Exclusively designed by LEAR of Hong Kong, BD4.2 is claimed to feature ground-breaking innovations:
1. Quad-bore configuration
2. Metallic acoustic transfer tubing
3. Adjustable bass control
4. Acoustic low-pass filter
First, separate acoustic transfer tubes, or bores, help minimize the possible interference with sound waves coming from each drivers, while shaping their linear characteristics in specific manner to tailor-fit them to the manufacturer's requirement. As far as I know, no IEM manufacturer has ever tried quad bore, especially when even a 12-driver JH Audio Roxanne has only triple bores.
Second, metallic bores have previously been implemented by Suyama of Japan, and such tubes tend to have lower resonance frequency compared to the ones made of materials with lower density. Moreover, they also yield stable high frequency response due to the tube's constant geometry. The same logic may apply here with BD4.2 as well.
Third, although making the low frequency response fully adjustable may sound tempting, adding an extra adjustable module always increases the cost of development and production. Moreover, most of the bass control implemented in conventional IEMs are poorly designed, and lacks accuracy.
Fourth, other than Ultimate Ears UE900 and Shure SE846, and I've never witnessed such filter placed at the output of an IEM. It usually utilizes a long acoustic transfer tubing, and requires a good amount of calculation, not to mention precise engineering to be practically beneficial.
Consequently, the ultimate question is: Are all of the innovations claimed by LEAR true, and if so, is it possible that they work to the overall benefit of users?
PRO: Well-damped time domain characteristic especially in the low frequency region, where the effect of the acoustic low-pass filter dominates. Channel matching is superbly good too. The IEM's high modifiability is a huge plus.
CON: Inverted polarity, which can easily be corrected by swapping the cable's two-pin plug inversely.
|The quad-bore shown on the right with the bass control on the left|
IN CONLUSION: LEAR BD4.2 is unlike anything I've ever measured so far. Yes, the claims made by the manufacturer turn out to be all true, and the accumulated effects from the innovations add up to the benefit of users.
The stock configuration presented by LEAR is superb too, but the fact that the sound signature can be finely adjusted without having to modify the IEM's internal components shall be praised & glorified the most. There are simply endless possibilities for users to discover by means of both simple acoustical & electrical tweaks. And because of that, I acknowledge BD4.2 as one of the IEMs with highest quality of all, and one of my most favorite headphones as well.
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