All my fault, really. I prefer the good old Imperial system, and that's what I used when sketching out the initial designs for the Harvey's; & why poor Dave has a heck of a time of it, rounding to the nearest sensible metric equivalent.
I was never able to lucidly explain why I disliked metric so much, until dear old LJK Setright, shortly before he died last year, expressed it with an eloquence I will never reach:
'A plague upon the decimal system, upon the Napoleonic French who encouraged or even enforced it, and upon the scientific establishment which is so unimaginably unimaginative as to be content with it! It is a system with few virtues and numerous vices, one of which is to tempt people to speak in decades when they should be speaking in round numbers.'
I couldn't agree more. Metric has this pitfall, for me at least, so I stick with what I like best. Odd, because I am of the generation that grew up after the change over to metric from Imperial, and I was never taught the old system at school. Oh well.
I was never able to lucidly explain why I disliked metric so much, until dear old LJK Setright, shortly before he died last year, expressed it with an eloquence I will never reach:
'A plague upon the decimal system, upon the Napoleonic French who encouraged or even enforced it, and upon the scientific establishment which is so unimaginably unimaginative as to be content with it! It is a system with few virtues and numerous vices, one of which is to tempt people to speak in decades when they should be speaking in round numbers.'
I couldn't agree more. Metric has this pitfall, for me at least, so I stick with what I like best. Odd, because I am of the generation that grew up after the change over to metric from Imperial, and I was never taught the old system at school. Oh well.
Modeling Bruce
OK, so I've laid out the $$ to MJK (Thanks Martin!) and am playing away...
I'm trying to sim Bruce. (I think this is Bruce?) I get something similar to Dave's plots for the Fostex 206, but I get the following for the system time response:
This is with 0.75 lb/ft^2 stuffing. With no stuffing I get about a 500 Hz ringing.
Is this what I should expect? I tried simming Martin's horn papers but I don't get the same results for the impulse.
OK, so I've laid out the $$ to MJK (Thanks Martin!) and am playing away...
I'm trying to sim Bruce. (I think this is Bruce?) I get something similar to Dave's plots for the Fostex 206, but I get the following for the system time response:
An externally hosted image should be here but it was not working when we last tested it.
This is with 0.75 lb/ft^2 stuffing. With no stuffing I get about a 500 Hz ringing.
Is this what I should expect? I tried simming Martin's horn papers but I don't get the same results for the impulse.
Well Scott, as to the merits of metric vs imperial measurements, once you add the human element, ANY system is subject to error and misinterpretation.
Personally, it was immersion in a commerical manufacturing environment including 2 major CNC machines of European origin that prompted my conversion. Why the owner couldn't find a beam-saw and P-t-P router of 'merican source is beyond me, but there you go.
While I'm not as fluently bilingual as my kids immediatley after attending French immersion K - 7, it's still not too difficult to convert from one to the other.
Personally, it was immersion in a commerical manufacturing environment including 2 major CNC machines of European origin that prompted my conversion. Why the owner couldn't find a beam-saw and P-t-P router of 'merican source is beyond me, but there you go.
While I'm not as fluently bilingual as my kids immediatley after attending French immersion K - 7, it's still not too difficult to convert from one to the other.
planet10 said:
well actually, 1/16" = .0625" =1.5875mm
.1mm = .004", and yup that's pretty tiny
what does get confusing is mixing formats of Imperial measurements on the same drawing
i.e. 16.25 " = 1'4 1/2"
just guess how many times that's been responsible for cabinets built off cocktail-napkin site sketches that are the wrong size.
Naturally. But I still hate metric with a passion. Like anything else decimalised for that matter.
Cheesehead -you'll probably struggle to get exactly the same response as I have my own ways of working with the sheets for double horns, and for some design details such as lining, rather than stuffing the filter chamber etc.
If you're wanting to get a handle on simulating horn enclosures, I'd suggest looking at single horns first like the Jericho, or the published Lowther designs as practice. Quite a learning experience & also gives an insight into both what is good, and less so good of the existing cabinets out there. There's some real surprises...
Cheesehead -you'll probably struggle to get exactly the same response as I have my own ways of working with the sheets for double horns, and for some design details such as lining, rather than stuffing the filter chamber etc.
If you're wanting to get a handle on simulating horn enclosures, I'd suggest looking at single horns first like the Jericho, or the published Lowther designs as practice. Quite a learning experience & also gives an insight into both what is good, and less so good of the existing cabinets out there. There's some real surprises...
At last, two Harveys!
Finally finished (in rough at least), my second cabinet.
As you can see from the pic, they are in a far from ideal location at the moment, but it's a;; the space I've got for now.
After trying a stepped front baffle for ease on the first cab, I tried the sloping edge for the second. It looks far better, so now I've got some fun ahead trying to remove the steps!
