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View Full Version : What room issues can affect visible woofer excursion and lack of bass?



mech986
02-06-2017, 01:17 PM
Have been on a somewhat confusing thread on AudioKarma about lack of bass (and a fixation on visible woofer movement) in a fellow's home when he moves speakers from a smaller room upstairs to a somewhat larger but much less sealed living room downstairs. I've offered many possibilities about why this may occur but he seems to have covered most of the issues except room treatment, and an adjoining room with 20 pairs of speakers for comparison and playing around purposes (with apparently the other wall to also be covered.

Any thoughts on why this guy can't get the bass response he want? And why apparent visible woofer excursion (not that it always contributes meaningfully to bass response or the "SLAM" that he wants) is affected by moving speakers from room to room, or in the below comment, lifting from floor to on top of another speaker?

Thread:
http://audiokarma.org/forums/index.php?threads/lack-of-bass.755097/

"I do have several decent EQ's but at this point they've not been set up here. On the A-700 amp, I'm using the tone bypass button, and did when I tried it in the living room as well. The SX1080 doesn't have that option but it does have a loudness lever which is always off. I've already seen the obvious change in woofer excursion on the Mach One's and JBL CF150's by simply raising and lowering the speakers in the living room, what I don't get is why the change. I'm not touching the volume or other controls, I'm simply picking the speaker up and placing it atop the TZ-9 tower, (with a piece of shelf liner in between so as not to scratch either speaker). The change in woofer movement is obvious. The volume knob is usually at about 9 o'clock "

My head hurts a bit from trying to follow this guy's equipment obsession and lack of desire to simplify things from a troubleshooting aspect.

Bart

grumpy
02-06-2017, 02:19 PM
In a nutshell, I'd say LF loading (or unloading) is causing the difference; this would include
speaker placement as well as different room dimensions. Apologies if this is discussed in the
referred to thread (as I don't have time right now).

A google search on "bass driver loading boundary reinforcement" produced this material,
which may be of interest.

http://arqen.com/acoustics-101/speaker-placement-boundary-interference/

emilime75
02-06-2017, 08:40 PM
I clicked the link with the intention of reading the entire thread...but just from his first post, I decided I have much better things to do with my time. It's pretty clear he isn't very knowledgeable and isn't an "audiophile" by any standards. Nothing wrong with that, it just is what it is.

Why 1 system has more bass in one room than in another is simple, room modes at the LP(listening position) due to room dimensions, speaker placement and location of the above mentioned LP will greatly affect the "thump" one hears and feels.

His comments on moving a speaker around and witnessing a change in excursion without any other changes in the system...well, I'm willing to bet something does change, most likely the volume knob. Every time he moves it he could easily be exciting different room modes causing different nulls and peaks in response. If placed into a position where it's causing a null at the LP, he's likely turning up the volume to try and get more bass from the system, causing the woofer excursion to go up while not actually hearing any greater bass response.

The statement "The stock radio in my work truck has more thumping bass" leads me to believe he thinks boomy, inaccurate bass response is what things are supposed to sound like, so there's a good chance many of his various speaker/amp/receiver/whatever combos actually sound great, just not to him.

Way too many variables there to even think about trying to figure this out for him without being there and hearing things, plus his evident lack of knowledge...save yourself the time...unless he's like a friend or something...

remusr
02-06-2017, 11:13 PM
Is it possible they are now connected out of phase?

Don C
02-07-2017, 07:18 AM
If he's changing the location of the speakers relative to the turntable, that could cause his trouble. Pointing it at the table or pointing it away. Or just putting the two close to each other. I've even seen people put the darn table right on top of the speaker. Some folks should just stick to digital.

Earl K
02-07-2017, 08:42 AM
Acoustic Feedback ( via the turntable ) can explain the observed excessive cone movement ( as Don has pointed out ) as a speaker is coupled>decoupled from the feedback loop .

A ( simultaneous ) lack of coherent bass can be explained by having an effective system of diaphragmatic bass absorbtion (https://www.google.ca/search?q=diaphragmatic+bass+absorbers&rlz=1C1CHBF_enCA703CA703&tbm=isch&tbo=u&source=univ&sa=X&ved=0ahUKEwjmp9PGsv7RAhUq4YMKHcRDDw8QsAQIMQ&biw=1264&bih=683)( ie; 20-40 pairs of unused wooferage, stacked against 2 walls within the pressure zone > all tuned to various box frequencies > & now acting as bass traps ).

