Why I dislike traditional bass management

gene

gene

Audioholics Master Chief
Administrator
Hey don't bring me into this, I just said I appreciated my pre/pro's flexibility on setting high and low pass filters for the mains / subs. :p

As far as mixing and matching ported & sealed subs (or full range mains I suppose) goes, all I can say is that it's not recommended by guys like Ed Mullen @ SVS and Mark Seaton among others. However, as always, YMMV.
It's not recommended because it takes more care than most consumers are able and/or willing to expend on it to make them work. I essentially turn my sealed subs into ported responses by increasing the slope of the HPF to match that of my ported designs.

One thing you have to be sure of is to check at low vs high SPL to make sure the ported subs don't exhibit port turbulence at high SPL to change their response curve compared to the sealed subs otherwise the combined response will also change.
 
TLS Guy

TLS Guy

Seriously, I have no life.
Gene said: -
In my primary system, I don't use bass management on my main speakers since they have gut wrenching bass at extreme SPL levels down to 18Hz. I struggled for years to find a way to route LFE to them while still running a dedicated subwoofer channel. No AV receivers will route LFE to the mains with the sub channel engaged and only a handful of pre/pros will allow this.
This is how I do it.

Unbalanced RCA to power amps driving the smaller lines.

Right and left balanced out to modified Shure SR 106 electronic crossovers low pass input to generate the BSC drive to the upper 10"drivers of the big lines. Low pass output is controllable to give flattest response.

Balanced sub outs to buffer amps, the output of the buffer amps is blended with the low pass outputs of the Shure SR 106 units with a mixer circuit I built. This fed to the left and right amps driving the upper 10" drivers.

Unbalanced RCA sub out to the amp driving the two lower 10" drivers.

The two lines are tuned one half octave apart as per the late John Wright of TDL, who advised this gives the flattest response.



FR and impulse response. HF droop at 15 Khz is due to omni mic.





Room response center front row 12' from speakers. This is with fronts center and surrounds driven.



Rear row center seat.



No Audyssey or other Eq is involved, just the careful balancing of the speaker systems.

Bass is powerful low Q and non resonant.
 
Last edited:
lovinthehd

lovinthehd

Audioholic Jedi
[QUOTE In my primary system, I don't use bass management on my main speakers since they have gut wrenching bass at extreme SPL levels down to 18Hz. I struggled for years to find a way to route LFE to them while still running a dedicated subwoofer channel. No AV receivers will route LFE to the mains with the sub channel engaged and only a handful of pre/pros will allow this.
[/QUOTE]


While I can appreciate your particular setup is good for your purposes, what can you offer to those without your custom speakers/room situation?
 
TLS Guy

TLS Guy

Seriously, I have no life.

While I can appreciate your particular setup is good for your purposes, what can you offer to those without your custom speakers/room situation?[/QUOTE]

The first thing is to avoid the standard crossover if you are using ported main and center speakers. You can't get the crossover right.

Optimal would be sealed speakers with an F3 around 80 Hz. Then set the crossover to 80 Hz. That is the way the current system was conceived.

Now if you want capable speakers that can handle full range then use it. Run your speakers full range and do not cross them. Gently supplement them with the sub bringing them in for starters at F3 of mains + 50%. So if the mains have an F3 of 40 Hz then start gently supplementing them with subs below 60 Hz.

Measuring systems are strongly recommended, use of auto Eq systems not recommended or encouraged.

That is the best advice I can give you.

If you have ported main speakers that buzz and rattle sent a full range signal, I don't think you can get it right with just a receiver or pre/pro.
 
Old Onkyo

Old Onkyo

Audioholic General
While I can appreciate your particular setup is good for your purposes, what can you offer to those without your custom speakers/room situation?
The first thing is to avoid the standard crossover if you are using ported main and center speakers. You can't get the crossover right.



Now if you want capable speakers that can handle full range then use it. Run your speakers full range and do not cross them. Gently supplement them with the sub bringing them in for starters at F3 of mains + 50%. So if the mains have an F3 of 40 Hz then start gently supplementing them with subs below 60 Hz.

Measuring systems are strongly recommended, use of auto Eq systems not recommended or encouraged.

That is the best advice I can give you.

