speaker vs tv placement for better acoustics

[ryanosaur]

There are no hard and fast rules for distance and diffraction that would apply to this scenario. The distance would depend on things like the shape of the doffeacting object, wavelength, and dispersion of the speaker. A speaker with wide dispersion will more readily diffract off nearby objects. A speaker with narrower dispersion has less sound radiating to the sides and so it will diffract less readily.

Thank you, Matthew. You can see what I'm working on at the other thread I started yesterday: B-M-WOW!

I've got room to move the tv back, no worries there. I actually want to move it down when I redo the shelving. Its not uncomfortably high now, but if I can pick up three inches, I'm gonna try. Likewise, I have some room to move the L/R out a bit more, but have to be careful as there is some need of that empty space on either side... especially that ladder on the left side.

 

[Matthew J Poes]

Thank you, Matthew. You can see what I'm working on at the other thread I started yesterday: B-M-WOW!

I've got room to move the tv back, no worries there. I actually want to move it down when I redo the shelving. Its not uncomfortably high now, but if I can pick up three inches, I'm gonna try. Likewise, I have some room to move the L/R out a bit more, but have to be careful as there is some need of that empty space on either side... especially that ladder on the left side.

No problem.

I hope it’s clear to
Everyone that I’m answering the questions at openly and honestly as I can. Do I think this is a life changing world class problem to be addressed, no really. But I also think we all fret over meaningful but small issues.

I will say that, like anything, taken to the extreme it can be very audible and problematic. Moving a center channel out of a cavity and into an open stand, for example, I find to be very audible. You have really good speakers so this all may be more obvious than it might otherwise be.

Here is the front stage of my theater. The frame is all 2x4’s and the speakers are a controlled directivity speaker with a 90 degree dispersion (response is down 6dB at 90 degrees). I placed the speakers to the outside edge of the frame and I had the edge of the frame profiled and then I put some insulation around it. I also insulated between the spans of the frame and all the panels where there aren’t speakers.

 

[Matthew J Poes]

Here is what it looks like closed up.

 

[ryanosaur]

No problem.

I hope it’s clear to
Everyone that I’m answering the questions at openly and honestly as I can. Do I think this is a life changing world class problem to be addressed, no really. But I also think we all fret over meaningful but small issues.

I will say that, like anything, taken to the extreme it can be very audible and problematic. Moving a center channel out of a cavity and into an open stand, for example, I find to be very audible. You have really good speakers so this all may be more obvious than it might otherwise be.

Here is the front stage of my theater. The frame is all 2x4’s and the speakers are a controlled directivity speaker with a 90 degree dispersion (response is down 6dB at 90 degrees). I placed the speakers to the outside edge of the frame and I had the edge of the frame profiled and then I put some insulation around it. I also insulated between the spans of the frame and all the panels where there aren’t speakers. View attachment 27639

I totally agree. I'm not asking because I think there is a problem, but because its the perfect time to learn and understand better! besides, this is the best time to fix it if there is something wrong.

Nice set up! who makes the speakers? (Not that I'm in the market, anymore. ha!)

 

[Matthew J Poes]

I totally agree. I'm not asking because I think there is a problem, but because its the perfect time to learn and understand better! besides, this is the best time to fix it if there is something wrong.

Nice set up! who makes the speakers? (Not that I'm in the market, anymore. ha!)

Earl Geddes made them. Gedlee Abbeys with custom crossovers. I built them from kits that Geddes supplied, but were available as completed speakers too. They aren’t available anymore, Geddes is retired.

http://www.gedlee.com/Loudspeakers/Abbey.aspx

 

[Swerd]

Having a hard time finding an answer to this. I know TVs are bad for acoustics. My rig is mixed usage, but I'm primarily audio, say 80%.
What placement guidelines should I employ to remove the TV from the equation as much as possible... just short of removing the TV?

First of all, where did you learn that TVs are bad for acoustics? I think you might be over-reacting to what may be a small problem that most of us live with without noticing it, including myself.

