Simplified REW Setup and Use (USB Mic & HDMI Connection) Including Measurement Techniques and How To Interpret Graphs - Page 445 - AVS | Home Theater Discussions And Reviews
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post #13321 of 13337 Old 01-23-2015, 12:47 PM
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Originally Posted by tvuong View Post
Here it is. Please let me know what you find. Thanks in advance.

https://www.dropbox.com/s/n7mkd7hde4...0hot.mdat?dl=0
An mdat of the entire frequency range (10-20K) or so?

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post #13322 of 13337 Old 01-23-2015, 01:24 PM
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^^ that was just 7-250hz subs only. Do you want to have the speaker(s) and subs from 10-20k? If so, center and subs, left and subs, right and subs are good? Or you like to have left plus right and subs also? Thanks.
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post #13323 of 13337 Old 01-23-2015, 01:29 PM
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Originally Posted by tvuong View Post
^^ that was just 7-250hz subs only. Do you want to have the speaker(s) and subs from 10-20k? If so, center and subs, left and subs, right and subs are good? Or you like to have left plus right and subs also? Thanks.
Left OR Right with subs.

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post #13324 of 13337 Old 01-23-2015, 01:36 PM
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Originally Posted by 3ll3d00d View Post
^
I didn't mean any particular scale other than "the same as your previous graph", it's just much easier to flip back and forth to compare quickly visually if they two graphs are otherwise identical.

What are you looking for anyway? For someone to say "yep, looks good" or "no, you need to sort it out"? If so, it is what it is really. Only you can really say whether you think there is an audible impact to that amount of distortion in the upper mid bass. In my room & at those levels, I would say no but then the changes (that I think would be) required to deal with it are not feasible for me so my view is almost certainly prejudiced by that fact. I would expect someone like Jim, who has put that effort in (and then some!), to say yes it would be worth it. My point is that it's really all quite subjective at this point, do you have the desire/commitment/space/funds to treat your room?
As always, thanks for the reply. I don't see treating my room in the near future. Any way, I had the whole house to my self earlier today, so I decided to play those bass heavy scenes from the bass demo disc downloaded here at -5MV with subs 2db hot (I believe Aud set my subs trims 2db lower than reference as seen from REW graph), a 6db low shelf centered about 30hz along with 14hz high pass filter (from jriver mc20), all I heard was deep clean and loud bass that shook my chair pretty good. I could not detect any bad sound at all . I am quite happy with this latest Aud run (closed mic with all positions within 3 inches from MLP) and subs pEQ 80hz bump combo.
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post #13325 of 13337 Old 01-23-2015, 01:38 PM
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Originally Posted by jim19611961 View Post
Left OR Right with subs.
Ok, I will post my mdat file with all of those measurements at -15MV later today. Thanks.
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post #13326 of 13337 Old 01-23-2015, 01:55 PM
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Quote:
Originally Posted by tvuong View Post
As always, thanks for the reply. I don't see treating my room in the near future. Any way, I had the whole house to my self earlier today, so I decided to play those bass heavy scenes from the bass demo disc downloaded here at -5MV with subs 2db hot (I believe Aud set my subs trims 2db lower than reference as seen from REW graph), a 6db low shelf centered about 30hz along with 14hz high pass filter (from jriver mc20), all I heard was deep clean and loud bass that shook my chair pretty good. I could not detect any bad sound at all . I am quite happy with this latest Aud run (closed mic with all positions within 3 inches from MLP) and subs pEQ 80hz bump combo.
I am a little confused now also. You say you like the way its sounds now (you said quite happy). You dont want to improve (treat) your room. So what it is you want help with?

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post #13327 of 13337 Old 01-23-2015, 02:08 PM
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@jim19611961 , here is the mdat file. All front three are crossovered at 90Hz. Thanks.

https://www.dropbox.com/s/x7rdhux718...0Jim.mdat?dl=0

Edit: To see if this latest run has less distortion.
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post #13328 of 13337 Old 01-23-2015, 05:25 PM
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Quote:
Originally Posted by tvuong View Post
@jim19611961 , here is the mdat file. All front three are crossovered at 90Hz. Thanks.

https://www.dropbox.com/s/x7rdhux718...0Jim.mdat?dl=0

Edit: To see if this latest run has less distortion.
You have 2-3% in the midrange. I dont know whats up with your system, but while a certain amount of bass distortion may go unnoticed, in the midrange, there is clearly something up.

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post #13329 of 13337 Old 01-23-2015, 07:43 PM
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^^ thanks for taking the time. When you said midrange, you meant from my center, left or right?
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post #13330 of 13337 Old 01-23-2015, 08:07 PM
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Quote:
Originally Posted by tvuong View Post
^^ thanks for taking the time. When you said midrange, you meant from my center, left or right?
You shouldnt have to ask. Just look at the full range distortion measurements. Its pretty easy to see.

