The No.1 Website for Pro Audio
high freqs reflextion question (small room treatment)
Old 24th May 2011
  #1
Lives for gear
 
andy3's Avatar
 
🎧 10 years
high freqs reflextion question (small room treatment)

Hello guys,

a 'friend' of mine told me that I want to cover RFZ panel with Plywood (cieling and sides) in order to leaving high freqs going reflecting.

Is this a common use or a B.S.?

Thank you in advance
:-)
Old 24th May 2011
  #2
Lives for gear
 
Jens Eklund's Avatar
 
🎧 10 years
If proper RFZ, splayed walls are built to redirect early reflections in order to minimize absorption. RFZ is a geometric solution to reach a good LEDE design developed by Peter D'Antonio 1984. Unfortunately, people sometimes use the term RFZ without knowing the true meaning of it.
Old 24th May 2011 | Show parent
  #3
Lives for gear
 
Jens Eklund's Avatar
 
🎧 10 years
If using only velocity based absorbers (porous only), you might end up with the all to common "dead room" with too short decay times in the mid and high range, but still too long decay times in the sub 100 Hz area, like this one for instance:

https://www.gearslutz.com/board/studi...gearslutz.html

Use velocity based absorbers on early reflection points only (unless measurements indicate the need of them elsewhere), and use pressure based absorbers to fix your modal problems. Even decay times is very important for a good acoustic space but unfortunately, a lot of people, even "acousticians", seem unaware of this.
Old 24th May 2011 | Show parent
  #4
Lives for gear
 
🎧 10 years
And just to clarify Jens, what decay time should we be aiming for?
Old 24th May 2011 | Show parent
  #5
Lives for gear
 
Jens Eklund's Avatar
 
🎧 10 years
Quote:
Originally Posted by Max Dread ➡️
And just to clarify Jens, what decay time should we be aiming for?
Depending on room size, approximately 300ms (200 dB/s decay rate) is good in a normal sized room.

This one will give some suggestions:
http://www.bobgolds.com/Mode/RoomModes.htm

As does this EBU-paper:
http://tech.ebu.ch/docs/tech/tech3276.pdf
Old 24th May 2011 | Show parent
  #6
Lives for gear
 
🎧 10 years
Thanks Jens. Just one more question if you don't mind. Kind of related to the thread....!

What would you use to determine what decay time the room has?
Old 24th May 2011 | Show parent
  #7
Lives for gear
 
Jens Eklund's Avatar
 
🎧 10 years
Quote:
Originally Posted by Max Dread ➡️
Thanks Jens. Just one more question if you don't mind. Kind of related to the thread....!

What would you use to determine what decay time the room has?
RT60 (T30; -5 to -35 dB) in 1/3 octave resulotion, and possibly in conjunction with waterfall or sonogram/spectrogram. RT is not really applicable in small rooms but it still gives some estimations.
Old 24th May 2011 | Show parent
  #8
Lives for gear
 
🎧 10 years
Thanks Jens. I did find it confusing using the waterfall for this because the waterfall graph presents the data so differently depending on how the parameters and controls of the graph are set up - especially the window and time range controls.

Not looked at RT60s yet, but perhaps if they are a good indicator I should do that....
Old 24th May 2011 | Show parent
  #9
Lives for gear
 
andy3's Avatar
 
🎧 10 years
Quote:
Originally Posted by Jens Eklund ➡️
If proper RFZ, splayed walls are built to redirect early reflections in order to minimize absorption. RFZ is a geometric solution to reach a good LEDE design developed by Peter D'Antonio 1984. Unfortunately, people sometimes use the term RFZ without knowing the true meaning of it.
So this 'playwood' thing isn't a B.S.? Please tell me a clear answer.

thanks
Old 24th May 2011
  #10
Gear Guru
 
Glenn Kuras's Avatar
 
🎧 15 years
Quote:
Originally Posted by andy3 ➡️
Hello guys,

a 'friend' of mine told me that I want to cover RFZ panel with Plywood (cieling and sides) in order to leaving high freqs going reflecting.

