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Bamberg Series 4.5K, ca 1997: The rich alluring sound that originally drew me into the performance.

Series 4.5k finished in Natural Cherry Direct side view of "tiered look", showing detail of contoured grille, baffle, and chamfered hardwood edges

Sound

The lower midrange; 160-320 Hertz. Perhaps the Power Region is the most overlooked region in the entire audible range. Are you missing it, and how can you be sure? The BESL Series 4.5k knows, and provides a certain satisfying richness to the sound, which is so often lacking in other loudspeakers.

Left-hand piano is delivered with authority, putting the "Grand" back into grand piano. Harmonically-rich instruments are portrayed with a seemingly enhanced vibrancy. Mid and upper bass is articulate, even "snappy". This range is responsible for much of the rhythmic quality in music, and here the Series 4.5k is a natural. The transition from low midrange to low bass is seamless, with no loss in tonality or cohesiveness. And why shouldn't it be? There is no lower crossover to get in its way!

The upper midrange has an immediacy that does voices justice, as they so well deserve. Sound staging is well-balanced, portraying a very neutral perspective. Definition and image focus remain intact from low to high playback level, and from front to rear in the sound stage. At all times there is the sense that sounds "bloom" from deep within the sound stage. The treble is delicate, inviting. Never overshadowing the "star" performer of the midbass woofer, it simply adds to the musical message. Yet the detail and transparency is there, waiting to draw you in.


Design

The Series 4.5k is based on a pair of world-class 7" woofers, the Scan-speak 18W/8545K. Once again, stiff-cone woofers provide increased realism to the sound. But such drivers also tend to have a lot of "personality". When it comes to designing with them, they need more "coaxing to behave" than the typical poly-cone woofer. Getting the tonal balance of the final system just right is tricky, but the rewards are great. In the Series 4.5k crossover, a lot of attention has been devoted to controlling the precise target function (tonal balance), and phase characteristic. This implies an advanced woofer network of course, yet only two inductors are in series with the woofers. The remaining elements are configured shunt-to-ground. The only series component in the tweeter network is a capacitor (with film/foil bypass cap). The remaining elements are again shunt-to-ground. To further improve the inter-driver phase coherency, a special faceplate was designed that moves the Scan-speak tweeter back an additional 1/4", yet introduces no further diffraction problems. In fact, the scallops allow the woofer frames to overlap the tweeter flange, thus allowing flush mounting and moving them closer together. Together with the 1800Hz crossover point, the original D'Appolito 3/2-lambda specification is maintained.

Nothing has been left to chance in the cabinet design. Dual-wall construction (1.5") is used throughout. The upper section is extensively cross-braced and activates the full acoustic volume. The (non-acoustic) lower section is also braced and houses the low-pass and high-pass crossovers with 16" of separation between them. A 1" thick base covers the lower access windows, and holds the large floor spikes. The speaker can be angled back by 4 degrees with the use of an additional front riser

In summary, the BESL Series 4.5k is intended for moderate size rooms fed by class-A-biased amplification, and bi-wired with high-grade cables. It has that "immediate" sound that makes you forget about your hardware. The BESL Series 4.5k sounds best without a subwoofer.

Series 4.5k pass band response

BESL Series 4.5k Specifications

Driver Complement

18cm woofers (2) Scan-Speak 18W/8545-K
29mm tweeter Scan-Speak D2905/9500

Impedance

Nominal 4 ohm
Minimum (@125 Hz / 20 kHz) 3.75 / 2.70 ohm

Sensitivity

2.83V@1 Meter full space 87.0 dB

Bandwidth

-3dB 42 Hz - 20 kHz
-6dB 30 Hz

Amplitude response

To 20kHz +2.5 dB

Inter-driver Phase response

Less than 45° phase difference from 700 Hz to 14 kHz

Maximum linear output

25W all frequencies 102 dB

Bass alignment

sealed 0.6 Qtc, adjustable
vented QB3, optional

Crossover

Alignment 4th L-R@ 1.8 kHz
Elements ~15

Dimensions, Weight

41.75"H x 11.5"W x 21"D, 123 lb.

