[zydeco]

Nuance

Ok. I’ve redone the sweeps over the entire 20 to 10,000Hz range with and without the room treat.  The graphs below show a) 1/3 octave smoothed full-range frequency response, b) bass frequency response, c) calculated RT60 and d) waterfall plots (with the "room treatment" overlayed on the "no treatment" plots). Green corresponds to room treatment and blue (aqua) shows responses when there is no room treatment. Your help in interpreting these graphs is much appreciated.

Regards,
Zydeco

[Ethan Winer]

The corner bass traps help to increase or decrease bass output??

Bass traps raise nulls and reduce peaks. So the correct answer is they give a flatter response. However, the main bass problems in most smaller rooms is a lack of bass from nulls. So usually the result after adding traps is having more bass.

--Ethan

[Nuance]

@zydeco

From your explanation of what you hear I would be almost tempted to think that you are talking about lack of envelopment which is a very different problem to solve than bass resonances.

Honestly looking at that frequency response it is pretty flat, especially if your talking about a measurement with no smoothing. Maybe the only thing you could look at would be figuring out what path length differences are causing those nulls from 100-200Hz. They are probably front wall and side wall related.

Your room is quite narrow and small and may be overdamped (i.e. rt60 too low), so you may want to actually pull some of those bookshelves out and use some diffusion like RPG BAD panels.

This is some very good advice.  The issue is obviously the room (duh), and due to the way it interacts with your speakers you may not be able to get that "enveloping ambiance" you once had (a product of moving to a smaller room).  I know that isn't what you want to hear...  Still, if the proper steps are taken you should be able to at least get things acceptable. 

I noticed you are using acoustic foam instead of of 703/704 or rockboard material.  The latter absorbs much better than foam, so that's something to think about.  Also, it is my understanding that you do not want corner traps to be pushed completely into the corner (a couple inches of space should be left).  Apparently it allows the sound to be double adsorbed, in a way. 

Looking at your waterfall plots shows the bass traps certainly reduced ringing and gave a more linear response.  However, I do like your idea of purchasing something for Gik or Real Traps and stacking them from floor to ceiling.  Both these company's also make their bass traps with a material that offers more absorption that foam, plus they cover them with a fabric (or whatever it is).  Win win. 

Your full FR response to 10KHz isn't too bad minus the steep rolloff before 10KHz; that's weird.  The plot you posted of the bass response needs to have the margins set to the standard 105 (top), 45 (bottom).  Use the Graph Limits button on the top left to do this.  Measure from 15-500Hz, then please repost the graph so its more readable. 

So where did you place your first reflection point panels?  Also, did you place a panel or two on the ceiling to reduce the ringing of the floor/ceiling bounce?  It would seem that there are still frequencies that are ringing, and they need to be tamed else they can smear other frequencies. 

Anyway, we'll be able to further assist once you post the new bass response measurement with the proper graph limits. 

[Nyal Mellor]

Hmm....

RT60 seems in the ball park, not too low. Some experimentation might be in order:

1) try removing all the books at the first lateral reflection points. This will increase the amount of energy reflected back to you which will tend to improve spaciousness at the expense of imaging focus
2) try moving the desk or things on the desk so there is not anything within 2/3ft of your head. This should allow more late reflections from the room to get into your ear.
3) try removing / covering some of the panels behind you and in front of the speakers so that they cover less surface area but still cover the reflection points

Do some listening before and after to a selection of your reference tracks and let us know how you get on.

[Duke]

Well this really isn't my area of expertise, but obviously that's not going to stop me. 

If I understand the sequence of events correctly, the large foam bass traps helped the bass but hurt the ambience.  My guess is they are absorbing too much midrange and treble energy.  My understanding is that a little bit of absorptive surface can go a long ways in small rooms because within a given time interval more reflections will strike it, and the shorter wavelengths die there. 

Your in-room response shows a roughly -4 dB dip that's about 1.5 two octaves wide in the upper midrange and lower treble region, and this would tend to make a system less involving because that's where a lot of overtones reside.  This looks to me like a loudspeaker issue, not a room issue.  You mentioned a crossover to a tweeter at about 4 kHz, and sure enough your in-room response fills back in there.  I suspect your midrange driver's power response exhibits a dip in the upper mid/lower treble region, and conversely your tweeter has strong output higher up.  You mentioned harshness, and that's often associated with strong output in the 4 kHz ballpark (which is where the ear is most sensitive).

If those problems do indeed originate with the speakers, you're not going to be able to fix them with room treatment.

