Hi everyone!
I’m building my first subwoofer and currently finishing assembling the panels.
Yesterday I read about standing waves and that squares and cubes were to avoid when designing a subwoofer.
My enclosure is already cut to size and partly assembled following my design of a ported, down firing sub with a square base (and the driver is to be mounted exactly in the center of this square).
I’m not worried about the panel vibrating, I ordered 1in thick mdf for it (I didn’t realize it was going to be that thick), but reading about standing waves yesterday worried me.
My internal dimensions are 26cmx26cm for the base and 63cm high (the slot port is at the top, 55.6cm from the bottom)
Thanks again for your help
I’m building my first subwoofer and currently finishing assembling the panels.
Yesterday I read about standing waves and that squares and cubes were to avoid when designing a subwoofer.
My enclosure is already cut to size and partly assembled following my design of a ported, down firing sub with a square base (and the driver is to be mounted exactly in the center of this square).
I’m not worried about the panel vibrating, I ordered 1in thick mdf for it (I didn’t realize it was going to be that thick), but reading about standing waves yesterday worried me.
My internal dimensions are 26cmx26cm for the base and 63cm high (the slot port is at the top, 55.6cm from the bottom)
Thanks again for your help
Sounds about right. This calculator shows the first mode at 308Hz for 55.6cm height, 272Hz for 63cm height. Your box is actually only 55.6cm high, so the lowest standing wave produced would be around 308Hz, disregarding the cone and open area of the port breaking up some of the standing waves.
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So I gotta ask the question: why does stiffness of the material mater that much?
I've built speakers with 1/2" standard ply ( a bit no no) and they sounded great.
And I've built horns for 18" subs, with 3/4" ply.
No rattle or buzzing.
Birch ply is about 5x the price of MDF - yeah it looks better..
Internal bracing achieves the same or better.
For a pro audio speaker, which will get banged around durring moves, a strong shell like baltic birch is likely good.
Seems to be some confusion here between standing waves (interior bounce) and panel vibrations (modified by construction factors).
Standing waves are simple to address with a million options from stuffing with a pile of old clothes to high-tech foam.
Despite the endless ink spilled on panel vibration, prolly not worth worrying about for anything over half-inch braced plywood.
Standing waves are simple to address with a million options from stuffing with a pile of old clothes to high-tech foam.
Despite the endless ink spilled on panel vibration, prolly not worth worrying about for anything over half-inch braced plywood.
A light weight, stiff panel is easier to damp and has less energy storage as a rule. The BBC white papers cover this in detail with frequency response data from tests.
I bet there are a million google hits for "LS3/5A". So somewhat inauthentic of you to skip-out on the backing up your post.
Now sir, you said "The BBC white papers cover this in detail..." so that means you can post some details.
Or were you repeating second- or third-hand what you think others have said? In which case, you need to explain to the forum that you meant to write, "I once heard somebody say that the BBC...." and so on.*
B,
* Actually, I have heard it said several times and prolly read the paper decades ago myself. But time for all of us to go back to primary sources on this often debated topic.
Now sir, you said "The BBC white papers cover this in detail..." so that means you can post some details.
Or were you repeating second- or third-hand what you think others have said? In which case, you need to explain to the forum that you meant to write, "I once heard somebody say that the BBC...." and so on.*
B,
* Actually, I have heard it said several times and prolly read the paper decades ago myself. But time for all of us to go back to primary sources on this often debated topic.
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Whats in a ‘TL’ (pipe with a closed end) if the driver is mounted upstream by a pressure node for the pipe geometry? Away from the closed end, thus A standing wave thats exactly in time like a fulcrum would be to a pump from that location with a dead end to it or surge tank i suppose??
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First hit from a 5-second Google search of "BBC white paper LS3/5a":
The design of the miniature monitoring loudspeaker Type LS3/5A - BBC R&D
Here's your starter for 10 - they are all here, and what a resource! Happy reading, and really no need for the tone of your comment my good man, the reason for my omission of a link was part laziness and part not wishing to insult readers' search skills. I promise to include links where mentioned in future postings.
Stay safe.
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IHMO a lot of people & threads try to design the ULTIMATE solution.
A great ambition, but a huge over investement in many cases.
Ex. my subs are intended for
- good frequency response (F3 ~30 hz to 120 hz)
- small size (~1 cu ft) so my wife doesn;'t complain
- low to med volume levels
- tons of available power, so efficency doesnt matter
That lets me make design compromises. Ex:
- panels don't have to be very strong - not worried about vibration
- I can use cheaper materials - don't need birch plywood
build a simple box, cosmetically that way I like, of the right size.
Building with consessions is HUGELY easier than a no-compromise solution.
(I gave up on those 10 years ago)
A high end manufacturer often cannot make such consessions
A reviewer will blast them for any short comings.
And many "audiophiles" have crazy silly expectations.
Some are prepared to pay rediculous premiums (ex. $3000 RCA interconnect cables) and they swear it sounds better.
To each his own - a fool and his money will soon be parted.
Personally - I happily make concessions, get it done and listen to the finished product.
A great ambition, but a huge over investement in many cases.
Ex. my subs are intended for
- good frequency response (F3 ~30 hz to 120 hz)
- small size (~1 cu ft) so my wife doesn;'t complain
- low to med volume levels
- tons of available power, so efficency doesnt matter
That lets me make design compromises. Ex:
- panels don't have to be very strong - not worried about vibration
- I can use cheaper materials - don't need birch plywood
build a simple box, cosmetically that way I like, of the right size.
Building with consessions is HUGELY easier than a no-compromise solution.
(I gave up on those 10 years ago)
A high end manufacturer often cannot make such consessions
A reviewer will blast them for any short comings.
And many "audiophiles" have crazy silly expectations.
Some are prepared to pay rediculous premiums (ex. $3000 RCA interconnect cables) and they swear it sounds better.
To each his own - a fool and his money will soon be parted.
Personally - I happily make concessions, get it done and listen to the finished product.
In a sub, the goal is to push any potential box resonances well above the bandwidth of the loudspeaker so that the resonances are never excited so it is as if they do not exist.
The stiffer the material, and the lighter it is, (don’t forget adequate bracing (also acts to reduce ballooning of the box), the higher teh potential resonances.
As well, particualrily in subwoofers one can get a huge gain in potentia box vibration issues in the box is to load a pair of driver push-push.
I did such a sub with 15mm BB and it worked superbly well. Have a ste of driver sdownstairs to make another set.
dave
Here standard BB is not much more than teh better MDFs, really high quality costs maybe 3x as much, not a hge differential given all the other resourses that you will put into the box.
dave
In a subwoofer one can sually keep teh dimensions small enuff that there are no standing waves that will ever get excited. The issues are box vibrations and balooning.
dave
One should not try to damp panels in a sub. That adds mass without adding stiffness, pushing potential resonances down in frequency and lowers the resonance Q, both making it more likely that the resonances will be excited.
The BBC approach was totally the opposite, nit suitable at all for a sub (and in my mind questionable with any loudspeaker).
dave
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