Well, isn't it a quarter wavelength effectiveness type thing? A quarter-wavelength trap is what I think that tube thing is.
Panel absorbers presumably resonate at a given frequency, and this vibration is dissipated as heat or changed in frequency. Someone might explain how it works for us!
Here is what Robert Harley says about panel absorbers:
"A very inexpensive and effective low-frequency absorber can be made in a few hours for less than $20. These devices, called panel absorbers, have very high absorption at low frequencies, and can be tuned to the exact frequency and bandwidth required.
Panel absorbers can stand free or be built right into an existing wall. The inside is sealed with caulking where the wood meets the wall to make it airtight, then filled with fiberglass insulation. Next, a sheet of Masonite or plywood is nailed over the frame. Many tiny holes are then drilled into the panel. Voila - a low-frequency panel absorber. (This type of perforated panel absorber is also called a Helmholtz resonator.)
Some panel absorbers have no holes, instead using a very thin sheet of material that flexes when struck by sound. The structure's absorption frequency is a function of the airspace depth (2x4s, 2x8s, 2x10s, or 2x12s may be used) and panel thickness. The Fiberglass inside the structure broadens the absorption peak. By changing the airspace depth and (in perforated absorbers) hole size, panel absorbers can be narrowly tuned to major resonance modes in small rooms."
(Harley, 1998, The Complete Guide to High-End Audio)
Hope that's of interest! Just need some more specific details now...
-Simon
Indeed, I look forward to a physics type explaining why in one app. it reinforces sound, and in another, it attenuates them!!
Not that I care too much about how it works, but I'm just starting to have serious thoughts about making one of these things.
My listening room is a converted garage, and it has a partition wall - behind the listening position. This crappy wall is plaster on 2 sides of a thin wooden frame. I gather many American homes use this kind of construction, and that it creates a very unpleasant ~60-60hz (iirc) resonance. This would be less an absorber, but more a changer/colouriser, from what I gather. Meaning it absorbs sounds, then re-releases them with delay of course, and with a chaneged frequency spectrum. Rather like a metal and glass rack I suppose!
-Simon
Konnichiwa,
I would say by designing a speaker that works in a way that interacts minimally with the room, so as to solve the problem at the source before it happens.
Anything else strikes me as placing the Cart before the horse or driver a car from the rear wheels......
In case you ask - You need a speaker with either crdiod or dipole radiation pattern in the rooms modal range (say up to around 250...300Hz in most normal rooms. One can operate really low frequencies (blow the lowest mode of the room) as omnidirctional radiator.
Above that one would like a radiation pattern that is cardiodic or hypercardiodic with little change in the off-axis flatness up to around 5KHz and an increasing HF rolloff with increasing off-axis angle above that but flat on-axis response.
The resultant Speaker will give an excellent freedom from room interaction.
One might, for arguments sake, theorise such a system using a 12" Subwoofer (*sealed, equalised) crossed ovver to a 12" dipole Woofer at 30Hz with the dipole woofer covering up to a 300Hz X-Over point and a labyrinth enclosure loaded with a suitable coax or fullrange driver placed in a 15" spherical waveguide (aka Horn).
Another option that copmes quite close is a conventional Driver in an open baffle with a sealed subwoofer.
If we have the baffle/driver combo in room with a -6db point of 50Hz and the Subwoofer lowpassed with -6db @ 50Hz we will have a cardiod response at 50Hz with a forward response at "0db") changing to dipole with rising frequency and to omnidirectional with lowering frequencies. One would recon that at around 30Hz the Baffle/Subwoofer combo would Omnidirectional.
A normal driver in an open baffle will usually show a rear response rolling off above 500Hz....1KHz (specifics depend upon the exact driver), so unlike as with full range dipoles (Ribbons, Magneplanars and Electrostatics) the rear response can be left mostly unabsorbed, as in the image critical range the rear response is well down, making the speaker again cardiodic above around 500Hz....1KHz. If a coax or fullrange driver is used the response will become hypercardiodic above several KHz, matching fairly well the above mentioned criteria.
Hope that helps.
The alternatives are in effect converting your listening room into an anechonic chamber using Bass Traps, pillows at first and second reflection points (as minimum), loads of diffraction devices and active bass absorbers or EQ for room modes. It strikes me as a course that is rather stupid (never mind the impact on the domestic decor), considering easier approaches are available.
Sayonara
IanHarvey said:
I would say by designing a speaker that works in a way that interacts minimally with the room, so as to solve the problem at the source before it happens.
Anything else strikes me as placing the Cart before the horse or driver a car from the rear wheels......
