Perhaps you could try a lower frequency crossover - what are the available crossovers frequencies? Can you play with the phase?
RPG Modex Plates (35Hz) placement question
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Perhaps you could try a lower frequency crossover - what are the available crossovers frequencies? Can you play with the phase?
Hi. I can play with 3 different crossovers, each with varying settings and yes I can play with phase. From the CB specs:
I have shown what happens when I reduce the crossover from 160 to 100Hz. 100Hz is better. I could test lower. Looks like 80Hz could be better still. What I find interesting is that 50Hz is smoothed but the very low end really drops away. Probably phase cancellation at the very low end?
I have shown what happens when I reduce the crossover from 160 to 100Hz. 100Hz is better. I could test lower. Looks like 80Hz could be better still. What I find interesting is that 50Hz is smoothed but the very low end really drops away. Probably phase cancellation at the very low end?
Not sure what it looked like before but there are still some pretty serious modal issues! Those long 'tails' extending out in the time axis below 100Hz really shouldn't exist. Each one of them is a resonance that takes a looooooong time to decay.
Yep. More work to do. But first, now that I have installed the Modex Plates, I need to take some new measurements. The above measurements were taken with them simply leaning roughly in the corners. It was worse before without anything - see below:
Whoa, yes that was bad!!
You might find it useful to compare your measurements against my Acoustical Measurement Standards for High End Audio (PDF!) - a white paper I coauthored just over a year ago with a fellow acoustician.
Yup...hopefully I am heading in the right direction (within numerous constraints) with the Modex Plates, heavier/larger carpet, rear wall Skyline panel.... I haven't decided on first reflection point treatment (only the left side of the room is available as the right side has a window and drapes) but I've have been looking at the 4" BAD panels. My wife just shakes her head in dismay.
EDIT: Just read your post and the note at the bottom again. Thanks, I will take a look! (Hopefully I won't come away from it too depressed...)
EDIT: Just read your post and the note at the bottom again. Thanks, I will take a look! (Hopefully I won't come away from it too depressed...)
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Thanks for the article. A very good summary of my recent reading of The Master Handbook of Acoustics. You've set some challenging goals. I do not expect to be able to reach all of them given the structure of my room (shape, Victorian-era wall construction, placement of doors) and my constrained ability to add treatment (I don't own the place, my wife doesn't understand why a desktop, all-in-one, CD player/speaker isn't enough). That said, I have installed the Modex T2 Plates (front side corners) and the 6' x 4' panel of Skyline diffuses (plus the thick and larger carpet). I will try to take some new readings this evening to take stock of progress.
PS: I still get horribly confused between -3dB representing a halving of sound pressure and your note of a c20% drop in perceived volume...
PS: I still get horribly confused between -3dB representing a halving of sound pressure and your note of a c20% drop in perceived volume...
For Roger and then Nyall - comments appreciated
First, thank you Roger for prodding me to experiment with the sub. Here is a series of tests dealing with some of the vagaries of the Theta Casablanca III.
A few things have changed since I did my last tests. First, the Modex Plates are installed (side walls, very front corners), the 6' x 4' panel of Skyline diffusers is installed and the larger/thicker carpet is in place. Also, after a debate on the REW forum, I changed the orientation of my mic to horizontal (using the 0 degree calibration file) and pointed in the general direction of the main speaker being tested.
Perversely, the way to get pure stereo, front L/R only, from a digital input into the Casablanca is to use Matrix mode and tell the Casablanca that there are no other speakers (as opposed to selecting "stereo"). Don't ask - it's a hangover from days gone by and, well, is the way it is. Obviously, a sub can be introduced by setting the number of subs to greater than or equal to one. Perversely, even if you select Full in the CB's crossover settings, as I was reminded while doing these tests, if Matrix mode is selected and subs >=1 then a signal is still (counterintuitively) sent to the sub (quite what, I do not know). If you select Full/LP then full range is sent to the main speakers and low pass is sent to the sub according to your crossover settings. For these experiments I had my crossover settings set to: Butterworth, 80dB, slope 24dB, normal phase for both the low and high.
The results of these tests were rather intriguing - especially the phase reversal at the sub (Rel Stentor II).
First, "pure stereo", Full / Sub=0:
Now "Full" in the crossover settings but with the sub enabled. Some sort of Lord-knows-what mix.
Then "Full/LP" and the sub enabled (crossover settings as noted above). Normal phase set on the Rel. So here I have LF going to 3 speakers but it just keeps getting worse.
