I made a pair of the popular "Viech" horns with and for a friend. They were done in MDF, with two extra braces. Considering that the Beyma fr driver in it costs only around $35, we were hesitant to use expensive quality plywood.
Well, we really can't complain about the result. The horn works as designed, it renders the bass tones dry and precisely (within the limitation of the design). So, based on this experience alone I have no hesitations using it again for other horn builds. I also made 2 pairs of bass reflex boxes out of mdf (always with bracing and damping), and one out of pinewood. Only the pinewood enclosure was a bit disappointing, it added its own sound to the music, I much prefer the "dead" character of MDF.
Well, we really can't complain about the result. The horn works as designed, it renders the bass tones dry and precisely (within the limitation of the design). So, based on this experience alone I have no hesitations using it again for other horn builds. I also made 2 pairs of bass reflex boxes out of mdf (always with bracing and damping), and one out of pinewood. Only the pinewood enclosure was a bit disappointing, it added its own sound to the music, I much prefer the "dead" character of MDF.
I'm not surprised the pine sounded bad, it's allmost impossible to get good quality pine these days, in the UK at any rate, the good stuff was all cut down by the Victorians. In my experience real wood can allways be a problem because it expands and contracts with moisture and can warp.
I think people get a bit snooty about MDF because it's a cheap material, but it definately has it's uses, though you wouldn't whant to make a boat out of it.
I think people get a bit snooty about MDF because it's a cheap material, but it definately has it's uses, though you wouldn't whant to make a boat out of it.
I'm very happy with the Baltic Birch, great results and long lasting
Birch - Wikipedia, the free encyclopedia
Birch - Wikipedia, the free encyclopedia
If you actually measure as Klang & Ton as well as Hobby & HiFi have done there is very little difference between MDF Plywood and MDF. Bracing and damping make all the difference. MDF and chipboard are brittle, hevy and is more affected by water than good quality ply. So sure for PA ply is the way to as per JBL et al. However hone Hifi speakers are not often dropped of trucks lugged around on a daily basis and sometimes left out in the rain, at least not mine 
I once built speaker of Baltic Birch, well braced nice sounding and good looking, but had I built them in MDF they would have sounded the same.
I once built speaker of Baltic Birch, well braced nice sounding and good looking, but had I built them in MDF they would have sounded the same.
not another MDF vs. BB ply hijack...
Please stop this diversion from the original thread. Sorry to all as I may have "hijacked" without intending to do so.
All "pro" MDF folks: great, keep your MDF, and don't follow Totem's example, and don't finish the interior and exterior surfaces with paint and primer or veneer, or whatever. It won't matter.
My comments (if you read into them) suggests that the poor qualities of MDF for loudspeakers can be mitigated by the use of techniques as performed by Totem Acoustics of Montreal, Quebec. The Totem loudspeakers are great examples of what can be done with MDF to make a very good sounding loudspeaker. Regarding bracing, use whatever you like.
The use of BB ply or similar (assuming a total density lower than that of the MDF ) means for a given strength and dimensional stability, the panels can be thinner. If thinner (and obviously lighter in this example), then the energy stored in the panels can be reduced, as can the bracing. That's it.
Please stop this diversion from the original thread. Sorry to all as I may have "hijacked" without intending to do so.
All "pro" MDF folks: great, keep your MDF, and don't follow Totem's example, and don't finish the interior and exterior surfaces with paint and primer or veneer, or whatever. It won't matter.
My comments (if you read into them) suggests that the poor qualities of MDF for loudspeakers can be mitigated by the use of techniques as performed by Totem Acoustics of Montreal, Quebec. The Totem loudspeakers are great examples of what can be done with MDF to make a very good sounding loudspeaker. Regarding bracing, use whatever you like.
The use of BB ply or similar (assuming a total density lower than that of the MDF ) means for a given strength and dimensional stability, the panels can be thinner. If thinner (and obviously lighter in this example), then the energy stored in the panels can be reduced, as can the bracing. That's it.
confused...
for a taste of what I mean, read this. There's a discussion of materials comparing MDF to acrylic.
Charactersitics of BB ply:
for MDF:
Stiffness: The Modulus of Elasticity is a measure of stiffness and is stress divided by strain. I could not find an MOE on BB ply, so I used the less strong and stiff common plywood for this specification.
Based on a particular stiffness required it is easy to see that BB ply (and the less known Apple ply) are at least 220% stiffer than MDF, and are about 10% lower in density than MDF. So an easy comparison. If using BB ply of 12 mm thickness (assuming good jointery and gluing techniques are used for both), an MDF thickness of approximately 40mm is needed. Assuming the same internal volume of a speaker enclosure, that also means the mass of the MDF enclosure will be twice as heavy (OK, 2.2 X's). Even if massive bracing is used on loudspeaker enclosure panels in a 18mm MDF enclosure, it is very unlikely that an MDF enclosure can overcome this disadvantage and to improve stiffness to that of a 12 mm BB ply enclosure.