In case you ask - You need a speaker with either crdiod or dipole radiation pattern in the rooms modal range (say up to around 250...300Hz in most normal rooms. One can operate really low frequencies (blow the lowest mode of the room) as omnidirctional radiator.
Above that one would like a radiation pattern that is cardiodic or hypercardiodic with little change in the off-axis flatness up to around 5KHz and an increasing HF rolloff with increasing off-axis angle above that but flat on-axis response.
The resultant Speaker will give an excellent freedom from room interaction.
One might, for arguments sake, theorise such a system using a 12" Subwoofer (*sealed, equalised) crossed ovver to a 12" dipole Woofer at 30Hz with the dipole woofer covering up to a 300Hz X-Over point and a labyrinth enclosure loaded with a suitable coax or fullrange driver placed in a 15" spherical waveguide (aka Horn).
Another option that copmes quite close is a conventional Driver in an open baffle with a sealed subwoofer.
If we have the baffle/driver combo in room with a -6db point of 50Hz and the Subwoofer lowpassed with -6db @ 50Hz we will have a cardiod response at 50Hz with a forward response at "0db") changing to dipole with rising frequency and to omnidirectional with lowering frequencies. One would recon that at around 30Hz the Baffle/Subwoofer combo would Omnidirectional.
A normal driver in an open baffle will usually show a rear response rolling off above 500Hz....1KHz (specifics depend upon the exact driver), so unlike as with full range dipoles (Ribbons, Magneplanars and Electrostatics) the rear response can be left mostly unabsorbed, as in the image critical range the rear response is well down, making the speaker again cardiodic above around 500Hz....1KHz. If a coax or fullrange driver is used the response will become hypercardiodic above several KHz, matching fairly well the above mentioned criteria.
Hope that helps.
The alternatives are in effect converting your listening room into an anechonic chamber using Bass Traps, pillows at first and second reflection points (as minimum), loads of diffraction devices and active bass absorbers or EQ for room modes. It strikes me as a course that is rather stupid (never mind the impact on the domestic decor), considering easier approaches are available.
Sayonara
Interesting stuff.
I think for those of us with 'bog-standard' gear, a bass trap or panel absorber makes a lot of sense!
-Simon
All very clever, but your approach means throwing away lots of my kit, which I cannot afford to do. It also looks like a low power option, which I'm not sure I can live with
I think for those of us with 'bog-standard' gear, a bass trap or panel absorber makes a lot of sense!
-Simon
Konnichiwa,
Not really, you only need to throw the sources of the problems, the speakers....
How so?
Let's postulate the following:
XLF - 12 Peerless XLS Driver or Eminence LAB 12 Linkwitz "Poles & Zero" Equaliser poleshifted to Qt = 0.5 @ 8Hz with suitable Poweramp (LM3886 Bridged/Parallel for 300W RMS into 4 Ohm?), X-Over 2nd order, -6db @ 32Hz
LF - Eminence Kappa Pro 12" Linkwitz "Poles & Zero" Equaliser poleshifted to Qt = 0.5 @ 32Hz with suitable Poweramp (LM3886 Bridged/Parallel for 300W RMS into 4 Ohm?), X-Over 2nd order, -6db @ 320Hz
MF & HF - Seas 6.5" XP Cone Coax crossed over at 320Hz & 3.2KHz, active with bridged LM3875 per driver.
Such a system could be realised on a fairly compact open baffle (15" X 36") and play VERY LOUD indeed, with around 600 - 800 Watt RMS on-board amplification (which would qualify as "high power" for you?), plus it could be easily be made timecoherent by using a subtractive filter between the Seas Coax cone and tweeter.
I thought this was "DIY Audio" and "Loudspeaker"? What excuse do you have for using "bog standard" gear?
Sayonara
SimontY said:
Not really, you only need to throw the sources of the problems, the speakers....
SimontY said:It also looks like a low power option, which I'm not sure I can live with
How so?
Let's postulate the following:
XLF - 12 Peerless XLS Driver or Eminence LAB 12 Linkwitz "Poles & Zero" Equaliser poleshifted to Qt = 0.5 @ 8Hz with suitable Poweramp (LM3886 Bridged/Parallel for 300W RMS into 4 Ohm?), X-Over 2nd order, -6db @ 32Hz
LF - Eminence Kappa Pro 12" Linkwitz "Poles & Zero" Equaliser poleshifted to Qt = 0.5 @ 32Hz with suitable Poweramp (LM3886 Bridged/Parallel for 300W RMS into 4 Ohm?), X-Over 2nd order, -6db @ 320Hz
MF & HF - Seas 6.5" XP Cone Coax crossed over at 320Hz & 3.2KHz, active with bridged LM3875 per driver.
