[gtaphile]

This is my first post in acoustics and after some thirty years listening to HQ 2 channel I finally got around to tackling my room. It's 11'6 by 18' 6 by 8 and I have a good combination of diffusion and reasonable broadband absorption after much experimenting. The imaging is excellent and wide but the mid bass and low bass have always been non existent. I finally had one of our engineers over to measure the in room response at the listening position using a kit that we use to tune sound systems in concert halls and he reports a large suck out between 120hz  and 240hz.  Its 14 db down at 136, 10 db down at 141, 8 db down at 146, and 6 to 8 db down up to 240hz. I have experimented with flipping the room and it wont work functionally. 

Phase response is exemplary. Frequency response above 260hz is excellent.   

Short of turning the room into a sound studio, which I don't want to do, I am ready to pack it up and set it up down stairs.

Is there another solution?
 

[Armaegis]

Well... the obvious first question: are moving the speakers or the listening position an option?

[mresseguie]

I don't know if this works for you, but adding two, three, or even four subwoofers in different locations within the room can work wonders. Duke LeJuene of AudioKinesis has the Swarm approach. Alternatively, you could check out Rythmik Audio or even Hsu Research for high quality yet inexpensive subs and midbass modules.

[JLM]

A diagram/images of your room along with a listing of the treatments used would be helpful.

Your room seems nicely shaped, but every room has its issues.

In my 8ft x 13ft x 21ft room (with near-field setup) the treatments are minimally effective.  But being an audiophile, a "speaker guy", and a strong believer in the contributions of the room/setup I've also been a user of EQ/DSP.  IMO using the correctly shaped room should be top priority, then setup, then treatment if needed, and finally EQ/DSP.  Note that EQ/DSP can only correct a single location in the room and the biggest reason for my use of EQ/DSP has been to replace the baffle step circuit in my single driver speakers (so that I could have a direct connection from mono-blocks to drivers).

But care must be taken with applying EQ/DSP to room suck outs.  For instance a 14 dB boost represents a 27-fold power increase, which could easily overload your amp, causing clipping distortion, and blown speaker drivers.  Fortunately the ear tends to "skip over" narrow dips in frequency response, but this does not appear to be the case in your situation.  So many automatic EQ/DSP systems ignore those narrow dips (which can be -30 dB, that would require 1,000-fold power increases).

I've also noticed that use of smaller mid/woofer drivers (less than 6 inch diameter) can result in loss of mid-bass "body".  If you look around you can find mid-bass boosters (look similar to subwoofers).  Hsu used to sell one. 

Take care.

[gtaphile]

Thanks for responding - the speakers are on the short inside wall appropriately spaced.  Behind the speakers there are three sets of two by two skyline diffuses. The imaging is simply excellent - wide, focused and layered.

There are 4 - 24 by 40 inch by 1 inch fabric wrapped acoustic panels along the left long wall equally spaced along the wall. 

There are 2 - 28 by 55 inch by 1 1/2 inch fabric wrapped panels on the window cove side walls directly left and right and slightly behind the listener position.

On the other long wall there is a 48 inch room opening into the hall from the speaker position forward. There are no treatments along the rest of this wall. Moving treatments around while measuring had no affect on the low end response. 

I have flipped the entire room with the speakers on the window wall and find that the image is somewhat collapsed as I am not able to place diffusers on the windows. In this position the seating position is more near field and when one leans fully forward the sound gets "fuller", when one sits back to norm position the sound gets noticeably "thinner".  There is not other place for the seating position.     

It would be a shame to insert a DSP in line with a $10K plus preamp. Wouldn't it?

The room is already crowded so placing subs would help but I am very reluctant as the drop out is not a notch its quite wide.

   

[JLM]

Recommend you check the acoustical specifications of the absorption materials, most are very poor/ineffective, especially in the bass/mid-bass range.  Seems like you have plentv of treatment already, but even the best materials are rather poor at absorption at those frequencies.  My guess is that you have a room full of ineffective panels.  Check out GIK here at Audio Circle for real world guidance and effective products.  Beyond proper room shape which you pretty much have, the aforementioned "swarm" concept is probably the best you can do, but it only applies to bass, not mid-bass where your problem lies.

You mention diffusers.  The laws of physics dictate that the panels be at least half the depth of the length of the particular sound wave to be effective.  So for 120 - 240 Hz the diffuser would have to be 28 - 55 inches deep (sound wave length = speed of sound in air divided by the given frequency).  That explains why they only work down to around 1000 Hz (when 7 inches deep).  And they need to be designed in a random pattern to cover the entire frequency range in question.  I envision such a panel to be roughly 20ft x 6ft x 5ft.  So trying to cover mid-bass one panel would be about half the size of your room!!

