# Measuring frequency response.



## HeavyGuy (Apr 24, 2011)

*Analyzing / measuring frequency response.*

Hi everyone.

I'm doing some school related research on loudspeakers. Basically what I need to do is to measure the sound quality of some speaker systems. I'm not expecting the results to be absolutely accurate but it would be nice if I could get some non-chaotic visual graphs. I've got a few lined up speakers, cheap condenser microphone and a PC with decent sound card, I only seek a bit of help from you.

First of all, which software suits me the best? Looks like TrueRTA is popular but seems that it's not free.

Second, should I even measure frequency response and what are my chances of succeeding if I haven't even got a SPL meter? I've read a lot about how to analyze the results and graphs and what kind of measurements there are, but the more I read the more confused I get.

In summary I'm looking for step-by-step instructions (ideally) for doing this. I will really appreciate any advices, links or thoughts from you.


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## faderpusher (Aug 16, 2011)

I have been doing a lot work in environments such as yours, even had some of the best software and hardware at my disposal. The last, and the most important piece of equipment is one that we all have access to, your ears.

The speakers themselves are a rather minor part of what you will have to deal with if you wish to actually accomplish what you are stiving for, a good sounding, intellegible system. If you are looking at good quality, highly efficient ( >102 db 1W 1m preferably >106) professional speakers, your biggest challenge will be the room acoustics. 

This, in my opinion is the most important part of the equation in your situation and is often ignored. Equipment will not solve your acoustic problems. Yes with prudent directional application of arrays or columns that are steerable you can solve many problems, but if you use a common sense approach, IMHO, you will be able to resolve many issues you currently have, possibly with the equipment on hand. 

I cannot tell you how many schools and auditoriums I have gone into where they were ready to scrap the current system because of intellegibility problems and been able to fix them, sometimes in under a few minutes using simply my ears and some common sense. 

If you do not feel comfortable or trust in your own senses, I would suggest getting with a professional. A few hundred in fees could save you thousands in purchases.

Best Regards
Dan


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## HeavyGuy (Apr 24, 2011)

Thanks for the answer. 
I will mainly use my ears but since this is a "scientific work" I just need some non-subjective proof (it doesn't have to be accurate).
My idea was to include room acoustics in the measurements and test all speakers in equal circumstances (same room).


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## faderpusher (Aug 16, 2011)

Sorry I missed the intent of the post. So can you delineate for the group what "scientific work" you are attempting to proof. Is this an educational thing for students? yourself? For what will the results be used for?


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## robbo266317 (Sep 22, 2008)

You can download REW here for free and use it to plot frequency response. This will only be as accurate as your microphone but for a school project should be fine. 
Download the software and have a play. Then ask questions if you need more help.

Cheers,
Bill.


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## HeavyGuy (Apr 24, 2011)

Hmm, I thought REW was intended only for room acoustic measurement, I'll give it a try.
faderpusher, that's just some long term school project, that's the reason I can be somewhat imprecise in my measurements because the main results will be based on my subjective opinion.


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## MikeBiker (Jan 3, 2010)

HeavyGuy said:


> Hi everyone.
> 
> I'm doing some school related research on loudspeakers. Basically what I need to do is to measure the sound quality of some speaker systems. I'm not expecting the results to be absolutely accurate but it would be nice if I could get some non-chaotic visual graphs. I've got a few lined up speakers, cheap condenser microphone and a PC with decent sound card, I only seek a bit of help from you.
> 
> ...


You may want to do measurements both inside a room and then outside to show how the room can affect the response. Some rooms can really change how a speaker sounds.


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## robbo266317 (Sep 22, 2008)

To help minimise room effects you can do a "close mic" sweep. ie the mic is placed about 1" in front of the individual drivers and this will effectively overpower any room reflections.

eg  

Cheers,
Bill.


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## HeavyGuy (Apr 24, 2011)

I managed to get SPL meter and did a few test measurements. 
Here's what I got: 



















First of all, is everything normal?

I've read REW online help thread and an article abour analyzing frequency response, however I'm still a bit confused. Shouldn't there be a a another line (the signal that REW generated) that I can compare to what I've got - so I could see how my speakers modify the sound. Oo is it possible to view this graph as a magnitude compared to the original (generated) signal, like THIS (CLICK) ??


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## GranteedEV (Aug 8, 2010)

The rising response above ~700hz is absolutely scary. Seems like some questionable speakers and/or SPL Meter calibration... no room would contribute that to the general trend in response.


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## MikeBiker (Jan 3, 2010)

HeavyGuy,

Is there anyway that you can double check your measurements with a member to see if your setup is correct? I don't know what speakers you used, but they seem to be quite horrible.


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