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Noob's adventure into accoustics


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6 minutes ago, Primare Knob said:
23 minutes ago, almikel said:
Now those as slats would be way cool

It would be a good reason for buying another tool.

Keep in mind you said earlier you didn't want to lose the head height...

...but if you were prepared to lose the head height, then a combination of limp mass (for bass trapping) and those amazing slats PtG posted for diffusion and broadband trapping would create a spectacular ceiling.

 

7 minutes ago, Primare Knob said:

I thought by reading a BBC document which uses hardboard instead of Vinyl, that filling it up with absorption drops the peak but widens the bandwidth.

Good work - yes that's correct, but limp mass will inherently have a lower Q (less sharp) than hardboard, and IMO anything that broadens the "narrowband-ness" of pressure traps is a good thing - so filling with absorption is good.

 

mike

 

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9 minutes ago, Primare Knob said:

You guys have made a strong case for the ceiling that I truely considering it.

I am thinking about a combination of limp traps and absorber with a diffuse pattern of slabs.

I hope to be able to DIY this, but it will depend on material costs as well.

The cost of those slabs could quickly become rather expensive.

The ceiling is such a good place for treatment - out of the way, and a large area.

 

21 minutes ago, Primare Knob said:
39 minutes ago, almikel said:
Now those as slats would be way cool

It would be a good reason for buying another tool.

 

11 minutes ago, Primare Knob said:

The cost of those slabs could quickly become rather expensive.

Ignoring the cost of the tool :), the material shouldn't be "too" expensive if you can DIY it. With a slat profile like that, you could ignore using a BAD pattern, and just have regular gaps...

...or just go back to plain profile slats for those sections - a 1D pattern will get some diffusion, but just a regular pattern will still get useful scattering (I'd go the 1D pattern, as there's marginal additional work required).

 

Another of Svenr's useful threads - this one for modular 1D BAD diffusers - he's using them on walls, but no different to ceilings.

cheers

Mike

 

 

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Guest Peter the Greek

If you got he limp mass route, do it in a manner that you can take it out if not happy.

(a) it looks rubbish (IMHO)

(b) they are VERY fickle about a target frequency - so bang it up, do some measurements, then pretty it up as you desire (assuming it worked)

 

 

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1 hour ago, Peter the Greek said:

 

(a) it looks rubbish (IMHO)

(b) they are VERY fickle about a target frequency - so bang it up, do some measurements, then pretty it up as you desire (assuming it worked)

 

 

good points

(a) Looks have never been my strong point for treatment

(b) they are narrow band devices - so they need to work where you have issues

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After reading a bit more on GearSlutz " to use pressure based absorbers and regardless of type used; they need to be placed at a surface related to the modal/SBIR –related problem that your trying to fix. "

 

This suggest that treating the ceiling isn't going to improve my biggest problems, as those a likely to be room width and length modal nodes.

The question that arises is the need and the how, to make a distinction between modal nodes and SBIR

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I have played around with the subwoofer placement and placed them half way the length off the room along the wall (green line) which produces a better response.

Wether if this is a bennifit or not I don’t know yet, as the ¼ along the front placement (blue line) produces a more identical ouptut compared with my front speakers, which I can’t really move a round a lot to improve their LF response. So I can tune acoustics for them and the subs in a similar way

 

I also mocked up some absorption pannels that I placed in the front corners of the room (red line). They do their work between 100Hz – 200Hz, but I get the idea that they are more effectieve on the Tangential room nodes, but perhaps these are inprovements in the SBIR nodes.

Subwoofer_Placement_and_Absorbtion.jpg

Edit:

When placing the subs halfway the room, it will control the modal length nodes around 35Hz and 70Hz. If I do a good job on the ceiling acoustics I can control the modal nodes around 70Hz and 140Hz. Then there will be left the width nodal node which I can't figure out which sub placement can deal with these using the simulator.

 

The dip in the graph from 50Hz - 60Hz has to do with the Axial width node at 50Hz, which doesn't seem to have a large effect, and the tangential Length/Width node around 62Hz, which seems to have a much larger effect. This could potential being fixed by raising the gain of the subs to lift the dip to about 85dB en EQ all the peaks down. The next room width nodal node is around 100Hz which might not be an big issue when perhaps using an aggressive cross over setting.

