I was looking at ways to model in AkAbak, a Karlson-like slot to reduce resonance peaks and dips by strategically placed Q-spoiler holes. IG81 suggested placing them at the 7/4-mode and 9/4-mode anti-nodes as described in this post:
http://www.diyaudio.com/forums/full-range/213594-karlson-8.html#post3518876
I modeled a 224 cm long TL with 3.5 in x 2.5 in CSA, driven at the end witha Fostex FF85WK. The TL starts at the top, goes down and has single fold at the halfway point so that the terminus exits straight up.
The holes were placed at the following locations:
7/4-mode: 32 cm, 96 cm, 160 cm
9/4-mode: 24.9 cm, 74.7 cm, 124.5 cm, and 174.2 cm
The hole diameters were determined by trial and error while trying to flatten the freq response (increase hole dia) while keeping bass extension low as possible (keep holes small as possible). I am sure better optimizations can be done - this was done rather quickly and manually.
The hole diameters ended up as:
7/4-mode: 0.25 in, 0.35 in, 0.60 in
9/4-mode: 0.0625 in, 0.40 in, 0.50 in, 0.50 in
The following plots show the base TL case with no holes, all 7/4-wave holes open, all 7/4-wave and 9/4-wave holes open.
As you can see, as expected, the addition of the holes drastically reduces the bass extension which was 37 Hz and ended up at about 77 Hz. However, the amplitude of the bass increased dramatically and the flatness of the bass frequency response was significantly improved. There are still some dips and peaks but I think with a little stuffing, this TL may actually work quite well. The FF85WK really is not a driver meant to operate anywhere near 37 Hz and 77 Hz is closer to its ideal limit I think and it shows.
Also included are the cone excursion and impedance for the case with all holes open.
The resulting TL, if it were built would resemble a large flute-like pipe with oddly sized holes.
http://www.diyaudio.com/forums/full-range/213594-karlson-8.html#post3518876
I modeled a 224 cm long TL with 3.5 in x 2.5 in CSA, driven at the end witha Fostex FF85WK. The TL starts at the top, goes down and has single fold at the halfway point so that the terminus exits straight up.
The holes were placed at the following locations:
7/4-mode: 32 cm, 96 cm, 160 cm
9/4-mode: 24.9 cm, 74.7 cm, 124.5 cm, and 174.2 cm
The hole diameters were determined by trial and error while trying to flatten the freq response (increase hole dia) while keeping bass extension low as possible (keep holes small as possible). I am sure better optimizations can be done - this was done rather quickly and manually.
The hole diameters ended up as:
7/4-mode: 0.25 in, 0.35 in, 0.60 in
9/4-mode: 0.0625 in, 0.40 in, 0.50 in, 0.50 in
The following plots show the base TL case with no holes, all 7/4-wave holes open, all 7/4-wave and 9/4-wave holes open.
As you can see, as expected, the addition of the holes drastically reduces the bass extension which was 37 Hz and ended up at about 77 Hz. However, the amplitude of the bass increased dramatically and the flatness of the bass frequency response was significantly improved. There are still some dips and peaks but I think with a little stuffing, this TL may actually work quite well. The FF85WK really is not a driver meant to operate anywhere near 37 Hz and 77 Hz is closer to its ideal limit I think and it shows.
Also included are the cone excursion and impedance for the case with all holes open.
The resulting TL, if it were built would resemble a large flute-like pipe with oddly sized holes.
Attachments
Last edited:
Interesting how it smoothed out the lower bass response, this was somewhat expected though. ~70Hz is about as low as the FF85WK plays decently in the little BLH I have them in. It was similar in the 224cm foamcore pipe. Power handling is probably not too high there though.
The peaking above ~200Hz might still be prominent as it was in my physical build, but stuffing might kill it just good.
IG
The peaking above ~200Hz might still be prominent as it was in my physical build, but stuffing might kill it just good.
IG
interesting - thanks for the work - would it somewhat resemble Sapkowski's patent? (which like the later Bose patent gives no credit to Karlson)
An externally hosted image should be here but it was not working when we last tested it.
Freddi,
Similar but mine has distinct holes based on modes rather than holes to look like a K slot. Patents will only reference prior art that they feel is different but if the same they won't reference it as it means they have nothing novel. So or is not surprising when someone takes credit they fail to reference Karlson's work.
Similar but mine has distinct holes based on modes rather than holes to look like a K slot. Patents will only reference prior art that they feel is different but if the same they won't reference it as it means they have nothing novel. So or is not surprising when someone takes credit they fail to reference Karlson's work.
