# Bad 40-60hz issue



## gperkins_1973 (Aug 25, 2008)

Hi guys,

I am playing around with some sweeps tonight because I have a major issue between 40 and 60hz with some hardcore ringing. Is this down to the room or something else. The rest off my sweep is cool. This is with Audyssey EQ only on the receiver. No BFD EQ. The graph has a time length 1000 m/s and its still there.

I am going to do all the measurements off my room tomorrow night but the room is 18 feet 9 inches wide, the subs are located in each corner facing inwards off the room. The LP is 9 feet away from each sub which is the centre off the sofa.

The room is 20 feet long but there is an understairs cupboard at the rear right hand side.

cheers

Graham


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## gperkins_1973 (Aug 25, 2008)

Here's a group delay pic.

cheers
Graham


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## xmor (Dec 4, 2007)

Dear Graham,

It doesn't seem that the ringing you have is somehow connected with the dimensions of the room. If you carefully observe, the amplitude remains unaffected. I believe it is hum noise from the mains. Do you have any kind of transformer of electrical appliance nearby? Check it out...

Harry


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## gperkins_1973 (Aug 25, 2008)

The mains socket is behind my left sub and I have a tacima 6 socket conditioner which all my amp, receiver, tv etc... is connected to it. How do I check and what first.

The wierd thing is that it is the same for 100hz and 150hz too.

cheers

Graham


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## JohnM (Apr 11, 2006)

Harry is spot on, that is mains hum (at 50, 100 and 150Hz). If you see any feature in a waterfall that is constant over time it is an interference tone, mains hum is the usual culprit but others can include air conditioning systems or even something like a car outside with its engine running.


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## gperkins_1973 (Aug 25, 2008)

John,

I only have the following connected:

Plasma
reciever
sky HD box
blu ray player
bfd
xbox 360

These are all connected to the tacima mains conditioner

The only other thing I have on is a table lamp, the phone and main room light.

John also how would that affect the sound. Would those frequencies be pronounced or is it purely a hum which only shows up in the graph.

Any suggestions

cheers

Graham


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## JohnM (Apr 11, 2006)

It could be a hum loop involving the measurement PC, if it is a laptop try runnning on batteries. Beyond that, try disconnecting items from your receiver to see what helps - you can use the RTA view on REW to see what is happening to the levels at 50/100/150 as you disconnect things. I'd start by disconnecting the Sky HD box.


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## gperkins_1973 (Aug 25, 2008)

Here's a new plot without the skyHD and the plug disconnected from the laptop.

cheers
Graham


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## robbo266317 (Sep 22, 2008)

An easy way to check is run the RTA feature in REW without any signals and see if you still get the peaks. 
I get a peak at around 15 Hz from the coal loader which is about a kilometer away. See graph here:- http://www.hometheatershack.com/for...8965-whats-your-ambient-noise.html#post167882


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## Wayne A. Pflughaupt (Apr 13, 2006)

gperkins_1973 said:


> The wierd thing is that it is the same for 100hz and 150hz too.


Harmonics – they usually occur at octave and/or half-octave intervals.




> John also how would that affect the sound. Would those frequencies be pronounced or is it purely a hum which only shows up in the graph.


Since REW takes in-room measurements, it’s noise that apparently is loud enough that it should be audible. If it’s not from the mains, like John said it could be the AC system, your refrigerator or even something from outside the house.

Regards,
Wayne


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## JohnM (Apr 11, 2006)

Also worth trying without the BFD in the path.


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## gperkins_1973 (Aug 25, 2008)

I looked on my previous graphs form other subs and I never had it before. I put the rta feature on and even when I turn off all the sockets in the room it still shows a massive spike at 50hz. The only thing I have changed since is the EQ.2 hpf, step down voltage transformer and that is it.

John I have disconnected the BFD already as I wasn't using it. 

I am stumped.


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## gperkins_1973 (Aug 25, 2008)

In the RTA window the hum at 50hz is showing at 65db. Yulks. I know zero squit about electrics which is a pain. I may have to get an electrian in to find out what is causing it.


