Knightly, what would be the outcome if I do this?

How to use REW, What is a Bass Trap, a diffuser, the speed of sound, etc.

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yoga
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Knightly, what would be the outcome if I do this?

Post by yoga »

The bass trap I am making as you know is 30cm depth and uses 88mm rockwool. I am making two panels of these dimensions.

If I am to make a resonating panel using 4mm plywood with one of them, how important is that gap between the resonating panel and the insulation held up by mesh wire to prevent touching the panel. I am estimating between 10mm to 20mm airgap, since I could not get my mesh to flatten out fully and the rockwool is not very flat, some lumps here and there.

I am worried that all the parts of the mesh is not touching the insulation, what will that do if it doesn't?

The bigger the air gap between the resonating panel and the insulation means? eg, wider Q (what is Q), higher frequencies or it does not dampen the panel and it means it does not absorb those frequencies? If so what frequencies is it affecting or changingin my bass traps. You estimated 120-140hz with these panels, so what am I looking at now and how good will they work.

With the other panel, I am going to not place a resonating panel infront of it and just add polyester baffling and cloth. What do I expect with this kind of trap. Its exactly the same build as the resonating panel, but without the front resonating plywood which I replaced with polyester baffling to substitue the airgap and used cloth to cover the panel.

Overcompressing fibreglass, rockwool or polyester baffling, what happens to it's properties. Because I overcompressed one of my insulation and the trap seems like it's not doing anything. Do you think its working but its only working on the bass frequencies because I compressed it. Does compressing insulation mean it absorbs bass frequencies better. At what point do we say, weve compressed it too much for it to work, or will that never happen with insulations like fibreglass, rockwool and polyester baffling.

I await your response, I am at my final stages of my diy traps and I need to know if I am going the right direction before finishing it.
knightfly
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Post by knightfly »

If I am to make a resonating panel using 4mm plywood with one of them, how important is that gap between the resonating panel and the insulation held up by mesh wire to prevent touching the panel. I am estimating between 10mm to 20mm airgap, since I could not get my mesh to flatten out fully and the rockwool is not very flat, some lumps here and there.

VERY important; not so much the AMOUNT of separation, just that the panel NEVER touches the wire or rockwool.

I am worried that all the parts of the mesh is not touching the insulation, what will that do if it doesn't?

Nothing; what few areas of the wire that don't touch will be too small to resonate enough to even be measurable, and they will be damped by the rest of their surface that DOES contact the rockwool.

The bigger the air gap between the resonating panel and the insulation means? eg, wider Q (what is Q), higher frequencies or it does not dampen the panel and it means it does not absorb those frequencies?

Not sure yet; I think it means that the wider air gap would be "softer" and therefore force less air through the absorbent, making the trap less absorbent overall - I have Cox and D'Antonio's latest expensive book on absorbers/diffusors, but have yet to find enough time to study more on this. "Q" is a vintage electronics term which stands for "quality" - it was first used on "tank" circuits in resonant filters for radio IIRC. What it means, is "peakiness" sort of - the higher the "Q", the narrower the bandwidth and the more pronounced the peak in response. So a "high Q" trap would be VERY efficient (high absorption) at a NARROW band of frequencies, where a "low Q" trap would have a broader range of effect, but not as DEEP.

If so what frequencies is it affecting or changing in my bass traps. You estimated 120-140hz with these panels, so what am I looking at now and how good will they work.

Judging what these will do is at best a wild guess, due to mounting differences, tightness of screws, type of weatherstrip used as a seal around the panel perimeter, etc - so I'd not risk any further wild guesses. I doubt that the frequency would change due to distance by more than a fraction of an octave, it would mainly be the Q (see above)

With the other panel, I am going to not place a resonating panel infront of it and just add polyester baffling and cloth. What do I expect with this kind of trap. Its exactly the same build as the resonating panel, but without the front resonating plywood which I replaced with polyester baffling to substitue the airgap and used cloth to cover the panel.

300mm is 1/4 wavelength of about 280 hZ; this will be approx. where the absorption will peak. Useful down to at least an octave below this, measurable even lower. As compared to the MEMBRANE version which PEAKS at that low a frequency.

Overcompressing fibreglass, rockwool or polyester baffling, what happens to it's properties. Because I overcompressed one of my insulation and the trap seems like it's not doing anything.

Higher compression equates to denser material; for a given thickness, and assuming 90 degree (head on) coincidence, denser absorbs better at lower frequencyies. However, by compressing this insulation you have also DECREASED the THICKNESS, which would LESSEN absorption mainly.

