Fonken FE167eN + FT17H MTM Floorstanders

[Toppsy]

Post Eggborough I have a little more enthusiasm for our hobby than I had before the meet. Whether that is a good thing or not time will tell. Hey

Anyway I'm really **ssed off just sitting here at home with nothing to do other than search the online web job sites for any job remotely near where I live or to which I can commute each day. But no more of my woes.

With the success of the twin driver MA Alpair10 mini onken speakers - that really didn't excel at Eggy, but sound rather good indeed at home and at my Son's place - I have been thinking a MTM configuration for a mini-onken (Fonkens) floorstanding speakers. using the now obsolete Fostex FE167e with Fostex FT17H tweeter helper.

They are based on the Planet10 Fonken167 floorstanders and as I have 2-pr the DaveD treated FE167eN drivers and a pair the FT17H they will only cost the price of a couple sheets of MDF. I know Birch Ply would (perhaps) be a better choice of material but these are a prototype in the development stage. If they prove a winner I may well build another pair in BB Ply when funds permit.

Below is a image of how they will look with some dims to give an idea of their size. I'm awaiting some feedback from DavD - the Fonken guru - before I go ahead and order the wood.

At least this build will keep my mind active and stop me thinking of other terminal things!

[Mike H]

Can I ask a dumb question ~ what is the advantage of having two drivers? Apart from larger cone area



 

[Toppsy]

Mike H wrote

Can I ask a dumb question ~ what is the advantage of having two drivers? Apart from larger cone area

Higher efficiency, less doppler distortion, greater dynamics, more impact, play louder.

Apart from that I just think they look great and with my commercial head on, could appeal to many outside the DIY community.

[planet10]

You'll want to get the drivers as close together as possible.

The reference textbook i am reading on Phycology of Hearing, doppler distortion is dismissed as irrelevant.

dave

[Toppsy]

Dave,

Thanks for the feedback on the driver alignment.

However to do either the options you have posted would require the front baffle to be increased by some 60mm in width and keep the main driver central the front baffle

This would require a full redesign the speakers to keep the O/A internal volume the same. If I keep the depth the same this would mean a reduction in internal height. Is this what you are recommending

My preference would be to keep the front baffle to 200mm wide so therefore have tweeked your layout a little to keep within this width and still allow me to use a grille covers to the drivers.

As you know my 2-pair of FE167eN drivers have different colour EnABLe treatment so a grille over the speakers is needed for aesthetics.

What is the benefit of offsetting the tweeter other than to reduce the distance between the 167's

EDIT

If the FT17H is placed central between the 167's then the c/c distance between them icreases by 5mm to 255mm.

[Toppsy]

I have just some quick redrafting the design to accommodate the offset tweeter as you posted Dave and still keep the main 167 drivers central to the front baffle.

The front baffle would have to be increased from 200mm to 270mm wide.
Keeping the depth of the cabinets the same this would reduce the internal height from 1100mm to 815mm. So a false base - as the originals - is needed to keep the same O/A height the speakers.

To my eyes these do not look as elegant as keeping the front baffle 200mm wide.

[richardcooper2k]

function vs. aesthetics - a commercial quandary

can the two be synthesised ?

if the tweeter is off centre, will it look better/any worse if the mid woofers aren't either ?

[Graeme]

Why do you need to keep the tweeter inbetween the 2 main drivers?
If the tweeter was above (boringly traditional i know) then this problem is solved.

Do you want the tweeter in the middle to make it more 'point source'?

[richardcooper2k]

if only one of the main drivers is crossing over to the tweeter that is ok

if both cross to the tweeter together at the same frequency i think they both need to be close

[Toppsy]

Richard,
These speakers are purely for my own use but should I decide to venture back into making speakers for a living it is a aesthetics has to be a consideration.

Graeme,

This design is a follow up to a pair of Scottmoose ML-TL cabinets that DaveD (Planet10) did with a pair of CSS EL166 woofers and Fostex FF85K in a D'Appolito configuration though Dave offset the tweeter as opposed to central mounting in a true D'Appolito configuration.

With respect the XO arrangement. The FE167's will be wired in parallel and both run full range. However I also intend to try a inline cap (say 80uF) to the upper FE167 to cut this at 400Hz. This to be arranged via a toggle switch so I can quickly swap between the two setups and decide which sounds the best. The tweeter will be wired direct to the speaker posts via a L-pad and inline 2uF cap to cut in at around 10kH and give some adjustment of attenuation. One must remember the Fostex FE167's are full range drivers, but need a little help in the treble.

I'll then repeat the exercise but with the 167's wired in series.

EDIT

Do you want the tweeter in the middle to make it more 'point source'?

The tweeter was placed such as it places it at ear height. Which I believe is the optimum location for the HF driver.

[chris661]

Watching with interest.

As a thought, to combat the need for a BSC circuit, why not low pass one of the Fostexes, so the drop in level when they hit baffle step will be accounted for?

This'd avoid playing with the BSC circuit as a whole, trading it for a series inductor on one of the drivers.

PS - I'd agree that the original, narrower baffle does look better. I seem to remember that the point to point spacing doesn't matter a whole lot as long as you're happy to stay at one height, or you'd likely get vertical lobing issues.

[Toppsy]

As a thought, to combat the need for a BSC circuit, why not low pass one of the Fostexes, so the drop in level when they hit baffle step will be accounted for?

Chris, this is my intention. See my last posting which I refer to wiring a inline 80uF cap to the upper FE167. This will give a low pass filter around 400Hz. I may need to go as high as 800Hz (40uF cap) depending how the listening tests go.

I should say that the FT17H is only there to help the 10kHz dip in the FR of the FE167 drivers.

[chris661]

... I fear you've made a mistake.

A capacitor in series acts as a high pass, which is why they're used for tweeters.

Perhaps you're planning on using a different crossover?

[Andrew]

I think Colin means a high pass filter, the intent was to limit bass freq from one driver only so the two weren't acting in tandem below 400Hz, or so. As a consequence the bass was better, much less boomy and because that driver wasn't trying to do big bass excursions, its treble seemed less ragged too.

The idea came from Scott who thought the two drivers together were a bit boomy and perhaps interacting in an odd way, both being in the same chamber etc.

Andrew

[chris661]

Hmmm...

I was thinking that it'd be to counterract the step drop in frequency response when the driver goes from radiating in 2pi (flat plane) to 4pi, omnidirectional. At this point, you lose some output as the sound wraps around the enclosure instead of being sent more directly to the listener. It's this effect that the lowpasses driver would compensate for.