Reinouts neue Lautsprecher

Nachdem sich Reinout seine Keramikmembranen mit Trentemöller zerschossen hatte, braucht der Mann Ersatz. Ich freu mich schon auf den Hörtermin in Holland… 

After the ceramic-crash of the Accuton-units I was a bit disappointed. The new units arrived swiftly and were even made more sturdier but when an audio colleague really wanted to buy the loudspeakers it was time to let them go. And a new project started !
The new loudspeakers were going to be more simple in construction:
a.. Open Baffle design (OB). An OB has a certain “ease of sound” which probably has to do with the fact that the units are running as freely as possible.
b.. 2-way consisting of a fullrange-unit running almost full spectrum. The real low region will be covered  by a serious woofer. Real 100% fullrange is physically nearly impossible. It is almost impossible for a single unit to perform great at low notes and deliver perfect highs as well (without very large horn-constructions). So this will be a FAST: Fullrange And Subwoofer Technology.
c.. Simple crossover. I will not try to completely flatten the response curves as every network will interfere with actual units.
Here started the quest for some serious units:
a.. Feastrex D9NF to be used as (nearly) full range unit. Theoretically it is a fullrange-unit but when relieved from the really low notes this unit starts to shine: wonderful mid and highs !
b.. Fertin 38EX woofer. This is a fieldcoil-design which is very interesting. You have the possibility to change the sensitivity of the unit by applying different voltages. And with the different sensitivity the Qts also changes. Very fun for now you can optimize this unit to the actual enclosure. Normally the Qts is a given factor; but now you can change that to the optimum.
For listening to the units and finding the optimal crossover-frequency I made a temporary setup with shores and 18 mm plywood. Crossover-frequency was established at 230 Hz. The Fertin takes care of the low; the Feastrex does the rest. What is also really nice is with this frequency the energy-rich bas notes will not reach the Feastrex. Essential as the Feastrex is no powerbeast and I do have a lot of power on tap…..
The crossover is second order affair using nice components:
a.. The huge bascoil (Mundorf VN390; EI150-size) with only 0.05 ohm resistance makes really low and dry bas-tones possible.
b.. The capacitors are old (but trusty) milspec paper/oil capacitors.
c.. The really different component here is the autoformer (Silvercore; the grey cylinder with multiple taps). The Feastrex and Fertin does not have the same sensitivity. When using the classic resistor-network in order to level those 2 units I found that the Feastrex was ripped of its magical mid/high. The autoformer is a much nicer and better sounding solution as this does not simply burn away energy….
The OB itself is made from a mix of materials: 30 mm plywood + 18 mm chipboard + 25 mm MDF; this in order to suppress any resonances. Of importance is that the backside of the baffle is formed in a way so that the units can breathe freely.

Just finished: the crossover-covers are ready and the essential OB-cover is in place before Alex (1½ year old son) probes the units with his enthusiastic little fingers….
Now it is playing time and with good result: effortless mid/high and great bas (dry and fast). I’m very happy with the result; it is a really natural performer.

2 thoughts on “Reinouts neue Lautsprecher

  1. Good afternoon Mathias, if you have enough space these OB’s work even better. If there is room to breathe you can place the OB’s in that way that backward-reflections will be less/not noticed.
    The bass-quality is really nice: dry + fast. Not boxy (obvious !) or with a bass-reflex hump in the response. Or even worse: port-flow sounds when using a badly designed bass-reflex.
    You’re right about the fieldcoil-costs that this option is expensive. But without this feature i would never have the opportunity to optimize the unit to it’s OB. It is exactly the other way around normal speaker designing and it is fun by changing the voltage to actually find out when the fieldcoil-woofer is at its best (in my OB). It is varying between a flabby bass (much of it but no definition) to a tight performer. You don’t need fancy measuring equipment…..your ears do this with ease.
    If you ever find affordable fieldcoils please inform me…….

    Happy building and listening.
    Regards, Reinout

  2. Hello Reinout,

    after having been infected with the idea that an OB might make very much sense in my listening situation where I have a serious problem with bass resonances but am able to place the speakers with enough room to be able to breathe freely this article definately comes right in time :-)
    If only fieldcoils wouldn’t be that expensive! Have fun listening music with your improved setup.


    p.s. Wolf, guess you are also reading this *hint, hint*

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