Dayton RSS 390 HF4 and NHT 1259 subwoofers. Relative Frequency Response in a Room. Searching for 20 hz deep bass.

[ligs]

4 minutes ago, Aadams said:

Harman does their blind testing at 78db at listening position.

 

Can you cite the reference? I happened to hit 80 db fortuitously!

[Aadams]

Here is the link courtesy of PeteB. Scroll down and watch the video if you want to see the source of the graphic below.

http://seanolive.blogspot.com/2012/

[ligs]

Thanks very much.

 

George

[ligs]

From the  measurements in the first post you can see all two subwoofers were quite flat to 31.5 hz band but in my room they dropped off at 25 and 20 hz. Recalling my old  Ratio Shack analog SPL meter has a few quirks which could help explain the measured drop off in the deepest bass. 1. C weighting of the test signal causes a drop of 6db at 20 hz. 2. The natural microphone response of the SPL meter subtracts another 4.2 db at the same frequency. So you need to add 11.2 db to the raw SPL measurement at 20 hz.. At 25 hz, you need to add 8.6db, 32 hz, 3.1 db and 40 hz , 1.5 db. Beyound 50 hz the responses is pretty level until 1000 hz and higher.  http://diyaudioprojects.com/Testeq/RadioShack_33-2050/RadioShack-Sound-Level-Meters.pdf

So after calibration for the frequency dependent response (20 to 40 hz) of the SPL meter, indeed the 20 hz response for NHT 1259 and RSS390 HF4 has raised to within 10 db of the 31.5 hz band. I guess if one really wants to have a subwoofer flat to 20 hz then you can equalize it electronically. Most subwoofer amplifiers do have built in equalizer allowing typically 6 db boost at the frequency of your choice. So theoretically I could equalize my home built sub woofers to -4db at 20 hz. That is close enough for me.

Alternatively you could apply the special Watkins  woofer circuitry(normally for 2-ohm voice woofer  coil) used in many classic Infinity Reference Standard speakers which  equalizes the bottom octave response. Here is a technical description for this technology.  http://www.cieri.net/Documenti/Infinity/Documenti tecnici/Infinity - Renaissance Speakers - Watkins woofer, EMIM, EMIT - White Paper.pdf

 

In my own case I have a setup  using the 10-inch Infinity Perfect 10.1 DVQ  subwoofer with two 4-ohm voice coils. I inserted a 20 mh laminate ERSE inductor and 1010 uf NP, (made from 4 Panasonic SA  low ESR electrolytic capacitors). As the following graph shows,  with this circuitry, Infinity Perfect 10.1 did measure -3db at 20 hz.

 

Some readers may recall that in the well written AR 9 manual, Tim Hall compared the unique woofer crossover in AR9 to an automatic transmission which applied frequency dependent boosting to the dual 12” woofers near resonant frequency. Interesting enough,  the special LC  circuit is 2500 uf and 10 mh and AR 9 has two 4-ohm woofers making it practically 2 ohms in the bass.  

Actually adding a large value capacitor to enhance the deep bass is fairly common. here is a  DIY project.

http://www.humblehomemadehifi.com/download/Humble Homemade Hifi_Black Box.pdf