I then tried reversing the phase on the Rel and things start cooking (well, relatively speaking). But why? I'd be really interested in people's thoughts on this.
Here are the first and last sets overlaid on each other:
Lastly, here are some of the charts which Nyal and Jeff's very good paper focus on. All are run with the settings of my last run (i.e. sub with reversed phase etc). I have tried to use the same ranges and settings in Nyal's paper.
ETC. Nyal, I've not looked at this before and I must admit I find it difficult to interpret. I would appreciate your thoughts.
Left and right spectrograms. Very low end is still awful and I suspect a challenge to fix:
Left and right mid-range RT60/20/30. I know I need to deal with left-side first reflections (in particular).
I would really appreciate any thoughts on these. The room setup is depicted in my first post. More work to do...
Thanks, Steve (and apologies for all the charts!!)
First, thank you Roger for prodding me to experiment with the sub. Here is a series of tests dealing with some of the vagaries of the Theta Casablanca III.
A few things have changed since I did my last tests. First, the Modex Plates are installed (side walls, very front corners), the 6' x 4' panel of Skyline diffusers is installed and the larger/thicker carpet is in place. Also, after a debate on the REW forum, I changed the orientation of my mic to horizontal (using the 0 degree calibration file) and pointed in the general direction of the main speaker being tested.
Perversely, the way to get pure stereo, front L/R only, from a digital input into the Casablanca is to use Matrix mode and tell the Casablanca that there are no other speakers (as opposed to selecting "stereo"). Don't ask - it's a hangover from days gone by and, well, is the way it is. Obviously, a sub can be introduced by setting the number of subs to greater than or equal to one. Perversely, even if you select Full in the CB's crossover settings, as I was reminded while doing these tests, if Matrix mode is selected and subs >=1 then a signal is still (counterintuitively) sent to the sub (quite what, I do not know). If you select Full/LP then full range is sent to the main speakers and low pass is sent to the sub according to your crossover settings. For these experiments I had my crossover settings set to: Butterworth, 80dB, slope 24dB, normal phase for both the low and high.
The results of these tests were rather intriguing - especially the phase reversal at the sub (Rel Stentor II).
First, "pure stereo", Full / Sub=0:
Now "Full" in the crossover settings but with the sub enabled. Some sort of Lord-knows-what mix.
Then "Full/LP" and the sub enabled (crossover settings as noted above). Normal phase set on the Rel. So here I have LF going to 3 speakers but it just keeps getting worse.
I then tried reversing the phase on the Rel and things start cooking (well, relatively speaking). But why? I'd be really interested in people's thoughts on this.
Here are the first and last sets overlaid on each other:
Lastly, here are some of the charts which Nyal and Jeff's very good paper focus on. All are run with the settings of my last run (i.e. sub with reversed phase etc). I have tried to use the same ranges and settings in Nyal's paper.
ETC. Nyal, I've not looked at this before and I must admit I find it difficult to interpret. I would appreciate your thoughts.
Left and right spectrograms. Very low end is still awful and I suspect a challenge to fix:
Left and right mid-range RT60/20/30. I know I need to deal with left-side first reflections (in particular).
I would really appreciate any thoughts on these. The room setup is depicted in my first post. More work to do...
Thanks, Steve (and apologies for all the charts!!)
Generally I would first look at what is required to fix the bass issues. The ones you have will definitely be audible not only as boominess, poor smoothness and loss of articulation in the bass but will also reduce overall system dynamics and perceived bass slam / impact.
Your bass controls are: subs (number, positioning, crossover points), listener positioning, EQ and bass traps.
After a solution has been found to the bass issues then I would look at the mid and high frequencies, check-step on how this changes your low frequency acoustic design and then go ahead and implement everything.
Speaking from experience I can say brick / concrete walled rooms need a lot of bass trapping to sound good. Rather than use off the shelf products it will likely be more cost effective and acoustically effective building some false walls and using custom designed products to assist in solving the acoustical issues.
No offense but it will likely be difficult for you to fix these problems by yourself, you may want to consider some support from a professional.
Your bass controls are: subs (number, positioning, crossover points), listener positioning, EQ and bass traps.
After a solution has been found to the bass issues then I would look at the mid and high frequencies, check-step on how this changes your low frequency acoustic design and then go ahead and implement everything.
Speaking from experience I can say brick / concrete walled rooms need a lot of bass trapping to sound good. Rather than use off the shelf products it will likely be more cost effective and acoustically effective building some false walls and using custom designed products to assist in solving the acoustical issues.
No offense but it will likely be difficult for you to fix these problems by yourself, you may want to consider some support from a professional.
