I got a sub a few weeks & have been experimenting with crossover freq & level settings. I am using the RS sound level meter, but feel I'm getting nowhere.

1) I set my main spks to Small & adjusted all spkrs to equal levels using the Avia DVD using pink noise. Then I changed to Large & the sub level went way down. I would think the Small/Large setting would only affect the main spkrs. That the sub would still get everything below the XO freq no matter what the mains received. I tried this a couple times. I do not notice this when using the test tone generated by the receiver. Am I missing some important concept here?

2) I tried the low freg sweep & my main spkrs alone have more hills & dips than the Coney Island Cyclone roller coaster. Between about 140 Hz down to about 45 Hz, the RS meter goes up & down 3 times. It varies, but increases about 6 dB max & then dips about 8 dB relative to 0 dB. Maybe freestanding in my back yard it would be flatter. But I cannot believe how large a level swing there is.

So I have no idea what is considered the low freq roll off for my spkrs. I have 3 major dips. I'm presuming some of the upswings would be considered spikes. But how does one figure out the best settings? Most magazine articles say to use the RS meter & the receiver's test tones. It's downright scary when I see what is happening when using the Avia sweep freqs.

I read about people using software programs & real time analyzers, etc. I have a basic system & do not want to spend more on lab equipment than I did on everything else. I do not have a laptop, but my desktop PC is very close to my TV viewing area. Is there any inexpensive software I can use along with a mic in order to help figure out settings? I'm presuming that the receivers that have an auto spkr setup function are doing essentially what I would do using my receiver's test tones & the RS meter. Or do some use sweep freqs and actually try to flatten out the response curve?

Any & all ideas & comments would be greatly appreciated.
Mike

I'll bet you're hearing room modes. Sound moves at about 1120 feet per second. Measure your room length, width, and ceiling height (round to the nearest foot). Divide 1120 by each of these numbers and you'll probably be close to the 3 peak frequencies you measures.

For example, if your room measures 18' x 12' x 8' you will have peaks at 63 Hz, 93 Hz, and 140 Hz. PRpbably the simplest treatment is bass traps although some receivers have a notch filter to tune out the dominant peak.

Mike, the two most commonly used software packages are TrueRTA at TrueAudio.com ($99 for the 1/24 octave version you need) and Room EQ Wizard (REW) available as a free download here:
http://www.hometheatershack.com/forums/bfd-rew-forum/
Although you can use your RS meters mic, most folks buy the Behringer ECM8000 mic and a source of phantom power for it:
http://www.musiciansfriend.com/product/Behringer-ECM8000-Microphone?fg=141&sku=270400
http://www.musiciansfriend.com/product/Behringer-MICROPOWER-PS400-Phantom-Power-Supply?fg=141&sku=336830
The REW link above is a source of much good room EQ information.

Then I changed to Large & the sub level went way down. I would think the Small/Large setting would only affect the main spkrs. That the sub would still get everything below the XO freq no matter what the mains received.

That's not my understanding. The result you're getting sounds normal to me.

As I see it, the ideal is to get a flat freq response from 20 to 20. Imagine a "large" main speaker which plays flat down to 20hz, or close to it. While you're at it, imagine an unlimited budget and anechoic room. Well if the sub is always getting that same bass input (nomatter whether the mains are large or small), then the sub is going to add to that flat freq reponse and screw it up.

So the result you're getting makes sense. The sub is only playing the freq that it needs to, because nothing else is.

But I think that my preamp has a setting which lets me double up. Even with the speakers set for large, the bass still goes to the subs. Sounded terrible.

I'll bet you're hearing room modes. Sound moves at about 1120 feet per second. Measure your room length, width, and ceiling height (round to the nearest foot). Divide 1120 by each of these numbers and you'll probably be close to the 3 peak frequencies you measures.

For example, if your room measures 18' x 12' x 8' you will have peaks at 63 Hz, 93 Hz, and 140 Hz. PRpbably the simplest treatment is bass traps although some receivers have a notch filter to tune out the dominant peak.


My room is about 14' x 12.5' x 8'. However it is open to the kitchen, which probably doubles the long dimension. I will have to measure that too.