Yeah bass frequencies behave differently than higher frequencies in-room.  Recommend reading Floyd Toole's "Sound Reproduction" (the book is way cheaper than more treatments).  There are many theories on room treatments (especially by those who sell - "over sell" them).  After experimentation I've stuck with Live End Dead End (LEDE) where absorption is located in the speaker end of the room and the side walls have "diffusion" (semi-randomly filled bookcases).  Note that Toole doesn't overdo his room at home.  He explains that we're all conditioned to hearing in a "typical" residential setting.

If the EQ/DSP does the job, only a compulsive audiophile (like me  ) would care what it cost or that it takes away from signal purity.   

The mid/bass module (subwoofer looking) that Hsu sold covered the frequency range you mentioned.

[bpape]

You likely have several instances of SBIR (phase difference between direct and reflected sound).  1 and 1.5" thick panels honestly are really narrow in scope and really only appropriate for voice only applications like conference rooms, etc.  To address the things you're seeing (and to better balance the decay time curve), you'd want something more in the order of 4" thickness and then some corner trapping.  SBIR can happen as low as 90-100 Hz and thin panels just aren't going to do that.

[GT Audio Works]

I find the rule of 3rds works well in placing speakers. http://www.psaudio.com/pauls-posts/rule-thirds/
5ths and 7ths will also do.
Also a good understanding of room acoustics can be found here https://www.wengercorp.com/downloads/Acoustics_Primer_White_Paper_Wenger.pdf
While they are talking rehearsal spaces the same theory applies.

I have had a fair amount of experience with this suck-out issue when setting up systems for customers.
It never fails to amaze me the number of times I have set up a pair of speakers that sounded just fine in my listening room sound completely different in another room. Equipment differences aside...the room is truly the largest variable.

You dont mention if you have a sub or not, but if absolute phase is inverted between the sub and main speakers such a suck-out will be the result. Any similar frequencies met in opposite phase by the sub and main speakers will attenuate the output of those frequencies.
A suckout in this 100-300 range will take all the warmth out of your system by accentuating the mids.
Absolute system phase/polarity is a very critical aspect many audiophiles overlook. If you preamp inverts phase and you dont reverse your speaker leads, you are fighting a losing battle from the start.
Here is a great app to check absolute phase/polarity to get your system on a firm foundation allowing you to progress from a point of reference. https://www.youtube.com/watch?v=IpYuuQgASVY
 
If rearranging your room is not an option then I recommend powered subs with eq adjust-ability weather its analog or dsp to null out room nodes, the more subs the better.

As bpap mentions SBIR must be addressed also.
Greg

[Elizabeth]

On e thing might be a combination of the speakers and room is the problem. So 'fixing' the room for these speakers.. Maybe you can borrow other speakers and see what they do?
It may be a whole different thing than just the room?

I had a problem with a bit of a lean sounding midrange, and found a different IC which solved MY problem with the sound, totally.
Not that an IC is your solution, just look at more than the one perspective of the problem.

[Russell Dawkins]

I am guessing a swarm-type system may be the proper fix, as mresseguie suggested, except two subs probably would not be enough.

[glynnw]

Perhaps DSP, like the DSpeaker unit and lots of horsepower on the sub drivers.

[poseidonsvoice]

Lots of experts on this thread. For the region from 100-300 Hz, this area is nearly universally dominated by SBIR and a small amount by the modal region. I wholeheartedly agree with bpape 

Your 1 inch treatments are not only too thin (I recommend 4 inches or more) but you should ask for your money back as it is a misapplication for your setup with regards to 2 ch audio!

Multiple subs will help a little in the 100-300 Hz area but not as much as:

1. Proper placement of speakers and listening position.
2. Proper thickness of absorbers and location of absorbers.
3. An understanding of SBIR, see here: http://arqen.com/acoustics-101/speaker-placement-boundary-interference/

For the area below 100Hz, the recommendation is multiple subs, room treatments/absorbers and finally a little EQ.

Acoustical problems require acoustical solutions.

But the above all depends on what YOU are willing to do about it as Armaegis has already asked.

Best,
Anand.

[GT Audio Works]

A lot of opinions to digest.... best advice before buying anything  is get an iphone app https://itunes.apple.com/us/app/audiotools/id325307477?mt=8  or some such inexpensive tool and do your own experimentation to see what works in your room with your system.
Document each change and proceed form each observed result.

[gtaphile]

The speakers are positioned according to the rule of thirds. Phase and polarity were checked and rechecked as well playlists were selected based on listening sessions with similar speakers in a large listening room that is 10 out of 10 as far as set-up and absorption/diffusion is concerned.         
I am trying to make progress without subs for now.
 

