RS Meter subwoofer graph - Page 2 - AVS Forum
Forum Jump: 
Reply
 
Thread Tools
post #31 of 47 Old 09-12-2008, 09:26 AM
AVS Special Member
 
Ethan Winer's Avatar
 
Join Date: Apr 2003
Location: New Milford, CT, USA
Posts: 5,748
Mentioned: 1 Post(s)
Tagged: 0 Thread(s)
Quoted: 7 Post(s)
Liked: 133
Quote:
Originally Posted by Steve Audio View Post

The problem is that 1/3 octave represents about the smallest region humans can reliably detect.

Not at all! Put some music through a parametric EQ, then boost 1 KHz by 10 dB with a Q of 10. Can you hear it?

Likewise with bass peaks and nulls. If you have a narrow null at 55 Hz where you sit while listening, music in the key of A will be very affected. Now, it's true that nulls often exist over small physical areas, so a deep null in one ear may not be as deep in your other ear. But the bottom line is that nulls can be very damaging, even if they are narrow. Especially when the nulls align with frequencies present in the music.

Indeed, the most common problem in home recording studios is that mixes sound fine in their bedroom studio, but sound very bassy in larger rooms or in the car. This is almost always caused by one or more deep nulls somewhere between 70 and 150 Hz, making the music sound too thin in the small room. So the mix is made with too much bass to compensate.

The microphone graph shown earlier in this thread was measured in a relatively large room with a lot of bass trapping. This graph is much more typical of a small untreated room, and the deep nulls in the middle of the graph show the problem well.



Quote:


The frequency response of the RS spl meter is specified as +/- 2db at 114 spl.

Yes, but note that no frequency range is specified!

Look at JP's measurement of the meter's electronics in THIS post and you'll see the HF fall-off is very similar to what I measured in my microphone comparison.

--Ethan

RealTraps - The acoustic treatment experts

To view links or images in signatures your post count must be 0 or greater. You currently have 0 posts.

Ethan Winer is offline  
Sponsored Links
Advertisement
 
post #32 of 47 Old 09-13-2008, 01:30 AM
AVS Special Member
 
J_Palmer_Cass's Avatar
 
Join Date: May 2005
Posts: 6,421
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 244 Post(s)
Liked: 96
Quote:
Originally Posted by Steve Audio View Post


Back to the topic at hand.

2) The frequency response of the RS spl meter is specified as +/- 2db at 114 spl. At less spl levels this is verified closely by the three links (correction tables/grapshs) I presented in a previous post. We also already know those correction tables are correct at the lower frequencies. However, they are also correct at the higher frequencies. (The electronics has already been measured as accurate to the A and C scales.)

The resonant frequency and/or drop off of a typical speaker does not change vs amplitude. Same with a kettle drum or triangle by the strength of the strike. The same with the RS meter.

Therefore, how could the RS meter change a whopping 10-12db average at 13khz, and 22-24db off average at 20khz from absolute accuracy frequency response? Has anyone else reported such gross inaccuracies as I have not heard of anyone?

Take care and hope this helps.

Steve



The microphone used in the RS SPL meters rolls off early in the high frequency audio range. So, you have the A and C scale weighting that must be added to the microphone "error" as compared with a flat measurement microphone.

Any brand SPL meter works just fine for use as an SPL meter. Expecting any brand SPL meter to measure "flat" from 20 to 20 kHz even with the use of compensation tables is kind of crazy when you think about it.

If you need accuracy, do not use an SPL meter as a measurement microphone. Use a measurement microphone. Most people properly use the RS SPL meter to calibrate the SPL levels of their speakers (broadband C scale). The use of an inverse C scale for compensation is reasonable for subwoofer work.
J_Palmer_Cass is offline  
post #33 of 47 Old 09-13-2008, 03:03 AM
Member
 
Steve Audio's Avatar
 
Join Date: Apr 2008
Location: Illinois
Posts: 77
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Liked: 10
Quote:
Originally Posted by J_Palmer_Cass View Post

The microphone used in the RS SPL meters rolls off early in the high frequency audio range. So, you have the A and C scale weighting that must be added to the microphone "error" as compared with a flat measurement microphone.

