Speaker System No. 1349 is a system design study that continues on from the lessons learned on the Nighthawk speaker. Generally the Nighthawk and 1349 speaker (featured in this blog post) have the following design goals...
- Coherent sound source by virtue of close driver spacing
- Exponential horn flare geometry for low horn colouration
- No phase plug or slot loading of midrange drivers for a more immediate sound
- Controlled directivity to limit (or control) interaction with room acoustics = more clarity
- Large soundstage scale that only this size of horn provides
The Nighthawk build represents the best that I've been able to achieve in terms of musical enjoyment. However the Nighthawk project was slatted for a pro-sound application and so the focus was on high SPL. Following the Nighthawk project, my goal with the 1349 project is to design and build an audiophile specific version.
Project 1349 is an amalgamation of the highest performing elements (in terms of sound quality) from previous projects...combined to create one ultimate system. These elements include...
Horn Loading the Scanspeak 10F/4424G Midrange Driver
The midrange produced by horn loading four of the Scanspeak 10F/4424G drivers is the best midrange I've heard. I've tried horn loading a variety of midrange drivers with my own subjective impressions...
Fostex FE126EN Sounded too forward and 'grating'
Markuaudio Alpair7.3 actually sounded very good but the physical frame size prevents a vertical array. This also produced a very flat midrange frequency response!
SB Acoustics SB12MNRX2-25-04: Although it measures well, it sounded far too soft and over damped.
Scanspeak 10F/4424G: The sound was very transparent and lively with an incredibly low noise floor through the midrange. What makes this scanspeak so special? I can only speculate that it may be due to the strong motor with copper shorting cap, and/or the patented Coated NRSC Fibre Glass Cone.
ES Horn Curvature
Performance will be improved further compared to the Nighthawk by incorporating the full ES wrap-around horn flare geometry on the horn mouth. This will virtually eliminate edge diffraction off the horn mouth, and completely smooth out the off-axis polar map.
Below is an example of the horizontal off-axis response offered by the ES horn flare geometry (ES-1200 Biradial)...
The original Nighthawk does not have the full ES-curvature and so the resulting polar map does not perform as well...
Increase bandwidth on midrange
By reducing the size of the midrange drivers from 10cm to 7.5cm I am able to extend the upper frequency limit on the midrange horn from 1.5kHz to 2.5kHz. This will sum to a flat response with the high frequency horn. This was observed in the E-250 project.
1349 incorporates a radial curvature (see first image in this blog post). The radial curvature solves two problems.
1) The radial curvature alters the shape of the midrange wavefront from cylindrical to radial. The radial wavefront matches the shape of the high frequency wavefront. This ensures matched output between the MF and HF horn regardless of physical listening distance.
2) The radial curvature increases the vertical off-axis coverage. It was found that the Nighthawk had too much vertical directivity as a result of the overall physical height of the horn. This was fine for listening while sitting down, and provided a 1m listening height, however I believe the overall soundstage could benefit from a few +dB early ceiling and floor reflections.
Larger High Frequency Horn
The high frequency horn size has been increased from 3kHz on the Nighthawk to 1.2kHz. Even though I'm using a 2.5kHz crossover point the larger horn provides the necessary pattern control at the crossover frequency to match perfectly with the larger midrange horn section.
High Frequency Compression Driver
At his time I'm a little on the fence on the appropriate compression driver for 1349. The best I've heard is the TAD TD-2001 however this driver is not readily available and does not physically time align with the Scanspeak midrange drivers because of the overall depth of the TAD. Second to the TAD is the RAAL 70-20XR in my ES horn. This tweeter had the same resolution as the TAD albeit with slightly less dynamics on the leading edge of transients. Another worthy candidate based on the published data is the Viawave SRT-7.
System integration would ideally mean a 4-way system using 80Hz, 350Hz, and 2.5kHz crossover points. Overall sensitivity would be around 109dB.
I'll briefly touch on the mid-bass solution which should be a front horn to match the quick impulse response of the midrange. To achieve this Mid-Bass 1274 is a good match utilizing two B&C 12PE32 mid-bass drivers to cover 80Hz-350Hz.
Again, keeping up with the rest of the system would require substantial bass 'scale' and so a reflex cabinet utilizing three of Faital's new 15XL1400 neodymium professional woofer should keep up.
Similar to the Nighthawk, 1349 would be CNC machined in quadrants.
Shown below is the stock material surrounding one quadrant as it would be orientated in the CNC machine.
Wood Type and Finish
This being an entirely subjective preference, I personally think that painted oak would look fantastic with this horn. Black may be too bold considering the already bolt shape, so perhaps white would look great.
Below is a small horn I made from oak, which was stained black. Notice how the wood grain texture still shows through which looks quite attractive.
1135 stained white may provide just the right amount of subtlety depending on your décor. Below is an example from the web on the painted white oak...
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