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Room null and poor bass response Studio Monitors
Old 29th December 2010
  #1
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Room null and poor bass response

Hi there, i have a couple of problems with my room, the first one is the lack of bass on it that i am almost sure s due my monitors (A7). But there is also a dip at 700hz that annoys me! I have been doing different tests, including moving monitors (screens) and adding a carpet (which evened up the high frequency response of the room, although those graphs are not attached), but the 700hz dip is still there.. mostly on the left speaker. (the right one has a another one at 500).

The room has been treated has mounted speakers and basstraps in the corners and panels on all the surfaces...
I am attaching a bunch of files (plans.. the only missing info is: height 86", and the ceiling panel, which is the odd shaped panel from the pics).

I put some time on testing the left side of the desk, since i though there was some bouncing there, but the only thing that made it change a bit, was removing the left screen (but 1-2 db only), i put acoustic panels on the desk to check and the results where the same, among other things i also blocked the back of the mic with a panel to protect from reflections from the back?, i switched speakers, nothing changed the dip...

Any help will be very appreciated, I took a few hours learning the sketchup program, taking pics, measuring etc so that you guys can have a better idea of what I have, thats how annoyed i am about the dip... how important is that? well, my mixes dont travel well so i am trying to have the least problems with the room so i can compensate as little as possible (i am buying a sub for the low end next year)...

Hope you guys can help!!
Cheers
Attached Thumbnails
Room null and poor bass response-left-no-eq.jpg   Room null and poor bass response-left-no-eq-1-3.jpg   Room null and poor bass response-right-no-eq.jpg   Room null and poor bass response-right-no-eq-1-3.jpg   Room null and poor bass response-studio-measurements.jpg  

Room null and poor bass response-studio-measurements-2.jpg   Room null and poor bass response-studio-measurements3.jpg   Room null and poor bass response-1227101711-00.jpg   Room null and poor bass response-1227101924-00.jpg   Room null and poor bass response-1227101922-00.jpg  

Old 29th December 2010
  #2
SAC
Registered User
 

Just a couple of comments.

For issues below ~300 hz, you will want to generate waterfall plots for the listening position as well as for the room modal response.

The frequency response is not the proper tool to use to diagnose and resolve comb filtering issues due to specular reflections.

For this you use the ETC response derived from the impulse response measurement for each speaker.

You are going to have significant reflections from the work surface.

Also, remove the frames from around the speakers! Soffit mounting requires the wall serve as a contiguous extension of the speaker baffle with NO irregularities that will serve as diffractive sources (as well as proper mechanical decoupling from the wall surface!). A sheet rubber surround can be used to bridge the gap between the speaker and the adjoining wall - but with no surface irregularities in the transition. You might want to refer to the Genelec 'tutorial' section of their website.

Also, what are the crossover characteristics of the speakers???? Do the speakers have an active signal aligned crossover, or a passive crossover?

You may also need to run ETC tests on the loudspeakers themselves as well.

Also, an easy rule of thumb is to remember F=1/T ; T=1/F. Thus, T= 1/700Hz = .00143 s This could correspond to a very early reflection/diffractive issue, a crossover acoustical origin offset or any number of issues.
Old 29th December 2010
  #3
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jhbrandt's Avatar
Six,

Yes to all of the above... One thing that may be a problem - the room looks tiny and the flush mounts look 'fluffy'. To properly flush mount speakers the plane surface must be rigid and massive as possible. If not, you will be suffering from SBIR which will add to the LBIR and then you're really Screwed..

How are the speakers mounted? Also your listening position looks to be too close & as SAC already pointed out, you will get reflections off that desk. Can you re-build the desk & possibly drop the LCDs down lower? Tilt the desk backward so that any reflections are directed below the operator's ears.

What are the room dimensions? LWH?