If you have ported main speakers that buzz and rattle sent a full range signal, I don't think you can get it right with just a receiver or pre/pro.[/QUOTE]
It is 1:30 am, so I can’t play with my system. How would I not set the crossover on my mains? If I select subwoofer I don’t think I have the option.
 
highfigh

highfigh

Seriously, I have no life.
I do think we need some sort of simple and advanced. Maybe a dual menu approach like Windows uses.

I also have heard reports that most people not only don’t understand this stuff, they fail to adjust the settings or utilize the autocorrection at all. I was talking to a guy who makes purchasing decisions for features on a popular line of receivers, and he told me that room correction is a tough call. If you go by the marketing data, it only sells in concept. Most people who say they want it don’t use it, and many of the remaining who do use it, do so incorrectly.

Maybe Alexa can help.
In the late-'70s,. a teen aged kid came into the stereo store where I worked and asked "What's your best speaker?" and, based on his appearance, I answered with "Best, or loudest?". His response was "What's the difference?".

"Alexa- make it sound good" might result in this-
 

Attachments

highfigh

highfigh

Seriously, I have no life.
I’m probably as in the know as anyone can be that doesn’t work for Dirac as I have a relationship with them. I’ve been beta testing all of their products and they have kindly let me have a copy of their Live software to use so that I can help educate people on it and use it in comparison against others.

I actually plan an editorial piece on this with Gene so I won’t say too much. Just know I’m working on a two part series that will go into the science of in-room measured response and it’s relationship to perceived sound. Then the second part will look at specific room correction on the market and put to the test how good a job it does getting it right.

Dirac is a more robust solution and it’s technically very good, but no matter how robust, it can never evade the laws of physics. That is, it still can’t fully disentangle the speaker from the room and a flawed speaker can’t be fixed if the problems are caused by driver problems, crossover problems, or dispersion.

As for it’s coolest feature, it uses a very good predictive modeling approach to establishing the settings. How this works I don’t know, those are the details I hope to get after CES. My understanding is that it takes some information on your room and with the measurements makes predictions of what would happen under various settings. It then comes up with an optimum solution that minimzes both spatial and spectral variance.
I don't know your experience with treating rooms, but if you have done this, was it by implementing a design based on calculations, or did you do it empirically?

My system only has two speakers because it's small and doesn't really lend itself to surround and because I care about listening to music more than movies. Because my room opens into another on the right side and to a hallway at the right rear, calculations would have been a PITA, so I fired up REW and placed the panels I had made for a demo in a theater room I was working on with a friend- my system had a deep notch in the typical region, I hated the sound and it caused wide variations as I moved through the room. Sitting closer to the speakers was OK, but being in the middle of the room isn't practical, so I decided to address the problem without disturbing everything else, aside from aesthetics. I placed the first panel in the corner behind the left speaker and it visibly improved the response. I added one to the left side, where the first reflection occurs and that helped, too. I added one in the right front and left rear corners and saw more improvement. I stacked one on top of the let rear and put one behind the right speaker- pretty soon, the notch was almost completely gone when measured at the listening position and I can move around the room, hearing much more consistent sound.

When I had a Denon AVR, I had tried to fix the response and because it was caused by the room and speaker positions, I found that the results of using Audyssey didn't do much for the phase issues. Have you set up a system and used room correction software in a room that's known to be considered 'bad' WRT acoustics? What were the net gains in sound quality?

What are the assumptions for the rooms intended for using electronic correction? Are the designers assuming bare floors, carpeted, drapes, all hard surfaces....?
 
H

Hobbit

Senior Audioholic
I'm relatively happy with the Audyssey MultEQ XT32 setup. The bass in my 5.2 setup is very seamless for music. Per Peng's suggestions I tweaked it a little. It's surely light years ahead of using an spl or setting up by ear. Maybe I'm lucky?!

The one thing that annoys me, and I don't see it ever addressed, is volume compensation. In my simple 2.1 bedroom system I really struggle with the sub. I seem to always be trying to balance it from not being too loud at low volumes, to the quite the opposite at mid volumes.
 
V

viseral audio

Audioholic
It's OK, I am here now. I will be the arbiter of Correct Thinking. I will lead mankind to a new golden age. But first, we must cleanse humanity of the False Thinkers. It will be a bloody process, but it is necessary.
NECESSARY it is, but its not a job for the squeamish so we are counting on you, tell Yamaha we want full control over our bass and not fisher price (for ages 5 and up) switching!
 