Any brand SPL meter works just fine for use as an SPL meter. Expecting any brand SPL meter to measure "flat" from 20 to 20 kHz even with the use of compensation tables is kind of crazy when you think about it.

If you need accuracy, do not use an SPL meter as a measurement microphone. Use a measurement microphone. Most people properly use the RS SPL meter to calibrate the SPL levels of their speakers (broadband C scale). The use of an inverse C scale for compensation is reasonable for subwoofer work.

I did some checking and there appears to be some lingering problems. All the graphs shown below are 1/3 octave response.

First, notice the graph comparing the multiple mics Ethan provided. Notice the earthworks mic and RS mic (direct aim) are quite different in the mid to upper registers.



Above, the Earthworks mic drops approx 4-5db on average (84db reference). The RS mic drops approx 24db on average, 84db reference. So a difference of approx 19-20db between the two mics.

Now notice the two graphs below. They were both tested in the same room (about 16 by 11-1/2 by 8 feet high), although a different room than the upper graph. The same equipment was used. From Ethan's page.

http://www.ethanwiner.com/believe.html

First the Earthworks mic. Reference 92db reference.



Now the RS mic graph. Reference is approx 89db reference.



Notice the earthworks mic drops from an average reference of approx 92db to 83db at 20khz. A 9 db drop. The RS meter drops from a reference of approx 89db to 78db, approx 11db drop.

So the two meters are fairly close in high frequency response in the 2 graph comparison (within approx 2db), yet 19-20db apart in the first graph comparing multiple mics.

Comb filtering is obviously not the cause over such a wide bandwidth towards the upper registers.

I think you can appreciate the problem I see.

Since no one else has ever mentioned any high frequency problems with the RS meter, and since all the links covering calibration pretty much concur, I have to conclude the RS meter is accurate at high frequencies.

Thunderstorm, so I must sign off.

Cheers,
Steve
Steve Audio is offline  
post #34 of 47 Old 09-13-2008, 09:08 AM
AVS Special Member
 
Ethan Winer's Avatar
 
Join Date: Apr 2003
Location: New Milford, CT, USA
Posts: 5,748
Mentioned: 1 Post(s)
Tagged: 0 Thread(s)
Quoted: 7 Post(s)
Liked: 133
Quote:
Originally Posted by Steve Audio View Post

Now notice the two graphs below. They were both tested in the same room (about 16 by 11-1/2 by 8 feet high), although a different room than the upper graph.

No, the two lower graphs were measured in my large (33 by 18 feet) home studio. The microphone comparison data was also measured in my home studio, but at a totally different place as shown in the article.

Quote:


Since no one else has ever mentioned any high frequency problems with the RS meter

JP's response curve for the RS meter's electronics clearly shows the roll-off, as do all of the measurements I've ever made using the RS meter. Why "others" don't report this is irrelevant. Steve, if you have an RS meter and a reasonably flat loudspeaker, why don't you just run a few sweeps yourself and post the results here. Put the meter fairly close to one speaker (only) to reduce room and comb filter effects.

--Ethan

RealTraps - The acoustic treatment experts

To view links or images in signatures your post count must be 0 or greater. You currently have 0 posts.

Ethan Winer is offline  
post #35 of 47 Old 09-13-2008, 09:17 AM
tkc
Member
 
tkc's Avatar
 
Join Date: Sep 2004
Posts: 163
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Liked: 10
Quote:
Originally Posted by Steve Audio View Post

Since no one else has ever mentioned any high frequency problems with the RS meter, and since all the links covering calibration pretty much concur, I have to conclude the RS meter is accurate at high frequencies.

