The B&W web site used to have a page that dealt with some of the Frequently Asked Questions for the Matrix speakers. When they redesigned their site that page was removed, so I created this page for those still interested.
I've since found it on the B&W Support site (in the "Upgrades" section) where there seems to be all sorts of useful information about B&W, Rotel and Classe products including owners guides, service manuals and so on.
Here is the text specific to the upgrade of B&W speaker crossovers:
Can I upgrade my speakers?
We always endeavour to use the best and most appropriate components in our products, commensurate with current knowledge and any cost constraints, so we believe they offer excellent value. However, many customers ask if they can upgrade their speakers in one way or another.
Before we discuss specifics, a word of warning......
If any person, other than an authorised agent of B&W Group Ltd, makes any modification to any B&W product, or if an agent of B&W Group Ltd makes a modification not approved by the company, the company reserves the right to consider any outstanding warranty on the product null and void.
That may seem a little draconian, but it's a bit of legalese we have to use because we have no clue as to how competent you might be. However, if that hasn't put you off, read on....
We are reasonable people and will always try to help you if you get in a mess.
Some ask if they can convert one version of a model to another (eg Matrix 801 Series 2 to Series 3). In general it is not easy to do this, because we have a tendency to change the way we put things together when we make a model change. That usually means that the new parts do not fit in the old system. That is certainly true of the Matrix 801 variants. In many cases it may be cheaper to trade in the older model for the newer one than buy all the new parts and have them fitted.
The most common questions about component upgrades refer to crossover components and internal cables, but occasionally people ask if they can substitute a more recent driver in an old system.
Cables are not really a problem as long as you can actually feed the cables where they have to go. Some of the routes are narrow. The hollow rod joining the Matrix 801 midrange enclosure to the main cabinet is a case in point. Beware of getting rattles when laying the cable. Make sure it cannot vibrate against drivers or the enclosure walls. In this respect it is better to use cable with a soft insulation.
We usually find that customers who alter crossover components are not fully satisfied with the results. They find that some aspects are improved, but others made worse. A classic case of this is when a polypropylene or other very low-loss type substitutes an electrolytic capacitor. We all know that polypropylene capacitors can sound inherently better, but the change in internal losses changes the response of the filter, which is designed assuming the losses of the electrolytic component. What usually happens when the low loss component is fitted is that the corners of the roll-off are sharpened, giving a peak in the combined response that can make the sound unpleasant in various ways depending on the crossover frequency. One way of getting round this is to wire a small resistor in series with the capacitor to approximate the original losses. I say approximate because the loss factor is a frequency dependent resistance. The actual value you need depends on the original capacitor loss factor and its capacitance value. The larger the value, the lower the resistance for a given loss factor.
The formula for the equivalent resistance is:
R = d / (2π fC)
where R = resistance in ohms, d = loss factor, f = frequency in Hz and C = capacitance in farads.
Loss factor is usually expressed as a percentage at 1kHz. For a "low-loss" electrolytic such as the values between 1μF and 20μF found in tweeter circuits, d is of the order of 0.025 (loss factor of 2.5%). For values in the hundreds of microfarads it may be of the order of 0.07 or 7%. Typically therefore a good electrolytic capacitor of 5μF would have an equivalent series resistance of 0.8Ω. If the capacitor has a much larger resistor in series with it anyway, it's probably not worth altering.
The same argument applies if you substitute a cored inductor with an air core type. Always try to duplicate the DC resistance as well as the inductance. Sometimes inductors are deliberately wound with relatively fine wire to give a certain resistance to add damping to the circuit. Iron dust cores (sometimes called P-cores) have higher losses at higher frequencies than at lower, due to eddy current effects. Substitution of an air core, even of the same DC resistance, may give a steeper ultimate slope in the stop band that can alter the phase relationship between the two drivers. That can also mess up the overall response and skew the optimum listening angle a little.
The term crossover is a little misleading. The networks add equalisation in the driver's pass band as well as dividing up the frequency range. Substituting a different driver more often than not needs a change in the crossover to give the appropriate equalisation for that particular unit. Simply plugging in a different (even nominally better) driver without attending to this often disappoints.
As you can see, it's a potential minefield and difficult to get the optimum result without proper measuring facilities. Adjustment just by ear tends to give good results on limited programme material and you can usually come across some other piece that sounds less than acceptable.
I asked B&W several times for permission to reproduce this but they never replied. If they ask I'll remove it.