Loud/harsh sound in midrange - Solved - AVS Forum
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post #1 of 21 Old 08-09-2013, 07:09 PM - Thread Starter
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Occasionally people report issues with loud, harsh, annoying sound occuring in the midrange, often blamed on horns or waveguides.
I have not really devoted any attention to this, as they seemed to relate to faulty horn/waveguide/cd-designs.
Not until I recently notice that some times dialogue scenes can be annoyingly loud and unpleasant to listen to.

These problems seems to be lower in frequency - below the cf for the wg/horn.

Regardless what is causing it, it will be possible to quantify the problem as something that can be measured and analyzed, and thus, it can also be fixed - for all speaker designs.
I think this can be either a frequency response issue, or time related (ringing/resonance).

My assumptions are based on these experiences:

- Dialogue in some movies can some times be so loud that it gets very unpleasant, occurs somewhere in the 300Hz..1KHz range.
- It is definitely not related to any waveguide or horn, as this speaker does not have any wg/h operating in this frequency range.
- Even playing at -6db can be slightly unpleasant (system is calibrated more on the low side, so this means -6dB or a little lower)
- It is not distortion related - lots of headroom left at this level, and the dialogue is nowhere near 0dB (at least, it should not be..)
- Speaker in-room is reasonably flat
- Room has reasonable acoustic properties
- Speaker has reasonable headroom (I have a tendency to end up listening to music at +6dB on these, still sounds even better.)


If this is to be investigated further, the process would be:

1. Measure the freq spectrum of the dialogue scenes that causes the too-loud issue, to determine frequency and level.
2. Analyze speaker in-room-at-lp freq response compared to (1.) to see if the issue is likely to be freq response related
3. If not (2.), then analyze for time related issues
4. If neither, it is simply too loud. (Solution: ear-plugs..)


Would be interesting to hear what others think - regardless if you have experienced this or something similar.
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post #2 of 21 Old 08-11-2013, 09:02 AM - Thread Starter
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This is caused by early reflections, at least that is part of the problem.
Since verification depends on listening, it is not easy to get a reliable, objective answer.

In this particular case, it is the Italian leather sofa that causes reflections close to listeners ears.
When I measure in this room, this reflection is removed, so I do not usually see it.
The reflection causes increased level in the mid around 600-1500Hz, and a narrow spike at 800Hz.
The spike is gone when the top of the sofa is covered with a suitable blanket.
It is also easy to see a comb filter effect from mid up in to the higher freq, most pronounced around 3k->7k.

I believe the reflection causes reduced clarity and imaging, and the unpleasant, loud sound on some dialogue.
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post #3 of 21 Old 08-11-2013, 02:30 PM - Thread Starter
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I can now confirm that the problem was early reflections from the sofa.
I do not know for sure whether it is due to frequency response deviations alone, causing louder level, or time related due to the phase shift and ringing cause by the reflections.

The difference is not subtle.
In this particular case the solution is a blanket over the back-rest of the Italian sofa, folded, so that there is enough absorption down in to mid range.
It can be seen on frequency response and on ETC, but it is not really that obvious unless you look for it.

It is also reasonable to believe that similar early reflections from the speaker itself can cause similar effects.
Diffraction around sharp edges are one example of such effects, though diffraction will usually case reflections of lower level, and thus will not be so damaging.
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post #4 of 21 Old 08-11-2013, 04:38 PM
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Agree. My old setup included a large curved leather sectional...and I could actually hear low level reflections off the leather surface. The "fix" was the same as yours...thick blankets and pillows whenever serious listening was involved. The new theater definitely does not include leather!

Leather isn't the only thing causing some of the reported problems, but it does in some cases.

Paul W

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post #5 of 21 Old 08-11-2013, 07:00 PM - Thread Starter
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Any reflective surface will of course cause similar problems, if located so that you get a strong reflection, but in this case it gets very extreme, because when I rest my head against the rear back of the sofa, the ears are only a couple of inches away from the reflective surface.

I made this room as a normal media-entertainment room, with comfortable seating for as many people as possible in the space available, and good sound for at least 3-4.
It is made to look as any ordinary living room, not an acoustic measurement lab.
The room even has a table in front of the sofas, and that is actually more a part of the acoustics than a problem.

But it never occurred to me that resting the head against the sofa should have such a devastating effect.
For measurements I have used to remove reflections from the sofas.
I really like my leather sofas, so I will fix this with blankets and pillows, the other sofa actually had them in place from the beginning.
Good sound is required, of course, but the interior also should look nice and have good functionality as well.

The problem is likely much less pronounced when more people are watching, because the reflections will be broken and absorbed by people sitting in the otherwise empty spaces.

Interesting that most of the theater-dedicated seating on the market are leather with high back.
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post #6 of 21 Old 08-11-2013, 07:11 PM
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How did you tell that the reflection/diffraction was due to the sofa? I am aware that this can be figured out with measurements, but how do you know what is causing this based solely on the measurement?
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post #7 of 21 Old 08-11-2013, 07:59 PM - Thread Starter
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By measuring with and without removing the reflection, and compare the measurements.
Both frequency response and time impulse (ETC) is used for analysis, and it may be required to use filtered ETC to see it.
It may not be very obvious what is causing a problem by looking at the measurements, but it is usually quite easy to see if there is a difference.