Do you think its working but its only working on the bass frequencies because I compressed it.

See above.

Does compressing insulation mean it absorbs bass frequencies better.

AGain, only PER UNIT THICKNESS - IOW, if you were to compress to half thickness AND put TWICE as much insulation, you would get better low frequency absorption. If just using one panel that's half as thick and twice as dense, then not so good; that would make for more uneven response.

At what point do we say, weve compressed it too much for it to work, or will that never happen with insulations like fibreglass, rockwool and polyester baffling.

Anything beyond just enough compression to hold things in place will start to change the properties, at which time you would need to hire an expensive acoustic test lab for exact results.

After way more study than I originally ever thought I'd have time for, I've come to the conclusion that "do it and see" is much less painful for us "math-challenged" types than trying to fry our brains with thousands of calculations, only to find out that someone forgot to tell us about a vital property during all the calculations.

My own approach to rooms is to build keeping modes in mind, make it more isolated than you need (treatments hurt isolation usually), then set up where modes are least likely to hurt things, listen/test, add heavy corner absorption/first reflection absorption/speaker boundary correction/rear wall deep traps, testing/listening at each step, then (and ONLY then) worry about individual problem frequencies that have NOT been "fixed" by all the above. These are more esoteric, and require more thought as to how many, how much, where, etc - we're getting into 2nd and 3rd order modes by this time and no two rooms will act identically.

Usually, unless you're building a mastering suite, by this time it's "good enough" (meaning, "I'm tired of building stuff, let's ROCK")... Steve
Soooo, when a Musician dies, do they hear the white noise at the end of the tunnel??!? Hmmmm...
yoga
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Location: Australia

Post by yoga »

knightly, i made a mistake with my materials. I realised i do not have enough material to use the 4-5mm plywood. The only material I have enough of is 2.5-3mm plywood. I need your calculations please to tell me what region of frequencies this thinner plywood will give me if I use it. Should I turn these into slat resonators maybe. I really want to make bass absorbers with what I have done so far, in the 240 below frequencies. I am thinking of placing these on the sides or the back of the room. I could use my 9mm mdf but i think 45hz is way too low for absorbers in my room.

You say the pegboard I have, have holes to board ratio is not good, so what are my other options here?
knightfly
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Post by knightfly »

That weight panel would, with your 300mm depth, give center frequency of around 85-90 hZ.

So far, I've yet to see any facts from YOU, describing your actual room or what you're trying to accomplish; if you get enough "data" from me and use it wrong, your room is STILL going to SUCK.

I'd really appreciate some feedback; like at least a rough sketch of your situation, some description, dimensions, etc; otherwise, I feel like I may very likely be giving "right answers to wrong questions"... Steve
Soooo, when a Musician dies, do they hear the white noise at the end of the tunnel??!? Hmmmm...
yoga
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Location: Australia

Post by yoga »

You are most likely correct, if the frequencies the traps are targetting is in the wrong position of the room. 85-90hz I will be happy with. There is a 1 octave range from that both sides, is that correct. Exactly what is 1 octave in regards to this. What would the frequency range from center point 90hz would be then with this 1 octave addition.

I have a 13 foot by 20 foot room with the typical room wall plaster and ceilings. I will be making a makeshift recording booth on one of the right hand corners on the back with no door. So it will look like this, refer to diagram 1.1. The opened vocal booth will have sound insulation, mostly foam tiles. I may put a movable panel at the entrance, to entrap the singers if need be to make it more dead.

diagram 1.1

back
3[ []
2[..]
1[..]
front

dot = space / needed to put those in, or else it doesnt look right on my diagram

I was going to put those panels, since that is the only space i have left either at the front or at "1" sides. My mix position is between "1" and "2" and at the center from side to side.

I think 80-90hz sounds like a nice frequency to attack at first reflections? I always have muddy bass frequencies within a mix, so my main objective in this room is just to attack the 240hz and below. So with 90hz as well as the other panel without the resonator will absorb 280, like you said, then this will be o.k.

You said "300mm is 1/4 wavelength of about 280 hZ; this will be approx. where the absorption will peak. Useful down to at least an octave below this, measurable even lower. As compared to the MEMBRANE version which PEAKS at that low a frequency. "

I would like to make that panel go a bit lower though, like 140-180hz. Will adding 50mm fibreglass insulation compressed to 15-20mm on top of the 88mm rockwool lower the center frequency. If so, to what frequency, and what do I have to add to this panel to hit it at 140-180hz.