Cheers,
John
Old 29th December 2010
  #4
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Thanks a lot for the prompt responses.
The mount were made for BM6A's and thus, they are a bit bigger than the A7 that i have. What i did was to build a U that holds the speaker and its attached to the bottom part of the mount (that is connected to the wall).
The listening position is 38% the lenght of the room (the best position i could find, as you might think, the tird angle of the triangle gives me nasty nulls due to symmetry).
Also the crossover frequency for the Adams is 2200hz.
I am taking some pics/making a graph of the speaker mount... also checking the genelecs tutorial as mentioned.
I guess then, if need to, will have to switch the monitors for the BM6A to flush them properly if the rest doesnt work.
As for the desk, i am building one based on the bristol models..(pic attached).
I think that might help, right?

Will keep testing, hope all works fine before the end of the year!!
Thanks a lot again.
Old 29th December 2010
  #5
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The desk.
Attached Thumbnails
Room null and poor bass response-desk.jpg  
Old 29th December 2010
  #6
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jhbrandt's Avatar
Six,

Nice desk... good idea.

Are the flush mounts solid? as in several layers of gypsum board or plywood? Or are they mounted in bass traps?

- John
Old 29th December 2010
  #7
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The Beatsmith's Avatar
 

Hey six, what are the Bristol models? I really would like the design of that desk. I am after the same thing but perhaps without the low monitor - i'd rather have the monitor on a stand behind the desk and leave room for a control surface(s).

Many thanks!

Eddie
Old 29th December 2010
  #8
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Hi Guys.
John the measurements are in the plans (height is 86")

SAC: I am going to re-do the measurements.
I can do what Fuzz measure allows me to do. My mic is the ECM with the general calib file (from EQRW) my interface is Ensemble (apogee)
I will upload the waterfall graphs to check, ..
Excuse my ignorance but whats a ETC measurement?

I guess i underestimated the importance of properly mounted speakers.. as you can see in the pictures, there is a gap (hence the frames to cover it). That might affect also my response. The speakers are also mounted on the bass traps, which are 4 inches thick, but there is a sturdy frame (although hollow) that really secures it... so they are not solid (4 inches wall) but is sturdy (doesn't move)

Anyways, i am gonna keep reading about mounted speakers.. and try to upload more graphs.

Thanks again for your time!

p.s. Beatsmith, send me a pm.
Attached Thumbnails
Room null and poor bass response-1229101133-00.jpg   Room null and poor bass response-1229101136-00.jpg  
Old 29th December 2010
  #9
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Hey
I found some ETC info

Envelope Time Curve - ETC - Impulse

will work on that.
Thanks
Old 29th December 2010
  #10
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HI
HERE ARE MY ETC'S
what do they mean, not sure quite yet, but reading...
Attached Thumbnails
Room null and poor bass response-etc-right.jpg   Room null and poor bass response-etc-left.jpg  
Old 29th December 2010
  #11
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johndykstra's Avatar
 

rewindow to 200msec.
Old 29th December 2010
  #12
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My waterfalls
Attached Thumbnails
Room null and poor bass response-waterfall-left.jpg   Room null and poor bass response-waterfall-right.jpg  
Old 29th December 2010
  #13
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johndykstra's Avatar
 

waterfall:

rewindow max freq @ 400hz.

rewindow duration out until the "foothills" of the low freqs reach zero
Old 29th December 2010
  #14
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RE-Window graphs

hope it helps
Attached Thumbnails
Room null and poor bass response-etc-right-200ms-100-db-.jpg   Room null and poor bass response-etc-left-200ms-120-db-.jpg  
Old 29th December 2010
  #15
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Waterfalls 400hz and 1000 ms
Attached Thumbnails
Room null and poor bass response-wfl-400-1s.jpg   Room null and poor bass response-wfr-400-1s.jpg  
Old 29th December 2010
  #16
SAC
Registered User
 

Sorry, I just rediscovered this thread!

Below you will see the range where you want to re-window the response.

200 ms is nice, but i doubt we are dealing with any reflections traveling 226 feet!

You will want to rewindow the response so that the time display is ~40-45 ms after the direct arrival time, and your gain display extends ~30 dB below the direct arrival level.

Also, from the CSD, this appears to be FM. Great! If hardware loopback is used (automatic device correction), then it is my understanding that the time displayed will be actual time of flight.Thisaditional step is important if the time measurements are to be meaningful!

