I built a pair of GM's 48" MLTL's for the JX92 along with my brother this past Summer. We built prototypes using cheap plywood to practice our cabinet building skills and tune the design before committing to version that can be placed in view by my wife.
After some tuning and adjustment we've become very happy with the sound and have been buildling cabinets out of African mahogany. Probably not a very green choice on our part. We've been working on the boards for over a month and are close to gluing the cabinets.
Recently I was researching solid wood for speaker cabinets and discovered that most opinions by folks on the forum are strongly against solid wood cabinets for loudspeakers.
My question to the forum, now that the only practical recourse is to follow through on the build and learn from it, is there anything we might do to compensate at this stage of the build to reduce the negative impact of the material properties of solid African mahogany vs. BB ply?
BTW, one of the reasons we didn't go with BB ply for the finished version is we have no experience with veneer and I was intimidated to try and learn how to work with it. That, and the fact that the milling and joining of good hardware is somewhat familiar. I have nothing against BB ply and I notice our original ply seems less "lively" than the mahogany.
Thanks,
Chris
After some tuning and adjustment we've become very happy with the sound and have been buildling cabinets out of African mahogany. Probably not a very green choice on our part. We've been working on the boards for over a month and are close to gluing the cabinets.
Recently I was researching solid wood for speaker cabinets and discovered that most opinions by folks on the forum are strongly against solid wood cabinets for loudspeakers.
My question to the forum, now that the only practical recourse is to follow through on the build and learn from it, is there anything we might do to compensate at this stage of the build to reduce the negative impact of the material properties of solid African mahogany vs. BB ply?
BTW, one of the reasons we didn't go with BB ply for the finished version is we have no experience with veneer and I was intimidated to try and learn how to work with it. That, and the fact that the milling and joining of good hardware is somewhat familiar. I have nothing against BB ply and I notice our original ply seems less "lively" than the mahogany.
Thanks,
Chris
Thanks Dave. Structural integrity and cabinet resonance seemed like the two most oft quoted concerns working with solid wood, your reply is fully in line with that.
I'm wonder if we apply silicon caulk the internal seams if that would help maintains the integrity of the cabinet better - functionally at least? Naturally that won't hold the wood in place.
We're using rabbet joints for a little added strength. We used screws on the prototype but did not plan to use them on the finished versions to improve the appearance. My brother picked out the wood glue. One of the Gorillia glue products that he's used on some mahogony guitar cabinets. Those cabinets seem to have held up well so far. We live in Vermont.
Your comments are appreciated.
Thanks,
Chris
I'm wonder if we apply silicon caulk the internal seams if that would help maintains the integrity of the cabinet better - functionally at least? Naturally that won't hold the wood in place.
We're using rabbet joints for a little added strength. We used screws on the prototype but did not plan to use them on the finished versions to improve the appearance. My brother picked out the wood glue. One of the Gorillia glue products that he's used on some mahogony guitar cabinets. Those cabinets seem to have held up well so far. We live in Vermont.
Your comments are appreciated.
Thanks,
Chris
Hi Chris
It is possible to worry too much(not that I'm guaranteeing your build)....
I used to build long case clocks(from trees that I'd chosen and had planked and kiln dried) from mid eighties to late nineties and there is still one I have in the family which hasn't moved at all(nearly 25 years).......In my experience the timber doesn't move at all if you seal inside and out(shellac, french polish or spirit based wood sealer will do).
although this is limited experience( I built about 8 of these in all as it was just a weekend hobby) I have been told by many cabinet makers that the secret of longevity is thoroughly sealing.
The other menace is varying temp and humidity in the environment they live. Controlling that will increase stability.
Having said that, all my loudspeakers are BB ply which I would advise for your next build. I don't veneer mine but spend more time choosing boards with a good, figured face.
Ed
It is possible to worry too much(not that I'm guaranteeing your build)....
I used to build long case clocks(from trees that I'd chosen and had planked and kiln dried) from mid eighties to late nineties and there is still one I have in the family which hasn't moved at all(nearly 25 years).......In my experience the timber doesn't move at all if you seal inside and out(shellac, french polish or spirit based wood sealer will do).
although this is limited experience( I built about 8 of these in all as it was just a weekend hobby) I have been told by many cabinet makers that the secret of longevity is thoroughly sealing.
The other menace is varying temp and humidity in the environment they live. Controlling that will increase stability.
Having said that, all my loudspeakers are BB ply which I would advise for your next build. I don't veneer mine but spend more time choosing boards with a good, figured face.
