# Dead spots



## CraigRobbo (Feb 14, 2010)

Hi guys,

I am having some major issues with a dead spot and my subwoofer.

My prime sitting position in the middle of the room is compleatly DEAD with space, the seat next to either side is great but the middle is just compleatly dead, it doesnt even sound like i have a subwoofer...

I have tried moving the sub into pretty much every postion with no joy at all, I even tried putting the subwoofer almost right next to me at the side of my chair and it was still dead - move my head to the other chair and the bass was deafning!

Unfortunaly the furniture is quite limited to how i move it due to the way the room is layed out and there isn't many options for re-arranging the room.



Please help???

Craig


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## bpape (Sep 14, 2006)

Any chance of posting a basic sketch of the room and/or some pics? Sounds like purely a width mode to me.

Bryan


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## CraigRobbo (Feb 14, 2010)

Sure,
Thanks for the help.

I have put the in RED my hifi gear
I have put in black the room plan
I have put in Blue where the bass is ok and where it is dead.

I havent put the subwoofers position because i have tried it EVERYwhere, even in the dinning room!

In this drawing i have been a bit generous with the spaces, the couch is infact right up as far as it c an go to the wall and the gap between the stairs and chair/couch is much much less than shown sorry.

Might be worth mentioning also that i have tried moving my mains around & unplugging them altogether too - Again made no differenc.

When i unplugged the mains the sub just sounded like a very slight 'farting' sound, again move over a seat and it was head crushing bass again :S

Thanks again

Craig


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## bpape (Sep 14, 2006)

So if you stay in your seating position left to right but move forward, the bass is OK too?

Bryan


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## CraigRobbo (Feb 14, 2010)

bpape said:


> So if you stay in your seating position left to right but move forward, the bass is OK too?
> 
> Bryan


Well in the forwards range i have to move right up to the front wall, so a simple 'lean' forward doesnt fix it, however going backwards from my seating position, maybe just 2 foot? but I cannot move back because of the door 

I just tried for an experiment putting a sheet on the back wall to soak up some soundwaves but that didn't help, not even a bit.

Thanks in advance

Craig


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## bpape (Sep 14, 2006)

Sounds to me like the other seats are overdone in bass as they're all boundary loaded to an extent and your seat isn't. I would guess that if you measured it, your seat is probably a more accurate reflection of the amount of bass in the room. 

To do anything on the rear wall, it would need to be more like 6-8" to impact bass frequencies.

Have you done any measurements with REW?

Bryan


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## CraigRobbo (Feb 14, 2010)

bpape said:


> Sounds to me like the other seats are overdone in bass as they're all boundary loaded to an extent and your seat isn't. I would guess that if you measured it, your seat is probably a more accurate reflection of the amount of bass in the room.
> 
> To do anything on the rear wall, it would need to be more like 6-8" to impact bass frequencies.
> 
> ...


Hi.

Thanks again, what you say makes sence but i can assure you its a 'dead' spot -

I have for testing ONLY the sub turned on full volume (hence ear crushing bass in the next to me seats)

Its not just the low bass but mid bass and the general responce of the sound in the prime location is just awful, it like a cheap tinny stereo you get from argos but i would asume what ever is causing hassel with the bass would also fix the rest.

Craig


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## bpape (Sep 14, 2006)

Well, if every other spot in the room is OK and you're not sitting centered in any of the room dimensions, I'm at somewhat of a loss to explain what the problem is - especially if it's over a broad range of the spectrum.

I would guess it's something that could be helped with treatment - just need to figure out where. Might be best to get/make a couple of broadband bass panels and experiment with placement. Odd shaped rooms and non-symmetric setups do make it a lot more difficult to theoretically determine where problems are coming from. Sometimes it's just the old trial and error method.

Bryan


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## Moonfly (Aug 1, 2008)

Are you still running all those 10" subs in your speakers as well as an active sub?


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## CraigRobbo (Feb 14, 2010)

Moonfly said:


> Are you still running all those 10" subs in your speakers as well as an active sub?


Nah

There in a seperate room 2 floors up.

I bought a dedicated 2ch system for music and kept the 9.2 specifically for games & movies.

Craig


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## Moonfly (Aug 1, 2008)

Right ok, so what exactly are you running in here now, you mention a sub, do you have an active sub in a 2.0 system?


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## CraigRobbo (Feb 14, 2010)

Moonfly said:


> Right ok, so what exactly are you running in here now, you mention a sub, do you have an active sub in a 2.0 system?


I am running an Arcam amp & MS 902i Speakers and an Eltax active subwoofer.

I know its not the best but it sounds alright - Except in the prime listening position.

Craig


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## Moonfly (Aug 1, 2008)

Subwoofer model number?

What experimentation have you done with subwoofer placement, cant see it in your image?


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## CraigRobbo (Feb 14, 2010)

Moonfly said:


> Subwoofer model number?


Its the eltax atomic 6.2a - I know its not big but remember that in my new house i listen at low levels and the sub is never over worked...
In every spot other than center it sounds really nice...But even the bass from the main speakers(if the sub is disconected) still sounds lacking and dull(not just low volume but like its sounds hollow so to speak)

Craig


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## Moonfly (Aug 1, 2008)

Have you double checked the speakers are in phase etc. Is there no position in the room you have tried the sub where it sounds good in both sitting positions, or if not at least good in the other spot.


