I'm building a small enclosure for an 8 inch subwoofer. My goal is to make it as small as possible for the desired sub bass extention (32hz f3). I'm also aware of the internal bracing needed to avoid unwanted cabinet resonances and I have some metal available so I'm thinking of reinforcing the cabinet with it. Wood can work too and is more common but it also can ocuppy more internal volume.
My question is. Can this metal pieces interfiere with the magnetic field of the driver to the point where the flux is "weakened" thus making it less efficient or reducing sensitivity? I can imagine the magnetic field pattern can change. And the flux would go to the metal bracing (partially) if it's a bit close to the magnet, instead of concentrating the field in the gap/motor structure.
My question is. Can this metal pieces interfiere with the magnetic field of the driver to the point where the flux is "weakened" thus making it less efficient or reducing sensitivity? I can imagine the magnetic field pattern can change. And the flux would go to the metal bracing (partially) if it's a bit close to the magnet, instead of concentrating the field in the gap/motor structure.
Unlikely if it is bot that close.
dave
Note: F3 is not relevant to humans (ref Toole). Pay attention to F6/F10 and expected room gain.
dave
Note: F3 is not relevant to humans (ref Toole). Pay attention to F6/F10 and expected room gain.
And it's one of those things Toole very quickly skimmed over in his book.
In a general room sense he's absolutely correct, but from a speaker system design stand of view, I am sorry but that's just WAY to simplified.
Besides, a part of those F6 and F10 points for example is the Q factor as well the steepness.
Which is inherently connected to the F3 point.
@dyllangm I don't really see why wood would (lol) occupy more volume?
Bracing just has to be stiff in the horizontal and vertical direction.
Some basic plywood is often more than adequate.
🙂
I believe he is equating volume with strength and he is correct of course. Whether or not it has credible application in this case is questionable. I believe he was concerned primarily with magnetic interference. I would guess not if one was reasonable about distancing.
Yeah that's true, but by avoiding it all together the question isn't important anymore either 😉
F3 only makes sense when you are talking about a crossover, but as to being where a speaker rolloff it is one of those old-timey out of date, not that useful a number. Much like THD.
Slowly people are starting to catch on, why don’t you?
dave
what kind of metal do you have in mind? Aluminium is widely used for speaker enclosures, including baffles. So aluminium does not seem to cause issues. It is even used as a membrane material.
Steel is not used in speakers apart from the screws. Steel sings much more than aluminium so I don’t think it is suitable from that point of view.
Slowly people starting to loose context, like you.
I am extremely familiar with Toole's work, even directly talked to him.
I am sorry, but a roll-off with a Q of 2 is not only very audible compared to a Q of 0.5.
It also put's all kinds of other issues and strain on a system if it's not done well.
Things like max cone excursion, proper well compromised port performance and behavior, the list goes on.
For smaller systems distortion is even also at play here.
Ignoring all these things is just beyond silly.
But hey, what do I know after 15 years of designing and optimizing systems for all kinds of companies.
Ehm, ?
Any 2nd order system or higher has a Q-factor.
That means every loudspeaker system, even open-baffle/dipole systems.
I would suggest reading more about control theory again, back to the books it is.
Including Toole, because if this is what you get out of it, I think you missed a couple of chapters.
It’s not about cabinet volume reduction, it’s about the sides of the cabinet flexing acting as speakers themselves. They are contributing to the overall output of the whole system. A well braced cabinet makes no noise but a flexible one adds to the sound. It’s science! Lol
You might have missed the point. He has the metal and asked if he could use it.
If you don’t have anything to add, don’t feel the need to post.
May not be important for you but for my knowledge and application case it is. Yeah now I'm more aware of the resonances of steel and the ringing (the metal pieces I'm talking about) and maybe is not the best idea. I was mainly thinking about metal because the pieces are thinner than the wood and giving it a specific shape it could brace pretty well. Also the added weight to the cabinet which can reduce vibration and securing it to the floor (if that makes sense haha).
I did a small not pro test today putting a steel piece to the magnet plates while playing a sine wave to see if spl decreases but I didn't really hear a significant difference. Anyways I think the occupied volume from bracing would only add like 1cm per side so its not gonna impact the size of the box that much so wood bracing will be the way to go. Thanks everyone!
I am worried the opposing specs: 32Hz F3, 8" speaker, small enclosure will lead to an abysmal sensitivity woofer, which will require tons of driving power.
There are companies building metal boxes for loudspeakers. If done well you can spare some space for making smaller loudspeakers.
the same with some pro equipment using polypropylene enclosures which get their rigidity by making complex forms stiffening out the polyprop and thus making very lightweight boxes.
the same with some pro equipment using polypropylene enclosures which get their rigidity by making complex forms stiffening out the polyprop and thus making very lightweight boxes.
assumption is no
there is shielded speakers
placed over the magnet
So be interesting to hear from engineers
if it has a effect.
8" put in a small box
relatively small already
not much panel area to worry about.
thick wood, double baffle
simple brace, all done
there is shielded speakers
placed over the magnet
So be interesting to hear from engineers
if it has a effect.
8" put in a small box
relatively small already
not much panel area to worry about.
thick wood, double baffle
simple brace, all done
As long as there are no steel parts clamping onto the magnet itself, I think any magnetic losses should be negligible. Now if we're talking about high frequencies, there could -- conceivably -- be special cases where a lively box picks up a tiny bit of energy from the voice coil and/or a field magnet. But with a sub I think you could even use a recycled air tank.
Not much driving power needed. The subwoofer is reasonably efficient, I modified the driver by adding a second magnet and extending the pole piece (increase in BL) the results are great. Forgot to mention the bass entention is achieved thanks to the pasive radiators tuned to about 32hz, tested in a previous build doing the "rice test" simple physics. Passives can really play surprisingly low in small enclosures 👍👍
You mean reinforcing the cabinet from the outside?
Would be interesting to see how reinforcement on the outside of the enclosure would do. Pro audio enclosures have wood bracing for the most part along with these thick layers of materials like polyprop you mention and others