Continuing on from the 1159 stand mount speaker is a new floor standing design. The 1198 floor standing speaker has the following changes compared to the 1159 stand mount...
- Purifi PTT6.5W04 replaces SB Acoustics SB15NRXC30
- Transmission Line Loaded replaces tradition bass reflex alignment
- Enclosure volume of 21 liters was 10.
- Bass extension of 30Hz was 41Hz
- 104dB SPL max was 100dB (@60Hz)
- 104dB SPL max was 90dB (@40Hz)
- Sensitivity of 90dB was 88.5dB
The 1198 shares the exact same high frequency horn as the 1159 which performs exceptionally well. For more information on the design of this horn please see my previous blog posts Here and Here.
The bass enclosure features a medium fill mass loaded transmission line that follows in the teaching of Peter Thomas from PMC Loudspeakers. Thomas provides some very valuable design insight in the book 'Loudspeakers For Music Recording and Reproduction'. It was this information and my own past projects that provided the guiding light for the 1198 cabinet design. The transmission line design operates under the quarter wave principal and assumes a 35% speed of sound reduction due to the mass loading.
Preliminary Design Images
Below are some initial design images for the 1198 floor standing speaker. The baffle is 900mm long not including the 40mm thick base plinth which is also solid hardwood. The rest of the enclosure is construction from 24mm thick baltic birch plywood for an extremely inert enclosure. The 1159 stand mount shared the same wall thickness and I don't think I've encountered a more dense enclosure. A knuckle wrap test will make you think to yourself "holy!"...if that's typical for your inner monologue!
The 1198 continues to mount the woofer from behind the baffle. This provides a clean appearance and also somewhat hides the surround on the Purifi woofer. Personally I don't like the appearance of the surround. I had considered methods to fully conceal the surround however this is impossible since the driver has a +/-14.5mm mechanical limit xmax.
The Purifi PTT6.5W04 has a nominal +/-10mm xmax which is just one parameter among many that puts it in a league of it's own and represents the most current driver technology on offer from any manufacturer.
The 1198 will require a removable rear panel so that the drivers and insulation can be added.
I have been commissioned to build the 1198 speaker however I will be offering the baffle or flat pack for DIY use. Commercial licencing is available to other manufacturers as well. For inquiries contact Joseph_crowe@josephcrowe.com
Expect the high frequency portion to perform the same as the 1159 stand mount speaker. There is also the possibility to replace the soft dome tweeter with SB Acoustic's beryllium version which I will testing shortly.
The bass portion will provide even better off-axis polar map matching at the crossover point since the larger woofer will have a little more directionality near the crossover point of 1.5kHz. The crossover on the high frequency will likely remain a simple first order with an L-pad. Combining the Purifi woofer with horn loaded tweeter creates a speaker capable of 100dB+ with less than 1% Total Harmonic Distortion. This is a very high SPL capability even for much larger speakers.
Stay tuned for further developments on this exciting project!