finalising the design/construction of my boxes, and am curious about this.
I wonder if this factor (sound coming from the box back thru the diaphragm) is one of the reasons for people liking the dipole sound??
Most boxes just get a bit of stuffing I guess, is the purpose of that stuffing to absorb the backwave? or some other factor/.
One of the things that has intrigued me is the 'reverse horn (?) of the B&Ws. From my poor understanding it somehow works by directing the backwave down a guide and absorb it there.
Has anyone experimented with this, if so what did you find?
Here is a link to someones practical implementation of it
http://home.wanadoo.nl/dezaire/ultiem/ultimate.htm, there is a diagram that you can download that shows how it was done. Basically by cutting holes in a succession of mdf plates you can sculpt the cone shaped cavity.
If part of the reason is to absorb the wave, I wondered why build it out of a solid material like mdf? Could you not substitute compressed f/glass, still have the sculpted shape yet provide better absorption?
What apart from the b&w trick are there? Is it worrying over nothing at the end of the day?
I have wondered why most cabinet stuffing (or internal foam) is placed on the walls? Would they not work (like room treatments I guess) by slowing the wave and converting it to heat?
If so, then like improving the bass performance of f/glass panels on the wall you space it off the wall, would not this stuff work better when placed in a zone of maximum velocity rather than max pressure? Ie, get the foam/fglass off the cabinet walls.
The arc tube traps work by forcing the equalization of internal and external pressure, how left field is the idea of mini tube traps within the box?? (just a silly curiosity question, doubt I will try it)
But a crazy idea I have thought of is instead of lining the walls with foam or glass, how about lining them with 'sand bags', a bit like the snake draught excluders under a door.
Fine loose sand (done in such a way that the sand does not escape) will certainly vibrate due to the bass, and unlike foam on the walls (if my theories above are somehow correct) will still provide the vibration/conversion to heat mechanism.
I wonder if this factor (sound coming from the box back thru the diaphragm) is one of the reasons for people liking the dipole sound??
Most boxes just get a bit of stuffing I guess, is the purpose of that stuffing to absorb the backwave? or some other factor/.
One of the things that has intrigued me is the 'reverse horn (?) of the B&Ws. From my poor understanding it somehow works by directing the backwave down a guide and absorb it there.
Has anyone experimented with this, if so what did you find?
Here is a link to someones practical implementation of it
http://home.wanadoo.nl/dezaire/ultiem/ultimate.htm, there is a diagram that you can download that shows how it was done. Basically by cutting holes in a succession of mdf plates you can sculpt the cone shaped cavity.
If part of the reason is to absorb the wave, I wondered why build it out of a solid material like mdf? Could you not substitute compressed f/glass, still have the sculpted shape yet provide better absorption?
What apart from the b&w trick are there? Is it worrying over nothing at the end of the day?
I have wondered why most cabinet stuffing (or internal foam) is placed on the walls? Would they not work (like room treatments I guess) by slowing the wave and converting it to heat?
If so, then like improving the bass performance of f/glass panels on the wall you space it off the wall, would not this stuff work better when placed in a zone of maximum velocity rather than max pressure? Ie, get the foam/fglass off the cabinet walls.
The arc tube traps work by forcing the equalization of internal and external pressure, how left field is the idea of mini tube traps within the box?? (just a silly curiosity question, doubt I will try it)
But a crazy idea I have thought of is instead of lining the walls with foam or glass, how about lining them with 'sand bags', a bit like the snake draught excluders under a door.
Fine loose sand (done in such a way that the sand does not escape) will certainly vibrate due to the bass, and unlike foam on the walls (if my theories above are somehow correct) will still provide the vibration/conversion to heat mechanism.
terry j said:
What, like glueing small bags of sand to the middle of large cabinet surfaces to dampen resonance?
Very interesting idea...
The B&W is a tapered 1/2 wave (sealed) transmission line. Like all "proper" transmission lines it sucks the backwave down the line and the damping material kills the backwave before it can reflect and return -- as Bud Fried was fond of saying -- it dramatically reduces (nothing is perfect) the time smear.
That little monitor really doesn't look large enuff to do what you want.
And probably easier to build like B&W's prototype.
I'm using similar techniques for some mid enclosures (Tysen and a Festrex project i'm working on). Being mid TLs, they are much similar.
dave
That little monitor really doesn't look large enuff to do what you want.
And probably easier to build like B&W's prototype.
I'm using similar techniques for some mid enclosures (Tysen and a Festrex project i'm working on). Being mid TLs, they are much similar.
dave
Re: Re: 'exotic' techniques for absorbing the mid backwave (and bass)
Kinda, but maybe not even gluing, but fixing top bottom and middle, heck even 'wire' them in with eyehooks, so the whole lot is fixed yet can vibrate away merrily.
thanks dave, I guess in the picture you have posted a lot of the size has also something to do with augmenting the bass??