Hi Steve,
As you can see, adding the sub has a strong effect on the <200 Hz response. I think you might find it interesting to try an alternate tuning strategy. Leave the Theta bass management with mains full range and sub on with the 80 Hz crossover. Set the REW to generate pink noise, and view the RTA. Use enough samples to make the display reasonably stable. You should see roughly the same response shape as the swept plots gave. The point of using the RTA is just to give a continuous result rather than making dozens of sweep runs. Save that for later, if you think you have found better settings.
Now, with the Theta, begin changing the time delay (or distance if that's how it's labeled) for the sub -- going in both directions from wherever it is at the moment. As you step it along (probably 1 ms or 0.5 ms increments), see if any patterns emerge in how the response changes, particularly the dips at 50 and 120 Hz regions. You can also try adjusting the level in the sub.
It might all lead to nowhere.
As you can see, adding the sub has a strong effect on the <200 Hz response. I think you might find it interesting to try an alternate tuning strategy. Leave the Theta bass management with mains full range and sub on with the 80 Hz crossover. Set the REW to generate pink noise, and view the RTA. Use enough samples to make the display reasonably stable. You should see roughly the same response shape as the swept plots gave. The point of using the RTA is just to give a continuous result rather than making dozens of sweep runs. Save that for later, if you think you have found better settings.
Now, with the Theta, begin changing the time delay (or distance if that's how it's labeled) for the sub -- going in both directions from wherever it is at the moment. As you step it along (probably 1 ms or 0.5 ms increments), see if any patterns emerge in how the response changes, particularly the dips at 50 and 120 Hz regions. You can also try adjusting the level in the sub.
It might all lead to nowhere.
Thanks Nyal. Building false walls is definitely not an option. As noted before, I rent the place and even drilling 8 holes for deep-set Rawl plugs to hang the Plates means I will have to do some work to "make good" the room when I leave. I'm not interested in spending the c£3m plus another £1.5m of renovation (at least and, yes, that's $7m+) that would be associated with owning a 2100sqft property in this part of London when I intend to only be here for another 5 or so years. So, as I mentioned before, it's a case of getting things the best I can within a broad number of constraints (including the fact that my wife would prefer that the space be devoted to another play area for my 9mth-old son). When I do buy - most likely in the US or NZ - I will dedicate some resources to a custom (or modified) and dedicated room. At that point I would be happy to deploy the skills and advice of a professional acoustician. For now, I will have to make do with relatively modest implementation of treatment (the doors in the room make even that challenging) to get the best I can out of a far from ideal situation - and leverage whatever support and advice experienced people are prepared to offer.
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Thanks Roger. I'm glad you prompted me to look at this again. I'm also glad the Rel had something to contribute! When I initially looked at REW tests I had observed the sharp negative impact of the sub below 40 Hz and stopped for awhile. Hitting the phase switch on the sub was an eye opener. Playing with timing delays for the sub makes a lot of sense and not something that had crossed my mind.
Regarding the dip in right side response around 120Hz, it seems to have been accentuated when the sub is involved yet I would have thought the sub would not have made any impact given crossover at 80Hz. I will also check placement more carefully.
The structure of the wall on the right side is very different than the left. First, there is the window right near the first reflection point. Second, the wall is thicker yet, despite being an external and load-bearing wall, it appeared to be lathe and plaster then cavity then brick and required very extended rawl fittings to get to the brick. I have no idea what the structure is below the window but it is not the same as the rest of the wall. So a bunch of structural, immoveable factors.
I'm sure I can get the SPL response better (ahead of equalisation). I'm also sure I can improve decay times for 100Hz and up. The 35Hz and 70-80Hz regions (for SPL and decay) have been the big challenges from the outset (see first post). The Modex Plates helped a lot but it's clear that the structure and shape of the room present a tall set of challenges. It may well be I don't get them conquered.
Non-expert advice: Have you considered using an equalizer having a variable gain, phase , frequency and Q factor to your subwoofer? I found that a Behringer Ultra Drive DCX2496 was much more efficient for bass correction than conventional sub-woofer filters. Ten years ago the the Wilson Audio WatchDog subwoofer already had a very useful analog equalizer with a F and Q control.
Hi. I've not. This is all preamble to eventually adding a Dirac Live module to the Casablanca.
