Something stirs in the Undergrowth

[IslandPink]

Unfortunately the SB acoustics mid drivers still have too low a resonance, so that's a blind alley - may find something else better for the future.
Anyway ... still sounds very good, and this afternoon I looked at the amps again and I have the 700Hz high-pass in the Yuichi channel. Have sometimes find it better to run without this , let the horn roll off itself . So I put the 0.47u cap across again (ie. full-range amp ) and listened. Tone has improved across the board. Vocals very nice . Haven't got the ribbon in yet, but I know that will take it up another notch .

[IslandPink]

Increments -
1. Moved Yuichi back about 15cm , based on path length calcs and the 700Hz crossover.
2. Looked properly at low pass in left amp channel. Values are giving a -6dB point at 700Hz , rather than a -3dB point as required . I dug out a 4.96k Vishay and a 0.01u Jensen and placed them between the 4P1L ( resistor in-line, cap to ground ) and 300B in place of the 8.2k/0.015u before. Bear in mind the 4.96k adds to the ~7.5k Zout of the 4P1L.

Male vocal tone and smoothness improving. John Martyn 'Bless the Weather' on at the moment. Voice and Danny Thompson's bass have both improved significantly with more body and colour.
'Horses' by Patti Smith sounded superb earlier on.

[IslandPink]

In the interests of going wideband again, today I made some new 'Little Feat' for the subwoofer.
The old ones had optimistic use of 1" dowel and polyester resin to fix, and bit the dust last time I used the unit.

[ed]

and bit the dust last time I used the unit.

I'm sure these won't fail you now!

swidt

well someone had to say it

[Scottmoose]

Bad...

What happened to the original shoes? Went sailin?'
(worse )

[Cressy Snr]

Nah, they're off doing the tripe face boogie.

[Dave the bass]

That'd make 'em all sweaty so they'll need to get cleaned up..but.....guess what....there's already a fat man in the bathtub...

SWYDT there Ed , I hope you're happy with yerself now!

[pre65]

That'd make 'em all sweaty so they'll need to get cleaned up..but.....guess what....there's already a fat man in the bathtub...

SWYDT there Ed , I hope you're happy with yerself now!

[IslandPink]

Aaaarg ! - but in a good way

[IslandPink]

So, it's al been a bit quiet but actually activity continues in some form so better write a short summary :
Folded horn still giving me problems, lacking tone in vocals after more listening ( as I said to Nick 'time is NOT a great healer' when you're talking about speakers) . Not sure the Delta Pro 8A works well enough at low levels.
So, decided to get some perspective by going back to the OB-based lower midrange.
Last time I was working on this I was trying to get a bass & mid together in a 'Quasar' series crossover combo, with the Yuichi coming in at 700Hz.
There were two problems eventually on this :
(I) I had the 700Hz point with -6dB ( half voltage ) which is a mistake - should be -3dB.
(ii) the 700Hz low-pass interferes too much with the blending of the bass & mid which has a cross around 180Hz - spoils tone & timing
OK, so I'd had a brief go at using the Supravox 285GMF as a midrange, but with the -6dB @ 700Hz low-pass. Not great.
I went back a couple of weeks ago and changed the amp components to get a -3dB point at 700Hz ( this is a lot different - the half voltage point is now at 1200Hz ! ) . Much better ! Tone on male vocals is a lot more convincing, low level ambience better than the horn, and the Supravox gives quite a bit of bass below 100Hz even in the 'upper' position on the baffle.

Next step - add some bass ..
Brought down the IPL SW3 sub and tried to use this to blend in up to ~100 to 120Hz to interface to the Supravox.
This didn't work - too much group delay from sub operating over that range, sounded slow and unconvincing however I tried to adjust. So -rejected - and in fact a few days later I managed to agree a sale of this unit to a friend at work - yippee more space and some money !

