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Post by karatestu on Feb 21, 2022 9:36:24 GMT
Can you heat the thing up like powdercoat requires? Plastic fitting etc will melt As good a finish is achievable with primer, filler, filler primer, top spray. I hate powdercoat on anything steel / aluminium that will be left outside. Why do they insist on using it, must be cost.. useless stuff. Black permanent marker like Shapie etc usually comes blue'ish. Might be some that better. A light dusting of spray paint😱 Brush on paint would be too heavy I would think. Thanks for your advice Steve. I have thoroughly gone off the powder coat idea now. There would be no plastic parts, just mild steel if I made the tweeter sphere out of steel as well. Spraying looks like it will be the best option then. I have just tried a black marker on an old Qtx yellow kevlar cone (£15 cheap Chinese crap) and it has done an acceptable job so far. It's not on full display anyway with it being up firing and obscured by the tweeter sphere directly above it. I don't really know why I am worrying about adding weight as I have already got a worm of blutack pushed in at the junction of the cone and dustcap. It sorted any break up nasties right out and upped the Q a bit for better sealed box use. I have in the past doped drivers the Richard Dunn way with lashings of contact adhesive and black plastidip spray. It resulted in a very smooth sound but I later realised it sucked up a lot of the life in the music. The blutack has worked much better and hasn't taken the life and dynamics away probably because there is only a small amount of the cone and dustcap which is actually in contact with the blutack. Anyway, the blutack will be replaced with blacktack in due course.
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Post by karatestu on Feb 21, 2022 10:05:03 GMT
Sharpies are available in metallic silver so i may try one of them so it will be similar to the cone of the 2" tweeter.
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Post by karatestu on Feb 21, 2022 10:16:56 GMT
Quote from diyaudio by an ex designer at KEF ( he wrote the white paper I quoted a page or three back
"KEF was possibly the first to introduce de-coupled drivers, with the R105.
The idea has been used by many people many times.
De-coupling is only effective at frequencies above the resonant frequency of the suspension, but can still work extremely well.
I have used it both for my KEF designs and for Pioneer and TAD.
The best solution is the dual driver bipolar type, as the reaction force should be fully cancelled at all frequencies, as long as the drivers are well matched and identically loaded. But if you roll one of them off at a lower frequency than the other (as you might be tempted to do in a bipolar design), then the attendant phase shifts will negate some of the force cancellation
The reaction force is typically 10-30 times stronger than the force generated by internal air pressure at the frequencies of the cabinet resonances, and with appropriate choice of de-coupling you can readily reduce cabinet resonances by 20db or more.
I have many times demonstrated the effect of de-coupling upon the sound quality, taking a pair of speakers matched to better than 0.5dB and then de-coupling just one of the pair. The improvements are not subtle.!"
I have tried dual driver bipolar with opposing drivers and it did reduce cabinet vibration a lot but I find this isolation I have now to be better. I can't have done the opposing driver thing well enough - maybe the magnets weren't connected together hard enough. It did sound absolutely awesome with both drivers (up and down firing) run wide open and the speakers in the middle of the room. It gives the full 6dB baffle step compensation which is too much in a small room against the wall. It would have been good for outdoor use or a large room but mine is small and the speakers have to be close to the wall. A shame really. I got away with it with most music but put anything on with a lot of bass (electronic, dub, some funk and jazz) then the bass swamped everything. I would do it again if I had a large room. Sadly that will never happen as I am very happy at my current abode and will probably not be leaving except in a box.
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Post by karatestu on Mar 12, 2022 7:26:54 GMT
The last few weeks brought a few speaker problems. How can you not notice a hump in the frequency response with most music and then you play a track of album that clearly sounds wrong. For me that happened with a couple of electric jazz tracks with flute on. One of the high notes played by the flute made me wince and want to cover my ears. Playing this track on other systems revealed that the flute is indeed "hot" but not to the hands over ears extent.
I initially thought it was a resonance from my tweeter sphere being to close to the up firing mid bass. So I jacked it up a bit. That helped but I still wasn't happy. It then dawned on me that since isolating the speaker from the floor and both drivers from their enclosure that I had a hump in the FR in the xover region. It seems that isolating the drivers has unmasked the higher output of the mid bass. I changed my passive line level 1st order high pass from 7KHz in small steps and ended up at 10KHz. I can't believe I am having to cross so high now but the issue is now resolved.
PTO.....
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Post by karatestu on Mar 12, 2022 7:49:12 GMT
I bought a couple of 20cm gooseneck mic holders to use to attach my tweeter sphere to the mid bass sphere. Whilst I temporarily hot glued them in place to test I thought I would try my 2" cone full rangers that I use for tweeters in dipole mode ie no enclosure. The main reason I ended up with a sphere above the up firing mid bass was so I could get the tweeter above the mid bass' cone. It just doesn't sound right when it is too far forward - phase and timing thing. When it is above the mid bass cone the music just locks in to place even with the phase shift of the high pass capacitor and the fact the mid bass is run wide open. I could live without the tweeter sphere as I don't need the dispersion or the crappy horn it creates. I tried a dome tweeter naked right above the mid bass's voice coil crossed at 10KHz. There was much to like about it but done tweeters just can't cut it with a 1st order high pass even as high as 10k. There is a kind of tinny sound I can't deal with anymore after hearing a small cone as a tweeter. I suspect the tinny sound is due to the back wave bouncing off the pole piece even though there is a felt pad in there. So I eventually got to mounting my 2" cone on the gooseneck holder right above the mid bass' voice coil. No enclosure, it's naked man. It looks like shite but I love the way it sounds. I wish I didn't as now I have a job on making it look acceptable. The music is so at ease and the old cliche of there being a sense of air is evident. It is lovely. At least I don't have to worry so much about cancellation at these high frequencies.