Matt's advice is generally correct, especially when he said there are no hard and fast rules…

There are no hard and fast rules for distance and diffraction that would apply to this scenario. The distance would depend on things like the shape of the diffracting object, wavelength, and dispersion of the speaker. A speaker with wide dispersion will more readily diffract off nearby objects. A speaker with narrower dispersion has less sound radiating to the sides and so it will diffract less readily.

Additionally, diffraction depends on frequency. At mid to high frequencies, where it is most notably a detriment, small objects near by are a bigger problem than large objects far away.

Diffraction occurs at different frequencies and depending on the frequency range can have a wide range of effects. Let me describe two common examples.

The biggest diffraction effect occurs at the upper bass/lower mid range, mostly in speakers with narrow cabinets. In the USA this is often called the "baffle step response". Sound waves that are longer than the speaker cabinet's width, the baffle width, will bend around the sides of the cabinet, propagating in all directions, 360° or 4π (four pi). Sound waves shorter than the baffle width reflect off the baffle, propagating 180° or 2π. As you might expect, the sounds that reflect off the baffle will be about twice as loud as the lower sounds that travel in all directions. In most bookshelf and narrow tower speakers, the frequencies of roughly 500 to 1000 Hz are involved. Uncorrected baffle step response results in weak sounding bass. Sometimes, depending on the music, it can make human voices, trumpets, or something in the same range, sound "shouty" or "nasal". Many people have speakers that do this and never notice it as a problem.

This diffraction effect is most often corrected by the speaker designer by including baffle step compensation (BFC) equalization in the speaker's crossover. Dennis Murphy is well aware of this, and builds BFC into all his speakers. When you use one of those BMR speakers sideways as a center channel speaker, the baffle width increases from about 8-9" to about 20". Dennis corrects for that in your BMR dedicated to center channel use. As far as your TV screen goes, I wouldn't worry at all about how it might affect yours speakers in the BFC frequency range.

Another kind of acoustic diffraction occurs at the edges of speaker cabinets. You may have noticed speaker cabinets with rounded edges, or with tweeters set slightly off-center. These are done to minimize diffraction effects that occur at higher frequencies in the range of 4 kHz or higher. Dennis Murphy has measured the frequency responses of small 2-way speakers identical except for the cabinet edges. One cabinet had edges not rounded over, and the other had edges rounded over to a ¾" radius. The resulting differences are minor but measurable. Dennis admits he isn't sure if this effect is easily heard by listeners. See the link for the frequency response graphs.

I would guess that the edges of your TV screen might have a similar minor effect on the sound of your front left & right speakers. The solution, as Matt already suggested, is as easy as moving your BMRs a bit further away from and slightly forward of the TV screen.

In other words, don't obsess over diffraction

 

[ryanosaur]

EDIT: I found the answer by putting a Blu-ray film in the OPPO and I could access to this setting. Marantz could have specified either on the display or at least in the owner's manual the condition for getting to it instead of mentioning that I can't access it!

So it seems that some design engineers figure that anyone knows but they don't put themselves in a layman's shoes. If they are not responsible for important omissions, then the marketing people are the ones.

Thanks for sharing this tidbit!

 

[ryanosaur]

In other words, don't obsess over diffraction

Hi Swerd!
I'm not! Promise! This was meant as a more intellectual question than anything.
Regarding where I heard TVs are bad for acoustics? Many places, including here. Can't site any specific post or writer, but as I am working with an almost blank slate in my room, I just want to learn as much as possible about making it as nice as possible from an acoustics perspective.
If anything, that metro rack I'm using as my equipment stand for the time being probably has more detrimental effect than the TV. And then there's the drafting table and large window about 3' in front of my right speaker...
And...
But I AM trusting in my ears to help me out as much as possible, and so far so good. If anything, things sound a little lively in the high end. I'll run Audyssey after my surrounds are set up and see what that does... and in a month or two, I'll get a proper mic and REW. so I can really see what's happening in my room.
If anything, I feel my front wall could do with some absorption, as I'm surrounded by drywall and glass on three sides. That said, the Wood Cathedral ceiling and medium pile carpet are probably pretty helpful. I'm not going to touch any kind of room correction, though, until after my Phil-3s are in place. (And IF I do, I want it to be as minimal as possible... I'm sure you've read some of the posts where guys have set up acoustic treatments before they even set up their systems only to find out the treatment is doing anything for them. *shrugs)

