[Fife12]

Was running Avia to recalibrate my home theater last night as I changed out my front speakers.

On the subwoofer test, I ran into a huge bass spike. As the frequencies started to drop, the volume started to decrease (which is normal). Once the frequency hit 60Hz, the sound almost faded.

Then at about 30Hz, my SPL meter as well as my ears heard that the speakers volume started to increase.

Does anyone know how I would fix this huge 30Hz spike?

Room size: 16 x 12 x 7.8 ft (L x W x H)
No room treatment except for large bookshelves behind listening position.
One large 8.5ft wide window on right side about 5 ft above the ground (24 inch high window). Window is covered with blinds.

Main speakers and 2 subs are 4 feet from front wall. Sofa is 4 feet from back wall. Speakers to lsitening position is 8 ft.

Bass used to boom until I moved my speakers and sofa more into the room.

When listening to music, the sound seems to be ok but maybe the bass is too much for my room as I can hear some coloring of the midrange. Currently using two 12" subs in Mono. My R/L main speakers are bolted right on the subs.

Will bass traps cure this or is this a crossover problem..?? Any other suggestions or recommendations?

TIA

[ctviggen]

To figure out whether it could be fixed with a crossover change, run the test twice, once with no subs and once with only subs.  If you can plot the results, you should see where the speakers naturally drop off and the subs pick up.  If the speakers are dropping off much higher than 30 Hz, there's not a lot you'll be able to do.  This will also help to see whether the subs are level matched with the speakers.  Another thing to do is to run the test with both subs and speakers and move around to see if you could move your position and experience less of a 30 Hz peak. Similarly, if you can move the subs, you could try that.  Another thing to do would be try one sub and running the test and then try the other sub and running the test.  (This only works if one sub causes more response than another; if you have the subs at equal locations in the room, then that's unlikely.)

If none of this works, then you're left with either room treatments or electronic techniques.  Room treatments work wonders, but they're also expensive.  This would work well:

http://www.audiocircle.com/index.php?topic=29174.0

You could use this just on the subs.  Or if you wanted to get really fancy, you could use it for your entire system.

[ctviggen]

Woops!  If your speakers are bolted to your subs, that doesn't leave much room for experimentation in terms of placement. 

[gitarretyp]

It is important to know where your speakers are rolling off, if you can control the crossovers. So, run a full measurement on the speakers and sub seperately. In my room, my mains start to roll-off ~80hz, but they're back to flat (actually, slightly above) by ~40hz, where my room has a large peak. The only reasonable (price and space wise) solution for me was an eq, the behringer dsp1124, for the sub. This way, i can essentially notch out the sub's output at ~40hz (and several other problem frequencies).

As for room treatments, i don't think bass traps will have much effect that low in frequency (unless you use a ton of them). An eq will likely be your cheapest and easiest solution. Ideally, both traps and eq would be the way to go. I'd experiment with your speaker and listening positions first, however.

[bpape]

It's most likely a room mode and most likely based on the room length (axial) or a tangential with the length and one of the other dimensions.  Try moving your seat to a better position.  Try the mic at 38% or 62% of the room length.

Bryan

[Fife12]

When using the Stereophile Guide to Home Theater Excel Spreadsheet at http://www.ultimateavmag.com/news/10388/index.html, I have only one single seating peak.

My data entered into the Excel sheet are:

Room Dimensions (inch)   Room Dimensions (ft)   Resonant Freq(Hz)

Length         194.00                       16.17                34.918

Width          150.00                       12.50                45.160

Height         93.00                         7.75                72.839

   

Seating Distance (inch)   Seating Distance (ft)   Seating Postition

From Back Wall      38.00                       3.17                1/5

From Side Wall      70.00                       5.83                4/9

From Floor             37.50                      3.13                 2/5

My speakers and subs are all THX Ultra. My fronts roll off at about 80Hz. 

Any other suggestions? Thanks

[MaxCast]

Numbers from you frequency test would be helpful to see how much spike at 30 and how much dip at 60.

Are your subs powered?
Would you be willing to separate the subs from the mains?
I don't think it applies in this case, but have you tried changing the phase of one of the subs and running a test?

eq's will help more for individual seating.
bass traps will help the entire room and "ringing" (search) but will probably take a lot.

[Ethan Winer]

Fife,

> When using the Stereophile Guide to Home Theater Excel Spreadsheet <

Take that sort of tool with a large grain of salt. The only way to really know what you have is to measure the low frequency response to a high resolution - with a bandwidth of a few Hz or less. But even that is not as necessary as you might think. Regardless of where the peaks and nulls happen to fall, the solution is still the same - bass traps.

--Ethan

[ctviggen]

It's interesting that you say you "only have one peak".  According to http://www.mcsquared.com/modecalc.htm, you have at least four axial modes less than 80 Hz.  Regardless, the recommendations I made still hold.

[Fife12]

Hi guys. Thansk for your suggestions.

Apparently I do not have a mic or EQ or software for graphing any of these.

The only thing I am going by is AVIA and my SPL meter. Using Avia, I can tell I am getting a huge spike in Bass as the volume from my SPL starts to dip from 60Hz to 50Hz to 40Hs. Then at clsoes to 30Hz, the volume increases!

What would you recommend I do to TRY to fix this without spending hundreds or dollars

Thanks

[Ethan Winer]

Fife,

> Using Avia, I can tell I am getting a huge spike in Bass as the volume from my SPL starts to dip from 60Hz to 50Hz to 40Hs. Then at clsoes to 30Hz, the volume increases! <

I don't have Avia, but if it measures no finer than 10 Hz you might as well not even use it at all because that low resolution is practically useless.

> What would you recommend I do to TRY to fix this without spending hundreds or dollars <

What, you have really expensive loudspeakers and you're worried about spending a little more money on bass traps to make the speakers actually work?

--Ethan

[bpape]

Agreed.  Treating the room is IMO the most cost effective money you'll ever spend on your system's sound.

Also, while the spreadsheet says you only have one mode, it's only measuring axial modes - not tangentials or obliques and certainly not the interaction of them, the SBIR effects of the speakers and the wall proximity, etc.

Bryan

[Glenn K]

Fife,

> Using Avia, I can tell I am getting a huge spike in Bass as the volume from my SPL starts to dip from 60Hz to 50Hz to 40Hs. Then at clsoes to 30Hz, the volume increases! <

I don't have Avia, but if it measures no finer than 10 Hz you might as well not even use it at all because that low resolution is practically useless.

> What would you recommend I do to TRY to fix this without spending hundreds or dollars <

What, you have really expensive loudspeakers and you're worried about spending a little more money on bass traps to make the speakers actually work?

--Ethan

Him and about 10,000 other people out there! I bet only about 5% of the rooms out there are treated. Kind of sad when you think about it.

Glenn

[Ethan Winer]

Glenn,

> I bet only about 5% of the rooms out there are treated. Kind of sad when you think about it. <

My understanding is that it's less than 1 percent. Which is even more sad.

BTW, how's your rock band tour going? Where are you today?

--Ethan

[Glenn K]

today???? I am sitting on a French island called Martinique. Drinking fruity rum drinks!!!!

Plane ticket - $725.00

Seeing a half naked french girls on the beach - PRICELESS!!!


Glenn

[bpape]

 

[Ethan Winer]

> Seeing a half naked french girls on the beach - PRICELESS!!! <

Outstanding!

Wish I was there ... FER SURE.

[Glenn K]

come on down!!! I got to tell you though it takes 12 hours to get down here. Flying time is 6 hours but you have to change planes 3 times and the last plane is a 10 seater!!