You could build a false wall covered with fabric.
I use panels made of polyester fibers that can't break or fly around.
As I said, I tested different fabrics over Rockwool. Results were worse than using the Rockwool acoustic tiles.
Of course they will provide additional absorption but also reflection when flow resistivity is too high. One has to balance absorber thickness and flow resistivity.
Are those Rockwool tiles laminated?
If panels are resonating then I would assume that panel area is a key factor in the delivery of resonant energy. An H frame type dipole looks like it would have more or less the same surface area as a typical enclosed box. A dipole flat baffle, if we want reasonable bass extension, might have as much or more than the same enclosed box. Each case will have sufficient radiating area and a resonant structure that needs to be dealt with.
There seems to be a continuing sentiment here that normal cabinets have "unfixable" resonances and internal reflections and that the only solution is a transmission line, a boffle or an OB. First this overstates the severity of the problem and the difficulty of the cure. Internal standing waves are easily dealt with with sufficient stuffing of fiberglass or rock wool. I state this from experience of taking internal cabinet measurements and an understanding of the materials and absorption characteristics. Structural resonances can be fixed as well, as long as we remember the key is sufficient panel damping rather than infinite cabinet stiffness.
Secondly, releasing the rear wave from our "horrible" enclosure doesn't get rid of the problem but just sends it elsewhere to be dealt with. As soon as you go to an open back speaker of any kind you have allowed the back wave of the woofer out into the room. A dipole my have a little more directivity at bass frequencies but at mid frequencies you are now radiating more at the back wall and will have to deal with that radiation.
Where before you had a cabinet that could fully absorb the rear wave now you have to achieve similar performance in your much larger room.
David S.
One could think of the back wave as an additional source in a multisub configuration which could actually be helpful in reducing modal problems below the Schröder frequency.
There are plenty of grille cloths that lose less than a dB at 10k. What were you using and how much reflection were you seeing?
David
If we compare a closed box woofer with a dipole (H frame) woofer, the H frame has to be quite larger than the CB to achieve the same SPL at say 40 Hz. I always found it harder to keep the H frame housing from resonating than an equivalent CB.
Regarding the "noise" reflected from the inside of a box: The back side of any cone/basket driver is a source of misbehaved frequency response and added noise of all sorts. I don't see many detailed reports of rear radiation in the forums. But believe me: The rear radiation of most drivers is more challenging in free air than it will be in a closed box.
Rudolf
Regarding the "noise" reflected from the inside of a box: The back side of any cone/basket driver is a source of misbehaved frequency response and added noise of all sorts. I don't see many detailed reports of rear radiation in the forums. But believe me: The rear radiation of most drivers is more challenging in free air than it will be in a closed box.
Rudolf
True, speaker grill cloth is very good. Unfortunately it is too open, so it cant keep the fiberglass from entering the room.
One also has to consider the DDR of the equipement in the experiment at the time. I feel that strides have been in improving the DDR of all equipment.
I haven't verified it qualitatively, but i'd bet that the low level ooze of time delayed stored energy from a typical MDF box -- the ooze that buries low level detail (most noticable as a loss of stage/image) -- is under that 30 dB threshold.
dave
StigErik ... I think what the fellas are trying to figure out is if the material(s) surface porosity are allowing the sound waves through. Might be the porosity is too high (passes right through and back without conversion) or not sufficient (too low .. direct reflection).
Not sure what you mean by that ?
They are fairly dense rockwool covered with some kind of fabric on one side. I used the "natural" type, where the fabric is not painted. The surface looks greenish ... It also comes in white and black paint, but the paint reduces the good acoustical properties unfortunately.
Yes of course.
The challenge is to find something that can hold back the rockrool dust, and still not hold back sound waves. It has to be a compromize.
Now, say you use a very stiff enclosure for the bass only....
panel resonances out of band, no excitation energy (or only via the "room's" acoustic environment and so much lower SPL than inside the cab).
Done!
