[michaelv]

Hi,
 I have a couple of questions related to bass trap. Here is the scenario: my room already has two bass traps in two front corner with foam bass trap behind(I had it before i build OC 4" bass trap). and foam bass trap in two corners behind speakers.

Last night, when i played one CD which might has very low frequency (sound likes thunder and the sound rumbles) which caused a ringing problem . Then, i played another CD which also had strong bass , but tight and fast and didn't have ringing problem

Here are questions:

1> Is this ringing sound a problem of lacking bass trap?

2> Does it make any difference if i leave foam bass trap behind 4" OC trap? I would like to stick foam trap to the joint between ceiling, sidewalls. Or do i need to build two more OC 4" trap and place in corners behind speaker?

3>  the ringing sounds like the wall vibrate whenever i hear thunder sound. Note that i don't have subwoofer for 2 channel music. Any suggestion to reduce the ringing problem?

thanks very much .

[ScottMayo]

It might be that your room reacts strongly to one frequency but not another - that's extremely common. Just slinging in foam is unlikely to solve this, though you might get lucky. Foam is generally poor at dealing with bass problems.

If you just want to experiment, get some Owens Corning 2" insulation and try stacking it in room corners, with air gaps behind it. If you want to pay for a design that eliminates the problem for good, that's a service I offer for fee. PM me if interested.

[michaelv]

So, air gap must be  needed when placing bass trap in the corner? I already had two bass trap which i made from OC 4". I guess i need to build two more for the back corner.

[ScottMayo]

So, air gap must be  needed when placing bass trap in the corner? I already had two bass trap which i made from OC 4". I guess i need to build two more for the back corner.

Air gaps help. How much air depends somewhat on what you need to trap.

[michaelv]

thanks, Scottmayo.  Do you mean that more air gap, more low frequency absorbed?   How about air gap in the panel at the reflection point?  I think i will create about  1" air gap for first refelection point.   Another problem is to figure out how to stack two 4" panel together in the corner.

[ScottMayo]

thanks, Scottmayo.  Do you mean that more air gap, more low frequency absorbed?   How about air gap in the panel at the reflection point?  I think i will create about  1" air gap for first refelection point.   Another problem is to figure out how to stack two 4" panel together in the corner.

I charge for the details. As a hint, though, you likely don't need an air gap at the first reflection points. It won't hurt but it probably won't help.

[samplesj]

I charge for the details.

This is just wrong.  This is NOT a commercial forum.  Furthermore this information is freely available from many locations.  Many of the people who do this for a living and have a real background in acoustics don't charge for this type of information.  One caution for the original poster is that reading Alton's book and buying a room design service from a respected vendor doesn't necessarily give someone the proper background to offer the same level of service themselves.

In answer to the original question here is a great FREE link that explains the relationship between air gap and frequency trapping.  http://www.ethanwiner.com/acoustics.html'>Ethan's FAQ.  A direct quote from his FAQ that deals with that is "For a given thickness of absorbent material, the ideal air gap is equal to that thickness because it avoids a hole in the range of frequencies absorbed."

[Ethan Winer]

Michael,

> Then, i played another CD which also had strong bass , but tight and fast and didn't have ringing problem <

I'd take that at face value, and assume the first CD simply has more bass ringing present in the track itself. This is not to say you wouldn't benefit from more bass trapping, because all rooms need as much as possible. However, it's also possible that the first CD was in a musical key that excited your room's natural resonances and the second CD was in a different key. This is the main problem with "reference CDs" because the key of the song is directly tied to the amount of modal ringing you'll get in a given room.

I have 36 bass traps in my living room HT and the bass is extremely tight at all frequencies. So I can hear very clearly how much boominess is in a track. Most pop tunes are very tight and clear, but live recordings usually have leakage where the bass on stage gets into all the vocal microphones. And that leakage is delayed enough to make the bass sound distant and less focused. I can hear this very clearly in the DVD Standing In The Shadows of Motown. The live band performances, while sounding great, have much more bass boom than the studio tracks.

--Ethan

[ctviggen]

36 traps?  And there's room for you?  I thought I will be doing well, once I get my ceiling, the back of my system, and the opposite corners trapped, and that would give me about 5-6 more traps to add my 6 I already have.

[CSMR]

This is just wrong.  This is NOT a commercial forum.  Furthermore this information is freely available from many locations.

Many people charge for freely available information, e.g. at schools, universities, and legal and financial consultancies. It is a perfectly normal part of the economy. I don't see why you take exception to it. (Of course right behaviour could be to do all one's work for free, but I presume you meant something stronger than that.) And given that he charges, ScottMayo could not have given a different reply.

[michaelv]

Ethan, thanks for the info. Most of my CDs don't have the problem with my current setup (2 bass traps in rear corner , and two foam bass traps in corners behind speakers). I will build two more OC bass traps anyway to take advantage of it. I guess the modal ringing will be reduced once all corners have 2'x4' 4" OC bass trap.

For now, due to room setup and configuration, i will leave bass traps on the floor at corner and use my current corner foam trap for the joint where ceiling and walls meet.


thanks again.

[ctviggen]

About this charging thing.  While it's true that you can get acoustic data on the net, it's also hard to figure out how to use such information. For instance, where do you put diffusive elements?  When do you use diffusive elements?  I'm still grappling with this issue, and I have a book on acoustics and two books on studio design.  I'm getting to the point where I'm about to pay someone to tell me what to do, as I simply don't have the time to figure it out myself.

