Bi-Amp BM5a Review
It 's rather ironic that the lowly (for Dynaudio pricing that is!) BM5a loud speaker offer some of the best theoretical and in-practical performance available from 100Hz up.
It is bi-amped, a feature which has numerous benefits:
1) no back EMF modulation interference between drivers
2) no power amplifier watts wasted on crossover losses
3) direct coupling to the driver resulting in superior electrical damping
It is quite apparent that after owner many speakers over several decades, that the massive physical supporting structure interferes with creating a wide and deep sound-stage. Bigger is not better. The fact is smaller speaker image better also because there are no phase aberrations introduced between multiple drivers which must be physically separated.
Another compromise is ported speakers which invariably increase output yet always introduce out of phase sound. This compromise also degrades the sound quality, sound-staging and imaging.
So what does it take to optimize the BM5a, a speaker which has fabulously sound quality?
Here is the list:
1) Use stands of 25" plus/minus one inch just as Dynaudio sells. I use steel 24" type with adhesive pads between the speaker and the stand. Note: I experimented with other heights ( around 30" )and the upper bass suffered greatly
2) keep the speakers a couple of feet away from the walls then tweak
3) ground all speakers to the same high current power conditioned output. Use extension cords.
4) toe the speakers in for correct spectral balance
5) use quality balanced XLR audio cables ( i use Monoprice) with a balanced A/V controller
6) Speaker settings: use 0db input only (do not use -10db as the internal op-amps have to work a lot harder)
7) Use with a top quality non-ported subwoofer. The 9s is probably an excellent fit, but i us a JL audio W7 13" driver with a Mackie FRS 1000w amplifier (direct coupled of course)
8) Plug the ports to reduce coloration. I use a sock
The woofer sounds best with its voice coil in the same physical plane as the BM5a driver. Further the quality is so high that I can hear the phasing relationship change when "moving" the woofer (electrically with the speaker distance setting in the A/V controller) and adjusting for maximum bass output. I set the high-pass on the speaker to 60Hz and the woofer to 80Hz in the controller
Dynaudio is correct in stating their speakers do sound better after substantial break-in period. As they improved I was able to better discern quality difference and make my own optimizations. So "we" worked hand-in-hand!
I've learned that the rear surround speakers are not nearly as important as the front three. So my system uses the KRK G2 6 speakers for the back. The KRKs offer more bass so they are a bit higher than 24".
The stereo sounds excellent but why not go to the next stage for listening pleasure? Note however the system has to have both theoretical pin-point sound-staging capability with no (including speaker!!) walls nearby and be optimized electrically. If you succeed then prepare to be amazed with the magical processing of Circle Surround II (CSII). With a European speaker it's no wonder that Opus 3 recording sound best as notes float around you as if they were laser etched with complete naturalness.
A certain Guitar Center has them on sale only in their stores. Don't tell anyone, especially the store personnel as they are clueless to sound quality!