April 2017: Recent update regarding speakers. Gone from ladder frame to 'Scaffold Frame' ! Not to everyone's taste, admittedly, but after going bafferless as an experiment. I was so shocked by the
result, there is no going back!
The metal scaffold transfers much less energy into the old wooden ladder frame which I was always struggling with. Careful isolation was needed for the full range units. (See OB Speakers TAB above for other creations) With this new design, the weight of the magnets (heaviest part) is now supported by a simple cable which provides the best isolation. Construction is also very simple.
I am using a pair of PRV 5MR450-NDY 'full
range' (rolls off 150Hz) drivers partnered with a pair of reversed Dayton
390 15" woofers. Reversing the
woofers simply makes construction easier, and seems to increase bass
I swapped over from the Alpair FR mainly because the PRV's have a rigid surround and only extend to 150Hz meaning they dont flap about trying to reproduce the lower frequencies. They also go much louder than the delicate Alpairs, are more efficient & dynamic.
The unobtainable 18" AE (Acoustic Elegance) Dipole woofers have been replaced by the Dayton 390 15", which have heavier aluminium cones and a more powerful motor. Arranged in series, they give more depth and slam, take more watts and yield higher SPL's without complaining. They generally take more abuse and dont bottom out as easily as the AE's.
In this F.A.S.T. configuration
(FullRange Assisted Subwoofer Technology) there is no crossover to sap
efficiency and resolution. The FR connects direct to the main amp &
handles from 250Hz up to 16k.
Dispensing with the baffle has resulted in a clearer more open sound. I guess the baffle was contributing to some muddying. Also imaging has improved, and the bass couples better with the room creating fewer modes. As as a result I was able to push the speakers back closer to the rear wall.
I have found the 390's need no eq to compensate for for bass baffle losses. This was a surprise to me as these units seem to deliver bass down to 20hz with amazing slam!
The woofers are actively controlled by a dedicated sub amp, a Behringer NU3000DSP with built in Digital Signal Processor to fix the crossover point & also iron out room modes.
The Behringer iNuke NU3000DSP powers the 15" woofers. This is primarily PA concert venue Class D full range amp. Not sure what it sounds like full range, but from 20 - 250Hz & it sounds great! Delivers effortless distortion free power, control & resolution..........everything you want in a sub amp.
The DSP section just plugs into a laptop via USB & uses software available from the Behringer site. All relevant parameters can be adjusted in real time from your listening position. The crossover page allows seamless integration with the full range unit. There is a choice of 4 variable slopes, plus crossover point & gain. There is also an 8 filter Parametric EQ page to set compensation for room modes & baffle deficiencies.
The stock fan is noisy, so I have throttled back with a resistor in series. I have also customised my unit spraying the fascia black & adding LED fan.........
This amp has the added feature of a user replaceable input cap which acts as a selectable high pass filter stopping unecessary low frequencies (already handled by the woofer) from reaching the Full Range driver. This has a dramatic effect of cleaning up the sound, I think mainly because the amp isn't having to work so hard reproducing the lower frequencies.
One the back are outputs linked directly to the volume control to drive the sub amp.
ISO-DAC is the latest upgrade, which is basically a Ciunas paired with a USB isolator. This cleans up the noise from the computer. The immediate effect of this was even more detail & refinement in sound quality and a holographic soundstage that is scary as it takes you by surprise.
Early days yet in the running-in process, but I suspect this unit will be in my system for a long time!
I would describe the sound from this system as dynamic, musical, but full of detail. Also unforgiving of poor recordings..........
The small PRV cones are very light & fast, especially with percussive instruments. They produce an incredible amount of treble.....hard to believe there isnt a tweeter in the system. If I listen to a tweetered system now, it sounds disjointed!
The twin PRV's have improved efficiency, dynamics, image focus and detail. Also seem smoother.
The woofers driven by the Behringer integrate seamlessly with the PRVs. They go floor-shakingly deep when the signal is present but there is no boom from room resonances such is the control from the PEQ. For serious bass I believe the woofer needs to be actively driven with PEQ. Control of the room modes is a necessity.
I can play a wide range of music on this system from softer accoustic jazz material to pumped up Level 42 playing at realistic levels. Modern electronic music which I was never too keen on makes sense now that I can hear/feel that bottom octave. Kraftwerk, Depeche mode never sounded so good not to mention the more modern Junior Boys and London Grammar. The system delivers it all in a musical, fatigue-free fashion.