Re that schematic, it does look kinda small, and if the box size is all about creating the curved chamber, then not a lot left to provide box size to provide deep bass.
That was the other question I forgot to ask, IF you did do the 1/2 wave transmission line, does the volume behind it still have to be that which unibox (say) says you need for you bass performance? (hope that made sense, kinda the earlier para re-worded)
That is his 'long' prototype that is pictured?
How *critical* is it to have it a tapered 1/2 wave transmission line? What about straight sides as an example.
I would imagine that if my mid cutoff point is 200 hz, I would not need such a huge chamber?
Lastly, any thoughts about how the results reflect the work?
Iain McNeill said:
Kinda, but maybe not even gluing, but fixing top bottom and middle, heck even 'wire' them in with eyehooks, so the whole lot is fixed yet can vibrate away merrily.
planet10 said:
thanks dave, I guess in the picture you have posted a lot of the size has also something to do with augmenting the bass??
Re that schematic, it does look kinda small, and if the box size is all about creating the curved chamber, then not a lot left to provide box size to provide deep bass.
That was the other question I forgot to ask, IF you did do the 1/2 wave transmission line, does the volume behind it still have to be that which unibox (say) says you need for you bass performance? (hope that made sense, kinda the earlier para re-worded)
That is his 'long' prototype that is pictured?
How *critical* is it to have it a tapered 1/2 wave transmission line? What about straight sides as an example.
I would imagine that if my mid cutoff point is 200 hz, I would not need such a huge chamber?
Lastly, any thoughts about how the results reflect the work?
Re: Re: Re: 'exotic' techniques for absorbing the mid backwave (and bass)
Bass extension in a half-wave TL is the same as sealed. Length needs to be 1/2 WL of the lowest frequency of interest (a heavy taper means it can be shorter). For a mid range TL it doesn't need to be too long and if a 1/4 wave line (like i'm doing -- i like the low pressure box), even shorter -- Tysen with ~300 Hz XO is 10:1, 8-9" long, The Featrex needs to be able to get closw to 100, so it is ~20" long, both are damped till aperiodic, stuffing density increasing towards the terminus.
It is about the same length as the production fiberglass Nautilus woofer (but more space taken up by material). For easier construction you could just fold the TL more conventionally.
dave
terry j said:
Bass extension in a half-wave TL is the same as sealed. Length needs to be 1/2 WL of the lowest frequency of interest (a heavy taper means it can be shorter). For a mid range TL it doesn't need to be too long and if a 1/4 wave line (like i'm doing -- i like the low pressure box), even shorter -- Tysen with ~300 Hz XO is 10:1, 8-9" long, The Featrex needs to be able to get closw to 100, so it is ~20" long, both are damped till aperiodic, stuffing density increasing towards the terminus.
It is about the same length as the production fiberglass Nautilus woofer (but more space taken up by material). For easier construction you could just fold the TL more conventionally.
dave
ok, wavelength at 200 hz is 1.72m.
1/2 is 850mm, 1/4 is around 420mm, call it 500mm so I have some latitude of x-over point.
tysen, umm I spose that is a type of profile?
Current mid chamber is around 10 l, if I were to muck about with this do I need to keep the volume at ten l? To prevent too long a tube, then I can put it in a spiral.
do you have any suggested reading? Sounds like you have tried this, how do you feel the results are?
1/2 is 850mm, 1/4 is around 420mm, call it 500mm so I have some latitude of x-over point.
tysen, umm I spose that is a type of profile?
Current mid chamber is around 10 l, if I were to muck about with this do I need to keep the volume at ten l? To prevent too long a tube, then I can put it in a spiral.
do you have any suggested reading? Sounds like you have tried this, how do you feel the results are?
The sandbag trick would not help against the backwave coming through the cone. But it would help against the vibrations of the panels.
A less messy and more modern method than the sandbag would be the following:
http://www.korff.ch/E/hawaphon.htm
Regards
Charles
A less messy and more modern method than the sandbag would be the following:
http://www.korff.ch/E/hawaphon.htm
Regards
Charles
I realise that charles, I changed the title of the thread to try and include that bass stuff.
thanks for the link, it's kinda what I was thinking, some sort of sack holding the loose material. I guess it is a way to retro fit the double skin build, that is filled with sand.
no-one has any opinion on whether it is useful to have the absorption on the walls themselves? or would it be better spaced off at least a few inches.
thanks for the link, it's kinda what I was thinking, some sort of sack holding the loose material. I guess it is a way to retro fit the double skin build, that is filled with sand.
no-one has any opinion on whether it is useful to have the absorption on the walls themselves? or would it be better spaced off at least a few inches.
terry j said:
Attached is a mid-line that comes to 100-150 Hz once you consider end correction and the taper.
