DIY Plans No.1736
Purifi is a high end driver manufacture located in Denmark. Purifi is in the process of releasing their new 8" woofer, model PTT8.0X04-NAB-02. Purifi reached out to me and asked me if I would be interested in developing new DIY speaker plans for this new driver. This plan would be intended for two channel music playback in a home setting. This speaker project will be No.1736. Once introduced, these plans will include all the assembly and detail drawings required to construct the complete speaker, including the crossover schematic and bill of materials.
I haven't received the drivers yet, but Purifi did send me the 3D CAD model to start on some preliminary design work. Shown below is the 3D CAD model sent to me from Purifi.
Erin's Audio Corner did a detailed test on the PTT8.0X04-NAB-02 which can be found here.
I've come up with a preliminary speaker design that has the following design goals. Please feel free to comment or provide recommendations on my own overall objectives.
- Easy to construct using 18mm plywood
- Uses standard off-the-shelf components
- Large stand mount in 2-way configuration
- Exponential horn (Faital STH100)
- 1" compression driver (model undetermined)
- Passive radiators (SB Acoustics SB15SFCR-00)
Solidworks Renders
I decided not to rebate the drivers in the name of simplicity. I will likely provide additional detail in the drawings if one wants to add the rebates. I also avoided adding any bevels since it's not clear at this point how much the speaker would benefit from this added complexity. This area is still undetermined.
Passive Radiators
I've had good results with the SB Acoustics passive radiators. The racetrack shape is useful for fitting them where needed. The high mechanical compliance allows bass frequencies to emanate unhindered while filtering midbass and midrange frequencies much better than a regular port.
The box size and tuning frequency is shown below. It's yet to be seen if the chosen passive radiators will achieve the desired tuning frequency. I've found that this is usually a case of trial and error since there are no software simulation options available for passive radiators.
Compression Drivers
There are a variety of compression drivers that would be suitable including the Faital HF108R and RCF ND-350. I've chosen a compression driver over AMT or regular dome due to the low distortion capability. There simply are no other substitutes if you need high output capability and low distortion. Even a dome tweeter mounted into a waveguide or horn will not perform as well as a good compression driver/horn combination in terms of openness and transparency. The Faital Horn STH100 horn features an exponential horn flare geometry which is rare to see. Nearly all plastic horn lenses are constant directivity type for use in pro-sound. The STH100 achieves constant directivity performance however as can be seen below.
Cabinet Construction
Due to the Russian war Baltic birch plywood is not longer available. For us here in Canada the only alternative is Chinese birch plywood and I suspect it is the same for other countries. The maximum material thickness that I've been able to source is 18mm thick. Normally I would use 24mm thick on an enclosure of this size. So to compensate I've added internal bracing in all directions.
The speaker stands are a variation of speaker stands No.1114 which can be found here.
Purifi Application Notes
In terms of crossover design I've been following Purifi's own technical notes on the subject which can be found at the link below.
I will be following these articles to ensure I'm getting the most from these excellent drivers.
Purifi's own blog has some interesting studies on distortion.
Stay tuned on further updates on this project.