by Curt Campbell
The Chevalier is a modern take on a traditional 8 ohm 3-way. The high & midrange frequencies are covered by the Morel TM4055-8 Soft Dome 1" Tweeter + 2" Midrange combination. The level of continuity generated by this configuration is wholly unique. The sealed back design on this driver simplifies cabinet construction, as the midrange does not require it's own chambered airspace from the woofer section. Bass is handled by the SB Acoustics SB23CACS45-8 8" Ceramic Cone Woofer. This is easily one of the best 8" bass drivers, regardless of cost.
This speaker can be built as a sealed box (acoustic suspension) or passive radiator terminated transmission line design. The sealed box enclosure volume is just over 1 cubic foot. The PR terminated t-line is 1.75 cubic foot and uses the SB Acoustics SB20PFCR-00 8" Passive Radiator.
Sealed enclosure (18.75" t x 11.25" w x 13.5" d) pdf
PR/T-line enclosure (29" t x 11.25" w x 13.5" d) pdf
I am very pleased with how the 50 liter PR version came out. I decided to make it a mass loaded transmission line. Even though I don't have software to model a PR terminated T-line, I made some educated assumptions to determine the enclosure volume volume and line length. While the results look somewhat sketchy on paper, the SB23CACS45-8 / SB20PFCR-00 proved a match made in heaven. I obtained my optimal target tuning results with no additional weighting of the PR. Sensitivity was surprisingly high for an 8 ohm design, seemingly near 87 dB in spite of the abundant bass it provides. Maximum SPL, based on woofer excursion modeled around 104dB but the design played surprisingly loud with no audible compromise in performance.
System tuning measured around 28 Hz and frequencies in the high 20's were easily audible. Considering its size and reasonable cost, the SB23 easily navigated the 800 Hz crossover point and provided very commendable performance. No, it’s not an Accuton, but offers surprising performance none the less.
Now the TM4055-8. A vintage design, and a bit challenging to work with, but I can see why they keep it in their lineup. Not surprisingly, response with the grill applied is very poor and should not be used under any circumstances. Morel needs to save the purchaser some $$$ and reinvent the grill as an optional component.
Getting the TM4055-8 to play nice, –even with itself, was a bit of a trial.
My first attempt at a conventional crossover was met with disappointment, as were the next few topologies. What I ended up with for the midrange dome was first order electrical HP and LP filters in series with a parallel notch filter. This yielded a topology with nearly perfect 4th order acoustic slopes at approximately 650Hz and 8000Hz. The tweeter was a more conventional 2nd order electrical topology which provided a 4th order acoustic slope.
Phase tracking was excellent although the tweeter is connected with reversed polarity. The woofer network was a quite ordinary 2nd order electrical that provided a 3rd order acoustic transfer function at roughly 800 Hz. Due to the mixed order slopes the woofer and mid sun in phase quadrature, and are both connected in normal polarity.
Overall I was very impressed with how this design came out. Bass is plentiful, clean and taut. The midrange is quite impressive and very clean, considering how much of it is provided by the woofer. Kudos to SB Acoustics for a line of very good, yet cost effective drivers. Upper midrange and tweeter are impressive as well, and exhibited the great, clean sound that Morel is known for. Not only did the design have better than average sensitivity, it seemed to thrive on power. The more I gave it, the more it shined. Apparent max SPL seemed far greater than the modeled max SPL of 102 dB based on the woofer Xmax. The Morel dome mid was especially impressive, as it played high SPL’s effortlessly. While the 50 liter enclosure volume is not small, it offers simple construction, and packs a lot of performance in this smaller package.