[hardax]

Trying to learn as much as I can about how to properly use a calibration disc (AVIA in my case) with a SPL meter.


After getting my speakers balanced as best I can, I performed a frequency sweep (? - where the disc plays a tone that starts out high and goes lower and lower?) and measured it with my SPL.


The neddle went to about +4 and stayed pretty much in the same position all the way down to the lowest tones.


I am ASSUMING that this is good? Is this what everyone call a "flat response"?


There's so many terms and proceedures to learn here but I am enjoying the process!


Thanks

 

[johnm_10]

Yup, pretty flat. If you have the RS SPL meter, then you might want to add 2-3 db to the sub woofer test to compensate for the meter's c-weighting.

 

[jhan1000]

Quote:

Originally Posted by hardax Trying to learn as much as I can about how to properly use a calibration disc (AVIA in my case) with a SPL meter. After getting my speakers balanced as best I can, I performed a frequency sweep (? - where the disc plays a tone that starts out high and goes lower and lower?) and measured it with my SPL. The neddle went to about +4 and stayed pretty much in the same position all the way down to the lowest tones. I am ASSUMING that this is good? Is this what everyone call a "flat response"? There's so many terms and proceedures to learn here but I am enjoying the process! Thanks

I wasn't aware that Avia had the ability to measure frequency responses.

 

[johnm_10]

He just ran a frequency sweep and watched his spl meter.

 

[craig john]

Quote:

Originally Posted by hardax The neddle went to about +4 and stayed pretty much in the same position all the way down to the lowest tones. I am ASSUMING that this is good? Is this what everyone call a "flat response"?

You assume correctly. This is *very* good, (and very flat), response.


How does it sound?


Craig

 

[Jesse S]

Don't forget that the RS meter is 7db too low at 20hz and 3-4 from 25-40hz, so if the meter was steady at +4 the whole time then you're actually seeing a decline in output in the bottom end. Anywho, not an accurate way to measure FR, use sine wavs and a spreadsheet instead.

 

[jhan1000]

Quote:

Originally Posted by johnm_10 He just ran a frequency sweep and watched his spl meter.

Okay, I just got home from work, and whipped out my Avia disc.... I do have couple of concerns to whether or not this is accurate enough.


1) As you go lower in the frequency range, correction factors need to be added. So wouldn't his response curve show increased gain at the lower frequencies?

2) I just did the same test as the OP did, and the frequencies decrease relatively quickly. I wonder if the RS SPL meter can provide accurate measurements, even if the the meter was set to fast.


As Jesse stated. the OP might better off making a CD of Sinewaves and plotting the frequency response curve himself, taking to account the correction factors.

 

[cyberbri]

Quote:

Originally Posted by Jesse S Don't forget that the RS meter is 7db too low at 20hz and 3-4 from 25-40hz, so if the meter was steady at +4 the whole time then you're actually seeing a decline in output in the bottom end. Anywho, not an accurate way to measure FR, use sine wavs and a spreadsheet instead.

You have to add 7db, etc. to the reading, meaning there is more volume than the meter shows. Hence calibrating to 82db for 85db, etc.


So if the meter is staying steady, the SPL is going UP, not down, as the frequency gets lower.

 

[wje]

Compensation chart for the RS meter: http://www.svsound.com/questions-faqs-rscomp.cfm

 

[Redskin]

Quote:

Originally Posted by cyberbri You have to add 7db, etc. to the reading, meaning there is more volume than the meter shows. Hence calibrating to 82db for 85db, etc. So if the meter is staying steady, the SPL is going UP, not down, as the frequency gets lower.

True, and in some peoples opinions, not a bad thing. We have more difficulty hearing lower frequencies than higher ones, so if your bottom end is stronger than your higher end, you may even prefer that. Do a search on "House Curve" to find out more information.

 

[braidkid]

Quote:

Originally Posted by jhan1000 As Jesse stated. the OP might better off making a CD of Sinewaves and plotting the frequency response curve himself, taking to account the correction factors.

Correct. Using AVIA for this purpose is trivial and not accurate.

 

[Redskin]

Quote:

Originally Posted by braidkid Correct. Using AVIA for this purpose is trivial and not accurate.