Matthew J Poes

Matthew J Poes

Audioholic Chief
Staff member
I don't know your experience with treating rooms, but if you have done this, was it by implementing a design based on calculations, or did you do it empirically?

My system only has two speakers because it's small and doesn't really lend itself to surround and because I care about listening to music more than movies. Because my room opens into another on the right side and to a hallway at the right rear, calculations would have been a PITA, so I fired up REW and placed the panels I had made for a demo in a theater room I was working on with a friend- my system had a deep notch in the typical region, I hated the sound and it caused wide variations as I moved through the room. Sitting closer to the speakers was OK, but being in the middle of the room isn't practical, so I decided to address the problem without disturbing everything else, aside from aesthetics. I placed the first panel in the corner behind the left speaker and it visibly improved the response. I added one to the left side, where the first reflection occurs and that helped, too. I added one in the right front and left rear corners and saw more improvement. I stacked one on top of the let rear and put one behind the right speaker- pretty soon, the notch was almost completely gone when measured at the listening position and I can move around the room, hearing much more consistent sound.

When I had a Denon AVR, I had tried to fix the response and because it was caused by the room and speaker positions, I found that the results of using Audyssey didn't do much for the phase issues. Have you set up a system and used room correction software in a room that's known to be considered 'bad' WRT acoustics? What were the net gains in sound quality?

What are the assumptions for the rooms intended for using electronic correction? Are the designers assuming bare floors, carpeted, drapes, all hard surfaces....?
I operate a side business called Poes acoustics providing acoustic consulting. I completed 2 years of a 4 year degree in electrical and computer engineering before switching to basically psychology and human development where I finished advanced degrees with minors in that, research design, and statistics. During my graduate school time and at my academic appointments there after I took advantage of my ability to take free classes and took PhD and Masters level courses in acoustical physics and audio engineering at both Purdue University and University of Illinois Urbana Champaign. I’ve taken additional online courses at MIT, Univ of Penn, Penn State, etc. related to architectural acoustics or sound proofing.

I don’t do a lot of jobs, but since 2002 I have been taking consulting jobs or small gig jobs providing services and support in acoustic design to commercial spaces like offices and hotels. I formed Poes Acoustics in 2017 after getting bigger jobs and forming partnerships with a number of home theater and home audio acoustics firms. I don’t usually have more than one client at a time because I just don’t have time, but currently am designing a dedicated sound room for a Chicago customer and doing both wall engineering and acoustic design.

So take that for what it is in experience.

As far as using calculated vs empirical all, not sure what you mean. Calculating is empirical. If you are asking my approach to acoustic design, I tend to follow my own take on what Toole advocates, but appreciate the differences in preferences that even he has acknowledged around room reflections. My model is that all listening rooms or home theaters should not be designed as environtmentless but should have a high degree of LF damping. As such, given a significant budget, I design the walls to be LF absorbers using decoupled mounting and CLD drywall. I add to that strategically placed treatments which are designed to absorb more at LF’s than mid and high frequencies.

In terms of how I engineer a solution, I rely on my education and experience along with computer modeling. For example the wall thickness and density is determined by the dimensions and how those associate with the lowest low order modes they correlate with. For example, my rooms longest dimension leads to modal interference at just under 50hz and 22hz. As such the rear wall is 14” thick. That air gap inside the wall coupled with the density and dimension of the drywall lead to a resonant peak at close to 50hz. It’s also has a membrane type bass trap on it along with a vessel trap (though that is on its way out, someone bought it).

Obviously everything is confirmed with measurements but a lot of this is not readily measurable either, so you have to rely on the models and theory to a point. For example, I can use my accelerometer to measure the resonant frequency of the wall, but in situ absorption methods don’t work well at 50hz. I know that my wall method absorbs but I can’t know it to the degree that a lab test of absorption would give you because no lab test exists for this kind of absorber. I know it for the same reason we know black holes exist. The models that accurately predict absorption also predict that a wall absorbs. That other similar types of absorbers that can be tested in real life absorb. That engineered rooms such as in studios have been noted to have unexpected alpha at low frequencies and it’s the only reasonable explanation.

As such i use a lot of modeling in my design work.

For speaker placement I have and can use ray tracing. There are free softwares for this as well as good pay ones. I have both at the moment. However in small rooms I’ve not found it useful. I honestly use my ears mostly. I measure, but optimal placement of the mains is more for imaging and that can’t be measured using the techniques I rely on. I primarily use measurements for bass integration and optimization and to confirm what my ears tell me with regard to treatment. I also use them because professionally you have to provide proof of what you did. With a commercial venue you are liable for your claims.
 
