Re: Re: Ethan Winer
Far be it from me to play the role of expert. Perhaps I should not have said "obsolete." The specific problem I mean to address is bass reflections. Ethan Winer supports an open forum in which much open debate is encouraged. In the coming months, I will be researching further to understand how much of Real Traps is hifi voodoo, as you put it, and how much is reasonable science, in addition to addressing specific resonant ...
...nodes? modes?
Dave
paulspencer said:
Far be it from me to play the role of expert. Perhaps I should not have said "obsolete." The specific problem I mean to address is bass reflections. Ethan Winer supports an open forum in which much open debate is encouraged. In the coming months, I will be researching further to understand how much of Real Traps is hifi voodoo, as you put it, and how much is reasonable science, in addition to addressing specific resonant ...
...nodes? modes?
Dave
I wouldn't use the term "reflections" in the context of bass and I believe it is "modes" and not nodes that are in question. I recall from high school physics that nodes and antinodes are the result of the combinations of the sound waves of 2 speakers radiating into half space. In a room we are concerned with room resonances or modes caused by standing waves. If I understand correct, the term modes rather and nodes applies here.
Some explanations from the book I referenced earlier (seriously consider this book - it's not easy to find good information on room acoustics that is for small spaces):
Room acoustics can be discussed in terms of two regions: the modal region and the geometric acoustical region. The Shroeder frequency is the point of transition between the two, typically 200 Hz. Above this point, sound travels as rays and it is relevant to think in terms of "reflections." Room modes above this are so densely spaced that the response is much smoother. In the modal region, room modes are spaced further apart, and this is what causes problems.
Bass absorption reduces the magnitude of the modes, but doesn't eliminate them. Now this is where my understanding begins to reach its limits ...
Monopoles are pressure mode transducers and have maximum pressure at room boundaries, this is why bass traps are placed in corners and on wall surfaces. Dipoles are the opposite and thus bass traps are much less effective, but I believe they have a smoother response that may not require traps. I'm not sure if they are worth using at all in this case.
Now put a dipole in the room and measure it. Then attempt to deal with any modes with helmholz resonators. Then if further attention is warranted, eq as a last resort. Much could be learnt from trying this.
Your room seems ideal for dipoles. It would be interesting in your room to try some diy panel absorbers on the end walls with helmholz resonators behind (which could actually be a very interesting visual feature and talking point - even if they don't end up performing well). Then you might use a acoustic diffusers where you have a single reflection between you and the speakers.
You may try dipoles only for bass or full range as well. If you go full range dipoles they will have near constant directivity and you reduce side wall reflections. This means there will be less coloration from the room and the off axis response will match the on axis response in character. The result is that you can afford to have a more live sounding room, rather than have to make it dead. You room treatment for the bass range will also reduce the interaction with the end walls, which is normally more prominent with dipoles.
I'm not one to think that dipoles are the best for every situation, but in your case they do seem ideal.
If you do get into dipole woofers, you might also look into the difference between H & W frames and U frame; the former has a figure of 8 dipole polar response and the latter is cardiod, with more interaction with the side walls. The latter relies less on polar response but gains 6db in output.
Some explanations from the book I referenced earlier (seriously consider this book - it's not easy to find good information on room acoustics that is for small spaces):
Room acoustics can be discussed in terms of two regions: the modal region and the geometric acoustical region. The Shroeder frequency is the point of transition between the two, typically 200 Hz. Above this point, sound travels as rays and it is relevant to think in terms of "reflections." Room modes above this are so densely spaced that the response is much smoother. In the modal region, room modes are spaced further apart, and this is what causes problems.
Bass absorption reduces the magnitude of the modes, but doesn't eliminate them. Now this is where my understanding begins to reach its limits ...
Monopoles are pressure mode transducers and have maximum pressure at room boundaries, this is why bass traps are placed in corners and on wall surfaces. Dipoles are the opposite and thus bass traps are much less effective, but I believe they have a smoother response that may not require traps. I'm not sure if they are worth using at all in this case.
Now put a dipole in the room and measure it. Then attempt to deal with any modes with helmholz resonators. Then if further attention is warranted, eq as a last resort. Much could be learnt from trying this.
Your room seems ideal for dipoles. It would be interesting in your room to try some diy panel absorbers on the end walls with helmholz resonators behind (which could actually be a very interesting visual feature and talking point - even if they don't end up performing well). Then you might use a acoustic diffusers where you have a single reflection between you and the speakers.
