Adding Subs. My observation.

[Chienmortbb]

I bought some speakers from @Phil Starr about a year ago, Two Wharfedale Titan 12" Active tops plus two JBL 15" powered subs. I have used the Wharfedale Titans before on their own but wanted to try them with the subs. The subs have a built-in LPF/HPF, but I still set the mixer output with an LPF/HPF centred on 100 hertz and fed the tops with an HPF with -3db at 100Hz.
 

When I switched the system on, there seemed to be little bass but inverting the sub signals brought in the low end. I was surprised by two things. Firstly, the sound was so much fuller but secondly, the increased low end seemed to be coming from the tops. The overall sound seemed much louder.

 

I had the subs together in the centre and used a selection of music recorded before they started compressing the heck out of recordings. The final test was to remove the HPF/LPF from the subs and rely on the internal filters. I could not really hear any difference between the internal filters and the one in the digital mixer.

[Phil Starr]

For anyone who doesn’t know them the Wharfedale Titans are little gems. 12” tops that only weigh 10kg, go as loud as anything and with a lovely clear vocal sound. They use the same horn driver across the range so this bargain basement speaker benefits. They make a great vocal PA but the lightweight cabs aren’t good with high bass levels. Not a problem with a sub.

 

You’d expect to ‘hear’ the bass apparently coming from the tops. Your brain takes the information from your ears and creates the picture of a band playing. You can pick instruments out of the mix and with stereo even place them in space but it’s all illusion. The brain takes the signals from all four speakers and ‘tells’ you there is a bass guitar just to the left of the drums. It’s wonderful when you are listening to music but the brain constantly confuses you when you are trying to be objective about sound.

[Bill Fitzmaurice]

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the increased low end seemed to be coming from the tops.

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You’d expect to ‘hear’ the bass apparently coming from the tops. Your brain takes the information from your ears and creates the picture of a band playing.

What's happening is that the low frequencies from the subs are not directionally locatable, as their wavelengths are too long compared to the distance between your ears. Really. Binaural hearing allows us to triangulate sound source locations only when the wavelengths are short enough so that the ear/brain can detect the difference in the arrival times at the left versus the right ear. That occurs on average above 100Hz. Since we can't tell where the low frequencies are coming from we take the directional cues from their harmonics, which are coming from the tops. This is what allows us to place subwoofers away from the tops, in both live sound and home theater. My HT folded horn sub sits 30cm to my side in my living room, where it does double duty as a table. My mains are 3 meters in front of me. I cannot tell that the sub is next to me, the bass seems to be coming from the mains, even when movie low frequency sound effects are reaching 120dB.