Sound? A bit Curate's egg if I'm honest. Huge amounts of detail, and decent, dynamic bass. Treble is much more refined since I bit the bullet and did the phase plug mod, but at the moment, the whole sound is top-end heavy for my ears, for want of a better word 'shriekey'.
I'm guessing at the moment that this is a high frequency resonance propagating along the hard 'skin' suface of the MDF that I used, because although it is most noticeable through the horn sections, it is not reduced (much) when I drop damping (socks!!) to temporarily block the horns.
I'm currently pondering methods to damp down the MDF, although it will be a while before I get to try any ideas out in practice!
Scott, you mentioned adding damping in the pair you built, can I ask what you used?
Overall, I'mm hearing far more positive things than negative when I listen to these speakers, but it would be nice to lose the negatives if I could.
Cheers
Dave
Finally finished (in rough at least), my second cabinet.
As you can see from the pic, they are in a far from ideal location at the moment, but it's a;; the space I've got for now.
After trying a stepped front baffle for ease on the first cab, I tried the sloping edge for the second. It looks far better, so now I've got some fun ahead trying to remove the steps!
Sound? A bit Curate's egg if I'm honest. Huge amounts of detail, and decent, dynamic bass. Treble is much more refined since I bit the bullet and did the phase plug mod, but at the moment, the whole sound is top-end heavy for my ears, for want of a better word 'shriekey'.
I'm guessing at the moment that this is a high frequency resonance propagating along the hard 'skin' suface of the MDF that I used, because although it is most noticeable through the horn sections, it is not reduced (much) when I drop damping (socks!!) to temporarily block the horns.
I'm currently pondering methods to damp down the MDF, although it will be a while before I get to try any ideas out in practice!
Scott, you mentioned adding damping in the pair you built, can I ask what you used?
Overall, I'mm hearing far more positive things than negative when I listen to these speakers, but it would be nice to lose the negatives if I could.
Cheers
Dave
Attachments
A thin layer of BAF wadding from Maplin on the floor of the filter chamber. That's it. Shrieking you should not be hearing though. Mine are also in MDF, but no-one who's heard them has found this problem: http://web.mac.com/scress1958/iWeb/Steves_Tube_Trials/FostexFest.html
What amp are you runniong at the moment?
What amp are you runniong at the moment?
My amp's a little (and cheap) Yarland push-pull. Usually very smooth.
Thinking back, 'shrieking' was a little excessive as a descriptor, but I often find my 'describing sounds' vocab quite limited.
I'm hearing a thinness and edginess at the moment that reminds me of all that I dislike about SS amps, along with a touch of that high pitched ringing that you get when you tap MDF. Long and short is it's annoying because so much of what I'm hearing is excellent!
I know that there are at least 10^6 other variables to consider, so I'll keep pondering...
Cheers
Dave
Thinking back, 'shrieking' was a little excessive as a descriptor, but I often find my 'describing sounds' vocab quite limited.
I'm hearing a thinness and edginess at the moment that reminds me of all that I dislike about SS amps, along with a touch of that high pitched ringing that you get when you tap MDF. Long and short is it's annoying because so much of what I'm hearing is excellent!
I know that there are at least 10^6 other variables to consider, so I'll keep pondering...
Cheers
Dave
panel damping
dfreemansc,
you may try the panel damping, if this really is the MDF ringing you hear. I use Parts Express # 268-015 asphalt-based material: http://www.partsexpress.com/pe/showdetl.cfm?&DID=7&Partnumber=268-015 on all my cabinets for many years with very good results.
VadimB
dfreemansc,
you may try the panel damping, if this really is the MDF ringing you hear. I use Parts Express # 268-015 asphalt-based material: http://www.partsexpress.com/pe/showdetl.cfm?&DID=7&Partnumber=268-015 on all my cabinets for many years with very good results.
VadimB
You may need to try a BSC filter
If you can't balance the high freq by playing around with stuffing, ect, give a LR baffle step filter a try. L = 1.5 mH, R = 5 ohm might be a good start. The purists might get offended, but it's a removable measure that can make the speaker more listenable. I've used them on fullrange speakers before without any negative effects. See Martin King's website for more information.
PJN
If you can't balance the high freq by playing around with stuffing, ect, give a LR baffle step filter a try. L = 1.5 mH, R = 5 ohm might be a good start. The purists might get offended, but it's a removable measure that can make the speaker more listenable. I've used them on fullrange speakers before without any negative effects. See Martin King's website for more information.
PJN
Virgin builder suffers premature exitability syndrome
I'm listening to my speakers again tonight, and getting a handle on what's going on (I think).
1. Good science involves changing one variable at a time, right? So I build my speakers (my first full-range), use drivers with less than 50 hours on them, make up some nice new Cat 6 cables for them, fit phase plugs, etc, etc. What a suprise, they're sounding on the thin side of neutral!
