Towards a complete Linn Kaber Aktiv solution using an rPi and AV receiv

[Tim Curtis]

The "symmetrical wear" effect explains why my vintage KEF Q60's still sound really good or at least not L/R different, but someday I might get some new KEF's and it will be interesting to compare.

[forty5cal1911]

Does this response look like a "typical" starting point to you at this stage?

Other than the midbass driver the response looks relatively typical and is workable. Linn publishes the driver specs as 125mm for the both the midbass and midrange. What the response tells us is that it is just two of the same midrange drivers. This speaker will not be able to produce any appreciable low bass which may be fine if you are going to use a subwoofer. Is that the case?

80hz low pass is going to be much too low for this driver.

At 40Hz we are down at least 15dB. Can Linn's claim of 40Hz for their Aktiv Kaber speakers be met?

No they cannot.

The 5" midrange is going to begin beaming around 3k but should be quite linear up to that point. You are going to need to bring the midrange down quite a bit in level to get everything matched properly but that shouldn't be an issue.

• The trebble is several dB lower than the mid. 
  
• The trebble falls off from 4K, not 2.8K
  

This is okay and will be fixed in the EQ and tuning. Do you have an idea of what you want the overall frequency response target to be?

The reason 2nd order crossover filters can be problematic is due to the phase issues that they introduce. This is dealt with sometimes by inverting the polarity of the midrange or midbass driver. This is why a 4th order filter is preferred as it sums perfectly at the crossover point both in phase and amplitude.

I will follow up when I've got some time this evening.

[oomzay]

This speaker will not be able to produce any appreciable low bass which may be fine if you are going to use a sub-woofer. Is that the case?

I'd rather not have a sub. In this room I'd rather end up with limited, but very clean bass. But wait! I think there is something more complicated going with the two drives working together. When I measure full system from listening positions things look very different indeed... Below is plot of room before [BLUE], and after a very crude manual EQ (with very obvious issues) [GREEN].

   

I think there is more to these speakers than the 1M measurements reveal. Is it like radio telescopes where the effective aperture is a function of the distance between multiple antennas/speaker centres? The bass looks, sounds and feels much more extended than the individual measurements suggested.

OOOOh! This is not bad at all! Aktiv has really fixed the sound stage... Amber Irish is in the room - exactly 12 inches to left of centre! ....I am grinning from ear to ear! ...and I think there are low hanging EQ fruits to improve this... I'll play with E.Q. some more tomorrow.