In this case the difference can be seen on the frequency response (narrow peak 800Hz, comb filtering higher up) and on the ETC.
The freq response clearly shows a potential problem, but the ETC only shows more energy inside the first 1ms, and without direct comparison it would not be seen as an error, a speaker with a less dead impulse response would actually mask it totally.

The problem is not that things can not be measured, the difficulty lies in how to interpret the measurements and how they relate to what we actually hear.
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post #8 of 21 Old 08-11-2013, 08:07 PM
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Hmm, I wonder if my couch is causing any problems. I do usually budge forward when listening carefully I wonder if that's cause I can sense bad reflections.
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post #9 of 21 Old 08-12-2013, 12:26 AM
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Quote:
Originally Posted by Okv View Post

The problem is not that things can not be measured, the difficulty lies in how to interpret the measurements and how they relate to what we actually hear.

+1

I know where your coming from, I have some stands near my listening position fixed into the wall for side surrounds and its made of wood and the reflections off it are hurtful to my ears, covering it with some foam greatly helps but it is still there to a degree. When I get a chance I am going to cut it out.

People often don't realize how the furniture and other items in your room might be messing with the sound, particularly whatever is close to your LP.
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post #10 of 21 Old 08-12-2013, 08:22 AM
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You may also find this helpful: http://www.realtraps.com/rfz.htm

Click on the link and scroll to the bottom to couch and chair reflections.


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post #11 of 21 Old 08-12-2013, 10:37 AM - Thread Starter
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Indeed, Ethan Winer had this all covered.

In my particular case it may be more severe because the sofa is angled, so that the reflection point is moved slightly farther away, causing a little larger time difference, but still close enough to be high in level.

Changes in sound due to moving your head are significant, but I believed that was something you could live with, changes in frequency response alone I feel does not destroy the listening experience.

The interior and decoration of a room and must be functional and esthetically pleasing, and minor sound issues must be tolerated.
For very critical listening, it is possible to take necessary actions when that is needed.
However, it seems that those early reflections (close in time to the direct sound) are very destructive, and must be addressed.

It will now be permanently fixed with blankets draped over the sofa backs, and when I have them in place, no one but me and Ethan Winer will know the true reason for them being there - it will look like some interior designer has made a visit and decided blankets are in fashion this year.
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post #12 of 21 Old 08-12-2013, 10:43 AM - Thread Starter
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Quote:
Originally Posted by Decadent_Spectre View Post

...
particularly whatever is close to your LP.

I think that is what is important - closer to the source, or the receiver (listener), means more contribution.
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post #13 of 21 Old 08-12-2013, 01:27 PM
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Any chance you could share the measurements?
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post #14 of 21 Old 08-12-2013, 05:40 PM - Thread Starter
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Not really, but I can extract some relevant charts, which shows this particular reflection, just give me minute..
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post #15 of 21 Old 08-12-2013, 06:08 PM - Thread Starter
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ETC and frequency response chart showing the measured effect of the sofa reflection:





Note the time and dB range on the ETC - reflection is very early, and level is down to what would seem very acceptable.

Frequency response measured will change noticeably when moving the mic around.
However, it can clearly be seen that the reflection causes significant deviation across the whole freq range shown, most noticeable in the range 2k - 8k.

There are other ways to analyse this also, but this is good enough to be very sure that there is a reflection causing measurable changes to the overall response, and that it is possible to reduce it.
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post #16 of 21 Old 08-13-2013, 01:09 AM
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Is the yellow frequency response plot near field? Also are you measuring for one speaker or both left and right when showing the comb filtering? How much smoothing?
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post #17 of 21 Old 08-13-2013, 07:54 AM
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I suspect yellow curve would be of the measurements with the reflection tamed by blanket
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post #18 of 21 Old 08-13-2013, 10:25 AM - Thread Starter
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All measurements are at lp1 - the main center listening position.
Both channels L+R.
Smoothing (I think) is 1/12 oct.

Yellow: Blanket absorption in place on top of sofa.
Purple: No absorption on sofa.

When measuring with both channels the mic must be exactly centered so that the distance to each speaker is the same within a few mm (less than 1/10 inch), or else the response at higher frequencies will be wrong due to phase error in the summation of the two channels.
I almost got it right here.
It is easier and more predictable to measure only one channel at a time.
What is most important is to NOT move the mic between measurements, if the mic is moved at all, the measurements can not be used to compare before-after to verify changes.
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post #19 of 21 Old 08-13-2013, 12:19 PM
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Great thread, I can definitely tell even with my microfiber couch in place that I have some reflections near the headrest. I will certainly try some additional absorbtion and see if I get some similar results.

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post #20 of 21 Old 08-13-2013, 12:33 PM
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Very interesting. When I get the opportunity to measure, I am def going to try this.
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post #21 of 21 Old 08-13-2013, 12:49 PM - Thread Starter
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Went shopping today, and got new blankets and pillows for the sofas - only me and Ethan Winer will know the real reason why they are there:

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