t-man Posted February 15, 2002 Share Posted February 15, 2002 I'm having trouble with a big dip in my frequency response (FR) of my subwoofer. Using the Rat Shak meter and test CD, I get a real nice and flat FR of my sub from 18-55 hz. at 55, it jumps about 10 db up, and then quickly falls 20 db until it bottoms out at 75 hz. It then recovers at about 80-85 hz and remains flat. If I turn my sub OFF, and run the same tones through my mains (full range, set sub to "no") I get an amazingly flat FR from 35-100 hz. Only +/- 3 db! Way to go KG 5.5!!! The KG - Denon combo seems to be nice and transparent by itself here. I wish I could have better bass management and have the bass crossover at closer to 40 or 50 hz as opposed to 80, and then I wouldn't have a problem. I could post the actual data if interested. My question is why is this happening? My sub is in a corner located immediately behind my right front KG. Will EQing help fix this, or am I stuck? a 20 db volume change on such a narrow spectrum is quite drastic, I think. Thanks, Troy ------------------ KG 5.5 (mains) KLF-C7 (center) KG 1 (rears) SVS 20-39CS+ (sub) Aura Bass Shakers (pair) Kenwood amp for sub and shakers Denon AVR 681/1601 Quote Link to comment Share on other sites More sharing options...
dougdrake2 Posted February 15, 2002 Share Posted February 15, 2002 Hi Troy - I think the problem is those darn bass shakers Seriously, are your mains set to small when you are using the sub, or large? It sounds like you are getting an interaction between your mains and your sub, which disappears around 80hz (coincidentally the same as the Denon fixed crossover where it pulls the bass away from the sub). Try setting them to small, and see what happens. Also, try sending bass to sub only and not front&sub. Also, you COULD use speaker level inputs to the sub, and connect your mains to the sub and bypass the Denon bass management. That would let you blend the crossover at a more suitable level. Doug ------------------ My System Quote Link to comment Share on other sites More sharing options...
t-man Posted February 15, 2002 Author Share Posted February 15, 2002 Yea, I turned off the shakers, and problem gone! Seriously, I do have all speaks set to small. Can't really run sub full range, b/c it's passive and doesn't have a seperate crossover. T-man ------------------ KG 5.5 (mains) KLF-C7 (center) KG 1 (rears) SVS 20-39CS+ (sub) Aura Bass Shakers (pair) Kenwood amp for sub and shakers Denon AVR 681/1601 Quote Link to comment Share on other sites More sharing options...
boa12 Posted February 15, 2002 Share Posted February 15, 2002 t, you've got the infamous pressure node w/ the sub, speakers & room. to take care of it u may need some kind of notch filter. w/ your receiver, if can u set the freq point somewhere in that range & drop some db there, it may help. ------------------ My Home Systems Page Quote Link to comment Share on other sites More sharing options...
Guest BobG Posted February 15, 2002 Share Posted February 15, 2002 The problem is standing wave/nodal pattern in the room. Do a search of the forum for these topics and you'll find lots of information. At low frequencies (wavelengths way largerthan the dimensions of the room) reflections cause big increases / decreases in level. You can take those same measurements at another place in your room and get very different results. Try walking around the room while listening to something with lots of deep bass. Put your head near the rear walls or in corners and you'll really hear some big bass nodes. Quote Link to comment Share on other sites More sharing options...
t-man Posted February 21, 2002 Author Share Posted February 21, 2002 Well, I played around with placement and re-tuned my sub with the supplied port blocker, and got a smoother response. The impact appears to be a bit subdued, though. In the picutre you can see the original sub placement, and I moved it to the other corner, but it's not really a corner, it's just a jut from the closet. My readings no longer have the 20 db variation within the narrow 35-45 hz range. Instead, I have a 12-15 db variation between a wider 45-65 range. The difference is that the change is much more gradual along a wider spectrum. My dbs drop quickly at the crossover point, but if I set my speakers to large, it stays flat. Should I keep the large setting? Troy ------------------ KG 5.5 (mains) KLF-C7 (center) KG 1 (rears) SVS 20-39CS+ (sub) Aura Bass Shakers (pair) Kenwood amp for sub and shakers Denon AVR 681/1601 Quote Link to comment Share on other sites More sharing options...