 

What would your thoughts be on this?

 

I also discovered that my ceiling height might be closer to 245cm reading the graph which puts it almost exactly at 1/2 the room length.

 

The theoretical response curve would look something like this

Theoretical_Response_With_Ceiling_Treatment_Subs_Halfway_LenghtRoom.thumb.jpg.4d00819ecf66568c00cb58760bce4ac3.jpg

Edited by Primare Knob
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On 1/16/2018 at 10:49 AM, Primare Knob said:

I have played around with the subwoofer placement and placed them half way the length off the room along the wall (green line) which produces a better response.

 

Subwoofer_Placement_and_Absorbtion.jpg

 

 

The dip in the graph from 50Hz - 60Hz has to do with the Axial width node at 50Hz, which doesn't seem to have a large effect, and the tangential Length/Width node around 62Hz, which seems to have a much larger effect. This could potential being fixed by raising the gain of the subs to lift the dip to about 85dB en EQ all the peaks down. The next room width nodal node is around 100Hz which might not be an big issue when perhaps using an aggressive cross over setting.

 

What would your thoughts be on this?

 

 

That green line shows an excellent improvement 20 - 60Hz or so. I'd leave 1 sub where it is and muck with the placement of the other sub to see if you can get an improvement in the dip below 70Hz, and the peak at 70Hz...

It does become tedious, as it's an iterative process...:( especially if the subs are heavy/bulky.

Where do you plan to cross your subs to mains?

The 70Hz peaks "appear" to be modal rather than SBIR (since same  freq) - although the 100Hz peak shifts a little in frequency - was the mike in exactly the same place across all those measurements? Given the subs moved a lot and the 100Hz peak moved such a small amount it's still likely modal rather than SBIR.

On 1/16/2018 at 10:49 AM, Primare Knob said:

 

The dip in the graph from 50Hz - 60Hz has to do with the Axial width node at 50Hz, which doesn't seem to have a large effect, and the tangential Length/Width node around 62Hz, which seems to have a much larger effect. This could potential being fixed by raising the gain of the subs to lift the dip to about 85dB en EQ all the peaks down.

 

At this stage in the process I wouldn't recommend attempting to fill dips with EQ - EQ is position dependent and you can make things worse elsewhere and run out of headroom very quickly.

I've found lopping peaks off with EQ isn't as bad (as EQ boost) at making things worse elsewhere...

 

On 1/16/2018 at 10:49 AM, Primare Knob said:

 

I also discovered that my ceiling height might be closer to 245cm reading the graph which puts it almost exactly at 1/2 the room length.

 

you own a tape measure right?

The "acoustic" measurements can be quite a long way out based on the flexibility of your boundaries - the models aren't perfect and make a lot of assumptions so that they're easier to drive - don't take what they say as Gospel - but they're still very useful.

 

On 1/16/2018 at 10:32 AM, Primare Knob said:

After reading a bit more on GearSlutz " to use pressure based absorbers and regardless of type used; they need to be placed at a surface related to the modal/SBIR –related problem that your trying to fix. "

 

This suggest that treating the ceiling isn't going to improve my biggest problems, as those a likely to be room width and length modal nodes.

The question that arises is the need and the how, to make a distinction between modal nodes and SBIR

and being a lazy DIYer myself, I totally understand that if going to the effort of ceiling treatment, it needs to achieve what you want 1st time, and in your case also look good.

 

I've not tried limp mass traps myself (yet), so I have no personal experience to be able to recommend a limp mass solution, and reviewing Svenr's posts, he deployed limp mass on the ceiling and a front wall bulkhead - so 2 modal directions (front to back and floor to ceiling) covered, rather than just 1 (floor/ceiling).

Also on his ceiling he had access to a 400mm gap, not 200mm (estimated) in your case.

I haven't seen @svenr on this forum for a while - if he pops up he may comment.

 

Heading down a slat + absorption path on the ceiling will provide good absorption down to 150Hz or so but keep higher frequency energy in the room - "in room" measurements would likely see benefits below 150Hz due to the size if you covered the ceiling - the ceiling absorption would be exposed to absorb "grazing" energy from all lateral modes.

 

Looking at the models - I would recommend using "fluffy" instead of anything denser above the slats - it's cheaper and models better.