Regarding energy storage: BB ply is made of constrained layers, while MDF is approaching a "homogeneous" material (even though it's not, but certainly more homogeneous than BB ply). Because of this, the behaviour of MDF when excited can result in a spurious release of energy once built up enough to vibrate a panel, and although not large in amplitude, higher in frequency, assuming the same energy is applied to both the MDF and the BB ply enclosure. Remember the Tacoma Narrows Bridge. The BB enclosure will vibrate also, but will do so in a more controlled manner with more amplitude, but lower frequency, right where it can be treated effectively. Dampening does little for higher frequencies.
Please, enough already.This discussion will go on ad nausea (and has here and elsewhere). Please, lets stop now.
for a taste of what I mean, read this. There's a discussion of materials comparing MDF to acrylic.
Charactersitics of BB ply:
- density = 680-700 kg/m³
- Modulus of Elasticity (MOE) = 1.2
for MDF:
- density= 700-870 kg/m³
- MOE = .53
Stiffness: The Modulus of Elasticity is a measure of stiffness and is stress divided by strain. I could not find an MOE on BB ply, so I used the less strong and stiff common plywood for this specification.
Based on a particular stiffness required it is easy to see that BB ply (and the less known Apple ply) are at least 220% stiffer than MDF, and are about 10% lower in density than MDF. So an easy comparison. If using BB ply of 12 mm thickness (assuming good jointery and gluing techniques are used for both), an MDF thickness of approximately 40mm is needed. Assuming the same internal volume of a speaker enclosure, that also means the mass of the MDF enclosure will be twice as heavy (OK, 2.2 X's). Even if massive bracing is used on loudspeaker enclosure panels in a 18mm MDF enclosure, it is very unlikely that an MDF enclosure can overcome this disadvantage and to improve stiffness to that of a 12 mm BB ply enclosure.
Regarding energy storage: BB ply is made of constrained layers, while MDF is approaching a "homogeneous" material (even though it's not, but certainly more homogeneous than BB ply). Because of this, the behaviour of MDF when excited can result in a spurious release of energy once built up enough to vibrate a panel, and although not large in amplitude, higher in frequency, assuming the same energy is applied to both the MDF and the BB ply enclosure. Remember the Tacoma Narrows Bridge. The BB enclosure will vibrate also, but will do so in a more controlled manner with more amplitude, but lower frequency, right where it can be treated effectively. Dampening does little for higher frequencies.
Please, enough already.This discussion will go on ad nausea (and has here and elsewhere). Please, lets stop now.
Sounds like you're saying ply is more springy then MDF, doesn't that make it good for energy storage and release?
I don't follow your logic in stating that MDF can produce a "spurious (odd choice of word) release of energy" because it is a "homogeneous" material surely a pile of sand is a "homogeneous" material, as for the Tacoma Narrows Bridge, how does that illustrate your point? Absolutely everything has a resonant frequency, the bridge was unfortunate in having one that was in tune with unexceptional winds.
Finally let me draw your attention to the title of this discussion "Why not MDF?"
I don't follow your logic in stating that MDF can produce a "spurious (odd choice of word) release of energy" because it is a "homogeneous" material surely a pile of sand is a "homogeneous" material, as for the Tacoma Narrows Bridge, how does that illustrate your point? Absolutely everything has a resonant frequency, the bridge was unfortunate in having one that was in tune with unexceptional winds.
Finally let me draw your attention to the title of this discussion "Why not MDF?"
MOE ?
What is Young's Modulus?
Stiffness proportional to thickness?
What is I (moment of Inertia of a flat panel) and how does I relate to stiffness?
http://en.wikipedia.org/wiki/List_of_area_moments_of_inertia
What is Young's Modulus?
Stiffness proportional to thickness?
What is I (moment of Inertia of a flat panel) and how does I relate to stiffness?
http://en.wikipedia.org/wiki/List_of_area_moments_of_inertia
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Here’s a solution that some may like. A better, tougher, heaver board then HD and Lowes’s MDF: MEDEX
Medex - “has a rock solid track record of superior design capabilities and environmental stewardship around the world”
http://www.alleghenyplywood.com/index.php?option=com_content&view=article&id=60&Itemid=78
Medex - “has a rock solid track record of superior design capabilities and environmental stewardship around the world”
http://www.alleghenyplywood.com/index.php?option=com_content&view=article&id=60&Itemid=78
Years ago before MDF was popular I found something kind of nice. It was a 1.25"
particle board with a .75" core of a VERRY low density particle density and the front
and back were standard density particle board. It worked out to be just a little heavier than 3/4" particle board. Around the same time Audio Concepts recomended
laminating formica on both sides of 3/4" particle board.
particle board with a .75" core of a VERRY low density particle density and the front
and back were standard density particle board. It worked out to be just a little heavier than 3/4" particle board. Around the same time Audio Concepts recomended
laminating formica on both sides of 3/4" particle board.
woody, this is something more like it
This is the basic idea behind some of the "fixes" I previously mentioned. It is not that MDF always must sound bad, it is just that some care needs to be taken with it. Simply paining both sides of a panel helps a huge amount.