Thank you for your Post, too! I'm very grateful for the interactions I've had, here. So much to learn.

And that tidbit about rounded and squared corners on speakers... I need to remember that! Thank you for sharing the link.

 

[Swerd]

I'm not [obsessing]! Promise! This was meant as a more intellectual question than anything.

I get that you're interested in understanding the reasons why when it comes to speakers and acoustics. Although I'm no expert, I kind of like answering your questions. I believe Matt does too.

Regarding where I heard TVs are bad for acoustics? Many places, including here. Can't site any specific post or writer, but as I am working with an almost blank slate in my room, I just want to learn as much as possible about making it as nice as possible from an acoustics perspective.

Be careful with broad generalizations. They tend to be right or wrong depending on specific details.

I'll run Audyssey after my surrounds are set up and see what that does... and in a month or two, I'll get a proper mic and REW. so I can really see what's happening in my room.

Just a heads up with Dennis's speakers and Audyssey. It has been my impression that many (most? some?) owners of speakers designed by Dennis (DIY, Philharmonic Audio, or Salk) who have tried Audyssey room correction software, decided to not use the EQ corrections. To use highly technical terms, it "sucked the life out of my speakers". There will always be someone who disagrees with me about this, but it seems like most owners of Dennis Murphy-designed speakers prefer their sound unmodified. Your preferences may or may not be different. I don't own a receiver that has Audyssey or any other brand of auto-room correction, so I'm a complete agnostic on the subject.

If anything, I feel my front wall could do with some absorption, as I'm surrounded by drywall and glass on three sides. That said, the Wood Cathedral ceiling and medium pile carpet are probably pretty helpful. I'm not going to touch any kind of room correction, though, until after my Phil-3s are in place. (And IF I do, I want it to be as minimal as possible... I'm sure you've read some of the posts where guys have set up acoustic treatments before they even set up their systems only to find out the treatment is doing anything for them. *shrugs)

Yes, I think you get that under most circumstances, Less is More. I also want to pat you on the head for realizing that a cathedral ceiling may actually result in better sound, especially bass, than a ceiling which is parallel to the floor .

 

[Swerd]

The biggest diffraction effect occurs at the upper bass/lower mid range, mostly in speakers with narrow cabinets. In the USA this is often called the "baffle step response".

I found a frequency response curve that shows a good example of the baffle step response in a small 2-way speaker. It either has no baffle step compensation (BSC), or not enough.

This otherwise good sounding speaker suffers noticeably from nasal sounding voices and instruments. The blue box shows the so-called baffle step, in the range of 500 Hz to 2250 Hz. The elevated response may not look that big, but it is about 3-4 dB higher than below 500 Hz. It's right in the mid range where our hearing is most sensitive. We definitely can hear that.

The green box shows a dip that often can occur at frequencies just a bit higher than the most prominent region of the baffle step. In these 2-way speakers, I would guess that it's caused by the crossover to the dome tweeter.

If proper BSC is used, the elevated response (shown in the blue box) will be lowered to the same level as below 500 Hz. It results in a flatter frequency response, apparently louder bass, and an overall better sound. It also reduces the speaker's sensitivity by about 3-4 dB.

 

[ryanosaur]

I've seen that discussed, @Swerd , about Audyssey in general. I'm more interested in hearing it on a newer system... as my last system, the infamous 10yr old HTIB from Onkyo almost needed it. If anything... my ears will adjust over time (the user break-in period, rather than speaker ) or when I actually check my room out with REW at that point in the future I'll see elevated highs.
Only time will tell.
Best to you! And HNY!