You may try dipoles only for bass or full range as well. If you go full range dipoles they will have near constant directivity and you reduce side wall reflections. This means there will be less coloration from the room and the off axis response will match the on axis response in character. The result is that you can afford to have a more live sounding room, rather than have to make it dead. You room treatment for the bass range will also reduce the interaction with the end walls, which is normally more prominent with dipoles.
I'm not one to think that dipoles are the best for every situation, but in your case they do seem ideal.
If you do get into dipole woofers, you might also look into the difference between H & W frames and U frame; the former has a figure of 8 dipole polar response and the latter is cardiod, with more interaction with the side walls. The latter relies less on polar response but gains 6db in output.
kneadle said:
??? Dipoles only reduce any sidewall reflections. The only way they will reduce the room's dominant length modes is to not excite them, i.e. output rolled off below ~75Hz.
Basstraps are Helmholtz resonators so these aren't BTs per se, but a mini-version of the diaphragmatic absorber I suggested, so not as effective.
IMO there is no 'gulf' between a HIFI and studio app, the sonic goals are identical, i.e. hear as accurate a reproduction of the signal as practical with current technology, ergo the ideal HIFI room is identical to a recording studio mixing room. Obviously, this isn't practical for most folks, but for those who have the luxury of a dedicated audio and/or video room, it seems somewhat of a waste to me to take a compromised approach to room design.
So I take it you've chosen to go this route rather than the closer to ideal studio design I suggested?
Room Eigenmodes (AKA standing waves) consist of nodes (positive pressure wave) and antinodes (negative pressure (rarefaction) waves).
GM
GM said:
Goodness. Ideal? I'm still trying to conceive of the Ding an Sich. Is it feasible? What do I need to do now? What will I need to manufacture myself? What problems should be solved permanently and which should be addressed more temporarily?
The beauty of the thing is that the room can evolve.
I really appreciate your suggestions, information and corrections. This is a great forum.
Dave
Hi Kneadle - Here is a photo of the listening end of my project studio. My room is 23x10x7 - sound familiar? It's 2x6 framed, well insulated and vapor barriered, carpet on the floor, sheetrock, flat latex. I have spent quite a bit of time with test tone generator, earthworks mic and spectrograhic analyzer learning about the eccentricities of this space. If you do the math for your space you will find that Dave in an earlier post is on the money about the problem spot being just over 100hz - mine is 110. I produce music as well as listen here so the low to moderate level nearfield monitoring I do is fundamentally different from your plans for a theater/listening space. Still, here are a few ideas. Getting your speakers and subs sorted out is the first step, I think. After that, comes the room. If your walls are block, that's about death for high freq. reflectivity and have to be covered. Here are some sites that talk about treating rooms that identify typical room mode patterns and might help:
http://www.asc-hifi.com/articles/iar89.htm
http://www.asc-hifi.com/acoustic_basics.htm
http://www.wsdg.com/resources/resour.php?SL=ta&BL=3
The simple treatments I have begun can be seen in the photo - stock high texture 2'x2' ceiling panels mounted casually with 1x2
stringers, backed with compressed open collumns of foam to reduce resonance of the spaces behind and the panels themselves. Don't know what the official acoustic rating of these things is, but putting your ear near one gives you a rough idea - half your head goes dead. These things alone made a huge improvement in my space. I plan to treat other corners of the room in similar fashion over time, and since I sometimes record live musicians in the space, I will build several 4'x7' movable panels using similar material to place about the room as needed. You can get standard ceiling tiles with perforated matte finish (more reflective I imagine but still useful and which shed less with contact) for as little as $30 per 16 - the heavily textured ones I use in the corners were $53/12 and took about 2 hrs to install.
You can spend a lot of $ on foam wedges and such that cost the manufacturer very little to produce and will kill everything in the house in a fire. I'm not sure they will do more than these panels,
which have UL fire resistance etc. I agree with another earlier post - as long as your walls aren't too reflective, deal with the bass modes and you should be ok. One other thought. Some smart people are of the opinion that some of the most serious problems in studios are caused by early reflection and reslutant
comb filtering and other nasty phenomena that distort your experience of the sound. Any reflective surface very near the speaker that can alter the path of the sound to your ear is a bad thing. So if your speakers are near the side walls its probably good to put some high freq. absorbant stuff up in the right places. End of rant.