You might take a look at the thick felt tweeter surrounds that Jimdgolding makes.  They would absorb some of the tweeter's off-axis energy as it radiates along the surface of the cabinet, which would be a step in the right direction in my opinion.  Also edge diffraction can be a source of harshness, and that's the main issue they address directly. 

http://www.diffractionbegone.com/

[Nuance]

Good theory Duke, but he said he once did have the ambiance and envelopment he now wants (again).  Had he never had it I would agree with you.  I do think you're correct about too much midrange/HF absorption, though.  Some diffusion/more reflection might work out nicely, which is what Nyal recommended (going the natural route). 

Since this isn't too large of a space, I'd place bass traps in the corners (already done) and panels at the first reflection points (side walls and ceiling).  I wouldn't treat anything else yet, even the rear wall, unless listening tests and measurements proved otherwise. 

Finally, you could aways try the 38% rule.  Keep the listening position 38% from the front or rear wall (the front wall is hardly ever plausible for most people, so try the rear wall in this case).  If your chart is accurate in the original post, move the listening position to around 72-73 inches from the wall behind it.  The wall already has a panel, so keep it there if you want to.  This will move the speakers further into the room/away from the back wall.  Re-position the first reflection panels in the proper spot, then give a listen.  Hey, its worth a shot.    Oh, and try moving the speakers a little closer together if necessary, as even a few inches can snap things into focus.

I sincerely hope you get things sounding they way they once did, or even better.  Good luck.

[Duke]

Good theory Duke, but he said he once did have the ambiance and envelopment he now wants (again).  Had he never had it I would agree with you. 

In the second paragraph of my post above, I attribute the loss of ambience to over-absorption of mid and treble energy by his large foam bass traps.   

Apparently I should have been more clear; the way I see it, Zydeco has two problems:  1) over-absorption that is killing the ambience, and 2) lack of energy in the upper mid/lower treble region that can probably be traced to the midrange driver.

I could be wrong on both counts.  Wouldn't be the first time.

[zydeco]

@ Nyal, Nuance & Duke

Just a quick note to give thanks for all the responses. It's going to take me a few days to absorp, tinker with the set-up and draw some conclusions. Back soon.

Regards, Zydeco

[eclein]

Thanks Ethan for that info...time to trap my room!!

[Nyal Mellor]

@Zydeco, NP, let us know how you get on...

[Nuance]

In the second paragraph of my post above, I attribute the loss of ambience to over-absorption of mid and treble energy by his large foam bass traps.   

Apparently I should have been more clear; the way I see it, Zydeco has two problems:  1) over-absorption that is killing the ambience, and 2) lack of energy in the upper mid/lower treble region that can probably be traced to the midrange driver.

I could be wrong on both counts.  Wouldn't be the first time.

No no - I think you're onto something.  In your OP it sounded like you were saying the speakers themselves were the problem, which is what my response was focused on.

zydeco,

Best wishes man.

[zydeco]

So, I’ve been going crazy with more sweeps to confirm speaker / cross-over performance and reconfiguring the the room to reducing HF absorption. It’s a bit too early to report back on the findings but it seems introduction of diffusion has taken things in the right direction. I am, for now, using some curved pieces of thin MDF as make do diffusers and I'm interested in going the next step with a DIY version or borrowed either a 1D (e.g., www.rpg-europe.co.uk/products/qrd734/index.html) or 2D (e.g., www.pmerecords.com/Diffusor.cfm) diffuser. Is it better to use a 1D or 2D on the sidewall of a small room? And what about the back-wall? Edit: An important point is that the listening position will be quite close to the diffuers - roughly 6ft from the both the sidewall and back-wall locations

Regards
Zydeco

[zydeco]

It feels as though I’m doing some hard-yards on speaker / room issues but, ultimately, it’s fun and I’m hopeful that the rewards will be great. The responses have reminded me that there are at least three elements to contend with 1) speaker / cross-over, 2) speaker location and 3) room acoustics. All this represents a large number of moving parts so I decided on a more methodical approach starting with the speakers / cross-over.

Speaker / Cross-over performance
My speakers comprise of 4-drivers: woofers, mid-range, tweeters (in MTM arrangement) and an up-ward firing ambience ribbon. An 3-way active cross-over is used with bass / mid set at 80Hz and mid / high set at 4.5kHz. The tweeter is run full-range with a mechanical roll-off around 18kHz while the ambience ribbon sees high-passed signal above 10kHz. Earlier sweeps show some odd HF behavior and, as pointed out by Duke, perhaps the issues are speaker related. My first efforts have gone into confirming the basic capabilities of the speaker / cross-over system with some in-room, on-axis, measurements with microphone at 50mm and 1.0m from the driver(s). Ideally, I’d have done these outside to minimize room effects but this is quite complex so, for now, I’ve just surrounded the speaker with acoustic foam for these measurements.