Here is a link to another article showing measurements of various RS meters against a calibrated mike.

http://www.audioxpress.com/magsdirx/...a/koya2811.pdf
tkc is offline  
post #36 of 47 Old 09-13-2008, 05:36 PM
Member
 
Steve Audio's Avatar
 
Join Date: Apr 2008
Location: Illinois
Posts: 77
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Liked: 10
Quote:
Originally Posted by Ethan Winer View Post

No, the two lower graphs were measured in my large (33 by 18 feet) home studio. The microphone comparison data was also measured in my home studio, but at a totally different place as shown in the article.

The middle graph is from the same page that you posted your 20-200hz graph, http://www.ethanwiner.com/believe.html

The only mention of room's dimensions on this page is
Quote:
This room is typical of the size you'll find in many homes - about 16 by 11-1/2 by 8 feet high. The loudspeakers used were Mackie HR824 bi-amplified active monitors and a Carver Sunfire subwoofer. The frequency response measurements were made using the ETF software with a precision Earthworks microphone..



The last graph is also from this same 16 by 11-1/2 by 8 foot high room according to your post at this link,

http://forum.stereophile.com/forum/s...page=2&fpart=4

Quote:
This next graph shows the very same measurement data expressed as 1/3 and 1/12 octaves:



referring to your 20-200hz graph posted above. Since your above graph is from the same webpage, and uses the 16 foot room, the last graph is also from this room since you used the exact same data used in the 20-200hz graph.

So according to your webpage and quotes from you, both lower graphs were done in the 16 x 11.5 x 8 foot room, not the 33 x 18 foot room. Might want to check your information again.

[/quote]JP's response curve for the RS meter's electronics clearly shows the roll-off, as do all of the measurements I've ever made using the RS meter. Why "others" don't report this is irrelevant.

--Ethan [/quote]

I think there are three areas I need to address.

1) Measuring the electronics is not measuring the entire RS spl mic. Your graphs already demonstrates that the RS spl meter is within approx 2db of the Earthworks mic at 20khz. So one cannot say that the mic is off by 20db if it has already been demonstrated to be within 2db.

2) JP only shows the electronics to be correct to C weighting, measuring 10db down at 20khz as it should. Notice the correction tables closely correspond to JPs findings, indicating the mic is accurate to at least 20khz. If the mic were off, the correction tables would have to correct for this error as well as the electronics error.

3) If one wants to get the correct tweeter setting and lower registers, it is relevant and already covered by the other graphs/correction tables. Correcting the RS meter at the low frequencies is also contained in the correction tables (approx 7db at 20hz etc.) and is supported by your own graphs.

With such a wide variance in your different RS meter graphs (approx 19-20db variance at 20khz), and the fact that your latest multipl mic measurements of the RS meter is so far removed from other reliable sources.

To get a better perpective of how different 2db vs 20db discrepancies are between the RS meter and the Earthworks mic (as per the different tests between the two mics); a 2db drop corresponds to the RS meter reading 80% of the same signal level as that of the Earthworks mic, while a 20db drop (Ethan's latestmulti mic test) corresponds to the RS meter reading only 10% of the same signal level as that of the Earthworks mic. Obviously, there is a huge discrepancy problem between the tests as the RS meter itself could not have changed that much.

TKC, Ethan has already demonstrated the RS spl meters to be within approx 2db of the Earthworks mic. Another quesion is how did the author arrive at some of his conclusions, (such as +/-10db) with the limited number of RS meters at his disposal? I hope this helps.

