View Full Version : Wavelength and reinforcement!

JBL 4645
09-06-2006, 11:18 AM
You’ve got the matching three-screen in place you’ve done the basic test tone test using the (wideband pink noise) and now you’re about to play the first of many demonstration test films all seams well you’re friends come around you place the same film in the DVD player the show is running smoothly but one of you’re friends is untested by the sound?

Afterwards you ask him did it sound good, and the answer was something was missing?

You’re slightly puzzled as to why? what could possible be wrong with the placement of the three-screen loudspeakers there brand new they have fairly large drivers in a large enclosure, what could be wrong and the answer is staring straight at you!

Play a sine wave tone in the low range between 60 and 100Hz over the left and right separately they should equal the same SPL db level when read by an SPL db meter, say 80dbc for example! Now play the same tone over the matching centre channel, the signal should read a rather less reading on the SPL db metre, and if so don’t worry.

Now place the centre channel in the same position as the one of the left or right loudspeakers. Now play the low frequency sine wave tone and note the SPL db level on the SPL db meter, it should read the same level!

Now this is due to wavelength of the frequency and it’s placement in 3-dimensional space across the front, plus the basic limitations of the loudspeaker dynamic frequency range to reach the listen position with very little strain place upon it.

Now you could move the centre channel back up against the wall, this will magical increase the wavelength and maximise the reinforcement of the centre channel, how it is placed and what it is placed on including the other two matching loudspeakers placed on the left and right is entirely up to you.



Pictures taken this morning!

Last night was “Troy” what grand epic of the historical battle that took place some 3200 years ago now long fader into a memory but those giant gods’ names will leave till the end of time!

The battle scenes where eye opening to create has much of it in camera and then add the rest in with CGI effects to take it even further was mind-boggling.

The sound was top 10/10 dialogue placed at the centre on the JBL control 5 was more felt than heard! It griped me to the showdown of “Troy” and Brad Pitt voice shouting out “Hector!” was very realistic 90dbc, just a bit loud you might think, but the frequency response and range was nicely equalised by the re-recording mixers, it had the right balance of being outside the gates of Troy.