# First Post, First Measurements, Challenges Lie Ahead - Please Help



## DLB (Nov 4, 2008)

Experts,

I have dedicated home theater / listening room 19'2"x15'3x92". I have JAMO DPEX7.1 speakers and Denon 4806CI Receiver with Audyssey MultEQXT. The speakers and receiver are THX UltraII certified. I'm using HTPC with Realtek ALC883 HD Audio Chipset and RadioShack 33-2050 SPL meter as a MIC via Line-in.

Here is a graph showing my sub and main and combined frequency response measures.








1) I spent a lot of time fiddling with mixer settings to finally get some decent measures. Thoughts, suggestions?

2) How reliable is an integrated Audio Chipset?

3) How reliable is the RadioShack SPL meter - with calibration file from HTS?

4) I did not use a closed loop calibration with other sound channel, do people typically see more reliale results using this method? If so what are the typical problems to look for when not using it?

Here is a picture of my home theatre.









5) My room is purely rectangular except for the small wall around the stage that houses my equipment rack on the right side of the screen and all of my panels and media hidden behind the left side. Also the stage and a stadium seating riser may have some impact. In using a room mode calculator, does this wall or risers negate a standard model using the complete rectangular room dimensions?

6) Right now, all my speakers except the sub are wall mounted. I am thinking about moving the front 3 speakers forward near the edge of the stage. I think this might help with music listening and should reduce first reflections from the stage wall that may be limiting my imaging. Thoughts? 

7) I'm also thinking about adding a second matching subwoofer as is required to fully achieve THX UltraII with my setup. Although since my room is much smaller than the standard THX UltraII room size, I'm not sure I really need it. Thoughts?

8) I have not added any sound treatments to the room yet. I have a fair amount of slap echo in the room, which I am hoping is the cause for the erratic measures at mid and high frequencies. It seems elementary to add sound absortion pannels to absorb first reflections. I'm thinking about making either 1" or 2" thick fiberglass panels wrapped in acoustic fabric mounted to walls and ceiling for this. I'm not far enough along to make any decision regarding low frequency sound treatments yet. Thoughts?

9) My budget is limited and while I love this hobby and am willing to invest some time into the audio calibration end as I have in the video calibration end, I am budget concious and don't want to waste money making any big mistakes with either sound treatetments to the room or further electronics investments for enhanced test and equalization equipment, or hiring any hack to make mistakes on my behalf with my money. Thoughts on hiring an expert? Thoughts on where to spend my money for best results?

10) Room EQ Wizard is awesome!!! I hope to rely on this tool similar to how I relied on ColorHCFR for video calibration.

Thanks,
Dave


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## tonyvdb (Sep 5, 2007)

First of all, Welcome to the Shack Dave.

I cant answer all your questions but here are the ones I can.


> 6) Right now, all my speakers except the sub are wall mounted. I am thinking about moving the front 3 speakers forward near the edge of the stage. I think this might help with music listening and should reduce first reflections from the stage wall that may be limiting my imaging. Thoughts?


Given the screen and speakers are recessed a fair bit by bringing them out to the sides even over and on the front walls and up a bit higher for the left and right speakers you would improve the imaging a fair amount. Give it a try first before you mount them.


> 7) I'm also thinking about adding a second matching subwoofer as is required to fully achieve THX UltraII with my setup. Although since my room is much smaller than the standard THX UltraII room size, I'm not sure I really need it. Thoughts?


Jamo subs are not known for great output so even just replacing it with something better would work. What kind of money were you looking at spending on a sub?
Try moving the sub into the spot where you sit and then crawl around the outside of the room with your SPL meter and play some test tones. WHen you find the best sounding spot that is where you should place the sub.


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## brucek (Apr 11, 2006)

> I spent a lot of time fiddling with mixer settings to finally get some decent measures. Thoughts, suggestions?


Your sub level is too low in relation to the mains...

Move your sub around to help with the dip at ~40Hz.



> How reliable is an integrated Audio Chipset?