Ed
Dave, I see. I thought it would be the joints that would fail. If a board cracks I'll get some experience figuring out how to repair that. The mahogany in my brother's guitar amp cabinets has held up well so far.
Ed, for sure we are planning to give an oil finish to the outside. I had not considered sealing the inside surfaces. That's a simple enough thing to do to try and improve the stabilty of thw wood. Thanks for that information.
Dave, you're familiar with the GM MLTL design based on the Jordan JX92. Can you suggest where I might buy some acoustic felt and speaker gasket material. I didn't use either on our prototypes - couldn't find it.
Thanks all,
Chrsi
Ed, for sure we are planning to give an oil finish to the outside. I had not considered sealing the inside surfaces. That's a simple enough thing to do to try and improve the stabilty of thw wood. Thanks for that information.
Dave, you're familiar with the GM MLTL design based on the Jordan JX92. Can you suggest where I might buy some acoustic felt and speaker gasket material. I didn't use either on our prototypes - couldn't find it.
Thanks all,
Chrsi
Not that familiar. We built a set of the triangular ones for a local. I sold my JX92 because i didn't like them.
Gasket material -- get some neoprene draft exclusion tape. I get it at Home Depot.
I've started using the 1/2" recycled cotton felt from bonded logic Natural Cotton Fiber Insulation, Natural Cellulose Insulation
Bob at CSS sells it in more accessible quantities.
dave
Cross grain joints are a problem with solid wood, where the wood on one side of the joint (the end grain) will expand and contract the most as opposed to the wood on the other side of the joint (the edge grain) will expand and contract very, very little.
You can ensure the wood is as dry as possible by leaving it in a heated, dry space for some time (weeks). Then, once the build is finished, apply sealer (not oil) to the inside and outside. Something that is virtually impervious to moisture is polyurethane - 2-3 coats will go a long way to minimizing seasonal movement.
Glued together the last cabinet tonight. Will be sealing the interior surfaces based on feedback. Will be ironic for sure if the crude ply test mules sound better than their mahogany competitiors. In any case, we will be sealing the interior surfaces. Thanks all for comments and suggestion. They sure are looking good though. Picked up the granite bases tonight too.
You should be fine. Mahogany (including african) is about the most stable of all hardwoods, and besides there are no wide cross grain spans with that design. Shellac makes the best sealer, but mix your own or get Zinsser 'Sealcoat'. Old canned shellac sometimes won't dry.
People generally won't recommend solid wood because, apart from stability issues, a speaker cabinet is not supposed to be resonant...
I prefer mahogany with the traditional garnet/ruby shellac french polished finish, but it's hard to do.
People generally won't recommend solid wood because, apart from stability issues, a speaker cabinet is not supposed to be resonant...
I prefer mahogany with the traditional garnet/ruby shellac french polished finish, but it's hard to do.
properly glued boards will not split at the glue joint. If they do the wood usually rips right beside the glue joint ie the wood fibers will tear. My 70 year old piano sound board is not finished on either side and is still holding up. As was said else where varnish inside and out to reduce the effects of moisture and humidity. End grain joints are tricky a trip to a library wood help but you have the speakers finished already. My wife put a f'ining house plant on my Bailey/Rodgers TL's and was nearly cause for divorce. She still doesn't get it. The wood moves bends and stretches with the seasons. Getting back to the piano it sounds different in the morning in the afternoon and in the evening and also different as the seasons change and whether the sun is shining in the room or not.
Hi multisync
I was told many moons ago when I bought my first expensive upright(by the piano restorer that sold it to me) that if you keep a bowl of water on the floor inside the piano it will minimise any movement and sound variation......
it worked for me.......but I'm probably venturing into egg-sucking territory
Ed
I was told many moons ago when I bought my first expensive upright(by the piano restorer that sold it to me) that if you keep a bowl of water on the floor inside the piano it will minimise any movement and sound variation......
it worked for me.......but I'm probably venturing into egg-sucking territory
Ed
Must have been the same guy who tunes/repairs mine. There is a small plastic bowl in our piano as well. Doesn't help that much. Where we live the humidity in the summer can hit 90% and low teens in the winter. Doesn't help the piano much. I was also told to keep it away from an outside wall as the outside walls are colder in the winter and not enough warm air circulates behind the upright. He also doesn't bother tuning in the winter till way into the heating season. Too rapid changes in house humidity. He says it takes a while for the house to dry out from the summer to the winter. The wide difference in sound gives me an excuse for my poor playing ability. "It's not me its the humidity". Hey maybe those cable listener's can blame the humidity on the difference in the sound quality of cables. As the humidity goes up down it will affect the dielectric absorption between the cables etc etc etc. Cloth cables sound different because the silk absorbs humidity etc etc etc.
sounds like a nightmare with those variations......I've also got a yamaha p80 stage piano which I've come to like very much, its constant and it saves a packet on tuners fees, Oh and its easier to get to gigs than the kirkman....if you havn't tried one of these I can thoroughly recommend them.
apologies for the OT Chris......
apologies for the OT Chris......