Below is 100mm wide slats with 100mm spacing, with above 200mm fluffy (5000 thingies) vs 200mm mineral wool (27000 thingies) - fluffy is blue

5a5f398d70500_slats200mmfluffyvs200mmmineralwool.JPG.51ed2d06a88b073b9ad664158a01f352.JPG

That's a good bass trap (blue line)  - you may only need some EQ below 100Hz (which is where EQ works very well).

 

cheers

Mike

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After putting the sub at ear height at the listen position and placing the mic at different positions it doesn't look like it is going to be better than placing them halfway.

It produces the flattest response from 20-40Hz and smallest null/dip between 40-70Hz.

 

Theoretically that null should mostly disappear when racing the speakers up, but the measured results are telling a different story.

 

I have become rather interested in this VPR type acoustic trap since it seems to have a broadband behavior and is also very good in taming decay times.

https://www.gearslutz.com/board/studio-building-acoustics/667929-my-experiment-metal-panel-absorber.html?s=5dfd1dfd745d261f103486db4ddcaca5

 

On top of that, it is rather easy to build. Glue a metal sheet onto an acoustic foam. I still have many pages to read through from that forum topic.

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17 hours ago, Primare Knob said:

After putting the sub at ear height at the listen position and placing the mic at different positions it doesn't look like it is going to be better than placing them halfway.

It produces the flattest response from 20-40Hz and smallest null/dip between 40-70Hz.

 

Theoretically that null should mostly disappear when racing the speakers up, but the measured results are telling a different story.

 

I have become rather interested in this VPR type acoustic trap since it seems to have a broadband behavior and is also very good in taming decay times.

https://www.gearslutz.com/board/studio-building-acoustics/667929-my-experiment-metal-panel-absorber.html?s=5dfd1dfd745d261f103486db4ddcaca5

 

On top of that, it is rather easy to build. Glue a metal sheet onto an acoustic foam. I still have many pages to read through from that forum topic.

After reading this thread I have become less enthusiastic about the VPR design. It does show clear signs of the use of thick absorbers in the room corners.

https://www.gearslutz.com/board/bass-traps-acoustic-panels-foam-etc/676662-trapping-traps-10.html

 

Still have many more pages to go through the earlier mentioned thread, as it look like the construction used in the multiple test setup ,isn't in line with the design of the VPR.

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I love Gearslutz - it has some incredibly smart people contributing, but there's so much information and you end up chasing embedded threads down rabbit holes...I was trying to find some good info on VPR traps, as I've only got a vague understanding of their design and operation - @Primare Knob - if you've got some other threads to post on VPR traps that would be appreciated.

 

On 1/18/2018 at 8:58 PM, Primare Knob said:

Theoretically that null should mostly disappear when raising the speakers up, but the measured results are telling a different story.

LoL - it's often not easy to reconcile theory with measurements - an example was my attempt to reconcile the generation of low bass in small rooms in this thread (completely off topic :offtopic:)

 

Despite numerous smart people contributing to the thread, I was left unclear on aligning the science/theory with the measurements - lack of understanding on my part the likely culprit.

 

What I did find interesting in my reading of the Gearslutz threads I scanned were comments on the inability of resonant traps (I assume membrane traps) to manage SBIR due to SBIR reflections traveling only a very few times (possibly only twice) through any treatment, whereas room modes travel many more times and allow the resonance of the membrane trap to do it's work - I'm still getting my head around this, but it flags the issue that SBIR is too often overlooked and not easy to treat - which I do agree with.

 

SBIR can be managed in various ways, and I've attempted to control it in my room with my speakers via the following:

I run PSE144's for top end (above 300Hz) and stereo18" mid woofers below (30Hz - 300Hz) and a single (large) sub below that (15Hz - 60Hz).

First reflection floor bounce SBIR doesn't exist for the 18"s due to their close proximity to the floor and frequency of operation..

I've not calculated the SBIR floor bounce from the PSE's, but their controlled directivity off axis would assist in reducing this (same for ceiling, sidewalls and front wall)

  • speaker positioning

My PSEs sit on top of my 18"s, and the "stack" is relatively close to the front wall and side walls (I have a very small room) - being close to boundaries (front and sidewalls) pushes the SBIR nulls/peaks up in frequency, where absorption is effective. I only  need to consider the 18"s in this context as the PSE's have no interaction with the front wall and immediate side walls due to their coverage pattern. I've used 150mm of Acoustisorb straddling corners in this case

 

Rear and side wall SBIR has no science applied, just more absorption (rear wall has 300mm of Acoustisorb - leaning on the rear wall with a gap at the bottom).