Second, about the frame around the speakers.
It needs to be removed and the surrounding area made flush with the baffle.This feature is fundamental to flush mounting!

Maybe if you hear this from a 'respected source' it will carry a bit more weight - so refer to the Genelec site that addresses this issue directly.

Please don't let such a small but critical feature undo all of your hard work!


"Is flush-mounting monitors a good idea?

ALL monitors that are traditional 'square box type' designs benefit from flush-mounting for the following reasons:
  • Edge diffraction is eliminated so the midrange is smoother
  • Eliminates the cancellation reflection from the wall behind the monitor
  • Acoustical loading is increased so the monitor does not have to work so hard at low frequencies
The following should be considered when flush-mounting any monitor:
  • For the benefits listed above the wall construction should be solid and consisting of heavy mass material. However this can lead to reverberation time problems at low frequencies
  • If the wall is totally solid and reflective then some lower midrange boost may occur, so make the wall slightly absorptive around the 200 to 500 Hz region - use 10 to 20 cm thick rock wool or foam plastic glued onto the front wall surface
  • Amplifier cooling, possibly forced air-cooling, should be sufficient if the amplifier is not separately rack mounted (rack-mount kits are available for the 1032A, (S30D - discontinued), 1037C and 1038B)
  • The monitor's acoustical tone controls must support the change in acoustical loading presented by the hard wall where the monitors are flush mounted and which implements then an ‘infinite baffle’ load. If these adjustments are not done, then a flat frequency response may not be achieved.
  • The flush mounting details around the enclosure should be as smooth as possible; otherwise the cabinet edge diffraction benefits will be wasted."
Attached Thumbnails
Room null and poor bass response-etc.png  
Old 29th December 2010
  #17
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Thanks SAC
I was reading you post about ETC... very interesting.
but will re-size the measurement windows made asap.
Yes i used FM and corrected the device.. the only thing i am not sure is if i have Protools running too (for the EQ), will that change much? i mean, there is a delay, but we are talking about relative time right? first arrival-reflections?

Thanks a lot for taking the time!
Old 29th December 2010
  #18
SAC
Registered User
 

Yes, running other DSP functions will affect the time.

They either need to be 'removed' or their cointributory latency adjusted.

The time we are 'after' is the actual time of travel of the signal from test speaker to mic.
Old 29th December 2010
  #19
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Ok, here are my ETC rescaled
Attached Thumbnails
Room null and poor bass response-etc-left-rewindow.jpg   Room null and poor bass response-etc-right-rewindow.jpg  
Old 29th December 2010
  #20
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Ok, i am measuring them again..
Old 29th December 2010
  #21
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Ok SAC.
Here are my new graphs... sorry about the other ones...
On these ones, i almost emptied the room, and the carpet is inside too...
I still hae the 700hz and the 120hz... i assume that the higher freq ones are due my desk.
thanks
Attached Thumbnails
Room null and poor bass response-etc-left-new.jpg   Room null and poor bass response-etc-right-new.jpg   Room null and poor bass response-freq-left-new.jpg   Room null and poor bass response-freq-right-new.jpg  
Old 30th December 2010
  #22
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jhbrandt's Avatar
Six,

You will most likely need to move the speakers. The grill and space between the trap and speaker most likely do not make a bit of difference since these are not properly flush mounted.

In spite of the trap, you have SBIR issues that should be resolved before any more testing is done. I believe that you will find by simply moving the speakers forward a bit will drastically change the readings. You may want to pull them out on stands.