First chart below shows measurements at 50mm from each driver. It looks as though drivers are more-or-less level matched, the mid-range extends much higher than seen in earlier but the tweeter starts to roll-off at 12kHz. Second chart shows the measurements at 1.0m (as well as entire speaker) with 1/3 octave smoothing. The extra distance has introduced 7 to 10dB and significant variability. I’ve been concerned about the HF roll-off but am increasingly think this result is an artefact. The R-S meter isn’t, generally, used at these levesl and directionality is an issue. Moreover, a sweep of 15 to 20kHz is definitely lound and pink noise signals measure same over range of 5-10kHz and 10-20kHz. And the speaker sounded fine in the other, larger, room.

So, then, my current thinking is that speaker / cross-over performance is fine (but, being a tragic I’m hoping to repeat measurements with a more accurate set-up). For now though I’m working on this  basis and focusing on the speaker location / room acoustics elements.

Speaker Location / Room Acoustics
The speakers are located in pretty much the only available location – out from the encloves either side of the fireplaces with the drivers about 3ft from the front wall. Moreover, to get a wide soundstage the speakers have been moved as far apart as practical which, in turn, means that the MTM cabinets are each about 1.5ft from the left / right bookcases. My thinking regards low frequencies is that the room is under-damped and that this is made worse by the fact that the listening position is close to the middle of the room. The hypothesis regards the high-frequencies is the room is over-damped and  the proximity of the speakers to the sidewall is an issue as the bookcases aren’t as good at diffusion as hoped.

The first, major, step will be to install some bass traps in the front left / right corners that provide better bass attenuation while avoiding killing the room ambience. This will take some time so, for now, I’ve focused on experimenting with HF issues via attempting to decrease absoprtion / increase diffusion within the room. To increase scatter off the back-wall I’ve removed the acoustic panels, and items off the desk, and used a large piece of thin MDF shaped into a broad curve as a make-shift diffuser. The sidewall book-cases have remained in place but I’ve made an effort to make the books uneven as well as put some irregular timber cuttings at the first reflection points.

The initial impression (after placing chaning the sidewalls) was that the centre image was distorted but the centre image came back into focus when I made sure that the left / right sidewall treatments were the same. It does seem, now, that the music is more enveloping with the backwall treatment seeming to be a major factor. So, it’s too early to draw conclusions but it looks as if we’re going in right direction. My next step is to figure out some more effective diffusers that are less of an eyesore than 4 x 8 ft curved MDF. The room layout means that diffusers at the sidewalls and backwall will both be about 6ft from the listening position. Which is more appropriate – 1D or 2D diffusers – for these locations? Or can the effects be had with simple irregular timber cuttings?

Regards,
Zydeco

[Jeffrey Hedback]

Very interesting progress and questions.

Specifically regarding the rear wall, I would "think" in terms of 2D but this could be acheived through using actual 2D diffusors or an array of 1D units that are 2'x2' each...rotated 90 degrees.  A diffusor that performs down to 500Hz is appropriate.

Now the sidewalls...as you've heard already the sidewalls in your space have great impact on your experience.  As you're not fond of absorption I think it is fine to pursue the path you're on to improve envelopment and spaciousness.  The BIG worry is that the wrong device will actually become a secondary point source and go too far.  The whole bookshelf system makes your question very hard to answer.  Nyal earlier referenced the RPG BAD panel which is not a 1D or 2D diffusor that works in the time domain.  It is instead (in simple terms) a strategic combination of hard and soft.  This type of diffusor is much better suited for this location.  However, the BAD panel itself can have an acoustical glare in this type application where the reflection is close and off-axis.  If you have pieces of foam available to experiment, place them behind your books and timbers and create spaces between the objects.  The goal is to have between 30% and 50%  "soft" exposed and the remainder hard surfaces.  A pic of the room in current condition may be helpful to get more specific.

[zydeco]

Thanks, Jeffery, for the response (and to all the others who’ve contributed along this journey). Here is a photograph looking down the length of the room (with my cheap camera). You can see the acoustic foam behind and between the speakers – effectively forming a “dead-end”. I’ve removed, for the purposes of the photograph, the curved MDF sheets that I set-up as make-shift diffusers.



Left speaker is close to the bookcase which has closed cabinets on the bottom and open shelves on the top – and upwards to the ceiling and lengthways to the listening position. Meanwhile, the right speaker is near an open cabinet filled with books (the green is some wrought iron metalwork) which is the same length as the bookcase but only 4ft high. I’m hopeful that the set-up could be made to work with subtle variations on these two bookcases (i.e., moving books in/out, adding some hard surfaces) as this is the most visually appealing solution. That said, if needed, then stand-mount panels aren’t out of the question if these can be moved. Your advice on the right type of panels would be great.

