Questions relative to fabrics found in movie theaters

[TLS Guy]

It depends what you are after. The low NRC for low frequencies inside a theater room explains the boomy bass. I want to recreate the same acoustic. Perfect sound and neutrality are very subjective.

A home theater and movie theaters are very different acoustic spaces.

I am yet to be in a movie theater where the sound is really good. Certainly I have never been in a movie theater with the sound as good as in my room. Not even close.

Now, a movie theater just wants to have people hear the dialog, so they don't complain. If a movie theater did not have acoustic treatment, it would be a concert hall. Good concert halls are live. Live music in a dead room sounds awful.

If a movie theater had the acoustics of a concert hall, the public would complain, and rightly so, as the long reflection times, would create havoc for movie watching.

However, a home theater has short reflection times, and reflections are to be encouraged. However, if the speakers have an off axis response substantially different from the direct axis sound, then this creates a less than optimal experience. The best sound in rooms of a properly designed home theater room, will be pleasing when there is the optimal mix of direct and secondary reflections.

The bottom line is that home theater rooms require a very different approach compared to a public cinema.

 

[ScareDe2]

A home theater and movie theaters are very different acoustic spaces.

I am yet to be in a movie theater where the sound is really good. Certainly I have never been in a movie theater with the sound as good as in my room. Not even close.

Now, a movie theater just wants to have people hear the dialog, so they don't complain. If a movie theater did not have acoustic treatment, it would be a concert hall. Good concert halls are live. Live music in a dead room sounds awful.

If a movie theater had the acoustics of a concert hall, the public would complain, and rightly so, as the long reflection times, would create havoc for movie watching.

However, a home theater has short reflection times, and reflections are to be encouraged. However, if the speakers have an off axis response substantially different from the direct axis sound, then this creates a less than optimal experience. The best sound in rooms of a properly designed home theater room, will be pleasing when there is the optimal mix of direct and secondary reflections.

The bottom line is that home theater rooms require a very different approach compared to a public cinema.

I am not sure what the sound axis and reflection time has to do with the sound concept explored in this topic. Feel free to add as much information as possible. This can be interesting.

A combinaison of specific fabrics and their geometry create a unique acoustic.

I am not interested in "good" sound, but rather a well flavored sound. A specific fabric inside a normal room can transform the listening experience. It's like spices added to a sound recipe.

I have experience modding headphones with fabrics. The Commando Cloth and Trevira works very well for something as small as an earcup or as big as a public cinema (they are mostly all privately owned). I tried dozens of other fabrics, didn't like them. Also tried home made acoustic panels for my listening room. Did not like them, although it helped defined percussions and detailed the sound. Not what I am looking for.

I am not trying to get a better sound. I am trying to recreate the same feel/sound flavor inside a movie theater. When you take a pair of Beyerdynamic DT770 250omhs for example, their earpads made of velour gets you very close to the sound you experience inside a movie theater. We are talking here of very small earcups relative to the size of a big theater room.

The fabric.

Back to the topic. Do you know what king of acoustic panel is this (filmed inside an abandonned movie theater from year 1989):

 

[ScareDe2]

Perforated corrugated sheet.

 

[TLS Guy]

I am not sure what the sound axis and reflection time has to do with the sound concept explored in this topic. Feel free to add as much information as possible. This can be interesting.

A combinaison of specific fabrics and their geometry create a unique acoustic.

I am not interested in "good" sound, but rather a well flavored sound. A specific fabric inside a normal room can transform the listening experience. It's like spices added to a sound recipe.

I have experience modding headphones with fabrics. The Commando Cloth and Trevira works very well for something as small as an earcup or as big as a public cinema (they are mostly all privately owned). I tried dozens of other fabrics, didn't like them. Also tried home made acoustic panels for my listening room. Did not like them, although it helped defined percussions and detailed the sound. Not what I am looking for.

I am not trying to get a better sound. I am trying to recreate the same feel/sound flavor inside a movie theater. When you take a pair of Beyerdynamic DT770 250omhs for example, their earpads made of velour gets you very close to the sound you experience inside a movie theater. We are talking here of very small earcups relative to the size of a big theater room.

The fabric.