Matthew J Poes

Matthew J Poes

Audioholic Chief
Staff member
I'm relatively happy with the Audyssey MultEQ XT32 setup. The bass in my 5.2 setup is very seamless for music. Per Peng's suggestions I tweaked it a little. It's surely light years ahead of using an spl or setting up by ear. Maybe I'm lucky?!

The one thing that annoys me, and I don't see it ever addressed, is volume compensation. In my simple 2.1 bedroom system I really struggle with the sub. I seem to always be trying to balance it from not being too loud at low volumes, to the quite the opposite at mid volumes.
Well that could be two things. The most likely is notion of equal loudness. We need bass to be hotter at low volumes. As we get louder the response shape needs to change for us to perceive it as equally loud across the bandwidth. What are known as equal loudness curves depict this. Active loudness compensation is now a common feature on home theater receivers and some 2-channel models. They have been developed by Dolby and Audyssey, possibly DTS? Yamaha and Sony have their own proprietary version.

Another possibility is that the sub is somehow compressing. Normally this is quickly followed by distortion, but many modern subs are very locked down. They have limiters that make them unable to distort. As such you can have a scenario where a sub level is right at normal listening but at high volume the sub simply won’t get any louder. If the rest of the system is getting louder, the balance changes.

What sub do you have and how loud do you listen?
 
Matthew J Poes

Matthew J Poes

Audioholic Chief
Staff member
Have you set up a system and used room correction software in a room that's known to be considered 'bad' WRT acoustics? What were the net gains in sound quality?

What are the assumptions for the rooms intended for using electronic correction? Are the designers assuming bare floors, carpeted, drapes, all hard surfaces....?
I’ve used correction in a lot of different systems and acoustic spaces. I don’t know if it’s exavtly fair to say that they set up room correction based on treatment assumptions. I think that these algorithms don’t really care that much about the treatment, they are designed to compensate in any environment. I believe that Dirac Live and Audyssey are sold for sure in large acoustic spaces and I believe they are not modified for this.

I know that they normally test them in rooms with different levels of absorption and assume that home will be all over the place. They seek robust correction in a variety of environments.

Room correction can’t change certain things in a system which are conflated with other “things” in a typical room measurement. For example, let’s take a peak in the bass caused by the subwoofer having a non-flat response. That peak may look different in different places around the room, but it’s effect will always be present. Thus as a minimum phase phenomena it can be corrected with eq. A peak caused by a mode is also minimum phase and can be corrected by eq, but modal peaks are position dependent. It’s effect is not felt throughout a room. As such that eq could actually make things worse near by. How near by depends. To know for sure we need many measurements around a varied space to confirm how the peak changes. If the peak remains in most measurements about which you sit, eq is a good fix. If it moved around and goes away or even becomes a dip in that same region of space, eq is a bad idea (and acoustic treatment may be a better idea).

At mid and high frequencies a different and more significant set of conflated issues take over. That is, the in-room measurement is a mix of direct and reflected energy. As such the response tends to follow the early reflection response. In fact an average of the listening window and power gives you something very close. Exactly how closely it matches this depends on the wall absorption. The more absorption the greater the ratio of direct to reflected energy and the closer the response would match the listening window (but don’t forget that research doesn’t support listening in an anechoic chamber). Room correction can only correct what it can measure in the room. Reflections, diffraction, resonates, along with all the linear distortions of the speaker combine in the measurements. However the fix to each of those is different. Eq is not the fix to all, it’s not even a good bandaid for some of them.

So a really robust room correction looks at all the measurements and basically looks for evidence that certain problems are moving around in space. If a peak changes it’s center frequency, that is likely diffraction. Can’t eq that. If a peak or dip changed amplitude in space but not frequency, probably a resonance or reflection. The source of the reflection matters for eq. If it’s in the room, then as long as you can show that it’s spatially robust it may be ok to eq. However that is rarely true. If it’s in the speaker it depends. If the peak or dip is constant with angle, you can also eq. IF it changes with angle (poor offaxis response) you can’t eq. However it’s hard for an automated eq system to manage this.

