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post #1 of 12 Old 05-05-2013, 06:41 PM - Thread Starter
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ok so i have a 10x15 room and i was wondering where the sound would be the best(where i put my speakers)

ive had my speakers along the 15' part of the wall and they sounded great. now, i recently moved my speakers to the 10' wall and the mids are sooo mudy and the bass is not there.

is there a way to fix this without having to move my system again? or is my new placement better than the old due to simplicity?

i have CV vs120s and a yamaha rxv375

-speakers: cerwin vega vs120s, cerwin vega LS12s, cerwin vega at12s, jbl S36II, pok audio psw10, realistic mc1000, paradigm 7se MKII, sanyo sx600

yamaha rxv375
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post #2 of 12 Old 05-06-2013, 09:23 AM
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Your current orientation is best, but you need to address the reflections coming off the side walls. Once you do that you'll have decent bass and a much better midrange. See this guide:

How to set up a room

Then see this short article. It's mainly about home recording, but all the same principles apply to hi-fi and home theater too:

Acoustic Basics

--Ethan

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post #3 of 12 Old 05-06-2013, 03:17 PM
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Where are the speakers relative to the walls and other room features in each set-up?

Where do you listen in each set-up?

Ethan's right about which is the preferred orientation, but it's not a requirement, especially with large speakers in a small room. Take a look at your room and your listening position to see if there are clues to the shift in sound quality.
- distance behind speaker
- distance from speaker to side wall
- distance between speakers
- distance off floor
- angle

- distance from listener to speaker
- distance from listener to walls

- presence of architecutural features, like windows, doorways, fireplaces, etc. that affect reflected sound, even if not a first reflection.

The reason I ask is that Ethan sells devices that can address a lot of issues, but you have to know what issues you want to address. For example, I have very little side wall reflection in my HT due to a doorway on one side (no wall present) and a fireplace with pellet stove insert on the other (complex reflection). Great for Ht or other multi-channel program, but not so good for stereo. You see, I like what lateral reflections bring to the sound field, so I also have a stereo room with far less stuff and lots of bare wall... and doorways. Nothing's perfect... but still good enough that speakers can disappear.

That's what I like...

Have fun,
Frank
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post #4 of 12 Old 05-06-2013, 06:32 PM - Thread Starter
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here is a bass trap im building. im planning to put one in my two front corners. what material would you suggest stuffing it with? also, im making acoustic panels for my celling and walls. i will cover most of the celling, and alot of the walls.

what type of fiberglass would you suggest for the acoustic panels? how thick should they be?

-speakers: cerwin vega vs120s, cerwin vega LS12s, cerwin vega at12s, jbl S36II, pok audio psw10, realistic mc1000, paradigm 7se MKII, sanyo sx600

yamaha rxv375
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post #5 of 12 Old 05-07-2013, 10:56 AM
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If I can take the time to read, understand and reply to you, please respond in kind. You appear to be building something, but whatever it might be (it's not a bass trap), it's irrelevant to your question.
Frank
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post #6 of 12 Old 05-07-2013, 11:12 AM
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Originally Posted by NotInvolved View Post

what type of fiberglass would you suggest for the acoustic panels? how thick should they be?

If that frame is as large as I think it is, you can just stuff it completely with common fluffy fiberglass.

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post #7 of 12 Old 05-07-2013, 03:40 PM - Thread Starter
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How is it not a bass trap? Its just a frame but it will be stuffed with fiberglass and put in a corner

-speakers: cerwin vega vs120s, cerwin vega LS12s, cerwin vega at12s, jbl S36II, pok audio psw10, realistic mc1000, paradigm 7se MKII, sanyo sx600

yamaha rxv375
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post #8 of 12 Old 05-08-2013, 05:23 AM
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Quote:
Originally Posted by NotInvolved View Post



here is a bass trap im building. im planning to put one in my two front corners. what material would you suggest stuffing it with? also, I'm making acoustic panels for my ceiling and walls. i will cover most of the ceiling, and a lot of the walls.

The general rule for optimal stuffing of porous absorbers seems to be that density should be roughly inversely proportional to thickness. IOW thin absorbers are optimal for their thickness with high density absorbant materials such as OC705, while thick absorbers such as this one may be optimal with far less dense materials such as what we see in products for thermal insulation in walls and ceilings.

The best guide that I know of is Whealy's porous absorber calculator which is an Excel spreadsheet that you can download for free from http://www.whealy.com/acoustics/Porous.html . Note that it handles porous absorbers that are partially empty space which when designed optimally can perform comparably to absorbers that are fully stuffed.

Your best guide is acoustical measurements of how things work in the real world, such as measurements done using Room Eq Wizard, etc.
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what type of fiberglass would you suggest for the acoustic panels? how thick should they be?