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post #13331 of 13337 Old 01-24-2015, 12:31 PM
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tvuong: for whatever reason I can't access your mdat files. But I just thought I'd throw this in, one more great use I've got out of the REW distortion measuring capability.

Anyway, I found that when some (quality) speakers measured elevated THD, and I mean over a small fraction of a %, it turned out that indeed the mid and "mid-bass" drivers were damaged. The higher the test level, the more the distortion increased, and I mean significantly increased, out of proportion. If your scenario seems a bit like this, do what you need to do to make sure it's not the amp channel that's at fault before saying it's the driver.

We also need to consider that speaker THD below 3% is traditionally actually considered "good". I can assure you that in a modern decent speaker, in the mids and highs at least, THD below 0.1% at a reasonable listening SPL (assuming capable amp), the levels we normally measure at, is very common. I'd say 1% is too much outside the bass range, if we're talking an indication of something "wrong", and not necessarily audibility to any specific individual.

Remember I can't see your graphs! Another clue to a damaged driver is look for the THD significantly peaking at a frequency (resonating). This could indicate a loose cone, or a damaged surround, or maybe even a damaged spider. Many modern drivers, and I'm talking even quite expensive ones, use glue to hold many (all!) of the parts together. I have seen this glue come loose in areas, and when fixed (quality adhesives) the distortion completely went away. It was kind of hard to find & figure out, until after I saw it the first time, but something to consider.

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post #13332 of 13337 Old 01-24-2015, 01:36 PM
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^^ Thanks. It could be the damage horn tweeter or mid range driver that shows distortion in graph. These are more than 20yrs old Klipsch speakers. The mid range drivers look to be in very good shape from what I can see. Any way, I am not hearing distortion at 10db higher than my norm level, I guest I am ok. I use this system for movies only. I might upgrade to some Crites' tweeters later.
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post #13333 of 13337 Old 01-24-2015, 02:17 PM
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^ I have never seen a damaged horn driver (even though I've had some for almost 40 years!) so I have no idea what might go wrong with them when they're showing a raised THD. If in fact there's any problem with them at all... One of the strengths of horn drivers is that they're...errr...strong.
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post #13334 of 13337 Old 01-24-2015, 03:14 PM
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Quote:
Originally Posted by jim19611961 View Post
Typically, the higher distortion will be found in nulls. And if your using processing (dsp, audyssey, eq) which is trying to boost nulls, then these places will have even higher distortion still.
No argument. Just want to add some further perspective.

If a speaker is outputting some low distortion at frequencies above and below a null, then it is reasonable to assume that the absolute level of the harmonic distortion products in the room is not actually elevated in the null region. The THD measures higher simply because the fundamental has been suppressed in the null. It's not like the speaker is actually under any additional stress or behaving with more non-linearity in the null region.

Until one tries to flatten a null with EQ. And that's generally not a good idea anyway, nothing to do with distortion, but other aspects of sound quality.

The implication is thus to ignore the distortion readings in the nulls, but pay a lot of attention to nulls when positioning and timing the speakers to try to minimize them where possible.

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post #13335 of 13337 Old Yesterday, 09:52 AM
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Originally Posted by Roger Dressler View Post
No argument. Just want to add some further perspective.

If a speaker is outputting some low distortion at frequencies above and below a null, then it is reasonable to assume that the absolute level of the harmonic distortion products in the room is not actually elevated in the null region. The THD measures higher simply because the fundamental has been suppressed in the null. It's not like the speaker is actually under any additional stress or behaving with more non-linearity in the null region.

Until one tries to flatten a null with EQ. And that's generally not a good idea anyway, nothing to do with distortion, but other aspects of sound quality.

The implication is thus to ignore the distortion readings in the nulls, but pay a lot of attention to nulls when positioning and timing the speakers to try to minimize them where possible.
No argument. Just want to add some further perspective.

Still, where one has a null, even with a flat distortion curve, one will hear more distortion because of the reduced output.

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post #13336 of 13337 Old Yesterday, 12:26 PM
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Originally Posted by jim19611961 View Post
No argument. Just want to add some further perspective.

Still, where one has a null, even with a flat distortion curve, one will hear more distortion because of the reduced output.
To what degree those harmonics are any more audible as the fundamental is suppressed is not easy to say under normal program listening. I wanted to avoid the subjective aspects and just comment on the operational mechanism behind REW's elevated distortion readings in the null regions.

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post #13337 of 13337 Unread Today, 06:08 PM
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Hi guys,
Question about frequency graph. Attached is the frequency graph of my center channel. I don't have sub included and have speakers set to large since I'm only concern as of now how my center channel on its own is performing. Took reading of only Center channel (attached). A few qustions

1 - Looking at the graph without any smoothing, I see some major dips. Can someone please interpret what these dips mean? How severe are they? Is my center channel performing bad?

2 - How do we handle these dips using room treatment? I do have 4" Wool panels (DIY). How do I know where to place them to fix the dip?

thx.
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