 

[Matthew J Poes]

First of all, where did you learn that TVs are bad for acoustics? I think you might be over-reacting to what may be a small problem that most of us live with without noticing it, including myself.

Matt's advice is generally correct, especially when he said there are no hard and fast rules…
Diffraction occurs at different frequencies and depending on the frequency range can have a wide range of effects. Let me describe two common examples.

The biggest diffraction effect occurs at the upper bass/lower mid range, mostly in speakers with narrow cabinets. In the USA this is often called the "baffle step response". Sound waves that are longer than the speaker cabinet's width, the baffle width, will bend around the sides of the cabinet, propagating in all directions, 360° or 4π (four pi). Sound waves shorter than the baffle width reflect off the baffle, propagating 180° or 2π. As you might expect, the sounds that reflect off the baffle will be about twice as loud as the lower sounds that travel in all directions. In most bookshelf and narrow tower speakers, the frequencies of roughly 500 to 1000 Hz are involved. Uncorrected baffle step response results in weak sounding bass. Sometimes, depending on the music, it can make human voices, trumpets, or something in the same range, sound "shouty" or "nasal". Many people have speakers that do this and never notice it as a problem.

This diffraction effect is most often corrected by the speaker designer by including baffle step compensation (BFC) equalization in the speaker's crossover. Dennis Murphy is well aware of this, and builds BFC into all his speakers. When you use one of those BMR speakers sideways as a center channel speaker, the baffle width increases from about 8-9" to about 20". Dennis corrects for that in your BMR dedicated to center channel use. As far as your TV screen goes, I wouldn't worry at all about how it might affect yours speakers in the BFC frequency range.

Another kind of acoustic diffraction occurs at the edges of speaker cabinets. You may have noticed speaker cabinets with rounded edges, or with tweeters set slightly off-center. These are done to minimize diffraction effects that occur at higher frequencies in the range of 4 kHz or higher. Dennis Murphy has measured the frequency responses of small 2-way speakers identical except for the cabinet edges. One cabinet had edges not rounded over, and the other had edges rounded over to a ¾" radius. The resulting differences are minor but measurable. Dennis admits he isn't sure if this effect is easily heard by listeners. See the link for the frequency response graphs.

I would guess that the edges of your TV screen might have a similar minor effect on the sound of your front left & right speakers. The solution, as Matt already suggested, is as easy as moving your BMRs a bit further away from and slightly forward of the TV screen.

In other words, don't obsess over diffraction

Diffraction happens at high frequencies as well. We are just discussing different kinds of diffraction effects.

http://www.gedlee.com/Papers/Philosophy.pdf

And more relevant to what i was discussing:
http://www.gedlee.com/Papers/AES06Gedlee_ll.pdf

These reflections and diffraction are not unique to waveguides, and the test has nothing to do with them, but his impetus and description was about minimizing diffraction in waveguides.

I think it’s a bigger concern than you make it out to be. Just because people live with it doesn’t mean it isn’t a problem.

 

[Danzilla31]

I get that you're interested in understanding the reasons why when it comes to speakers and acoustics. Although I'm no expert, I kind of like answering your questions. I believe Matt does too.
Be careful with broad generalizations. They tend to be right or wrong depending on specific details.
Just a heads up with Dennis's speakers and Audyssey. It has been my impression that many (most? some?) owners of speakers designed by Dennis (DIY, Philharmonic Audio, or Salk) who have tried Audyssey room correction software, decided to not use the EQ corrections. To use highly technical terms, it "sucked the life out of my speakers". There will always be someone who disagrees with me about this, but it seems like most owners of Dennis Murphy-designed speakers prefer their sound unmodified. Your preferences may or may not be different. I don't own a receiver that has Audyssey or any other brand of auto-room correction, so I'm a complete agnostic on the subject.
Yes, I think you get that under most circumstances, Less is More. I also want to pat you on the head for realizing that a cathedral ceiling may actually result in better sound, especially bass, than a ceiling which is parallel to the floor .

