I would assume that a t-line gives a 3db+ increase over a closed box in the bass. So then it has to be converting sound energy to do that. But with equalization and powerful amps sealed makes a lot of sense.
Honestly, I can't think if anything good about the back wave of a driver, so, to me, absorbing it is the best thing to do, high or low freqs, its all un-useful.
Damp the cabinet and some internal absorption and don't worry too much about box shape and where and what amounts of damping. Its all too low the significant range to be of much bother. Its what happens outside that matters, not what happens inside. And yes the two are pretty well independent one hardly affects the other.
Quite agree.
On the subject of the internal walls, the velocities are low and the pressure high, as you've said. But, it's a very convenient place to put some sort of damping material, so it's just a question of choosing the most appropriate in this situation. Usually cited as being effective as a lining is carpet or thick, dense felt. To be used in addition to stuffing the box, of course.
As much as possible needs to be done to absorb rear radiation, as a speaker cone isn't much of a barrier at middle frequencies...
It can, but it needs to be fairly close. Ordinarily higher frequencies will gain independence from the source, then become chaotic in the larger box and resonate, and thus not be very useful. To me this suggests that absorbing them isn't a bad thing.
We are talking about two different resonances here:
1. The box walls could behave as vibrating plates, they could be excited by the speaker driver at various "eigenfrequencies". This effect can be reduced by setting the width/length of each surface a golden ratio. Also the thicker is the wall, the higher is the eigenfrequency, and more energy is stored - more difficult to dampen. Bracing will also push the frequency up. This kind of vibration can be reduced by bitumenous felt or similar attached to the internal walls.
2. Standing waves. Golden ratio also helps, and this kind of resonances can be reduced by stuffing (long haired wool, mineral wool, other stuff with high specific heat, since sound energy will be absorbed through friction).
General concensus is that stuufing is good for closed boxes, but not good for ported boxes (and obviously not for horns).
1. The box walls could behave as vibrating plates, they could be excited by the speaker driver at various "eigenfrequencies". This effect can be reduced by setting the width/length of each surface a golden ratio. Also the thicker is the wall, the higher is the eigenfrequency, and more energy is stored - more difficult to dampen. Bracing will also push the frequency up. This kind of vibration can be reduced by bitumenous felt or similar attached to the internal walls.
2. Standing waves. Golden ratio also helps, and this kind of resonances can be reduced by stuffing (long haired wool, mineral wool, other stuff with high specific heat, since sound energy will be absorbed through friction).
General concensus is that stuufing is good for closed boxes, but not good for ported boxes (and obviously not for horns).
You can't just throw stuffing in a box. You need a cylindrical enclosure built around a f-glass beehive.
Seriously though I've found the quality and quantity of box noise matters more than a lot of things including electronics. It depends to on listening volume, size of box, the crossover point etc. There is a nice natural ring that adds space and depth to the sound. Works with room as well.
Bracing is key, the right sound absorption, and probably avoiding obvious axial modes, though modes can be equalized out.
Out of curiousity, has anyone here heard an infinite baffle set-up? Does it sound strange not hearing any box or backwave.
Box noise is easy to attenuate; matrix bracing on small centres and the appropriate stuffing well placed (even in ported boxes, but it's position must be part of the initial design). Worrying about golden ratios is another example of audiophile self flagellation.
I have never given much credence to "box sound" as I have tried on many occasions to measure it with no success. And I am not alone on this either. There are some examples of simulations showing it is present, but I have never seen a clear measurement of it. And, as stated, it is easily removed ... so why not just do that!?
Years ago, I had a setup with IB bass and OB mains, in an industrial space ...but there was still 'box'. Like most IBs (every example that I've seen), it had a manifold that connected the LF drivers to the larger space.
I set it up this way to corner load the LF drivers. IMO, the LF gain (reduced excursion) from corner positioning beat 'not hearing any box'. I didn't A:B test the difference, cos it didn't occur to me, plus building a second 'box' would have required about a ton of materials
Currently, I have a straight midbass horn that I use outdoors. The rear chamber is cut down from a 200 litre food drum, and has a screw-on lid big enough to load a 12" driver. Without the lid, there's essentially no box or backwave. I keep the lid on. The LF sags when the cap is off, and again, LF gain (reduced excursion) trumps 'not hearing any box'.
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It can sound disappointing due to the multiplicity of other distortions it can uncover.
I wasn't. It's quite in order to line the internal walls, using appropriate materials, to reduce reflected back-wave energy. The materials used will naturally be a lot denser than that used for stuffing.
Panel resonances are indeed a different matter...
Yeah that's what I did on my current build. A sealed two way with a matrix of solid wood 3/4" bracing, I posted a pic of the bracing a few pages back. You could literally support a house with it.
I also followed the common wisdom and filled it with loose fiberglass. But I;m starting to second guess the common wisdom. I want more of a musical sound, with a little reverb (see previous posts)
I read an experiment were a speaker was placed face down in sand chamber and a lot of noise from the box was isolated.
I might just pull the fiberglass out and report back, before an argument breaks out
. I know everyone says "stuff away" and I do like the sound of the fiberglass much better than other stuffing, but it does obviously filter out mid's and highs more than bass and so leaves it's own fingerprint on the sound.I'm thinking that the right shape and resonance free enclosure might be the optimum. I'm starting to think a speaker is more like a musical instrument, in that it needs a certain cohesion in the way the internal energy dissipates.
33Polkhigh, you may be interested in this review of the Morel Fat ladies (based on the musical instrument comment) Morel Fat Lady Loudspeaker (TAS 209) | The Absolute Sound
Tony.
Tony.
Interesting read, "In Russell’s view, the damping material inside a speaker cabinet doesn’t just “damp” the energy of the backwave, it muffles and distorts it, stores it, and then releases some of this muffled, distorted, and stored energy back out through the enclosure and the diaphragm of the driver after a delay in time, messing up the clarity and speed of the signal."
It sounds like they use inherently damped very stiff materials like carbon fiber along with cabinet geometry to avoid resonant modes without stuffing. I'm not opposed to stuffing, but how the sound energy behaves inside and dissipates from the cabinet is important, probably more so with mid range or full range drivers.
Fair enough, but this is a bit of a different topic. On the other hand some of your ideology isn't sitting right with me, such as..
What if it's the other way around leaving the fingerprint?
Sounds great, what did you have in mind? There are some specific enclosures that are best not used with stuffing and it helps that these are too small to support higher box modes.
So the stuffing gets hot, remembers how that came about and then recreates sound at those frequencies?
I don't think this takes away the need to stuff, where sound may work back through the cone.
You hear a lot about this "stored energy" thing and I, like you, find it untenable. I don't know of any passive mechanism in vibrations that can do this. I'd be happy to never hear this term again.
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