One Driver to Rule Them All

I often describe Cathode Bias as a hobby that got out of control, but in the past couple weeks I was able to return to my hobbyist roots with a personal project which I have been wanting to do for over 10 years. I finally prioritized and made it happen over the holidays. I built a backload horn cabinet for the latest Fostex 8" range-driver: the FE206NV2.

The concept of "full-range" or "wide band" drivers is to use only one driver to cover the majority of the audible range, or at least the more important parts, without any crossover components. This is a simplistic and pure design. Like every speaker engineering problem there are limitations which make covering the audible range difficult to achieve. One is the ability to produce reasonable bass response from the speaker which can also cover the important mid-range, especially off-axis. To do this requires exploring acoustical tricks including horn loading.

A backloaded horn is a speaker enclosure design where the driver's back wave travels through a folded, expanding path (the horn) before exiting, efficiently amplifying bass and mid-bass frequencies for high efficiency output. Using a 8" driver like the Fostex won't provide earth moving bass, but the horn helps fill in the lower frequency ranges which may otherwise be missing altogether. One drawback is the frequencies from the horn exit are out of phase with the front of the driver, which could cause cancellation and comb filtering, but in practice I haven't found this to be a significant detriment.

The FE206NV2 and similar full-range drivers use light weight cone designs which makes them very efficient with good dynamics, but they can't handle a lot of power or play to high SPL levels. In many ways this makes them ideal for quieter environments like a home system where dynamics can be a critical element to listening experience. My intention in building these was to use them as main speakers in our condo (with typical condo noise concerns) in Florida. These speakers also pair well with low power tube amps like single ended triodes, which makes for a very minimalistic overall system design.

The Build

For this build I used the Fostex "reference" design, which is a design Fostex provides with their drivers.

While there are a lot of pieces to this design, it is fairly easy to build by DIYers with some basic woodworking tools and skills. All the cuts and angles are square, so aligning the cabinet is pretty straight forward, if a bit finicky. I modified the design slightly to use rabbets on the outer case of the cabinet. I do this with all my cabinets as I find it makes for a strong joint which is easier to clamp and square up. The most finicky part was the finish, which with all the "steps" of the horn exit requires some patience. But overall I would recommend this design.

I used Baltic Birch exclusively for this build. Fortunately there is a good supply of Russian made Baltic Birch in my area at reasonable prices. To be honest I don't totally understand how Russian products are imported into the US currently, but politics aside, Baltic Birch is one of the best products available for speaker cabinets. All the layers (of which there are 13 in 18mm or 3/4" stock), are made of birch hardwood. This makes for a very dense and stable material to work with. If you are going to take on this project, I highly recommend seeking out Baltic Birch in your area.

For the finish I used a water based poly and no stain to keep the natural hue of the birch. This was at the recommendation of my wife and design consultant: Eylin Baus. For future projects I will probably use an oil based product. I'm always sucked in by the easy of use of water based products, but ultimately find that oil products produce a more consistent finish with their longer open time.

I seriously considered painting the speakers. As a side note, the local Benjamin Moore store recommended their Command product for speaker cabinets, and I'm sold on it after using it for my last project – specifically for speakers which may see significant movement (like for pop-up events).

The Listening

These speakers have met my expectations in the short time I've listened to them. There is a very delicate and precise mid-range presence which I haven't experienced from other speaker designs. Female voices and plucked strings jump from the speakers in a way that will catch your attention.

I've owned two other pairs of full-range speakers, so I had a good idea what to expect. As a reference, I also own a pair of 8" Fostex FE206ES-R in a bass reflex cabinet. These were special edition driver by Fostex and a speaker I've loved for years. They set a high bar. Overall I think the new speakers live up to that standard, but while I can't compare them directly (the ES-Rs are in Tahoe), I feel the ES-Rs have everything that the new FE206NV2 have, but maybe just more of it.

The backloaded horn does help with the bass response of these speakers, but don't expect them to shake your pant legs. Which for me is fine given the installation constraints in our condo. The bass (if a bit constrained) is clear and concise, echoing the mid-range.

Conclusion

Given my listening experience, I highly recommend this type of speaker design if you haven't tried one on your HiFi journey. While there is some complexity in the cabinet, the circuit couldn't be simpler which makes the project approachable with surprising results, if you can accept the constraints of lower power handling and lack of extended high and low frequency listening. For me I see this as an ideal tradeoff for to get that mid-range magic in our environment which limits the size and output of the speakers which can be installed.