Just wanted to chime in and say thank you to you and other experienced members who have given great insight on why Audyssey isn't always in fact a lot of eq isn't always the best option.

When I started everybody kept going on about running eq. So I thought Audyssey and items like this were absolutely necessary to setting up a theater or music area these days

So I buy a lottof of new gear for the new house over this past year building my all SVS dream system. I know there's better out there but in auditioning and trying there subs they won me over with great service and now I'm a SVS buyer for life plus I like the quality of both speaker lines for what you pay

So I go to all this trouble to set an up 3 towers in the front 2 PB 4000's ultimately near field in the back surrounds ceilings etc. Run all this Audyssey XT 32 stuff. And for the life of me highs are shrill or muted and there's issues with my bass that never went away

Until I turned off all eq. Any manual adjustments were very simple from there to got it exactly dialed in.

I know my experiences aren't applicable to everyone Audyssey I'm sure does help some but I'd have never looked outside the conventional box if it wasn't for you guys and your knowledge so a really big thank you to all of you.

P.S. Us new bloods like you old schools answering our questions too! Pretty appreciative of it!

 

[ryanosaur]

P.S. Us new bloods like you old schools answering our questions too! Pretty appreciative of it!

Word!
Rock horns all around!

 

[Danzilla31]

Diffraction happens at high frequencies as well. We are just discussing different kinds of diffraction effects.

http://www.gedlee.com/Papers/Philosophy.pdf

And more relevant to what i was discussing:
http://www.gedlee.com/Papers/AES06Gedlee_ll.pdf

These reflections and diffraction are not unique to waveguides, and the test has nothing to do with them, but his impetus and description was about minimizing diffraction in waveguides.

I think it’s a bigger concern than you make it out to be. Just because people live with it doesn’t mean it isn’t a problem.

Yeah but how measurable do you really think it is Mathew? Is it really that noticeable especially to an untrained regular Joe like me versus a trained critical reviewer and tester?

I'm curious because this is why I switched to pro amps on my amplifiers. I'm sure some can but I couldn't tell the difference between 0.0035% on the good amp and 0.5% distortion even when I did a blind quick switch test with my friends between the pro amps I use know and the more expensive home theater amp I eventually flipped. I'm wondering if the same thing applies here

I bet some could but I sure couldn't.

P.S. the distortion #'s are a bit off but you get the picture one was much lower then the other

 

[Verdinut]

Thanks for sharing this tidbit!

You are quite welcome!

 

[Swerd]

Just wanted to chime in and say thank you to you and other experienced members who have given great insight on why Audyssey isn't always in fact a lot of eq isn't always the best option.

You're very welcome . Keep treating me like an expert, and I'll have to make you my assistant .

I think it's important to remember that Audyssey and its competitors are a continuing work in progress. While it may be easy to dismiss it as promising more than it delivers, it clearly can succeed at automated bass management and setting up a system of surround sound speakers directly from test signals and microphone input. That's better than anything imaginable 15-20 years ago. These systems also claim to be able to equalize speaker’s room response across the full audio spectrum, but in my opinion those results, so far, have been mixed. With some rooms and speakers this Room EQ can work reasonably well, but with other speakers and rooms it works poorly. Consider it a work in progress.

If this software continues to develop, and computer processing speed continues to increase, I can see a future where automated EQ and fully active crossovers, all directed by software will replace passive crossovers. But I don’t see this happening soon. At present, I think the home audio industry is waiting for this to happen, but is also content to wait for competition to force them into acting. I'm only predicting this based on past performance, so I could very easily be wrong about this.

 

[Danzilla31]

You're very welcome . Keep treating me like an expert, and I'll have to make you my assistant .

