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Weird Bass Reponse on my Speakers.

I just got a Talon ROC 2002 subwoofer dedicated mainly for 2-channel system. I tried to setup crossover point by using Radioshack SPL meter to find out what frequency that my Sonus Faber Extremas started to dip. I got weird results using Stereophile Test CD 1 (1/3-octave warble tone at -20dB). Here they are(SF Extremas only no subwoofer).

Frequency----------------SPL Meter Reading
1KHz--------------------->70 dB(reference level)
200Hz-------------------->62 dB
160Hz-------------------->63 dB
125Hz-------------------->58 dB
100Hz-------------------->52 dB
80Hz--------------------->53 dB
63Hz--------------------->60 dB
50Hz--------------------->70 dB
40Hz--------------------->61 dB
31.5Hz------------------->55 dB
25Hz--------------------->52 dB
20Hz--------------------->below 50 (unmeasurable by RadioShack SPL meter)

From the readings above,SPL readings started to dip at 200Hz(62dB) until it reach 52dB, which has the lowest value, at 100Hz and climbing up to 70db(reference level) again at 50Hz. And then I got lower dB as the frequency went lower.

So, I set the crossover frequency of my sub at 40Hz. and the SPL reading for lower-bass after combining subwoofer are:
(Upper Frequency responses are still the same)
50Hz---------------------->70 dB
40Hz---------------------->70 dB
31.5Hz------------------->70 dB
25Hz---------------------->68 dB
20Hz---------------------->54 dB

Here are my question:
1. Is the dipping between 63-200Hz and going up at 50Hz considered normal?
2. Is there anything wrong my speakers? Could it be other tube gears or my room that make cause this problem? (My listening room has no left wall at all)
3. How's your opinion on Lower bass responses after combining the subwoofer?

I'm pretty happy with the result musically but I think mid-bass responses might still be the problems for me.
My equipments are:
CDP: BAT VK-D5SE
PRE: BAT VK-5i (w/ Amperex 6DJ8 orange globe tubes)
AMP: BAT VK-60

Thanks for looking!
ted263
sol322
426 posts
 
Ted:
You definitely have very nice equipment .
Now to the bass..
IF you have a camera tripod you can attach the SPL and set it in your chair at the same position your head is and measure / writing results easier ...... see following comments below
1-First try to measure again at higher volume. At the low levels you´re measuring outside noise might be affecting the readings and with more energy in the room your results can spread better and be closer to the actual SP you get under listening conditions. Go to let´s say 85 for the 1 kHz and repeat your measurements with and without sub as you did before.
2- Repeat the same FOR EACH SPEAKER (disconnect the other one taking all precautions to avoid damages!!!!!!! like short circuits) and with no sub. This will provide you with information on the different response you get at each speaker position in other words you´ll know your enemy better). As you pointed out the room is not symetrical so don´t expect to get even bass response specially not having a wall in one side, hey I also live in the less than perfect real world room most of us do..
3- As Chilidog says each room / setup is different. Mine is a rebel I´ve been trying to tame.....
Move your listening position i.e. measuring point one two feet forward and backwards and you´ll notice changes in the bass response, hopefully you might find a better place for your chair/speakers combo that will be more satisfying.
Don´t dispear have patience be methodic on your approach keep a log and have fun!!!
Luis
rives
953 posts
 
Clearly there's a dip around 100Hz (at least at the listening position). Although the Radio Shack SPL meter is not linear (we make a CD that corrects for it's non-linearities)--it's not THAT far off. Now the question is why do you have that dip? Chances are it is a null at your listening point. You can measure this by setting your CD player to repeat the 100Hz tone. Then walk around the room and plot the response of the 100Hz at different points. If you're listening point is in a null, the solution is pretty simple--you need to do some shifting of speakers and listening position (I say simple, but it really isn't that simple, because it will likely cause a null at another frequency). CARA software can help with this, they look for optimum positioning with the least nulls and peaks. You can also use the rules of 1/3 and 1/5 that tend (not always) minimize these problems as well. Lastly, our website offers some help on speaker placement at www.rivesaudio.com It's in the Acoustical Issues Section--go to the listening room and select speakers. There's a download there for a short paper on placement, but I have to admit it does not have a lot about peaks and nulls (we should probably update it some).
If your problem is not caused by a peak or null, then it could be the room construction. Some rooms flex in such a manor that they actually create their own notch filter. Fortunately, this is typically not too difficult to fix. First you need to find out which part is creating the notch. In my experience it's usually the ceiling or floor of an older type house. The older construction allows it to sag and flex and essentially soak up a particular frequency--kind of like a resonator. Basically what ever it is needs to be re-enforced and made rigid. This can be easy in some houses, but difficult in others.
Hopefully, the problem is just speaker and listening position.
lugnut
1,190 posts
 
I believe it is Rives that offers a test cd that is calibrated to compensate for the Radio Shack SPL meter. Hey, I don't know if I stated that correctly but hope you understand the intent.
sean
6,231 posts
 
Follow this link. It is a step by step program on how to correct the frequency response irregularities of your analogue RS SPL meter. I have done this to a few meters and it works MUCH better. Combine this with using a higher grade external electret mic and you've got a very good SPL meter for well under $75 total. Sean
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