Confused Nubie......

Dear moderator and all friends... I try to learn everything I could get from my dial up from this forum, and then it brought me to buy Alton Everest's Master handbook of acoustic and follow kendale suggestion to buy Home Recording Stuido : Build it like the pros by Rod gervais. These book and forum also other acosutic forum open my eye about how the acoustic treatment can open up new possibilities to enhance my mix. But at the same time, I getting more frustated and confused about alot of things in acoutic practically. But, when I observed my self, I found that lack of my english, converting inch/feet to meter/cm/mm also bugging me, and make me lost focus. It's like think twice :D And super bugging me is when talking about modes, how this impact to room tune etc. I'm lost my way how to start when I want to build my own studio (DIY) because hiring acoustician in not in my option list. I collected my room data : L : 386cm, H : 286 W : 234cm and download more than 2 excel files of mode calc. Of course one of them is from this forum. I also visit and trying the http://www.hunecke.de/english/calculato ... modes.html Then I introduced to see the first 4 modes for my Axial, Tangential and obligues. yes, Also other modes. If I'm not misunderstood, this calculation will not replace actual measurement using mic, measurement soft etc. This math calculation only give us a picture, what happen with (especially) lo freq in my room.... But, what should I really pay attention of the freq list in the spreadsheet? The 1st 4 modes? What's that mean? Which (freq) I should treat? Which freq I should trap with bass trap?etc, etc.... And what I confuse also :

Page 176 (Rod Gervais' book) One advantage to a panel absorber is that they are able to be "tuned" fairly closely to specific frequencies...........This trap's strength is also its weakness because it cannot be used as a wide broadband treatment.

And in page 181, there's a statement that

This resonator (hemholtz fig 9.15) is fairly broadband in nature and will handle freqs ranging from 66.44 to 155.82hz.

Are they opposite with Ethan's articles?

Although there is no denying that a Helmholtz trap can be very effective, the fact that it works over a narrow range of frequencies limits its usefulness. While it can be sized to absorb the dominant resonant frequencies in a particular room, it cannot absorb all the other low frequencies. And broadband absorption is needed to prevent acoustic interference that skews the frequency response throughout the entire bass range.

Or I have wrong interpretation? Please light my fire..... Thanks

Joe, You should start with broadband absorption, since there is a broad range of frequencies to be handled. Panel absorbers or OK when after your basic treatment you're still stuck with specific frequencies which you couldn't get under control with your base absorption/treatment. Also panel traps can vary from bandwidth somewhat (higher or lower Q depending on design). But basically they are indeed mainly aimed to handle descrete frequencies, which is what Rod likely refers to. Sometimes ones resorts to paneltraps to safe space. But it's exactly (combined with damping by absorption effects) the more space you save the higher Q you get (becomes more narrowbanded). Helmholtz resonators is a broad concept. The slat/slot wall treatment standard here at John Sayers forum is also Helmholtz and is relative broadband from nature. Also here Rod refers to a comparable principle (I don't know if that's a measured corner type or not in that page you refer). If there is a difference or seemingly difference between Rod's book and Ethan's site or FAQ you better follow Rod's book.

audio wrote:

I collected my room data : L : 386cm, H : 286 W : 234cm and download more than 2 excel files of mode calc.

Is your room already built? If so, a mode calculator is of no use. That is, it will not tell you how to treat your room. All of the advice in my Acoustics FAQ applies to a room the size of yours too.

If I'm not misunderstood, this calculation will not replace actual measurement

Exactly.

what should I really pay attention of the freq list in the spreadsheet?

Again, that information is of no use if the room is already built.

One advantage to a panel absorber is that they are able to be "tuned" fairly closely to specific frequencies...........This trap's strength is also its weakness because it cannot be used as a wide broadband treatment.

That's not always true. The wood panel traps shown in my Plans article are relatively broadband, being effective over a range of about an octave.

This resonator (hemholtz fig 9.15) is fairly broadband in nature and will handle freqs ranging from 66.44 to 155.82hz.

You can make panel traps narrow, and you can make Helmholtz traps broad. Panel traps don't work as well when narrow though. --Ethan

Wow.....Thanks Eric and Ethan, I read alot your pots....

Ethan Winer wrote:

Is your room already built? If so, a mode calculator is of no use. That is, it will not tell you how to treat your room. All of the advice in my Acoustics FAQ applies to a room the size of yours too.

Why I missed this? Is there any statement like this in the books or this forum? So, Room Modes and its Calculator is usefull to design/make a decision what room ratios and volume will be? And if the room is already built, I should not invest alot of time to playing with this calc? My limited logical agreed with Eric (thanks Eric), The 1st I have to do is make a broadband absorber because so many freq to treat. But Which broadband absorber panel you mean Eric? I'm little bit afraid to understand the "broadband panel"... :) Is placing fiber in the corner absorb broadband freq? And after that I built the specific trap if there'are freqs to treat. But, what method is the right one to determine what freq should I treat? especially when designing the slat resonator? Measuring with Mic and Measuring Soft?