Proceeding very bravely, and of course with any final design verified by the means mentioned above:

1-2" thick absorbent layer: 705 or equivalent in competitive products including rock wool
2-4" thick absorbent layer: 703 or equivalent in competitive products including rock wool
4-8" thick absorbent layer: 701 or equivalent in competitive products including rock wool
8"-thicker absorbent layer: Insulation batts, possibly somewhat compressed during installation or equivalent in competitive products including rock wool.

Notice that these recommendations overlap somewhat, there are no absolute rules as other aspects of the design and application are relevant.
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post #9 of 12 Old 05-08-2013, 09:09 AM
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Originally Posted by NotInvolved View Post

How is it not a bass trap? Its just a frame but it will be stuffed with fiberglass and put in a corner
Exactly. A frame stuffed with fiberglass and put in a corner is not a "bass trap" no matter how many vendors sell things that look like this as a bass trap. At best, it's a broadband absorber with some mid-bass absorption.

A true "bass trap" absorbs bass, only. They are necessary because most residential spaces already have all the broadband absorption they need, except in the "modal region" where wavelengths are comparable to room dimensions. Absorption requirements in the modal region vary as well, depending on the presence and severity of resonances in addition to modal interference patterns.

I expect that paragraph is confusing... but it's an accurate statement. Play with Whealy's simulator and see if you can get the curve higher below 100Hz than above... (Neat link, Arny!!)

Now, take your box, make 5 of the 6 sides thick plywood, the sixth of thin hardboard, filled with fiberglass of mineral wool and sealed air tight, and you're getting close to the modular absorption units the BBC developed.
http://downloads.bbc.co.uk/rd/pubs/reports/1992-10.pdf

Scroll down to Fig 21 and look closely at the construction details that yield an absorption curve that peaks at 65Hz and falls off at higher frequency. This curve shape is the hallmark of a true, broadband bass trap. It's achieved with a 580x580mm frame 187mm deepmade of 9.5mm plywood, filled with 4" of fiberglass, with a front face of 3.2mm hardboard. It's a sealed box - no air leaks. Note the dimensions are chosen for compatibility with existing studio acoustic treatments - their "modular approach."

Build your project like that and you'll have a true bass trap.

Have fun,
Frank
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post #10 of 12 Old 05-09-2013, 10:45 AM
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Quote:
Originally Posted by fbov View Post

A frame stuffed with fiberglass and put in a corner is not a "bass trap" no matter how many vendors sell things that look like this as a bass trap. At best, it's a broadband absorber with some mid-bass absorption.

That's not necessarily true. Yes, some products sold as bass traps don't absorb much once you get below 250 Hz. But an absorber doesn't have to be a tuned type to be a true bass trap. What matters is how well it absorbs bass frequencies, and there are many valid reasons to prefer broadband bass trapping over tuned.
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Scroll down to Fig 21 and look closely at the construction details that yield an absorption curve that peaks at 65Hz and falls off at higher frequency. This curve shape is the hallmark of a true, broadband bass trap.

This is exactly my point. That absorber is not a broadband bass trap. It's a narrow band trap that absorbs well over a range less than one octave, centered at 63 Hz whether that frequency happens to be what the room needs or not. Now, consider the graph below showing the LF response in a typical untreated room:

art_measuring1.gif

Clearly, this room requires bass trapping that's effective from 40 Hz all the way up to and beyond 300 Hz. After adding broadband bass traps all of these problem frequencies are improved:

rew_response.gif

Sorry for the disparate graph sizes and frequency range, though the data is the same.

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post #11 of 12 Old 05-10-2013, 07:54 AM
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Quote:
Originally Posted by Ethan Winer View Post

...Clearly, this room requires bass trapping that's effective from 40 Hz all the way up to and beyond 300 Hz. After adding broadband bass traps all of these problem frequencies are improved:...

--Ethan

That's an absolutely excellent example of using measurements to diagnose a problem and select the correct device(s) to address that problem. Inferring response form the curves, if the OP's room shows a similar response pattern, the device he's constructing will serve him well.

I will simply point out that you're not trapping "bass" at 300Hz. It's a broadband absorber with bass extension, not an actual "bass trap."

HAve fun,
Frank
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post #12 of 12 Old 05-10-2013, 12:35 PM
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Quote:
Originally Posted by fbov View Post

I will simply point out that you're not trapping "bass" at 300Hz

I always considered the "bass range" to encompass all frequencies up to about 300 Hz. To my way of thinking there's low-bass (up to about 60 Hz), mid-bass (60-150 Hz), and high-bass (150-300 Hz). Are there even formal definitions for these ranges? Here's one person's opinion:

http://www.troelsgravesen.dk/frequency_ranges.htm

Here's someone else's:

http://correlative.com/cms/audio-recording-techniques-equalization.html

And here's yet another:

http://www.avforums.com/forums/speakers/1179209-bass-midrange-treble-what.html

If we go by the Schroeder frequency, which varies by room, the bass range is that where modes dominate. This is usually between 100 and 300 Hz. But the highest fundamental pitch on my Fender Precision Bass is 311 Hz, and that sounds mostly like a bass note.

What do folks here think?

--Ethan

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