Having bass traps on first reflections focusing on the frequencies I like, is that good for the room and is it better positioned elsewhere. At the moment, the back seems like a no, no space. Theres a door there which I will just cover with Foam so it can still be used as a door.

If bass traps were placed unevenly in a room, will it shift the stereo image from the mix position. eg, more 100hz bass traps on the left side back of the room. Will that mean, the bass or instruments on that frequency will sound like it's being panned to the left?
knightfly
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Post by knightfly »

Am I to assume by the Ansi "graphics", that you're on a Mac? If so, check out this shareware cad program

http://www.lemkesoft.de/en/caddownld_en.htm

And some other files

http://www.lemkesoft.de/en/index.htm

Now, first off I would NOT use a reflective trap at "mirror" points if that's what you mean; for a pressure zone trap, such as a membrane/panel trap, and to some extent also the Helmholtz ones to work at optimum, they need to be placed in the room where high SPL points are for their particular frequency. For that, I'd need more than a few brackets and parentheses to figure it out. Including all THREE dimensions of the room to start.

Also, in this forum there is no such thing as "standard" construction - the problem is, each country has its own "standards", so I can't take for granted that I know what you mean by that. Aussies tend to build a lot of brick walls with inner insulated stud walls and a layer of cladding of some sort, where this is rarely done in other countries, for example.

Wall stiffness makes a BIG difference in the amount of bass trapping needed within a room, so knowing the actual EXACT construction will tell me a lot about how much trapping a room will need, and all THREE dimensions inside the room (between solid surfaces, not absorbers) will help figure out what frequencies should be targeted.

If you can't draw something on the computer, can you possibly draw it on paper and scan it in, or take a closeup digital pic, or something similar? Without more detail and planning, I'm afraid your approach is going to disappoint you big time... Steve
Soooo, when a Musician dies, do they hear the white noise at the end of the tunnel??!? Hmmmm...
yoga
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Location: Australia

Post by yoga »

Atleast answer some of my bass traps questions in regards to it's functions and frequency responses.
knightfly
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Post by knightfly »

How about if instead I "teach you to fish" - here's the formula I use, along with some conversion factors.

Panel traps have APPROXIMATELY an octave either side of peak that's useful; peak coefficient of absorption runs somewhere around .6 to .7 at resonance, dropping to around .25 an octave either side.

Forgot; an octave is either twice or half the frequency, so an octave below 90 hZ would be 45 hZ, but an octave ABOVE 90 hZ would be 180 hZ. Middle C on a piano is 262 hZ, the low B string on a 6-string bass is 31 hZ, typical resonance of a kick drum shell is around 300 hZ, the "crack" of a snare is somewhere around 1-2k, depending on tuning; here's more

http://www.listenhear.co.uk/general_acoustics.htm

This way, you can change any part of the equation you want and see just what will happen.

Let me know if you have problems using the formula... Steve
Soooo, when a Musician dies, do they hear the white noise at the end of the tunnel??!? Hmmmm...
yoga
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Joined: Sun May 22, 2005 12:44 am
Location: Australia

Post by yoga »

knightly, im afraid of the sea. Bad fishing accident.

Thanks for the answer though. Seriously, I would really love to even know more about Acoustics, but that's not my forte. I think knowing just enough theory for me is enough, because this acoustic thing has really taken up alot of time, brain power which I could have used to become a better musician and I tell u now, I am not even a good musician it be.

Its like going to the cake shop. You love the cheese cake, all you want to do is eat the cheesecake. You don't want people telling you, mate, heres the recipe, make your own. All I want is to eat the cheesecake, know where to buy the cheesecake and how much the cheesecake costs to have it.

These forums are great to learn alot, but sometimes alot is too much and all you want is just enough. These forums have enabled me to make some decent looking bass traps. They should work, but may not work to their best because I have not studied hard enough about the subject, but I've spent 6 months reading, researching, writing, shopping and building about Acoustics and it's come to the point now where it's time to finish what Ive begun and further down the track, if I decide, I can delve further into improving the mess Ive made with my acoustics of my room.
Sword9
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Post by Sword9 »

So basically you want his consulting services for free?

