A Sound Renovation for the Green Room - Page 6 - Home Theater Forum and Systems - HomeTheaterShack.com
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post #51 of 68 Old 03-15-17, 09:14 AM Thread Starter
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Re: A Sound Renovation for the Green Room

The tweeter's failure mode leaves me with a nagging sensation. Why hadn't I noticed it sooner? Of course, hindsight's always 20-20! It's clearly evident in the SPL graph, but on my behalf the tweeter hasn't totally given up the ghost. It still functions at the lower end of its crossed frequency range! The dip is not as noticeable to these ears as the graph would have me believe. Again to my credit, I think it took a while to detect because of the masking effect presented by the right and center channels. I've never heard of such a failure mode, though. Can a tweeter fail "halfway" so it's only reproducing part of it's normal range, or would that be a crossover problem?
A Sound Renovation for the Green Room-layout-1-fr-lr-only.jpg

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post #52 of 68 Old 03-15-17, 09:53 AM Thread Starter
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Re: A Sound Renovation for the Green Room

Quote:
Savjac wrote: View Post
I am sorry Lou but I cannot do the measurement thingie just yet. Next time we get together you can show me or....maybe I could just read the manual
I dont learn as well by reading something as by doing it...so you have left me done and dusted.
You're not alone. Seeing is easier than doing for me as well. Once I get the hang of it, I won't mind sharing; so no worries, we can take a look at your setup during our next audio get-together!

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post #53 of 68 Old 03-15-17, 11:00 AM
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Re: A Sound Renovation for the Green Room

Quote:
Lumen wrote: View Post
The tweeter's failure mode leaves me with a nagging sensation. Why hadn't I noticed it sooner? Of course, hindsight's always 20-20! It's clearly evident in the SPL graph, but on my behalf the tweeter hasn't totally given up the ghost. It still functions at the lower end of its crossed frequency range! The dip is not as noticeable to these ears as the graph would have me believe. Again to my credit, I think it took a while to detect because of the masking effect presented by the right and center channels. I've never heard of such a failure mode, though. Can a tweeter fail "halfway" so it's only reproducing part of it's normal range, or would that be a crossover problem?
Attachment 138634
Good Morning Lou

I am not sure but it would be my thought that either the tweeter works or it does not. I am not sure I have ever encountered a driver like your tweeter working over a selected frequency and not the rest of its inherent range.

I wonder if maybe there is an actual crossover issue in the one speaker ? Let me rephrase that statement, It would appear that there may be a crossover issue in the one speaker.

Good Listening

Jack

"For those who believe no proof is needed for those who don't believe no proof is possible"
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post #54 of 68 Old 03-17-17, 09:56 AM Thread Starter
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Re: A Sound Renovation for the Green Room

I initially considered drivers to be digital in nature - that is, they either work or they do not. However, further investigation reveals that some engineers believe in partial failure modes which leave the driver damaged, yet operational. An example of a failure mode similar to my own appears in this Speaker Failure Analysis article, where the author states:

"For a host of reasons, glue attachment of the voice coil to the cone or spider may fail. The immediate result of even a partial failure is the voice coil is no longer precisely centred. An off-centre voice coil will scrape against the pole pieces and this soon damages the wire it is wound from, possibly creating shorted turns in the process. This highly audible defect is called "poling" by repairers. Broken or cracked attachments vibrate severely under normal drive forces, so this is also highly audible as buzzing noise or distortion. Repair is sometimes possible but re-coning or replacement is often needed."

While I have heard HF distortion, it's difficult to tell whether it originates from the tweeter, midrange, or source material. But that still doesn't explain the main failure mode of partial output. I did find related posts on the Electrical Engineering Stack Exchange, which support my recent experience:

"...However, one can imagine a scenario where something else in the speaker is damaged, such as the surround (the rubber coil that allows the cone to vibrate freely) or the spider (cloth "guide" inside the speaker, behind the cone) or leads leading into the cone are damaged, but the coil still operates. Any of these issues have the ability to reduce the volume level of the speaker."

and

Another part of the speaker that can fail is the joint between the coil and the cone. If the force on the coil exceeds the strength of that joint, it's possible that it may fail partially or completely. If this happens, motion of the coil will not be properly conveyed to the cone, causing the speaker to sound rather weakly. Additionally, the speaker will likely be more effective at producing sound when driven in the direction that would pull the coil against the one, than when driven in the opposite direction. Thus, the sound will not only be quieter than it should, but distorted as well.