Is this a common use or a B.S.?

Thank you in advance
:-)
For early reflection points (RFZ) you want to absorb the high frequencies so putting plywood would work in reverse. So you called the BS right. heh
What Are Early Reflection Points. Acoustic Panels and Bass Traps.
Old 24th May 2011 | Show parent
  #11
Lives for gear
 
Jens Eklund's Avatar
 
🎧 10 years
The RFZ uses geometry to redirect early reflections instead of absorbing them like the traditional LEDE principle.

The proper way to treat a room is to take measurements and treat accordingly. Use the ETC and trace your early reflections and absorb or redirect them. Use broadband absorption sparsely or you might end up with a dead room with uneven decay times (too long in the bass and too short above).
Old 24th May 2011 | Show parent
  #12
Gear Guru
 
Glenn Kuras's Avatar
 
🎧 15 years
A word of caution about tuned traps vs velocity based...

1)Smaller rooms (99% of the rooms here on GS) have problems throughout the frequency range and tuned traps can not deal with all of them. Velocity though can work over a greater range which is better suited as a starting point.

2)As a company that builds both I can say that building something tuned can be very tricky and if build wrong will be a huge waste of time and money. Also I have seen "online calculators" used for tuned traps that are way off. Not so long ago I tested a trap that should have been tuned at 60hz but actually test more like 90hz.

3)If you think you are going to over absorb to much high end with a velocity based trap (broad band) then simply putting a limp membrane on the front (FRK, cardboard, paper) will help to solve this problem.

I am a believer in tuned traps, but I also understand there place and would not recommend someone with a small room to only focus the treatment with them. I like to think of them as more "icing on the cake" then anything else.
Old 24th May 2011 | Show parent
  #13
Lives for gear
 
andy3's Avatar
 
🎧 10 years
Quote:
Originally Posted by Glenn Kuras ➡️
(FRK, cardboard, paper)
kraft paper is ok?

Thx y'all!
Old 24th May 2011 | Show parent
  #14
Gear Guru
 
Glenn Kuras's Avatar
 
🎧 15 years
Quote:
Originally Posted by andy3 ➡️
kraft paper is ok?

Thx y'all!
sure that will work fine.
Old 24th May 2011 | Show parent
  #15
Gear Maniac
 
🎧 10 years
Quote:
Originally Posted by Jens Eklund ➡️
The RFZ uses geometry to redirect early reflections instead of absorbing them like the traditional LEDE principle.]
IS there any source regarding RFZ panel technology (websites, pdf, etc that i can read?) , i'm confused, i thought it was absorptive material...

ty.
Old 24th May 2011 | Show parent
  #16
Gear Guru
 
1 Review written
🎧 15 years
Levels

Andy, I recommend that you put a bit more effort into your questions.
e.g. Kraft paper is just fine without context, but it would be very destructive on the face of reflection killing panels.
Jens has carefully answered you at quite a high level. However IMHO, the tone and content of the questions suggests that there is a disparity here.

Simple answer, kill all reflections around your mix position. Place a mirror on the side walls and ceiling, and perhaps floor. If you can see the tweeters from where you sit, you also have a HF reflection. As these reflections arrive at the ears at different times, they do not add up coherently. They fight and result in aneven messy sound. See comb filtering.
So, no ply wood, no FRK, no B.S.

Better answer, if you are really interested, find out what RFZ means.
As Jens has pointed to, a part of this can involve directing the destructive reflections away from the ear in order to preserve liveness in the room.

The 'standard' recommendations for corner trapping and a RFZ achieved by local absorption alone work extremely well. For the money and effort.
If you want something more sophisticated, might be time to hire a pro rather than try to become one yourself.


DD
Old 24th May 2011 | Show parent
  #17
Gear Guru
 
Glenn Kuras's Avatar
 
🎧 15 years
Quote:
Originally Posted by andy3 ➡️
kraft paper is ok?

Thx y'all!
Jens got off on the tuned thing but the question was about early reflection points. Just want to point out that you DO NOT want anything reflective for those areas.