Cheers,
Steve
Steve Audio is offline  
post #37 of 47 Old 09-14-2008, 08:31 AM
AVS Special Member
 
Ethan Winer's Avatar
 
Join Date: Apr 2003
Location: New Milford, CT, USA
Posts: 5,748
Mentioned: 1 Post(s)
Tagged: 0 Thread(s)
Quoted: 7 Post(s)
Liked: 133
Quote:
Originally Posted by Steve Audio View Post

The middle graph is from the same page that you posted your 20-200hz graph, http://www.ethanwiner.com/believe.html

Yes, and apparently you missed this from that page:

"Figure 3 below shows the response I measured at seven locations one inch apart. These measurements were made in my rather large, well-treated home recording studio,

not the same room as the graphs in Figures 1 and 2 above."
Quote:


Your graphs already demonstrates that the RS spl meter is within approx 2db of the Earthworks mic at 20khz.

Say what? None of my graphs show the RS meter as being with 2 dB of the Earthworks at 20 KHz!

Quote:


your latest multipl mic measurements of the RS meter is so far removed from other reliable sources.

I'm not sure what you're getting at, but I'm quite certain my most recent test comparing 10 microphones is highly accurate. If my measurements disagree with the home-made tests behind the RS meter correction tables I've seen, I'll trust my results every time.

--Ethan

RealTraps - The acoustic treatment experts

To view links or images in signatures your post count must be 0 or greater. You currently have 0 posts.

Ethan Winer is offline  
post #38 of 47 Old 09-14-2008, 01:02 PM
Member
 
Steve Audio's Avatar
 
Join Date: Apr 2008
Location: Illinois
Posts: 77
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Liked: 10
Quote:
Originally Posted by Ethan Winer View Post

Yes, and apparently you missed this from that page:

"Figure 3 below shows the response I measured at seven locations one inch apart. These measurements were made in my rather large, well-treated home recording studio,

not the same room as the graphs in Figures 1 and 2 above."
Say what? None of my graphs show the RS meter as being with 2 dB of the Earthworks at 20 KHz!



I'm not sure what you're getting at, but I'm quite certain my most recent test comparing 10 microphones is highly accurate. If my measurements disagree with the home-made tests behind the RS meter correction tables I've seen, I'll trust my results every time.

--Ethan

My apologies about the room size for figure 3. However, room size is unimportant when measuring the average overall response from mid frequencies to high frequencies as narrow band comb filtering peaks and nulls and room nodes do not affect the overall average from, say 250hz peak to 20khz (98.7% of the audio band), as we shall see below. Notice the average peaks and valleys that occur between the two mics in these two graphs, the bottom two graphs I presented in my previous posts.

Earthworks mic, 92db reference.




RS meter, 89db midrange reference.



The response differences between the mic/meter is still only approximately 2db different at 20khz while yet the newer multi-mic graphs (red line and green line in below graph) shows a radically approx 20-22db difference between the RS and Earthworks at 20khz. It is visually quite obvious. By the way, is either room furnished or bare?



If I may suggest, you might consider repeating your RS mic test again. By the way, nice looking products.

Cheers,
Steve
Steve Audio is offline  
post #39 of 47 Old 09-15-2008, 08:51 AM
AVS Special Member
 
Ethan Winer's Avatar
 
Join Date: Apr 2003
Location: New Milford, CT, USA
Posts: 5,748
Mentioned: 1 Post(s)
Tagged: 0 Thread(s)
Quoted: 7 Post(s)
Liked: 133
Quote:
Originally Posted by Steve Audio View Post

say 250hz peak to 20khz (98.7% of the audio band)

Not to nit-pick, but audio frequency ranges are best expressed logarithmically. The range from 20 Hz to 20 KHz encompasses a little more than 10 octaves. So from 250 Hz to 20 KHz is just over 6 octaves = ~63%.

Quote:


Earthworks mic, 92db reference.

Just to be clear, the microphone I used for that test at the listening position of my 33 by 18 foot home studio is a DPA 4090. I've used two different Earthworks microphones for testing. One was owned by pro acoustician Terry Montlick when we tested EQ versus bass traps HERE in the ~17x11 room. The other was owned by my friend Grekim Jennings when we did the comparison of ten microphones.