No ceiling or floor treatment - my ceiling is very low, but same as yours - exposed rafters - crying out for some limp mass traps to experiment...except in my lightly constructed room, I don't have any significant low bass issues that need "solving", and my "lazy DIY" gene kicks in, with a 2nd sub project (I have the driver and amp) languishing waiting for a simple box to be built.

 

My room sounds great, the bass is awesome - my motivation is low for additional DIY...but this thread has piqued my interest in building "something".

 

cheers

Mike

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My guess that I can't change the through around 68Hz has to do with the construction of the ceiling.  (10mm pine with at most, 100mm insulation, and a sheet metal roof.) As my measurements seems to proof that leaky constructions are intensifying nulls. Raising the subs to the mid point doesn't fix this, and is introducing other problem which are likely have to do with SBIR.

 

The question then arise, if 200mm fluffy or foam like insulation can go down that low to 68Hz and less. Isobond seem to be able to do this, but is rather expensive and has to be ordered and shipped from overseas.

 

The other funny thing is that at 101Hz I should have a null from the second room width node 0,2,0 which would be present along the walls and in the middle of the room if I read the theoretical graph correctly, but instead it is showing a rather large peak. This could be a flaw in the online tool, as REW is predicting a peak.

https://amcoustics.com/tools/amroc?l=487&w=337&h=250&r60=.4

 

 

After all this testing, it is starting to look like one of my subs is rather iffy, as it is starting to produce a whistling sound when running sweeps and doesn't produce a smooth roll off on the low end.

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On 1/20/2018 at 12:26 AM, almikel said:

What I did find interesting in my reading of the Gearslutz threads I scanned were comments on the inability of resonant traps (I assume membrane traps) to manage SBIR due to SBIR reflections traveling only a very few times (possibly only twice) through any treatment, whereas room modes travel many more times and allow the resonance of the membrane trap to do it's work - I'm still getting my head around this, but it flags the issue that SBIR is too often overlooked and not easy to treat - which I do agree with.

I have read this also and fail to really understand the difference, as it become clear that only the really smart people seem to have a bit of grip on understanding acoustic behavior. I thought this had something to do with phase angle of the sound wave.

The other thing that the people of GearSlutz seem to find more important and harder to accomplish is group delay, whatever this may mean.

 

It seems rather easy to control modal room nodes by just treating the corners, but a lot harder to control the decay time of low frequencies

 

I got this from GS:

" First, I don't see a reason for less efficiency at lower listening levels and I never experienced less efficiency at lower listening levels. Hard to test at very low levels because the signal-to-noise ratio would suffer a lot.

Plus, from a mechanical point of view there's no energy loss because of a thicker plate (it doesn't "need more energy": the acceleration is lower because of the higher mass, that's the reason it resonates at a lower frequency in the spring-mass-system).

Keep in mind that the thicker plate has generally higher inner modes because of its stiffness than the thinner plate. In case they share a resonant frequency the thicker plate might take longer to get in resonance because of its higher mass and keep "ringing" longer than the thin plate. "

 

My guessing on this would be, that because of the repeating nature of the room nodes in frequency and location, these VPR's become more effective in comparison to SBIR, as (guessing again) their frequency and location are only predictable at the very first point of contact, and seems to be changing for ever after that.

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13 hours ago, almikel said:

if you've got some other threads to post on VPR traps that would be appreciated.

The biggest problem I am running into at GearSlutz is that there is a lot of talk, but not much show. Although they have knowledgeable people they never show their true skill, probably because of commercial interest for their own well controlled studios.

 

Then there are a lot of the average Joe, which you can divide into 2 groups. The ones that claim improvement by ear without any backup by measurements, and the group that does testing and show their measurements. Not many of those use a very thorough testing procedure or show many pictures of the test. None so far have even tried to duplicate the true VPR design most likely because of laziness. The closest thorough test is the one, in the thread that I linked before, but also that one doesn't come close to the true VPR design and the results show for it. This makes it very hard to filter out the effect of the steel plate. Some still see "major" improvement, but nobody has come even close to the results of the original design.