I find the rule of 3rds works well in placing speakers. http://www.psaudio.com/pauls-posts/rule-thirds/
5ths and 7ths will also do.
Also a good understanding of room acoustics can be found here https://www.wengercorp.com/downloads/Acoustics_Primer_White_Paper_Wenger.pdf
While they are talking rehearsal spaces the same theory applies.

I have had a fair amount of experience with this suck-out issue when setting up systems for customers.
It never fails to amaze me the number of times I have set up a pair of speakers that sounded just fine in my listening room sound completely different in another room. Equipment differences aside...the room is truly the largest variable.

You dont mention if you have a sub or not, but if absolute phase is inverted between the sub and main speakers such a suck-out will be the result. Any similar frequencies met in opposite phase by the sub and main speakers will attenuate the output of those frequencies.
A suckout in this 100-300 range will take all the warmth out of your system by accentuating the mids.
Absolute system phase/polarity is a very critical aspect many audiophiles overlook. If you preamp inverts phase and you dont reverse your speaker leads, you are fighting a losing battle from the start.
Here is a great app to check absolute phase/polarity to get your system on a firm foundation allowing you to progress from a point of reference. https://www.youtube.com/watch?v=IpYuuQgASVY
 
If rearranging your room is not an option then I recommend powered subs with eq adjust-ability weather its analog or dsp to null out room nodes, the more subs the better.

As bpap mentions SBIR must be addressed also.
Greg

[gtaphile]

The speakers, electronics and cables are not significant contributors to the problem. This is the second speaker set and both sets have the same issue. One is a full range floor stander and the other is a full range stand mount. Updating my balanced cables smoothed out the upper mids and treble response quite a bit actually and still yielded the suckout.       

On e thing might be a combination of the speakers and room is the problem. So 'fixing' the room for these speakers.. Maybe you can borrow other speakers and see what they do?
It may be a whole different thing than just the room?

I had a problem with a bit of a lean sounding midrange, and found a different IC which solved MY problem with the sound, totally.
Not that an IC is your solution, just look at more than the one perspective of the problem.

[artur9]

You could try plugging your numbers into http://tripp.com.au/sbir.htm and seeing if it is SBIR.

I had a droop between about 150-200Hz that lined up perfectly with SBIR calculations.

[Letitroll98]

The speakers are positioned according to the rule of thirds.

The rule of thirds places your speakers in a null zone that decreases bass humps, not so good for suckouts.  Try moving the speakers about 6" wider or narrower.

[JLM]

The speakers are positioned according to the rule of thirds. Phase and polarity were checked and rechecked as well playlists were selected based on listening sessions with similar speakers in a large listening room that is 10 out of 10 as far as set-up and absorption/diffusion is concerned.         
I am trying to make progress without subs for now.

Have you tried repositioning the speakers and/or listening position?  Wondering how you know the above referenced set-up and treatment was "10 out of 10" in another room when you can't solve the apparent SBIR issues in your own room.  You mentioned above trying a setup along the wide side of the room and that moving forward (versus normal position) helped.  What was "forward" and what was "normal"?  Again, diagrams/images would help.

Agree about not jumping into subs.  Subs are over-applied by some and over-avoided by others.  A true subwoofer works at frequencies below typical speakers (say under 50 Hz).  The frequencies you stated having problems are low to middle C (120 - 240 Hz, lower midrange).  So subs aren't the answer.


I see three possible solutions: move the speakers (recommended), replace the existing treatments with more effective ones (something similar to GIK 244 panels), or a mid-bass module like these -

http://www.hsuresearch.com/products/mbm-12mk2.html

http://www.diysoundgroup.com/midbass-module/mbm-12.html

[Hipper]

You mentioned leaning forward and getting a fuller sound. Can you move your chair forward so your ears are positioned where you heard that fuller sound?

Your colleague measured your room response. You can do this yourself using free software called Room EQ Wizard (REW). It's tough to learn but will pay dividends. With this you can move speakers and chair around and measure each position. If you record each position using a diagram of your room you can home in on the position which has the best balance.

Normally The Thirds gives a good response but if that doesn't work in your room there is perhaps something unusual about it.

In order to use room treatment to control bass energy in the room you need larger panels. The GIK Soffit Bass Traps I have are 2' square by 4' long (they also make the triangular shaped Tri-Traps which are less intrusive but less effective too). I have them in the four corners but also some on the wall-ceiling corners. It may be surprising but these can have an effect on nulls as will as peaks.

[rollo]

 Hire Brian and get the room treated properly.   Best move I and my customers did was to hire an acoustic engineer and change the room, speaker placement and the like. With a 10K preamp why are you fooling around ? Eh! Eh!

charles