Zydeco

Edit: Just found that the RPG BAD panels can, in fact, be purchased here in Australia. You mention that this design is well suited to the sidewalls but that these particular panels might have glare issues. Is this still the view after seeing the set-up? If so, then what alternatives are there for the side-walls? Also, does the same design work for the back-wall or is a more traditional 1D or 2D QRD better in that location?

[Jeffrey Hedback]

Hello zydeco,

Wow...this is a tough challenge as the MTM design combined with the left and right immediate reflection conditions are really messing things up in the time domain.

About the BAD panel, on the positive...it really cleans up the lower mids and this would immediately be helpful in your case.  However, you're so close that this glare issue (meaning mid energy that would be diffused if the distance was greater will reflect off the perf board in the panel) is something I'd worry about.  The BAD ARC panel improves this concern...but you're sooo close I'm not sure that will remedy.

I think I remember you did not like just a good performing absorber.  If that is the case, then the BAD ARC panel (2'x4'x4") is the "best" option.  You can slightly move the arc in relation to your speakers and get control.  It's possible that a phase grating device like the Auralex SpaceCoupler can do better, but it's a more complicated system.  The good thing about the BAD ARC is they're great on the rear wall.

I realize this answer may only bring up more questions...but your space is tough.  Hope this helps.

[zydeco]

Jeffery

Your post has made me wonder if this crusade is worthwhile – I mean when others with lots of experience say that it’s a tough job then it’s a tough job. I guess that one answer might be to put absorption on the sidewalls / bookcases and diffusionon the back-wall but the idea of pursuing aggressive room treat isn’t that appealing given the time / cost and low WAF if the chance of success is small due the intrinsic issues. So, whilst I’ve not given up, I’m wondering if I’d be better off either replacing the speakers with a design that better suits the room or moving to headphones (which could work in this one user set-up. You mentioned the MTM issue but doesn't this design limit horizontal dispersion? Any ideas on an appropriate speaker design that is better suited to the constraints? How would open baffle or wave-guide or studio monitor work? Or am I looking for headphones?

Cheers,
Zydeco

[Jeffrey Hedback]

Zydeco,

I don't think it's time to walk the ledge of the building.  How does is sound?  I remember that once you adjusted some items on the shelving, the imaging squared away.  But, beyond that...how does it sound?

MTM- has offers nicely behaved horizontal dispersion (when set vertically) yes...but your drivers are all within very short distances of objects and the conditions are different from L side to R.  So this will cause coloration.

As for other speakers, let's see others thoughts.  There are options...planar speakers would negate this sidewall issue tremendously...others designs have the ambience oriented tweeters that could work as well.  However, even a great waveguide designed like AetherAudio would suffer the same time skewed coloration.

If your system sounds close, I do think there are options still acoustically.  No need to go to headphones.

[Nuance]

Some reflections are good, even side-wall first reflections points (depending on the room and quality of the speakers, of course).  But only you can decide what "good" is, and if it sounds pleasant to your ears. 

I'll admit, that room looks very small, but possibly doable...I dunno.  What are the dimensions of the room ( L W H)?  In my opinion you certainly need more diffusion.  Have you removed the foam from behind the speakers and compared?  With panels placed behind my speakers the sound got worse (objective and subjective).  Since your room is tiny perhaps more reflection will add ambiance.  Give it a try, then compare by listening and measuring.

[Nyal Mellor]

Hey Zydeco

Glad to hear things are moving in the right direction with regard to the imaging and envelopment and that some of my suggestions seem to have been useful!

With regard to the sidewalls I think the best you can aim for is acoustical balance - as in try and get the left and right sidewalls as similar as possible from a reflective/absorptive/diffusive viewpoint.

I still think some BAD panels would be effective, and as Jeffrey pointed out it might be worth going with the curved panels (BAD arc) for the sidewall due to the high angle of incidence. I see now from the photo which I didn't appreciate before that your bookshelves do not extend all the way to the floor and in fact the area around the acoustical center of the speakers (between the midrange and tweeter) is mostly reflective. In this case it would be definitely worthwhile mounting the RPG panels to stands so that they cover an area 1ft below and 2ft above the acoustical center of the speakers.

On the back wall I might be tempted to leave a curved piece of MDF or plywood in place if it is working out for you rather than introducing any more absorption into the room.

You also mentioned that there are still some bass issues? Can you explain further what you are hearing?