Charted some Rives Test CD output

[moggi1964]

I ran the test CD a couple of times following the instructions. The first run I got very excited bcause the lower frequencies were pretty flat then it all went to hell.

I moved the seating position back a bit and re-ran the test and produced a variable bunch of results.

I think I may be able to replicate the lower responses from the first graph by moving the subwoffer around the room but what on earth do I do to tame the higher frequencies? I noticed the higher ones could waver suggesting that reflections are involved. I am thinking about ATS 2" wall mounted acoustics; are they the right first step?

I have linked to a Word screen capture and the Excel file on the links below. The Excel file is easier to read. They take a moment to download and are appx. 200kb each.

Thanks.

http://www.the-examined-life.com/Roomfrequencydoc.doc

http://www.the-examined-life.com/Frequencyresponsegraphs.xls

 

[Savant]

moggi,

Shouldn't the 1000 Hz level be 0 dB for both runs? Even if you used the first run as the reference for the second, you should still have 0 dB at 1000 Hz for the first. Or did you use a different frequency band for the 0 dB reference?

Assuming there are no background noise influences, the overall response appears to be OK. I would argue that the second run is better than the first. Either way, I am not a fan of "flat." It's more "natural" to have some rise in the low frequencies. Your response appears to have some of this, assuming you used C-weighting per the Rives instructions. The fluctuations in the higher frequencies could be improved (smoothed out) with room treatments. Any anomalies you have in the low frequencies will not be apparent from a test such as this. The resolution is not fine enough to make any judgments or recommendations.

Aside from all this, there is the most important question: How does it sound?

 

[moggi1964]

Jeff,

1000hz should be at 0 on the first chart; I entered it incorrectly.

I guess my main concern is the way the meter fluctuates up and down on many of the middle to high frequencies. I can be watching the dB meter go from 71 to 76 on the same frequency during the 30 second tone. Isn't this a sign of lots of reflections?

The sound isn't great, it seems echoey and 'sharp' . Voices that should sound warm, don't.

I followed the instructions for C-weighting and slow response but thanks for the reminder; first time I tried this I didn't use the slow response.

I would like to get most of the response a little flatter (I'm not sure how important the 16k and 20k are) but I do agree that the second run is a better one though if I could replicate the 80hZ and below of the first run with the high frequencies of the second I would likely settle for that.

Plenty more runs to go

Thanks for your response, it is appreciated and helpful.

 

[Savant]

If you had the meter set on "Fast," that may explain the fluctuations you observed. Background noise intrusion may explain some of them as well.

If you're an adult, it's unlikely you can hear much of anything in the 16k or 20k bands. They're typically not something worth fretting over.

Acoustical treatments will be able to clean up the mid and high frequency problems you've described - echoes, "sharpness," and poor vocal quality. Of course, we'll need to know more about your room to help you with that.

 

[moggi1964]

I'm pretty sure it was set on slow as the fluctuations were a few seconds apart. There is no background noise above ambient noise where I am. I will be running it again so will double check.

Room is in a basement; 14x11x9 feet (HxWxH) with a very small window at the rear and a door to the right. There is also an alcove that goes under the basement stairs. Floor is carpet on concrete. Walls and ceiling are drywall.

I have attached a basic diagram.

Thanks.

 

[Savant]

There is no background noise above ambient noise where I am.

I actually understand that, even though it seems - at first glance - to be contradictory. In fact, in light of this statement, I should reword my post to read "ambient" as opposed to "background." Regardless, fluctuations on a sound level meter are nothing to get too worked up about. Microphones are sensitive things. As long as you're not talking about HUGE swings, I would advise against hitting the "panic" button.

As for the room, it needs some help for sure. At the very least, you should be considering some acoustical treatments for the first reflection points on the walls and ceiling. Start with something like a 4'x4' area of treatment for the side walls at the first reflection points. Use the center channel as your guide and you can either figure out the exact placement using Snell's law on your graphic, or using the mirror trick. Follow that up with a 4'x4' area on the ceiling about halfway between center channel and couch, and then another 4'x4' area centered on the rear wall. I would suggest you start with all absorption - 2-inch thick minimum; 4-inch thick (or more) preferred. If you should decide later that the room is too "dead" for your liking, you can install diffusion (or tuned reflection) over the absorption to retain some low frequency control.