Then you have another issue. While rooms are minimum phase and speakers are generally minimum phase, stochastic room/speaker interactions (what happens above the transition zone) is generally mixed phase. PEQ is minimum phase so you can’t fix a mixed phase system with a minimum phase filter without introducing more problems. Harman uses minimum phase filters but does so in a safe way. They only use in-room measurements for issues at and below the transition zone. They fully characterize a speaker and apply eq to speaker problems in the stochastic zone based on free space characterization. These problems are still minimum phase and so correctable. Dirac uses a mixed phase filter and can basically fix both minimum phase and linear phase problems. It’s trick is that it has to discern the minimum phase speaker problem and address it in a way that assumes the speaker has a constant response with changing angle. Where it doesn’t (and most don’t) it needs to figure that out and not correct. It does that by taking a lot of measurements over a varied space and looking at differences in each for clues of a speaker that has a poor polar response. This is why single point measurements are a bad idea and further why I don’t recommend doing it with Dirac.

I won’t speak for Toole, but I think his argument is that this automated approach is not needed. That it makes more sense to build Better speakers and apply correction to minimum phase problems. These problems that arise in the stochastic region are likely not audible. Whatever correction is fixing may not matter much and runs the risk of making things worse. I e echoed this by saying that I have found that good speakers in a good room are often not helped even by Dirac. It’s effect is subtle or inaudible, and further testing would be needed to know that it’s subtle effect is good. I’ll have much more to say about this in the article with some citations for the claims I’m making.

Now what is my subjective experience? Subjectively i round it makes a big difference in sound. It’s hard to tell the improvement in the bass from the improvement everywhere else. To account for this I manually improve the bass using PEQ and establish room curves that the auto eq follows. That way the only correction is applied to the mid and high frequencies. I can easily toggle Dirac on and off (as I can with ARC, YPAO, and Audyssey. I find the benefit in the bass is almost always better, but i find that most of these can be bettered by me manually. Dirac being an exception. In the mid and high frequencies my experience has been that Dirac is the only one I found to be innocuous or an improvement. The rest were a mixed bag that I inevitably turned off (I have only used ARC on subs so I don’t know what it’s like). With poor speakers in poor rooms, often massive linear distortions or the response are the most audible detriment. In these cases all of them seem to make things better because they make the linear response more listenable.

But...I can’t help but go back to the fact that those are flawed speakers and rooms, that eq isn’t the solution. Yes it made it more listenable but it still was a bad system. Room correction can’t turn a bad speaker into the equivalent of a good one.

Why do I still use and like room correction? Well room curve and ease of use. It’s handy to have something that can correct the bass quickly and easily. Room curve, I like different curves sometimes. Different recordings may merit a different tonal balance (circle of confusion) and it can be a handy way to do that. Sure tone controls can too, but I like this approach. I also have no room correction other than in the bass on my system right now, so I obviously go back and forth myself.
 
highfigh

highfigh

Seriously, I have no life.
As far as using calculated vs empirical all, not sure what you mean. Calculating is empirical. If you are asking my approach to acoustic design, I tend to follow my own take on what Toole advocates, but appreciate the differences in preferences that even he has acknowledged around room reflections. My model is that all listening rooms or home theaters should not be designed as environtmentless but should have a high degree of LF damping. As such, given a significant budget, I design the walls to be LF absorbers using decoupled mounting and CLD drywall. I add to that strategically placed treatments which are designed to absorb more at LF’s than mid and high frequencies.

In terms of how I engineer a solution, I rely on my education and experience along with computer modeling. For example the wall thickness and density is determined by the dimensions and how those associate with the lowest low order modes they correlate with. For example, my rooms longest dimension leads to modal interference at just under 50hz and 22hz. As such the rear wall is 14” thick. That air gap inside the wall coupled with the density and dimension of the drywall lead to a resonant peak at close to 50hz. It’s also has a membrane type bass trap on it along with a vessel trap (though that is on its way out, someone bought it).

Obviously everything is confirmed with measurements but a lot of this is not readily measurable either, so you have to rely on the models and theory to a point. For example, I can use my accelerometer to measure the resonant frequency of the wall, but in situ absorption methods don’t work well at 50hz. I know that my wall method absorbs but I can’t know it to the degree that a lab test of absorption would give you because no lab test exists for this kind of absorber. I know it for the same reason we know black holes exist. The models that accurately predict absorption also predict that a wall absorbs. That other similar types of absorbers that can be tested in real life absorb. That engineered rooms such as in studios have been noted to have unexpected alpha at low frequencies and it’s the only reasonable explanation.