[samplesj]

This is just wrong.  This is NOT a commercial forum.  Furthermore this information is freely available from many locations.

Many people charge for freely available information, e.g. at schools, universities, and legal and financial consultancies. It is a perfectly normal part of the economy. I don't see why you take exception to it. (Of course right behaviour could be to do all one's work for free, but I presume you meant something stronger than that.) And given that he charges, ScottMayo could not have given a different reply.

Please read the http://www.audiocircle.com/index.php?topic=9409'>Circle Guidelines for this Circle.  Here is a relevant quote from that thread by Rob Babcock.  "Please, Vendors, I ask that this Circle not be used as a market to push your products. The intent is to create a repository of knowledge and facilitate the exchange of ideas- this is compromised when the poster has to fend off sales pitches. Any blatently commercial posts may be moved or deleted at the Facilitators option."

This is also not Scott's only adpost in this circle.  If he has nothing to add freely then why contribute to the thread at all unless its marketing?

[ScottMayo]

Please read the Circle Guidelines for this Circle. Here is a relevant quote from that thread by Rob Babcock. "Please, Vendors, I ask that this Circle not be used as a market to push your products. The intent is to create a repository of knowledge and facilitate the exchange of ideas- this is compromised when the poster has to fend off sales pitches. Any blatently commercial posts may be moved or deleted at the Facilitators option."

Whoopsie. Feel free to delete them as needed. I'd forgotten to check the guidelines on that point.

[csero]

About this charging thing.  While it's true that you can get acoustic data on the net, it's also hard to figure out how to use such information. For instance, where do you put diffusive elements?  When do you use diffusive elements?  I'm still grappling with this issue, and I have a book on acoustics and two books on studio design.  I'm getting to the point where I'm about to pay someone to tell me what to do, as I simply don't have the time to figure it out myself.

My "simple" answer is: there is no right amount of acoustic treatment for all kind of music if you are using stereo.

[MaxCast]

Please read the Circle Guidelines for this Circle. Here is a relevant quote from that thread by Rob Babcock. "Please, Vendors, I ask that this Circle not be used as a market to push your products. The intent is to create a repository of knowledge and facilitate the exchange of ideas- this is compromised when the poster has to fend off sales pitches. Any blatently commercial posts may be moved or deleted at the Facilitators option."

Whoopsie. Feel free to delete them as needed. I'd forgotten to check the guidelines on that point.

Scott, perhaps your sig line could indicate your offerings.  You could then post helpful info with out a "sales pitch" in a thread.  A person could then link to you for more detailed information.
...just a thought.

[bpape]

csero,

If I understand you correctly, I'd have to disagree.  There is an appropriate amount and type of treatment for every room for a given purpose.  HT is one thing, recording something else, 2 channel, yet something else.  

If you treat the room appropriately for it's intended purpose, and you find some recordings objectionable, IMO there is either an issue with the recording or the system.

Just my 2 cents.

[ScottMayo]

csero,
If I understand you correctly, I'd have to disagree.  There is an appropriate amount and type of treatment for every room for a given purpose.  HT is one thing, recording something else, 2 channel, yet something else.  

Room treatment is generally designed to deal with a specific number of sources in specific places, and a specific number of listeners in specific places.  If you've got one listener and two speakers, there's one (or at least not many) optimal arrangements for them and the treatments. If you add 3 more speakers, you can generally just add more treatments without wrecking the stereo handling. My room is set up for 5.1 sound, and handles stereo without any loss. I can imagine exceptions to this principle, but they wouldn't be any fun.

Changing the treatments for different kinds of music, though... that only makes good sense in a recording studio. Some music is recorded in more resonant rooms, brighter rooms, etc. to suit the music. But once those decisions are made and captured, you're usually best off playing it back in a room that meddles as little as possible. Unless they really messed it up.

This isn't to say I couldn't get some interesting effects by playing new age music with all the treatments taken out. OooooEEEEeeeeoooo.... But if you're after hearing what the musicians and studio were trying to achieve, that's not the way to get there.

I suppose I'd say it this way: treatments are not supposed to sculpt the sound, they are intended to prevent the room from sculpting the sound. I suppose you could use them to sculpt frequencies in complex ways, but it would get infuriating to manage. Imagine closing and opening helmholtz resonators and moving bass traps around based on what you wanted to listen to. I'm just not that zealous. Sometimes I meddle the output on my sub, and that's about as far as I ever feel I need to go.

[Ethan Winer]

Bob,

> 36 traps? And there's room for you? <

It's not a huge room, but at 25 by 16 by 11 feet high at the center peak, there's still lots of available corners. Available from my perspective that is, if not my wife's.

Any time you'd like to stop by for a visit let me know.

--Ethan

[ctviggen]

I do plan on dropping by; it's just the time contraints that are the problem. I'm still trying to lose weight (after bloating out to 260+ pounds) by biking, so I'm riding lots of rides this year.  However, those rides will be complete by the end of Sept., then I go on vacation.  When I get back, I'll make an appointment; I won't be riding nearly as much, so I'll have much more time.  Can we combine play and work? I'll bring a layout of my room and you can counsel me as to what I should concentrate on next.