HTH.

 

[moggi1964]

What can I say?

Thank you for the detailed suggestions and the time you have put into establishing the best way forward for me.

I will try the ideas you put forward and let you know how I do.

I found a few rolls of R19 in the attic just yesterday; that should do the job shouldn't it? I'm not very handy bit I am sure I can knock together a few frames and try that out. If it seems effective I can always save up for 'attractive' versions form a company that makes them.

Thanks once more.

Morris

 

[Savant]

R19 is a bit flimsy for making panels. If you compress it - and possibly layer it - it will perform better. In its natural state, the density is about 1 lb/ft³, which is about 3-6 times less than what's preferable. Thus, if you take (at least) three layers of it (assuming it's 3" thick - or so - to start with) and compress it down to an overall thickness of 3", you'll be in the ballpark. (Note that I would advise that you remove any backing material if you do this.)

 

[moggi1964]

Thanks for the tip.

I seem to have about 5 rolls of it up there so probably enough to do two or three frames when compressed.

I'll have a look at itand see that it is in good condition before I embark on any projects.

Cheers!

 

[moggi1964]

Decided it is better value to buy some manufactured acoustic panels.

In the mean time I have moved the subwoofer around and finally remembered to shut the door when doing a run and here's what I got.

I expect the acoustic treatments to reduce the echo and tinnyness so will run the analysis again when they get here.

Your thoughts are welcomed.

 

[bpape]

Any chance of getting something a little finer in detail? It's really hard to tell from coarse measurements. Also, you may want to retake the measurements at say 6" Left of center and 6" forward/backward from where the mic was for these runs. Do each individually and also together (left and forward, left and backward).

This may or may not improve anything but it will show you what abberations are seating related and which are not.

Bryan

 

[TLS Guy]

I ran the test CD a couple of times following the instructions. The first run I got very excited bcause the lower frequencies were pretty flat then it all went to hell.

I moved the seating position back a bit and re-ran the test and produced a variable bunch of results.

I think I may be able to replicate the lower responses from the first graph by moving the subwoffer around the room but what on earth do I do to tame the higher frequencies? I noticed the higher ones could waver suggesting that reflections are involved. I am thinking about ATS 2" wall mounted acoustics; are they the right first step?

I have linked to a Word screen capture and the Excel file on the links below. The Excel file is easier to read. They take a moment to download and are appx. 200kb each.

Thanks.

http://www.the-examined-life.com/Roomfrequencydoc.doc

http://www.the-examined-life.com/Frequencyresponsegraphs.xls

The mid HF problem shows a typical speaker, far too prevalent, that is shot of the mark.

Athena don't state the crossover, but I can tell you it is in the neighborhood of 2KHz.There is a null at crossover, likely because there is a second order crossover, putting the drivers out of phase in the crossover region. The tweeter polarity should probably be reversed, but they didn't because auto Eq set ups will would show an out of phase condition which it would not be.

Then there is a typical rigid woofer cone break up mode at 4KHz, which was not notched out in the crossover.

That is pretty typical of what is on offer, and I hate the sound that makes. room treatment will not cure it.

Those speakers might well be improved by reversing the tweeter polarity and putting a notch filter in the crossover, centered at around 4.5 KHz with a Q so that it covers the 3 to 6 KHz area

 

[moggi1964]

Bryan,

I am going to try running the REW which I downloaded yesterday, hoping that will give me a better picture. I will also do the analysis you suggest and post results.

Thank you for the direction.

 

[moggi1964]

TLS Guy,

well I guess you learn something new every day

I wouldn't know where to begin to reverse tweeter polarity and am off now to google "a notch filter". With that knowledge in your possession you might suggest I DON'T touch my speakers

Seems I may just have to live with the blips then unless I can EQ them out and that is not in the budget this year.

Thanks for your input.

 

[TLS Guy]

TLS Guy,

well I guess you learn something new every day

I wouldn't know where to begin to reverse tweeter polarity and am off now to google "a notch filter". With that knowledge in your possession you might suggest I DON'T touch my speakers

Seems I may just have to live with the blips then unless I can EQ them out and that is not in the budget this year.

Thanks for your input.