I have creating my own version of that style of panelling using a foam core and 1/8" Masonite glued to both sides of it. I've made a platform of this construction for a turntable to sit on. The only issue I've had with it is that I used HDF (Masonite) and under the weight of my table it has been deformed. Ultra lightweight, and completely "dead" when you wrap on it.
This is similar to some well known after-market shelves that have been sold over the years. One very well known equipment stand producer make 100% of his stands out of MDF with a finish painted on.
The exact specifications for BB ply can be had (an excellent download is the Handbook of Finnish Plywood), but the MDF specs are much looser. Some assumptions must be made, for example, the Finns use 680 kg/m³ for the density of BB ply. Numbers for MDF are typically 700 kg/m³ - 870 kg/m³
but can be much lower (600) or higher (upto 1200). I assume MDF density to be 785 kg/m³. I also assume that the BB is no stronger than regular plywood, but is actually much stronger.
Guys, remember that I am not trying to "outrage" any, and make statements that MDF can never be accaptable, merely that a simple MDF box, even with bracing is no match to BB ply in terms of sttrength, and stiffness. We can argue the sonic differences, but there is no denying the differences in physical characteristics and to consider the differences in the "sound" of a material.
If any are turntable fans, how many have put a turntable into a newly constructed plinth, made of a different material than a "stock" plinth for the same table? Any differences? What are they?
This is the basic idea behind some of the "fixes" I previously mentioned. It is not that MDF always must sound bad, it is just that some care needs to be taken with it. Simply paining both sides of a panel helps a huge amount.
I have creating my own version of that style of panelling using a foam core and 1/8" Masonite glued to both sides of it. I've made a platform of this construction for a turntable to sit on. The only issue I've had with it is that I used HDF (Masonite) and under the weight of my table it has been deformed. Ultra lightweight, and completely "dead" when you wrap on it.
This is similar to some well known after-market shelves that have been sold over the years. One very well known equipment stand producer make 100% of his stands out of MDF with a finish painted on.
The exact specifications for BB ply can be had (an excellent download is the Handbook of Finnish Plywood), but the MDF specs are much looser. Some assumptions must be made, for example, the Finns use 680 kg/m³ for the density of BB ply. Numbers for MDF are typically 700 kg/m³ - 870 kg/m³
but can be much lower (600) or higher (upto 1200). I assume MDF density to be 785 kg/m³. I also assume that the BB is no stronger than regular plywood, but is actually much stronger.
Guys, remember that I am not trying to "outrage" any, and make statements that MDF can never be accaptable, merely that a simple MDF box, even with bracing is no match to BB ply in terms of sttrength, and stiffness. We can argue the sonic differences, but there is no denying the differences in physical characteristics and to consider the differences in the "sound" of a material.
If any are turntable fans, how many have put a turntable into a newly constructed plinth, made of a different material than a "stock" plinth for the same table? Any differences? What are they?
Well personally I use 1” thick MDF with a little trick I picked up from a small speaker manufacture *** line the surfaces with lead *** easy to find at local roofing outlets.
The fellow mentioned above, could take $100 worth of parts (or less) and sell a 15” high pair of triangle speakers for $2,500.
I don’t line large subs, only smaller “satellite” speakers. Should also mention, I never build any small cabinet square, typ triangle shapes.
The fellow mentioned above, could take $100 worth of parts (or less) and sell a 15” high pair of triangle speakers for $2,500.
I don’t line large subs, only smaller “satellite” speakers. Should also mention, I never build any small cabinet square, typ triangle shapes.
Before I got shamed out of using MDF, I used 3/4" MDF (NOT Lowe's/HD -- a supplier to local cabinet shops) laminated to 1/4" Hardibacker (a cement/fiberboard used as an underlayment for ceramic tile) with Liquid Nails. The inside of the cabinet is lined with 5/8" acoustic fiberglass and outside veneered. I still recommend this as a viable construction technique.
I had two problems with the MDF construction, well, three: 1. MDF dust gets everywhere and a mask is mandatory. 2. The finished cabinets are REALLY heavy and expensive to ship. 3. The cabinets are prone to corner damage during shipping as the edges are easily crushed. But, for one-off DIY work, have at it!.
Here are photos of the technique:
And the final product:
Bob
I had two problems with the MDF construction, well, three: 1. MDF dust gets everywhere and a mask is mandatory. 2. The finished cabinets are REALLY heavy and expensive to ship. 3. The cabinets are prone to corner damage during shipping as the edges are easily crushed. But, for one-off DIY work, have at it!.
Here are photos of the technique:
And the final product:
Bob
Attachments
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insufficient shear strength or stiffness of the core material for the load imposed.
It is unlikely to be failure of the HDF skins.
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