Dave: What's the resonant freq. of baltic birch? Low midrange? You push it up by making the panels small, it's still there, and is contributing in the most sensitive range of human hearing. Have you ever measured the freq. response of one of these panels? A vibrating panel produces noise, and not at a low level.
MJL21193 said:
Panel resonances are pushed up into the 1khz plus range, and are high Q. They are there but there is not enuff energy at the right frequency to excite them, If they are not excited then they don't contribute to the sound. If something does excite them (usually not from inside the speaker) the high Q means they are of very short duration which further makes them innocuous.
dave
As Dave notes, it's about pushing the natural resonance points out of the cabinet's most critical operational passband, either by going up or down. Once it's out of this, it's much less problematic.
To cite the steel example, yup, it does ring. No argment. But using an appropriate gauge for a given application will push the resonant point below this passband. About 10 gauge should do if I remember what Greg told me correctly.
MDF cabinets attempt a similar thing, but being far less massive need to be much thicker, obviously. Much thicker than most people realise -although it's dense, MDF isn't very stiff at all. For a typical FR driver application, you really need about 1 1/4in thick panels minimum to push panel resonance down into a place where it doesn't do any damage. Either that, or line the regular 3/4in material with at least 1/4in of concrete board, as Bob Brines does with his MLTLs. That works, but you then run into other problems such as energy storage. If you can't go to something with the density and stiffness-weight ratio of steel, better to push them up, out of the way, IMO.
To cite the steel example, yup, it does ring. No argment. But using an appropriate gauge for a given application will push the resonant point below this passband. About 10 gauge should do if I remember what Greg told me correctly.
MDF cabinets attempt a similar thing, but being far less massive need to be much thicker, obviously. Much thicker than most people realise -although it's dense, MDF isn't very stiff at all. For a typical FR driver application, you really need about 1 1/4in thick panels minimum to push panel resonance down into a place where it doesn't do any damage. Either that, or line the regular 3/4in material with at least 1/4in of concrete board, as Bob Brines does with his MLTLs. That works, but you then run into other problems such as energy storage. If you can't go to something with the density and stiffness-weight ratio of steel, better to push them up, out of the way, IMO.
MJL21193 said:
Well then, why not settle the issue for yourself by building a pair of a simple FR design (like say the Metronomes or a BIB)from each material.
I'm sure that like most of us crazy speaker hackers, you've probably got multiple well broken in pairs of at least one driver type with which you could conduct such an A/B test. It sounds like you're experienced with kind of comparison, so I hesitate to offer any suggestions, but I've always found a group of 4 or 5 more interesting than just 1 or 2.
Have fun, and let us know what you determine.
planet10 said:
I don't dispute the effectiveness of this method, but how do you acheive such stiffness? Not from the plywood alone, you must use a lot of bracing - a matrix? You use no damping at all?
Does damping choke low level detail? Sound emits from the speaker cone into the space in front of the speaker. If there is any low level detail, it will be there. My box can't suck that out of the driver, though a poorly designed crossover can.
chrisb said:
Do I detect a note of patronizing amusement in your post? That's fine, I'm pretty much used to it by now.
I don't use full range drivers. I am not the minimalist type. I need specialized drivers and the power to drive them. I don't like horns, or valves and I especially don't believe the full audible spectrum can be reproduced by a single driver.
I know, I'm a creten. An A/B test to prove to myself that I'm wrong! A splendid idea.
I actually only have one speaker that is built with MDF, that's my my big sub; and that only partially, as the the outer layer is 1/2" maple veneer particle board. My main speakers are a combination raw particle board and spuce sheating (yes, spruce sheating) plus a layer of polyester filler (Bondo). They are a two way TL with very little stuffing. A year ago I duplicated these in MDF for my brother. I used the same drivers, which I measured. They were within 3% of mine( Vifa makes them consistant). Same stuffing(BAF), same crossover. I couldn't hear a difference. Neither could anyone else (maybe they were humouring me).
MJL21193 said:
In a box like the Fonken the largest unbraced panel is just over 4" -- sometimes they will get out to as much as 6-8". The bracing doesn't need to be a matrix you just have to orient it correctly (ie the ubiquitous shelf brace is one of the least effective.