I know there are smarter and more experienced enthusiasts than I who may present evidence and arguments against what I have found so far. But in the end, I still have a partially functioning tweeter, whose failure mode was verified by swapping drivers in the left and right mains - the problem followed the driver! Installing a totally new driver in place of the malfunctioning one solved the problem. This should be confirmed with my next round of measurements.

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post #55 of 68 Old 03-20-17, 10:14 AM Thread Starter
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Re: A Sound Renovation for the Green Room

Success! Both tweeters are now functional:

A Sound Renovation for the Green Room-layout-4-fr-lr-only.jpg

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post #56 of 68 Old 03-21-17, 11:14 AM Thread Starter
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Re: A Sound Renovation for the Green Room

Please feel free to add your comments and/or suggestions! These charts show the improvement realized first by adding 2 bass traps (2T), and then by adding 3 more (5T). As more traps are added, frequency response starts flattening out and resonant modes start decaying more rapidly.

Frequency Response Improvement (Left Channel)
Maybe quotes should go around the word improvement. Adding traps sure doesn't make the FR plot look pretty. You'll need to turn to the waterfall for that. A quick glance at the Sub-Only plot shows that the sub dominates the combined responses (L+R+Sub and Center+Sub).
A Sound Renovation for the Green Room-layout-4-fr-0t2t5t-l-only.jpg

Frequency Response Improvement (Right Channel)
Same here! Maybe quotes should go around the word improvement. Adding traps sure doesn't make the FR plot look pretty. You'll need to turn to the waterfall for that. A quick glance at the Sub-Only plot shows that the sub dominates the combined responses (L+R+Sub and Center+Sub).
A Sound Renovation for the Green Room-layout-4-fr-0t2t5t-r-only.jpg

Frequency Response Improvement (Center Channel)
My novice eye has yet to detect much improvement here as well. The traps' effectiveness down low is extremely limited to nonexistent, as is expected.
A Sound Renovation for the Green Room-layout-4-fr-0t2t5t-c-only.jpg

Frequency Response (Subwoofer Channel)
As expected, there's only slight improvement where FR is leveled from about 75 to 150Hz. Larger and/or more traps would be needed to make a significant dent above 40.
A Sound Renovation for the Green Room-layout-4-fr-0t2t5t-sub-only.jpg

Bass Resonance Improvement (Left+Right+Sub Channel)
LEFT = 0 Traps & 2 Traps / RIGHT = 0 Traps & 5 Traps

These waterfall comparisons are best viewed "live" in REW, but I tried to make them as revealing as possible. The baseline measurement with 0 traps is always the same color, and is shown transparent. Examining the first slice of the 5T plot reveals that FR is smoothed from around 65Hz to 120Hz, and to a lesser extent from around 120Hz to 300Hz. Noticing where the distance increases between succeeding slices tells us if and where ringing has been improved. Ringing has been totally subdued by trapping at around 300/210/180Hz and partially subdued at 205/150/130/95/75Hz. Severe ringing still exists at 45/22/19Hz, which are too low for traps to be effective.
A Sound Renovation for the Green Room-layout-4-wf-0t2t-lr-s12.jpg A Sound Renovation for the Green Room-layout-4-wf-0t5t-lr-s12.jpg

Bass Resonance Improvement (Center+Sub Channel)
LEFT = 0 Traps & 2 Traps / RIGHT = 0 Traps & 5 Traps