 

There are designs out there, that mimic the original, and there is a lot of discussion about the best way to mount them, but I haven't found any proof yet of people having actually build them and or tested them.  All of this makes it very hard to justify to source all the materials, and put one together myself. Makes it even harder when knowledgeable people taking all these shortcuts aren't directly producing great results, but at the same time seem to disregard the fundamental design principal of the VPR.

 

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21 hours ago, Primare Knob said:

I have read this also and fail to really understand the difference,--- I thought this had something to do with phase angle of the sound wave.

 

more to do with SBIR existing for specific instances of placement (speaker and listener) and the boundaries - 1 or only a few reflections creating the nulls - it's not "steady state" room resonant behaviour - and you need to get treatment in the way to damp it - particularly hard for floor bounce SBIR at lowish <500Hz frequencies. Room modes exist throughout the room. Damp a mode anywhere in the room and the response drops at all places in the room.

What the GearSlutz thread seemed to imply also is that resonant traps need a few cycles to do any good. I would expect if you put a tuned resonance trap in the way of SBIR it will still do it's job. Of course moving the speaker or listening position will move the SBIR nulls in frequency, possibly away from the tuning frequency of the traps.

 

22 hours ago, Primare Knob said:

It seems rather easy to control modal room nodes by just treating the corners, but a lot harder to control the decay time of low frequencies

decay times are caused by room modes - lower modes are harder to treat because of the longer wavelengths and the size of treatment - corners are still best because bass "collects" in corners.

 

On 1/20/2018 at 12:33 PM, Primare Knob said:

My guess that I can't change the through around 68Hz has to do with the construction of the ceiling.  (10mm pine with at most, 100mm insulation, and a sheet metal roof.) As my measurements seems to proof that leaky constructions are intensifying nulls. Raising the subs to the mid point doesn't fix this, and is introducing other problem which are likely have to do with SBIR.

 

I'm confident in the science that leaky rooms do not intensify peaks or nulls.

The fact that the 68Hz peak didn't change when lifting the speaker would lead me to think it isn't related to a ceiling mode.

On 1/20/2018 at 12:33 PM, Primare Knob said:

The other funny thing is that at 101Hz I should have a null from the second room width node 0,2,0 which would be present along the walls and in the middle of the room if I read the theoretical graph correctly, but instead it is showing a rather large peak. This could be a flaw in the online tool, as REW is predicting a peak.

https://amcoustics.com/tools/amroc?l=487&w=337&h=250&r60=.4

 

the tools just aren't that sophisticated when you're referring to a mode created in your listening room by a boundary in another room - you would need to model the wall in between as a membrane. The good thing is that you understand that other house boundaries can have a big effect at low frequencies. You may see modes created by the external brick skin on a brick veneered or double brick house or even the next door neighbour's brick house!

 

Don't get too caught up with which boundaries are causing issues - that said, if you do determine another boundary is causing issues, then if the velocity is high, some fluffy on the room boundary (either side) may make a big difference - only experimentation will determine this.

 

Goup Delay is simply a non linear phase change with frequency. Linear phase filters have zero Group Delay.

The natural high pass rolloff of a woofer in a box has group delay as the acoustic filter of the box/driver isn't linear phase. Ported speakers have more group delay than sealed as the filter (driver + box + port) is steeper

 

A key thing I learned from @davewantsmoore is that all wiggles in a frequency response create phase changes.

 

Given you've been mucking with the Impulse Response graphs in REW, it's worthwhile to understand that the Frequency Response (more accurately termed the Amplitude Response in the frequency domain), the Phase Response (also in the frequency domain) are both inextricably connected to the Impulse Response (in the time domain)

 

In a room response where you have deep nulls in the frequency response, you also get big changes in phase (Group Delay).

Where these nulls/dips are caused by modal behaviour, what GearSlutz is saying is that it's (relatively) easy to treat so that the null becomes more of a gentle dip, and the Group Delay is reduced.

A deep null from SBIR is much harder to treat, so left untreated it will have higher Group Delay.

 

In a theoretical scenario, where you have a Frequency Response dip created by SBIR vs the same dip created by a mode, if you were able to treat each such that the Frequency Response was flat in both cases - in both cases you've reduced the Group Delay to zero (ie solved both).

