# Bass Trap Advice Needed



## MarkyM (Dec 10, 2010)

Hi,

Here is a sketch of my basement HT/listening room:









Obviously, not ideal for acoustics and I am breaking several rules of thumb here. But this is what I am stuck with so I'd like to make it sound as good as possible at the primary listening position (the "X").

I already have treated the area under the stairs where the system is located with 2" Auralex foam and LENRD bass trap foam wedges. Also, the wall and wall/ceiling corner just behind the listening couch is also treated as above.

Here's a pic:









I have used REW and have a BFD so have equalized the main peaks from the SVS PCI 20-39 sub below 80 Hz so the low bass is now pretty smooth.

What I have now at the main listening spot is deep cancellations between about 125 and 175 Hz.

Would strategic placement of some bass traps that are effective absorbers in this frequency range help to reduce these nulls?

I am suspecting that the low ceiling directly between the listening area and the speakers may be part of the problem. It is drywall boxed-in ductwork.

Thank You Very Much in Advance!

--Mark--


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## bpape (Sep 14, 2006)

The Auralex really isn't doing much in the low frequencies. The first 2 things I would recommend is getting the sub out of that low area behind the speakers and getting the seating away from the wall as much as you can.

Bass control can certainly help but we need to have a good starting point and identify specifically where the cancellations are coming from. I would suspect that doing the 2 things above will help somewhat.

Bryan


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## MarkyM (Dec 10, 2010)

Thanks Bryan,

But as I said in my post, the bass below 80 Hz is OK now. And the LENRD bass traps ARE working. 

This has been there since 2002 when the basement was built-out, but I am doing some upgrades to the system now. 

As I remember, the LENRD wedges made a huge difference. The system was unlistenable before them. There were bass nodes and echoes all over the place before. 

There was a large peak between 40 and 50 Hz that the BFD removed nicely. I was able to get the response pretty flat below 80 Hz (with only 3 filters active on the BFD) with help from Wayne over on the REW forum.

Here's the graph from REW with both the sub and mains on:









As you can see, not too bad below 80 Hz but there's that massive null at 140 Hz and a couple of smaller nulls to either side of 80 Hz.

If I move forward about 24" (closer to the optimum 38% point from the back wall), things are smoother but I really don't want to pull the furniture out that far into the room for many reasons, one of which is that the speakers would be too far apart then and they really can't be moved in towards each other much.

As I said, I am stuck with the room configuration as it is. 

It doesn't sound terrible (I have been living with it for 8 years) but I am wondering now how it could be improved at the primary listening location. 

From what I've read so far, I need to find out where the cancelling reflections are coming from and locate traps there. I just hope its not from that low ceiling between me and the speakers since there's no room there for anything too thick.

Thanks,

--Mark--



bpape said:


> The Auralex really isn't doing much in the low frequencies. The first 2 things I would recommend is getting the sub out of that low area behind the speakers and getting the seating away from the wall as much as you can.
> 
> Bass control can certainly help but we need to have a good starting point and identify specifically where the cancellations are coming from. I would suspect that doing the 2 things above will help somewhat.
> 
> Bryan


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## bpape (Sep 14, 2006)

Well, the first thing I'd do is check your levels. Looks to me like the sub is high compared to the rest. While the null will still be there, it will at least be in the same range as the rest. Looks like the sub is maybe about 6db too hot.

It would be very easy for a harmonic at 70Hz in the cove area to be causing part of the cancellation - hence my desire to get the sub out of there if possible.


Bryan


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## MarkyM (Dec 10, 2010)

Thanks Again Bryan,

The only other possible location for the sub would be just to the right of the front right speaker.

I'll try that if you really think that will make a big difference.

--Mark--



bpape said:


> Well, the first thing I'd do is check your levels. Looks to me like the sub is high compared to the rest. While the null will still be there, it will at least be in the same range as the rest. Looks like the sub is maybe about 6db too hot.
> 
> It would be very easy for a harmonic at 70Hz in the cove area to be causing part of the cancellation - hence my desire to get the sub out of there if possible.
> 
> ...


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## bpape (Sep 14, 2006)

I'd give it a shot and see. Doesn't cost anything to try it.

Bryan


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