:)

Mr. Widget
02-07-2017, 10:36 AM
My head hurts a bit from trying to follow this guy's equipment obsession and lack of desire to simplify things from a troubleshooting aspect.
Yeah, mine too. Thanks for sharing. :banghead:


Widget

JeffW
02-07-2017, 12:08 PM
Ditch the turntable until you get the room/system sorted. I haven't read the thread, but judging from the replies here it sounds like he has a turntable in the mix.

I think it's hard for people to wrap their head around what turntable induced woofer pumping is/looks like. The first time I experienced it, I had just dug an old turntable out to give a few old albums a spin. I had grills on my speakers and only noticed something was out of whack when the meters on the amp started going up and down, and not in sync with any bass content. It was slow enough that I couldn't perceive it as bass - lots of cone movement with zero added low end in the music. The power needed to make the cones move like they were would have made very loud sound had it been a little higher frequency. And it wasn't acoustic feedback, the music wasn't playing loud at all.

If I had been having "bass issues" and saw the cones moving like that and not hearing any bass, it might have led me to think something in the room/speakers was out of sorts. Luckily, my current turntable set up suffers from none of that and I can crank albums up with reckless abandon. I don't know if this has anything to do with the system in question, but it was enough to convince me that (most) turntables probably aren't the source you need when chasing this sort of issue.

mech986
02-07-2017, 12:53 PM
Thanks for the many replies folks. Here are some follow up results to my questions, some of which don't seem to make logical sense at first.

Fellow swears he has checked polarity conscientiously numerous times so doesn't feel polarity or phase issues are the problem. Although I've not had him give us a report on actually testing that as requested.

He doesn't use a turntable in either system, only a CD player. The acoustic feedback or table/arm/cartridge resonance is something we discussed with him.

i agree with EarlK regarding the distributed bass trap of the adjoining room speakers. The other issue is the fact there are two arched openings in his living room which bleed off acoustic energy easily. But the guy is part gear head and intends to keep bringing in more speakers to the next room, says he's intent on filling the other wall with another wall of speakers. He stated recently he's tried to cover / plug the arched openings with sheet styrofoam on plywood but did not notice much difference in the bass response, only getting more treble back due to reflections. He does have a few heater and vent registers in the room, and can't leave the area plugged because of lack of heat flow.

He stated he's taken the exact same speakers and system electronics from the upper room to the lower room (using stereo only components) and observed that cone motion or loss of same after doing so. Problem is, he hasn't yet responded to requests to change his layout or setup positioning much because of the constraints he's already dealing with. He has stated he uses no tone controls, bass boost or loudness, switched amps multiple times and found differences but not a lot of improvement, working with 50 to 150W amps and receivers.

He's apparently a 60 y/o guy, likely lives alone but in an urban area where gear and speakers seem plentiful. He has not responded to my question of location (where we might get another AK member over to listen to confirm). He claims to have been hearing tested a number of times over the last 2 years and says despite having worked a long time in a noisy environment, he's been told his hearing is still pretty good, able to hear 40-15khz (no curves or graphs shown so IMO that's not going to be a flat response).

JBL content - he said he could not get a pair of JBL L112's to make any bass or "slam" in his living room, which I thought the L112 should be able to provide, at least on a direct axis basis, with ease. He does say he has a pair of either JBL L250 or 250Ti speakers waiting to be put into the system to test. If he says they don't work either, something IMO is seriously wrong with his system, his setup, or his room, or all three together. IMO, even in an anechoic environment, the L250 should be able to get you a solid bass response.

ordinarily I would think this guy a troll, but he has not been argumentative in the least, and does express bewilderment at why this room doesn't seem to work. He has not yet responded to our suggestions about trying to find and work out room nodes.

lastly, and perhaps telling, he says he used to, paraphrasing here, work in a club with a killer sound system consisting or stacks of JBL multi woofer towers with horns on top, each driven by monster amps, and that had "slam" in spades, so he's using that aural memory as a reference basis. Of course, he can't have nor wants the same speakers or sound output as his neighbors are 35 feet away, not the 1/4 mile as in his old residence.

IMO, and I've suggested it, is to simplify the systems under test, remove the speakers in the adjoining room (or at least short all their terminals), he has them set up to a demonstrator type switching system with 4 amps for "stero store"-like comparisons. But that hasn't happened yet.

sigh, it just eats at me to not be able to figure this out quite yet. There's always a potential DSP solution I Suppose.

bldozier
02-07-2017, 05:37 PM
Your sure it's not the Mary jane
interesting thread

remusr
02-12-2017, 11:12 AM
I have encountered an Internet phenomena - controversial nonsense discussion with no intent to confirm suggested solutions. Pure mindless entertainment for some. Timewaster for others. Could this thread be an example?