Does anybody here have any knowledge of enclosures built around dense FG panels?
A wood skeleton frame with solid baffle could be constructed and infilled with dense FG ..(like a frame/panel door). I've read the spec sheets on 8lb cu.ft. glass and it attenuates over 90% @ 2" thickness.
I realize the trick here would be to "pretty up" the raw panel .. can be done easy enough. Impact durability would be low on the panel as a trade off ... but might it work well as there wouldn't be any interior box reflections to deal with?
A wood skeleton frame with solid baffle could be constructed and infilled with dense FG ..(like a frame/panel door). I've read the spec sheets on 8lb cu.ft. glass and it attenuates over 90% @ 2" thickness.
I realize the trick here would be to "pretty up" the raw panel .. can be done easy enough. Impact durability would be low on the panel as a trade off ... but might it work well as there wouldn't be any interior box reflections to deal with?
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Although the sound attenuation of fiberglass is great for higher frequencies it will become quite transparent at low frequencies. If you want an open baffle condition for LF then you will have it, but then the fiberglass won't be achieving much other than killing any dipole action from the midrang up.
David S.
In this particular case .. yes, dipole bass is the desire. The midrange would be sans back panel. I've experimented with a "U" frame mid cabinet structure and thought about the dense FG as a more _dead_ side panel alternative. I like the sound of the "U" frame mid with this particular driver. It brings a bit more "tone" into the sound.
Is the consensus that for bass frequencies the dense FG panel is useless .. for attenuation purposes? ... in any thickness? (within reason here)
@croat47 ... yep. any number of finishes could be used to make such an enclosure "nice" looking. If a fellas strong talent was metalworking for instance, I don't see why the frame/baffle couldn't be steel/aluminum either.
Fiberglass has very high absorption for any frequency where it is about 1/4 wave thick or thicker. In fact the curves I've seen show that it has decent absorption to thickness equals 1/6th wavelength dimensions. As you make it thicker it absorbs proportionally to a lower frequency.
David S.
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Remember, for many, the box needs to be 'sealed' or 'ported' in order to achieve improved sensitivity at l.f. so an open frame with absorbing panels is not a box speaker in my books. If the box has to support pressure waves (e.g. bass reflex) then it needs to be rigid and non-porous.
As for putting the box in the walls of the room - this is potentially another ideal situation. But again, I believe this is more like an IB than what is typically though of as a box speaker. And let's face it, this is impractical for most people.
Most people use box speakers that are either floorstanders or on standmounters and they position them to suit their local domestic constraints. The box could be made wide with rounded shapes to minimize diffraction, like the Poor Man's Strad.
As for putting the box in the walls of the room - this is potentially another ideal situation. But again, I believe this is more like an IB than what is typically though of as a box speaker. And let's face it, this is impractical for most people.
Most people use box speakers that are either floorstanders or on standmounters and they position them to suit their local domestic constraints. The box could be made wide with rounded shapes to minimize diffraction, like the Poor Man's Strad.
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All good/true points. All designs are not suitable in every case. However, ... being a DIY venue though, we're able to embark on directions that might not be suitable for "mass production" in certain cases. Things that may have been chucked in favor of other considerations. (such as, $$$ .. etc.)
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Agree! - but I think I need a solid box to get the bass extension benefits, could I use the fibreglass inside the box - box would have to be pretty large though.
I wasn't suggesting you chip out a hole for the box in the wall at all...
Hardly practical. But all this talk of open baffle and fibreglass doesn't help the cause. I'd see that as being FINITE baffle, if you follow. Not INFINITE baffle.
Steen Duelund's diagram does make you see the whole room/loudspeaker interaction. Steen actually mentions that uncoloured speakers sound WRONG initially. We're not used to the sound, being so used to boxiness. He likes closed box, will compromise to Dynaco style aperiodic damped port. But never reflex. Seems to me it's the front baffle that needs some thought. The other 5 panels can be whatever you fancy.
Bang and Olufsen made panel speakers for a while, like the Beovox P30 pictured below. Just a 6" plus tweeter. Relies on wall reinforcement for bass.
Also below is a regular sort of reflex box that is quite well thought out IMO. The bracing reinforces the solid timber front baffle where the grain is weak. The rest is chipboard I think. I still like the AR-LST shape. Seems a good compromise.
Hardly practical. But all this talk of open baffle and fibreglass doesn't help the cause. I'd see that as being FINITE baffle, if you follow. Not INFINITE baffle.
Steen Duelund's diagram does make you see the whole room/loudspeaker interaction. Steen actually mentions that uncoloured speakers sound WRONG initially. We're not used to the sound, being so used to boxiness. He likes closed box, will compromise to Dynaco style aperiodic damped port. But never reflex. Seems to me it's the front baffle that needs some thought. The other 5 panels can be whatever you fancy.
An externally hosted image should be here but it was not working when we last tested it.
Bang and Olufsen made panel speakers for a while, like the Beovox P30 pictured below. Just a 6" plus tweeter. Relies on wall reinforcement for bass.
Also below is a regular sort of reflex box that is quite well thought out IMO. The bracing reinforces the solid timber front baffle where the grain is weak. The rest is chipboard I think. I still like the AR-LST shape. Seems a good compromise.
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So, Steen preferred aperiodic box speakers (to OB's) - why ? (not that I agree or disagree with him)
I see the diagram of the 'two closed rooms' but I've got this feeling I'm not understanding all that this is trying to teach me ?
What I was thinking about in terms of a wider baffle for reduced diffraction is this (attached) :
I see the diagram of the 'two closed rooms' but I've got this feeling I'm not understanding all that this is trying to teach me ?
What I was thinking about in terms of a wider baffle for reduced diffraction is this (attached) :
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A lot has been said...my 2 cents...random points to ponder.