Back to the topic. Do you know what king of acoustic panel is this (filmed inside an abandonned movie theater from year 1989):

View attachment 55353

The most important feature of a home listening room is the ratios of its physical dimensions.

All room with a speaker system will have the first arrival direct sound and then a myriad of secondary reflections. Like this:-

If you cancel those crucial secondary reflections you get bad sound period. However those secondary reflections largely come from the off axis response of the speaker. So if there is discongruity between the axis and off axis sound, then there is a problem. In a room the time delays between the two are not long enough to impair speech intelligibility. However in a large movie theater long reflection times certainly would impair speech clarity, and so taming of reflections is required.

 

[ScareDe2]

The most important feature of a home listening room is the ratios of its physical dimensions.

All room with a speaker system will have the first arrival direct sound and then a myriad of secondary reflections. Like this:-

View attachment 55357

If you cancel those crucial secondary reflections you get bad sound period. However those secondary reflections largely come from the off axis response of the speaker. So if there is discongruity between the axis and off axis sound, then there is a problem. In a room the time delays between the two are not long enough to impair speech intelligibility. However in a large movie theater long reflection times certainly would impair speech clarity, and so taming of reflections is required.

The sound concept explored in this topic tells that canceling the reflections doesn't necessarily gives you a bad sound. It depends on the geometry, position, quantity and combinaison of fabric and material used. You could get a surprisingly quiet, calm and acoustically comfortable room where you can enjoy listening to your music even tho it's a more dead room.

Generally speaking, a room must preferably sounds natural as you describe. I already knew all of this but the thing with the off axis and direct axis : what exactly are you trying to reach for ? You measure the db level at different axis position and you want it to be the same at every position?

 

[TLS Guy]

The sound concept explored in this topic tells that canceling the reflections doesn't necessarily gives you a bad sound. It depends on the geometry, position, quantity and combinaison of fabric and material used. You could get a surprisingly quiet, calm and acoustically comfortable room where you can enjoy listening to your music even tho it's a more dead room.

Generally speaking, a room must preferably sounds natural as you describe. I already knew all of this but the thing with the off axis and direct axis : what exactly are you trying to reach for ? You measure the db level at different axis position and you want it to be the same at every position?

The problem is that for a lot of speakers, if not most, the frequency response as you move the measuring mic from the zero axis out to 90 degrees, the response is inclined to substantially deteriorate as you move away from the axis, from ten to 90 degrees.

Here is the axis and off axis position of one of my main speakers from 2 meters from the tweeter axis all the way out to 90 degrees. The blue line is the axis response the black out to 90 degrees.

As you move further off axis you want to see a gradual roll off of the HT response above around 5 KHz. What you don't want is increasing dips and peaks as you move off axis.

The reason a poor off axis response does not sound good is that the first arrivals are dominated by the axis response, and the reflections by the off axis responses.

The human brain cries foul if the secondary response do not closely mirror the first arrival on axis response.

A speaker with a response as above will sound good in multiple rooms and not require massive room treatments. In fact it will sound best with some reflections. This will result in a much more lively engaging response, and help preserve the original ambience of the venue, especially when these new up mixers, especially Dolby Digital plus are engaged.

Designing a speaker with the a response like shown above, is a formidable challenge. The response above is known as a quasi anechoic response, and is most reliable above 300 Hz.

 

[ScareDe2]

Just to be clear, you want the off axis attenuation to match perfectly with the axis response
or be as smooth as possible with fewest dips and peaks?
or either ?

 

[TLS Guy]

Just to be clear, you want the off axis attenuation to match perfectly with the axis response
or be as smooth as possible with fewest dips and peaks?
or either ?

You want a very smooth response, especially in the speech discrimination band of 350 Hz to 4 KHz, and 5 KHz preferably. But you don't want big peeks and dips anywhere in the audio band. The off axis response will roll off at some point and the higher the better. The off axis response needs to mirror the axis response very closely in the speech discrimination band. As you move further off axis, then the HF should roll off smoothly. The response I showed you is what would be regarded as a very good result, but those are the usually on the higher end speakers. Of late however more affordable speakers are doing much better in quite a few cases.

 

[ScareDe2]

What about the reflective surface? Would you benefit from this very good off axis response if it is reflected on an irregular surface or on a diffuser?