Steve, I don't know how you and John do it for free so much. It'd burn me up to let that much business slip through my hands. I'm glad you do what you do though, and thanks for all the hard work.
SaM Harrison
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Nashville, TN
yoga
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Location: Australia

Post by yoga »

It's a forum, people come here to discuss things and try to find answers to their questions. Some questions can involve someone else doing the work to find answers, definitely. Doesn't neccesarilly mean that the person asking teh question has been lazy. Knightly has been given a gift, the gift of acoustics, as well as a good forum and following. It be a waste for him not to share it, cause he's after the quick buck or because of one selfish persons opinion. I think pointing out that he should be charging for his services goes to show how selfish a person you are. A humble and wise person does not need verification from others to show how generous they are or to be brown nosed as pointed out by you. Just knowing he is helping out someone is all the gratitude a humble person needs. By me addressing my questions to him, already shows that I respect his answers on the topic. Why would a student in search for answers ask a teacher who knows nothing.

I think before you brown nose, you should think about the affect you have by the words you type. It can cause a negative effect on this topic or the people involved. It's like you selling something online and me posting saying, I've seen that cheaper somewhere else. If you have no positive answers to post on this topic in question, then start a new topic of your own and don't tamper with this one.
knightfly
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Post by knightfly »

Knightly has been given a gift

Given, my ass; try 25 years of study in conjunction with 40 years experience.

Some questions can involve someone else doing the work

Within reason; yours seemed about to go on forever, so I offered you a way to get answers on your own.

It be a waste for him not to share it

I share it to the tune of about $120,000 a year - spoon-feeding takes too much time away from others and their questions, so when I can I try to help members learn to figure out their own answers.

Just knowing he is helping out someone is all the gratitude a humble person needs


What a load of crap; humble people starve if they do everything for free - if you lived in my area, would you spend all your free time (including some you don't have) mowing my lawn, fixing my cars, etc? That's what I thought.

Why would a student in search for answers ask a teacher who knows nothing

While that's true, consider this: If a student really IS a student, he will try to LEARN when given the opportunity. You seem perfectly content to continue asking "what-if's" without ever wanting to figure out how you can get the answers yourself.

Your attitude seems to be that I OWE you hours and hours of time - I gotta tell you, I don't mind helping those who (a) help themselves and (b) appreciate it; but neither seems to be the case here. If Sword9's "brown nosing", maybe it's because he's more in touch with the REAL world where people pay for what they get - (and where you also PAY when you go to the grocery store, or buy a pair of shoes... )

That's enough for me; if I say more I'll just get really irritated... Steve
Soooo, when a Musician dies, do they hear the white noise at the end of the tunnel??!? Hmmmm...
yoga
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Location: Australia

Post by yoga »

sorry knightly,
I didn't you realise you weren't humble, my mistake.

Given, my ass; try 25 years of study in conjunction with 40 years experience.
I think that much time devoted to one subject is a gift or either it took you that long to get it right.

Within reason; yours seemed about to go on forever, so I offered you a way to get answers on your own.
I do search for answers on my own and it does seem to go on forever specially when some answers are not to the point and vague because one does not put it in lamans terms sometimes or the answer is coumaflaged with opinions about the question than just give the answer to the question.

I share it to the tune of about $120,000 a year - spoon-feeding takes too much time away from others and their questions, so when I can I try to help members learn to figure out their own answers.
From what I see, this forum really doesn't have posts popping out every second. Maybe your use to the slowness of people posting once a week and can't handle the pressure when someone posts 1-2 posts per day while they're building the traps they're talking about while waiting for responses while at the same time looking for the answer themselves. $120,000 a year is a lot, I wish I could even come close to that figure, I guess you should really place it in your "read first" column that a certain class of people pre-requisites before posting, in that way you get the type of people you want coming into your forum. A bit arrogant of you to state how much you're worth. I guess it's your forum.

What a load of crap; humble people starve if they do everything for free - if you lived in my area, would you spend all your free time (including some you don't have) mowing my lawn, fixing my cars, etc? That's what I thought.
I wouldn't mow your lawn, etc, I'd simply say "I do not have the time". You can still be humble and honest about it, if you didn't have the time, you should have just said it. I do not have the time and to be fair to everyone on this forum I will only answer 3 posts per person. You could have also said, I'm really busy at the moment or just said, hey my time is worth money, instead of some brown noser pointing it out. I mean' it's your forum, unless you don't want people thinking of you the wrong way about what you really feel about answering these posts.
Humble people don't starve only Hungry people do. It seems like you're hungry if your not getting the most from answering these questions.

While that's true, consider this: If a student really IS a student, he will try to LEARN when given the opportunity. You seem perfectly content to continue asking "what-if's" without ever wanting to figure out how you can get the answers yourself.
A good student also likes to dig deeper into the answer or questions.

