Speakers - A blast from the Past - Lessons for the future?

[Simon Hickie]

I've been digging around a lot recently regarding open baffle designs. Whilst there's a lot of mad stuff out there, one design in particular hit something of a chord (so to speak). It's the Wharfedale SFB/3 https://www.inner-magazines.com/audioph ... dale-sfb3/ and http://www.troelsgravesen.dk/Wharfedale ... /SFB-3.pdf from 1956.

The two standout features are (a) both front facing drivers, a 12 inch and a 10 inch, are run crossoverless and (b) that the 3 inch mid/tweeter is upwards firing. At 90cm wide, the speaker approaches 3 x the size of the larger driver. Some experiments elsewhere on positioning are here http://www.hi-fiworld.co.uk/loudspeaker ... onses.html

Gilbert Briggs' design never fully took off commercially and the takeover of Wharfedale by Rank in 1958 marked the transition from innovation to mass market appeal. Today, it means that the box shifters concentrate on narrow baffled high WAF designs that are constantly fighting with the room.

What implications does this have for a DIY OB design? We know that 'full range drivers' are full of compromises: too small and they cannot shift enough air; too large and treble beaming becomes an issue. We also know that conventional crossovers come with a range of ‘issues’. The SFB/3 offers a total cone area in the region of 860 cm2. This equates to one 15 inch driver or about four 8 inch drivers.

The problem with a 15 inch driver is what happens at higher frequencies: it’s not going to be as agile as a smaller driver with or without doping. However, 4 x 8 inch drivers is going to be quite demanding in terms of baffle space. So here’s an ‘in my head’ idea. Two x 8 inch Doc Mod drivers on a minimum 24 inch wide baffle plus a suitable tweeter with single capacitor protection. When wired in parallel, the mutual coupling gives a +6db response so tweeter padding could be reduced with a smaller resistor. I’ve no idea how the bottom end will hold up as the baffle step will begin at around 200hz. And at that frequency, a first order low pass inductor will be huge (around 14mH).

I have a pair of 8 inch doc modded drivers available. I’ll give it a go with a single 8 inch per side along with a 4 inch full ranger I have, but roll the full ranger off below 500hz or so with a 22uF cap. I’ve also got some old bits of plywood and MDF so will get busy this weekend.

[hillsanddalesrover]

To be honest Simon, if you want to make a successful open baffle speaker, join Audio Talk and submit your post on there.

The members over there will help you.

I'm not suggesting that any advice on here will be bad, but they (Audio Talk) have much more practical (read empirical) experience.

[Simon Hickie]

Thanks HDR. I'm a member there too. However, I was resurrecting an idea floated by the Doc back in 2015 with a single 8 inch doc mod driver and tweeter on a five foot (!!!) high baffle.

[Dr Bunsen Honeydew]

I am great believer in that we are discoverers not inventors, everything exist, it is just waiting for someone to trip over it. In audio there is little now to trip over, it is all there in one form or another. The skill is making it play music.

[Simon Hickie]

Well, the single 8 inch driver prototype is now underway with cutouts done and holes drilled. Gaffer-taping the 'wings' will happen after dinner. I guesstimate a 33uF cap and a resistor around the 5.6 ohm mark should be there or thereabouts for a 300ish hz roll off of the full ranger, thus relieving it of any bass duties. I have a selection of resistors and caps to play with, so listening and experimenting is the order of the day. The front baffle with the wings offering a bit of stability will be around 30 inches wide. With side wall and floor reinforcement for the bass driver the results will be interesting!