A box (if a speaker has one) must be well damped and yet stiff enough to prevent flex. Also when one uses a combination of materials the box becomes sonically more inert than if a box of the same thickness used just one material for example a 25mm thick MDF box vs say 3 layers of 6mm ply with 2 layers of 3mm of resin bonded fiberglass sandwiched betweem the ply layers (6+3+6+3+6 = 24mm).
Curved walls reduce standing waves but if one actually bent the ply (instead of using layers) - and 6mm ply is easy to bend - the pre-stressed (aka bent) ply would be stiffer than the same ply before it was bent hence making the box stiffer but not adding to its weight and retaining much of the damping wood provides.
OB's advantage extends beyond the 100-500Hz range. OB helps eliminate low bass standing waves. In either case (sub 100 and 100-500) it is the reflected energy from the backwave that is the cause of all trouble. If the back wave of the speaker can be absorbed and the energy converted to another form (say heat) then OB and box should sound close. If the backwave hence hit a loose curtain of glass wool fibers or something similar the absorbent material would absorb much if not all the back wave before it hit the rear panel of the speaker.
What if we place a vertical brace say 5-6" behind the baffle in a traditional box speaker and then attach a sheet of foam, polyfill or other absorbent material to this vertical brace? Would/Could enough of the back energy be absorbed? If this is achieveable then all we have is a baffle and about 6" of side walls to contend with. The baffle is common to both OB and Box speakers.
The main problem with boxes in my opinion is reflected energy. Damping material will attenuate reflections, but not in any way eliminate them. Greater distance between the speaker cone and the damping material helps, but even if we have a meter or more, reflections are still measureable and audible.
Even the best damping materials will give us reflection just 10-15 dB below the direct signal if they are placed 10 cm from the source, and that just got to have a significant effect.
Even the best damping materials will give us reflection just 10-15 dB below the direct signal if they are placed 10 cm from the source, and that just got to have a significant effect.
I agree. The question then is that unless OBs are placed 1m or more from the rear wall there would be reflections to contend with OBs too right?
An OB largely by definition (to produce adequate bass) becomes a large baffle floorstanding unit (like the Hawthorne Silver Iris or Jamo 909). Placing these large baffles a meter from walls flies in the face of WAF. That however is a seperate argument but is probably why boxes remain popular.
Correct, room reflections is really the same problem as internal box reflections, but the room is larger and those reflections makes different audible effect than box reflections.
I have tried as hard as I can to get rid of the reflection from behind my dipoles. Even at 1,5 meter and a lot of expensive damping material, the reflections are still there ... although low in level.
An OB needs to be large for good bass support, but not for the midrange and treble, where the wave lengths are much shorter. The Jamo, to take one example, is way too big for good midrange polar response, as Stereophile's measurements show quite clearly.
I have tried as hard as I can to get rid of the reflection from behind my dipoles. Even at 1,5 meter and a lot of expensive damping material, the reflections are still there ... although low in level.
An OB needs to be large for good bass support, but not for the midrange and treble, where the wave lengths are much shorter. The Jamo, to take one example, is way too big for good midrange polar response, as Stereophile's measurements show quite clearly.
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So if I understand correctly, these room reflections are an issue in the mids, not the bass, because the distances involved are not so relevant below.... well Stig is using 1.5m baffle-to-wall separation which is a wavelength of 220Hz.
This means box colourations in the bass is not the motivation to use OB, the motivation to use OB for bass (< 220Hz?) is how the bass couples with the room. And some will argue that OB is still not ideal for bass because it's so darn inefficient, requires large baffles and/or EQ so it's much better instead to use multiple boxes.
The issue with box colourations, as mentioned already, remains the mids. And OB goes a long way to helping out compared to a lot of box designs, but it doesn't necessarily address it completely because you just shift the problem to the room. And Stig has found that these reflections are no easier to solve in the room even with 'expensive damping'.
Does the Nautilus speaker point the way to better absorption of the back-wave for mids ? or some kind of heavily damped TL ?
This means box colourations in the bass is not the motivation to use OB, the motivation to use OB for bass (< 220Hz?) is how the bass couples with the room. And some will argue that OB is still not ideal for bass because it's so darn inefficient, requires large baffles and/or EQ so it's much better instead to use multiple boxes.
The issue with box colourations, as mentioned already, remains the mids. And OB goes a long way to helping out compared to a lot of box designs, but it doesn't necessarily address it completely because you just shift the problem to the room. And Stig has found that these reflections are no easier to solve in the room even with 'expensive damping'.
Does the Nautilus speaker point the way to better absorption of the back-wave for mids ? or some kind of heavily damped TL ?
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Yes, a properly designed TL should be good for absorbing the midrange back-wave. Its a wonder why so few actually do this.
I agree that most of the point with OB's in the bass is how they couple to the room. Theoretically, they dont energize standing waves at all, quite the opposite of the multiple boxed subwoofer arrangement. But an other thing is that a flat baffle or H-baffle will have the same acoustic impedance on each side of the driver cone. This is far from the case with closed of reflex boxes.
I agree that most of the point with OB's in the bass is how they couple to the room. Theoretically, they dont energize standing waves at all, quite the opposite of the multiple boxed subwoofer arrangement. But an other thing is that a flat baffle or H-baffle will have the same acoustic impedance on each side of the driver cone. This is far from the case with closed of reflex boxes.
Just for interest, here's an established design using a tapered transmission line for the midrange. A sort of heavily damped cheesewedge open at the back. The Fried Studio V. FWIW, it uses a series crossover too, but we won't go into that. LOL
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That's an interesting point - how much difference between front and back loading of a cone in OB vs box is there and how much of a difference is significant - what does it do to the sound and is this another contender for the source of 'box colourations' ?
p.s. I like the cheese wedge