I'm unsure if this speaker combo even needs scrutiny. I only included it because it was a recommended measurement in the REW 101 Guide. As before, these waterfall comparisons are best viewed "live" in REW. Examining the first slice of the 5T plot reveals that FR is smoothed from around 70Hz to 170Hz. Noticing where the distance increases between succeeding slices tells us if and where ringing has been improved. Ringing has been totally subdued by trapping at around 200Hz and greatly improved at 150/125/95/75Hz. Severe ringing still exists at 45/22/19Hz, which are too low for traps to be effective.
A Sound Renovation for the Green Room-layout-4-wf-0t2t-c-s12.jpg A Sound Renovation for the Green Room-layout-4-wf-0t5t-c-s12.jpg

Decay Improvement (Left+Right+Sub Phase=0)
LEFT = 0 Traps / RIGHT = 5 Traps

On the left we see that ringing at 45Hz does not decay 20dB within the recommended 160msec target. On the right we see that 5 traps brought the decay under control even though ringing still exists! This is actually proof of the traps effectiveness in action. To quote The ABC's of ASC's Tube Traps: "It’s worth keeping in mind that ASC’s tube traps aren’t bass absorbers per se, they are resonant absorbers. They won’t remove the bass energy from your room, rather they will tame the resonances caused by this energy. Bass peaks will still be strong at the room’s resonant frequency, but the absorption of this resonance will reduce their severity."
A Sound Renovation for the Green Room-layout-4-decay-0t-lr-s12.jpg A Sound Renovation for the Green Room-layout-4-decay-5t-lr-s12p0.jpg

Decay Improvement (Left+Right+Sub Phase=90)
Dialing in the sub's phase control for proper support through the 80Hz xover region shows that decay times are greatly improved and well within target.
A Sound Renovation for the Green Room-layout-4-decay-5t-lr-s12p90.jpg

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Last edited by Lumen; 03-22-17 at 10:44 AM. Reason: Corrected C-Only graph; Added Sub-Only graph; Added graph comments
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post #57 of 68 Old 03-21-17, 11:24 AM Thread Starter
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Re: A Sound Renovation for the Green Room

And here are the plots showing subwoofer phase support through the 80Hz crossover region. Which would you choose?

A Sound Renovation for the Green Room-layout-4-phaseadj-lr-s12.jpg

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post #58 of 68 Old 03-21-17, 01:48 PM Thread Starter
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Re: A Sound Renovation for the Green Room

Results of the room/system calibration and center channel upgrade are impressive so far:
  • line-of-sight to surrounds established for first time
  • semi-nearfield LP eliminates many damaging reflections
  • bass has regained it's punch
  • speech intelligibility has been greatly improved

Yet I'm left with only a lukewarm feeling. The system could be taken up another notch, but I'm not sure how to proceed. Maybe it can't be done with my current gear (is a miniDSP in my future)? I'm hoping to learn enough from my REW threads to find out!

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post #59 of 68 Old 03-22-17, 11:09 AM Thread Starter
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Re: A Sound Renovation for the Green Room

I updated the graphs above with observations. Please feel free to critique or comment!

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post #60 of 68 Old 03-22-17, 02:57 PM Thread Starter
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Re: A Sound Renovation for the Green Room

And just to put your suspicions to rest, no it's not business-as-usual. I plan on taking your advice rather than asking for it, but then doing what I want anyway. The current 5-trap layout with sub next to the LP is a temporary solution until I develop something better. So far, it's my favorite.

Room Layout #1 (original before this renovation):
Well-integrated bass with reasonably flat FR and excellent support through xover region. Fair SS&I. But too many traps required, so fairly lifeless.

A Sound Renovation for the Green Room-layout-1.png


Room Layout #2:
Very poor LF response. No amount of good symmetry/aesthetics makes up for sound this bad!!

A Sound Renovation for the Green Room-layout-3.png


Room Layout #3:
Good LF response with engaging tactile feedback. Very good SS&I. Least aesthetic of options, but who cares!

A Sound Renovation for the Green Room-layout-2.png


Room Layout #4:
Fair LF response with some extreme LF feedback (expected more sitting right next to sub). Very good SS&I. Good symmetry/aesthetics.

A Sound Renovation for the Green Room-layout-4.png

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