I don't know what reliable means. Even the cheapest soundcard will offer accurate results once you have executed the soundcrad calibration routine and saved the file in REW. Once saved, take a measurement of a looped back cable and it should return a perfectly flat line response. You can't get more accurate than that.



> How reliable is the RadioShack SPL meter - with calibration file from HTS?


Certainly accurate enough for home use up to ~3KHz.



> I did not use a closed loop calibration with other sound channel, do people typically see more reliale results using this method? If so what are the typical problems to look for when not using it?


I recommend not using the 'Use Left Channel as calibration reference'. Stick to using the right channel with the soundcard calibration file you created. It's less noisy, and easier to setup, and equally accurate (if not better) than the other method.

brucek


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## thewire (Jun 28, 2007)

DLB said:


> 1) I spent a lot of time fiddling with mixer settings to finally get some decent measures. Thoughts, suggestions?


We know what your speakers measure so you have a good start. 



> 2) How reliable is an integrated Audio Chipset?


My own personal experience with them is limited to mostly Realtek. They may have hardware conflicts etc like any hardware. They might share some irq resources with a specific PCI slot, which also may increase this possibility. If your computer is properly setup, should be no problem.



> 3) How reliable is the RadioShack SPL meter - with calibration file from HTS?


You may get some mixed opinions there. Some may say low as 10Hz, others 15Hz. It could be as high as 3K or then maybe 2K. The meter states to be within +-2dB. The mic file was created with HTS approved methods by comparing directly mics (calibrated ones) to find the appropriate accuracy and is acceptable for the home environment. If for example you are spending hundreds of thousands on the studio, this would not be suitable.



> 4) I did not use a closed loop calibration with other sound channel, do people typically see more reliale results using this method? If so what are the typical problems to look for when not using it?


 You should be able to use a headphone jack male to male and do a loopback. Check that any monitoring of windows sounds is disabled prior to doing this, or it might hurt the chipset. Without doing this there may be some info in the measurement not accounted for. A typical problem might be noise in the signal. One simple way to tell is if your measurements are not consistant while you are not changing any of the variables.



> Here is a picture of my home theatre.


 Looks nice. :T



> 5) My room is purely rectangular except for the small wall around the stage that houses my equipment rack on the right side of the screen and all of my panels and media hidden behind the left side. Also the stage and a stadium seating riser may have some impact. In using a room mode calculator, does this wall or risers negate a standard model using the complete rectangular room dimensions?


A subwoofer does not see imaginary boundries...however. An area still has room modes if it has surfaces and these are difficult to predict. Room mode calculators are based on the six surfaces in the room, and also do not account for furniture, damping, and other variables. They are primarily used as a tool to estimate sort of like having a map of the sound inside the room.



> 6) Right now, all my speakers except the sub are wall mounted. I am thinking about moving the front 3 speakers forward near the edge of the stage. I think this might help with music listening and should reduce first reflections from the stage wall that may be limiting my imaging. Thoughts?


This might improve things some yes, espicially for your particular speaker with very good off axis response. Typically it is best to sit at least around 8.5 feet from the speaker, but this is just something else to consider. If moving the seating is an option, this is usually better than moving the speaker, since this should appear to be anchored to the screen. If sitting to close maybe move back some. The speakers themselves look very close together. Moving them appart some so that the left and right seem to come from the edges of the screen may improve things also.



> 7) I'm also thinking about adding a second matching subwoofer as is required to fully achieve THX UltraII with my setup. Although since my room is much smaller than the standard THX UltraII room size, I'm not sure I really need it. Thoughts?


All THX certified products work in every room. The difference is that a THX select2 for example will not be required to go as loud as a Ultra2. An Ultra2 will be capable of achieving the same exact result as having a less amount. The difference is how loud you would prefer it to be at.



> 8) I have not added any sound treatments to the room yet. I have a fair amount of slap echo in the room, which I am hoping is the cause for the erratic measures at mid and high frequencies. It seems elementary to add sound absortion pannels to absorb first reflections. I'm thinking about making either 1" or 2" thick fiberglass panels wrapped in acoustic fabric mounted to walls and ceiling for this. I'm not far enough along to make any decision regarding low frequency sound treatments yet. Thoughts?


