To take a pro 18" down to 20Hz

[technofreak]

I've been playing around with Equalizer APO for a few days to get room modes under control. Main culprit is 39 Hz boom. Also needed boosts at 24, 45 and 87 Hz (the last null being impossible to get totally rid of).

Overall, I'm pretty pleased with that driver; it blends in with the mains seamlessly, has good efficiency and very life-like sound with no audible distortion even below 20 Hz. The end result is this (no smoothing applied to graph):

 

[Inductor]

I'm very curious about your last impressions. I will check about a more tight alignment, what should be Fb (?) for the same Vb (364L from #23). The peak is a blueprint from frequency of driver, symptom not that problematic with smaller volume probably (but a different project from yours.) What's the size of your room or venue?

 

[technofreak]

Hi Inductor,

My room is about 4,5x3,5 meters, listening position is about 1,4 meters from the back wall. If you run the numbers, the first axial mode is right at ~39 Hz. The null at ~45 Hz seems to be the second axial mode. And all these peaks and nulls have been here with any speaker setups

Here's a plot for different box tunings (~19 Hz as built, 25 Hz and 30 Hz), 30 Hz is optimal for maximum total SPL view, but, like all things in audio, it's about what compromises you are willing to make. I also added comparison between EQ-d and non-EQ-d response at listening position:

 

[Inductor]

An alignment of 364L Vb and 12/14Hz looks like a viable option. This driver does subsonic fr easy go to 15 Hz with 800/1000W RMS power in speaker installed (ref 900/1800W from spec).
Dayton Audio RSS460HO-4 18" Reference HO Subwoofer 4 Ohm
Taking the driver/CABINET SIZE/port to your spec, 364L/Vb (calibrated) u have (below). Have fun

(1) with (4x) port 10.3 cm (diam.), 14.0 Hz
Surface : 333.29 cm2 - length 126.26 cm

(2) with (3x) port 10.3 cm (diam.), 14.0 Hz
Surface : 249.97 cm2 - length 92.70 cm

(3) with (3x) port 10.3 cm (diam.), 15.0 Hz
Surface : 249.97 cm2 - length 79.18 cm (port resonance 217 Hz)
F-6 dB/F3 in room: 13.8 Hz
SPL 1m/1 speaker (60.54 V/812.4 W): 119.2 dB with thermal attenuation 114.5 dB.

Hi, Inductor,

364 is the net volume (driver, ports and bracing subtracted). Ports are 110 mm external (103 internal), sorry for mixup, I posted that while tired of a day full of woodwork. I aim for 18 Hz Fb.

And yes, home theater will be on the usage list of my sub.

 

[technofreak]

Yes, that Dayton is a great driver, pity it's so expensive here in Europe (261.78 USD on Parts Express; 384.54 EUR/412.65 USD on Europe Audio). And no other drivers that could match its U.S price while performing similarily, either.