Actually this is a good example of why thinking you can Eq away loudspeaker problems is often fallacious.

Assuming the null in the 2 KHz region is due to the drivers being out of phase at crossover, the most likely explanation, then boosting that region will boost both drivers, but they are still out of phase, and canceling each other. Eventually you will over drive it, but increase power greatly to both drivers. This will drive the tweeter at its resonant frequency and sound awful.

To reverse the polarity of a tweeter, you remove it and reverse the connections.

Here is a parallel notch filter you can put in series with positive feed to your woofer.

C = 6.673 µF
L = 0.167 mH
R = 10.15 ohms

Note: R should be adjusted by sub-
tracting from it the DCR of the coil.

You can get the parts from Madisound.

If you PM and send me your Email. I will send you a pdf of the circuit.

 

[Savant]

TLS Guy,

How likely is it that the Rives test tones (at exactly 2 and 4 kHz) pinpointed these exact loudspeaker issues? (I'm really asking - I've only ever seen well defined crossover notches when much more complex analyses, such as sine-sweeps, are performed.) Aren't these narrowband issues? I would think the probability that a single sine tone was able to fall exactly at the crossover frequency is low. Further, I believe the ear would naturally smooth out such narrowband problems when listening to standard program material (music, movie soundtracks, etc.).

I'm not arguing with your analysis - just wondering about the relative importance these two frequencies when they are narrowband problems. Room acoustics problems cover a wide range of frequencies and it would seem that less effort would be involved (hanging panels) for relatively (much) greater improvement. If the notch problems at 2 and 4 kHz are still an audible problem after treatment, that might be a better time to get out the soldering iron.

moogi has described a system that sounds "echoey" and "sharp" with vocals that aren't "warm." These are not problems I would ascribe to a couple of narrowband loudspeaker anomalies. While said anomalies might contribute to making bad sound worse, I would argue that the room acoustics - in this situation - are the prime source of poor sound quality. N'est pas?

 

[TLS Guy]

TLS Guy,

How likely is it that the Rives test tones (at exactly 2 and 4 kHz) pinpointed these exact loudspeaker issues? (I'm really asking - I've only ever seen well defined crossover notches when much more complex analyses, such as sine-sweeps, are performed.) Aren't these narrowband issues? I would think the probability that a single sine tone was able to fall exactly at the crossover frequency is low. Further, I believe the ear would naturally smooth out such narrowband problems when listening to standard program material (music, movie soundtracks, etc.).

I'm not arguing with your analysis - just wondering about the relative importance these two frequencies when they are narrowband problems. Room acoustics problems cover a wide range of frequencies and it would seem that less effort would be involved (hanging panels) for relatively (much) greater improvement. If the notch problems at 2 and 4 kHz are still an audible problem after treatment, that might be a better time to get out the soldering iron.

moogi has described a system that sounds "echoey" and "sharp" with vocals that aren't "warm." These are not problems I would ascribe to a couple of narrowband loudspeaker anomalies. While said anomalies might contribute to making bad sound worse, I would argue that the room acoustics - in this situation - are the prime source of poor sound quality. N'est pas?

It seems to me highly likely. The null is just how a second order crossover looks when the drivers are out of phase. Crossover region on that type pf speaker is usually between 1.8 and 2.5 KHz. The break up mode of rigid mid woofers like that is almost ALWAYS at 4 KHz. A fiber glass cone like that will be rigid, and it WILL have a cone break up peak in the 4 KHz area. If they did not notch it, it will show up. These first break up modes are huge peaks, and if not dealt with would show up under his conditions of test in my view.

The OP describes very well how those sought of problems sound.

Unfortunately driver design has gone in wrong dead end direction over the last 40 years. Result, speakers are lousy more often than not.

 

[moggi1964]

Well my first step will be to hang the acoustic panels when they arrive and run a set of tests as per Bryan's suggestion. I will also run those tests before I hang the panels too (so I guess THAT is my first step ).

THEN, if I am still getting the issues I raised I will break out the screwdriver and after a quick trip to the local Radio Shack for a soldering iron, attempt the changes TLSGuy suggests.

The nice thing is that any changes are reversible.

I do appreciate this myriad of thoughts, questions and suggestions from respected contributors. Thank you.