How to identify and fix specific frequency issues?

needhelp

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Hello all, I am new here. Was directed here by someone so I am hoping to possibly get some help with my issues please.

So guys, I use my one car garage for my entertainment where I sit on a Saturday evening, have a beer or two while listening to my Radio/DJ software playing back my fav playlists. 2 main issues I have always had is only with the bass with different tunes playing with a sort of "flapping" noise and others vibrating with the speakers on top of the sub or the roof so there is no consistency with all mp3's. Other issue is for some tunes you don't hear the same bass at different spots in the room.

I have beaten this topic to death on different forums with guys telling me I should insulate the brick garage which might help but I think aside from that since we have different objects along both sides of the walls then insulating will not make all that much of a difference. So I am stuck with the room as it is and trying to find something which will help the current situation as it is. Reason why I am here now on this forum is because the person who had directed me here had this to say:

"First you would need to find out which frequencies cause it. For that you can use a sine-wave generator and then go through the entire spectrum and make note of where your issues are.
And then you can try to notch out those trouble-areas and see if that works for you.

You could always try looking for a notch-eq instead, if you can't do anything about the room itself.
With such an eq you might be able to attenuate the frequency-ranges that cause this resonance."

Since most of my mp3's plays fine, it's the problem mp3's which I am trying to make better. I have done all the testing with the mp3's, playing the same tunes from different sources so I know for sure it's not the quality of those mp3's that's the issue. Another thing is whenever I should play any internet radio station or Spotify .e.tc, I do not have these problems, every song plays perfect. Therefore I have to believe that it's got to be certain frequencies in some tunes which are giving me the flapping and vibration issues. Also I am not understanding why with some tunes I can hear the same bass no matter where I sit or stand while with some others it's the opposite?

So guys, any possible fixes for this situation please? I had started looking into Ai Auto-Eqing softwares which is what led me here.
 

John Mulcahy

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To track down specific things in the room vibrating when certain frequencies occur you could use the REW signal generator to play sine waves and when you find a frequency that makes something buzz or vibrate see if you can secure it.

Bass response in rooms varies with position, that is a basic property of reproducing sound in an enclosed space. Certain frequencies will be boosted and others reduced, depending on the dimensions of the room and the position of the speakers and the listener. You can explore that using the room simulator if the room is rectangular.
 

needhelp

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Thanks John, will look into this and report back. Meantime, I have never gotten an explanation from anyone so far regarding this issue of not hearing the same bass in different spots of the room, if the room's acoutics is what's causing this then why don't I have this problem with ALL mp3's and only some please?
 

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Thanks John, will look into this and report back. Meantime, I have never gotten an explanation from anyone so far regarding this issue of not hearing the same bass in different spots of the room, if the room's acoutics is what's causing this then why don't I have this problem with ALL mp3's and only some please?
Simple answer is you DO have that problem with all sources. It is physically impossible to have low frequencies reproduced the same everywhere in a room unless your "room" has no walls :). Depending on the construction of the room the resonances may be very narrow (e.g. concrete or brick walls) or more broad (e.g. some timber constructions) and most noticeable when music contains the particular frequencies of the resonances.
 

needhelp

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AAAh I see, FINALLY I got an answer for this, thanks! I made a mistake by not writing down some of the problem tunes so it may take me a couple or few days to find and note the tunes, I will try to find 5 tunes with the issues to work with.

I am seeing the Signal Generator page but can you tell me exactly which download item on the downloads page is the sine wave generator please?

Also, how do I actually use it when playing an mp3 as I am not clear on how to use it for this purpose?
 

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The generator is part of REW. It would not be used with an MP3, the generator is a source of signals so your PC's headphone output would be connected to an input on your system to play the frequency you select.
 

needhelp

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Hmm, I am trying to understand what you've written so please bear with me as I am not nowhere as technically savvy with all of this as you guys here so I would need to go in slow motion.

I am thinking I would install the Generator on my pc, play a problem mp3 then run the sine wave at different hz selections then the sine wave should sound a specific tone when it finds the problem, is this not how this works?
 

John Mulcahy

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No, MP3 tracks are not involved at all. You notice problems when a track you are playing contains a tone (some content at a particular frequency) that causes the problem. Rather than playing music and hoping it has the problem tones, you can play the generator and adjust the frequency of the generator's tone until the problem occurs. You can then go to whatever is vibrating and see if you can secure it to stop it.