Cheers, NNK
http://www.asc-hifi.com/articles/iar89.htm
http://www.asc-hifi.com/acoustic_basics.htm
http://www.wsdg.com/resources/resour.php?SL=ta&BL=3
The simple treatments I have begun can be seen in the photo - stock high texture 2'x2' ceiling panels mounted casually with 1x2
stringers, backed with compressed open collumns of foam to reduce resonance of the spaces behind and the panels themselves. Don't know what the official acoustic rating of these things is, but putting your ear near one gives you a rough idea - half your head goes dead. These things alone made a huge improvement in my space. I plan to treat other corners of the room in similar fashion over time, and since I sometimes record live musicians in the space, I will build several 4'x7' movable panels using similar material to place about the room as needed. You can get standard ceiling tiles with perforated matte finish (more reflective I imagine but still useful and which shed less with contact) for as little as $30 per 16 - the heavily textured ones I use in the corners were $53/12 and took about 2 hrs to install.
You can spend a lot of $ on foam wedges and such that cost the manufacturer very little to produce and will kill everything in the house in a fire. I'm not sure they will do more than these panels,
which have UL fire resistance etc. I agree with another earlier post - as long as your walls aren't too reflective, deal with the bass modes and you should be ok. One other thought. Some smart people are of the opinion that some of the most serious problems in studios are caused by early reflection and reslutant
comb filtering and other nasty phenomena that distort your experience of the sound. Any reflective surface very near the speaker that can alter the path of the sound to your ear is a bad thing. So if your speakers are near the side walls its probably good to put some high freq. absorbant stuff up in the right places. End of rant.
Cheers, NNK
Attachments
nonamekid said:
Again, I came to the right place for advice.
In fact, NNK, the secondary use for my room is to record some acoustic instruments. I'm glad to hear that your space can produce useful recordings.
Dave
PS--where does the number 100-120Hz come from? How do you figure that in theory? It's one thing for it to be true in reality...
kneadle said:
You're welcome!
Ding an Sich. ??
First you need to come up with some final room dims. Ideally you want the tapered walls to slope outwards toward the rear at a minimum of 1"/ft out to the room's width where it will be terminated by the false wall, but with only an 11ft width to work with this makes for a rather narrow front wall, hence my slightly non-ideal suggestion. If you choose the peaked rear wall, then there's no way to meet this, but any taper is better than parallel.
The two tapered and rear false wall's construction requires knowing the surface density in lbs/ft^2 of various materials available locally (PB, chipboard, MDF in various thicknesses) to determine wall thickness. A distributor (not retailer) should have the manufacturer's spec sheets. Ideally you need to measure the room's modes to get the design ~right from the get-go, but using room dims was good enough for me the one time we did this (also a basement, though somewhat larger) and you can always buy thinner sheets to further mass load them if you feel they don't attenuate the LF enough.
Once these are up, you'll probably find that they are still too reflective for higher frequencies so padding/cloth material is added to them to suit, same as shown on Ethan's drawings/pics. we tossed rolls of R19 fiberglass insulation into the cavities before covering the framing, but I'm not sure if it's required or not. Anyway, can't hurt and isn't expensive, at least down here.
Ethan's ceiling treatment should work great, but considering your low ceiling you might want to do as we did and just double up acoustic ceiling tiles after stuffing the floor joists with R19, then all that's left is to add thick jute or felt underlayment (3/4" min.) and a high density carpet on the floor.
GM
GM said:
Sorry, a little philosophy term there. It is a term some German feller invented to help discuss the question: is ideal a reality? You know, "I don't actually want to work for a living."
Great line from Family Guy : Peter Griffin mentions his great great uncle, a dutch philosopher. He's sitting on a stool in a sparsely furnished apartment in 19th Century Netherlands, with his chin propped up by his fist. His wife yells, "Will you take out the trash?!?" Upon which Philosopher Griffin answers, "Why?"
Hilarious.
What's a dim? Dimension? The room is, quite precisely, as it stands now, 22 ft by 11 ft by 7 ft 5 inches. The drop ceiling is mounted directly upon 10 inch rafters (is that the right construction term? Joists?), putting the drop ceiling precisely at 6 ft 7 inches.
The door to the room begins roughly 2 ft from the rear wall, entering from the side wall. It is precisely 30 inches wide.
I have not had time to measure the freq response. I am still unpacking. Will advise.