I'm with some proper sealing the mahogany will hold up OK. Your finish sounds interesting. Would be interested to see an image of that.
There has been very little reply to the issue of cabinet resonance. I am guessing perhaps nobody has ever committed this design to either a solid wood cabinet or not to mahogany. I defintely can tell the mahogany is more "lively" than the cheap, home depot birch ply we built the prototypes from. The cabinets are assembled now except for the top and bottom pieces. While it's still in a easily accessible state we my brother and I and considering the addition of bracing to dampen out the resonances better. We never considered that with the ply test mules.
My piano is electric. The old upright died a long time ago. You can guess, the humidiy did it's job over the years. But if the speakers last as long as the old upright did, I'll be long dead before they fall apart at least.
Chris
There has been very little reply to the issue of cabinet resonance. I am guessing perhaps nobody has ever committed this design to either a solid wood cabinet or not to mahogany. I defintely can tell the mahogany is more "lively" than the cheap, home depot birch ply we built the prototypes from. The cabinets are assembled now except for the top and bottom pieces. While it's still in a easily accessible state we my brother and I and considering the addition of bracing to dampen out the resonances better. We never considered that with the ply test mules.
My piano is electric. The old upright died a long time ago. You can guess, the humidiy did it's job over the years. But if the speakers last as long as the old upright did, I'll be long dead before they fall apart at least.
Chris
Cabinet resonance: ideally it should not be resonant except for the driver and the air column inside of it. The conventional approach is to make the cabinet as inert as possible. To do this choose high mass, high stiffness and high damping materials.
Now that said, there are many people who feel that making the cabinet intentionally resonant can have some benefit. The general line of thought is that something is inherently lost in the recording process and a somewhat 'live' cabinet can lead to a more lifelike illusion of music than the conventional approach.
I don't really take sides on this. Some of the best speakers i've made were large TQWT constructed of very light 1/4" plywood. OTOH, I've also chopped up some dismal failures using this approach. I've found that most of the time going for rigid and well damped is much more likely to lead to success. You may want to listen to them as is. And then screw and glue some reinforcement to the insides to hear the difference.
AFA french polish, any good finishing book will explain the process. Traditionally mahogany was done in either 'red polish', or stained dark brown and then finished. Not a speaker but here's the color:
Now that said, there are many people who feel that making the cabinet intentionally resonant can have some benefit. The general line of thought is that something is inherently lost in the recording process and a somewhat 'live' cabinet can lead to a more lifelike illusion of music than the conventional approach.
I don't really take sides on this. Some of the best speakers i've made were large TQWT constructed of very light 1/4" plywood. OTOH, I've also chopped up some dismal failures using this approach. I've found that most of the time going for rigid and well damped is much more likely to lead to success. You may want to listen to them as is. And then screw and glue some reinforcement to the insides to hear the difference.
AFA french polish, any good finishing book will explain the process. Traditionally mahogany was done in either 'red polish', or stained dark brown and then finished. Not a speaker but here's the color:
An externally hosted image should be here but it was not working when we last tested it.
unfortunately high mass fights the high stiffness. Low mass, high stiffness works better.
What you want is an arrangement of materials & box design such that panel resonances are high in frequency & high in Q.
dave
Speakers are finally completed
After a lot of time spent working finishing these speaker cabinets I can finally say they are done. My first wood finishing project since highschool shop class. They didn't come out too bad. My wife likes them well enough for me to use them in the man room.
The wood is african mahogany and we put them on granite bases so they wouldn't fall over and kill the cat (my s.o.'s phobia, not mine).
After a lot of time spent working finishing these speaker cabinets I can finally say they are done. My first wood finishing project since highschool shop class. They didn't come out too bad. My wife likes them well enough for me to use them in the man room.
The wood is african mahogany and we put them on granite bases so they wouldn't fall over and kill the cat (my s.o.'s phobia, not mine).
Attachments
Looking good!