Thanks Nyal. Building false walls is definitely not an option. As noted before, I rent the place and even drilling 8 holes for deep-set Rawl plugs to hang the Plates means I will have to do some work to "make good" the room when I leave. I'm not interested in spending the c£3m plus another £1.5m of renovation (at least and, yes, that's $7m+) that would be associated with owning a 2100sqft property in this part of London when I intend to only be here for another 5 or so years. So, as I mentioned before, it's a case of getting things the best I can within a broad number of constraints (including the fact that my wife would prefer that the space be devoted to another play area for my 9mth-old son). When I do buy - most likely in the US or NZ - I will dedicate some resources to a custom (or modified) and dedicated room. At that point I would be happy to deploy the skills and advice of a professional acoustician. For now, I will have to make do with relatively modest implementation of treatment (the doors in the room make even that challenging) to get the best I can out of a far from ideal situation - and leverage whatever support and advice experienced people are prepared to offer.
Hi Steve, where are you in London? I lived there for 8 years before moving to California. All my old college / university friends are still there doing the city job thing - bankers, lawyers, insurance, etc.
I suggested building a false wall because it would be a very cost effective way to add a lot of bass trapping. Honestly a consultation with an acoustician is less money than you probably think it is and you could easily waste that money on a couple of poorly selected bass traps. It pains me to see people fail to improve their listening room acoustics because they have a fear of spending money on services and instead want to just buy products. The best you are likely to get on a public forum are some suggestions on root causes and solutions, not any holistic and engineered plan that solves the issues. Anyway, I have probably overstepped the mark of what I should be saying. Hey no hard sell here, just trying to be honest, I'm a straight up guy and I would hate for you to spend 5 years in that bunker of a listening room not enjoying the sound. The listening room should hopefully be a retreat from life, a time to enjoy music without distractions, it's difficult it being that when there are so many bad bass issues in it.
Short of consulting with a professional I would add as many Modex Plates Type 2s as you can fit into that space.
That be me. I live in South Kensington, not far from Kensington town hall.
You are right. I've been chatting with Jason Hawkes from Novatone. He recommended the T2 MPs. I'm sure more would be good. He has seen pictures of the room and provided some general advice but you are right that having him pop over for an hour or two would likely be valuable. Ideally I would like to build my own knowledge base first though. This has already been, and continues to be, a fantastic learning exercise. I've read a lot about acoustics in the last 6 months. For that alone, it's been valuable.
To that end, I played around with RTA this evening. Interesting results. If I move my listening position forward about a foot or so things get better (flatter SPL response and better spectrograms). (I also added delay to the sub to 8ms.) It begs a question of speaker placement, though.
My existing setup was anchored on two "guidelines". The first is Ethan's 38% guideline (from the rear wall in my case). The second was to keep the distance to left, centre and right speakers the same - this was constrained by listening position and setting the centre channel back against the disused fireplace (thereby setting the radius of the arc for L/R placement). (The third was to maintain a distance between the L/R speakers that was in line with Eggworks recommendation of a minimum distance of 7.5 feet. At the moment it's about 8ft.)
Simply moving the listening position forward a foot or so feels very much too far forward versus the L/R speakers and their toe-in.
Am I right to understand that shifting the speakers back a little, perhaps even a little closer together, and managing the distance difference versus the centre speaker via the Casablanca's Delays is a worthwhile pursuit - that at these low frequencies one should let the room dictate terms (so to speak)?
Honestly forget the speaker placement guidelines. The only things that matter are what the measurements say and what it sounds like in your room.
A good starting point is going to be moving things around until you get better bass response. Then worry about fixing the soundstaging and imaging. I would simplify things down - take the sub out of the equation, just measure one speaker at a time and see where that gets you in terms of positioning.
The center channel delay is there to be used....so use it!!
Did you try measuring with the existing Modex Plates on the back wall? BTW, how much do they cost in the UK?
I stayed several times in the zone of South Kensington in my youth with colleagues when visiting London - the zone is plenty of small non expensive hotels always full of young people. I remember we changed trains at Notting Hill Gate to go shopping electronic parts and hardware at Tottenham Court Road and LPs at the HMV of Oxford Street. Sometime in the end of the 70's ...
I stayed several times in the zone of South Kensington in my youth with colleagues when visiting London - the zone is plenty of small non expensive hotels always full of young people. I remember we changed trains at Notting Hill Gate to go shopping electronic parts and hardware at Tottenham Court Road and LPs at the HMV of Oxford Street. Sometime in the end of the 70's ...
A lot cheaper than in the USA that's for sure. They are made in Germany by Renz under license from the Fraunhofer institute and then shipped to the US, that must be why they are so pricey here. I'd love it if they were cheaper, then I'd use a lot more of them in my room acoustic treatment designs.
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