Problems caused by things that are loose and start vibrating are different from varying bass response. The differences in bass response at different listening positions or with different speaker or sub positions are characteristics of the room. You can try and tackle them by choosing a different place to sit, or putting your speakers or sub in different positions, or by adding acoustic treatments in the room, or by applying EQ at the problem frequencies to reduce the boost they get from the room's characteristics. The process can be considerably helped by making measurements of the room's frequency response, how it reproduces different frequencies, but it's all a big topic and can be very time consuming.
 

needhelp

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That being the case then this might be a moot point. Reason being, I cannot do anything about the speaker location as it's in the only spot in the Garage which is in the middle of the back wall. Also there are times when some tunes vibrate the ceiling alone and not any of the speakers so I cannot see that I will be able to do anything with that?

I was looking for a way to adjust the eq and/or crossover's settings to prevent these problems from occurring when certain tunes are playing but from your explanation, seems nothing can be do aside from room modification and equipment positioning, do I have this correct now please?
 

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Problems caused by things that are loose and start vibrating are different from varying bass response. The differences in bass response at different listening positions or with different speaker or sub positions are characteristics of the room. You can try and tackle them by choosing a different place to sit, or putting your speakers or sub in different positions, or by adding acoustic treatments in the room, or by applying EQ at the problem frequencies to reduce the boost they get from the room's characteristics. The process can be considerably helped by making measurements of the room's frequency response, how it reproduces different frequencies, but it's all a big topic and can be very time consuming.
See the part in bold.
 

needhelp

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Yes, I got that part but issue is when we adjust the eq or xover to correct the problem while one tune it playing, another tune will require having to adjust again and so on and so on. We haven't been able to find any one setting with which all tunes will play without the issues and we have been at this since last year.

This is precisely why I am looking at an "auto" eq hoping to find something which might do the correcting on the fly. One company told me last week they are working on a plugin for this purpose but of course don't know for sure that it will work or when.
 

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There are already systems that will automate the EQ process for you, such as Audyssey or Dirac. REW can also generate EQ settings based on measurements made in the room, but a separate equaliser or software (e.g. EqualizerAPO for Windows) is needed to apply the EQ.
 

needhelp

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tHAT I can at least try with a demo of REW and I have a spare DBX EQ which works on one channel or might be better to test with the EqualizerAPO. Tell me this please, if testing with REW and APO, would I be able to do this only on the sub as whatever I might use I don't want it to interfere with or adjust anything at all with my mids and highs?
 

John Mulcahy

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You choose what frequency span you want affected by EQ. It is generally best not to apply EQ above a couple of hundred Hz and your problem areas are probably below 100 Hz.
 

needhelp

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My bass is set at 80hz on the Rane xover so that shouldn't be a problem

Ok, thank you very much for all of the help and info. I should be able to get to my rig tomorrow and will try and report back!
 

needhelp

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Oh, I am installing both softwares now meantime, can I ask for help here in this thread or should I create a new thread or post in a different sub forum please?
 

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For a general setup question probably best posting a thread on whatever specific issue you are having. Anything following on from your original topic may as well continue in this thread.
 

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Hey John, so I was advised to choose the PC's sound card's "Speakers" option on the Equalizer APO forum. Now reading through the "Getting started with REW" documentation it is showing I will need a MIC so I am guessing this is for an RTA setup but please clarify?
 

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If you just want to listen for things buzzing you won't need a mic, but to make measurements that can be used for EQ a mic is required.
 

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Well, if I am following this accurately so far, I am thinking the purpose of the APO is for it to be used instead of any external hardware to correct the problem frequencies? If not then what's the purpose for the APO please?
 

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Sorry for the late response. I have been having trouble getting APO to work on my win7 music machine and after trying everything today I am going to try upgrading it to win10 to see if that will help.

Meantime I would like to get some clarity on the different bass at different spots issue please. Since with different mp3's I hear the lack of bass at different spots meaning with one tune I might hear the lack of bass at point X, with another tune I might hear it at point Y and with another at Point Z and with some might be at Points X and Y or any combinations of the three. I would like to know how using an RTA Mic will help this issue with ALL mp3's?
 

John Mulcahy

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"Bass" is probably different frequencies on different tracks. To know what is happening with the different frequencies you would need to make measurements. "Lack of bass" could be a modal effect (certain frequencies will appear very quiet at certain places in the room) or mean that in other positions you are getting a modal resonance boost making it seem relatively lower at the positions you find too quiet. Frequencies where the response is very low due to a modal resonance effect can really only be addressed by either adding acoustic treatment (probably a lot of treatment if the frequencies are low) or sitting somewhere else (usually more practical).
 

needhelp

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Ok thanks, that's a very good explanation and yes you are correct in that the bass "sounds lower" in different spots.

Since I can't place the speakers anywhere else and can't do anything about the room then no way this can work right?
 

John Mulcahy

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You could apply some EQ to raise the level around the problem frequencies, but any change you made would apply everywhere so making it a bit louder in the quiet spots would also make it louder where it was already loud enough. To get a more even distribution of low frequencies in a room you would need to add more subs in different positions.
 
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