As such i use a lot of modeling in my design work.

For speaker placement I have and can use ray tracing. There are free softwares for this as well as good pay ones. I have both at the moment. However in small rooms I’ve not found it useful. I honestly use my ears mostly. I measure, but optimal placement of the mains is more for imaging and that can’t be measured using the techniques I rely on. I primarily use measurements for bass integration and optimization and to confirm what my ears tell me with regard to treatment. I also use them because professionally you have to provide proof of what you did. With a commercial venue you are liable for your claims.
I was taught that empirical means using observation to drive future changes in the process, so it's more of a "try it and see what changed" approach and my question was really about measuring the in-room response, making changes based on what was seen along with the knowledge of what might be needed under certain conditions.

Is that 14" thick wall filled, or does it just have the membrane?

I worked on a home theater that had speakers (including the subs) in fixed locations at the front and the walls/ceilings were to be insulated to prevent sound leakage. Once the system was set up, we saw that a deep notch existed in the 80Hz area and EQ/changing the distance setting did nothing to help. Since the system had a Denon AVR, delay for each channel was limited and Audyssey's effects didn't cure the problem. Calculations for modes with the room's dimensions didn't match what was heard and seen in REW, either. Moving my head or the mic only a few inches yielded different sound and response and if something was placed in the path from the left front to the right wall, the problem was diminished, so I made some absorptive panels and tried them- they helped, but not enough. Out of frustration, I thumped the wall with my fist and it rang like a drum, at about 80Hz. Turned out that the insulation guys had neglected to put anything in that wall- we opened it from the backside and saw that it was empty. Once it was insulated, the problem was gone.

Ironically, the homeowner owns an insulation company.

Another house I did has a ballroom in the basement- it was built in about 1917 for a brewery owner and the walls of that room are 16" thick masonry with plaster, the floor is terrazzo on concrete and the ceiling is wood lath & plaster. I walked in and the reflections/flutter were amazing- using the ClapIR app, which I use for a simple test, showed RT60 over 6 seconds for some frequencies and we talked about treatment as soon as the discussions began. Unfortunately, the wife decided that she didn't want to see treatments or speakers, so they ended up in the cabinet below the screen. So much for any thoughts of having control over the system design, so I explained that I couldn't be held responsible if the sound was bad. However, since they were putting a heavy rug in front of a large pit sofa, the direct sound was blocked from hitting the back wall and any reflections from the sound that made it to the one side wall that was closer to the speakers wasn't loud enough to cause problems with the sound.
 
Matthew J Poes

Matthew J Poes

Audioholic Chief
Staff member
I was taught that empirical means using observation to drive future changes in the process, so it's more of a "try it and see what changed" approach and my question was really about measuring the in-room response, making changes based on what was seen along with the knowledge of what might be needed under certain conditions.

Is that 14" thick wall filled, or does it just have the membrane?

I worked on a home theater that had speakers (including the subs) in fixed locations at the front and the walls/ceilings were to be insulated to prevent sound leakage. Once the system was set up, we saw that a deep notch existed in the 80Hz area and EQ/changing the distance setting did nothing to help. Since the system had a Denon AVR, delay for each channel was limited and Audyssey's effects didn't cure the problem. Calculations for modes with the room's dimensions didn't match what was heard and seen in REW, either. Moving my head or the mic only a few inches yielded different sound and response and if something was placed in the path from the left front to the right wall, the problem was diminished, so I made some absorptive panels and tried them- they helped, but not enough. Out of frustration, I thumped the wall with my fist and it rang like a drum, at about 80Hz. Turned out that the insulation guys had neglected to put anything in that wall- we opened it from the backside and saw that it was empty. Once it was insulated, the problem was gone.

Ironically, the homeowner owns an insulation company.