 

[TLS Guy]

What about the reflective surface? Would you benefit from this very good off axis response if it is reflected on an irregular surface or on a diffuser?

The answer to that is no.

I am very laid back about room treatments. The most important reflections are in the bass decades as they frequently cause large peaks and nulls. These to all intense and purposes defined by the physical dimensions of the room, specifically ratios of length, width and height. These issues are not amenable to passive acoustic treatments.

As far as other reflections, the floor is dominant and best dealt with by carpet. Wool is best if you can afford it.

Otherwise the room reflections tend to be kind and beneficial to good speakers. Furnishings help balance things out. I do not personally use acoustic treatments beyond that. I do use treatments behind the walls, ceiling and floors though, to prevent resonance. My room sounds excellent.

This is the room curve at the MLP without any Eq.

 

[ScareDe2]

I will say that in all my years, one of the best sounding rooms I was ever in was one which all the walls were covered in carpet.

I had been in several which had been fully treated with good acoustical tiles, and I felt like they were just too dead to me. No reflections is not ideal is what I was thinking.

The carpet was a pretty standard issue berber. It was dark, for the theater, but it struck a great balance between cost and effectiveness. I've never seen it done before, or since then, but it stuck out in my mind as one of the best solutions I've ever seen.

I would think materials used on furniture is just not going to be a major impact in the grand scheme of things. As long as it isn't a huge wooden or glass table.

Back to your post. Short pile or long pile?

I am testing my acoustic with some carpets and I find a preference for short pile wool carpet. I think in most movie theaters the carpet is short pile as well. Why would short pile sound better than long pile? I have no idea.

 

[BMXTRIX]

Back to your post. Short pile or long pile?

I am testing my acoustic with some carpets and I find a preference for short pile wool carpet. I think in most movie theaters the carpet is short pile as well. Why would short pile sound better than long pile? I have no idea.

The room I was in used a short pile berber type carpet like you would find in a office or similar. Dark color. In recent testing, black berber carpet did a better job and light diffraction for front projection than black paint did. I thought that was interesting.

Why short pile over long? I really have no idea. I'm not even sure what testing has been performed against carpet on walls vs. other materials. I'm sure some have done so. But, carpeting a full wall is relatively inexpensive and can be quick compared to building acoustical panels I'm sure.

 

[ScareDe2]

I did not expect much but asked an AI about this matter and here is the answer :

"In general, short pile carpets are better for room acoustics than long pile carpets. This is because the shorter pile of the carpet will absorb more of the sound waves in the room, reducing the amount of echo and improving the overall acoustics. Additionally, short pile carpets are less likely to produce sound-reflecting echoes, which can make a room sound more "live" and noisy. If you're looking to improve the acoustics in a room, a short pile carpet is a good place to start."

That seems counterintuitive to me.

https://carpet-rug.org/wp-content/uploads/dlm_uploads/Acoustical-Characteristics-of-Carpet.pdf

6. Increasing pile height while holding pile weight constant in loop pile fabrics results in improvements in absorption.

AI from https://chat.openai.com/ : In general, cut pile carpets are better than loop pile carpets for improving room acoustics. This is because the cut pile of the carpet has more surface area to absorb sound waves, reducing the amount of echo and improving the overall acoustics of the room. Additionally, the cut pile of the carpet is less likely to produce sound-reflecting echoes, which can make a room sound more "live" and noisy. If you're looking to improve the acoustics in a room, a cut pile carpet is a better choice than a loop pile carpet.

How Acoustic Carpets Can Absorb The Sounds of the Room

Acoustic carpets absorb undesired noise in an office, hotel or bar and improve the feel of the room. Here's the architect's guide to acoustic carpeting.

blog.egecarpets.com

• Cut pile carpet provides a greater Noise Reduction Coefficient (NRC) than loop pile construction with otherwise identical specifications, as it provides more “fuzz”.

I guess at the end of the day, it is whatever fits your taste and practice.


when you say short pile is better, do you mean for cut pile or loop pile ?

AI:
When I say that short pile carpets are better for room acoustics, I am referring to both cut pile and loop pile carpets. In general, short pile carpets of either type will have a higher surface area to absorb sound waves, reducing the amount of echo and improving the overall acoustics of the room.