Yes i've tried this. Works well. And the guru i learned it from was using it long before i 1st did.
Tysen is the name of a speaker (and our godson), FF85KeN is in a 10"1 mid TL that exits out the back (no fold)
dave
Attachments
The absorbtion would work down to lower frequencies compared to placment directly on the wall.
Regards
Charles
planet10 said:
tysen, nice sounding name! For some silly reason I tend to like first names that sound like last names.
yeah, beats me too.
Ok, confusion time. A TL has to 'exit' somewhere?? I thought the B&W thing was sealed? (thought you said exit in your post, but I can't find it now, must be going mad)
Are there any hard and fast rules? You say it works well, so it seems worthwhile getting a bit more data in order to do any experiments rationally.
In what way does it work well? 'less box', clearer, what?
Is the volume behind the driver important?
I don't want to bore you with all these questions, are there any links, or is this an immature field.
terry j said:
Nautilus is a 1/2 wl line, which by definition is sealed. If there is an open terminus, it automajikly becomes a 1/4 wl line.
By remove the back wave you lose a lot of the time smear from reflections, increasing downward dynamic range, The box is more detailed and less "boxy"
Yes. But as long as the box is not too small it gets pretty forgiving.
A skilled MJK operater could probably get some useful sims -- the damping density push above the limits of his sw. An impedance curve on the finished box also provides useful feedback,
dave
thanks dave
another 'difference' between the pics you've posted and the B&W ones is that the b&w's are conical, yours are kinda rectangular in cross section.
I thought there might have been more discussion on this, maybe there is another forum that has more bods in this kind of area? audio circle or something?
got it about the improvements from removing the backwave, one final confusion to clear up a bit, are you saying (that apart from no box at all?) this tapered rear box trick is better than straight normal stuffed chambers?
Trying to get a guage on 'is it worth the hassle' (esp as it seems there are no hard and fast design guidelines)
another 'difference' between the pics you've posted and the B&W ones is that the b&w's are conical, yours are kinda rectangular in cross section.
I thought there might have been more discussion on this, maybe there is another forum that has more bods in this kind of area? audio circle or something?
got it about the improvements from removing the backwave, one final confusion to clear up a bit, are you saying (that apart from no box at all?) this tapered rear box trick is better than straight normal stuffed chambers?
Trying to get a guage on 'is it worth the hassle' (esp as it seems there are no hard and fast design guidelines)
terry j said:
Siegfried Linkwitz measured a 40dB return loss on the Pluto mid-bass which lives in a piece of 4" pipe filled with an appropriate density of Acousta-Stuf.
http://www.linkwitzlab.com/Pluto/construction.htm
They sound more natural than more conventional speakers although some of that comes from the uniform polar response and lack of diffraction.
terry j said:
The B&W picture i posted is rectangular -- it has flat, parallel sides. Lots of folds and not severe so that it is a spiral. The quadratic taper in the production Natilus gives them a more dramatic taper while retaining a similar cross-section aspect ratio and non-parallel sides. This should impact things positively.
Yes. As a generalization. A definitive answer requires context.
dave
Hi Terry
Brett and I were talking about this 2 weeks ago ,I drew up some silly google sketchup tapped horn for the 10" driver that went to the ground and acted as the stand .
I'll be interested how you go ,another idea was to use acoustic wedges mounted on the rear baffle face the driver I think these need to be 1/2 or 1/4 the wave length .
Cheers
Brett and I were talking about this 2 weeks ago ,I drew up some silly google sketchup tapped horn for the 10" driver that went to the ground and acted as the stand .
I'll be interested how you go ,another idea was to use acoustic wedges mounted on the rear baffle face the driver I think these need to be 1/2 or 1/4 the wave length .
Cheers
I don't know about exotic, but that reflected wave IS a problem in small boxes and light cones. A lot comes back out thru the cone. As you say, it's one reason the open baffle type sounds so good.
A bigger box helps, but isn't always possible. Small box and light cone can be difficult.
I've used 100% wool felt ($$$) to good effect. Gary Pimm is using a cotton insulation made of recycled blue jeans. The stuff is pretty amazing. Absorbs down at lower freq. than most fiberglass or rock wool. My guess is that it's pretty linear, too.
http://www.bondedlogic.com/ultratouch-cotton.htm
Have also seen a "curtain" of material hung about 2/3 of the way back in tha box. Kills reflections. But that is in a big box.
A bigger box helps, but isn't always possible. Small box and light cone can be difficult.