It is important to both listen to the room and measurement. How you do so would be mostly based on your time to do so, and ability to listen. In my opinion it is to early to start the setup of speakers and measurements of the room until we are sure the soundcard is good. Hopefully others will chime in.



> 9) My budget is limited and while I love this hobby and am willing to invest some time into the audio calibration end as I have in the video calibration end, I am budget concious and don't want to waste money making any big mistakes with either sound treatetments to the room or further electronics investments for enhanced test and equalization equipment, or hiring any hack to make mistakes on my behalf with my money. Thoughts on hiring an expert? Thoughts on where to spend my money for best results?


If you enjoy the many hours of setup, learning, and dedication it takes, then by all means do so. I would suggest visiting the acoustics forum here, or search your area for a certified professional. I know I sure wish somebody would search for me in my area.


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## DLB (Nov 4, 2008)

Tony, Bruce, Thewire,

Thanks for your insights! I'm going to try and take some more measurements tonight. 

I think I have concluded from your responses to the posted graph that my sound card and RadioShack SPL meter are working so I'll continue with this setup for now.

11) How does the RS SPL meter compare to the microphone that came with my Denon for the Audyssey MultEQXT setup? Any CAL files out there for the Denon Mics?

12) When I was taking measures, I experimented with 256K, 512K, and 1M samples and from 1 to 8 sweeps. I didn't see much difference except for occasionally at very low frequencies. I'm curious if the experts typically use 256K & 1 sweep for speed when making adjustments and then go to something else like 1M and 4 or 8 sweeps to grab a final graph. Advice?

13) On the levels, there is a solid bar and then a gap with a red line roughly 6-9dB above the bar. The top of the solid bar appears to be the the amplitude reference for the settings. What is the red line?

14) When Calibrating the SPL, using the Sub always yielded lower levels than the mains, so I had to calibrate the SPL so that I use more of the full scale range for subs and then recalibrate the SPL using the mains when taking higher frequency measures so that I don't clip. This is apparant in the graph above. When I started typing this, my question was why is this, but have since had an epiphany. I could just raise my sub level until they calibrate out to the same level! Sleep might help....or not.

I forgot about putting the sub in seating position and taking measurements at points around the room to find the best sub location technique. I think I am going to begin with this tonight, although my placement flexibility is limited because my 700W sub is enormous!

I can definitely boost the sub levels. The THX level setting on the sub is only like 25 or 30% of full scale plus there are several settings in the Denon to boost the sub levels so I can get the volume up, but need to work on the frequency response.

More later. Thank you,
Dave


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## thewire (Jun 28, 2007)

I can answer question #14

In a THX setup the volts at each speaker is a predefined amount. This is what the THX setting is on your powered subwoofer is. It does not mean that changing that value will make the subwoofer not meat THX criteria. A THX component is tested for every detail, except for those such as an auto-setup like Audissey, decoding etc. If it meats criteria that is a THX mode.


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## brucek (Apr 11, 2006)

> How does the RS SPL meter compare to the microphone that came with my Denon for the Audyssey MultEQXT setup? Any CAL files out there for the Denon Mics?


No, any mics that are part of a receiver auto-cal system are usually quite poor and are compensated for internally in the receivers firmware. Don't use them with REW.



> When I was taking measures, I experimented with 256K, 512K, and 1M samples and from 1 to 8 sweeps. I didn't see much difference except for occasionally at very low frequencies. I'm curious if the experts typically use 256K & 1 sweep for speed when making adjustments and then go to something else like 1M and 4 or 8 sweeps to grab a final graph. Advice?


Longer sweeps offer a better signal to noise ratio to the tune of about 3dB for each doubling. You require a faster computer with ample RAM to use the higher sweeps.

Adding more sweeps also improves signal to noise by 3dB per doubling. Spiky noise is especially reduced when adding more sweeps.