Edit. DanDan beat me to it!
Old 24th May 2011 | Show parent
  #18
Lives for gear
 
Jens Eklund's Avatar
 
🎧 10 years
Quote:
Originally Posted by Audioactive ➡️
IS there any source regarding RFZ panel technology (websites, pdf, etc that i can read?) , i'm confused, i thought it was absorptive material...

ty.
RFZ is a design concept that uses angled walls, flush mounted speakers, etc. in order to reach the LEDE (Live End –Dead End) criteria. You can create a “RFZ” (now referring to the actual sweet spot that has no strong, early reflections), either by redirecting the reflections away from the sweet spot, absorption, or a combination of the two. If using a lot of broadband absorption and perhaps not only at reflection points, there’s a risk of running into the problem of too short decay times in the mid and high frequency range and it might be tricky to obtain a good termination of the ISD-gap (Initial Signal Delay):

Sound system engineering - Google Böcker
Old 24th May 2011 | Show parent
  #19
Gear Maniac
 
🎧 10 years
Thanks.

So, if i use High density Panel, maybe covered with kraft, slightly angled in order to deflect ER and redirect them towards the back wall i'm creating a "RFZ".
Old 24th May 2011 | Show parent
  #20
Gear Guru
 
1 Review written
🎧 15 years
Detail

Audioactive, you would be taking just one aspect of some RFZ designs and applying it without context. Answer is maybe. Often when this is done, the back wall would be fully absorbent or if it is back far enough, absorbent at LF but with a HF diffusing front. Your current plan, unless there is more to it, will direct the destructive HF reflections to the ears of the person sitting behind you. Typically a producer or client....heh

DD
Old 24th May 2011 | Show parent
  #21
Gear Maniac
 
🎧 10 years
Dan you're super right!!

and in that position, (couch where clients sit) there is also some LF Mode going on.. heh

but the room is quite dead, trying to find a compromise.
Old 24th May 2011 | Show parent
  #22
Gear Guru
 
1 Review written
🎧 15 years
Dead Right!

Audioactive. It is difficult to achieve acoustic control and liveness. It takes a great amount of effort and skill. I believe it would be silly for an amateur to attempt such.
However I have an over-riding opinion on all of that. i.e.
Acoustic treatment with intelligence, even a small amount of it, yields dramatic benefits to listening and recording. Even temporary measures like duvets hanging on mic booms, large cardboxes stuffed with newspaper as bass traps, etc. etc. Guerrilla acoustics.
As I said, the 'standard' recommendations at RealTraps, GIK, Everest and so on, all work extremely well.
Typcially they do result in very dead small rooms. The presumption that this is a problem seems a tad irrational to me. I mix and master professionally. I am amazingly good at it......heh heh
I find dead listening rooms to be very accurate in terms of mix translation. Furthermore I find them very calming to work in. People do find the environment a little strange for a little while. Then they tend to decide that they like it or confirm that they really don't like it. Neither opinion tends to be connected with results.
Dead can work very well, it needs to be balanced with context. Typically the tweeters need to be turned down 2-4dB.

DD
Old 24th May 2011 | Show parent
  #23
Lives for gear
 
🎧 10 years
Interesting stuff DanDan....

If it's not an intrusive question I'd be intrigued to know what kind of decay time you've measured in your room.

Also, if the oft recommended approach of facing bass traps with card, foil, thin wood, fence posts, etc. is as simple and effective as has been suggested on these forums many times, may I ask if you have employed the technique and if not why (or is it just that you prefer the dead room)?

Cheers

Max
Old 24th May 2011 | Show parent
  #24
Gear Guru
 
1 Review written
🎧 15 years
Ping

Can't remember specifically, but typically I see figures as low as 100mS and less in the mid and highs in simply treated rooms. There is almost invariably one very low very long mode. It is of note that this mode is practically inaudible at the centre and near the centre of the room, but is maximum at the back wall, where clients often sit.....