I think it's important to remember that Audyssey and its competitors are a continuing work in progress. While it may be easy to dismiss it as promising more than it delivers, it clearly can succeed at automated bass management and setting up a system of surround sound speakers directly from test signals and microphone input. That's better than anything imaginable 15-20 years ago. These systems also claim to be able to equalize speaker’s room response across the full audio spectrum, but in my opinion those results, so far, have been mixed. With some rooms and speakers this Room EQ can work reasonably well, but with other speakers and rooms it works poorly. Consider it a work in progress.

If this software continues to develop, and computer processing speed continues to increase, I can see a future where automated EQ and fully active crossovers, all directed by software will replace passive crossovers. But I don’t see this happening soon. At present, I think the home audio industry is waiting for this to happen, but is also content to wait for competition to force them into acting. I'm only predicting this based on past performance, so I could very easily be wrong about this.

Well..... Being your assistant is a lot better then being your beeeeeaaattcchh!!!

 

[Matthew J Poes]

Yeah but how measurable do you really think it is Mathew? Is it really that noticeable especially to an untrained regular Joe like me versus a trained critical reviewer and tester?

I'm curious because this is why I switched to pro amps on my amplifiers. I'm sure some can but I couldn't tell the difference between 0.0035% on the good amp and 0.5% distortion even when I did a blind quick switch test with my friends between the pro amps I use know and the more expensive home theater amp I eventually flipped. I'm wondering if the same thing applies here

I bet some could but I sure couldn't.

P.S. the distortion #'s are a bit off but you get the picture one was much lower then the other

These effects are extremely measurable. They are what cause in-room measurements to look so rough. Most speakers are fairly smooth anechocily at high frequencies (if competently designed and built) but in room they look a mess. This is why.

The issue is more audibility which is why I said it’s more a last 10% thing. It’s audible, as proven by blinded research, but it’s also potentially dwarfed by bigger problems.

Still, if setting up speakers and looking for the best sound, this is an issue to address. I think people put far more effort into far sillier things.

As for distortion, well yeah, of the right type, distortion isn’t usually a big problem. THD is a terrible metric of sound quality. I always quote Geddes on this, but even Toole notes it’s nothing more than an engineering tool where 0 is best and the absolute value itself is meaningless (paraphrasing). He contends (as does Geddes) that THD is not a metric of merit for consumers. The number just doesn’t matter.

It is my opinion that most modern amplifiers are good enough that distortion isn’t the main concern. Clean power output is number one, noise floor is number two, and channel separation would be number three but way down on the list (not that i lose sleep over it, but some amps have very poor channel separation that might verge on audible). All other aspects (like distortion or bandwidth) are already so good as to be inaudible.

Pro amps are a great example of the problems with comparing amps via thd. Most are Class D these days and many aren’t the most sophisticated designs (compared to a Hypex). Their lack of open loop gain at high frequencies limits the amount of negative feedback and the distortion rises dramatically. However it’s still low in absolute terms and it’s mostly at high enough frequencies that many of the harmonics are not a concern. Between auditory masking, the acoustic low pass filtering of a speaker, and the fact that the harmonics are up at very high frequencies where are hearing is insensitive, you don’t notice it.

Think about it, a 2nd harmonic of 10khz is 20khz. You won’t hear that too well.

But alas we have gone a bit off topic. None of this was my point. A clean front stage and minimizing of diffraction and very early reflections is obviously a pet peeve of mine and so I sometimes stick it into related topics. I had planned to actually do a test of this in an actual room to visualize the magnitude of the effect and this thread has made me want to do that again. I plan to take a very wide dispersion speaker and place it in an open room and measure it. Then introduce common things around it and remeasure. Things like a tv cabinet, tv (or stand in), etc. My hunch is that the magnitude of the problem will be large but the fix will be simple. I myself curious just how far an object needs to be moved from a speaker before the measurements clean up. I’ll also test acoustic baffles as a potential fix.