I've used 100% wool felt ($$$) to good effect. Gary Pimm is using a cotton insulation made of recycled blue jeans. The stuff is pretty amazing. Absorbs down at lower freq. than most fiberglass or rock wool. My guess is that it's pretty linear, too.
http://www.bondedlogic.com/ultratouch-cotton.htm
Have also seen a "curtain" of material hung about 2/3 of the way back in tha box. Kills reflections. But that is in a big box.
Dave,
What do you use to model the 1/2 wavelenght mid TL? I have desire to want to do the same for my abbey-clone like speakers. I putzed around with some TL alignment spreadsheets but that didn't help.
Josh
What do you use to model the 1/2 wavelenght mid TL? I have desire to want to do the same for my abbey-clone like speakers. I putzed around with some TL alignment spreadsheets but that didn't help.
Josh
cannot remember what I typed in, but I did find an old thread by rick 57, about two years old I think (sorry, must have not searched hard enough) Dave was saying much the same thing back then.
But I don't really want to learn a whole new files of data (TL's etc) and try and reverse engineer this, just for a mid box.
I might just take the dumb route and make a few different test boxes, and just try them side by side, first of all to see if I can even hear a difference. Hopefully any /better or worse' will jump out as exceedingly obvious (simply cannot bother with tiny effects in audio, just not me)
Dave, must be very slow this week, even tho you did mention it it only just dawned on me that that big tapered tube you showed was the testing box for the nautilus. duh.
Heck, it is huge, and for such a small bass driver. Is that the size they went with in the final model? Of all the reports on the nautilus, what were the impressions of 'bass weight'? (doubt it would satisfy me, for my tastes there is something about BIG bass drivers)
Anyway, we all know the famous shape, and nested on top of the snail bottom are the two swept pods, one for the tweeter and one for the mid I presume. Thankfully a welcome difference in size!
Does anyone know the x-over points in the nautilus? Mine is around 200 hz.
I did find a cutaway pic of those chambers, that will be my 'monkey see monkey do' starting point when I mock up some differing chambers. One noticeable thing in those cutaways is the obvious bulbous shape just behind the driver, which then ends in a taper.
That seems quite different than any suggestion of a simple decreasing taper the entire length.
Pan, that bit where you mentioned a partition, if it was 'airtight' I can see that being effective (tho thinking more in the bass a la the tube trap). The rear partition must act as a sink when the front partition gets pressurized, pressures will tend to equalize hence the pressure wave must attempt to pass thru the material, taking energy in the process. And of course in the reverse.
The same amount of material placed directly on the wall on the other hand, well the internal volume then is one amorphous mass that is free to pressurize and depressurize at will, very little is 'pushed' thru the material.
Again, really, why does all the stuffing usually get put directly on the box wall??
But I don't really want to learn a whole new files of data (TL's etc) and try and reverse engineer this, just for a mid box.
I might just take the dumb route and make a few different test boxes, and just try them side by side, first of all to see if I can even hear a difference. Hopefully any /better or worse' will jump out as exceedingly obvious (simply cannot bother with tiny effects in audio, just not me)
Dave, must be very slow this week, even tho you did mention it it only just dawned on me that that big tapered tube you showed was the testing box for the nautilus. duh.
Heck, it is huge, and for such a small bass driver. Is that the size they went with in the final model? Of all the reports on the nautilus, what were the impressions of 'bass weight'? (doubt it would satisfy me, for my tastes there is something about BIG bass drivers)
Anyway, we all know the famous shape, and nested on top of the snail bottom are the two swept pods, one for the tweeter and one for the mid I presume. Thankfully a welcome difference in size!
Does anyone know the x-over points in the nautilus? Mine is around 200 hz.
I did find a cutaway pic of those chambers, that will be my 'monkey see monkey do' starting point when I mock up some differing chambers. One noticeable thing in those cutaways is the obvious bulbous shape just behind the driver, which then ends in a taper.
That seems quite different than any suggestion of a simple decreasing taper the entire length.
Pan, that bit where you mentioned a partition, if it was 'airtight' I can see that being effective (tho thinking more in the bass a la the tube trap). The rear partition must act as a sink when the front partition gets pressurized, pressures will tend to equalize hence the pressure wave must attempt to pass thru the material, taking energy in the process. And of course in the reverse.
The same amount of material placed directly on the wall on the other hand, well the internal volume then is one amorphous mass that is free to pressurize and depressurize at will, very little is 'pushed' thru the material.
Again, really, why does all the stuffing usually get put directly on the box wall??
JoshK said:
Haven't built any 1/2 wave TLs. I'd suspect you select a suitable volume for sealed and then stretch it out so that it ia a 1/2wl long (a heavy taper will allow it to be shorter)
dave
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