Karlson in his original Acoustic Transducers and Fulmer both talk about use of holes. It could be just a few of varying size but don't think there was mention of spacing. A test enclosure with a removable panel for the holes would be interesting. I don't have any drivers under 8" which are worthwhile.
I didn't keep the FC pipe for very long, just measured and listened a bit. It had enough promise that building a wood version could be fun and I may yet do it, really can't say when though.
IG
Goes to show how good mass loading is.
Related question to the 'holes', and perhaps onken style enclosure etc. So given the same apparent terminus area, the higher the aspect ratio of the vent and/or the number of high aspects vents totalling the same terminus area, generally the 'better' the results ?
I use better very ambiguously here, but generally it does good things no?
Related question to the 'holes', and perhaps onken style enclosure etc. So given the same apparent terminus area, the higher the aspect ratio of the vent and/or the number of high aspects vents totalling the same terminus area, generally the 'better' the results ?
I use better very ambiguously here, but generally it does good things no?
I agree that mass loading does wonders. I don't think these tuning holes are anything like Onken style channels which have added viscous drag induced damping that may or may not improve the sound depending on the driver and box it is in. I think the main concept that I see here with tuning holes is the fact that it can be used as a last resort to fix a nasty peak or dip in an existing enclosure without resorting to willy nilly 'drill and try' approach.
Hmmmmm... Ocarina speaker! Now that is something that sounds interestingMaybe a shakuhachi speaker?
a loudspeaker that John Neptune would love
to be authentic, wouldn't that need to be make from bamboo culms? - you'd be restricted to approx 7" OD, length is not a problem (Moso can reach 65ft), but precision boring could be an issue as well
Freddi: the Fulmer patent is very interesting, and quite clearly written
Yeah, remember I simmed it as best I could using MJK's original software and it looked so good in 2pi with Altec 421-8H MI drivers, I've kept a NIB pair all these years to hopefully one day corner load a pair.
Have you still got the build article? Scaled down, it might make a good FC project.
GM
(I've got 421 too - hope they haven't sagged from storage) hey GM - this is all that's on the net - I'd love to see your sim as my old kluge with AJhorn may have been wrong (?)
http://img455.imageshack.us/img455/8639/ful11oy.jpg
http://img455.imageshack.us/img455/2694/ful20tm.jpg
http://img455.imageshack.us/img455/5733/ful37mu.jpg
http://img451.imageshack.us/img451/8349/fuld3px.jpg
http://img239.imageshack.us/img239/3074/fulstra1uh3.jpg
http://img455.imageshack.us/img455/8639/ful11oy.jpg
http://img455.imageshack.us/img455/2694/ful20tm.jpg
http://img455.imageshack.us/img455/5733/ful37mu.jpg
http://img451.imageshack.us/img451/8349/fuld3px.jpg
http://img239.imageshack.us/img239/3074/fulstra1uh3.jpg
Me too, but I 'lost' all the info in what was literally a computer meltdown last year that damaged my backup HD in the process, so I'll have to reconstruct it all again.
Thanks for the article re-post, I had 'lost' it too. Since not all its partitions were damaged, I'm hoping that the rest just have access issues and can be found/copied with a bit of probing by someone 'practiced in the art'.
Anyway, IIRC it had a nice round response rolling off below ~40 Hz down to the 421's ~32 Hz Fs, so in a corner shouldn't need any BSC plus sufficient low distortion power handling down low for all but some movie LFE or large pipe organ symphonies.
Mine sag quite a bit, so store them face down and have to set them out face up in July/August noonday sun to compensate. I have to periodically do this with the 515s also to absorb dust, etc., into the surround's goop while it's redistributing/flowing back out.
GM
Thanks for the article re-post, I had 'lost' it too. Since not all its partitions were damaged, I'm hoping that the rest just have access issues and can be found/copied with a bit of probing by someone 'practiced in the art'.
Anyway, IIRC it had a nice round response rolling off below ~40 Hz down to the 421's ~32 Hz Fs, so in a corner shouldn't need any BSC plus sufficient low distortion power handling down low for all but some movie LFE or large pipe organ symphonies.
Mine sag quite a bit, so store them face down and have to set them out face up in July/August noonday sun to compensate. I have to periodically do this with the 515s also to absorb dust, etc., into the surround's goop while it's redistributing/flowing back out.
GM
- Status
- This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.