KEF Q55 - Crossover Changes?

[R_Van]

The KEF Q55 is one of my pairs of speakers but they are also the primary speakers I use. I do like many of the qualities of these and it may be notable that I am using them in a small living room for listening to music and for home theater use but there are no additional speakers involved for HT use.

These have been powered by a Technics receiver since I purchased them in 2023. I agree with many of the comments I have read regarding these speakers in that they can be or appear to be bright. However, I think my assessment of this feature might be different if I have a better power source driving them. I just purchased a Hafler DH-200 and DH-101 for this purpose and to power my Snell K/II speakers. In trying to learn about these speakers I stumbled onto a review of them that stated they replaced the OE capacitors and resistors in the crossovers with Solen fast caps (250 V, 8.2 uF and 10 uF) and the 3.3 Ohm and 6.8 Ohm 5 W resistors were replaced with Mills wire wound 3.5 Ohm and 7 Ohm 12 W resistors, respectively.

The person that made these changes described them as as an immediate improvement and not subtle. They added the bass improvement was fuller, more natural, and more 3-dimensional. They had similar comments regarding the mid-range and high frequencies and felt the high frequencies were more balanced between the two speakers.

This was an owner review on Audio Review. I attempted to register for an account on the forum and contact this individual because they also stated they welcomed inquiries. Unfortunately, I was unable to successfully register so I was not able to contact this individual.

Can anyone here guide me in this specific crossover alteration and more generally? Isn't there some software available that could assist in analyzing this or other crossover design changes that could be used in a predictive manner to help sort what changes would result in a change expected or known to produce better performance?

 

[voodooless]

Can anyone here guide me in this specific crossover alteration and more generally?

It’s really easy: don’t! There is nothing to be gained from “upgrading“ crossover components. Any claimed improvements are very likely attributed to confirmation bias. Altered crossovers should be properly measured and evaluated so you know what they do.

However, I think my assessment of this feature might be different if I have a better power source driving them

Most likely not. Most amps are perfectly capable of driving most speakers. As long as you use them within their power envelope, they won’t make a difference. Vintage amps may be a wildcard. If the caps haven’t been replaced you’ll have no idea what you’ll get.

If you really want to change the sound, look for EQ options, room treatment or simply experiment with speaker placement. These coaxials should not be pointing right towards you. Toe them out slightly for smoothest sound.

 

[NotInYourHead]

The higher value of the new resistor might have reduced the treble response which before is a little bright. The resulting better bass-treble balance can explain the "bass improvements".

 

[Randolf]

The Q55 is a vintage 2 1/2 way early UNI-Q design from 1997-2000. I would not recommend to invest too much in it, e.g. beyond just replacing eventually meanwhile out of spec electrolytic capicitors.

A serious crossover upgrade requires to measure all drivers without crossover individually and simulate the crossover e.g. using VituixCAD. If you want to keep the crossover layout and just upgrade the parts quality please note that you also need to take the parasitic parameters into account. Especially the resistances when going from electrolytic to MKT or MKP capacitors goes down quite a bit, which can change the crossover characteristic quite a bit. Without simulation, measurements carefull A/B listening it is just a shoot in the dark.

 

[Randolf]

Maybe you want to have a look at this entertaining little Video:

Basically he did a Mono A/B subjective test on a inexpensive loudspeaker with electrically as similar as possible cheap vs. very expensive crossover. The video also provides some useful background information on crossover parts quality for beginners.