Something stirs in the Undergrowth

[IslandPink]

The proper 'corner' GRF or the 'rectangular GRF' which looks a lot compromised ?
http://www.44bx.com/tannoy/grf.html

[andrew Ivimey]

Corner

[IslandPink]

Respect Due.
Good piece of info there, then.

[IslandPink]

Ran across this while reading more of the Ron Clarke postings :
http://www.troelsgravesen.dk/FE126E.htm
Look at the differences in Fs, Qts and Vas - it's a different speaker to the datasheet !

[pre65]

Are you interested in the FE126 Mark ?

[IslandPink]

No, sorry ! There are a number of better ones in their range - some of which I have ... Just makes you think, though, how far some drivers can be from the stated specs.

[IslandPink]

Bit of progress either side of a weekend away -
A wedge to get the tweeter pointing towards me - a surprising amount of work to make this small piece of wood

Also - replaced a 2.7k in the amp ( part of low-pass at 7kHz for mids/bass ) with variable 4.7k carbon-track preset, to allow some tweaking.
I set to 2.1k and did some brief listening this evening . Small increment in treble integration . impression though was of low bass being too high relative to midrange, so a change of resistor in series cross necessary- from 2.2k to 3.3R , I'll try that tomorrow.
Nice though - good tone on Jaco's bass. More listening definitely recommended !

[IslandPink]

Just playing with tweeter HP to integrate better to FX120's - not working quite right, so this evening went to 2.2uF cap for HP instead of 3.9 to get a change - for better or worse.
Lucky accident - rather good.
Now I should really go back and check if Chris was right about lack of crossover steepness causing distortion with the 3.9uF ( 1st-order ). More experiments to understand this - just run tweeter alone with 3.9uF, or I'll have a look at the Pinkzilla crossover and see what I used as a choke on that 'transitional' 2nd-order for guidance. Meanwhile sound is good, listening getting more fun by the day !

Simon wrote ( elsewhere ) :
"I've thought about using the 208Ez with the Beymas above 1K say, but I wonder if the added complexity might not justify the cost of the Beymas? Tricky without trying it to know.

I've also thought about running the 285GMF up higher too, something you suggested by email. When I first had the OBs up and running with the 285GMF and Alpair 12P I think I had the Supravox unfiltered, so going quite a bit higher than 1K. It was definitely an improvement rolling them off from around 150Hz but I think that was as much to do with only having one driver covering from c150Hz up.

But even if I did use the 285s up to 1K, I'd still need something at the bottom. Like another 285 lol "

Not sure how much the Beymas cost. You can get a very nice result with the 208Ez and the Aurum G3 ribbon, and probably one of the cheaper Aurum ones would be good enough too - as long as at least 96db/w or so. Basically the 'Pinkzilla' crossover ( mod of Basszilla ) covers this ( search) - crossover is something like 4.5k, first-order-ish, but there's a soft notch filter on the 208 as it goes down, to smooth out the descending response, then the ribbon comes up from 5KHz up. Sounded great - I mean not just 'pretty nice' - really impressive ! - but had trouble getting the low end of the FE208 to work with anything on OB as it rolls off too quick below 200Hz due to the low Qts and relatively small size.

Haha - yes 2 pairs of 285GMF - it really would work - was there once , briefly - but I think you can do better for mids with FX120 though.

[simon]

The TPL-150 is £328 each without horn at Blue Aran, the Aurum Cantus G3 $210 at Parts Express, so probably at least £210 each.

Another thought - I wonder how the Fostex T90A compares with the TPL-150 or G3? Useable down to 5k, and I already have them. The 285GMF looks like it might work up to 5k, and could perhaps be used without a filter. Then just protect the T90A at 5k and pad it down. Much depends on the 285GMF I guess but could be worth a try...

[Ant]

Simon, have a look at the sb acoustics ring tweeters, they will go down to about 3k ish. On my mets I rolled the top of the faital driver off from about 4 k and rolled the bottom of the tweeter off with a cap so it starts to roll off about 5 k ish. With just a cap on it its not a steep rolloff so there is usable output below that mine is (i think) the sb29rdc. Iirc there is either a 4r or 8r versions

[simon]

It's just an experiment really Ant, the 208s are currently running from c150Hz to 8k and overall the OBs are rather nice. But for a bit of playing I could try the 285GMF up to 5k and see how it sounds.

[IslandPink]

Go ahead & listen - might work - but I tend to think the advantage of the 285 up there is just that it works OK so can be crossed at eg. 1kHz with a low slope. It's not really got fidelity above 1k.
Likewise with a tweeter, to get a nice blend to the 208 you need something that on paper can get down to 1.5 k or so - hence you can cross with a low slope higher-up like 3.5k or above. There should be a cheaper Aurum tweeter that still goes lowish , not quite as sensitive as the G3 ?
Sorry to be controversial but I don't like the SB acoustics tweeter - doesn't do much for me. Guess I'm just a ribbon or compression driver guy ! ( They seem to have so much more treble tone and low-level qualities ) . Some of the bullet tweets are really nice, but only the expensive ones !

OK had a look and the G2si that Dick Olsher uses for Basszilla looks very good. Not quite as low freq but with a choke and a cap should work from 3.5k upwards. Quite a lot cheaper. 96db/w .

[Ant]

Each to their own mark
Must admit though, the sb does have its foibles; I.e I have issues with its off axis performance, it beams something rotten if the speakers arent toed in bang on. The other one with the smaller mounting flange and bigger magnet doesnt do it for some reason.

And I do often wonder what a ribbon would be like in these speakers.......

[chris661]

Just playing with tweeter HP to integrate better to FX120's - not working quite right, so this evening went to 2.2uF cap for HP instead of 3.9 to get a change - for better or worse.
Lucky accident - rather good.
Now I should really go back and check if Chris was right about lack of crossover steepness causing distortion with the 3.9uF ( 1st-order ). More experiments to understand this - just run tweeter alone with 3.9uF, or I'll have a look at the Pinkzilla crossover and see what I used as a choke on that 'transitional' 2nd-order for guidance. Meanwhile sound is good, listening getting more fun by the day !

I'd grab a medium-sized inductor and give it a try. Something of the order of a couple of mH, which would just start reducing output below 1kHz or so. That won't mess anything up where the crossover region is happening, but will decrease the amount of lower-mid energy that gets to the ribbon.

Glad you're enjoying the system. It's all about the music, after all.

Chris

[simon]

Go ahead & listen - might work - but I tend to think the advantage of the 285 up there is just that it works OK so can be crossed at eg. 1kHz with a low slope. It's not really got fidelity above 1k.

My thoughts too.