It depends what you are trying to achieve. If when using the sweep from Avia your needle stays within 4dB, you are doing pretty well. Is it 100% accurate...NO...but it gets you in the ballpark. I have my sub eq'd flat. When I run this same test without the eq, the needle is all over the place. With the sub eq'd, it reacts the same way hardax's does. I think it really depends what hardax is going to do with the information once he gets it. If he is simply trying to see if he found a good spot for his sub, and it sounds good to him...I say good enough. If his intent is to really tweak, and get into sub eq and room treatments, then more research needs to be done.

 

[jhan1000]

Quote:

Originally Posted by ******* It depends what you are trying to achieve. If when using the sweep from Avia your needle stays within 4dB, you are doing pretty well. Is it 100% accurate...NO...but it gets you in the ballpark. I have my sub eq'd flat. When I run this same test without the eq, the needle is all over the place. With the sub eq'd, it reacts the same way hardax's does. I think it really depends what hardax is going to do with the information once he gets it. If he is simply trying to see if he found a good spot for his sub, and it sounds good to him...I say good enough. If his intent is to really tweak, and get into sub eq and room treatments, then more research needs to be done.

Using this method, if a subwoofer was flat, shouldn't the the RS SPL meter decrease during this sweep because of the absence of any correction?


I do agree that most people are happy with the ballpark measurements. If he's happy with how the subwoofer sounds, then he might as well leave well enough alone.

 

[hardax]

Thanks for all the comments everyone. Glad to hear that I am "in the ball park".


******* hits the nail on the head as far as my desire or even ability to get things tweaked are concerned.


My theater is modest compared to most and I really just want to get my system sounding good to my ears with minimal "stressing" over the small details. Maybe in my next house (which will have a dedicated theater) I will be more detail oriented.


One thing I do notice (or don't notice actually) is that I really don't get that "hit you in the chest" bass I was expecting with my set up. I have an HSU STF-3.


With the flat response I think I have I assume I have picked the correct spot for my sub but at my listening position (were the readings were taken) the bass is definately there but just not as strong as I was expecting?

 

[cyberbri]

Quote:

Originally Posted by hardax Thanks for all the comments everyone. Glad to hear that I am "in the ball park". ******* hits the nail on the head as far as my desire or even ability to get things tweaked are concerned. My theater is modest compared to most and I really just want to get my system sounding good to my ears with minimal "stressing" over the small details. Maybe in my next house (which will have a dedicated theater) I will be more detail oriented. One thing I do notice (or don't notice actually) is that I really don't get that "hit you in the chest" bass I was expecting with my set up. I have an HSU STF-3. With the flat response I think I have I assume I have picked the correct spot for my sub but at my listening position (were the readings were taken) the bass is definately there but just not as strong as I was expecting?

How loud are you listening to movies (ie., how much under "reference 85db")? Bass really starts to kick in, literally, the most at higher listening levels. You might try turning up the gain on your sub a little, run it a little hot, and see how that sounds.

 

[jhan1000]

Quote:

Originally Posted by hardax Thanks for all the comments everyone. Glad to hear that I am "in the ball park". ******* hits the nail on the head as far as my desire or even ability to get things tweaked are concerned. My theater is modest compared to most and I really just want to get my system sounding good to my ears with minimal "stressing" over the small details. Maybe in my next house (which will have a dedicated theater) I will be more detail oriented. One thing I do notice (or don't notice actually) is that I really don't get that "hit you in the chest" bass I was expecting with my set up. I have an HSU STF-3. With the flat response I think I have I assume I have picked the correct spot for my sub but at my listening position (were the readings were taken) the bass is definately there but just not as strong as I was expecting?

\\


I guess it depends on the room size as well. A STF-3 in a large room may not give you that "hit you in the chest" sensation.

 

[johnm_10]

hardax, if you want to get a little more fancy with it w/o buying expensive equipment, your next step might be plug your spl meter into your soundcard and download this software: http://homepage.ntlworld.com/john.mulcahy/roomeq/


It will graph your responses very quickly and it compensates for the weighting of the meter. This is a huge advantage in trying to find the best placement for your sub.


Happy holidays!