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## JohnM (Apr 11, 2006)

If you disconnect the REW output connection from your laptop is the 50Hz signal still there? If so, it is acoustic noise that the mic/meter is picking up. In that case, switch off the sub and see if the noise is still showing, if it is then the source is outside your system, if it goes away it is a ground loop within the AV system somewhere - the thread on BFD hum has lots of possible causes and cures for that.


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## gperkins_1973 (Aug 25, 2008)

John,

When I disconnect the phono from the reciever which goes into the output off the sound card it is still there. When I turn the sub off it is still there.

When I turn the plug off which has the conditioner connected for all AV equipment it is still there. Also when I turn the other plug off it is still there. 
So I can only presume it is something outside this room.

cheers

Graham


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## JohnM (Apr 11, 2006)

Does it change if you move the cable from the meter, or use a much shorter cable? Are you using an SPL meter or a mic? 

You mention a step-down transformer, what is that powering and does disconnecting it from the mains help?


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## gperkins_1973 (Aug 25, 2008)

The step down voltage convertor is for the EQ.2 hpf I bought from the states. Even when I turn that off at the wall it is still there.

I am using a phono lead which has single lead one end and a red/black the other. When I plug in the red I get the hum. When I plug in the black I don't.

cheers

Graham


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## gperkins_1973 (Aug 25, 2008)

Here's the waterfall and group delay with the black lead plugged in.

If defo better but there still looks like some dodgy group delay at 60 and 100hz.

Could it be a dodgy lead. The lead is about 10m long. Is that too long?

cheers
graham


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## gperkins_1973 (Aug 25, 2008)

One other thing I have noticed is that when I connect the EQ.2 in the chain I can hear a hum coming through the subs. With it disconnected it goes away. It is a similar hum that I get with the BFD connected.

I will have another look at the BFD hum thread again.

cheers

Graham


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## robbo266317 (Sep 22, 2008)

Hi Graham, 
10 m is a looong cable. You dont have anything shorter?


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## gperkins_1973 (Aug 25, 2008)

I am going to buy a shorter one today. I could get away with a 5m one. I use the same identical cable for the output which goes to the reciever.


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## Wayne A. Pflughaupt (Apr 13, 2006)

gperkins_1973 said:


> Here's the waterfall and group delay with the black lead plugged in.
> 
> If defo better but there still looks like some dodgy group delay at 60 and 100hz.


Well, the steady-state signal is gone, so it looks like you had a bad cable. But on the other hand, you shortened the window from 1000 to 300 ms, so it’s hard to tell for sure...


















gperkins_1973 said:


> Could it be a dodgy lead. The lead is about 10m long. Is that too long?


Would only be an issue if it’s a poor-quality cable (e.g. poor shielding) and you have it near something that could generate EMI into it.

Regards,
Wayne


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## gperkins_1973 (Aug 25, 2008)

Wayne,

It was a pretty cheap cable to be honest. I am going to buy another cable this weekend and see if that helps. There is still a slight hum there but hopefully the new cable will show that up.

cheers

Graham


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## xmor (Dec 4, 2007)

Is there anything that produces audible hum in the room? Do you have any kind of fluorescent lights or electronic dimmers? I believe it is more than obvious that something like that is happening. You can as well check with the RTA module. A spike should be clearly visible at 50Hz....I hope you'll sort this out...

Harry


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## gperkins_1973 (Aug 25, 2008)

The spike in the RTA was originally 65db which is pretty loud. When I swapped the red lead on the phone lead with the black one it reduced alot but it was marginally still there as you can see in the graph.

No other fluro lights or electrical dimmers in the room. When I connected the BFD when I first got it a year or so ago I noticed a very small hum through the subs but ignored it as it was not audible enough from where I sat. But even then it didn't show up a spike in the waterfall. I get the same hum when the EQ.2 is connected. 

I will take some more measurements with a longer decay time to see before and after so you can see how much is still left.

cheers

Graham


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