FE207E on Open Baffle

[Dave the bass]

Steve S will be impressed to see that i have fitted some nice 80/20 wool nylon carpet to the rear.

...and DTB is impressed 'cos you also have a bass guitar in your room

DTB

[al newall]

Dave.

I'm one of those sad persons who keep a bass guitar, just in case i might have the time to learn to play properly it one day. I gave up with electric guitar years ago. My fingers was too big.
I've had it about six years and not done much with it. It's only a cheap active Harley Benton, but a couple of bass players who've tried it, think its remarkably good to play, compared with what they had to learn on.

[iansr]

Steve S will be impressed to see that i have fitted some nice 80/20 wool nylon carpet to the rear.

80/20 !! Are you crazy Al? Everybody knows it has to be 100% wool

[iansr]

Hi Guys


Now this is quite troubling as the Mets sound excellent and have had a lot of work put into them. But now they sound "hi-fi" The baffles are so much more musical than the Mets it is unreal. The missus, who's feet you can see in the picture was gobsmacked that a pair of cardboard baffles groaning and creaking under the weight of the drivers as they played some John Martyn were doing things with which the Metronomes simply could not compete.

Steve

That's done it. There I was planning my 5' Mets for
living-room-friendly use and you go and tell us this! And I'd just about managed to talk myself out of buying some Feastrex drivers for an OB set up.

Keep the reports coming Steve. I'd be interested to hear how far out from the wall they have to be for optimal performance, with and without the subs.

[Cressy Snr]

That's done it. There I was planning my 5' Mets for
living-room-friendly use and you go and tell us this! And I'd just about managed to talk myself out of buying some Feastrex drivers for an OB set up.

Keep the reports coming Steve. I'd be interested to hear how far out from the wall they have to be for optimal performance, with and without the subs.

Hi Ian

There's nothing wrong at all with the bigger metronomes I have heard. Don't forget that my originals are not the same as the ones Scott and Dave designed.

Mine was fundamentally flawed in terms of pipe length as I went with classic Voigt quarter wave theory, long since superseded. Scott did his best to make a reasonable compromise out of them.

The 127s that Anthony made were Scott's design and sound much better than mine. You need have no fear building any of the bigger ones as they have been designed properly from the beginning.

It is a testament to their sound that I've had them for two and a half years with no changes.

Steve

[Cressy Snr]

I moved the tweeter mounting plate today as last night I discovered a bit of a problem with them as they were positioned before.



The tweeter plate has been repositioned on a batten with a 10 degree offset on the top. This has brought the tweeter plate horizontal, with respect to the main baffle slope, so that the tweeter is firing straight up at the ceiling with no obstruction.

Closing the curtains and listening last night caused the soundstage height to reduce, treble levels to drop and the speakers to stop, as Ed would put it "talking to each other", appearing as individual entities instead of being "invisible", as they had been during the day.

Examining the situation revealed, that with the curtains closed, the tweeters were firing straight into them, causing most of their sound to be absorbed. The baffles therefore reverted to monopole treble, causing beaming and a sweet spot, outside of which the image was not formed correctly, plus a very audible reduction in space and ambience.

Having moved the tweeter plate so the HF unit is firing vertically has already led to an improvement in air and space over the sloping tweeter version. With the curtains closed there is no effect on the soundstage, treble levels or imaging. That's that bit sorted then.

Steve

[steve s]

[quote="al newallPicture posted to clarify my answer to a question from Steve.
Steve S will be impressed to see that i have fitted some nice 80/20 wool nylon carpet to the rear.[/quote]


very impressed al...

did you find it made a difference?

nice work steve...

more OB converts

[Cressy Snr]

nice work steve...

more OB converts

Hi Steve,
As you know I was a bit sceptical about open baffles and small rooms. At your place, baffles have plenty of room to breathe and Nick has his own space in which to put his.

It was Al's baffles at Owston playing "Jack of Speed" that made me think. Yours and Nick's are known quantities, great sounding, but far too big for my room, but Al's seemed to be of a more manageable size for smaller rooms and very good sounding on the Steely Dan track to boot.

I got hold of a pretty tatty copy of Brigg's book for not much money due to the condition. Reading about the way he went about designing his baffles and the way he took real rooms into consideration when designing them made me think they might not be that bad a proposition and having heard Al's I thought I might give it a go at some point. I then got into the PX25 build and the speaker idea went on the back burner.

Then came an email from Andrew I telling me how much he didn't like the sound of my speakers at Owston and offering me a pair of Fostex FE207Es to ease my troubles, for a small fee of course. Well I snatched his hand off, thinking I was going to use them in a pair of bigger Metronomes.

They of course ended up being used on baffles with the FE108EZ drivers from the Metronomes used as tweeters.

Reading Peter's article on Briggs' baffles and Briggs himself, it certainly seems that, when he designed these speakers, he was thinking about every aspect of real room performance and how to get a realistic sound stage with width, depth and height whilst preserving domestic harmony.