Air space damping, no panel damping. That just takes you in the wrong direction. Lower panel resonance, greater energy storage, & lower panel resonance Q.
The box doesn't suck it out, it buries it in the low level noise prodcued by the cabinet.
XOs? XOs are the weakest point in any speaker. The best XO is no XO, and if you do have to use one, simple is better (ie a single cap on a supertweeter) or active... help in the bottom. XOs should not be anywhere between 300 & 6-10k. XOs are evil.
dave
Banned
Joined 2002
Dave: A little off topic again, but I noticed on your site that you deal vintage drivers. I have a pair of 8" woofers from a pair of Criterion 77 speakers. They are in pristine shape. Do you have any experience with these? I measured the T/S specs, and wasn't impressed. They are as follows, both drivers measure within 5% of each other, this is the average:
Fs - 107 Hz
Qms - 7.5
Qes - 2.3
Le - .52
Re - 6.3
I was thinking small OB, with that impossibly high Qes. Any ideas? Trash or Treasure?
Fs - 107 Hz
Qms - 7.5
Qes - 2.3
Le - .52
Re - 6.3
I was thinking small OB, with that impossibly high Qes. Any ideas? Trash or Treasure?
Banned
Joined 2002
MJL21193 said:
I'm working on an active system, or at least I was , until I joined this forum. Now im trapped here, I don't do anything except wear my typing finger (one, index)down and sing the virtues of MDF
Chrisb & Dave are helping me get my boxes done, other than that im doing th rest my plan is to use 2 Class A @ 15watts each driver per. In a set of book shelf type speakers on stands. Having a balanced pre-amp to run the Aleph's and then active xover's for the bass driver / tweeter. Im hoping to get some pics of my new Babies
Cost me a arm & a leg for the drivers.
Banned
Joined 2002
building with real wood
Good morning folks:
I am the fellow that makes speakers from real wood. I am currently making my cabinets from fine grain first growth Douglas-fir. The wood is well dried and stable I have had it stored in my house for approximately ten years.My house is stable year round at aproximatwely 38% humidity. The wood grain is extremely uniform with greater than 25 growth rings to the inch.The wood has uniform density and is more stable than any other material I have used. I use planks upto 12 inches wide with no concerns. 12 inches because that is the maximum feed width of my thickness planner. I have laminated up planks to wider widths for other projects with no troubles.
What is the deal you ask?
I use only clear wood.
I use straight grained wood.
I use stable dry wood
I take the time to do proper joinery
I seal the wood with oils inside and out
I finish with simple poly eurathane finishes.
I have not had any major suprises.
I really like the things I can do with real wood.
If I had to choose I would use Baltic Birch. I am not wood scientist or a physics dude. But I think the modulus of elasticity on sideways stabilty of plywood exceeds that of MDF. If you take a piece of ply wood and a piece of MDF and bend them sideways the MDF has great flexibilty, the cross link nature of plywood leads to less flexibilty. Hence larger panels do not resonate. I do not know for sure. I did pick out the MDF from the plywood in the taste test last summer in the sense that the MDF sounded more bright.
Anyway... I prefer to make things from real materials when ever I get the choice. Right now I am using stone wood and metal. I try not to be too positional but I think that when you spend the time to make something you should not be too caught up in how long it takes or how much work it is. Most of the things I make will last for a very long time and continue to look and perform to the standard I expect.
On a final note If all goes astray and things do not work out. I have solice in the knowlege that no matter what, it will burn and heat my house for me.
One more thought
You have to go with what you know. If this is a first project or an experiment go with cheap material for the prototype. Once you are happy with the design and performance make furniture if you have the skills and the tools.
Most of all spend you time making things that is really what it is all about.
Good discussion
Good morning folks:
I am the fellow that makes speakers from real wood. I am currently making my cabinets from fine grain first growth Douglas-fir. The wood is well dried and stable I have had it stored in my house for approximately ten years.My house is stable year round at aproximatwely 38% humidity. The wood grain is extremely uniform with greater than 25 growth rings to the inch.The wood has uniform density and is more stable than any other material I have used. I use planks upto 12 inches wide with no concerns. 12 inches because that is the maximum feed width of my thickness planner. I have laminated up planks to wider widths for other projects with no troubles.