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## CraigRobbo (Feb 14, 2010)

Moonfly said:


> Have you double checked the speakers are in phase etc. Is there no position in the room you have tried the sub where it sounds good in both sitting positions.


Yeah tried the phase thing thats what i thought at first - I even tried taking the mains out altogether and still no joy.

The sub i have tried in every possible position and location you can think of - Even in the dinning room!

Do you fancy popping down and having a look maybe Dan?

Craig


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## Moonfly (Aug 1, 2008)

I might be able to make time, but before that, is there any position in the room you have put the sub that has sounded good in the current dead spot, even if it ruined the response in the current good spot.


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## CraigRobbo (Feb 14, 2010)

Moonfly said:


> I might be able to make time, but before that, is there any position in the room you have put the sub that has sounded good in the current dead spot, even if it ruined the response in the current good spot.


As of yet i havent been able to find any spot that has made the prime location good... 

I didnt bother checking the already 'good spots' after i repositiond i was mainly concerned witht he prime.

Thanks mate

Craig


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## Moonfly (Aug 1, 2008)

If it is indeed as bad as it seems, then thats a dead spot and will stay dead, by the sounds of things even with a second sub. All you can try is something with the room acoustics or moving the sitting position. Brian is better than me re the room acoustics. You could really do with getting REW up and running as well so we can see the systems response and compare sitting positions.


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## CraigRobbo (Feb 14, 2010)

Moonfly said:


> If it is indeed as bad as it seems, then thats a dead spot and will stay dead, by the sounds of things even with a second sub. All you can try is something with the room acoustics or moving the sitting position. Brian is better than me re the room acoustics. You could really do with getting REW up and running as well so we can see the systems response and compare sitting positions.


I had a feeling it was all in the room (so to speak)

Would you be able to bring your mic & setup down as i havent got anything that could really do it (or any clue on how to use the software ! LOL)

Would be greatly appreciated!

Craig


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## Moonfly (Aug 1, 2008)

I could bring the mic but I dont have a portable machine that can run REW anymore. Finding time would be the hard thing. Check you have a machine you can run REW on and we can work something out.


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## CraigRobbo (Feb 14, 2010)

Moonfly said:


> I could bring the mic but I dont have a portable machine that can run REW anymore. Finding time would be the hard thing. Check you have a machine you can run REW on and we can work something out.


I would think my laptop can run REW - its fairly powerful

Jump on MSN and we can have a chat on RE to it.

Thanks

Craig


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## Moonfly (Aug 1, 2008)

I can try fit some time in, but Ive been really short on that lately as work has picked up and I need to work all I can due to the worst 6 months Ive ever had. Ive not been online much for the same reasons.


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## CraigRobbo (Feb 14, 2010)

Still having no joy with this guys - I have tried putting a big rug/quilt on the floor to help soak up some audio, i have tried putting a sheet behind me, i have sat the sub on rubber feet, tried sitting it on concreate blocks - Nothing has helped thus far...Help?

Craig


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## Moonfly (Aug 1, 2008)

You need to get REW up and running so you can see the issues. You can then better focus your efforts etc.


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## CraigRobbo (Feb 14, 2010)

Moonfly said:


> You need to get REW up and running so you can see the issues. You can then better focus your efforts etc.


Thanks Dan.

At the mo I cannot afford a microphone, iin honesty -I havent got a clue how to use REW or even how to interpretate the outputs / results it gives or how to imply them to help.

Craig


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## poldus (Nov 14, 2010)

Had exactly the same problem. Most likely a width mode. Nothing would make it usable as a listening position. REW revealed a big null from 30 to 20hz. Just move away from that spot since there is no viable amount of room treatment that will overcome it.


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## Kaisergrendel (Jul 19, 2011)

CraigRobbo said:


> Thanks Dan.
> 
> At the mo I cannot afford a microphone, iin honesty -I havent got a clue how to use REW or even how to interpretate the outputs / results it gives or how to imply them to help.
> 
> Craig


I'm curious about this, do they have to be ones meant to be used for measurement and nothing else, and how much do the cheapest ones cost?


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## SAC (Dec 3, 2009)

poldus said:


> Had exactly the same problem. Most likely a width mode. Nothing would make it usable as a listening position. REW revealed a big null from 30 to 20hz. Just move away from that spot since there is no viable amount of room treatment that will overcome it.



Yes, you are most likely dealing with is a modal null which are determined by the massive room boundaries.

Small signal equipment variables are superfluous to this issue.

The only practical solution is to relocate the listening position. Note that the center of a rectangular room is a region rife with null issues - hence the growth in generalizations such as the 38% rule (which is NOT a 'rule' but a suggestion) suggested to help folks avoid such issues. 

In the design and construction stages there are methods by which to alter the modal spatial distribution, but neither treatment, nor changes in equipment, nor processing are going to solve the null.


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## bpape (Sep 14, 2006)

Agreed. Within practical limits, you're not going to totally address the nulls with treatments when they're very low in frequency and modal in nature. The best thing is to avoid listening where they occur. 

I prefer to broaden the 'suggestion'. While 38% is theoretically optimal in a perfectly rectangular, perfectly rigid, perfectly empty space, no rooms really are that way. A vast majority of the time (not always), somewhere between 33 and 38% of the room tends to get you the best results.

Bryan


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