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Author Topic: Subwoofers and SPL measurements Sam D. Chavez Film God Posts: 2153 From: Martinez, CA USA Registered: Aug 2003 posted 12-05-2019 09:39 AM                       It is hard to determine the location of the Lfe subs in most systems but I had one instance some years back where we made use of leftover subs from Sensurround located in the left back and right back of the large house. Every time a low freq. effect occurred it was clear the subs were behind you and the audio reached your ear before the main audio. It wasn't subtle. An extreme case with W horns but...  |  IP: Logged Frank Angel Film God Posts: 5305 From: Brooklyn NY USA Registered: Dec 1999 posted 12-05-2019 10:29 AM                        As always, thanks guys. The Dolby Stereo Technical Guidelines is a big help. In these particular college Screening Rooms, the subs are going to be free standing in the front corner of the room, no other location possible -- that's a good thing. Adding a second unit next to the one is a possibility if need be. The coupling effect when putting them in close proximity is indeed quite dramatic. We did this with two JBL 18in subs in Community fiberglass enclosures and the output rose nearly 25% when they were moved next to each other, if memory serves.  |  IP: Logged Marcel Birgelen Film God Posts: 3357 From: Maastricht, Limburg, Netherlands Registered: Feb 2012 posted 12-05-2019 11:18 AM                     quote: Sam D. Chavez It is hard to determine the location of the Lfe subs in most systems but I had one instance some years back where we made use of leftover subs from Sensurround located in the left back and right back of the large house. Every time a low freq. effect occurred it was clear the subs were behind you and the audio reached your ear before the main audio. It wasn't subtle. An extreme case with W horns but... Yeah, but what you're describing, while obviously related, I'd personally call another issue. I'd say it's a general audio sync issue (a "lip-sync issue" but now for the low frequency domain only), which will be much more evident in larger venues. But even the timing of the stage speakers can become challenging in such venues. Generally speaking though, ranges between -100 ms to +25 ms should be pretty much undetectable for human beings. If you move beyond that domain, the issue will eventually become so irritating to many people, the localization of the actual sound will play second fiddle to that irritation. Still, I think that in that same venue you're describing, you would've a hard time giving the subs an exact location (without obviously knowing their location beforehand). While the capability to localize a sound drastically reduces at the lower end of the audible frequency domain, I don't think the frequency-range of a particular sound has much impact on the way we perceive "async audio". Another thing to account for though (audio is a never ending accumulation of interesting challenges): If there is a large delay between the stage speakers and the subs, is the potential combing / destructive interference you can cause on the overlapping spectrum, especially if you do bass management  |  IP: Logged

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