[Canopydown]

This is my first REW sub measurement taken in a house I just moved into. Room is 12'x20'x8' and sub is in r/f corner. I have played with sub eq settings but I have a peak around 60hz that does not change much no matter what I do. Is this a room mode? How would you guys address this? Also any other comments about my graph would be appreciated. Mains were also included in the sweep.

 

[Wayne A. Pflughaupt]

Hey canopy,

If the 60 Hz peak is a room mode, then an EQ filter @ 60 Hz will cut it. If that’s not happening, then you may have some other noise source in the room polluting the measurement. This appears possible in your case, seeing how your level is so low (assuming you did the SPL calibration, which is required if you want the graph SPL markings to be accurate). Generating a waterfall graph would tell us if it is an extraneous noise source.

Regards,
Wayne

 

[Canopydown]

Using the eq to cut at 60hz made no difference. I could cut at 50hz or 70hz and see a difference. I will generate a waterfall after I get off work and post it. Also I did do SPL calibrate using sub and then also using mains but even so I would get a message after a measurement saying the signal was low, not sure why that's happening. Any ideas?

 

[fusseli]

I suppose that 60Hz peak could be power line artifact getting into your computer's soundcard and influencing your measurement, especially if EQ won't cut it when you re-measure. You should try and mess around with placement and try more EQ stuff though to verify. Do you live in a place with 60Hz mains? Is there a washing machine or something running in the house? Haha

 

[MikeBiker]

I'm suspecting that there is some 60Hz power line noise getting into the the system like Fusseli suggests. Recheck all the wiring and try to use a different outlet if possible.

 

[Canopydown]

^ by 60hz mains do you mean power? I live in US so power is 60hz right? No washing machines or other appliances on except gas stove since I was cooking dinner at that time.

Also, I was using laptop on batteries with USB soundcard. If I plugged laptop into wall I got a loud buzzing out of main speakers. With it on batteries there was almost no buzzing but I could hear a slight amount when up very close to speaker. My audio rack is remote mounted in the garage and I have a RCA cable run through wall that allows me to be in the tv room but connect to my receiver in the garage. This rca that I use to send the line out from soundcard sits next to some power cables in the wall maybe its picking that up?

 

[fusseli]

Ya, 60Hz mains for your power at the wall outlet. Just thought to verify as some countries are on 50Hz. Try a different powerstrip or outlet on a different circuit if you can. If your computer is a laptop then try unplugging it from the wall and measuring off of battery power.

 

[Canopydown]

Yeah I did the sweep unplugged from wall. When plugged in I got a loud buzzing from mains.

 

[Canopydown]

Here is my waterfall. What do you think?

 

[fusseli]

Not bad other than the junk at 60Hz and 180Hz

 

[Wayne A. Pflughaupt]

Here is my waterfall. What do you think?

The natural state of an audio signal is to decay over time. Notice at 60 Hz there is no indication of the signal strength reducing. In other words, you have a steady-state 60-cycle signal there – something is generating noise. Typically it’s an appliance – washer, refrigerator, central A/C, etc. I’m just surprised that it’s so loud (judging by its level on the graph) and that you can’t actually hear it. (BTW, the 180 Hz tail is merely a harmonic of whatever’s generating the 60-cycle noise.)

Regards,
Wayne

 

[Canopydown]

Thanks for your help guys. I am going to try another rca for the test signal sent from soundcard->aux in on receiver. My house is old and we had it remodeled recently. At the time I ran an rca through the walls on both r/f and l/f of room to use for multi subs. It was unavoidable that in places it comes near power wires. Maybe its picking this noise up.

I did have a horrible ground loop hum that I fixed a few days ago by properly grounding the catv at the service drop point to the main grounding strip of my fuse box.

Other than that how does the graph look in general? Do I need any bass traps or other things? I have 6 4'x2' panels of ATS rockboard 80 that I am going to start placing at reflection points for the mid-highs. I have wood floors and not much furniture which results in some very bad flutter echoes.

 

[Dr_Suess]

Another simple test would be to go to your breaker panel and turn off all the power except one known circuit. Use an extension cord to plug everything in from the known circuit (Use something that has a plug on it). Do a test, if 60 hz is gone you have isolated the problem. Then I validate your grounding is good. The fact that your CATV had issues is a tell tale sign. Turn the breakers back on. If you have a volt meter measure the AC and DC voltage between your nuetral and ground at your plug location. You should see 0 VAC/VDC if you have a voltage you will need to call in an electrician to correct your grounding. Your amplifier/equipment uses either the ground or nuetral (polarized) as a ground reference for shielding. These are relatively easy tests. Also if you do have a grounding issue you could be subject to your equipment prematurely failure do to transients.

Hope this helps.

 

[Kevin R. Anderson]

I had this problem. You can use the RTA feature of REW with the room as quiet as possible, then observe the RTA as you make changes to your electrical system and see if it drops

It could also be a 60-cycle hum manifesting itself through the subwoofer. Unplug the subwoofer completely and see if the 60Hz spike disappears.

Mine turned out to be the fridge running upstairs above the theater, so it was intermittent and drove me crazy for 6 months before I finally made the connection.

 

[Wayne A. Pflughaupt]

Other than that how does the graph look in general? Do I need any bass traps or other things?

Sub response is fairly flat, although that slight sag in the 30 Hz region probably makes things sound a bit thin. Re the waterfall, it was generated with too low a signal to be of any use (except for helping us confirm the noise problem). You need to get about 50 dB between the signal average and the room’s noise floor. The latter will require changing the lower graph parameter to 30-35 dB.

Regards,
Wayne