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Post by speedysteve on Mar 12, 2022 8:10:52 GMT
Sort of snake charming vibe🙂 Like it
If you have a measuring mic and free software like Holmimpulse, you can accurately time align. Very worthwhile.
You can do an approx by ear though, as you have found. Just sorta sounds right and snaps in.
The high frequencies of tweeters mean only small amounts of movement (millimeters) are needed.
Deep bass needs metres and metres so not practical physically. You don't have that problem though.
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Post by petea on Mar 12, 2022 8:51:13 GMT
Interesting observations / solutions. I think I prefer the aesthetics of this over the 2 spheres.
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Post by karatestu on Mar 12, 2022 11:48:07 GMT
Sort of snake charming vibe🙂 Like it If you have a measuring mic and free software like Holmimpulse, you can accurately time align. Very worthwhile. You can do an approx by ear though, as you have found. Just sorta sounds right and snaps in. The high frequencies of tweeters mean only small amounts of movement (millimeters) are needed. Deep bass needs metres and metres so not practical physically. You don't have that problem though. Thanks for your thoughts Steve. I don't do measurements, never have. I do appreciate the help they would give me but I haven't the inclination to put the effort in to learning how to do it accurately. Ears and a wide selection of music will have to do. Yes, the sound just falls into place when you get it right. These dipole tweeters really are the icing on the cake, well my ears tell me they are.
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Post by karatestu on Mar 12, 2022 11:52:26 GMT
Interesting observations / solutions. I think I prefer the aesthetics of this over the 2 spheres. Thanks for your input Petea. I don't know what I am going to do to make it more visually appealing. I don't like the look of the gooseneck but Speedysteve does. I have my thinking cap on. I just love this dipole tweeter and what it does for the music so I will be moving heaven and earth to make it work.
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Post by MartinT on Mar 12, 2022 11:55:58 GMT
Once you've used the gooseneck to get the final position, you could use a pipe bender on a nice piece of chrome tube to make the final version?
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Post by speedysteve on Mar 12, 2022 12:06:12 GMT
Interesting observations / solutions. I think I prefer the aesthetics of this over the 2 spheres. Thanks for your input Petea. I don't know what I am going to do to make it more visually appealing. I don't like the look of the gooseneck but Speedysteve does. I have my thinking cap on. I just love this dipole tweeter and what it does for the music so I will be moving heaven and earth to make it work. 😂 Wide open Cobra head about to strike, jaws gaping or real smaller shark jaws framing... Gotta make an impact but not affect the sound.
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Post by karatestu on Nov 26, 2022 7:08:56 GMT
Latest experiment here ix with the SB acoustics SBA65WBAC25-4 in a tapering tube with open end and stuffed with fibre glass (more densely with distance from thd back of the driver). Looks like this.... Another wonderful bodge with an old plastic kids chair leg and some gaffa tape. Looks like shit but...........
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Post by petea on Nov 26, 2022 10:33:10 GMT
Interesting. And I like the counter-weights!
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Post by karatestu on Nov 26, 2022 18:13:41 GMT
Interesting. And I like the counter-weights! Well spotted A hole saw on string
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Post by karatestu on Nov 26, 2022 18:32:13 GMT
I discovered that I preferred the outcome with as little as possible above the up firing mid bass. I also fell out with the SB acoustics SBA65WBAC25-4 in dipole mode. Something was not quite to my liking. So I reverted back to using a visaton closed back dome tweeter above the centre of the MB. I liked that but had to put a padding resistor in circuit. But i was missing something that the SB acoustics SBA65WBAC25-4 provided. So to enable as little above the mb as possible I decided to use the tapering chair leg as enclosure and progressively stuff it with fibre glass. The end is open. The 2" cone tweeter is above the centre of the up firing mb. It is probably too early to say but I think this is my favourite lash up yet. The SB acoustics SBA65WBAC25-4 imo wipes the floor with the dome tweeter in every way. No padding resistor needed either so nothing between amps and both mid bass and tweeter but wire. The 2" cone has a large dome in the centre which has good dispersion like a small dome tweeter and the surrounding cone acts as a small wave guide i guess. There is more detail, vibrancy and atmosphere as well as better imaging and soundstage. I never thought that i appreciated imaging and soundstage that much. But it turns out I actually do. The icing on the cake for me. I never imagined semi omni could image this well. Wait til next weeks installment when I will have probably fallen out with it and tried something else
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