boa12 Posted February 21, 2002 Share Posted February 21, 2002 t, does the eq on your denon let u choose freq points below 100hz? does the bass not sound as tight w/ the large setting? ------------------ My Home Systems Page Quote Link to comment Share on other sites More sharing options...
KGeist Posted February 21, 2002 Share Posted February 21, 2002 A 70 Hz notch would correspond to the first null of a vertical standing wave where the ceiling height is approximately 8 Ft. Although this could be the source of the problem, it is probablity more likely to be due to interference effects between the speaker/receiver and subwoofer crossovers. In other words, the two crossover alignments are not "in sync" with one another throughout the crossover band. The exercise of moving the speakers around the room is probably helpful, and may be the only practicl option you have other than setting the speakers to full range. Kerry Quote Link to comment Share on other sites More sharing options...
boa12 Posted February 21, 2002 Share Posted February 21, 2002 kerry, what i've been tryin to get at is couldn't one eq at least one of the pressure nodes some, sorta like the notch filter on my b&k pre/pro does. my guess though is t's receiver won't eq below 100hz if that would even help. ------------------ My Home Systems Page Quote Link to comment Share on other sites More sharing options...
KGeist Posted February 21, 2002 Share Posted February 21, 2002 Boa, In a room, any measured dips in amplitude response are almost always due to some sort of cancellation and therefore it is not wise to try and EQ them out. Adding more energy at the problem frequency doesn't change anything except make your amplifier work a lot harder. With an equalizer, you can EQ the peaks, but its best to leave the dips alone. Kerry Quote Link to comment Share on other sites More sharing options...
boa12 Posted February 21, 2002 Share Posted February 21, 2002 kerry, yea that's what i was talkin - EQing the peaks down. that's what i do w/ the nasty peak i have in the nasty lil 10hz or so notch across the 50hz crossover. thanks. ------------------ My Home Systems Page Quote Link to comment Share on other sites More sharing options...
t-man Posted February 21, 2002 Author Share Posted February 21, 2002 Yea, I have some nasty null points, right where the best music bass typically is. I moved seating position back a bit, but still have a problem. Most of my readings are say...70db-ish. My nulls are as low as 60 db (40 AND 75 hz), and the peak is at 80 db (60 hz). I imagine I would need a ton of AMP power if I had to EQ my frequencies 10-15 db across the board to match my null point. Is that what you suggest as the only solution here? I have no crossover setting avail on my Denon. It's fixed at 80 hz, I believe. I feel the bass is tighter set to "small". With adjustments to overall volume, I now have a flat FR between 80 - 100 hz. It' dips just before this at 70 hz. Thanks guys! Troy ------------------ KG 5.5 (mains) KLF-C7 (center) KG 1 (rears) SVS 20-39CS+ (sub) Aura Bass Shakers (pair) Kenwood amp for sub and shakers Denon AVR 681/1601 Quote Link to comment Share on other sites More sharing options...
boa12 Posted February 21, 2002 Share Posted February 21, 2002 t, does your denon have eq settings? probably not at 60hz though. what u would maybe wanna try is setting the point at 60hz & Dropping it there (-10db). ------------------ My Home Systems Page Quote Link to comment Share on other sites More sharing options...
t-man Posted February 21, 2002 Author Share Posted February 21, 2002 I have Treb and Bass control, but have no idea what frequency it's at. I could try and adjust that and see what happens. Troy ------------------ KG 5.5 (mains) KLF-C7 (center) KG 1 (rears) SVS 20-39CS+ (sub) Aura Bass Shakers (pair) Kenwood amp for sub and shakers Denon AVR 681/1601 Quote Link to comment Share on other sites More sharing options...
