[DSK]

I'm currently building some standmount speaker boxes (22"h x 9"w x 13.75"d), all panels are 1" MDF, baffle is 1.25" MDF, with full shelf brace half way back and a strut brace from middle of the shelf brace to the middle of the back panel.

I will use poly batting for internal damping and wasn't going to use any panel damping as a braced, 1" thick box this size shouldn't need it. However, I have spent so much time trying to make these boxes the best I can that I am reconsidering. I realise most people use vinyl sheeting of various descriptions. However, the thicker the box panel, the thicker and more massive the damping material needs to be to be effective. I haven't tried it but have doubts as to how effective vinyl tiles etc would be.

Today, in the local hardware store, I saw 1.5mm (1/16th") thick lead sheets and thought that they may be a good idea, adhered to the inside of the box with contact adhesive (like constrained layer platforms) or silicone. If necessary, I could use a tack in each corner to help support the weight. They would take up very little box volume, be extremely massive, and I presume would damp any box resonance better than anything else.

Anyone tried this? Worthwhile? Any better alternatives?

Thanks for any advice you can give.

[andyr]

I'm currently building some standmount speaker boxes (22"h x 9"w x 13.75"d), all panels are 1" MDF, baffle is 1.25" MDF, with full shelf brace half way back and a strut brace from middle of the shelf brace to the middle of the back panel.

I will use poly batting for internal damping and wasn't going to use any panel damping as a braced, 1" thick box this size shouldn't need it. However, I have spent so much time trying to make these boxes the best I can that I am reconsidering. I realise most people use vinyl sheeting of various descriptions. However, the thicker the box panel, the thicker and more massive the damping material needs to be to be effective. I haven't tried it but have doubts as to how effective vinyl tiles etc would be.

Today, in the local hardware store, I saw 1.5mm (1/16th") thick lead sheets and thought that they may be a good idea, adhered to the inside of the box with contact adhesive (like constrained layer platforms) or silicone. If necessary, I could use a tack in each corner to help support the weight. They would take up very little box volume, be extremely massive, and I presume would damp any box resonance better than anything else.

Anyone tried this? Worthwhile? Any better alternatives?

Thanks for any advice you can give.

Hi Darren,

Re. lead sheet ... yes it sounds like it's a good thing to do and might     help your 25mm MDF walls but I fear you have lost your opportunity to apply the lead efficaciously!   

I know Whatmough uses lead-lined boxes in his top-o-the-line speakers.

I think you would need to use full-spread contact adhesive to lock the lead to the MDF (for a CLD approach) and so you need to have done this before you glued the panels together to make the box!  It's no good just adhering the lead to the MDF at several points.  So don't stress about it!!   

And BTW, I think vinyl tiles would be completely useless!

The only other way of doing something, that I can think of - which is no good for you as you've already spent all that effort spray painting - would be to use some sort of threaded rod which you passed right through the cabinet, which (as you clamped it up) would compress the two sides together ... ie. the opposite of using an internal wooden "expansion" brace.

regards,

Andy

[DSK]

I think you would need to use full-spread contact adhesive to lock the lead to the MDF (for a CLD approach) and so you need to have done this before you glued the panels together to make the box!  It's no good just adhering the lead to the MDF at several points.  So don't stress about it!!   

Actually, considering the full shelf brace that is 1" thick and supports both sides, top and bottom panels (approx half way between the baffle and the rear panel), and the 1" x 2" brace that extends between the middle of the shelf brace and the middle of the rear panel, the largest unsupported areas are approx 5" x 16" (side panels either side of shelf brace), 8" x 7" (rear panel above and below strut brace), 7" x 7" (baffle under midwoofer), 6" x 9" (top and floor panels either side of shelf brace).
These spans are not very large and given that they are all 1" thick should be very rigid.

All of these spaces are accessible through the midwoofer cutout (~6.5" diameter) and shelf brace cutouts (~6" diameter). As lead sheet is pliable, all of these spaces could be lead lined if desired.

I disagree that the entire box panels need to be lead lined to be effective. The larger the unsupported span, the greater the resonance amplitude, the lower the resonance frequency will be and therefore the more difficult it is to damp. When you rap your knuckles on a plasterboard wall, there is a hollow sound until you come to the studs and noggins. This is the same on a speaker box ... the middle of the unsupported spans will give the hollow knock until you get toward the walls and braces where there will be a dull thud. Therefore, the key places to damp are the centre areas of the unsupported areas. Sure, lining the entire panels may measure even better, but I very much doubt we would hear a difference .... especially given that most boxes don't use lead and many don't use anything at all to reduce panel resonance. Another example is when applying anti-resonance material to the thin metal chassis of a hifi component ... it is not necessary (or sometimes even desirable) to cover the entire chassis, just to add strips at intervals of say thirds of the chassis width. This virtually eliminates resonance at the lined areas, and causes the unlined areas to be smaller so the resonance will be of lower amplitude and higher frequency.

I believe that adding say 6" x 6" lead sheet squares to 8" x 8" panel areas is fine, dimensions wise. What I'm not totally sure about, is whether 1.5mm thick lead sheet is sufficiently thick and massive to be effective on 1" thick MDF. Typically, the thicker the substrate to be damped, the thicker and more massive the damping layer needs to be.

I would love to hear from anyone who has compared with and without lead lining.

[Christof]

I am going to line the inside of my next cabinets with Ice and Water shield.  This stuff is like an adhesive backed sheet of tar that sticks to nearly anything.  It's avaliable at most hardware stores or lumber yards. 

[DSK]

I am going to line the inside of my next cabinets with Ice and Water shield.  This stuff is like an adhesive backed sheet of tar that sticks to nearly anything.  It's avaliable at most hardware stores or lumber yards. 

Christof, that might be what we call Flash-Tac (from memory) over here. It comes in rolls of various widths and lengths and is used to seal gaps in rooves and spoutings etc. It is a very thin layer of aluminium backing on a very sticky, black tar-like substance about 1/8th inch thick and can easily be applied around corners etc. Actually, this is what I went to the hardware store to check out when I spied the lead sheeting next to it. I have a little bit of this somewhere in the garage and have been meaning to try it out on some scrap MDF and give it the knock test. The sticky black tar would act as a lossy layer (constrained layer) between the panel and the aluminium backing. However, although it is thicker than the lead sheeting, it is nowhere near as massive and I felt it wouldn't be as effective.

Or, perhaps you mean the heavier but stiffer bitumen sheeting that is less pliable and wouldn't curve around tight corners?

[jules]

If it's damping mass at key points that you're aiming for, you could try screwing a few large lumps of lead on strategically where they do the most good.

In relation to the polybatting ... have you considered wool? I've read various reports suggesting that it is superior to poly and we happen to have quite a large supply of the best stuff right here in OZ ... www.melandapark.com/ ... at about $10 a kilo.

jules

[DSK]

If it's damping mass at key points that you're aiming for, you could try screwing a few large lumps of lead on strategically where they do the most good.

  I should have carved the whole box out of a great big chunk of lead  In order for the damping material to be effective, it needs to be in intimate contact with the substrate. So, it would need to be glued and completely flattened against the MDF panel. Usually screws and nails are undesirable in constrained layer platforms as they form a direct bridge between the substrate and constraining layer... vibrations would travel across the constrained layer via the screws or nails and reduce the efficacy of the isolation of the component sitting on top. However, in this case there isn't a component sitting on the constraining layer and the constraining layer (lead) will not resonate.

In relation to the polybatting ... have you considered wool? I've read various reports suggesting that it is superior to poly and we happen to have quite a large supply of the best stuff right here in OZ ... www.melandapark.com/ ... at about $10 a kilo.

I've also read that 'teased long fibre wool' is better than polyester though a bit more difficult to use. I read somewhere of one person using it in hair nets. Not sure of how much to use or exactly what to ask for though. The fleece on the website you listed looks a bit dense.

[Daryl]

Hi DSK,

I have similar cabinets that I have built but much smaller (18.125"x7.25"x8.75).

I use .75" panels throughout and two shelf braces horizontal above and below the tweeter.

I don't think any panel damping is really necessary if you keep a good ratio of panel thickness to span length.

I am very happy with my cabinets which are noticably heavy and solid.

I would not recomend polyester/Dacron/Acousta-Stuff or Wool all of which are fairly similar in their characteristics.

I would recomend Fiberglass at 1lb/ft^3 which not only has a far greater sound absorbtion but also gives a greater effective increase in cabinet volume compared to the above mentioned materials.

Below are two pictures of my cabinet and one picture of one of my subwoofer cabinets with 1" panels (20"x29.5"x20").

Daryl

[jules]

Nice designs Daryl and the bracing shelves [which I have to admit are the same pattern as mine] would be hard to better.

Not sure that I follow your logic on the attachment system Darren. If the point of lead is to damp vibration at the point where it would be at its max. then sheets are probably an inefficient way to achieve that end. If there's a problem with screwing things to a cabinet then surely we're pretty stuffed as far as the drivers go? With a lump of lead it should be pretty easy to screw and glue to the extent that the connection would be as near to "oneness" as the rest of the box construction.

VMPS have suggested the use of wool and I think there was a post or two in their circle on the topic [with comparisions to fibreglass]. Aus. merino is particularly fine and this post gives my own take on it  ...

http://www.audiocircle.com/index.php?topic=21199.msg187974#msg187974

I used about 1 kg for a total volume of 2 cubic feet.

Daryl, do you have some figures on the relative qualities of wool etc etc? Could you also expand on your point about volume? As I understand it, the volume of damping material is so insignificantly small that it doesn't count and surely the difference between the vol. of wool and that of fibreglass is going to be even more insignificanter.

jules

[DSK]

Not sure that I follow your logic on the attachment system Darren. If the point of lead is to damp vibration at the point where it would be at its max. then sheets are probably an inefficient way to achieve that end. If there's a problem with screwing things to a cabinet then surely we're pretty stuffed as far as the drivers go? With a lump of lead it should be pretty easy to screw and glue to the extent that the connection would be as near to "oneness" as the rest of the box construction.

Jules, I think you misunderstood my post. Your previous post suggested to "screw the lumps of lead to the box" and I was merely suggesting that they would need to be glued on for max efficacy (ie. ensure that the entire face of the lead is in contact with the MDF panel face), the screws would only be used if necessary to support the weight. I wasn't disagreeing with your suggestion of a lump of lead and was actually explaining why screws wouldn't be as bad in this application as they are in constrained layer platforms. I don't understand your comparison with the mounting of the drivers?

I used about 1 kg for a total volume of 2 cubic feet.

That seems like a lot ... most stuff I've read suggests using 0.25kg (0.5 lb) per cubic foot of volume. Have you experimented with the amount Jules?

Daryl, nice boxes. I tend to agree with you that sufficiently thick panels and bracing reduce (eliminate?) the need for extra panel resonance damping materials. I just figured that there is very little cost or effort to add some lead, so I'd do it if anyone had found it helped.

Some people swear by BH5, others suggest it makes no difference to panel resonance. Perhaps those who found no improvement already had thick panels and bracing? 

[jules]

sorry Darren ... I was probably being a bit casual in my terms there when I said "screw"  . Given the mass of a lump of lead I reckon I'd be using every possible means at my disposal to make sure they stayed exactly where they were put [and made the best contact possible]. The idea of a couple of kilos of lead letting go at the wrong moment [in transit?] is too horrible to contemplate.

I also have to totally agree with you about amount of wool. I bought 1.5 kilo and probably had more than half left over. I found advice on how much to use a little hard to come by but it seems that the aim is quite a lot less than it would be possible to squeeze in there. I found the wool staple made it possible to fashion the mass together into a sort of coherent whole [inside the box] that pretty much held it's shape while staying away from the cones but still keeping close to the walls. Alan Hulsebus of Orca recommended a little free air space passage, if I can describe it that way.  Since I put it in there it hasn't moved.

I don't think I'd use wool when there was an open port as it would invite wool moths and create a nasty problem but since you're system doean't have a port [and mine has a fine mesh covering] you wouldn't have that prob..

jules

[Daryl]

Daryl, do you have some figures on the relative qualities of wool etc etc? Could you also expand on your point about volume? As I understand it, the volume of damping material is so insignificantly small that it doesn't count and surely the difference between the vol. of wool and that of fibreglass is going to be even more insignificanter.

Hi Jules,

In the Loudspeaker Design Cookbook (sixth edition, I don't have the seventh) their is a section where the same driver/enclosure combination is measured with various combinations of materials and densities.

A table of measured parameters is provided covering each combination and a frequency response chart is included for each.

Wool is not included in the information but is similar to Polyester/Dacron/Acousta-Stuff.

Fiberglass and acoustic foam are by far superior for absorbtion of sound and increased enclosure compliance.

Sound absorbtion is the most important aspect as you would not want reflections or standing waves within you enclosure.

Fiberglass and acoustic foam are so effective that if you use 100% fiberglass fill or 50% acoustic foam fill enclosure shape is ilrrelavant even cubes with all three dimensions will not exhibit standing waves.

The volume point....

Damping materials increase the compliance of the air in the enclosure which allows a smaller enclosure to be used.

The driver/enclosure in the measurements in the LDCB have a resonant frequency around 80hz so the lowest frequency on the provided charts (20hz) is well into the region where cabinet and suspension compliance are in control of SPL.

If you look at 20hz on all of the charts in the series you can see that 1lb/ft^3 fiberglass and 50% acoustic foam show and increase of about 3db which far better than the others.

Daryl

[DSK]

Fiberglass and acoustic foam are so effective that if you use 100% fiberglass fill or 50% acoustic foam fill enclosure shape is ilrrelavant even cubes with all three dimensions will not exhibit standing waves.

The driver/enclosure in the measurements in the LDCB have a resonant frequency around 80hz so the lowest frequency on the provided charts (20hz) is well into the region where cabinet and suspension compliance are in control of SPL.

If you look at 20hz on all of the charts in the series you can see that 1lb/ft^3 fiberglass and 50% acoustic foam show and increase of about 3db which far better than the others.

Hi Daryl, this is interesting info. I'm no speaker designer but everything I have read suggests using approx 0.5lb of poly/Dacron/etc per cubic foot of enclosure size, generally loosely distributed throughout the enclosure. I've never seen anything recommend 100% fill.

When you say "1lb/ft^3 fiberglass", do you mean to use fibreglass that has a density of 1lb/cu.ft, or do you mean to use 1lb weight of fibreglass per cu.ft. of enclosure size?

If I understand things correctly, increasing mass (thicker MDF panels) will lower the natural resonant frequency, whereas increasing rigidity will increase the natural resonant frequency. By using thicker panel walls and bracing we are therefore increasing mass AND rigidity, so I'm  not sure what it does to the final resonant frequency. But more importantly, the amplitude of resonance is lower (less flex for the same input energy) so the resonance is less destructive. I guess we could view a flexible wooden floor versus a concrete slab as an analogy here.
Applying lead lining adds mass without a corresponding increase in rigidity but supposedly damps some of the resonance in the same way (but less radically) as adding mass loading or damping material to a thin metal component cover.

PS. Anyone reading this should take it with a large grain of salt. I am purely surmising based on what I have read and what (I think) is common sense. 

[Rocket]

Hi Darren,

I have 2 sheets of 'no rez' left over from my speaker project if your interested in purchasing them which
should be enough to line your speakers.

Regards

Rod

[DSK]

I was interested to come across this in an online review of a Focus Audio speaker ....

...That this is a dense box is immediately apparent the first time you try to move it by yourself. It’s 85 pounds and it does not cooperate. The front baffle is constructed of 2" MDF, while the sidewalls are 1" thick, and there are numerous cross-braces in the horizontal plane and one in the vertical. According to Kam Leung, the designer of the FS-888, Focus Audio had experimented with additional damping materials, including lead sheet and bituminous compounds, but found that these deadened the box so much that the resulting sound was sterile. Instead, he preferred to keep the cabinet just slightly resonant, which, he believes, helps retain the emotion and expressiveness that have become Focus Audio hallmarks...

I don't know whether this means that we (or they) like box induced distortion/colouration, or that speaker drivers are designed (or at least auditioned) in boxes and therefore removing the box colouration too much changes what the designers heard and intended for us to hear ????

[DSK]

Hi Darren,

I have 2 sheets of 'no rez' left over from my speaker project if your interested in purchasing them which
should be enough to line your speakers.

Regards

Rod

Thanks Rod, but I honestly don't think that they would be 'massive' enough to provide any real damping of panel resonance on standmount boxes that are 1"+ thick and are also well braced. I think something more like the lead sheeting would be required and I'm not even sure how much benefit they would provide ... hence the original post in this thread.

Could you tell me the weight and size of each No Res sheet?

[Rocket]

Hi Darren,

The link to the 'no rez' product is provided for your info:

http://www.gr-research.com/components/no_rez.htm

I found it easy to use and added a fair bit of mass to the cabinet.  You could probably buy 4 sheets of blackhole5 for $280au which will work well.

Regards

Rod

[Christof]

It seems to me that there are materials that are much more lossy that lead?  We need to prevent the transfer of energy through the cabinet so we must allow the problem energy to turn to heat via friction right as it tries to travel through the material in question, or am I wrong about this?
c-

[Bwanagreg]

I've used roofing felt inside a speaker cabinet to great effect. Cheap, too. I came across the idea from this guy:

http://www.silcom.com/~aludwig/Loudspeaker_construction.html

I put a layer of roofing felt under a sheet of Sonic Barrier, a cheaper version of the "no rez" panel sold by Parts Express.
http://www.partsexpress.com/pe/showdetl.cfm?&DID=7&Partnumber=260-535

[jules]

I was interested to come across this in an online review of a Focus Audio speaker ....

.... but found that these deadened the box so much that the resulting sound was sterile.[/glow] Instead, he preferred to keep the cabinet just slightly resonant, which, he believes, helps retain the emotion and expressiveness that have become Focus Audio hallmarks...

I don't know whether this means that we (or they) like box induced distortion/colouration, or that speaker drivers are designed (or at least auditioned) in boxes and therefore removing the box colouration too much changes what the designers heard and intended for us to hear ????

Darren,

I've seen the idea about deadened cabinets somewhere else too, so I reckon there's something in it.

I think the point might be that the cabinet can act in a way similar to an auto shock absorber on the actual movement of the cone. Hence, if the whole thing is just total "damping" you could actually drain some of the life out of the drivers. In terms of what Christof said above, we don't want a whole lot of driver energy simply being absorbed and converted to heat by the damping material. A parallel might be the way turntables are designed. In a way, it would seem like a good idea to use something like silicon under the vynil but many turntables are solid and make direct contact [in a questionable sort of way] with the black stuff. There's certainly a compromise involved with turntables [what's the Fs of a piece of vynil supported at the edge and the centre] but it comes down to a question of live or dead.

jules