 

At some stage if you keep researching this area you'll come across the term "Minimum Phase". It's a difficult concept to wrap your head around exactly what it means (I haven't), but some understanding is useful especially when applying EQ.

One explanation of Minimum Phase which isn't bad is in the FAQs for REW

https://www.roomeqwizard.com/help/help_en-GB/html/minimumphase.html

 

At a mathematical level "Minimum Phase" is a special case.

In any non Minimum Phase system, to calculate the Impulse Response you need both the Frequency (Amplitude) Response and the Phase Response.

With a minimum phase system, if you have either the Frequency (Amplitude) Response or the Phase Response, you can calculate the other, and with both Frequency and Phase responses you can then determine the Impulse Response.

 

The above is relevant to understand how REW determines "Excess Phase" which can be useful in guiding when EQ may help, but ignoring the maths, the effects of a minimum phase system are important for rooms.

 

Examples of minimum phase systems include:

  • a woofer in a sealed box in an anechoic environment
  • old school analog EQ
  • some regions in a room at low frequency - peaks are "usually" minimum phase, Slow gentle dips can be, but if they're sharp, then that's typically cancellations and are never minimum phase

Where this post is getting to is that "minimum phase" room issues can be greatly helped with minimum phase EQ.

If you have a peak in room response, which is "likely" minimum phase, then an equivalent minimum phase EQ "cut" will correct both the amplitude and phase response - ie when a minimum phase issue is addressed with minimum phase EQ it will be fixed in amplitude, phase and time.

 

Use minimum phase EQ cut on a peak that's not minimum phase and you muck with the room phase response and the time response - likely making issues greater elsewhere in the room

This is how EQ has developed such a bad reputation, through poor application - you should never use EQ in non-minimum phase situations.

 

Deep nulls or dips, whether created by modes or SBIR, are never minimum phase, so you should never attempt to fix these with EQ.

 

These days with DSP EQ available, in the pro world at least, you have the option of applying "Linear Phase" or "Minimum Phase" EQ.

Linear Phase EQ has no place in correcting room response IMHO - this will muck with phase also.

I do like and use Linear Phase crossovers - this is a different application.

 

The above all got a little Off Topic :offtopic:- so apologies to PK - but relevant to achieving a good room response.

On 1/20/2018 at 1:18 PM, Primare Knob said:

There are designs out there, that mimic the original, and there is a lot of discussion about the best way to mount them, but I haven't found any proof yet of people having actually build them and or tested them.  All of this makes it very hard to justify to source all the materials, and put one together myself. Makes it even harder when knowledgeable people taking all these shortcuts aren't directly producing great results, but at the same time seem to disregard the fundamental design principal of the VPR.

 

too many variables for a reliable DIY outcome - way more than a limp mass trap on the ceiling, and way way way more that absorption with/without slats on the ceiling.

Be careful of too much analysis causing paralysis - take the plunge on "some" treatment and go from there...

...if treating the ceiling is too much of a plunge (I still think this is a great option), then focus on absorption targeting lower frequencies (large/wide/deep and straddling corners). 

It doesn't matter which corner you straddle - but covering the "tri corners" is best.

 

If low frequency performance is required from absorption then they need to be large - minimum 200mm deep, straddling corners around 1200mm wide, floor to ceiling would work pretty well down to 100Hz or so.

 

cheers

Mike

 

 

 

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Guest Peter the Greek

The way I figure it, if Keith Yates and Dennis Erskine aren't using these various bass trap designs, they're not worth considering. I've seen neither use any kind of pressure trap (in recent years). They both use the riser and various custom Helmholtz style things, plus multi-subs.

 

Here is an interesting one....no idea how its "tuned"

 

image.png.6036c033332dffbd352d78bc96cf2356.png

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14 hours ago, Peter the Greek said:

The way I figure it, if Keith Yates and Dennis Erskine aren't using these various bass trap designs, they're not worth considering. I've seen neither use any kind of pressure trap (in recent years). They both use the riser and various custom Helmholtz style things, plus multi-subs.

 

Here is an interesting one....no idea how its "tuned"

 

image.png.6036c033332dffbd352d78bc96cf2356.png

What am I looking at? Is this some kind of a bulk head style helmholz trap, or is this a riser type?