I usually use 2 sweeps of 256K.



> On the levels, there is a solid bar and then a gap with a red line roughly 6-9dB above the bar. The top of the solid bar appears to be the the amplitude reference for the settings. What is the red line?


The VU meters show the RMS level as a coloured bar and a numeric value at the bottom of the meter and the peak value as a red line and a numeric value at the top of the meter. Levels are in dB below Full Scale.



> When Calibrating the SPL, using the Sub always yielded lower levels than the mains


They are calibrated with different pink noise that offers a different high and low cutoff. Be sure to calibrate with the correct pink noise signal.



> I can definitely boost the sub levels.


Use your receiver internal test tones to initially set the sub and main levels, and then perhaps touch up after a sub+mains REW sweep.

Hopefully, you have read and are completely familiar with the REW HELP files.

brucek


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## DLB (Nov 4, 2008)

I have officially relocated my sub from where it was in the picture left of the scrren in front of the stage wall to behind the equipment rack on the right side of the screen.

I had a real flat response in either the center of the screen wall or back wall of the room except for a couple really bad nulls right near the crossover frequency so I chose to avoid these locations. 

The position I chose was the best compromise between response flatness and limited peaks and nulls that are really bad.

I struggled a lot tonight with whether to use boundary gain compensation or not. I like to feel the deep base when watching movies so long as it doesn't color the rest of the range very much, so right now am leaning towards not using BGC.

Here is a graph of sub with mains at new sub location.
The Blue line is not using BGC or any equalization at all.
The Gold line is using BGC and MultEQXT Audyssey auto equalization.
The Red line is the same Audyssey equalization as the Gold line, but with BGC turned off.








I think the next step is to experiment with moving the front and center speakers forward into the room in hopes of widening the sound field and improving my imaging, but I don't know how much I can realistically improve this without at least putting up some room treatments to address first reflections.

Thoughts, ideas, suggestions?

Thanks,
Dave


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## DLB (Nov 4, 2008)

I have spent a lot more time reading, experimenting with speaker placements, and began experimenting with room treatments for first reflections. 

I'm realizing that this thread is crossing lines with the Room Acoustics Forum. Not sure if I should ask to move it or not???

Looking at my graph in the post above, I am basically varying +/- 10dB around a 75dB reference level. This is mostly true through the audible frequency range to 15KHz+ except for some sharp null points. This seems like a lot to me knowing that an increase of 6dB doubles the sound. I'm also getting some ringing and combing type issues, which I was hoping to tame by setting some 48x24x2" 703 panels at first reflection points. I was disapoointed to see hardly any improvement however. I'm beginning to think I am going to need a lot of absorbers. Or would diffusers help address the ringing and combing issues also?

I haven't found many before and after examples of treated rooms with measurements, but here is one (I'll post link when I get enough posts). The author built 14 absorbers in total for a 18'x11'x8' room. He said he calibrated SPL for 70dB, but I suspect his pink noise was a main speaker type pinknoise and his sub levels were actually more like 75 or 80dB by looking at his initial graph. And actually, don't trust his calibration at all since all frequencies appear similarly attenuated in the after graph, which is unlikely at low frequencies. If he did do it correctly he is achieving an 8 to 10dB improvement in the peak frequencies, which is substantial. I wish he had measurements through the entire frequency range though. Can someone point to some other examples?

I have read that about the best anyone can expect in a home is about +/- 5dB around the reference. I would have hoped for +/-3 dB or better.

I also keep reading about concerns of making a room too dead. Based on my measurements today, albeit with only 6 panels, It seems like the whole room would have to be covered in 2" or more absorbers to have a chance of this ocurring. Can anyone give an example of a room that was too dead and the environment that caused it?

Thanks,
Dave


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## DLB (Nov 4, 2008)

Did I mention that REW is awesome?:yay:


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## brucek (Apr 11, 2006)

> Not sure if I should ask to move it or not???


You're definitely outside the scope of this forum section.

Probably best you start a new thread in the Acoustics section. 

brucek


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