Hi all, i am go to build a set of these speakers, thinking to use poplar plywood 28 mm thick, any toughts on that? thanks for answer 🙂
Forget it!
No, wait : a Voigt pipe ( sort of chamber and Big Exponential Vent) might be of interest in 2024 if there's a driver that works with it.
Which driver is?
No, wait : a Voigt pipe ( sort of chamber and Big Exponential Vent) might be of interest in 2024 if there's a driver that works with it.
Which driver is?
With the old technical hat on, for a given material & panel size, rigidity increases (doubles) as to the cube of the thickness; 28mm relative to, say, 18mm is definitely a decent step up -but not quite as much as often thought.
Poplar plywood tends to be at the lower end of the density spectrum and often has voids, so I'd be wary, especially for the latter reason -less for finishing, but if you have an internal cavity, or loose piece of material, it can drive you mad trying to track down the vibrations, and while there are fixes, they're a PITA to do.
Material aside, regarding Voigt pipes -depends which one. There are good examples, but there are some (many) fairly ropey types out there, and most derived from, say, on-line calculators are pretty poor. Which were you thinking of?
Poplar plywood tends to be at the lower end of the density spectrum and often has voids, so I'd be wary, especially for the latter reason -less for finishing, but if you have an internal cavity, or loose piece of material, it can drive you mad trying to track down the vibrations, and while there are fixes, they're a PITA to do.
Material aside, regarding Voigt pipes -depends which one. There are good examples, but there are some (many) fairly ropey types out there, and most derived from, say, on-line calculators are pretty poor. Which were you thinking of?
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I'm a cabinet maker in the campervan industry and work with birch and poplar plywood all day long. Very different products and i'd choose birch every time.
So would I -albeit for audio I'd go a bit further & want it to be a genuine void-free Baltic birch type rather than some of the cheaper birch ply products.
Interestingly you can hear the difference when driving a campervan with cabinets built in poplar over birch. The birch is much denser and quieter.
Denser is not an asset unless it is a side effect of adding stiffness.
dave
dave
As this is a DIY project, if you really want to go down the rabbit hole and engineer the crap out of it, get a sample of each type of wood and measure the properties. I get a sample, constrained at the corners, and wrap on it to see where it resonates. The properties can then be estimated using the equations for a constrained flat plate, for use in a finite element model of the speaker. For the birch plywood at my local lumber yard I found E = 1026885
I use a set of Matlab / Octave scripts, rectangular_plate_fea.m ver 1.9 February 26, 2013 written by Tom Irvine Email: tom@vibrationdata.com. A quick search will locate his website.
I use a set of Matlab / Octave scripts, rectangular_plate_fea.m ver 1.9 February 26, 2013 written by Tom Irvine Email: tom@vibrationdata.com. A quick search will locate his website.
I was unable to find the rectangular_plate_fea.m on the web, so I have uploaded the folder with the script files here. These .m file scripts run using Octave or Matlab and let you find the resonance frequencies (eigen values) for flat plates with different constraints on the edges. I enter the size of one side of a cabinet and then select the fixed edges to compute the panel resonance frequencies. I found with my last build that I only needed to use 1/2" birch plywood to achieve panel resonances outside of the range I used the drivers.
This video again! There is significant misinforation in the video — you have to know more than he does to know what is what. I woud not build his voigt variation.
A voigt needs to be modeled for the driver to be used and it should be mass-loaded.
dave
Indeed! In my time only marine grade was considered the optimum due to having highest MOE for a given thickness.
The math, comparison to MDF.
Re voids; if you mass load it on top with at least as much weight as the speaker weighs it generally will quell any audible 'color'. Altec A7 utility speakers used horrible 5/8" crating plywood, but mass load them with at least ~265 lbs factory spec and they're quiet as the proverbial mouse, though long term he added significantly more.
mass loading 1
mass loading 2
mass loading 3
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Disclaimer: I wrote 'sort of'...
Yes, I know, as put as suffix for the phrase it comprehends both - chamber and long tunnel, but it may be applied as ' I don't remember very well' related to age, both me and Voigt eh eh!
The poplar & birch propension don't interest me 'cos wood is a B series material for cabinetry, so, why worry?
My advice would have been to line the interiors ( or whatever piece you intelligent engineer seem to reputate basic for the entire project ) with lead sheets and forget it
Yes, I know, as put as suffix for the phrase it comprehends both - chamber and long tunnel, but it may be applied as ' I don't remember very well' related to age, both me and Voigt eh eh!
The poplar & birch propension don't interest me 'cos wood is a B series material for cabinetry, so, why worry?
My advice would have been to line the interiors ( or whatever piece you intelligent engineer seem to reputate basic for the entire project ) with lead sheets and forget it