Another house I did has a ballroom in the basement- it was built in about 1917 for a brewery owner and the walls of that room are 16" thick masonry with plaster, the floor is terrazzo on concrete and the ceiling is wood lath & plaster. I walked in and the reflections/flutter were amazing- using the ClapIR app, which I use for a simple test, showed RT60 over 6 seconds for some frequencies and we talked about treatment as soon as the discussions began. Unfortunately, the wife decided that she didn't want to see treatments or speakers, so they ended up in the cabinet below the screen. So much for any thoughts of having control over the system design, so I explained that I couldn't be held responsible if the sound was bad. However, since they were putting a heavy rug in front of a large pit sofa, the direct sound was blocked from hitting the back wall and any reflections from the sound that made it to the one side wall that was closer to the speakers wasn't loud enough to cause problems with the sound.
You have the term right. In my field we call our research empirical and I was treating this as if it was similar for a similar reason, but your definition is more precisely correct. Today the term is often used in the social sciences to refer to rigorous observation based research of real phenomena. Not necessarily just observe and see what you get. We call that exploratory research and it’s often frowned upon. Instead it often is theory driven and the observations are used as a means to confirm the theory as true.

In my acoustics work I use both an empirical and analytic approach.

All walls are resonators and those resonances can cause cancelation of sound just as you found. An uninsulated wall made with normal drywall and 16” studs can have a resonance that is closer to 80hz, that makes sense. Without insulation the Q of the resonance is very high and often there is little ability to dissipate that energy. It acts more like a resonance than what someone expects or a panel trap. My approach damps the drywall and provides greater span between the secured ends, along with allowing for quite a bit of articulation. It is imparative that insulation be added, the difference is significant.

In my 14” wall, the source side is two layers of 5/8” drywall with green glue on 24” spaces hat channel. The hat channel is tied to rubber isolated clips to wood studs spaced 16” apart. Inside the wall is insulation for a gap that is something like 10-12” deep. It’s hollow as the wall is a double stud wall. Then on the receiver side there is another stud wall, polymer diaphragm, rigidly secured double layer of drywall. This time it is a 5/8” and a 1/2” layer with green glue. This prevents the acoustical impedance of the two walls from matching and changes their resonances. It makes it so technically sound in the receiver side could more readily transmit to other parts of the house through that wall, but it also doesn’t matter. My goal was to contain sound in the theater, keep sound out of the theater, and absorb LF’s through the walls.

I would have to dig it up now, but somewhere on my laptop I have modeling data, accelerometer measurements, and some microphone measurements near the wall. It’s also notable that in my room there is no evidence of a mode at the frequencies suggested by the long dimensions of each wall. The only really strong one that remains intact is the ceiling reflection which is an SBIR effect at ~250hz or so. Any room with an 8’ solid ceiling and no significant bass traps across most of the ceiling will have this same mode. I actually have detected it in measurements from over a dozen spaces, and it’s absent from those spaces with an acoustic ceiling.
 
Y

yepimonfire

Audioholic Samurai
I'd agree with some of the points. Personally, I would never opt for 80hz as a standard xover point, it's just too high, and group delay and an audible disconnect from the rest of the speakers has always been apparent to me. In my personal experience, IF the speakers can handle it and IF the room acoustics support it a crossover of 60hz or below sounds much more natural and integrated to me. Scientifically speaking, the wavelengths are much larger below 60hz so there is less funny interaction based on the distance of the speakers to the subwoofer. Theoretically, you shouldn't be able to tell where frequencies below 80-100hz originate, but in practice, I've always been able to detect the location based on the direction of the punchiness feeling, mostly occuring in the 50-100hz range.

I've tried the whole LFE + Main setup where there's no high pass to the speakers but the bass is still duplicated to the subwoofer and more often than not it's given me worse results, both in measurements and by ear.

Sent from my moto e5 play using Tapatalk
 
highfigh

highfigh

Seriously, I have no life.
All walls are resonators and those resonances can cause cancelation of sound just as you found. An uninsulated wall made with normal drywall and 16” studs can have a resonance that is closer to 80hz, that makes sense. Without insulation the Q of the resonance is very high and often there is little ability to dissipate that energy. It acts more like a resonance than what someone expects or a panel trap. My approach damps the drywall and provides greater span between the secured ends, along with allowing for quite a bit of articulation. It is imparative that insulation be added, the difference is significant.

In my 14” wall, the source side is two layers of 5/8” drywall with green glue on 24” spaces hat channel. The hat channel is tied to rubber isolated clips to wood studs spaced 16” apart. Inside the wall is insulation for a gap that is something like 10-12” deep. It’s hollow as the wall is a double stud wall. Then on the receiver side there is another stud wall, polymer diaphragm, rigidly secured double layer of drywall. This time it is a 5/8” and a 1/2” layer with green glue. This prevents the acoustical impedance of the two walls from matching and changes their resonances. It makes it so technically sound in the receiver side could more readily transmit to other parts of the house through that wall, but it also doesn’t matter. My goal was to contain sound in the theater, keep sound out of the theater, and absorb LF’s through the walls.