(No, I'm not saying what my day job is, I'm too embarrased!)
2. I seem to have a sensitivity to the ringy-thing that MDF does in the same kind of way that I have a sensitivity to marzipan - I can spot it from 500 yards, and always hate it! Yup, 400-500Hz would just about nail the annoyance band for me, and I think this resonance, starting in the CC and propagating up the horn is what I have been noticing. (Stick your ear hard against the side of an MDF cab while it's playing, and that narrow band yuk that you hear is what makes my teeth grate!)
3.I had no experience of the psychic nature of full-range speakers before now. Night before last I mention they sound edgy, tonight they start smoothing out! (Perhaps tonight I should proclaim that they sound rubbish, so that tomorrow they'll sound sublime! )
I guess the way forward is clear - a little judicious damping, along with a spoonful of patience, and all should be great!
BTW Just in case anyone reading my earlier posts thought that I felt that Scotts design wasn't spot on, go and wash your mind out with something soapy. Right now. If the overall sound wasn't so addictively good I wouldn't be niggling over the end result of my choice of wood! Thanks again Scott!
Cheers
Dave
I'm listening to my speakers again tonight, and getting a handle on what's going on (I think).
1. Good science involves changing one variable at a time, right? So I build my speakers (my first full-range), use drivers with less than 50 hours on them, make up some nice new Cat 6 cables for them, fit phase plugs, etc, etc. What a suprise, they're sounding on the thin side of neutral!
(No, I'm not saying what my day job is, I'm too embarrased!)
2. I seem to have a sensitivity to the ringy-thing that MDF does in the same kind of way that I have a sensitivity to marzipan - I can spot it from 500 yards, and always hate it! Yup, 400-500Hz would just about nail the annoyance band for me, and I think this resonance, starting in the CC and propagating up the horn is what I have been noticing. (Stick your ear hard against the side of an MDF cab while it's playing, and that narrow band yuk that you hear is what makes my teeth grate!)
3.I had no experience of the psychic nature of full-range speakers before now. Night before last I mention they sound edgy, tonight they start smoothing out! (Perhaps tonight I should proclaim that they sound rubbish, so that tomorrow they'll sound sublime!
)I guess the way forward is clear - a little judicious damping, along with a spoonful of patience, and all should be great!
BTW Just in case anyone reading my earlier posts thought that I felt that Scotts design wasn't spot on, go and wash your mind out with something soapy. Right now. If the overall sound wasn't so addictively good I wouldn't be niggling over the end result of my choice of wood! Thanks again Scott!
Cheers
Dave
I am sorry, peterbrorsson, but the natural resonanse frequency can not be ascribed to a material itself. In this particular case, it's a property of the pannel. It does depend on the material the pannel is made of, but also depends on the dimensions of the pannel, the way it's attached, etc...
So, if 400 Hz really is a frequency that bothers, we have to find the pannel that makes this sound. The best way to find it is to use a stettoscope: doctor's or mechanic's (the one with a solid metal rod at the end). If you can't get a hold of one, the next best thing is a home-made one. Get a funnel and a piece of rubber or plastic hose. Fit one end over the spout and the other in your ear. Now, play some music (or better a pink noise) and go over the whole cabinet, putting the open end of the funnel on every pannel. If you are so sensitive to the frequency that bothers you, you should have no problem locating the pannel that produces it. Be careful with volume - it's really loud through this device.
Once you've found the offending pannel(s) - we have to damp it.
One way is to use the damping sheet I suggested before. Another is to attach a rib, going along or diagonally across this pannel. A piece of hardwood (3/4-1 x 1.5-2") should work. Glue it with a hard glue, like TiteBond, the nerrower side to the pannel. Couple screws will help too. This should shift the resonance up and lower its amplitude at the same time.
Hope this helps,
VadimB
So, if 400 Hz really is a frequency that bothers, we have to find the pannel that makes this sound. The best way to find it is to use a stettoscope: doctor's or mechanic's (the one with a solid metal rod at the end). If you can't get a hold of one, the next best thing is a home-made one. Get a funnel and a piece of rubber or plastic hose. Fit one end over the spout and the other in your ear. Now, play some music (or better a pink noise) and go over the whole cabinet, putting the open end of the funnel on every pannel. If you are so sensitive to the frequency that bothers you, you should have no problem locating the pannel that produces it. Be careful with volume - it's really loud through this device.
Once you've found the offending pannel(s) - we have to damp it.
One way is to use the damping sheet I suggested before. Another is to attach a rib, going along or diagonally across this pannel. A piece of hardwood (3/4-1 x 1.5-2") should work. Glue it with a hard glue, like TiteBond, the nerrower side to the pannel. Couple screws will help too. This should shift the resonance up and lower its amplitude at the same time.
Hope this helps,
VadimB