Cheers,
John
Old 30th December 2010
  #23
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Hi John.
I did 2 things:
I covered and "pressure" mounted one of the speakers, i used styrofoam to close all the gaps. Then measured again. (Freq and ETC).
On the other speaker i moved the speaker inwards, then outwards, then in the center (levelled with the wall), measured the 3 things. The main difference was the 450 hz mull when i pull the speaker (desk?), other than that are they considerable differences?
It might also be that in the case of the left speaker, what i did with the styrofoam wasnt proper?
Attached Thumbnails
Room null and poor bass response-stuffed-blue-vs-non-stuffed-yellow-etc.jpg   Room null and poor bass response-stuffed-blue-vs-non-stuffed-yellow-.jpg   Room null and poor bass response-control-blue-out-red-green-etc.jpg   Room null and poor bass response-control-blue-out-red-green-freq.jpg   Room null and poor bass response-mount.jpg  

Old 30th December 2010
  #24
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jhbrandt's Avatar
Six,

I think that is probably what is causing most of the problems.

I recommend that you buy a couple pieces of 3/4" plywood and make a baffle for the front of those traps. It should fit the front of the speakers with enough room to put neoprene weather stripping around the speakers and press them into the plywood so that they are flush. The plywood should extend from floor to ceiling, double layer and horizontally until the wall angle changes. This will give you a proper plane surface. You will notice an LF boost @ 6db/octave due to the space loading.

The flush mount panels should be rigid and well connected to the frame. The speakers should be isolated on neoprene or foam.

Cheers,
John
Old 30th December 2010
  #25
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6',

you don't have a true soffit mount. stuffing the edges will do little to nothing of benefit. You need a rigid, thick face on those, and a flush even mounting. Near direct contact with the wall and the speaker. The speaker should be stand mounted behind the wall, with no physical contact to it.


Honestly, as much as you hate to hear it, I would start from scratch.

The room is very bottom heavy in the ringing department. THe ETC is showing a very dead space but with a lot of modal ringing.

The front wall trapping scheme is VERY thick, and chewing into your floor space. Proper done soffits, moved closer to the true front wall would leave alot more room at the back for a complete wall thick trap. Not to mention, 22" is a relatively small width for a soffit.

Is your room truely 8" narrower at the front than the back?

There's an order of operations to treating a room. Now that you are becoming comfortable with measurement techniques, I think you'll find the "remodel" to be much easier than your first go round. Not to mention you have a lot of salvageable materials, and the cost can probably be kept rather low.
Old 30th December 2010
  #26
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Hi there, and thanks again for your input.
This room costed 6 grand to treat, and was built from scratch (walls too), not be my, but by an acoustician. It belonged to a studio i used to work and and took over when they moved out and i quit the company. I was here when they built it.
So all the measurements (distance) are from the plans, originally made for the room...

It had Dyn BM6As when built, and worked fine for us to audio post (TV and film)
I recently started doing my music mixes here, and thats when i realized i was mixing bass too LOUD and decided to start with the tests..
Thats the only reason i might be apprehensive on to get my hands dirty and change major structural features of the room, i am planning to change the desk for a more friendly one... but as far a moving the walls, well i had no idea it was that bad.
I guess we got scammed then when we paid for the treatment.

I have a question though, to John:
If i add a plywood sheet to flush the speakers, wouldn't that block the fibreglass of the front panels and make them reflective instead of absorbent?
Ive seen on other studios that they build a wooden box that covers the speaker and the rest of the wall is framed and hollow to leave space for the fibreglass to fill the squares. .wouldn't that also be an option?

Thanks again for the interest
Old 30th December 2010
  #27
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jhbrandt's Avatar
Quote:
Originally Posted by sixfeetunder View Post
...This room costed 6 grand to treat, and was built from scratch (walls too), not be my, but by an acoustician. ....I recently started doing my music mixes here, and thats when i realized i was mixing bass too LOUD and decided to start with the tests..
Thats the only reason i might be apprehensive on to get my hands dirty and change major structural features of the room, i am planning to change the desk for a more friendly one... but as far a moving the walls, well i had no idea it was that bad.
I guess we got scammed then when we paid for the treatment.
Probably not on purpose. There are many engineers claiming that they know how to build studios. That is why people think that acoustics is a 'black art' or has more to do with VooDoo than physics. It's not. It is just that Acoustics is counter-intuitive and you can end up throwing good money after bad to fix the un-fixable...

Your room is fixable. John D had a great suggestion about turning things around, if you don't want to do the flush mounts properly. But you will still need more trapping on the back wall.