The half-width Briggs inspired baffles I'm playing with, seem to illustrate very well and ultimately vindicate his "real rooms" approach to speaker design. Sadly as Peter says in his article, such important considerations have since been turned on their heads, and we have instead to put up with hideous plastic coned apparitions that need to be in the middle of the room to work properly.

I didn't think it was possible realistically to put a pair of open-baffle speakers in a room the size of mine without ending up in the divorce court, but Melanie loves them. Obviously though they go pretty deep, they are not really big enough for subterranean bass levels. The subs do help out in that department though and I've had enough experience with subwoofers by now to be able to get them to integrate properly with the baffles.

I'm in the position now where I would find it very difficult to go back to boxes.

I'll keep posting as I tweak them further.

Steve

[al newall]

Putting carpet on the back certainly helps focus the image when using baffles close to walls.
The effect is understandably reduced when away from walls. I am able to move my baffles about 4 foot from the rear wall and so have mixed feelings.
It also has, IMHO, the effect of reducing the dynamic impact of some music.
Maybe i overdid the carpetting and need to remove some, i'll find out soon. Not sure which is the most important area to cover. The bit around the drivers or the wing?

[Scottmoose]

deleted

[al newall]

Thanks Scott, that makes sense.
Nothing worse than a resonant cavity.

[Cressy Snr]

Here is an idea of what the baffles might look like when the final models are built in proper birch ply.



Speaker grill slats off an old radiogram give a cross between Art Deco and Mackintosh.

I took the bottle tops off the backs of Andrew's phase plugs and replaced them with a couple of countersunk steel screws. This deadened the plug's interface with the motor magnet and removed a bit of ringing in the upper midrange.

All the same, I'll probably go for a pair of Planet10 phase plugs in the final model.

Steve

[simon]

I'm in the position now where I would find it very difficult to go back to boxes.

Geez, that James D has a lot to answer for!

[Cressy Snr]

I'm in the position now where I would find it very difficult to go back to boxes.

Geez, that James D has a lot to answer for!

Yes,
James does have a lot to answer for but now I'm stuck with baffles I'd better get this pair up to scratch.


So.........

Cold light of day this morning and I'm listening intently and getting more and more pissed off. Despite all the fiddling with different phase plugs etc I'm still hearing that damn whizzer. Maybe I've been spoiled by the superb midrange quality of the FE108EZ driver but I've decided I hate whizzers-or should I say dammared Fostex FE207E whizzers. I'm sorry folks but compared to the little driver the big Fostex's whizzer sounds like a megaphone.

One minute I think I've got rid of the cupped hands sound, then I put something on that reveals it again and we are back to square one, because once you've heard it in that track, you then start hearing it on those others from which you thought you'd banished the bloody thing.

A major rethink was in order here so I got out the scalpel and swiftly cut off both of the whizzers. Blessed relief from the megaphone sound at last but now there was a hole in the lower treble.

Much head-scratching led to an inductor being placed in series with the big driver, to roll off its top end and upper mids. The upward firing FE108EZ tweeter was brought round onto the front of the baffle and its series cap changed from 3uF to 20uF to put in some midrange and fill the hole in the lower treble.



So now we have the big driver being a bass/mid unit up to about 1200Hz then the little driver takes over the rest of the frequency range.

Because the FE108EZ is open-backed I still have dipole upper mids and treble so there is not a discontinuity in radiation pattern between the two drivers. It sounds pretty good at the moment, but a bit of cap tweaking is probably in order, maybe 15uF rather than 20 to fine tune the crossover point. I'm pretty close with the crossover I think, it's just a matter of tweaking it up a bit.

Height of soundstage has dropped a bit due to reassigning the tweeter to a midrange/HF unit but the freedom from that whizzer sound is more than enough compensation.

The big driver is 4dB more efficient than the little driver, which is about right. I wired a 100R wirewound pot into each mid/tweeter but it needed very little adjustment to pad down the driver. Measuring the pot resistance after adjustment gave just over 0.5R so a 0.56R resistor will replace the pot tomorrow.

[cressy]

i'll second that, i was a little underwhelmed hearing the first mdf incarnation, adding the 108 was better and i seem to recall mentioning the crossover was abit low. there was a hole in the midrange that i could hear. it sounded abit unnatural to me, sort of super natural. seemed to have too much atmosphere. i walked in today after work and heard some will smith then michael jackson (sister had the remote) it was a lot lot better no hole in the mid . im not sure about the moving of the 108 but i didnt hear them after the wizzer was taken off and the 108 was still on the back so i cant comment on that. they sounded to me on a short listen so much more natural in this incarnation because i wasnt drawn to a particular frequency range or an instrument wheras before it was dragging my ears to the crossover point and to the decay on say a hi hat. a hell of a lot better today. today i was impressed. are these the speaker equivalent of a breadboard? i'll have to get that spare carpet underlay out of the loft and let him have a play with that!