New Open Baffle Project
Posted: Tue Aug 13, 2019 9:26 pm
I have been running with a pair of modified Allison 6 speakers for about a year and a half in my new listening room. With many genres, the SQ is excellent. But the upward firing 8 inch bass/mid unit has a tendency to excite not only room modes in the listening room, but also sound almost as loud in adjacent room as in my listening position. The deal-breaker, however, is relatively poor performance with classical music, and large scale orchestral music in particular.
With this in mind and wishing to stick with a DIY approach, an open baffle (OB) has presented itself as a possible route. Without wishing to repeat what has been discussed in various fora and articles, here are some of the salient sources:
http://www.quarter-wave.com/OBs/OB_Design_Part_1.pdf
http://www.quarter-wave.com/OBs/OB_Design_Part_2.pdf
http://www.quarter-wave.com/OBs/U_and_H_Frames.pdf
https://www.diyaudio.com/forums/full-ra ... ticle.html
https://audiokarma.org/forums/index.php ... ny.566879/
http://www.hi-fiworld.co.uk/loudspeaker ... rt-15.html
https://www.hi-fiworld.co.uk/index.php/ ... rials.html
http://www.hi-fiworld.co.uk/loudspeaker ... onses.html
https://www.hi-fiworld.co.uk/index.php/ ... ffle-.html
The hi-fi world articles in general and those on the Wharfedale SFB3 are particularly interesting. The 12” bass and 10” bass/mid drivers are run wide open and the upward firing tweeter with a single 4uF capacitor. All this should sound very familiar to aficionados of the Doc’s speaker philosophy.
Whilst going for an SFB3 type design is tempting, we are not exactly blessed at the moment with suitable drivers. Troels Gravesen has had a go with his OBL11 http://www.troelsgravesen.dk/OBL11.htm and OBL 15 http://www.troelsgravesen.dk/OBL-15.htm designs. However, even a quick glance reveals relatively high expense and moreover a crossover with more than just a 4uF capacitor.
So, taking into account MJK’s work on open baffle, U and H frames as a starting point, I have decided to go with a design that sits somewhere between an open baffle ‘slab’ and a U frame with separate full range driver over. I’ve decided to go with the Monacor SP-382PA 15 inch bass driver with a view to rolling it off electrically from somewhere between 175hz & 200hz. Everything else will be served by the Monacor SPX-32M full range driver with the high pass set at around 450-500hz. Crossover duties will be implemented digitally with a miniDSP 2x4. The miniDSP will output to something suitable for the power section, with four discrete outputs needed for the four drivers.
I am not keen on using EQ digital or otherwise to achieve a decent bass response. I am also aware that running a small, inexpensive 3 inch full range driver for the top six or seven octaves may be a little ambitious, and that more conventional mid & tweeter setup may prove better. However, this would introduce crossover complications.
I have toyed with using a pair of 12 inch bass drivers per side in a double U frame configuration. However, they only shift a little more air than a single 15 incher (total cone area of 2 x 12 inchers of about 1060 cm2, compared with 825 cm2 for the Monacor 15 inch. There was also the small matter of finding a 12 inch driver with a high enough qts. The Monacor SP-382PA is at the lower end of what works at around 0.75. However, with an Fs of 25hz and a very smooth and steady roll off, it should work well enough.
Plywood cutting should happen in the next week or two, so I will post some pictures and first impressions then.
With this in mind and wishing to stick with a DIY approach, an open baffle (OB) has presented itself as a possible route. Without wishing to repeat what has been discussed in various fora and articles, here are some of the salient sources:
http://www.quarter-wave.com/OBs/OB_Design_Part_1.pdf
http://www.quarter-wave.com/OBs/OB_Design_Part_2.pdf
http://www.quarter-wave.com/OBs/U_and_H_Frames.pdf
https://www.diyaudio.com/forums/full-ra ... ticle.html
https://audiokarma.org/forums/index.php ... ny.566879/
http://www.hi-fiworld.co.uk/loudspeaker ... rt-15.html
https://www.hi-fiworld.co.uk/index.php/ ... rials.html
http://www.hi-fiworld.co.uk/loudspeaker ... onses.html
https://www.hi-fiworld.co.uk/index.php/ ... ffle-.html
The hi-fi world articles in general and those on the Wharfedale SFB3 are particularly interesting. The 12” bass and 10” bass/mid drivers are run wide open and the upward firing tweeter with a single 4uF capacitor. All this should sound very familiar to aficionados of the Doc’s speaker philosophy.
Whilst going for an SFB3 type design is tempting, we are not exactly blessed at the moment with suitable drivers. Troels Gravesen has had a go with his OBL11 http://www.troelsgravesen.dk/OBL11.htm and OBL 15 http://www.troelsgravesen.dk/OBL-15.htm designs. However, even a quick glance reveals relatively high expense and moreover a crossover with more than just a 4uF capacitor.
So, taking into account MJK’s work on open baffle, U and H frames as a starting point, I have decided to go with a design that sits somewhere between an open baffle ‘slab’ and a U frame with separate full range driver over. I’ve decided to go with the Monacor SP-382PA 15 inch bass driver with a view to rolling it off electrically from somewhere between 175hz & 200hz. Everything else will be served by the Monacor SPX-32M full range driver with the high pass set at around 450-500hz. Crossover duties will be implemented digitally with a miniDSP 2x4. The miniDSP will output to something suitable for the power section, with four discrete outputs needed for the four drivers.
I am not keen on using EQ digital or otherwise to achieve a decent bass response. I am also aware that running a small, inexpensive 3 inch full range driver for the top six or seven octaves may be a little ambitious, and that more conventional mid & tweeter setup may prove better. However, this would introduce crossover complications.
I have toyed with using a pair of 12 inch bass drivers per side in a double U frame configuration. However, they only shift a little more air than a single 15 incher (total cone area of 2 x 12 inchers of about 1060 cm2, compared with 825 cm2 for the Monacor 15 inch. There was also the small matter of finding a 12 inch driver with a high enough qts. The Monacor SP-382PA is at the lower end of what works at around 0.75. However, with an Fs of 25hz and a very smooth and steady roll off, it should work well enough.
Plywood cutting should happen in the next week or two, so I will post some pictures and first impressions then.