Ethan Winer wrote:

audio wrote:

One advantage to a panel absorber is that they are able to be "tuned" fairly closely to specific frequencies...........This trap's strength is also its weakness because it cannot be used as a wide broadband treatment.

That's not always true. The wood panel traps shown in my Plans article are relatively broadband, being effective over a range of about an octave.

This resonator (hemholtz fig 9.15) is fairly broadband in nature and will handle freqs ranging from 66.44 to 155.82hz.

You can make panel traps narrow, and you can make Helmholtz traps broad. Panel traps don't work as well when narrow though. --Ethan

Ethan, to broad the Hemholtz, vary slat and slot width? Can I use my corner with 2 type of low freq absorber? The middle area is hemholtz, and the top is Fiberglass trap (http://www.ethanwiner.com/acoustics.htm ... ss%20traps) ?

A simple setup is to be found on several sites: Minitraps from Realtraps: http://www.realtraps.com/placing_mt.gif Ready Acoustics solution: http://www.readyacoustics.com/images/st ... l-view.jpg I think there are more sites with suchs setups. Couldn't find one at GIK acoustics now. You see these pictures look principly alike. No matter which products you use, the idea here is to use the corners for efficient broadband bass trapping. Hang panels on the first reflection points (walls and ceiling). And hang some more panels to get a equal distribution of absorption over the room and prevent flutter. This approach gives a broadband absorption. Further you can use the Helmholtz approach (slat/slot wall/corner absorption) of which you can find almost countless designs here in the forum. Just search these threads. There isn't a forum where so many practical designs are shown. See working to controlling specific frequencies as some last resort to solve specific remaining problems.

audio wrote:

Why I missed this?

I have no idea. It's clearly explained here: www.realtraps.com/modecalc.htm

Is there any statement like this in the books or this forum?

Yes, I just made that statement in this forum. :) If there is a difference between what I say or what someone else says, better follow what I say. 8)

And after that I built the specific trap if there'are freqs to treat. But, what method is the right one to determine what freq should I treat?

Most rooms benefit from broadband absorption rather than trying to target specific frequencies. Let's say you have peaks or nulls (or both) at 50 Hz, 100 Hz, 150 Hz, and 200 Hz. All rooms have more problem frequencies than that, but let's say for now it's just those four. In order to improve each frequency a little, but not a lot, let's say you need four bass traps. So that's 16 bass traps, and you still don't have enough for those frequencies, and you have none for other problem frequencies. Many people don't realize this, but you can have peaks and nulls at all low frequencies. Not just those that resonate in the room. This is why broadband absorption is generally the better choice.

to broad the Hemholtz, vary slat and slot width?

I've never experimented with that type of absorber so I honestly don't know the best way to tune it. --Ethan

Ethan Winer wrote:

If there is a difference between what I say or what someone else says, better follow what I say. 8)

:D :D :D :D :D :D :D

Most rooms benefit from broadband absorption rather than trying to target specific frequencies. Let's say you have peaks or nulls (or both) at 50 Hz, 100 Hz, 150 Hz, and 200 Hz. All rooms have more problem frequencies than that, but let's say for now it's just those four. In order to improve each frequency a little, but not a lot, let's say you need four bass traps. So that's 16 bass traps, and you still don't have enough for those frequencies, and you have none for other problem frequencies. Many people don't realize this, but you can have peaks and nulls at all low frequencies. Not just those that resonate in the room. This is why broadband absorption is generally the better choice.

Thanks Ethan, adding something to my mind

[quote=audio]to broad the Hemholtz, vary slat and slot width?

I've never experimented with that type of absorber so I honestly don't know the best way to tune it. --Ethan[/quote] Really? Ethan Winner never experiment with Hemholtz? God, please tell mr Hemholtz to pray for Ethan, so we can have more knowledge about hemholtz trap a la Ethan Winner :)

I already built the front (behind speakers) corner traps, 50mm Rockwool, from floor to ceiling(H286cmxH60cm). I also built the fiberglass (semi-rigid rockwool) panel trap hanging in front wall (w120cmx60cm), and also hanging trap L180cmxW120cm. I also built triangle "splayed" trap W120cmxH60cmxD30cm. I put the membrane traps in corner-top-rear wall. 60cm Height, 60cmwidth,approx depth 30cm. I also put the trap width-center in rear wall H120cmxw60cm. I placed the speakers in 60cm off the front wall. I have speakers specs that roll off in 40hz. I still felt "null" in some low freq in (38% of lenght/148cm) listener positioning area. More bass trap?

audio wrote:

More bass trap?

More is always better, but understand that it's impossible to make any domestic size room perfectly flat. If you can get to within a 10 dB window, with modal ringing below 300 Hz less than 200 milliseconds, you're doing really well. --Ethan

Eric_Desart wrote:

I think there are more sites with suchs setups. Couldn't find one at GIK acoustics now. .

It is something we are working on now, but I do want to point out that any of these kinds of "room setup" pictures are only guides. Depending on the room size, what it is used for and so on can change which acoustic products (and setup) would work best. :D Glenn