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10" mid bass horn |
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Deadbeat 
Old Croc 
Joined: 12 March 2008 Location: Singularity Status: Offline Points: 3167 |
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 Posted: 02 December 2008 at 6:31pm |
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I left the end of the bung flat so I can try screwing on various end caps. Is it really necessary to go as far as shaping it to fit the dustcap?
Path length correction. You can even try more concentric axial plugs. There are two main limiters to HF extension in something like this...the first is the obvious LPF effect of the front chamber, and the other is path length difference from various parts of the cone.
With luck, you could do a FK1 and get it to go high enough so you could mount your HF on the other side of the rear chamber and have a point source. What are your plans for what's going atop these?
It's good to see I'm not the only spreadsheet user (or should that be ludite?) I've had a look at CAD, but it's going to use a lot of time learning how to use it well. I would prefer to use that time cutting up wood, drawing arcs on pieces, taping rulers together and measuring angles etc. aFor now anyway. Nah, it shouldn't be 'luddite'. I used a calculator, now I use a spreadsheet - got one for lots of things (calculating tractrix, getting rough horn length and mouth sizes, etc). And if one knows their geometry everything falls into place. I'm actually learning CAD solely to use a CAM machine...sadly, some things require dead accuracy...
I've done some more plots today, I'll put them up when I've collated them. Nice plots. Yeah, I'd say check all room modes and possible internal cab stuff as well. You can never be too sure...
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Away on extended leave.
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Rico
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Joined: 21 February 2008 Status: Offline Points: 101 |
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Posted: 02 December 2008 at 7:59pm |
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This Horns looks amazing
Do you have some plans to share with us of this nice horns? |
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doober
Young Croc 
Joined: 03 January 2006 Location: Cornwall UK Status: Offline Points: 1118 |
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Posted: 02 December 2008 at 9:08pm |
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Yes, I really should consider CAD, it just looks like it could take a while considering the level I'd want to use it at, I'm not keen on anything simple like square boxes. It could end up being a very wise investment for the future though.
Deadbeat- I see the point about path lengths, however if I only take this section up to 500hz I'm looking at approx 70cm minimum wavelengths, the path differences would have to be quite big to have an effect. I expect the bends in the horn path to mess things up well before throat geometry. I'm planning a horn loaded 6" for the next band up. I need to make a bit more progress with the low mid first though to decide where the 6" needs to take over. After looking at the most recent plots (above), and doing some calculations based around the frequencies, I've managed to blame the largest peaks and dips on the ~1m thick stone/earth wall which was ~2m behind the measurement mic. The peaks are in different places than in the measurements I took indoors. I really need to try some plots in a wide open space. Rico- no plans exist really, I worked it out as I went along really. I do have dimensions of most pieces on various bits of paper, ply etc, but I'll probably change a few bits on the next one to make it a slightly easier build. Once I'm happy with it I'll happily pass on whatever plans I can come up with. |
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Deadbeat
Old Croc
Joined: 12 March 2008 Location: Singularity Status: Offline Points: 3167 |
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Posted: 02 December 2008 at 10:20pm |
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Completely forgot about the big u-bend when writing that, yes it will
 . The only way you could get past that is with a turbo-esque super-multi-cell. And that's nigh impossible!Disregard that. You know what this reminds me of...re-entrant compression drivers. If you're outdoors and want a no-hassle 2pi, go out to a field, place the speaker face up (dig a hole for it if you're keen) |
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Away on extended leave.
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doober
Young Croc
Joined: 03 January 2006 Location: Cornwall UK Status: Offline Points: 1118 |
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Posted: 03 December 2008 at 6:01pm |
Hmmm, next project perhaps
I tried another plot in slightly better conditions, but left the mic a bit high off the ground (oops), resulting in a loss higher up. 
Looks a lot smoother now. I'll try some measurements in a field when I sort out a decent inverter or quiet generator. In the meantime I'm confident it'll do what I want in terms of FR, it's time for some extensive listening tests next. I need to try a few tweaks here and there but I'd rather leave this until I've built another one so I can do a/b comparisons. The next one will be made from decent ply and hopefully will eventually be the full 10" 6" 1" box. It's nearly time to work out a starting point for the 6" section and see how I can package it all neatly. Kieran. |
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davey t
Young Croc
Joined: 11 March 2004 Location: Bristol UK Status: Offline Points: 1428 |
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Posted: 03 December 2008 at 10:41pm |
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looks amazing! I've been thinking through 10" or 12" low mid wbin-esqe design but you have put the effort in and taken it to the next level! definately beats bill fitz's tops.
How heavy did it turn out? those wood pieces seem pretty thick. Try taking a plot with the mic in line the horn mouth |
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Minirig portable soundsystem movement
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tommysb
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Joined: 24 April 2006 Location: Finland Status: Offline Points: 1036 |
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Posted: 04 December 2008 at 10:11am |
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Are those plots calibrated?
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doober
Young Croc
Joined: 03 January 2006 Location: Cornwall UK Status: Offline Points: 1118 |
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Posted: 04 December 2008 at 5:07pm |
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It weighs about 30kg at the moment. This will change when I use 15mm ply instead of 18mm chipboard for the outside, and 12mm ply instead of 12mm mdf for the initial horn. The rest will stay as is, 12mm ply. I will need some extra bracing on the side panels, there's a fair bit of resonance at high power levels. the box also needs to be 20cm taller to allow for the 6" mid horn above. I'm hoping it will be a one man lift when finished, so <50kg is the target, not bad for a 3 way fully horn loaded box.
The spl is calibrated, the input level is not. I'll do some more accurate plots when I try some different drivers. Could anyone remind me how to do a plot for 1w/1m at a greater distance, ie how to calculate input power to compensate for 6db spl loss per doubling of distance? |
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mobiele eenheid
Old Croc
Joined: 15 August 2004 Location: Netherlands Status: Offline Points: 1568 |
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Posted: 04 December 2008 at 5:34pm |
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100 W (28,28 V@8Ohm)/ 10 metre is common because it's closer to real life use. To calculate any distance you can take the 10*log of the input power. I.e. 10*log 1 = 0, 10*log 500 (W) = 27 (dB).
Best regards
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doober
Young Croc
Joined: 03 January 2006 Location: Cornwall UK Status: Offline Points: 1118 |
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Posted: 04 December 2008 at 8:55pm |
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Thanks mobiele eenheid, I really should have known that.
Next question- how do I accurately measure the power going in, do I use a sine wave at a frequency of known impedance? bandpass filtered pink noise? something else? This is all a bit more precise than my old favourite method of just having a good listen (although I'll do that as well of course.) |
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overdrive
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Joined: 13 July 2004 Location: Netherlands Status: Offline Points: 21 |
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Posted: 05 December 2008 at 11:56am |
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Nice build! What kind of driver are you using?
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doober
Young Croc
Joined: 03 January 2006 Location: Cornwall UK Status: Offline Points: 1118 |
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Posted: 05 December 2008 at 3:40pm |
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Driver is currently an old Zomax 10", I don't have any accurate t/s parameters for it, I happen to have a few of them so I thought i'd try it for now.
It's got a big magnet and the suspension feels quite tight, my attempts at measuring the t/s gave quite odd results. I plan to try Beyma 10g40 and 18sound 10mb600 at some point. |
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Deadbeat wrote: