I have decided to build Ron's Dallas II horns with FE206E. I have a question regarding which type of plywood to use.
In particular, after some search, I managed to find two types of (good quality) 18 mm (0.700") plywood: the first is made of birch (no Baltic I assume, the seller told me that it is Russian) and the second one is made of okoume ( a tropical wood).
Is there a difference on the type of wood or anyone could do the job? I asked both sellers insistently and they both asuured me that the plywoods they supply are void free.
Any help on making my decision is welcomed.
Evangelos
In particular, after some search, I managed to find two types of (good quality) 18 mm (0.700") plywood: the first is made of birch (no Baltic I assume, the seller told me that it is Russian) and the second one is made of okoume ( a tropical wood).
Is there a difference on the type of wood or anyone could do the job? I asked both sellers insistently and they both asuured me that the plywoods they supply are void free.
Any help on making my decision is welcomed.
Evangelos
Tropical wood is harder, and therefore more rigid and reflects high frequencies better.
Birch is "shallower" and I assume it damps vibrations and highs better, at the expense of less rigidity.
I don't know which is the best for horns, I never built any.
May I suggest 18mm is a little weak for a 20cm driver ? I'd rather use 22 or 25mm.
My favorite material is MDF because it is easy to finish, and because of its ultra-fine particle structure, it allows a smooth cutting and assembling with no micro-holes that could affect sealing. It is not ultra rigid though, but very heavy so I assume it damps vibrations well. I think its very smooth surface doesn't helps damping highs, and I'm aware it isn't the best choice for speakers.
Using it in strong thicknesses is recommended, and this material is quite cheap.
Just my 0.00000000002€
Birch is "shallower" and I assume it damps vibrations and highs better, at the expense of less rigidity.
I don't know which is the best for horns, I never built any.
May I suggest 18mm is a little weak for a 20cm driver ? I'd rather use 22 or 25mm.
My favorite material is MDF because it is easy to finish, and because of its ultra-fine particle structure, it allows a smooth cutting and assembling with no micro-holes that could affect sealing. It is not ultra rigid though, but very heavy so I assume it damps vibrations well. I think its very smooth surface doesn't helps damping highs, and I'm aware it isn't the best choice for speakers.
Using it in strong thicknesses is recommended, and this material is quite cheap.
Just my 0.00000000002€
I've read many posts that recommend staying away from MDF, expecially with horns.
The plywoods you're looking at are a much, much better choice. However, I'm not sure which is better. Hopefully some others will chime in. I recall reading that the Russian plys are pretty good, but not positive on that one.
Also, many recommend using plys that have many layers. Often the better plywoods use 9 or more layers and are void free for the most part. It seems that the plys that used to be void free are no longer guaranteed.
A little more on MDF, one other reason many are staying away from it is that the dust is not only hard to clean up, it's also quite toxic. (Just a side note.)
The plywoods you're looking at are a much, much better choice. However, I'm not sure which is better. Hopefully some others will chime in. I recall reading that the Russian plys are pretty good, but not positive on that one.
Also, many recommend using plys that have many layers. Often the better plywoods use 9 or more layers and are void free for the most part. It seems that the plys that used to be void free are no longer guaranteed.
A little more on MDF, one other reason many are staying away from it is that the dust is not only hard to clean up, it's also quite toxic. (Just a side note.)
youyoung21147,
Thanks for your reply.
The Dallas II cabinet is designed for 18 mm material. Therefore, it's not an issue of choosing a thicker material.
Regarding MDF vs. plywood, much debate has been taken place in this and other fora and there seems to be a general consensus that, for a BLH, the material of choice is plywood. I had been thinking of it for some time and ended up going for plywood.
Regards,
Evangelos
Thanks for your reply.
The Dallas II cabinet is designed for 18 mm material. Therefore, it's not an issue of choosing a thicker material.
Regarding MDF vs. plywood, much debate has been taken place in this and other fora and there seems to be a general consensus that, for a BLH, the material of choice is plywood. I had been thinking of it for some time and ended up going for plywood.
Regards,
Evangelos
Plywood!
Both plywood types you mention should be infinitely better than MDF.
In Canada birch plywood is sold as Russian plywood. It is very good for horns, quite dense, no void and a real pleasur to work with.
I built two horns with MDF and two identical horns with plywood and the plywood horns a much much better (sound is more focussed, more lively).
Both plywood types you mention should be infinitely better than MDF.
In Canada birch plywood is sold as Russian plywood. It is very good for horns, quite dense, no void and a real pleasur to work with.
I built two horns with MDF and two identical horns with plywood and the plywood horns a much much better (sound is more focussed, more lively).
Everybody seems to like plywood better.
I don't build my cabinets myself, a friend who learns carpenting does it for me and he likes working with MDF more, though I'd prefer him to use plywood, at least to give it a try.
I'm quite curious to know why plywood is better, I never found any explanation to that? Do you guys have any ?
I don't build my cabinets myself, a friend who learns carpenting does it for me and he likes working with MDF more, though I'd prefer him to use plywood, at least to give it a try.
I'm quite curious to know why plywood is better, I never found any explanation to that? Do you guys have any ?
Energy
MDF stores energy (in the form of damping), some is transformed in heat and some is transferred back to air as vibration.
Plywood stores less energy (it is stiffer)
Knock on MDF and knock on plywood of same thickness, you will get a higher pitch sound on plywood, indicating a higher res. frequency.
MDF stores energy (in the form of damping), some is transformed in heat and some is transferred back to air as vibration.
Plywood stores less energy (it is stiffer)
Knock on MDF and knock on plywood of same thickness, you will get a higher pitch sound on plywood, indicating a higher res. frequency.
I seem to recall that MDF resonates circa 1000Hz, whilst plys vary with type -average I believe is around 2400Hz, but don't take those as gospel! I tend to use MDF myself, a) for cost reasons, and b) because of the greater consistancy possible with MDF -no voids etc. A good plywood of equal size is around 3 times stiffer in compression and tension than MDF, so probably a combination of the two materials, a la Lynn Olson's Ariel would work best for regular cabinets. For a horn, i'd go with the ply.
Solid hardwoods (and some softwoods like pine when properly dried out) are also extremely good, but you have to be a real craftsman to know what you're doing with those -it's not just a matter of selecting the correct wood. It has to be aged properly, has to have the correct grain etc etc etc., otherwise, you're going to get the sonic signiture of the cabinet material, which for most of us, is not a good thing, unless you're designing a speaker in the same way as you'd design a new instrument. If you're not a violin maker or have a similar level of knowledge to Terry Cain, best avoid I reckon because, unless you're very lucky, the results you get will be inferior to those if you'd taken the easier (and much cheaper route.) I don't pretend to have that knowledge or ability, hense my liking for MDF. Oh, and chipboard by the way. Not to be sniffed at -it's much better than people believe, and it's spectacualrly cheap, which is nice.
Just to add my own warning to that mentioned above: MDF dust is carcinogenic, so make sure you've got a very good filter-mask on when working with it.
Best
Scott
Solid hardwoods (and some softwoods like pine when properly dried out) are also extremely good, but you have to be a real craftsman to know what you're doing with those -it's not just a matter of selecting the correct wood. It has to be aged properly, has to have the correct grain etc etc etc., otherwise, you're going to get the sonic signiture of the cabinet material, which for most of us, is not a good thing, unless you're designing a speaker in the same way as you'd design a new instrument. If you're not a violin maker or have a similar level of knowledge to Terry Cain, best avoid I reckon because, unless you're very lucky, the results you get will be inferior to those if you'd taken the easier (and much cheaper route.) I don't pretend to have that knowledge or ability, hense my liking for MDF. Oh, and chipboard by the way. Not to be sniffed at -it's much better than people believe, and it's spectacualrly cheap, which is nice.
Just to add my own warning to that mentioned above: MDF dust is carcinogenic, so make sure you've got a very good filter-mask on when working with it.
Best
Scott
You should build with the Okoume because then you would be the only Okoume Dallas in the world.
I built mine with three sheets of .500" void free russian Baltic Birch 5'X5' sheething. $21.00usd a sheet and all I could find in my area. I did alot of math to keep the sound path the same size so if you can get .700" do it.
I cut four 17.7" X 48" panels and drew the cart/chord points on the wood. then I measured the drawing to make a cut list. Then I nested the pieces to 49" X 11.040" panels. Would you like me to post the cut list ?
I built mine with three sheets of .500" void free russian Baltic Birch 5'X5' sheething. $21.00usd a sheet and all I could find in my area. I did alot of math to keep the sound path the same size so if you can get .700" do it.
I cut four 17.7" X 48" panels and drew the cart/chord points on the wood. then I measured the drawing to make a cut list. Then I nested the pieces to 49" X 11.040" panels. Would you like me to post the cut list ?
O.K thanks for the explanation.
I assumed MDF was toxic and I don't like dust anyway, always nocive. Now I'm sure it's dangerous lol
I'll tell my friend about this next time he builds something with MDF, though I suppose (I hope) he already protects himself.
It's very interesting for me to learn about materials : I always thought that a lower resonnant frequency meant a more discrete box sound, which would be less noticed at lower freq. I never guessed it meant a bigger energy storage (which is logical in fact lol
)
When I knock on wood, I mainly take care to hear the weakest pitch to determinate the wood density/thickness. Now I will test the frequency also. I have no sample of ply or MDF to make the test right now !
Thanks guys !
Be sure my next projects (that are not begun) will be done with plywood
I assumed MDF was toxic and I don't like dust anyway, always nocive. Now I'm sure it's dangerous lol
I'll tell my friend about this next time he builds something with MDF, though I suppose (I hope) he already protects himself.
It's very interesting for me to learn about materials : I always thought that a lower resonnant frequency meant a more discrete box sound, which would be less noticed at lower freq. I never guessed it meant a bigger energy storage (which is logical in fact lol
)When I knock on wood, I mainly take care to hear the weakest pitch to determinate the wood density/thickness. Now I will test the frequency also. I have no sample of ply or MDF to make the test right now !
Thanks guys !
Be sure my next projects (that are not begun) will be done with plywood
squalor said:
squalor,
Thanks for the tips. Both types I found are 0.700" thickness, so there seems it's an easier job with measurements.
Also, I forgot to mention that both are about the same price: around 50 euros for a sheet of 4' x 8'.
Jeremy was kind enough to e-mail me his, modified to mm, plans of the Dallas II, which also include the cut list.
Regards,
Evangelos
youyoung21147 said:O.K thanks for the explanation.
I assumed MDF was toxic and I don't like dust anyway, always nocive. Now I'm sure it's dangerous lol
I'll tell my friend about this next time he builds something with MDF, though I suppose (I hope) he already protects himself.
It's very interesting for me to learn about materials : I always thought that a lower resonnant frequency meant a more discrete box sound, which would be less noticed at lower freq. I never guessed it meant a bigger energy storage (which is logical in fact lol
When I knock on wood, I mainly take care to hear the weakest pitch to determinate the wood density/thickness. Now I will test the frequency also. I have no sample of ply or MDF to make the test right now !
Thanks guys !
Be sure my next projects (that are not begun) will be done with plywood
If you ever want to take a walk on the wild side, here's something to think about. Russ Andrews suggests than energy storage in cabinets is a bigger problem than people realise generally -he suggested a thin-wall design of laminate plaster-board. Our good friend Nuuk on this forum (runs Decibel Dungeon too) then decided to go even further, and try making a cabinet out of polystyrene sheeting.
At his suggestion, so have I. I have a pair of TQWTs, made entirely out of polystyrene, baring a small amount of MDF for a frame the driver is mounted to that are currently lurking in the garage -i use them for testing. The sound is in many ways extraordinary. Polystyrene sheet is quite cheep and fairly easy to work with too, so it's a thought. Just remember: polystyrene glue does not stick polystyrene to polystyrene!
Cheers & good luck with the next projects everyone
Scott
With great difficulty!
Seriously, it's a bit of a pain. Araldyte works quite well, but it can get a bit expensive when gluing large panels! I don't know if you've an interest in sports cars, but an amusing story: the UK company Caterham, when they started styling a new car (which became the short-lived 21) bought a load of polystyrene blocks to attach to a chassis, the intention being to take a chain-saw to it, to shape the stuff into the final car-body style. Then they found out that polystyrene cement doesn't work too well at sticking the stuff to itself! As soon as the saw was applied to one end, the other end of the 'car' kept falling off! Odd, as when we were kids, it worked fine for plastic model kits, but there you have it. I've also found that a mixture of acrylic glue with polystyrene cement added to it works quite well.
I haven't got a digital camera at present unfortutunately, so I've no postable pictures of my polystyrene pipes. They're not in the best of aesthetic shape at present anyway, living as they do in the garage with the spiders for testing things. No reflection on the capabilities of their build material -just that they had the cheapest, most expendable drivers in them, and I'd run out of room inside! Basically, they look like any Lowther Club of Norway Voigt Pipes (deliberate due to the low driver Q -it needs all the gain possible from the pipe, hense then normally avoided So=0 design) with a 3"x2" circular port).
If you want to test the concept out yourself, give it a whirl: buy some cheap-full range jobs from somewhere like CPC or PartsXpress, and some sheeting from the local DIY merchant. Following Nuuk's lead, I made a frame for the drivers to attach to out of MDF, then added the panels. It works very well -I was impressed. The open baffles I'm currently fooling with use polystyrene extensively -once I've completed them, I'll make sure some pictures are posted -I'll grab a friend with a decent camera and get her to take some shots. In the meantime, you can at least see Nuuk's here:
http://myweb.tiscali.co.uk/nuukspot/decdun/project.speakers2.html
Cheers
Scott
Seriously, it's a bit of a pain. Araldyte works quite well, but it can get a bit expensive when gluing large panels! I don't know if you've an interest in sports cars, but an amusing story: the UK company Caterham, when they started styling a new car (which became the short-lived 21) bought a load of polystyrene blocks to attach to a chassis, the intention being to take a chain-saw to it, to shape the stuff into the final car-body style. Then they found out that polystyrene cement doesn't work too well at sticking the stuff to itself! As soon as the saw was applied to one end, the other end of the 'car' kept falling off! Odd, as when we were kids, it worked fine for plastic model kits, but there you have it. I've also found that a mixture of acrylic glue with polystyrene cement added to it works quite well.
I haven't got a digital camera at present unfortutunately, so I've no postable pictures of my polystyrene pipes. They're not in the best of aesthetic shape at present anyway, living as they do in the garage with the spiders for testing things. No reflection on the capabilities of their build material -just that they had the cheapest, most expendable drivers in them, and I'd run out of room inside! Basically, they look like any Lowther Club of Norway Voigt Pipes (deliberate due to the low driver Q -it needs all the gain possible from the pipe, hense then normally avoided So=0 design) with a 3"x2" circular port).
If you want to test the concept out yourself, give it a whirl: buy some cheap-full range jobs from somewhere like CPC or PartsXpress, and some sheeting from the local DIY merchant. Following Nuuk's lead, I made a frame for the drivers to attach to out of MDF, then added the panels. It works very well -I was impressed. The open baffles I'm currently fooling with use polystyrene extensively -once I've completed them, I'll make sure some pictures are posted -I'll grab a friend with a decent camera and get her to take some shots. In the meantime, you can at least see Nuuk's here:
http://myweb.tiscali.co.uk/nuukspot/decdun/project.speakers2.html
Cheers
Scott
About those enclosures that use thin walls, I saw a commercial-artisanal design that used naval techniques to make a bass-reflex cabinet with curved sides and 3mm thick wood panels. Quite impressive to see from the inside. I got no review on this speaker, apart from the manufacturer's point of view off course !
If I find the link again, I'll post it for you to see.
If I find the link again, I'll post it for you to see.
I believe the use of plywood for horns is an artifact from the good old days when we built Lowther horns using thin sheets of plywood.
The enclosure colouration added a certain signature to the sound, the driver/cabinet combo sounded more pleasing.
In general, heavy materials store energy longer, causing some kind of time-smearing. However, it takes more energy to exite in the first place.
Concrete is good for low freq. but store too much energy for mid/high freq. where it rings like a bell...
The trick is to use different materials for low/high freq. Ideally materials with equal density glued together or some kind of constrained layer construction.
For a full range horn I would go for high quality plywood inside the cabinet, especially in the high pressure region behind the driver and MDF for outside panels.
BTW, rigidity of a wooden panel has nothing to do with "reflecting high frequencies", it simply shift the resonance higher in freq. where it easy to damp effectively.
Cheers
JB
The enclosure colouration added a certain signature to the sound, the driver/cabinet combo sounded more pleasing.
In general, heavy materials store energy longer, causing some kind of time-smearing. However, it takes more energy to exite in the first place.
Concrete is good for low freq. but store too much energy for mid/high freq. where it rings like a bell...
The trick is to use different materials for low/high freq. Ideally materials with equal density glued together or some kind of constrained layer construction.
For a full range horn I would go for high quality plywood inside the cabinet, especially in the high pressure region behind the driver and MDF for outside panels.
BTW, rigidity of a wooden panel has nothing to do with "reflecting high frequencies", it simply shift the resonance higher in freq. where it easy to damp effectively.
Cheers
JB
kenev said:
Water based contact glue, i.e. Copydex is the stuff to use.
Rub it into both surfaces to ensure it gets a good hold of the beads, dry and assemble (make sure you've got it aligned right, you'll never get it apart!)
You can get it by the gallon.
I must say that I am surprised by this application though as poly sheet will reverbarate like a b*tch due to it's closed cell structure.
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