As was mentioned, african mahogany was a good pick as it is quite stable. To elaborate on the discussion about wood expansion, the issue is that wood expands/contracts more in width (across grain) than in length (with grain). So the cracking problem arises when you don't match edges. The long glue joints between the front, sides, and back of these speakers will be fine. Problems may occur depending on how you attached the base and top. The base should be attached to allow movement - for example just with caulking, as the granite won't expand/contract at the same rate as the wood. If you used a solid wood piece for the top, then one set of joints on opposing sides may cause problems. E.g., if the grain on the top piece runs from side to side on the speaker, the joints between the top and sides will be ok, (end grain meeting end grain) but the front and back of the speaker are end grain meeting the long grain of the top. The front and back will expand more in width than the top does in length along the joint edge as the weather warms up and humidity rises.
My suggestion for a solid wood top on a solid wood speaker would be to rabbet the top edge of the top, and then dado the front, back and sides to accept the top. (See the diagram in the first link below for the general idea).
The top should be slightly smaller in the cross-grain direction than the distance between the insides of the dados to allow movement. If you build in winter with dry wood, you need to allow more space as the top will expand with rising humidity. Build in summer when the humidity is high, and you can fit the piece more snugly as it will contract in winter.
Seal the joint inside the box with a caulk that stays flexible.
There is special hardware for floating panels. To keep a floating panel from moving off centre or rattling there are these:
Panel Barrels - Lee Valley Tools
Typically used in cupboard doors with solid wood centre panels. Notice in the picture that the panel will move the same as the sides of the frame (grain is running in same direction) but will expand/contract (in width, across grain) more than the top piece of the frame (grain running side to side relative to panel).
Another way to attach a solid panel is shown here:
Expansion Washers - Lee Valley Tools
Note the cross-grain direction of the panel matches the direction of the slot in the washer. As the panel expands/contracts across the grain, the screw is able to slide in the washer. If you had screwed the brace to the panel in the normal manner, it would constrict this cross-grain movement and the panel would be more likely to split.
If you want a more complete explanation of wood movement, this book is the reference work:
Understanding wood: a craftsman's ... - Google Books
All that said, given the stability of mahogany and the relative small cross-grain width of the sides, front, and back on your speaker, they may be fine if you aren't in a place where the difference between summer and winter humidity levels is dramatic. Here's hoping!
bb
As was mentioned, african mahogany was a good pick as it is quite stable. To elaborate on the discussion about wood expansion, the issue is that wood expands/contracts more in width (across grain) than in length (with grain). So the cracking problem arises when you don't match edges. The long glue joints between the front, sides, and back of these speakers will be fine. Problems may occur depending on how you attached the base and top. The base should be attached to allow movement - for example just with caulking, as the granite won't expand/contract at the same rate as the wood. If you used a solid wood piece for the top, then one set of joints on opposing sides may cause problems. E.g., if the grain on the top piece runs from side to side on the speaker, the joints between the top and sides will be ok, (end grain meeting end grain) but the front and back of the speaker are end grain meeting the long grain of the top. The front and back will expand more in width than the top does in length along the joint edge as the weather warms up and humidity rises.
My suggestion for a solid wood top on a solid wood speaker would be to rabbet the top edge of the top, and then dado the front, back and sides to accept the top. (See the diagram in the first link below for the general idea).
The top should be slightly smaller in the cross-grain direction than the distance between the insides of the dados to allow movement. If you build in winter with dry wood, you need to allow more space as the top will expand with rising humidity. Build in summer when the humidity is high, and you can fit the piece more snugly as it will contract in winter.
Seal the joint inside the box with a caulk that stays flexible.
There is special hardware for floating panels. To keep a floating panel from moving off centre or rattling there are these:
Panel Barrels - Lee Valley Tools
Typically used in cupboard doors with solid wood centre panels. Notice in the picture that the panel will move the same as the sides of the frame (grain is running in same direction) but will expand/contract (in width, across grain) more than the top piece of the frame (grain running side to side relative to panel).
Another way to attach a solid panel is shown here:
Expansion Washers - Lee Valley Tools
Note the cross-grain direction of the panel matches the direction of the slot in the washer. As the panel expands/contracts across the grain, the screw is able to slide in the washer. If you had screwed the brace to the panel in the normal manner, it would constrict this cross-grain movement and the panel would be more likely to split.
If you want a more complete explanation of wood movement, this book is the reference work:
Understanding wood: a craftsman's ... - Google Books
All that said, given the stability of mahogany and the relative small cross-grain width of the sides, front, and back on your speaker, they may be fine if you aren't in a place where the difference between summer and winter humidity levels is dramatic. Here's hoping!
bb
- Status
- This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.