Your attitude seems to be that I OWE you hours and hours of time - I gotta tell you, I don't mind helping those who (a) help themselves and (b) appreciate it; but neither seems to be the case here. If Sword9's "brown nosing", maybe it's because he's more in touch with the REAL world where people pay for what they get - (and where you also PAY when you go to the grocery store, or buy a pair of shoes... )
You are right, then next time Knightly, put it on your forum. "Pay me", don't hide it with the words "Make a Donation". Are you afraid that you will be taxed on it. The store is a store where you pay for things, where does it say on your forum that it says, this is a payed forum. The definition of forum does not state = a place for people to buy information. This is not the real world, this is the internet. Cyber World. If you want to make more money than your $120,000, place more banner ads, but don't take it out on the person trying to learn and create something from your forums.

The pope doesn't go, "what the hell are these people going to me for advice. So what if people look up to me, time is money, take these paupers, poor children and disabled people out of here. Bring in the rich educated christians who will gladly donate to our funds."

That's enough for me; if I say more I'll just get really irritated... Steve you may as well delete this whole topic. ITS RUINED!
knightfly
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Post by knightfly »

I'm sorry you feel it's ruined; I was hoping you could make the attempt to "trade places" with me for long enough to see that I was initially trying to get you to make an effort too.

I'll try to explain my point of view; I'd appreciate it if you read this at least enough times to learn enough about me not to be so judgemental - remember, I've already BEEN where YOU are right now, and I remember MOST of it (believe it or not)

I'm not the Pope; he gets supported by the Catholic church, I work for a living (typically 12-16 hours a day) and consult on this particular subject during time off. It's taken this long because acoustics is every bit as deep as you're finding out, and probably a thousand times MORE; I know of people 90 years old who are considered gurus in this field, and they STILL study.

When I mentioned $120k, that's approximately the amount of time I DONATE here, based on my usual fee of $120 per hour - when you consider the length of time invested in learning enough not to have to reach for 6 different books before answering most questions, it's a bargain.

25 years ago I built my first studio; it was such a FLOP that my wife could hear what I was playing on the piano from inside our HOUSE, a separate building 100 feet AWAY. That's when I figured that I needed to know a lot more about this if I was ever going to have a usable studio (neighbors with loud cars, loud dogs, lawnmowers, tractors, trucks, all kinds of other country noises, and me trying to make recordings WITHOUT "special sound effects"...

The alternative was to pay someone who already KNEW all this stuff a TON of money to build a quiet studio for me; not an option with a fairly average paid job and two kids, so I STUDIED.

At that time, the internet was just some military think-tank oddity, so I bought books, subscribed to magazines, (few did any good), drew plans, found out why they sucked, drew more plans, threw them away, and am just now reaching the point where I can afford to build a usable but small commercial facility, just in time to RETIRE - hopefully into something FUN to do.

I do this part mainly because I remember what it was like trying to find out about this subject and because I know how disappointing it was when I found out that my carefully constructed WRONG studio was about as sound-proof as a cardboard box - it's still together, but only being used as a storage room.

When I first started learning about acoustics, it was ONLY so I could afford a workable studio, nothing more; then it sort of took on a life of its own, even though I still prefer to write, play, record and mix music, and make videos.

I wouldn't have gotten so pissy with you if you'd seemed willing to do part of the work of learning, but I only have so much time I can afford to give away, and it didn't seem fair that 15 other people in the Construction forum were still waiting answers and yet you couldn't make an attempt at figuring things out even after I gave you the formula -

You're right, this IS a "free" site - the amount that comes in as "donations" doesn't even support the server fees. Apparently you're not the only one who seems to think that "free" means "worthless" - internet or no internet, each of us only has a given amount of time, so in my opinion time is only free if it doesn't cost you anything.

Your comment about being "slow" mainly shows your lack of realization at both the complexity of acoustics, and my hope NOT to say something that misleads; this makes it kinda hard to just "whip out answers" since the amount of thought REAL answers requires is sometimes unbelievable.

Bottom line is, I'm not asking you to PAY - just make half an effort to meet me halfway, and SHARE what time I DO have to spend here with the others on the site.

Thanks for at least reading this, I hope it made a bit more sense - remember, I'm just a guy trying to help - no holy water available... Steve
Soooo, when a Musician dies, do they hear the white noise at the end of the tunnel??!? Hmmmm...
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