Using approx dimensions yields peaks at 40 Hz, 86 Hz, and 140 hz. My L & R bookshelf spkrs are supposedly -3 dB at 65 Hz. So it appears I have a room mode peak right where the spkr freq response is dropping off. Would this mean that a peak actually extends the low end of the spkrs? Is this good or bad?

I'll go thru the setup again & will have to carefully make note of the freq peaks.

Thanks for the information.

What kind of receiver do you have, what kind of sub, what is the crossover frequency range of the sub, is the phase control on the sub 0/180 or continuously variable?

If you have a "basic" system chances are you have a reciever that gives you a few crossover frequency options, being 60/80/100/120hz. If you can shut off the crossover in the sub or have a crossover bypass input use that. Otherwise, set the sub's cross-over to it's highest point (usually 120 or 140), start with 80hz on the reciever's crossover.

Run some pink noise and change the phase until the SPL is the "highest" on the meter, then level match the speakers and the sub.

Use your SPL meter and some test tones to map the frequency response from say 30 - 120hz. Then set the cross-over on the receiver to 100 and do the same.

Pick the better of the two.

Now, it can get much more complicated if you want it to, with sub placement (if you have options for where to put the sub), RoomEQ software, TrueRTA, bass traps, etc., but start with the above to see if the sub starts to sound better.

Mike, the two most commonly used software packages are TrueRTA at TrueAudio.com ($99 for the 1/24 octave version you need) and Room EQ Wizard (REW) available as a free download here:
http://www.hometheatershack.com/forums/bfd-rew-forum/
Although you can use your RS meters mic, most folks buy the Behringer ECM8000 mic and a source of phantom power for it:
http://www.musiciansfriend.com/product/Behringer-ECM8000-Microphone?fg=141&sku=270400
http://www.musiciansfriend.com/product/Behringer-MICROPOWER-PS400-Phantom-Power-Supply?fg=141&sku=336830
The REW link above is a source of much good room EQ information.


Thanks for the links. I read thru some of it & sure is a lot of information there. I'll have to re-read some of it & give it time to digest.

What kind of receiver do you have, what kind of sub, what is the crossover frequency range of the sub, is the phase control on the sub 0/180 or continuously variable?

If you have a "basic" system chances are you have a reciever that gives you a few crossover frequency options, being 60/80/100/120hz. If you can shut off the crossover in the sub or have a crossover bypass input use that. Otherwise, set the sub's cross-over to it's highest point (usually 120 or 140), start with 80hz on the reciever's crossover.

Run some pink noise and change the phase until the SPL is the "highest" on the meter, then level match the speakers and the sub.

Use your SPL meter and some test tones to map the frequency response from say 30 - 120hz. Then set the cross-over on the receiver to 100 and do the same.

Pick the better of the two.

Now, it can get much more complicated if you want it to, with sub placement (if you have options for where to put the sub), RoomEQ software, TrueRTA, bass traps, etc., but start with the above to see if the sub starts to sound better.



Onkyo 504 receiver with XO freqs of 40/50/60/80/100/120/150/200 Hz.
HIT100 sub and I disabled the XO freq control. Phase is either 0 or 180. I did the phase test & set the sub at 180. Truth be told, I could not tell much difference between the two settings. I finally gave a nod to the 180.

I tried receiver XO at 80 Hz & 100 Hz. Again, really difficult to tell the difference. And I went thru the setup several times. Perhaps I am expecting a larger difference. What throws me off is all those peaks & dips between 40 Hz to 140 Hz.

That's when I thought I'd turn off everything but the L & R front spkrs just to make sure what I was measuring & listening. I have no idea what is the real rolloff freq of the main spkrs. Do I presume it is the lowest freq dip? Or is that also caused by a room mode? Or do these room modes only cause positive peaks?

I wish I could map freq response with something other than the Avia DVD. It sweeps thru the freqs and does not allow time to read the freq, read the sound level meter & then write down the data. I need something where it steps & holds the freqs for at least a moment in order to "digest" the data. I guess I'll have to enlist my wife's help, even though listening to test tones is not her favorite thing to do!

Thanks for the comments. I'll let you know what results I get upon further experimentation.