Quote:


The response differences between the mic/meter is still only approximately 2db different at 20khz

That's not a valid comparison because the speakers in my home studio are JBL 4430s and the speaker used for the other tests was a Mackie HR824. Also, using third octave averaging hides a lot of detail. In my graph comparing 1/12 and 1/3 octave averaging, look how much louder the RS meter seems to be at 20 KHz when averaged to 1/3 octave. Versus 1/12 octave averaging which is much closer to reality. So between the different speaker types and using averaging, such a comparison is not practical. I also don't recall if the RS meter was pointed up or at the speaker for the 1/3 versus 1/12 octave graph.

Quote:


By the way, is either room furnished or bare?

My home studio has a bunch of "stuff" in it.

Quote:


If I may suggest, you might consider repeating your RS mic test again.

I have more confidence in that roundup comparison than other comparisons I've done in the past. In this case I was very careful to ensure identical microphone placement to 1/8 inch, and there were five people watching to make sure everything was done as intended. This is why I said earlier that if my test conflicts with other tests made by amateurs, I'll trust my own test every time.

--Ethan

RealTraps - The acoustic treatment experts

To view links or images in signatures your post count must be 0 or greater. You currently have 0 posts.

Ethan Winer is offline  
post #40 of 47 Old 09-15-2008, 09:42 AM
AVS Addicted Member
 
JOHNnDENVER's Avatar
 
Join Date: Dec 2005
Posts: 13,377
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 1 Post(s)
Liked: 12
Let be real here... Are you guys really doing any sort of room EQ at those high freqs?

For most people, I try to get a decent sub curve, for a few really picky people I will try to get a good curve into the upper ends of the dialog freqs.

I'm just not how much if any practical impact there is with the type and degree of roll off the somewhat lowly regarded RS meter has is all.
JOHNnDENVER is offline  
post #41 of 47 Old 09-15-2008, 10:52 AM
Member
 
Steve Audio's Avatar
 
Join Date: Apr 2008
Location: Illinois
Posts: 77
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Liked: 10
Quote:
Originally Posted by JOHNnDENVER View Post

Let be real here... Are you guys really doing any sort of room EQ at those high freqs?

For most people, I try to get a decent sub curve, for a few really picky people I will try to get a good curve into the upper ends of the dialog freqs.

I'm just not how much if any practical impact there is with the type and degree of roll off the somewhat lowly regarded RS meter has is all.

Hi John,

High frequency reflections are almost always (never say never) less than 1/3 octave so they are not noticeable. However, once in a while, the FR curves show a peak that is more than 1/3 octave wide. Some tweeters also have a general average rolloff (more than 1/3 octave) at the higher frequencies and are thus noticeable.

The RS meter is "not bad" accurate up there and therefore only the analog RS meter needs to use the correction tables. Check the links I provided above for any correction you deem necessary.

Hope this helps.

Cheers,
Steve
Steve Audio is offline  
post #42 of 47 Old 09-15-2008, 10:58 AM
Member
 
Steve Audio's Avatar
 
Join Date: Apr 2008
Location: Illinois
Posts: 77
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Liked: 10
Quote:
Originally Posted by Ethan Winer View Post

Not to nit-pick, but audio frequency ranges are best expressed logarithmically. The range from 20 Hz to 20 KHz encompasses a little more than 10 octaves. So from 250 Hz to 20 KHz is just over 6 octaves = ~63%.



Just to be clear, the microphone I used for that test at the listening position of my 33 by 18 foot home studio is a DPA 4090. I've used two different Earthworks microphones for testing. One was owned by pro acoustician Terry Montlick when we tested EQ versus bass traps HERE in the ~17x11 room. The other was owned by my friend Grekim Jennings when we did the comparison of ten microphones.



That's not a valid comparison because the speakers in my home studio are JBL 4430s and the speaker used for the other tests was a Mackie HR824. Also, using third octave averaging hides a lot of detail. In my graph comparing 1/12 and 1/3 octave averaging, look how much louder the RS meter seems to be at 20 KHz when averaged to 1/3 octave. Versus 1/12 octave averaging which is much closer to reality. So between the different speaker types and using averaging, such a comparison is not practical. I also don't recall if the RS meter was pointed up or at the speaker for the 1/3 versus 1/12 octave graph.



