In this blog post I want to feature a project that I built recently for Don Sachs of Don Sachs Audio. Don approached me a while ago looking for his "End Game" speaker and decided that something custom would be required since there was very limited selection in the market for a horn loaded open baffle speaker.
I went through a number of design iterations and eventually came up with what you see above.
- 1.40" SB Audience 65CDN-T
- 10" Scanspeak woofer using SD-1 motor technology
- 15" SB Audience 15OB350 woofer
- 95dB Sensitivity
- 2.5-way configuration (180Hz LR4 + 1.2kHz xover 1st order)
I went through a number of passive crossover topologies listening to each one but ultimately decided on a simple first order for the mid and high frequency. The 15" woofer is low passed with a steep filter at 180Hz leaving the 10" to cover the critical 180Hz-600Hz region on its own.
10" Scanspeak for Midrange
The 10" scanspeak retains a nice sound character even up to 4kHz. So I decided to to allow the woofer to play up into this region although attenuated down by my shallow low pass crossover slope. The 10" woofer has no high pass filter and so it is also contributing to the overall bass output (2.5-way configuration). The sensitivity of the 10" is -5dB down compared to 15" woofer however actual measurements reveal that they are in fact only about -3dB apart once the proper low pass filter is implemented for the 15". This achieved a perfect target curve between the low and mid frequency in terms of in-room response. The physical location of the 10" in relation to the 15" allows for some mutual summing to occur between the two woofers thereby creating a flatter in-room bass response compared to a single bass driver.
The mid-size format compression driver (2.50" diaphragm) uses my custom 3D printed rear cover which enlarges the rear chamber volume. This lowers the compression driver's FS from 480Hz down to 280Hz. This made a subjective improvement to the compression driver's sound character below the 1.2kHz crossover point. Since using a shallow slope the compression driver is still providing strong content an octave below the 1.2kHz crossover point, so at 600Hz the compression driver maintains good phase response due to the enlarged rear chamber. Intermodulation distortion is kept at bay by virtue of both the MF and HF drivers sharing the load in this critical frequency region.
Baffle and Support Legs
The baffle is CNC milled on both sides from 10cm thick cherry. The support legs are precision CNC plasma cut from 6mm thick mild steel plate and then professionally powder coated black. I decided to go with the ISO Acoustics GAIA ll feet which is critical for maintaining low intermodulation distortion in the midrange and treble. The horn is integrated into the solid cherry baffle which is simply an aesthetic choice, but also allows the sound wave exiting the horn to extend uninterrupted for another millisecond before reaching the edge of the baffle. This improves the impulse response.
Video Training Series
While developing the crossover I decided to conduct a long format training video on my overall process, as a step by step instructional video.
- Collecting raw frequency and impedance response data
- Measurement setup and troubleshooting
- Software and hardware requirements
- Using the software step by step
- Step by step process for subjective evaluation and making necessary adjustments
- Rigging up test crossover
- Strategies for passive crossover design to achieve desired frequency response changes
- Tips and tricks to get better sound
The video series will be available to purchase on my site and will comprise three parts, each part is around an hour long for a total of three hours of video content.
Feedback from Don Sachs
I asked Don to provide a short paragraph review and photo that I could include on my site. He instead provided a lengthy review on his overall listening impressions for the 1695 open baffle speaker.
Review of Joseph Crowe Open Baffle speaker Model 1695
"I started working with Troy on this custom project over a year ago. I have owned horn speakers, and also open baffle speakers and I wanted a combination of the two. An open baffle speaker with a horn on the top end. Troy proposed an initial design, and then as he tested drivers the design evolved into this lovely speaker. The baffle is milled from solid cherry and the horn for the compression driver is milled as part of the baffle. The attention to detail is apparent and appreciated. The baffles are tapered so they are wide enough for the 15 inch passive subwoofer on the bottom and taper down to just the width of the horn at the top. The baffles also are beveled so that front surface is only as wide as the drivers or horn to minimize edge diffraction. Finally, the speaker leans back slightly so that all the drivers are time aligned. They are a joy to behold in the living room. A few friends have come by and remarked at how beautiful they look.