Dave
Hi Kneadle - The math for room modes works like this: Enclosed chambers with relective walls have resonant frequencies. "(Find the) fundamental bass resonance of the room. What is this frequency for your room? It's the half wavelength frequency for the speed of sound travelling this longest dimension. To figure this out, simply calculate 550 (which is half the speed of sound) divided by the longest dimension in feet. For example, a room with a longest dimension of 15 feet would have its fundamental resonance at 550/15= 37 hz."
The matrix of room resonances is bit more complex. Since you have three demensions, you have three sets of resonances, one fundamental for each wall length and their overtones, ie double the fundamental, triple the fundamental, quadruple the fundamental, etc. If any of those multiples are close to each other (say within 10hz) they can amplify one another and act as "wolf notes" of the room and skew your perception of music auditioned there, not to mention recorded. You'll hear these at various places in the room but especially in corners as described in the links above. If you were to run a sine wave through your system at 50 hz the room would pretty much hoot at that frequency and you could stick your head into the half and quarter collumns at mid walls and corners and hear the zones real clearly. Putting speakers in these hotspots would be terrible.
Your room looks like this:
22 11 6.5
fund. 25hz 50hz 84.6hz
OT 1 50 100 169.2
OT2 75 150 253.8
OT3 100 200 338.4
OT4 125 250 423
OT5 150 300 507.6
etc.
So, Since your room's width is exactly half it's length your problem modes will be a function of that relationship and the multiple nature of overtones. It should ring badly at 50, 100, 150, 200, 250hz... (The worst possible room is a cube because all the resonances are the same). This means you will probably need to change the length (it's too narrow to mess with the width) of the room with partitions, movable or otherwise if you want to tame these overlapping resonances. Do the math with various lengths and see what creates the fewest overlaps across the three collumns - should give you an idea of what you need to do. Because the resonances gather in corners, I think treating corners is the place to start with bass issues, hence the treatment in my photo. High frequency flapping about a space is a different issue - all this stuff is in those links. Read up and have a go at it. BTW, I think treating a room to deal with the worst of the problems is probably a better solution than trying to EQ it - been there...
Cheers, NNK
The matrix of room resonances is bit more complex. Since you have three demensions, you have three sets of resonances, one fundamental for each wall length and their overtones, ie double the fundamental, triple the fundamental, quadruple the fundamental, etc. If any of those multiples are close to each other (say within 10hz) they can amplify one another and act as "wolf notes" of the room and skew your perception of music auditioned there, not to mention recorded. You'll hear these at various places in the room but especially in corners as described in the links above. If you were to run a sine wave through your system at 50 hz the room would pretty much hoot at that frequency and you could stick your head into the half and quarter collumns at mid walls and corners and hear the zones real clearly. Putting speakers in these hotspots would be terrible.
Your room looks like this:
22 11 6.5
fund. 25hz 50hz 84.6hz
OT 1 50 100 169.2
OT2 75 150 253.8
OT3 100 200 338.4
OT4 125 250 423
OT5 150 300 507.6
etc.
So, Since your room's width is exactly half it's length your problem modes will be a function of that relationship and the multiple nature of overtones. It should ring badly at 50, 100, 150, 200, 250hz... (The worst possible room is a cube because all the resonances are the same). This means you will probably need to change the length (it's too narrow to mess with the width) of the room with partitions, movable or otherwise if you want to tame these overlapping resonances. Do the math with various lengths and see what creates the fewest overlaps across the three collumns - should give you an idea of what you need to do. Because the resonances gather in corners, I think treating corners is the place to start with bass issues, hence the treatment in my photo. High frequency flapping about a space is a different issue - all this stuff is in those links. Read up and have a go at it. BTW, I think treating a room to deal with the worst of the problems is probably a better solution than trying to EQ it - been there...
Cheers, NNK
Listening Room construction is a great subject and probably one of the most overlooked items that affects sound reproduction.
One member of the Pacific Northwest Audio Society, Winston Ma, has what some have called the finest listening room in existence. I've been invited over several times, but haven't been able to make the pilgrimage. You can read an article about the room at:
http://www.positive-feedback.com/Issue3/maroom.htm
BTW: Winston Ma was one of the judges at "The Puget Sound" DIY speaker contest held last Saturday.
Best Regards,
TerryO
One member of the Pacific Northwest Audio Society, Winston Ma, has what some have called the finest listening room in existence. I've been invited over several times, but haven't been able to make the pilgrimage. You can read an article about the room at:
http://www.positive-feedback.com/Issue3/maroom.htm
BTW: Winston Ma was one of the judges at "The Puget Sound" DIY speaker contest held last Saturday.
