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Post by karatestu on Jan 16, 2021 6:53:44 GMT
Some developments in speaker land since I last visited here.
The isobaric 12" bass idea was knocked on the head a while back as even isobaric loading and an aperiodic vent couldn't get the box down to an acceptable size. They are now reserved for another project and will stay at the family farm where I work rather than home. Might try open baffle with them as they have a fairly high qts.
So, I fell back to the safety of two doped 5.25" mid bass run full range in a bipole up and down firing configuration. I really liked this even without the oomph of the 12 inchers. Baffle step correction is taken care of for free and even then I could site the speakers almost touching the wall with no boom and a very healthy bass output. I could happily end the journey there, very happy.
The urge to experiment returned though so I bought four more 5,25 " mid bass, doped them and added them in. This was not as good but was fun to try. I decided to buy four 6.5" mid bass and use them in a bipolar up and down firing configuration. Doped of course and run full range. Bingo - this is it. Exactly the right amount of displacement. Loving it. Can't get these right back to the wall like the version with 5.25" version but not far off. Has all the benefits of the smaller version plus increased sensitivity, lower inter modulation distortion blah blah.
Tweeters - still using four (front, up, in & out firing) but I put them in their own little 12 cm cube which is mounted above the top baffle. This had to go behind the uo firing mid bass and this along with getting the tweeters as close together as possible was a revelation.
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Post by MartinT on Jan 16, 2021 11:52:05 GMT
We're going to need photos! The firing up and down, is this an arrangement like the KEF Reference 104/2?
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Post by karatestu on Jan 16, 2021 14:20:28 GMT
Hi Martin, Speakers are still in prototype stage and built out of scraps of chipboard and fence post This is top of speaker showing up firing 6.5" mid bass and a separate tweeter "cube" on top. Thus is the underside showing down firing mid bass What it looks like from distance. This is when the drivers were the smaller 5.25 " version I want the finished article to look a bit like this but a rounded cube shape without drawers of course See here
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Post by MartinT on Jan 16, 2021 14:51:37 GMT
Ok, are they firing in opposition, i.e. compressing and expanding the air inside?
Have you thought about mounting the lower driver upside down (and reversing the connections) to nullify distortions between the two?
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Post by karatestu on Jan 16, 2021 15:20:38 GMT
Ok, are they firing in opposition, i.e. compressing and expanding the air inside? Have you thought about mounting the lower driver upside down (and reversing the connections) to nullify distortions between the two? Yes they are wired in phase for bipole operation - baffle step compensation and much reduced cabinet vibrations for free I have tried one of them with magnet out and wiring reversed before. (in a slightly different cab) I did read it reduced 2nd order harmonic distortion. But it is also said that there is all sorts of diffraction nasties from the basket and magnet if mid range frequencies are being produced from it like in my case. I have tried it both ways and not sure which I prefer. There was certainly less of the mid range audible with the magnet out version - no dustcap area on that side. I might try it again just to be sure.
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Post by karatestu on Nov 5, 2021 16:11:15 GMT
This speaker saga has had many twists and turns since I last posted on this thread. I got fed up with trying things that didn't work or things I couldn't get to work. A lot of it sounded like absolute crap but I learned a few things on the way like there is a good reason why nobody produces things like the your latest great idea My speaker thread on HFS is now on page 173 and most people don't even look at it cos they got bored and it's boring. Anyway, it turns out multiple drivers playing the same frequencies doesn't work MOST of the time. The one thing that I was quite happy with is the bipole up and down firing mid bass. But you need the speakers in a big room and well away from walls as you get the full 6dB baffle step compensation with that set up. I had to drop the idea in the end as it was really good on normal music but I love some music that has really heavy bass lines and it was a bit too much to handle. The multiple tweeter set up in a sphere with them pointing in different directions was entertaining while it lasted. With a first order high pass even up as high as 6kHzit just doesn't do the business. Thats why I sat jaw on the floor when I added more tweeters - the distortion disappeared as they had much less work to do especially when I had four tweeters per channel. I got rid of one kind of distortion and replaced it with another The effect of this treble bouncing around off all the boundaries was mesmerising with some music but others were just too confused and busy. I was getting fed up with 1st order high pass filters and small dome tweeters. I didn't realise there were other options. I bought a very small SB acoustics 2" cone full range driver for another project. I decided to give it a try with my diy set up. It absolutely smoked the single and multiple tweeters with a 1st order high pass. They are amazing these little things. Aluminum 2" cone with a plastic dust cap - goes all the way up, has good dispersion and can take low frequencies without throwing a fit like tweeters do. I just had to make a suitable enclosure. I am obsessed with spherical enclosures now because once having heard my four tweeters in one I was gobsmacked by the improved ease of the music and the increased imaging. It was amazing. So I decided to put this 2" full range cone in a sphere too. 15cm diameter is enough volume for this tiny cone driver. I have it crossed over to the mid bass at 7kHz with a passive 1st order line level high pass (polystyrene capacitor using the resistor to ground already in the power amp) where the mid bass rolls off acoustically - no filter on the mid bass and it is still pointing upwards. Things then progressed further when I ditched the cheap Chinese drivers I had been doping and used a good quality B&W mid bass driver from some other speakers I used to use. I tried it no doping and there was some break up that made it unlistenable. I didn't want to go back to doping drivers if I could avoid it so added a small worm of blutack at the junction of the cone and the dust cap. That has sorted it right out plus it lowered the sensitivity a bit to match the small 2" tweeter better. It raised the qts which made it more suitable for closed box bass and lowered the resonant frequency (Fs). It's been a winner winner chicken dinner all round. Those cheap chinese drivers really are crap. Doping really smooths them out but you lose too much dynamics and vibrancy. The blu tack on the B&W 6.5" driver gives the best of both worlds really. It has tamed any nasties in the break up region but has kept the dynamics and vibrancy. The blu tack is only damping the very edge of the cone and dust cap rather than with doping where the dust cap is totally covered with contact adhesive.