Reviews

All were mighty impressed. (Sound familiar?) I am definitely a pleased customer. To be honest, I'm not sure what was more impressive, the quality of the sound, or the cabinets. (Before I forget,could you drop me a note with exactly what you used to finish the wood- per your earlier comments I may add another coat some day) I'd go on about what I like, but that will have to wait until I have more time to pick the right words. The one quick comment, is I can now tell very clearly the sonic flaws in my room. We'll have to talk about what I can do to create a better sound environment. NB

The speakers are in my living room and sound even better than they look! The soundstage is impressive as hell, and I'm very glad you recommended the sealed alignment. It's my opinion that sealed-boxes sound better for jazz and classical music. I'll write more about them later. I want to give them a chance to break in, and my new amplifier is also on its way. MS MS Full Review

By now is a week that listening 4.5. Without preambles I say that it is an exceptional speaker. It is a pleasure to listen the music, any kind of music. An enormous cleanliness characterizes the low range and midbass range, an airy stage, deep, there is air between the instruments and a perfect focusing. Every instrument is behind, tremendously behind, to the speakers that seem to not to exist. The dynamics is as much and surely enough. A high range cleaning up and finished up to the perfection, without ever getting tired and without skipping any detail. In this diffuser, however, the thing that is to absolute level more than all is the stage. Only detail not to the level of the rest, but it is just perhaps due to the big stage reconstruction, it is the presence of the middle range. Especially on the female voices I would have preferred more warmth and presence, not that there is not, but a little warmth more...and it was the perfection. 
A big job however, in relationship to the price, but especially in absolute. In high fidelity the perfection doesn't exist, for this it is "high fidelity", but these speakers they are very near....! PF

I got a chance to examine the crossovers over the weekend, and I'm thoroughly impressed! The parts quality is high, the parts count is low, and your build quality and layout is excellent! WAY nicer looking than the (competitor) crossovers....MP

Series 4.5k high-pass and low-pass networks

Drivers / Hardware Kit $ (Special order)
  • 2 Scan-Speak D2905/9500 tweeters with BESL flared faceplates
  • 4 Scan-Speak 18W/8545K woofers
  • 1 Base fastener set
  • 1 S4 #6 screw set
  • 8 HD Spikes
  • 10' Ultimate Gasket Tape
  • 8 grille snaps
  • 8 deluxe 3-way gold binding posts
  • 1/2 yd. grille cloth--brown or black

Crossovers Kit $ (Special order)
  • ~15 high-grade elements
  • Mundorf® tweeter capacitors, and Perfect Lay 14-gauge woofer inductors
  • Axon® film/foil bypass capacitors in tweeter network
  • Complete and detailed plans with schematic to fabricate the Low-pass and High-pass crossover networks, wired point-to-point, and tie-wrapped for reliability
  • Each network fabricates onto 1/4" MDF boards (not included); 9" x 3.5" W; 4 boards total
  • Networks mount inside lower false cavity, accessible from speaker's bottom
  • Includes input/output leads, and final voicing tips
  • This kit is only available with driver/hardware kit purchase!

Baffles / Grilles set $105 (Special order) /pair
  • Acoustically-correct BESL 1" Front baffle and 1/2" grille frame (unpainted)
  • Off-center tweeter mounting, flush-mounted woofers
  • Includes deep tweeter recess to accept custom BESL Horn Flare Plate
  • Compound radius baffle edges

Series 4 Cabinet Plans $65 (free with drivers & crossover kit purchase)
  • Complete and detailed plans needed to build the 64-piece cabinet featuring tongue-and-groove construction for easy and accurate assembly
  • Box volume & inner panel dimensions, optional venting details
  • Front panel driver mounting diameters, depths, and positions
  • Suggested bracing method, tips for improved acoustic response, stuffing guidelines
  • Construction/assembly instructions
  • Does not include crossover schematic!


Series 4.5k Plans Cover Sheet