 

An riser isn't a great option for my room. I am looking at a single 4 seater couch which is going to be in the direct pathway when entering the room. When I build a riser I need to build a cut out and steps for the entry in the back of the room, which is making entering into the room even more difficult.

 

The only thing I can do, is build a stage underneath the equipment, but if I understand you correctly it is not an great option to put a "riser" trap underneath the equipment.

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16 hours ago, almikel said:

Be careful of too much analysis causing paralysis - take the plunge on "some" treatment and go from there...

Sorry, your talking to the wrong guy.:blush:

I probably come across as a stubborn guy (which I truly am), but when given advise I will start looking for answers in the form of measurements data. I will keep doing this until I have found and understand the data, or drive myself nuts and crazy enough to just take the plunge.

16 hours ago, almikel said:

...if treating the ceiling is too much of a plunge (I still think this is a great option), then focus on absorption targeting lower frequencies (large/wide/deep and straddling corners). 

It doesn't matter which corner you straddle - but covering the "tri corners" is best.

 

If low frequency performance is required from absorption then they need to be large - minimum 200mm deep, straddling corners around 1200mm wide, floor to ceiling would work pretty well down to 100Hz or so.

Treating the ceiling is on the menu, but I am still looking for answers into:

1- which type of absorbent to use: ridged vs fluffy, density vs gas flow resistance

2 -design type to use for the slabs to create a diffuse patern

3- whether or not to use a reflective layer over the absorbent layer. (My room could use some absorbent to eliminate "echo's")

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My biggest problem at this point in time with corner based absorbers are based on the following.

 

1- They don't help with decay times or taming the LF below 80Hz-100Hz (Don't know if EQ can either help taming decay times at this point in time.)

2- Real estate: The front corner of the room only has room for 60cm wide straddling panels. When straddling corners, it's going to claim back the real estate that I have created by placing my speakers well into the room for optimal dipole usability. One of the back corners of the room has a door, so straddling a corner here is not an option either. I can move the screen forward of the wall, but again a flat mounted trap will need less space

 

These are my main reasons for looking into flat mounted traps that can go down to 40Hz or more. The reason for looking into a VPR is that they seems to be truly broadband and easier to construct than other types.

 

@almikel I shall take some time to take your info and try to understand the basics, and apply this to my measurement.

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Guest Peter the Greek
1 hour ago, Primare Knob said:

What am I looking at? Is this some kind of a bulk head style helmholz trap, or is this a riser type?

That is a little "room" in the back corner of a very large room. So about 3300 high if memory servers me with those baffles built inside of it.....just an example, you can't do it.

 

Re your other queries, everything else I can think of if rather invasive/structural.

 

Have you considered getting Paul Spencer over? he might just look at it and say - this'll work. Or Gordan at Acoustic Vision?

Edited by Peter the Greek
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http://www.mh-audio.nl/ACalculators.asp#showcalc

I came across this calculator. This might be a possibility for turning the ceiling into a LF trap as well.

I looked into turning the ceiling into a LF qrd diffuser, but as expected this needs a lot of real estate. The best I can do is trying to turn it into a "tuned" LF scatter using 67cm wide slats and gaps.4ca76a823a7e2018aa412fcc4f16ab05.jpg

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7 hours ago, Primare Knob said:

All the time, but my experience so far is that, if I don't ask the right questions, I don't get the right answers.
 

I actually think you have enough knowledge now to ask the right questions and be able smell BS, The key question is:

  • what are the most effective treatments to manage bass in my room but still maintain imaging and liveliness?

Some professional consultancy now could save a lot - a colleague ages ago had an opinion that all money spent on architects was well spent - drawings and plans cost a lot less than any building that needs to be re-done.

11 hours ago, Primare Knob said:

Treating the ceiling is on the menu, but I am still looking for answers into:

1- which type of absorbent to use: ridged vs fluffy, density vs gas flow resistance

you have the modelling tools for mullti-layer and absorber here

http://www.acousticmodelling.com/multi.php

http://www.acousticmodelling.com/porous.php

IMO fluffy models better - confirm that for yourself - but all absorption traps (unless truly massive) will struggle <100Hz

11 hours ago, Primare Knob said:

2 -design type to use for the slabs to create a diffuse patern

 

Go easy on yourself - just use slats in a 1D pattern (or 2 layers in a 2D pattern) - those slabs PtG posted look amazing, but are a lot of DIY work - you'll keep treble in the room and generate diffusion with slats in a 1D pattern (or 2 layer slats if you want to).