I had a lot of foil faced 'Bass' traps in my room. I found it sounded pingy to my ear. Measurements showed any increase in decay times at 4K and 8K relative to the midband. This is not nice and is again typical of a simply treated room.
Remove all the honks and some boom and you are left with a very bright harsh sound.
Dead rooms work fine, but you need to turn down the clarity, i.e. the treble.

Room tweaking is very like adjusting the graphic at a gig. Or Mastering for that matter. It is best done by ear and brain and is a question of balance of tone as heard, not as imagined or hypothesised.

DD
Old 24th May 2011 | Show parent
  #25
Gear Guru
 
Glenn Kuras's Avatar
 
🎧 15 years
Quote:
Originally Posted by DanDan ➡️
Can't remember specifically, but typically I see figures as low as 100mS and less in the mid and highs in simply treated rooms. There is almost invariably one very low very long mode. It is of note that this mode is practically inaudible at the centre and near the centre of the room, but is maximum at the back wall, where clients often sit.....

I had a lot of foil faced 'Bass' traps in my room. I found it sounded pingy to my ear. Measurements showed any increase in decay times at 4K and 8K relative to the midband. This is not nice and is again typical of a simply treated room.
Remove all the honks and some boom and you are left with a very bright harsh sound.
Dead rooms work fine, but you need to turn down the clarity, i.e. the treble.

Room tweaking is very like adjusting the graphic at a gig. Or Mastering for that matter. It is best done by ear and brain and is a question of balance of tone as heard, not as imagined or hypothesised.

DD
There is a balance that is for sure.
Old 24th May 2011 | Show parent
  #26
Lives for gear
 
🎧 10 years
Thanks for the response and info.

So you weren't tempted to try materials with less ping - such as cardboard or wood slats or half (round) fence posts for a little more liveness? Or was it a case of not wanting to introduce too much MF/HF decay relative to the short decay time of the LFs (other than the modal ringing of the first room length mode as you mention)?

Sorry to labour the point! Just want to get your approach clear in my mind.
Old 24th May 2011 | Show parent
  #27
Lives for gear
 
andy3's Avatar
 
🎧 10 years
yeah, I don't want to cover my diy rockwool rfz with rigisd stuff. That's the point.
If I just feel that they absorb too much freqs (probably not) I will try with the kraft cover.
My room is small and the more I absorb, the better, I guess.

Thank you mates!
Old 24th May 2011 | Show parent
  #28
Gear Guru
 
Glenn Kuras's Avatar
 
🎧 15 years
Quote:
Originally Posted by andy3 ➡️
yeah, I don't want to cover my diy rockwool rfz with rigisd stuff. That's the point.
If I just feel that they absorb too much freqs (probably not) I will try with the kraft cover.
My room is small and the more I absorb, the better, I guess.

Thank you mates!
I had a feeling getting off topic would confuse someone. You do not want to cover the panels that would go in the RFZ. You want then to absorb as much high end as possible.
Old 24th May 2011 | Show parent
  #29
Lives for gear
 
🎧 10 years
Quote:
Originally Posted by Glenn Kuras ➡️
I had a feeling getting off topic would confuse someone. You do not want to cover the panels that would go in the RFZ. You want then to absorb as much high end as possible.
Sorry - that was partly my fault, the off topic meanderings. Apologies to the OP.
Old 24th May 2011 | Show parent
  #30
Gear Maniac
 
🎧 10 years
Talking about RF Zone , what's the relationship between the Early Reflections and The decay time?
📝 Reply
Post Reply

Welcome to the Gearspace Pro Audio Community!

Registration benefits include:
  • The ability to reply to and create new discussions
  • Access to members-only giveaways & competitions
  • Interact with VIP industry experts in our guest Q&As
  • Access to members-only sub forum discussions
  • Access to members-only Chat Room
  • Get INSTANT ACCESS to the world's best private pro audio Classifieds for only USD $20/year
  • Promote your eBay auctions and Reverb.com listings for free
  • Remove this message!
You need an account to post a reply. Create a username and password below and an account will be created and your post entered.


 
 
Slide to join now Processing…

Forum Jump
Forum Jump