Such a system could be realised on a fairly compact open baffle (15" X 36") and play VERY LOUD indeed, with around 600 - 800 Watt RMS on-board amplification (which would qualify as "high power" for you?), plus it could be easily be made timecoherent by using a subtractive filter between the Seas Coax cone and tweeter.
SimontY said:I think for those of us with 'bog-standard' gear, a bass trap or panel absorber makes a lot of sense!
I thought this was "DIY Audio" and "Loudspeaker"? What excuse do you have for using "bog standard" gear?
Sayonara
LOL, thanks for that!
That would certainly be a beast of a system. I'd love to see such a thing done.
I'm only 22 you know, I'm still learning!!! I bet you didn't have such an ideal system when you were my age! Seriously though, this is all giving me some stimulating thought, and probably others too...
-Simon
That would certainly be a beast of a system. I'd love to see such a thing done.
Inexperience, lack of knowledge, lack of funds, ...should I continue?
I'm only 22 you know, I'm still learning!!! I bet you didn't have such an ideal system when you were my age! Seriously though, this is all giving me some stimulating thought, and probably others too...
-Simon
Yeh, I think you know what I meant by low power. I guess I meant inefficient.
With open baffles I believe you need crap loads of power. At the moment, I have plenty - but not suitable for this. Also, your proposal does sort of require the builder to know about amps, but I've yet to build my first gainclone - it is on the cards tho!
One more thing that would worry me with such a system - fullrange drivers have a bit of a reputation for harsh and bright sound, despite lacking treble extension. This hardly excites me, as I'm very sensitive to harshness. It seems on the surface that FR drivers tend to be 'tamed' in systems by partnering them with slushy valve amps - just what I've noticed, not saying its always the case. Actually, I did notice in the Gaincard systems gallery, lots of these nutters had FR driver speakers with their gaincard...
-Simon
Konnichiwa,
Yes, I'm looking for myself at a "grown-up" version of this when I move into a larger house - this will have a 21" Sealed box "XLF" woofer, 21" Woofer with X-Over @ 125Hz and a 15" (Tannoy) Coax as "fullrange, with ribbon or ring radiator supertweeter. Tannoys and Supertweeter Passive, the rest active.
No, I did not.
I had three nice systems though.
One using a DIY EV based Speaker (15" SP15 Woofer, 1824M Midrange Driver with 8HD horn and T35 Tweeter, passive X-Over) driven by east german Koelleda Studio valve Amp's, one large box (dual walls, sandfilled) with a 12" Studio Coax driven by matching Solid State Amp's (both in my bedroom converted to midown studio) and in the living room a DIY "Tower" speaker, 3-Way active with Chip Amplifiers and dual 8" Woofer, 5" wideband and Piezo "super" tweeter.
I don't think so. My Supravox Open Baffles work fine with 5 Watt (#45 PP Amplifier) at near realistic levels for large scale classical. Sensitivity 96db/W/m, easy 8 Ohm load, 7Ohm minimum.
This no doubt caused by misapplied Lowthers. The right fullrange chassis operated as intended (Lowther front AND rear hornloaded, Supravox open baffle) sounds evenly balanced.
Sayonara
SimontY said:
Yes, I'm looking for myself at a "grown-up" version of this when I move into a larger house - this will have a 21" Sealed box "XLF" woofer, 21" Woofer with X-Over @ 125Hz and a 15" (Tannoy) Coax as "fullrange, with ribbon or ring radiator supertweeter. Tannoys and Supertweeter Passive, the rest active.
SimontY said:
No, I did not.
I had three nice systems though.
One using a DIY EV based Speaker (15" SP15 Woofer, 1824M Midrange Driver with 8HD horn and T35 Tweeter, passive X-Over) driven by east german Koelleda Studio valve Amp's, one large box (dual walls, sandfilled) with a 12" Studio Coax driven by matching Solid State Amp's (both in my bedroom converted to midown studio) and in the living room a DIY "Tower" speaker, 3-Way active with Chip Amplifiers and dual 8" Woofer, 5" wideband and Piezo "super" tweeter.
SimontY said:
I don't think so. My Supravox Open Baffles work fine with 5 Watt (#45 PP Amplifier) at near realistic levels for large scale classical. Sensitivity 96db/W/m, easy 8 Ohm load, 7Ohm minimum.
SimontY said:
This no doubt caused by misapplied Lowthers. The right fullrange chassis operated as intended (Lowther front AND rear hornloaded, Supravox open baffle) sounds evenly balanced.
Sayonara
Kuei,
Thanks for answering my queries, but don't feel you must, I do realise I go on a bit, sometimes without being sure of what I'm saying, hence upsetting your friend [unintentionally].
