Something stirs in the Undergrowth

Dedicated to those large boxes at one end of the room
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Ali Tait
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#2281 Re: Something stirs in the Undergrowth

Post by Ali Tait »

Bummer Mark, I’m sure a few choice words escaped..

Nice work, like the blu tak idea.
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IslandPink
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#2282 Re: Something stirs in the Undergrowth

Post by IslandPink »

Thanks.
Slow progress due to knackeredness from a walk on Friday, plus dental problems.
Here though, still-life with wires :
OB_Cross_wires.JPG
I decided on single-core copper about 18ga for the woofer, and a short length of TQ Blue for the Fostexes. I nicked the Z-bananas from the butchered TQ wire and soldered them onto the single-gauge, to fit into the Supravox connectors. Now I can wire-up the crossover ; I worked out a rough plan for that while in the bath on Sunday.
I'm just short of an idea for a neat clip ( with nail or screw ) that can clamp wires to the OB wood. I might be able to use a tack to go through the TQ Blue stuff through the middle - I think there's enough room between the two wire bundles to be safe ( need to double-check ) .
"Once you find out ... the Circumstances ; then you can go out"
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Ray P
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#2283 Re: Something stirs in the Undergrowth

Post by Ray P »

IslandPink wrote: Tue Feb 26, 2019 10:31 pm I'm just short of an idea for a neat clip ( with nail or screw ) that can clamp wires to the OB wood. I might be able to use a tack to go through the TQ Blue stuff through the middle - I think there's enough room between the two wire bundles to be safe ( need to double-check ) .
Self-adhesive velcro pads?
Sorry, I couldn't resist!
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Ali Tait
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#2284 Re: Something stirs in the Undergrowth

Post by Ali Tait »

Some of these Mark?



Will have a look, should have some here, I’ll put them through your letterbox. I don’t find the adhesive is the best, I scrape the foam off with a sharp knife and superglue them on.
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IslandPink
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#2285 Re: Something stirs in the Undergrowth

Post by IslandPink »

Thanks for the suggestions, chaps, and offer.
I have a desire to keep the wires a bit apart and parallel, mainly for aesthetic reasons , as they come out of the box that way, so I'm inclining towards this sort of thing, Just need to check the dimensions. I can get a pack of only 25 of these apparently !
dual_clip.png
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IslandPink
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#2286 Re: Something stirs in the Undergrowth

Post by IslandPink »

Managed to get some time today, so a couple of pics of significant progress.
First, crossover for left speaker has now been fully wired-up , picture here of it just before the connecters were wired-on and the box shut . This took more work than I expected, when removal of the enamel on the big choke wires was included, plus some pondering about the best layout and checking the polarity ( which was wrong in one case ) of the speaker wires.
OB_Cross_complete.JPG
With the cover on now ; the blue TQ wire has also been pinned into position on the baffle with three small tacks that go through the dead space between the wires. Just need a clip/clamp for the bass wires now.
OB_Left_done.JPG
I might get the two OB's running temporarily as a stereo pair tomorrow - but it's just be bass and Fostexes running open, no tweeters ( till I get the amp going ) . Should be worthwhile though.

In the meantime I have also got a first draft of the tweeter make-up pieces modelled on Pro-E by a friend at work. One or two tweaks to those on Monday and we can hopefully get them 3D-printed.
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IslandPink
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#2287 Re: Something stirs in the Undergrowth

Post by IslandPink »

Well, I did get the two speakers working yesterday, with just bass and FX120's operational ( no tweeters ) and it was quite disappointing. Every small gripe I had about the mono system was just amplified by playing in stereo. The midrange seemed to become really rough and lacking subtlety.
So today's intention to progress the second OB details and the tweeter amp just died a death.
At this point I'm trying not to get mad but to get even. Watch this space :roll:
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simon
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#2288 Re: Something stirs in the Undergrowth

Post by simon »

Probably not the issue, but I've found that some speakers that haven't been used for a while sound pretty underwhelming until they've "warmed up" again. And then I remember why I liked them when they open up again.
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#2289 Re: Something stirs in the Undergrowth

