The No.1 Website for Pro Audio
QRD Diffuser for Tracking AC Guitar
Old 10th October 2018
  #1
Here for the gear
 

QRD Diffuser for Tracking AC Guitar

Hi,

I have a one room studio that is essentially my live and control room. It's filled with bespoke panels and bass traps. It's dead and is great for mixing.

However, as expected, a.c. guitars and other acoustic instruments sound like trash in there. The microphone doesn't lie, and it takes all the tricks I have up my sleeve to make it passable. Sometimes it's better just to use my mobile rig and record a.c. guitar in a big room in my house, but I work to tight deadlines and that wastes a lot time.

I was considering making a free-standing QRD diffuser that I can place infront of the a.c. guitar when recording. This would hopefully give it a fuller 'big room' sound.

A few questions-
- Will this actually work? Will it improve the sound of my a.c. guitar recordings significantly? I've seen a few people mention it online but nothing major.
- For this purpose, does it matter the material/specific type of wood?
- I'm planning on making two double QRDs about (60cm x 120cm each), and then attaching them together with a couple hinges so that they will remain upright through counter-balancing each other. Would that work? Or do I need to make feet?
- Will i need to varnish it?
- The plan is that one of these QRD panels will be facing the body of the guitar, and the other the neck. Is it worth having each side reflect a different frequency range that corresponds to the part of the guitar faces (i.e. more low freq reflection from QRD facing the guitar, more high freq for neck)?
- Any other considerations I'm missing?

Any insight and sharing of expertise would be much much appreciated.
Old 11th October 2018
  #2
Lives for gear
 
Jens Eklund's Avatar
Quote:
Originally Posted by act_your_rage View Post
I was considering making a free-standing QRD diffuser that I can place infront of the a.c. guitar when recording. This would hopefully give it a fuller 'big room' sound.
It won't:

Help: Studio is too loud

experimental skyline diffusor with pics - comments appreciated

DIffusers

Ceiling above drum?
Old 11th October 2018
  #3
Here for the gear
 

Interesting! I would have thought that more absorption would just make the room sound even smaller. It seems counterintuitive to my uninformed brain. But you say it's about increasing the ITD-gap. Is that similar to increasing the pre-delay? Should I be recording the guitar in the deadest part of the room (e.g. mixing position, behind the gobo), but with a diffuser facing the guitar at the furthest position to get some late reflections?

To be honest, I may have misspoke saying I want a 'big room' sound. I'm not tracking drums, I just want my acoustic guitar recordings to sound fuller and less flat. I just associate that with a bigger room. Am I wrong? Any advice on how I could make acoustic guitar sound good in a dead room? I do have wooden floors, but a huge rug.

Thanks for sharing your expertise. You may have just saved me hours and hours of wasted time!
Old 11th October 2018
  #4
Deleted 4adc64a
Guest
It may help if you link to a recording that features the tones you're trying to achieve and a sample of your own recordings? There maybe some room for improvement on the mic/positioning/processing front in addition to the room.
Old 11th October 2018
  #5
Lives for gear
 
Jens Eklund's Avatar
Quote:
Originally Posted by act_your_rage View Post
Interesting! I would have thought that more absorption would just make the room sound even smaller. It seems counterintuitive to my uninformed brain. But you say it's about increasing the ITD-gap. Is that similar to increasing the pre-delay? Should I be recording the guitar in the deadest part of the room (e.g. mixing position, behind the gobo), but with a diffuser facing the guitar at the furthest position to get some late reflections?

To be honest, I may have misspoke saying I want a 'big room' sound. I'm not tracking drums, I just want my acoustic guitar recordings to sound fuller and less flat. I just associate that with a bigger room. Am I wrong? Any advice on how I could make acoustic guitar sound good in a dead room? I do have wooden floors, but a huge rug.

Thanks for sharing your expertise. You may have just saved me hours and hours of wasted time!
Yes, If you check my links, you´ll find that the important aspect of a good sounding room (apart from getting the modal range under control) is to maximize the ITD-gap (assuming a return from the room is wanted at all, not dry sounding i o w). The longer the ITD-gap (if recording rooms we usually call it ITD-gap unlike “ISD-gap” when discussing control rooms, but it´s basically the same thing); the “larger” the room appears to be. If the termination of the ITD-gap is properly diffused (not restricted only to the high mids up, but the entire range down to the modal region); the energy return won´t affect the “tone” of the direct signal, thus providing a “neutral” but still not “dead” sounding recording environment.