Then damping for mids and highs.
Don't get me wrong Dave .... I have a hard time imagining any sound reproduction without some sort of resonance ... to a point, I embrace it 😛 Resonance to me is like salt, pepper, thyme, mace, cinnamon .. all can add something special or totally ruin.
For me, the frames (U or H) depths can add in just enough control over the "spice" .. and their use includes the released rear wave front which can add to the rooms reproduction atmosphere. This rear wave can be attenuated (to suit) right at the rear opening ... no need to go nuts with room treatments.
I've got nothing against box cabinets and their coloration(s) ... but .. I sipped the OB Kool-Aid and that's that I guess. ... no going back now.
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And this is why I am one of those that finds it hard to accept that a box is the best solution despite a consideration of the physics and published data - too many people finding the opposite. So I want to understand why. It must be that these people started with poor boxes, or they like the reflected sound ambience (i.e. nothing to do with box colourations per se), or they have been sipping more than the kool-Aid 😀
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Its not my place to tell people what they should and shouldn't like. If a cabinet adding some resonance floats your boat, thats fine. I get drawn in by the visual side. I'm a sucker for any tall slim cabinets made in Rosewood and would probably forgive a number of sins if the speakers look sexy enough.
Keep in mind that just because you like a particular speaker, warts and all, isn't necessarily vindication of a design premise. There are plenty of examples of designs that start from the wrong place but, due to enough positive attributes, end up being nice overall. A bit like the old Porsche 911s: "Lets hang a big aircooled engine over the back axle and see what we get". With enough evolution it has turned into a pretty nice car.
But the topic seemed to be how to push cabinet resonances to the minimum and if that is the case then we really must be guided by the physics of the situation.
David S.
Keep in mind that just because you like a particular speaker, warts and all, isn't necessarily vindication of a design premise. There are plenty of examples of designs that start from the wrong place but, due to enough positive attributes, end up being nice overall. A bit like the old Porsche 911s: "Lets hang a big aircooled engine over the back axle and see what we get". With enough evolution it has turned into a pretty nice car.
But the topic seemed to be how to push cabinet resonances to the minimum and if that is the case then we really must be guided by the physics of the situation.
David S.
Yes, that can work very well, but I think it needs to be moderate sized (or smaller) subwoofer.
David S.
Perhaps not but to my ears it goes a long way toward reducing the boxes effect (read colouration) on the driver.
Even though Dave and I aren't on the same page in this discussion, I hardly think he would say that.
Can't speak for others but I tend to over build not under.
Interesting, can't say I have a strong opinion one way or the other. Reflected sound can be 'interesting'.
Ah yes, the kool-aid days...living life like a Ken Kesey novel, our own version of Gretchen Fetchin...and a big ol' jug 'o' Kool-Aid...those were the days. 🙂
I wouldn't dream that I could design a premise on any given day of the week. ... I'm just copying an age old enclosure style.
... bet they come in Rosewood, too 😛
I remember reading a thread here where a fella was experimenting with driver baskets/mufflers for the rear wave attenuation. Seemed like a sensible alternative. Essentially, two layers of attenuation with an airspace between (for a closed box). Could prove to be a better way for U/H frames as well ... keeping panels resonances lower than what a naked driver would induce.
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I've often wondered..perhaps someone with more experience could shed some light, with all this painting of resonance as being evil, don't we have the technical ability to manipulate resonances to the point where they become just another tuning method for a speaker as a whole device?
I mean, we can tighten cabinets with rods, add or subtract a myriad of materials, add weight, et cetera... perhaps rather than view cabinet interaction as something that we should kill, would it be better..or even possible to use it as a tool for fine tuning?
What if we could (as a simple example) tune a cabinet resonance at fs, or cure a dent in response?
Do cabinets have to be sonic black holes? Maybe if that woofer in a U-Frame is 3db down at some point, the baffle could be trained with bolts or materials to resonate a little where we want?
*shrug*