Post by steve s »

That's a fair point Simon...
The tube manual is quite like a telephone book. The number of it perfect. It is useful to make it possible to speak with a girl. But we can't see her beautiful face from the telephone number
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IslandPink
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#2290 Re: Something stirs in the Undergrowth

Post by IslandPink »

There's a bit of running-in to be done on two of the FX120's and the cap in the crossover.
One thing that isn't helpful is that the two FX120's on each side are now running un-filtered a bit higher than they were with the mono set-up. On that there's a low-pass filter around 5 or 6kHz , 1st-order. Doesn't sound like much but I suppose the pair of FR drivers are probably interacting more ( lobing etc ) at the HF than they were on the previous set-up.
The plan continues with this, anyway - get the crossover boxed up and neat on the R speaker, finish off the tweeter amp, etc.
However there was always a plan to try the ribbon crossover a little lower , that seems wise now based on the current troubles.
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chris661
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#2291 Re: Something stirs in the Undergrowth

Post by chris661 »

What happens if you disconnect one of the FX120s?
Just wondering if cancellations are the issue.

Chris
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IslandPink
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#2292 Re: Something stirs in the Undergrowth

Post by IslandPink »

It gets messy, because they are in series ( partly to replicate what James had with the 16 ohm AER's ) and the cap size in the series crossover is smaller as a result, so the crossover wouldn't work right - or you'd have to add an 8R resistor in place of the missing speaker - which might actually be OK ... hmm. but mindful of the work Steve C was doing, not sure. The upper mids and treble should be OK on that though, except they'd be 3dB lower relative to the bass... hmm...
I do have experience of a single FX120 running on a sealed 30L box, and that sounded a lot nicer - so I do think it's got something to do with HF lobing/cancellations.
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#2293 Re: Something stirs in the Undergrowth

Post by Max N »

How far away are you from the speakers at the listening position?
I use MTMs and I have to be a fair distance from them before they sound really good. Also ear height is fairly critical (but gets less critical as distance increases). If the baffle is inclined, you need to take that into account - your ears need to be on-axis if that makes sense so each driver is equidistant.
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#2294 Re: Something stirs in the Undergrowth

Post by chris661 »

IslandPink wrote: Mon Mar 04, 2019 6:11 pm It gets messy, because they are in series ( partly to replicate what James had with the 16 ohm AER's ) and the cap size in the series crossover is smaller as a result, so the crossover wouldn't work right
Hi Mark,

Worth a quick read here: http://sound.whsites.net/parallel-series.htm#s12
Series crossovers don't mind about impedance variations so much - the slopes will change in frequency and Q, but will always sum flat.

Chris
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IslandPink
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#2295 Re: Something stirs in the Undergrowth

Post by IslandPink »

Max N wrote: Tue Mar 05, 2019 12:22 am How far away are you from the speakers at the listening position?
I use MTMs and I have to be a fair distance from them before they sound really good. Also ear height is fairly critical (but gets less critical as distance increases). If the baffle is inclined, you need to take that into account - your ears need to be on-axis if that makes sense so each driver is equidistant.
Hi Max
Thanks for the info. I suppose most MTM's cross over by 3kHz or so. Eg. the Ariels !
I sit about 3m from the OBs.
The baffle inclination is only slight ( 5°) as per James's design. I think this helps get the acoustic centres ( before crossover ) of the 285GMF and the AER about equidistant to the listener. As far as the distances of the two FX120's to the listener, this slant should be more or less lost in the noise till past 5kHz. However something is going on, I did notice some degradation of the sound in going from one FX120 to two, on the mono version ( with low-pass crossover on the mids ).
I think it will get better again once I get the tweeters in and the low-pass on the Fostexes. I have already heard what one Fostex sounds like ( many times ) and that is nice.
Having only one FX120 on there is not a long-term solution, I need more than 89dB/w
The other option is to look at some of the newer FR 8" again -eg. the Cube Audio. Bit pricey, but could stretch to that .

However the long-term plan is to find a way to use horns, I have more ideas in the pipeline.
"Once you find out ... the Circumstances ; then you can go out"
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