My home studio has a bunch of "stuff" in it.



I have more confidence in that roundup comparison than other comparisons I've done in the past. In this case I was very careful to ensure identical microphone placement to 1/8 inch, and there were five people watching to make sure everything was done as intended. This is why I said earlier that if my test conflicts with other tests made by amateurs, I'll trust my own test every time.

--Ethan

We are dealing with overall fr response, which is 98%.
Octaves has nothing to do with anything (except read graphs easier) except reduce the percentage. We are dealing with 20,000 - 250.

Neither the mic change, room change, nor speaker change is material to the generalized average response unless they have whopping fr abnormalities.

Let's not confuse the issues.

---------------

Why "others" don't report this is irrelevant."

[quote]Yes it is quite relevant. The forums is a place to share information as one can see by all the activity. If others were have gross problems (20-24db down from accurate at the highs) with their meters, you can bet they would be disseminating that info in strings and posts all over the forums, including magazine articles and the correction tables.

By the way, what is in the other test room you forgot to mention? Any furnishings, draps, rugs etc?

Hope this helps.

Cheers,
Steve
Steve Audio is offline  
post #43 of 47 Old 09-15-2008, 12:07 PM
AVS Special Member
 
Ethan Winer's Avatar
 
Join Date: Apr 2003
Location: New Milford, CT, USA
Posts: 5,748
Mentioned: 1 Post(s)
Tagged: 0 Thread(s)
Quoted: 7 Post(s)
Liked: 133
Quote:
Originally Posted by JOHNnDENVER View Post

Let be real here... Are you guys really doing any sort of room EQ at those high freqs?

Hell no!

I'm not much of an EQ believer at all, though it can be useful in the lowest octave or so to reduce peaks (only) where bass traps are less effective. Anyway, this is about measurement microphones. For some reason Steve seems to think my assessment is not accurate, though I have no idea why.

--Ethan

RealTraps - The acoustic treatment experts

To view links or images in signatures your post count must be 0 or greater. You currently have 0 posts.

Ethan Winer is offline  
post #44 of 47 Old 09-15-2008, 12:11 PM
AVS Special Member
 
Ethan Winer's Avatar
 
Join Date: Apr 2003
Location: New Milford, CT, USA
Posts: 5,748
Mentioned: 1 Post(s)
Tagged: 0 Thread(s)
Quoted: 7 Post(s)
Liked: 133
Quote:
Originally Posted by Steve Audio View Post

Octaves has nothing to do with anything (except read graphs easier) except reduce the percentage.

Again, this is beside the point, but octaves are the only practical way to assess audio frequency ranges. Just as dB is the only practical way to assess volume levels. Not because it makes it easier to read graphs, which is true, but because our ears respond to both frequency ranges and volume levels logarithmically.

Quote:


By the way, what is in the other test room you forgot to mention? Any furnishings, draps, rugs etc?

Which room? Most tests are done in the 17x11.5 foot "lab" room at the RealTraps factory. We measure it empty, then again with the various absorbers under test. This makes the change from "no traps" to "with traps" as large as possible.

--Ethan

RealTraps - The acoustic treatment experts

To view links or images in signatures your post count must be 0 or greater. You currently have 0 posts.

Ethan Winer is offline  
post #45 of 47 Old 09-15-2008, 12:32 PM
AVS Addicted Member
 
JOHNnDENVER's Avatar
 
Join Date: Dec 2005
Posts: 13,377
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 1 Post(s)
Liked: 12
I think your accuracy is more than fine. I don't think using the mic in the RS meter has much if any bearing on real world installation / audio quality. I've been using the RS meters for years now, my rooms sound as good and show curves just as good or better than anybody elses.
JOHNnDENVER is offline  
post #46 of 47 Old 09-15-2008, 09:06 PM
Member
 
Steve Audio's Avatar
 
Join Date: Apr 2008
Location: Illinois
Posts: 77
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Liked: 10
Quote:
Originally Posted by JOHNnDENVER View Post

Let be real here... Are you guys really doing any sort of room EQ at those high freqs?