Best Regards,
TerryO
sberube said:
Sonopan panels are actually made of wood fibre and industrial wax. Their main use inside speaker enclosures is for sound deadening/mass loading, much the same as tar felt but less messy and cheaper. The pegboard design means they take up less internal volume than their thickness would lead one to assume. They are primarily used in construction for soundproofing purposes but the manufacturer lists loudspeaker applications as one of its intended uses as well.
Missing Dimension
I think we are missing an important dimension? You have a "drop" or "acoustic" ceiling which means in terms of low frequencies the true ceiling height is above where the floor joists are decked with flooring.
What is the measurement from the basement floor right up into the joists above? Joist size? Joist spacing?
Cheers,
Shawn.
Oops! You did post the ceiling spec in post 48.
I think we are missing an important dimension? You have a "drop" or "acoustic" ceiling which means in terms of low frequencies the true ceiling height is above where the floor joists are decked with flooring.
What is the measurement from the basement floor right up into the joists above? Joist size? Joist spacing?
Cheers,
Shawn.
Oops! You did post the ceiling spec in post 48.
Holy Moly! Who resurrected this thread?
In the two years since I last paid attention to this thread, I got sick of my present digs, so I bought a new house to get a whole new ballgame going on. Bigger basement, taller ceilings, non-leaky basement, etc., etc.
Construction on the HT/studio commences in October 2006, right after I put a new roof on the garage. In the meantime, I've been miserably awaiting October 2006, reading, studying and learning about the ideal room.
Want me to post plans and progress?
Dave
In the two years since I last paid attention to this thread, I got sick of my present digs, so I bought a new house to get a whole new ballgame going on. Bigger basement, taller ceilings, non-leaky basement, etc., etc.
Construction on the HT/studio commences in October 2006, right after I put a new roof on the garage. In the meantime, I've been miserably awaiting October 2006, reading, studying and learning about the ideal room.
Want me to post plans and progress?
Dave
Let's get the ball rolling, eh?
Scroll down to the picture entitled "Basement III."
That space measures 19' 10" x 13', and 7'6" from the floor to the bottom of the floor joists. That's pretty close to the golden ratio for listening rooms, as far as my research goes.
I have these two primary goals:
1) Sound isolation. The boys' rooms are directly above, and we all need privacy from each other. Soundproof would be ideal, but way too hard.
2) Frequency management, especially bass.
Here are some concerns:
A) Ventilation without sound transmission. I don't need think I need a direct heat or AC register, but I do need decent air circulation.
B) Multi-functionality. This is mostly a re-sale issue. I'm sticking with a rectangle-shape in an effort to maintain a broad appeal to the market when I have to sell the house (may it never be!). No goofy "theater" shape. Besides, let's keep it simple.
C) Some measure of fiscal responsibility. Would that I could spend what I want! The good news is that, if I stretch construction into infinity, my budget is also infinite.
D) I forget the rest, but there's more.
What would you do?
Dave
Scroll down to the picture entitled "Basement III."
That space measures 19' 10" x 13', and 7'6" from the floor to the bottom of the floor joists. That's pretty close to the golden ratio for listening rooms, as far as my research goes.
I have these two primary goals:
1) Sound isolation. The boys' rooms are directly above, and we all need privacy from each other. Soundproof would be ideal, but way too hard.
2) Frequency management, especially bass.
Here are some concerns:
A) Ventilation without sound transmission. I don't need think I need a direct heat or AC register, but I do need decent air circulation.
B) Multi-functionality. This is mostly a re-sale issue. I'm sticking with a rectangle-shape in an effort to maintain a broad appeal to the market when I have to sell the house (may it never be!). No goofy "theater" shape. Besides, let's keep it simple.
C) Some measure of fiscal responsibility. Would that I could spend what I want! The good news is that, if I stretch construction into infinity, my budget is also infinite.
D) I forget the rest, but there's more.
What would you do?
Dave
kneadle said:
1.526 : 1 : 0.577
The golden ratio at 1.618 : 1 : 0.618 would give 19.634 x 12.135 x 7.5'
Adding a 10" thick false wall (ie bass trap) or floor to ceiling bookcase on one side would make it real close to perfect (to the ratio anyway, it is the AES recommended shape). A collection of objects could be conciously used to create an average close to the target (that makes more sense)
All that furniture, bookshelves, record shelves act as diffusors/damping and should be planned.
dave
- Status
- This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.