# Subwoofer measurements - strange results



## rubberbudgie (Mar 5, 2016)

I have recently setup my audio equipment into a new room and have taken a few measurements and the bass is all over the place.

I was just wondering if anyone has any ideas as to what is going on.

My mic is a UMIK-1. The red line is the subwoofer facing sideways at half volume level, the blue line is facing forwards at the same volume level.

Please let me know if you need any more graphs or any information about the room.

Thanks for any assistance you can provide.


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## willis7469 (Jan 31, 2014)

Well, what sub is it? It's rolling off very high. Is this measurement with the mains? I'm gonna guess you have the X/O engaged on the sub, and in the avr. Which connection are you using? Lfe in, or the red/white RCA in?


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## rubberbudgie (Mar 5, 2016)

willis7469 said:


> Well, what sub is it? It's rolling off very high. Is this measurement with the mains? I'm gonna guess you have the X/O engaged on the sub, and in the avr. Which connection are you using? Lfe in, or the red/white RCA in?
> 
> 
> Sent from my iPhone using Tapatalk


Thanks for the reply.

The subwoofer is a Sony active subwoofer, nothing flash but has done the job nicely for the past few years.
The only controls on the sub are the level and two settings, one called Movie and one called Music.

On the back the only input is an RCA input which is connected to my subwoofer output on the 7.1 pre-out on my AVR.

The measurement was subwoofer only so no mains. Crossover setting on the AVR was set to 80hz but even when set to another setting it doesn't seem to change the result for some strange reason.

I have attached a graph of the front L+R + Subwoofer measurements, the green line is with the crossover set to 80hz and the purple line is with it set to 150hz. As you can see there isn't much change between the two apart from the big dips on the 80hz measurement.


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## willis7469 (Jan 31, 2014)

Yeah it's interesting the xo change didn't do much at all. Where is the sub located? And have tried to move it at all? Or is that even an option?


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## rubberbudgie (Mar 5, 2016)

willis7469 said:


> Yeah it's interesting the xo change didn't do much at all. Where is the sub located? And have tried to move it at all? Or is that even an option?
> 
> 
> Sent from my iPhone using Tapatalk


The sub is located away from the wall in between the MLP and the front left speaker. It's an odd place I know, I'm going to try moving it around once I get a longer RCA cable that I don't have to join multiple times.

The XO setting has never really made much of a difference now that I think about. I've never really worried about it because up until recently I've only really used my system for SACD playback so bass has never really been too much of an issue, but now with a lot of titles being released on high resolution blu-ray audio it seems to need a lot more bass than SACD not to mention DTS-HD. 

If I need to buy another sub (or 2) to replace this one then so be it but I'd really like to make sure it's nothing environmental or even user error first. 

I know that the room definitely needs treatments but rather than just throwing bass traps and sound absorption around I'd prefer to do it somewhat scientifically hence why I bought the UMIK and starting using REW.


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## DqMcClain (Sep 16, 2015)

The massive dip at 70Hz on the green line is either a phase response issue with the XO, or a wild room mode. Unfortunately, the big dips higher up could correspond to either scenario, as they appear to be related harmonically (or geometrically, depending on which way you like to think). Can you put the sub someplace completely ridiculous in the room (like 3 feet off-center in any direction) and measure again? If the graph changes dramatically, you'll know it's a room interaction, and not an electronic issue. This would only be for measurement purposes, and to eliminate a possible cause for the issue... not for real-world use. 

However, I'm leaning towards an electronic issue because neither setting appears to have a roll-off appropriate to their intended function. If it IS an issue with the crossover, since the crossover is buried in the AVR it could have more unpleasant ramifications. Can the AVR crossover be bypassed, and have full-range signal sent to the sub? If so, then purchasing a sub with a built-in crossover (preferably something variable) will solve that problem without having to replace the AVR.


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## willis7469 (Jan 31, 2014)

I think that's a great plan. Finding out about your room is a good head start. I would also try to remeasure in different locations. Dq has given good advice, and I would add that the drop at 40hz looks about right for a Sony (htib sub?) There's plenty of info in the 30's and I think in the end, an upgrade is in order. Interested to see the remeasure results. 


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## rubberbudgie (Mar 5, 2016)

Thanks for your suggestions.

I just lost the whole message I just typed because of some error with the page so I'm not going to be as concise this time around but the main points are:

There was indeed a phase switch hidden away at the back of the sub and it was set to reverse so I have corrected that.

I have moved the sub as far away from it's previous location as I could (only about 1.5 feet though)

I have set it to Movie mode rather than Music mode as it seems to sound better on that setting

The new reading is the yellow line, quite a bit different even with just moving it a few feet so on the weekend I will try moving it to the back of the room and re-measure it again.


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## rubberbudgie (Mar 5, 2016)

OK so I have moved the subwoofer to the rear of the room and have put down a rug which covers most of the tiled floor area and the difference is really amazing as you can see from the graphs.

