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Discussion Starter · #1 ·
I am new to the home theater scene so I decided to trust the manufacturer Onkyo. I purchased the 990THX home theater in box. From what I understand the crossover has been tuned (and is permanent) for the THX environment. Lately I have noticed some bad sounds coming from it. I hear a crackling/popping sound during certain frequency ranges of a movie. Usually some low rumble in the background of something like Battlestar Galactica with its ship engine in the background. I would almost describe it as a rattling of a broken speaker. Or I wonder if its being sent a frequency out of its range (so the crossover isn't working)


Any tests I can run on a sub? Any clues or suggestions?
 

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Sounds like you are bottoming out the sub. That happens when you over drive the speaker with too high of volume or too low frequencies. You either need to turn it down or possibly have to get an in-line subsonic filter that will block low frequencies that are below the subs low end rating.

You can get a CD with test tones or sweep tones that go down to 20Hz to see how low of frequencies your sub can handle.
 

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ransac


You know mate that was one word on the tip of my tongue (bottoming out) makes my skin crawl it does.


Johne_G




Now I have been running Kenwood KRF-X9050D THX select AVR for 6 years now! But there are many approaches I take with the playback of films.


I can playback films at (0db) but that's only with the use separate amplification audio limiters for the three-screen fronts and equalizers for all the loudspeakers in the room.


It would be very rare for me to (bottom out) the two sub bass units that I'm running, one for what I call (sub bass extension) where all the fronts and surrounds low end passes though series of low pass filters and onto an audio mixer, (LFE.1) is also sent to the mixer and is amplified and played separately away from all other sub bass frequencies where they tend to over taxi the sub bass
and worse I have noticed degrading in the reproduction in the room.


So what type of films have you been playing for it to (bottom out) on?


Tell what type of films and I'll see if I have them and I'll run some tests, I also need to know which part in the film the problem first occurred at?


One other important note is, have you engaged the (THX bass manager) to on and worse I doubt you have read the owners manual thoroughly otherwise you wouldn't be bring this matter up. No matter its good that you have this might be a reminder for those who skip though the user manual at warp speed and miss some vital information.


Or worse the manufacture is negligent in providing this information.


Before turn (THX bass manger) on! where it will produce a raw output of pink noise, and if your not careful with firstly turning down the sub bass units volume to minimum and with the setting of the fader set to (0db) grandly and very slowly turn the volume up on the sub bass unit while looking at the (SPL db level) make sure the metre is placed at the listening position and set for varies levels to start of with.


65dbc 75dbc and 85dbc. But before adjusting the level of the sub bass volume, set the level of the (THX bass manger) to around (-10db).


Still get back to me I'll be online all day and will go though this, one step at a time.
 

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Discussion Starter · #4 ·
ok, so the technical term for this is bottoming out. good to know. It happens in all movies now. Last night I noticed it in Ultraviolet.


I actually did read the manual. Its a small 64 page manual. Before purchasing this system I read several reviews (home theater mag Nov. 2006 is one) and they mention that the crossover is fixed, there is no crossover bybass, only a output level on the sub. The max level on the output of the sub is also the "THX Position" This system was tuned for THX. I don't think there is a fader. I don't have any controls over frequencies go to speakers. I tried the movie scenes with different equalizer presets and they ALL (stereo, movie, ProIIx, ProIIx THX) have the same sub problem.


I was under the impression with the reviews that this system should already be configured to its optimum and I should not need to change any settings.


I found the article from home theater mag. Maybe this chart of frequency response will help?
 

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Ultraviolet, I haven't got that one so there's no way for me to test it out to see which part of the frequency spectrum that's cursing the sub bass to bottom out.


What level do you play the films that is indicated in db on the Onkyo's display?


Give me another to look at that you have in your collection and providing it's still cursing (bottoming out) snags I would turn the volume down on the sub bass slightly before it goes completely!


Adding to this, well I'm not nearly at a loss for words, the sub I would say your overloading it. Did you check to see if your (THX bass manager) is engaged, as this will prevent it from being overloaded via the excessive output from the sub basses output. Are sure there THX is fixed at 80Hz and there is no way of switching it to large that is if you wanted larger loudspeakers you can use the RCA phones and add separate amplification and other audio processor.
 

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Discussion Starter · #6 ·
There is no THX bass manager mentioned in the manual. I can mess around with the receiver. Any suggestion of how to find it? Do you have Pirates of the Caribbean, Dead Mans Chest? I just purchased it and can watch it tonight to see what happens. I usually hear it in quiet scenes where I wouldn't even expect to hear any bass. Its like the wrong frequencies are going out the sub.


I have been playing it at only -30db. Ofcoarse THX recommended setting is listening at 0db.
 

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I'm not saying for sure it is bottoming. Bottoming is when the cone excursion is greater than the physical stops. This is where the VC former is banging into the end cap. Not good.


When I have bottomed subs, it is a frightening sound. Like a loud clack. Makes you dive for the volume control to turn it down. It can result from frequencies that are lower than the sub can handle or the volume is too high. This is where subsonic filters or limiters come in. It is possible your AVR is supposed to provide the SS filter as this is a system and not a component set up. I suggest you call Onkyo support or contact the store you bought this from. You could be hearing bad amp noise being transmitted to the driver. anyway, if you aren't running hot and you don't have much control over the settings, then you should call for support.
 

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Discussion Starter · #8 ·
my volume setting is low and I only notice it in scenes that aren't very loud. from this discussion it appears to be a filter problem. the very low frequencies aren't being blocked. like the low rumble of the background noice in battlestar galactica.
 

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It is possible that it is a signal problem. Noise on the signal getting to the amp, getting amplified and reproduced by the driver. So it sounds like a bad driver, but is really a signal issue. Unplug the sub cable at both ends and reconnect using a twisting motion to ensure a tight, clean fit. Other than that, you would have to use the process of elimination. Connect the sub to a different AVR and play a DVD to see if it repeats. Plug a different sub into your AVR, play a scene and see if the noise repeats. If you are running very low, I'm starting to believe it isn't the sub.


Of course, being an HTIB, and no offense intended, it could just be a really crappy sub.
 
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