 

12 hours ago, Primare Knob said:

3- whether or not to use a reflective layer over the absorbent layer. (My room could use some absorbent to eliminate "echo's")

you'll get diffuse reflection from the slats - I wouldn't bother.

 

11 hours ago, Primare Knob said:

My biggest problem at this point in time with corner based absorbers are based on the following.

 

1- They don't help with decay times or taming the LF below 80Hz-100Hz (Don't know if EQ can either help taming decay times at this point in time.)

 

Corner absorption traps will significantly help with room decay times - it will depend on their size as to their effect <100Hz.

IME cleaning up 100Hz - 500Hz with absorption makes a truly massive difference to the "in room" sound.

In my "leaky" room, lopping off peaks <100Hz with EQ has worked very well - refer my above post - peaks in that range are typically "minimum phase", so respond well to minimum phase EQ "cut" - if applied well the EQ will reduce decay times.

12 hours ago, Primare Knob said:

2- Real estate: The front corner of the room only has room for 60cm wide straddling panels. When straddling corners, it's going to claim back the real estate that I have created by placing my speakers well into the room for optimal dipole usability.

For absorption to trap bass consider 600mm wide / 200mm deep in the corners as the bare minimum, and a compromise - you'd get better performance covering your ceiling (with/without slats).

 

12 hours ago, Primare Knob said:

These are my main reasons for looking into flat mounted traps that can go down to 40Hz or more. The reason for looking into a VPR is that they seems to be truly broadband and easier to construct than other types.

 

As with most things, there's no free lunch - truly broadband absorption and thin????

Try them  - I'd love it if they worked.

 

IME if you have a lightly constructed room, absorption works fine down to 100Hz or so and EQ works fine below there.

If you have rigid walls your challenges are greater.

 

9 hours ago, Primare Knob said:

http://www.mh-audio.nl/ACalculators.asp#showcalc

I came across this calculator. This might be a possibility for turning the ceiling into a LF trap as well.

I looked into turning the ceiling into a LF qrd diffuser, but as expected this needs a lot of real estate. The best I can do is trying to turn it into a "tuned" LF scatter using 67cm wide slats and gaps.4ca76a823a7e2018aa412fcc4f16ab05.jpg

I Haven't looked in depth  at this tool, but on scanning I don't see too much difference to http://www.acousticmodelling.com/multi.php

You may find it more useful.

 

cheers

Mike

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16 hours ago, almikel said:

I Haven't looked in depth  at this tool, but on scanning I don't see too much difference to http://www.acousticmodelling.com/multi.php

You may find it more useful.

I wasn't really referring to the calculator, but to the helmholz type trap. I didn't know that such a trap existed, or that the other calculator already came included with this.

 

 

 

I have done some modeling with multi layered absorbers with different layer of viscosity. It doesn't model any significant benefit doing that. It seems that if you stick with a gas resistance flow between 7500 - 12500 Pa.s/m2 you get very similar results. People keep referring to stick with fluffy, but what does fluffy actual mean? It's not a unit/value that is useful or consistent.

 

I have done some modeling for the Helmholz slotted panel traps, and using 90mmx45mm slabs with 2mm slots gives a peak absorbance around 70Hz (Room height node). If this is useful or if I can make this work requires some more research. But in the worst case I end up with a nice looking ceiling, and in the best case I end up with a nice looking ceiling that also works.

 

The funny thing is that the Helmholz works better with 5000 Pa.s/m2 absorbent, while with a general absorber trap, this is less useful. At some point I will have to choose between diffusion/scattering or bass trapping.

Helmholz_different_absorber_viscosity.jpg

Helmholz_different_slot_width.jpg

Helmholz_different_slat_width.jpg

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On 1/21/2018 at 7:15 PM, Peter the Greek said:

Keith Yates and Dennis Erskine

Which trap design do they use then? By the looks of it, these guys don't do your typical small room theater either.

Keith Yates: http://keithyates.com/

Dennis Erskine: http://erskine-group.com/home-theater-acoustic-design/

 


 

 

 

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