If small room:

Use absorption (as deep as practically possible, absolute minimum about 8”) on areas close to the source/receiver that otherwise results in early, strong reflections. Use geometry to redirect energy away from the recording zone. Use diffusers on areas far away from the recording zone and make sure that the return from the diffuser can bounce back to the recording zone (don’t use more broadband absorbers than needed; use pressure-based absorbers that reflects above the modal range on all surfaces except early reflection areas) from other surfaces.
Old 11th October 2018
  #6
Here for the gear
 

Quote:
Originally Posted by Jens Eklund View Post
Use geometry to redirect energy away from the recording zone.
Is this with absorbers? How do I use geometry to redirect energy away, just have the absorbers at an angle pointed away from the recording zone rather than straight on?

Quote:
Originally Posted by Jens Eklund View Post
use pressure-based absorbers that reflects above the modal range on all surfaces except early reflection
It is very small room with lots of absorption (bass traps, cloud, first reflection panels for mixing position, and a gobo. Would tuned panels be better?

Should the back wall diffuser be facing the guitar (and therefore behind the microphone's cardiod pattern)?
Old 11th October 2018
  #7
Here for the gear
 

Quote:
Originally Posted by Deleted 4adc64a View Post
It may help if you link to a recording that features the tones you're trying to achieve and a sample of your own recordings? There maybe some room for improvement on the mic/positioning/processing front in addition to the room.
I can do so later. However, I hate having to fix it with processing. I generally use a AT4033/CL going into a UAD Apollo. I used to love recording MS position but the room doesn't make the Figure8 side sound nice. I've experimented with every mic position possible, but to no avail!
Old 11th October 2018
  #8
Lives for gear
 
Jens Eklund's Avatar
Quote:
Originally Posted by act_your_rage View Post
Is this with absorbers? How do I use geometry to redirect energy away, just have the absorbers at an angle pointed away from the recording zone rather than straight on?



It is very small room with lots of absorption (bass traps, cloud, first reflection panels for mixing position, and a gobo. Would tuned panels be better?

Should the back wall diffuser be facing the guitar (and therefore behind the microphone's cardiod pattern)?
A pressure-based panel usually reflects above (and below if large enough) the effective range, if deep enough; the panel can be made to absorb most of the modal range and reflect above it.

If you only use velocity-based absorbers to treat a room, it will obviously become very dry (at least in the absorbers effective range). If you want to restore some life to a dead room, you need to replace broadband absorbers with pressure based (you still need as much absorption as possible in the modal range). For diffusers to be meaningful, the return from them needs to be able to return to the sweet spot (recording zone or listening position if control room). If these return paths are treated with broadband absorbers, the energy is lost.

In a good sounding room (that is not very dry); I would experiment with omni mics if you want more room sound (or use two or more mics, one for close, direct sound (then possibly cardioid) and one (or more) for room sound.
Old 11th October 2018
  #9
Here for the gear
 

Quote:
Originally Posted by Jens Eklund View Post
A pressure-based panel usually reflects above (and below if large enough) the effective range, if deep enough; the panel can be made to absorb most of the modal range and reflect above it.

If you only use velocity-based absorbers to treat a room, it will obviously become very dry (at least in the absorbers effective range). If you want to restore some life to a dead room, you need to replace broadband absorbers with pressure based (you still need as much absorption as possible in the modal range). For diffusers to be meaningful, the return from them needs to be able to return to the sweet spot (recording zone or listening position if control room). If these return paths are treated with broadband absorbers, the energy is lost.

In a good sounding room (that is not very dry); I would experiment with omni mics if you want more room sound (or use two or more mics, one for close, direct sound (then possibly cardioid) and one (or more) for room sound.
Thanks, I will look at pressure-based absorption.