Quote:
Originally Posted by sixfeetunder View Post
I have a question though, to John:
If i add a plywood sheet to flush the speakers, wouldn't that block the fibreglass of the front panels and make them reflective instead of absorbent?
Ive seen on other studios that they build a wooden box that covers the speaker and the rest of the wall is framed and hollow to leave space for the fibreglass to fill the squares. .wouldn't that also be an option?
Yeah, I have seen that too. WAAYYY too much. It is wrong, most of the time. Have another look at the genelec site. They actually show the right way to flush mount speakers. NOT in a soffit over a window with a cavity below.. but flush in a wall of concrete (ideal).

If you do the plywood like I suggested earlier, the center sides of the flush panels are open. (It will make it reflective, but that will not affect your trapping and will also make your room more enjoyable to be and work in.) LF will slosh in there and get trapped. This works very well.

Also, if your speakers are self-powered, you will need ventilation. You will need to create a little tunnel from the bottom of the plywood panel (cut an opening near the floor) so that air will convect up and across the cooling plate or fins on the back of the speaker and exit up top near the ceiling in a similar opening as on the floor. Cover the openings with open-weave fabric. Everywhere else behind the plywood will be bass trapping absorbent material.

Cheers,
John
Old 30th December 2010
  #28
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Quote:
Originally Posted by jhbrandt View Post

If you do the plywood like I suggested earlier, the center sides of the flush panels are open. (It will make it reflective, but that will not affect your trapping and will also make your room more enjoyable to be and work in.) LF will slosh in there and get trapped. This works very well.


John
That is interesting.
When you say the center side, you mean the panel parallel to the wall? If so, what should i do if i am planing to put a 5.1 setup? I would have to put a plywood sheet over the front too?

I guess Johns idea will probably have to be the way to go...
I have a quick question though, he wrote this:

"The front wall trapping scheme is VERY thick, and chewing into your floor space. Proper done soffits, moved closer to the true front wall would leave alot more room at the back for a complete wall thick trap. Not to mention, 22" is a relatively small width for a soffit."

Are you suggesting to move the panels closer to the front wall, but then saying that 22" is a small width for a soffit? Wouldn't that make it even narrower?

Having said that, thanks a lot for you suggestions, i think we are getting close to wrapping up this thread, unfortunately for me that means that the money spending will probably have to start soon...
Old 30th December 2010
  #29
SAC
Registered User
 

Please Read the full Genelec article on flush mounting that we provided early on in the thread..

Every installation issue is covered in detail!

The majority of this thread has simply been the result of not referencing the proper method and then, after the proper method is provided, the positing of serendipitous options varying from the proper method.

I'm sorry, but the 'expert' who designed/installed the speakers was wrong.

The speaker MUST be mechanically decoupled from the wall in order to prevent the wall from acting as a secondary transmission source!

And the transition characteristics (as well as an effective method!) between speaker and wall are addressed as well.

The proper answer is to correct the sources of the problems rather than to incompletely attempt to treat resulting symptoms.
Old 30th December 2010
  #30
Gear Guru
Proof

A studio I designed recently had A7's.

I would imagine it not too difficult to make a frame to fill and seal that gap. They look a bit recessed to me also. Bring them out to flush at the back of those angled corners. They are there for a reason.
The ADAMs controls are at the front, as are the ports and the amplifiers, and they do not run hot, so you should be safe there. Furthermore the onboard controls are well capable of dealing with the LF boost, which will likely be much less than expected.

Having said that, I see plenty of leaky and half soffit designs at Johnlsayers.

I suggest that you take your problems one by one, biggest one first. Identify the cause without doubt, fix and move on. Maybe the cause is poor soffit execution or edge diffraction but I am not feeling it. 700Hz?

I don't think it is possible to run FM through PT to use an Eq, but by all means shut down PT when measuring.

Are you near the mic when measuring. A human body can cause anomalies in exactly the territory of your dip. Step away from that microphone. 2M is good.

Don't be shy about turning down the tweeters. Boost the bass also if necessary.



DD
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