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Post by MikeMusic on Nov 5, 2021 16:22:38 GMT
Braver than I am by a long way Don't feel confident or competent enough to do any of that. Have you looked at John saga on his speakers ?
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Post by karatestu on Nov 5, 2021 16:27:51 GMT
But that's not the end of it. With my new found love for all things spherical I had to find or make a suitably sized enclosure for the up firing mid bass. I ended up buying some mild steel hemispheres 30 cm diameter and 3mm wall thickness. A sphere is the strongest shape in natural world. By it's very shape, steel being super stiff and being 3mm thick this enclosure is not going to flex with internal bass pressure. When they are clamped to a circular ring of plywood sandwiched in between they don't ring one bit. A great big whack and there's nothing, just a very short noise on impact. I'm well impressed with them although I haven't got round to putting the mid bass in the spheres yet. I have cut the holes for the drivers though and done a little mock up of roughly what it is going to look like. I have made a temporary base and single leg just for the photo but the final build will be similar just with different materials. The tweeter sphere is a prototype at the moment. I will be doing them again properly with a rounded over baltic ply baffle for the tweeter to be rebated into. The mid bass is getting a similar baltic ply mounting ring that will enable rebating for the driver plus a round over to blend it in to the lovely spherical shape. We don't want to go to all this trouble and then have any nasty sharp edges to re radiate as the wave diffracts. Imaging must be the best it can be. Anyway here is the staged pics of what it will loosely look like. that mid bass is the old doped one not the B&W ones I am now using Oh forgot to mention the tweeter sphere is right above the up firing mid bass and acts as a diffuser. See below Anyway, what y'all think ? Any good, does it look ok as a general idea ? I can take criticism. Honest
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Post by MikeMusic on Nov 5, 2021 16:36:41 GMT
The ears have to be the judge. The manufacturing is way above my little head
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Post by karatestu on Nov 5, 2021 17:22:02 GMT
The ears have to be the judge. The manufacturing is way above my little head I have proved the concept works very well for my room and ears with cubic steel lined wooden mid bass enclosure with the little tweeter sphere supported above it. However I have not had the up firing mid bass in a sphere yet. It won't be long til I find out. I will have to be careful with breaking up the inside dimensions a bit and put the right amount of fibre glass inside. But I fully expect it to sound awesome After these are finished I'm through with messing about with speakers (for a while). Modern speakers tend to be aimed at the wife friendly market with over complicated xover's that suck the life out and sit on the music whilst being sold with a healthy dose of marketing bullshit combined with bling willy waving credentials. Not for me.
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Post by MartinT on Nov 5, 2021 19:53:43 GMT
Very innovative ideas, actually. I dare say a lot of speaker manufacturers have all manner of 'mule' designs for listening to their experiments. Where did you find those steel hemispheres? They look ideal. If you ever find larger ones I can envisage a pair of subwoofers in development.
Anyway, please don't stop, reading about your trials is interesting and I enjoy following where you've got to.
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Post by karatestu on Nov 5, 2021 20:16:36 GMT
Very innovative ideas, actually. I dare say a lot of speaker manufacturers have all manner of 'mule' designs for listening to their experiments. Where did you find those steel hemispheres? They look ideal. If you ever find larger ones I can envisage a pair of subwoofers in development. Anyway, please don't stop, reading about your trials is interesting and I enjoy following where you've got to. Thanks for the comments Martin. It's taken a lot of work and pain to get this far. I have tried all manner of things most of which were complicated and involved multiple drivers. I ended up doing a full circle and finishing up where I started off. But with a few things added that I learned along the way. Bigger steel hemispheres do exist - especially on alliexpress. They are what people make fire pits out of. As you get bigger the wall thickness increases. I am much happier working with metal than wood. Melting things together is much easier It is hard to find bigger spheres than 30cm in this country at the moment what with everything going on and the import charges may be prohibiting. As soon as I find some I will be buying some. I quite fancy a 8" or 10" down firing bass drivers with an up firing mid and little 2" cone tweeter in a sphere above the mid. The people over at hfs seem to be getting bored of me so I may be spending more time here. Until you get bored of me too.
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Post by karatestu on Nov 5, 2021 20:21:52 GMT
Oh forgot to say I got the hemispheres at fhbrundle.co.uk.
There are bigger ones available but the next size they have is 50cm. Maybe I should buy some.50cm sphere with 5mm walls is 61.6 Litres. Should be able to fit a 12" in there.
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