One issue I am probabaly having is that my gobo vocal booth (essentially three broadband absorbers on high feet), are absorbing inside the 'booth', but also from the rest of the room. This is a significant amount of additional velocity-based absorption in a small space. Should I cover the outside of these panels with something more reflective... either pressure-based panels, or even possibly QRDs? This would keep the booth absorbed and dead, but add more life back into the rest of the room?

How far away from source/recorder would you recommend a QRD is placed for it to be effective? (Assuming no absorption in its return path)?

Thanks again for all this advice. Really appreciate it
Old 11th October 2018
  #10
Lives for gear
 
Jens Eklund's Avatar
Quote:
Originally Posted by act_your_rage View Post
Thanks, I will look at pressure-based absorption.

One issue I am probabaly having is that my gobo vocal booth (essentially three broadband absorbers on high feet), are absorbing inside the 'booth', but also from the rest of the room. This is a significant amount of additional velocity-based absorption in a small space. Should I cover the outside of these panels with something more reflective... either pressure-based panels, or even possibly QRDs? This would keep the booth absorbed and dead, but add more life back into the rest of the room?

Possibly yes.

Quote:
Originally Posted by act_your_rage View Post
How far away from source/recorder would you recommend a QRD is placed for it to be effective? (Assuming no absorption in its return path)?

Thanks again for all this advice. Really appreciate it
There are so strict limits, but I would say that an ITD-gap of at least about 10 ms or so (excluding floor naturally) would be my personal limit.
Old 11th October 2018
  #11
Here for the gear
 

Quote:
Originally Posted by Jens Eklund View Post
Possibly yes.



There are so strict limits, but I would say that an ITD-gap of at least about 10 ms or so (excluding floor naturally) would be my personal limit.
Perfect. My gobo is around 3.4 metres away from my mixing position. I will make some QRDs to attach to the outward-facing parts of my gobo instead.

Thank you so much!
Old 11th October 2018
  #12
Lives for gear
 

You mentioned a rug on wood floors. Getting rid of the rug would be the first thing to do. Acoustic instruments (guitar, piano, violin, etc) sound much better on wood floors. A wood floor and good reverb might be enough to get what you want.

After that go for diffusion to make it really top notch.
Old 11th October 2018
  #13
Here for the gear
 

For this purpose, which is better... QRD or Skyline diffusers?
Old 12th October 2018
  #14
Lives for gear
 
Jens Eklund's Avatar
A 2D panel (QRD or PRD) needs to be deeper compared to a 1D diffuser to reach the same performance in the lower range, so unless you can build it very deep; 1D is a better choice in my opinion. Even if one can make it very deep, I would personally still opt for 1D due to other reasons like less absorption (compared to 1D panel) and doubtfulness of the use of scattering energy in the vertical plane.

1D diffusor - vertical or horizontal?
Old 12th October 2018
  #15
Old 12th October 2018
  #16
Old 12th October 2018
  #17
Lives for gear
 

Quote:
Originally Posted by Jens Eklund View Post
How well does this compare vs a QRD?

Side question, for simulation is the incident wave assumed to be spherical our planar?
Old 13th October 2018
  #18
Lives for gear
At the end of this video you can hear the difference of an acoustic played near absorption vs a diffuser

YouTube
Old 13th October 2018
  #19
Lives for gear
 
Jens Eklund's Avatar
Quote:
Originally Posted by johnnyc View Post
How well does this compare vs a QRD?

Side question, for simulation is the incident wave assumed to be spherical our planar?

QRD and Skyline Well Dividers?

What to look at when buying diffusers?

I assume planar unless you specify distances. Won't make a huge difference anyway unless very large total sample width and source and recover are very close (which wouldn't make any sense anyway).
📝 Reply

Similar Threads

Thread / Thread Starter Replies / Views Last Post
replies: 74 views: 129074
Avatar for bobbybovine
bobbybovine 18th January 2012
replies: 1099 views: 223393
Avatar for moogplayer
moogplayer 4 days ago
replies: 9 views: 2808
Avatar for Jens Eklund
Jens Eklund 27th September 2012
Topic:
Post Reply

Welcome to the Gearslutz 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…
🖨️ Show Printable Version
✉️ Email this Page
🔍 Search thread
🎙️ View mentioned gear
Forum Jump
Forum Jump