The crossover is very simple, and the horn and 10 inch midrange drivers have a very gentle slope. There is no need for complexity in the crossover, such as notch filters and the like to tame difficult drivers. The individual drivers were chosen to allow for the simple crossover. Try as I might, I cannot hear any single driver, as the integration is excellent. Lynn Olson looked at the crossover schematic and remarked that the drivers must be really good to pull that off, and it was probably the best dipole design he had ever seen. Lynn is a tough crowd, and I wish he could hear them. They are a 2.5 way, with the 15 inch acting as a subwoofer. The sound is stunningly good, and the timbre and tonality are spot on. Dynamic range is shocking, and bass and midrange will hit you in the chest at high levels. External subwoofers need not apply. They sound fast and nimble. They vanish like a stand mounted mini monitor, but they have that full, rich, and lightning quick bass.
I build high end tube amps and preamps for a living. I am driving this speaker with a slightly modified Lampizator Pacific DAC, a custom tube preamp based on the 6SN7 tube and a 300b push pull pair of mono block amps. The preamp and amps are part of a cost no object design project with Lynn Olson, and these are the final prototypes before manufacturing. There are no coupling caps after the DAC as preamp and amps are all transformer coupled with custom wound iron. Let’s just say that the signal chain in front of these speakers is a very top end all tube system that is very resolving and very fast. The hallmarks of the 300b push pull mono amps in this system are very low distortion, very high slew rate, coupled with large current delivery, so they are extremely fast and throw an immense and totally immersive sound stage. Sort of like omnimax theatre for the ears. The sound could be described as “trippy”:) Troy’s speakers really show this off and they are quite simply one of the best speakers I have ever heard, let alone had the pleasure of experiencing in my personal system. They are about 30 inches from the front wall in a room with a high ceiling that rises from about 10 feet high over speakers to over 20 ft overhead at my listening position. I have about a 9 ft triangle with speaker spacing and distance to my listening position. Speakers are aimed at my shoulders. The sound stage is easily a few feet wider than the speakers, with excellent depth, and of course it is floor to ceiling in height. The speakers are slightly warm, very rich and highly detailed. You can hear every nuance and detail without a trace of brightness. The midrange and compression drivers are first rate. The 15 inch subwoofer driver
is very nimble and quick. It is a beautifully balanced presentation with exactly the right amount of bass energy in my room and unrivalled clarity. Most importantly, the instruments and vocals are as natural as I have ever heard from any speaker. A piano sounds like a piano. The low notes of the left hand are presented perfectly, and you can hear the harmonic beats wavering as the notes fade away. Cymbals and triangles hang in the air and decay as they should. Of course, vocals and guitars, mandolins, violins, cellos, acoustic bass, reed and brass instruments are all very convincing. You can hear the wooden sound of the clarinet or the hollowness of an instrument or percussion body, the clack of keys and breathing of the bandoneon. These things are hard for most systems to present correctly. You can easily follow individual instruments in an orchestra, or voices in a choir. I could go through a list of tracks and point out things, but really, the speakers throw a huge soundstage, and everything sounds vividly real. They will play screamingly loud with 25 watts/ch as they are about 94 dB efficiency, and an easy, well behaved 8 ohm load. I am sure they would play with low powered tube amps. Oh, and of course they will rock out to Pink Floyd or Santana or the Grateful Dead at concert levels in my room. Live jazz recordings sound like you are in the club.
To sum up, I am shocked at how good these speakers are. Try as I might, I cannot hear any serious flaws in the sound. They are considerably better than any speaker that has ever graced my system. You are drawn in and cannot stop listening to them. Warm and rich, but spectacular detail. To use an old phrase, they are lush, but not mush. They are not warm and fuzzy, just that they have a certain richness and fullness to the sound due to the wonderful midrange and bottom end, and they have that horn speed and clarity on top without a trace of brightness. Just detail. The whole package is quite immersive and addictive, and the few visitors who have heard them have been smitten as well. A few jaws have dropped. I am impressed and thoroughly addicted to them, and I don’t see how Troy did it at this price point! I presented at the Pacific Audio Fest in Seattle in June and heard many a speaker that sold for $25,000+. There is not one speaker I heard in that entire show I would trade for these. One very satisfied customer here."
I typically need to know the listening room size so that I can achieve the desired bass response, but otherwise all of my products will have the same sonic character as the 1695 project. If you are interested in a custom speaker system please contact me (Troy J. Crowe) for a quote at firstname.lastname@example.org or call 613-920-5934.