I would have to dig it up now, but somewhere on my laptop I have modeling data, accelerometer measurements, and some microphone measurements near the wall. It’s also notable that in my room there is no evidence of a mode at the frequencies suggested by the long dimensions of each wall. The only really strong one that remains intact is the ceiling reflection which is an SBIR effect at ~250hz or so. Any room with an 8’ solid ceiling and no significant bass traps across most of the ceiling will have this same mode. I actually have detected it in measurements from over a dozen spaces, and it’s absent from those spaces with an acoustic ceiling.
If only we had known the wall wasn't insulated- it would have saved a lot of time, but then, I wouldn't have 'leftover' absorptive panels to use in my room. It's great- I don't have to be neurotic about the sound now.

Are your surfaces non-parallel?

I worked for an audio contractor and they hired Cinema Design Group for the demo theater, which we installed. The walls and ceiling had metal studs & joists because it was classified as a retail space by the inspection department. The cables were run, the walls were insulated, we hung the membrane and attached 3/4" fire-resistant particle board before the drywall went up. The room only had a solid core double door, which was weatherstripped. Once it was in operation, almost no sound was audible outside, but it was 2005, so I doubt they used an RTA to measure the response. I also doubt the ceiling had any treatment. It was OK.
 
GrimSurfer

GrimSurfer

Senior Audioholic
Pure Gold, Matt. Rich in content, logically laid-out, and superbly written. Thank you very much for this...
 
GrimSurfer

GrimSurfer

Senior Audioholic
If only we had known the wall wasn't insulated- it would have saved a lot of time, but then, I wouldn't have 'leftover' absorptive panels to use in my room. It's great- I don't have to be neurotic about the sound now.

Are your surfaces non-parallel?

I worked for an audio contractor and they hired Cinema Design Group for the demo theater, which we installed. The walls and ceiling had metal studs & joists because it was classified as a retail space by the inspection department. The cables were run, the walls were insulated, we hung the membrane and attached 3/4" fire-resistant particle board before the drywall went up. The room only had a solid core double door, which was weatherstripped. Once it was in operation, almost no sound was audible outside, but it was 2005, so I doubt they used an RTA to measure the response. I also doubt the ceiling had any treatment. It was OK.
Before getting back into audio, I spent a lot of time renovating my home prior to retirement. Whenever I removed drywall, I'd install Roxul (now Rockwool) Safe 'n Sound. It went into the outer walls for insulation and into the inner walls for sound absorption. I could have used acoustic sealers on the studs, but it was overkill at the time. I was just aiming for sanity for when grandchildren came on the scene.

Regardless of the original intent, it did pay off acoustically. I only wish I knew then what I know now, as I would have installed a limp/loaded mass membrane in my back wall to better control bass.

Such is life...
 
Last edited:
highfigh

highfigh

Seriously, I have no life.
I'd agree with some of the points. Personally, I would never opt for 80hz as a standard xover point, it's just too high, and group delay and an audible disconnect from the rest of the speakers has always been apparent to me. In my personal experience, IF the speakers can handle it and IF the room acoustics support it a crossover of 60hz or below sounds much more natural and integrated to me. Scientifically speaking, the wavelengths are much larger below 60hz so there is less funny interaction based on the distance of the speakers to the subwoofer. Theoretically, you shouldn't be able to tell where frequencies below 80-100hz originate, but in practice, I've always been able to detect the location based on the direction of the punchiness feeling, mostly occuring in the 50-100hz range.

I've tried the whole LFE + Main setup where there's no high pass to the speakers but the bass is still duplicated to the subwoofer and more often than not it's given me worse results, both in measurements and by ear.

Sent from my moto e5 play using Tapatalk
The crossover frequency needs to be determined by the HP driver- using 60Hz with anything smaller than a 6-1/2" is going to be noticeable in anything other than a small room and even then, it needs to be able to handle a good amount of excursion in order to produce the low frequencies well.
 
newsletter

  • RBHsound.com
  • BlueJeansCable.com
  • SVS Sound Subwoofers
  • Experience the Martin Logan Montis
Top