What is the deal you ask?
I use only clear wood.
I use straight grained wood.
I use stable dry wood
I take the time to do proper joinery
I seal the wood with oils inside and out
I finish with simple poly eurathane finishes.
I have not had any major suprises.
I really like the things I can do with real wood.
If I had to choose I would use Baltic Birch. I am not wood scientist or a physics dude. But I think the modulus of elasticity on sideways stabilty of plywood exceeds that of MDF. If you take a piece of ply wood and a piece of MDF and bend them sideways the MDF has great flexibilty, the cross link nature of plywood leads to less flexibilty. Hence larger panels do not resonate. I do not know for sure. I did pick out the MDF from the plywood in the taste test last summer in the sense that the MDF sounded more bright.
Anyway... I prefer to make things from real materials when ever I get the choice. Right now I am using stone wood and metal. I try not to be too positional but I think that when you spend the time to make something you should not be too caught up in how long it takes or how much work it is. Most of the things I make will last for a very long time and continue to look and perform to the standard I expect.
On a final note If all goes astray and things do not work out. I have solice in the knowlege that no matter what, it will burn and heat my house for me.
One more thought
You have to go with what you know. If this is a first project or an experiment go with cheap material for the prototype. Once you are happy with the design and performance make furniture if you have the skills and the tools.
Most of all spend you time making things that is really what it is all about.
Good discussion
MJL21193 said:
you're probably right - just remember all of us are capable of that, at any time
I don't use full range drivers. I am not the minimalist type. I need specialized drivers and the power to drive them. I don't like horns, or valves and I especially don't believe the full audible spectrum can be reproduced by a single driver.
If nothing else, audio reproduction is about the art of balancing compromises. For me the great thrills of the DIY journey have been self discovery and acceptance of personal technical limitations.
Since a synopsis of my audio philosophy wasn't made clear in the post to which you're referring, let's say that we're presently on different pages of the book, and leave it at that?
Actually, I should think it is - and maybe you're not (for you, now) The only way I've ever learned anything new in this hobby of over 40years is by testing my preconceptions.
e.g.
how loud do I really need to listen?
how many watts does it take to absolutely NEVER clip?
how much more realistic will those extra n.2 channels of mono sound? (just how many is it now for "full" surround sound anyways?)
how thick does a cable need to be for bass frequencies?
how can less be more?
oh, there's more questions than that to which there is no "one right answer"
I actually only have one speaker that is built with MDF, that's my my big sub; and that only partially, as the the outer layer is 1/2" maple veneer particle board. My main speakers are a combination raw particle board and spuce sheating (yes, spruce sheating) plus a layer of polyester filler (Bondo). They are a two way TL with very little stuffing. A year ago I duplicated these in MDF for my brother. I used the same drivers, which I measured. They were within 3% of mine( Vifa makes them consistant). Same stuffing(BAF), same crossover. I couldn't hear a difference. Neither could anyone else (maybe they were humouring me).
Of course fully realizing that this type of debate is never settled with words, it's been my experience that at the bottom octave or so, the transient smearing that is more likely to occur with massive MDF boxes vs light and stiff plywood is far less noticeable than in the vocal range.
Chris,
you might have hit bullseye by just using the keyword - "smearing".
MDF stores a lot of energy and returns it very slowly, and with ugly resonance peaks. Fine in a subwompher, where that stolen energy just comes back to bolster the falling flank of the sinewave.
Ugly, though, if the stolen goods are given back in midrange - they'll smear up the transients of the following waves.
Just a gut feeling and experience - nothing I could really explain in German, let alone in coherent English.
Greets,
Pit
you might have hit bullseye by just using the keyword - "smearing".
MDF stores a lot of energy and returns it very slowly, and with ugly resonance peaks. Fine in a subwompher, where that stolen energy just comes back to bolster the falling flank of the sinewave.
Ugly, though, if the stolen goods are given back in midrange - they'll smear up the transients of the following waves.
Just a gut feeling and experience - nothing I could really explain in German, let alone in coherent English.
Greets,
Pit
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