Two things now ongoing :
On mids, still want to try the Faital 8FE200 as it looks amazing on paper. I ordered one and received a parcel from CPC today - containing a 6FE200A so will report back later on this . The 8" one, if good, could free up the Supravox again -....
So, bass option - I have decided ( since nobody else will do it ) to final try the slot-loaded OB bass as mentioned first by Nelson Pass then picked up recently by JC Morrison and Jeffrey Jackson. The Supravox just happens to have the same Fs and Qts as the Eminence 3015LF's JC used for the bass set-up at ETF with the big WE horns. So far so good.
I Emailed JC and he was very helpful, with a few detailed thoughts about the compression ratio vs. Qt and ways they'd reduced comb-filtering by wedging the slot, on the most recent builds.
So, I started on this, just made one piece of wood ( the one with the hole ) so far, but can progress a bit more tomorrow.
The idea is to use the Quasar OB more or less unchanged but fire the 12" driver downwards into a slot that comes out just above the ground at the front, or if that doesn't work, fire it sideways & have the slot vertically along one side o fthe OB. Then there will be an 8" driver higher up on the baffle for the mids, then the Yuichi and ribbon perched on top as before. This way I don't have to build another OB thing to do bass and put more bulky 'stuff' in the front of the sitting room.
The bass will have its separate amp. The bass set-up should be a couple of dB more efficient than the 285GMF on OB conventionally, plus it'll reach lower.

More soon ....

[steve s]

Sounds interesting Mark and not too far off what I have been doing but I'm calling the slots ports

I started around 5 years ago with a pair of 12's and a lowther it worked well and I had some nice comments about them... even Ed liked them

Since then my latest speakers have further extended the length of the ports
Think square tubes in front and behind the drivers
Set at around at around 1/2 the area of the driver
The BBC used a similar principal on the ls5/1 but I've modified it for ob as the sound needs some direction to improve cancellation effects
It's the best bass I've had... whilst I feel I am still retaining that open baffle life
Let's see how it sounds at Owston???
No guarantees it will sound like it does at home

[IslandPink]

Ah, good effort, good to see you're heading in a similar direction. Now, the Fs ( resonance ) of the driver should go down, but since you're increasing the velocity of the air on both sides of the driver you'll not get the gain of 2 dB or so that you get from the Pass/Heil approach where the front is slot-loaded but the back is open OB . At the end of the day it's how it sounds and you may have enough efficiency anyway - I wish I could get to Owston but will have to relay on a reports from Nick et Al ( eg. Ali ! ) .

Just a few links for those who are interested :
Nelson's very good article from a few years ago -
http://www.firstwatt.com/pdf/art_slob.pdf
JC Morrison's fine build for a big room at ETF 2016 - uses 8x Eminence Kappalite 3015LF :
http://vinylsavor.blogspot.co.uk/2016/1 ... art-5.html
Pic 9 shows a bit of detail from the back -
http://www.monoandstereo.com/2016/11/th ... urney.html
JJ's no-compromise new rig uses only one 16" driver , but knocks a hole through the wall so the back-wave has to go round the house to get back to the listening area ! :
http://hifiheroin.blogspot.co.uk/2017/0 ... ctric.html

ps. JC says he's preparing a posting for Labjc on this whole subject - should be good - will post link when it comes out.

[Ali Tait]

Thanks for the links Mark, will have a good read.

[IslandPink]

Slow progress been a bit of a struggle to do anything this week.
Anyway
1. Faital 8FE200 finally on its way yesterday after 6" unit was returned - expected tomorrow or Monday.
2. see below, slot/OB bass testbed with Supravox taking shape. Hoping to listen to something early next week. Off to my mother's now ...

[IslandPink]

Bit more detail work today, ready for assembly of the slot bit ( and perhaps some lash-up of OB ) tomorrow.
Just tested the Supravox for resonance in open air using the series resistor and voltmeter method. Came in at 54.5Hz. Maybe it would get closer to the datasheet value of 47Hz with more running-in ? - maybe not.