The crossover still doesn't seem to be having any effect on the measurements although I'm wondering if this is due to how I am measuring it as I am using HDMI channel 4 as the output. I have tried it also with HDMI channels 1 + 2 as they should be passing LFE information to the SUB output as they are set to small but that seemed to have no effect either. I might try using good old RCA inputs and see if that makes any difference.

But at least the subwoofer isn't behaving as erratically as before and while still not perfect it is still a big improvement nonetheless.


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## willis7469 (Jan 31, 2014)

It definitely looks better. Im still gonna lean toward an electronic anomaly though, since the same basic shape of the graph is still there. I'm wondering if, and what, and how the "movie" or "music" movie modes effect the output signal. Have you measured them against each other? The drop at 40 won't change since that seems to be the roll off point and nothing will change that. But the area between 40 and 80 seems to be something like a dual XO, or "sound mode", or something like that. Maybe even amp or driver failure? In any case, I'd recommend an upgrade if you have budget to work with as 40hz is way to high for any "subwoofer". Do you have a friend you could borrow one from just to measure?
I'm guessing your using ASIO since you have channel selection?I use to use 3.5 to RCA. It works fine but I've had more consistent results with hdmi. I don't use ASIO so I can't offer anything there. Also make sure you don't have any EQ engaged in the PC. I found out the hard way that I had one engaged and it messed up all my measurements. 


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## tonyvdb (Sep 5, 2007)

In one of your first posts you said that the graph is sub only no mains? If that is the case your graph should not be showing much if anything above 110Hz. Something is amiss...either your crossover is not doing anything or you have a lot of background noise in the room. Are you certain that the calibration file is correct?


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## robbo266317 (Sep 22, 2008)

I always use REW in RTA mode, with no signal going to the amp, before I do a measurement to see where the noise floor is in relation to the signal I am measuring.

Note: this is not so much of an issue since we knocked down and rebuilt several years ago and the new house is considerably quieter.


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## rubberbudgie (Mar 5, 2016)

willis7469 said:


> It definitely looks better. Im still gonna lean toward an electronic anomaly though, since the same basic shape of the graph is still there. I'm wondering if, and what, and how the "movie" or "music" movie modes effect the output signal. Have you measured them against each other? The drop at 40 won't change since that seems to be the roll off point and nothing will change that. But the area between 40 and 80 seems to be something like a dual XO, or "sound mode", or something like that. Maybe even amp or driver failure? In any case, I'd recommend an upgrade if you have budget to work with as 40hz is way to high for any "subwoofer". Do you have a friend you could borrow one from just to measure?
> I'm guessing your using ASIO since you have channel selection?I use to use 3.5 to RCA. It works fine but I've had more consistent results with hdmi. I don't use ASIO so I can't offer anything there. Also make sure you don't have any EQ engaged in the PC. I found out the hard way that I had one engaged and it messed up all my measurements.


I have compared movie and music modes and movie mode follows the exact same as music only it is a few db higher.
I have been using HDMI from my laptop for testing and selecting channel 4 when doing my sub tests. I've done some testing using Channel 1 (Front left) with Channel 2 (Front Right) as the reference so I can get a Stereo signal to test with but the results are pretty much the same.
I've been doing some research on the AVR and there is mention of an LFE issue with HDMI so I'm going to keep looking and see if it could be related.

The AVR is due for replacement but other than the XO issue it performs like a champ so it would be good to try and see what's up with it.

I am going to borrow one of my mates subwoofers to test with to see if it's my sub causing the issue, I will report back when I have some more results.



tonyvdb said:


> In one of your first posts you said that the graph is sub only no mains? If that is the case your graph should not be showing much if anything above 110Hz. Something is amiss...either your crossover is not doing anything or you have a lot of background noise in the room. Are you certain that the calibration file is correct?


You are right in that the crossover isn't doing anything. I can set it to 40hz or 200hz and the readings are the same. 
Do you mean the Mic calibration or the sound card calibration? Mic calibration file was downloaded from minidsp so I am assuming it's correct.



robbo266317 said:


> I always use REW in RTA mode, with no signal going to the amp, before I do a measurement to see where the noise floor is in relation to the signal I am measuring.
> 
> Note: this is not so much of an issue since we knocked down and rebuilt several years ago and the new house is considerably quieter.


I did the same thing using RTA and my noise floor is around the 55 - 60db mark.


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## ocramida (Apr 26, 2016)

rubberbudgie said:


> I have compared movie and music modes and movie mode follows the exact same as music only it is a few db higher.
> I have been using HDMI from my laptop for testing and selecting channel 4 when doing my sub tests. I've done some testing using Channel 1 (Front left) with Channel 2 (Front Right) as the reference so I can get a Stereo signal to test with but the results are pretty much the same.
> I've been doing some research on the AVR and there is mention of an LFE issue with HDMI so I'm going to keep looking and see if it could be related.
> 
> ...


Hi 

So did you ever get to the bottom of this. I'm seeing the same phenomena where my xover doesn't seem to be doing anything. My nulls are at 40 and 60 HZ, while my sub is flat up to 40.

I'm using a PowerSound Sub.


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