The inspiration for this project came from a Fostex enclosure plan for the FE127 4" full range driver. Unfortunately I didn't have a pair of Fostex drivers to hand but I did have a pair of Visaton FR10 which I'd tried before in my Mini T-line with disappointing results. Not only was there a lack of bass but top end was coarse and rough. Only the addition of a tweeter improved the result. With this double bass reflex enclosure I hoped that the FR10 would perform better at the bottom end and with the addition of some filtering, a sweeter top end too.
To make the enclosures I commandeered a pair of old bedside cabinets that had been gathering dust in the spare room and were no longer needed. A bonus was that the dimensions were similar to the Fostex plan and complete with a shelf divider. For the sides I found some sheets of plywood amongst the accumulation of junk in my garage. They'd originally been used for a model railway layout and were in a poor condition but would do the job.
Holes cut for the driver, terminal plate and 65 x 54mm port tubes. The shelf was raised to reduce the volume of the top chamber to 7 litres and increase the lower one to 17 litres which pretty much agrees with the Fostex plan.
Found that I'd cut the holes for the port tubes undersize (a senior moment), too late to rectify the problem so ended up glueing them in postition over the holes. The top chamber was lined with BAF wadding.
After a considerable amount of filling and sanding I finished the cabinets with DC-Fix gloss black vinyl, almost piano black. This is an excellent product, easy to apply and hides a multitude of sins.
Dimensions (mm): 600H x 300D x 210W
Cabinet Material: 15mm Chipboard and 12mm plywood
Cabinet type: Double Bass Reflex
Approx total internal volume: 24 Litres
Dismissing the cost of a pair of Visaton FR10, my total outlay for this project amounts to about £9 made up of 4 port tubes, 2 terminal plates and a roll of 675mm x 2m vinyl.
The FR10 in this enclosure is capable of producing a reasonable amount of extended bass and in that respect I feel this is a successful project. Unfortunately the top end is far from satisfactory and despite trying notch and BSC filters I was unable to obtain an acceptable result. This driver really needs a tweeter which defeats the object of it for hi-fi purposes at least.
At some point I will try the Monacor SP-60 4" midwoofer in this enclosure with a satellite tweeter.
Monacor SP-60. A contender for full-range?
This is not a full range driver but I was surprised by the amount of top end energy, similar in many ways to the FR10 being a bit harsh and peaky.
I connected a 0.4mH coil in series to the SP-60 to give a 6db per octave roll-off from 3000Hz with the intention of adding a tweeter. This turned out to be unnecessary to my ears.
The roll-off has tamed the top end without much loss of detail when listening on axis. Bass performance is excellent.
It might also benefit further from a phase plug.
Tang Band W4-657D
This is a beautifully engineered driver with die cast basket, aluminium phase plug, rubber roll surround a aluminium cone. Initial listening impressions were encouraging but top end was over-bright and aggressive. Bass was strong and extended, no problems there.
To tame the top end I considered a 5dB notch filter centered on 7K recommended by posters on the DIY Audio forum. Instead I tried a 0.27mH inductor which gives a gentle roll-off from about 4K. To my ears this has resulted in a very well balanced speaker with no obvious lack of any top end detail and is enjoyable to listen to for extended periods. WAF is high.
Drivers obtained from Blue Planet Acoustic.