It looks as if even when you were younger you were accustomed to fairly elaborate and no doubt high quality systems. Your 'grown up' di-pole and sub system sounds interesting, I'm thinking it would take up a lot of space! (I'm sure it would be worth it though)
re. the low-power thing, I think I had my mind on EQing the bass and hence reduced 'power handling' (cant think of the appropriate phrasing), and the need for large drivers and powerful amps, just to clear that up. I forgot some (yours) are ran with no EQ, and of course can be sensitive/efficient (when bass is not concerned)...
You are correct in assuming I'd read about Lowthers sounding nasty. I am now a little better informed though
I am starting to get the feeling I am missing out by never having heard a valve amp, a class-A amp, a horn-loaded speaker, an electrostatic, planar or ribbon, or an open-baffled one! The most elaborate I've heard is a transmission-line (gorgeous lower-mid bass and mids!!) I am very used to the 'same old' commercial stuff (though some is quite nice, most stuff in the hi-fi shop I do some work in is mediocre compared to even my modest setup! e.g. only a speaker costing £2000 sounds more detailed) Anyway, I shall stop wittering on and get back to work now!
-Simon
Thanks for answering my queries, but don't feel you must, I do realise I go on a bit, sometimes without being sure of what I'm saying, hence upsetting your friend [unintentionally].
It looks as if even when you were younger you were accustomed to fairly elaborate and no doubt high quality systems. Your 'grown up' di-pole and sub system sounds interesting, I'm thinking it would take up a lot of space! (I'm sure it would be worth it though)
re. the low-power thing, I think I had my mind on EQing the bass and hence reduced 'power handling' (cant think of the appropriate phrasing), and the need for large drivers and powerful amps, just to clear that up. I forgot some (yours) are ran with no EQ, and of course can be sensitive/efficient (when bass is not concerned)...
You are correct in assuming I'd read about Lowthers sounding nasty. I am now a little better informed though
I am starting to get the feeling I am missing out by never having heard a valve amp, a class-A amp, a horn-loaded speaker, an electrostatic, planar or ribbon, or an open-baffled one! The most elaborate I've heard is a transmission-line (gorgeous lower-mid bass and mids!!) I am very used to the 'same old' commercial stuff
(though some is quite nice, most stuff in the hi-fi shop I do some work in is mediocre compared to even my modest setup! e.g. only a speaker costing £2000 sounds more detailed) Anyway, I shall stop wittering on and get back to work now!-Simon
Konnichiwa,
I figure on placing this in a 24" X 24" X 48" package, actually.
The carry the LF down to around 50Hz, not that different from many standmounting Speakers....
If you find your self in Londra, the Capital of the Dark Empire of Granbretan, drop by at my place.
Sayonara
SimontY said:
I figure on placing this in a 24" X 24" X 48" package, actually.
SimontY said:
The carry the LF down to around 50Hz, not that different from many standmounting Speakers....
SimontY said:
If you find your self in Londra, the Capital of the Dark Empire of Granbretan, drop by at my place.
Sayonara
Just to back up what T (KYW) has said, full-range units in an open baffle don't scream (at least my modified Goodmans 201's don't) and can be easily driven from something like a Gainclone or valve amp.
I have my 4 x 2 foot baffles in a room roughly 13 by 12 feet and if you can live with the physical presence, they are not too big for the room.
When you hear the sound of a simple OB system like this, you will understand why we are so keen to 'shout' about them! While cost is a big problem for most people when it comes to experimenting, this sort of system really can be tried out for peanuts if you go for those Chiare drivers and start with a simple plywood/chipboard baffle and a chip amp. (What ever next - a chipboard amp?)
I have my 4 x 2 foot baffles in a room roughly 13 by 12 feet and if you can live with the physical presence, they are not too big for the room.
When you hear the sound of a simple OB system like this, you will understand why we are so keen to 'shout' about them! While cost is a big problem for most people when it comes to experimenting, this sort of system really can be tried out for peanuts if you go for those Chiare drivers and start with a simple plywood/chipboard baffle and a chip amp. (What ever next - a chipboard amp?)
<300 hz frequencies are those with the most energy. So, to be able to reproduce them with the least distortion (-> with the most ease), there are two options:
1. High sensitivity drivers (large and light, with big magnets) which are also easy to drive.
2. _Big_ amps that drive low sensitivity drivers (small and heavy, with small magnets).
Option 1. is by far the most easy one and practically the better sounding one.
Once you've heard a "1." setup you'll probably curse at all commercial 6.5" low sensitivity drivers who are only used for their looks.
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