boa12 Posted February 22, 2002 Share Posted February 22, 2002 t, i checked the specs of your 1601's bass tone control & it's at 100hz. you need something more precise to do any EQing. ------------------ My Home Systems Page Quote Link to comment Share on other sites More sharing options...
t-man Posted February 22, 2002 Author Share Posted February 22, 2002 Boa, Thanks. I'm considering getting an ART EQ, but am leaning towards one of the Berhinger Feedback Destroyers to get parametric EQ ability. Prob is that my wife has me on a spending freeze, and this would really piss her off, even though it's only a $125 investment. Maybe I can sneak one in the closet on my birthday (: Troy ------------------ KG 5.5 (mains) KLF-C7 (center) KG 1 (rears) SVS 20-39CS+ (sub) Aura Bass Shakers (pair) Kenwood amp for sub and shakers Denon AVR 681/1601 Quote Link to comment Share on other sites More sharing options...
boa12 Posted February 22, 2002 Share Posted February 22, 2002 good luck there t. i like that word, "investment". ------------------ My Home Systems Page Quote Link to comment Share on other sites More sharing options...
Ray Garrison Posted February 22, 2002 Share Posted February 22, 2002 t-man, You cannot equalize out a frequency response notch that is caused by destructive interference of various wavefronts coming off walls, ceiling, floor and driver. If you have a narrow (high Q) dip where the sound pressure level drops enough to be noticeable, your only realistic solution is to try and alter that dip by moving the location of the sub, or move the listening chair so you're no longer sitting in the notch. Moving the sub will only make a significant difference if the frequency where the notch is occuring is high enough that the length of the soundwaves is significantly smaller than the dimensions of the room - if you had a notch at, say, 30Hz, which has a wavelength of 37 feet or so, moving the sub by a few feet one way or the other isn't going to change much of anything. Boosting the frequency at which the notch occurs will not make it go away - if ten added to negative ten equals zero, multiplying both by a factor of 20 will give you two hundred added to negative two hundred, which is still zero. You could easily damage the amp or sub by trying to boost the output at some specific frequency where the notch occurs, as you could keep increasing the equalization applied at that frequency until something breaks and never eliminate the notch. Taking the other approach, reducing everything AROUND the notch to bring the overall response curve DOWN to a more linear response, is an interesting idea - at least you won't break anything. My gut feeling is that this is not going to work, at least not very well, but to be honest I have no idea why I feel that way. Be sure to keep us posted? ------------------ Music is art Audio is engineering Ray's Music System Quote Link to comment Share on other sites More sharing options...
montigue Posted February 22, 2002 Share Posted February 22, 2002 yes Ray your right. the positioning is everything on a sub. I can walk around my living room and get deeper bass in one corner, boomy in another and tighter in a different location. i found that flanking the sub with the mains in a corner is the best. But T, you will also notice a difference with a better amp. Like the Samson series. (tighter more accurate) Quote Link to comment Share on other sites More sharing options...
boa12 Posted February 22, 2002 Share Posted February 22, 2002 Like i've been sayin/implyin, you can't change the characteristics of pressure nodes from the room effects & such w/ EQ, but you can try to change their relative intensity for hopefully a more linear overall response. works w/ my b&k notch filter like i said above. that is by dropping the intensity or loudness of the peak in the 46-54hz range relative to those levels in the other freq ranges. from my own experiments, the overall bass response comes out smoother this way. problem is i also have a few other peaks so i could use another 2 or 3 notch filters. & one w/ a wider range of coverage to boot. i also have a big peak in the 28-36hz range. but no biggy as I like that low bass. ------------------ My Home Systems Page This message has been edited by boa12 on 02-22-2002 at 07:28 PM Quote Link to comment Share on other sites More sharing options...
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