper bass and more sensitivity than one could get otherwise.
Later Years top
The concept of combined electrical/mechanical loudspeaker design and equalization is beyond most people's comprehension, so B&W eventually went back to designing dumber speakers that don't take advantage of this filter.
As I recall, the Nautilus did away with this filter. That means that the Nautilus series is designed with a slightly more boomy bass that won't extend as deeply as the earlier speakers that are designed expressly for use with this EQ.
In other words, the original Matrix speakers are designed for a Bessel (underdamped) response, meaning there isn't a bump (resonance) in the bass response typically around 100 Hz.
When B&W went more mass-market after the mid-1990s, they retired this brilliant concept, as it was beyond the comprehension of everyone that didn't have at least a bachelor's degree in engineering.
Later speakers, like the Nautilus, are less damped, meaning that there is more of a peak in the bass response to try to eke out as much midbass as possible without the benefit of the intelligent optimization of this equalizer.
Other Brands top
Krell and others have made filters that do the same thing, in much larger boxes of electronics. A beauty of this device is that it can lie behind your amplifiers and not take up any more rack space.
Using the data, an engineer could make his own filter; second-order high pass filters are first-year engineering exercises.
About $250 when new in the 1990s, which is equivalent to about $350 today with inflation.
To use it, simply insert it in a tape-monitor or external-processor loop, or insert it between your source and your power amplifier.It has a mute relay which takes a second to unmute, and mutes instantly, as power is applied and removed. This is to prevent turn on and off thumps from getting from your system to your power amplifier.
The box shown at the top holds only the audio electronics. Its DC power supply is separate, and permanently attached:
B&W Bass Alignment Filter with captive power supply. enlarge.
The attached power supply will vary with country. This sample is rated for 110 VAC input.
If your speakers came with this EQ, it's set for your speakers.
If you have to buy one separately, it comes optimized to one model of speaker.
If you need to set it for a different speaker than as shipped, the manual shows how to set this filter for use with any of the Matrix 800, Matrix 801, Matrix 802, Matrix 803, Matrix 804 or Matrix 805 speakers.
Ads for the Matrix 801 and 802 Series 2 of 1987 also mostly mandated the use of this filter.
After the mid-1990s, since people aren't engineers and never really understood how to use these filters, B&W has since dumbed-down their speakers for reduced performance without this filter. In other words, the Matrix and Matrix Series 2 use this filter as an integral part of a more advanced design, but since people weren't using these as they were supposed to, B&W dumbed-down their speakers to do as best they could without the added intelligence this dedicated compensation network adds.
Following the directions, this is a second-order high-pass filter with a "Q" of 2.0. The frequency is set to correspond with your particular model of speaker.
If you have any other sort of speaker and are an engineer, the manual also shows how to adjust this filter for any other frequency or Q.
Other Uses top
Each of the two channels is adjustable separately.
For mono use, each can run by itself.
For mono use, the filters can be cascaded. THis means the output of one can be fed into the other, and thus the effects of two filters are used for a fourth-order response.
This can be useful to estimate the effect of various filter settings on a second-order (sealed-box) speaker. If you know your speaker's response (for instance, the original sealed-box 801 is aligned for a Q of 0.7 and an F of 37 Hz), you could program it into one filter, set the other filter to your proposed setting, and by measuring the cascaded response, simulate the response of an entire filter/speaker system without needing the speaker or to make acoustic measurements.
Instruction Manual top
Here's B&W's instruction sheet. (B&W's figure three has an error.)
Tuned Frequencies top
The frequencies to which these settings tune this filter for various B&W speakers are:
THD: Set for Matrix 805
THD, 1V rms input, D1-D9, 22kHz BW. (Rohde & Schwarz UPL, Left and Right.)
This is excelent, and pretty much the THD floor of the state-of-the-art analyzer.
Frequency Response: Set for Matrix 805
Frequency response, 1V rms input. (Rohde & Schwarz UPL, Left and Right.)
Frequency response, 10-100 Hz only. (Rohde & Schwarz UPL, Left and Right.)
Frequency response, 100 - 1,000 Hz only. (Rohde & Schwarz UPL, Left and Right.)
Frequency response, 1 kHz - 22 KHz only. (Rohde & Schwarz UPL, Left and Right.)
Note the exteemlt expanded scale, no other audio gear is thsi flat, and it's flatter than the specification for the Rohde & Schwarz UPL analyzer! Note how I've expanded the scales to crazy values as te frequwncy range climbs.
As expected, when set for the B&W Matrix 805, the frequency response is flat (0 dB) for most of the range, boosts to a maximum of +6.1 dB at 37 Hz, and drops-off below that.
Impressive is how well balanced are the two channels.
Group Delay: Set for Matrix 805
Group Delay and Frequency Response, 30 Hz - 100 Hz. (Rohde & Schwarz UPL)
Group delay is a maximum of 18 ms.
Frequency Response: Set for Matrix 804
When set for the Matrix 804 (as an example), indeed, the frequency response was flat (0 dB), boosted to a maximum of +6 dB at 27 Hz, and dropped-off below that.
Frequency response was well within ± 0.1 dB to way beyond the audio range, down only 1 dB at 300 kHz, and down 3 dB at 570 kHz, which is the bottom of the AM radio band. The high-frequency response was limited more by my audio test equipment than the B&W filter itself.
Midband gain was within at least a tenth of a dB of 0dB.
Here are more measurements, as set for Matrix 804, filter response only:
-12 dB at 12 Hz (rumble reduction)
-6 dB at 16 Hz (rumble reduction)
0 dB at 19.5 Hz
+6 dB at 27 Hz
back to unity around 100 Hz and above, as expected.
THD + Noise
While THD is rated at <0.005% at 1 kHz at 2 V RMS, I only barely can measure 0.0007% (zero point triple-zero seven percent or -103.5 dB) at 1 kHz at 3.16 V RMS, which is just a little above the 0.00045% residual level of my VP-7721A laboratory audio analyzer, all measured at 30 kHz bandwidth.
Signal to Noise Ratio
Residual noise in an unweighted 30 kHz bandwidth measures -114 dB V RMS (2.0 microvolts RMS ) on my VP-7721A laboratory audio analyzer. Considering that the residual noise level of this analyzer is rated at 10 microvolts and measures 3.9 microvolts RMS from a 600 Ω source, this filter's lower output impedance is actually improving the input noise figure of the analyzer!
Referred to the 2 V RMS output of a CD player, this gives us at least a 120 dB signal-to-noise ratio, since the noise I'm measuring is limited more by my instruments than the B&W filter.
As only the deepest bass is optimized, and the optimization is never more than a mild 6 dB, there won't be much audible difference with or without the filter to the casual listener. It will be about the same or less than moving the 32 Hz slider up by 6 dB on an octave equalizer — but the beauty of this filter is its exact calibration in frequency, phase and time to the B&W Matrix speakers.
To hear the filter's effects, one needs music (or test tones) with very low frequencies. This filter doesn't alter the midbass, where casual listeners hear things. One needs to be a relatively experienced listener to notice the improvement.
If you have a set of B&W Matrix loudspeakers and don't have this dedicated equalizer, you're missing out because B&W Matrix speakers are designed specifically to be used with this filter, as your loudspeaker manual will remind you.
If you use your speakers full-range, you need one of these filters.
If you use subwoofers, it doesn't matter, and in fact, might be better to skip the filter, depending on where you might put in in your overall system topology.
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