For most people, I try to get a decent sub curve, for a few really picky people I will try to get a good curve into the upper ends of the dialog freqs.

I'm just not how much if any practical impact there is with the type and degree of roll off the somewhat lowly regarded RS meter has is all.

Hi John,

You bring up a couple of interesting questions of a general nature.

I will answer your last question first. If the tweeter has a peak or valley, or general roll off of 1/3 octave or more, you will notice a sonic difference. If the RS meter drops that much on "top", then one will adjust the tweeter way too high.

To now answer your first sentence, let me expand on how one can enhance specs and graphs etc.

With electronic components one could extend the frequency response of an amp by using a non-linear signal generator to enhance either the lows or highs or both specifications.

I suppose one could also lower the distortion spec by feeding a small signal of opposite polarity from, say the second or third harmonic.

I knew a new company that fabricated nearly all the specs of an amplifier; they had no test equipment except a digital voltmeter.

Generally, with room/speaker measurements, one could place the mic so that the front to back, side to side, and floor to ceiling nodes would be near each other on the graph and at their peaks. This means mic placement is crucial. The room dimensions would also influence these measurements, how close each peak is to the others.

So while one room may have peaks and valley spread apart, just the right room dimensions could produce peaks (and nulls) from each room dimension adjacent to each other.

Other methods include rotating the speakers away from the mic, or placing the mic facing away from the speakers (There is a difference). One could also aim the mic at the tweeters, midrange, or at the woofer to manipulate the response.

Another way is to use an equalizer and set it to boost or reduce adjacent frequencies. See this link.
www.rane.com/ppt/allaboutequalizers.ppt

On click 23 or so (or for that matter there are several pages so read closely) the page will show a peak but flattened on top like a table top. Then notice the middle sagging. In otherwards, there are actually two peaks. One could raise or lower two or more equalizer adjustments, and with the desired Q, one could produce just about any graph one wants with whatever peaks one wants, at whatever frequency one desires.

Another way to influence the measurement/graph is to reverse polarity one of the two speakers. This will cause a near doubling of the amplitude of the peaks and nulls one measures (esp at low frequencies), thus exaggerating the measurement/graph.

Hope this helps John.

Quote:


Not because it makes it easier to read graphs, which is true, but because our ears respond to both frequency ranges and volume levels logarithmically.

With all due respect, we are not talking about listening/hearing, but how two mics correlate from 250hz to 20khz, which is 98% of the frequency range. Are you sure you had the RS mic pointing directly at the front of the cones/speakers as the RS meter is very directional and being off a little will cause a huge HF rolloff.

Hope this helps.

Cheers,
Steve
Steve Audio is offline  
post #47 of 47 Old 09-16-2008, 10:56 AM
AVS Special Member
 
Ethan Winer's Avatar
 
Join Date: Apr 2003
Location: New Milford, CT, USA
Posts: 5,748
Mentioned: 1 Post(s)
Tagged: 0 Thread(s)
Quoted: 7 Post(s)
Liked: 133
Quote:
Originally Posted by Steve Audio View Post

Are you sure you had the RS mic pointing directly at the front of the cones/speakers

Quite sure.

--Ethan

RealTraps - The acoustic treatment experts

To view links or images in signatures your post count must be 0 or greater. You currently have 0 posts.

Ethan Winer is offline  
Reply Subwoofers, Bass, and Transducers

User Tag List

Thread Tools
Show Printable Version Show Printable Version
Email this Page Email this Page


Forum Jump: 

Posting Rules  
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off