Hello,
I'm new to home theater, and I’ve finally taken the plunge and ordered my complete home theater system:
Axiom speakers: M60ti's, VP150, QS8's
Definitive Technology sub: Super Cube I
Pioneer VSX49TXi
QS8 stands
I also have a 65” Mitsubishi rear projection HDTV, which is 62” high. My room is 18 ft. X 16 ft.
My questions are:
1. I’ve read that the tweeter heights of the fronts and center should be the same, for better panning effects. Is this very important? Should I try to raise the M60ti’s on some sort of stands so that they'll reach the height of the center, which will sit atop the TV?
2. Should I angle the center speaker downward towards the listening positions?
3. Which corner should I place the subwoofer in: closer to the listening positions, or closer to the front speakers?
4. I plan to use Sound King 12 AWG oxygen free wire (from partsexpress.com) for all the speakers. Is this adequate or should I invest in more exotic wire?
1) The tweeter heights do not have to be 100% equivalent in height.
2) Yes, angling your centre speaker downward a bit will help in regards to your first question.
3) You really have to move the sub around the room to find the best sounding spot for your situation. However the most common locations is placing the sub right at the front beside their main speakers or right at the back behind/alongside their listening area.
4) That cable should be fine.
Enjoy your new system!
In reply to:
You really have to move the sub around the room to find the best sounding spot for your situation.
MC1,
Chess is right, and if you feel like some experiments, try the
subwoofer-crawling. This technique surely helps optimizing the sub placement.
While having the tweeter all at the same level is optimum, it's not essential. Though you bring up a point about putting the M60's on stands.
I recently experiemented with putting a pair of M60's on stands for a completely different reason, and really liked the effect.
I've always found floorstanding speakers to lose some upper-bass clarity (as compared to a bookshelf speaker). This lack of clarity has always bothered me. To the point in fact, that I've never personally owned a pair of floorstanding speakers.
I put a pair of M60's on some small stands and gave them a listen...I liked the effect. It seemed to clear up that upper-bass quite a bit. Call me crazy, but when my new M60's arrive, they're going on stands.
MC, I'd say: 1. No; 2. yes; 3. Right in corner nearest front speaker nearly always best;4. That would be fine, may be heavier than you really need unless you have very long runs.
In reply to:
Right in corner nearest front speaker nearly always best
John,
I think that is a bit of overstatement. While the front corner is indeed one of the most popular locations and works fine in many cases, the results really depend on each room. For one, our living room makes it way too boomy when I place the sub in any of the room's corners.
Hi Sushi,
I agree. Start with a corner, and if it's too boomy, gradually move the sub away from the corner along one wall or the other until you get as smooth bass as possible for your preferred listening locations. It will never be perfect for every listener because of the vagaries of standing waves and room modes.
Regards,
Alan and Masa, I'll stay in the corner. In the corner, with the subwoofer cone within about 1 1/2' of the floor and each wall the maximum number of room resonances are excited. Assuming that the three room dimensions differ significantly(no cubes)the bass response there is both the loudest and the smoothest. Since it's louder there, the bass has to be rebalanced, but the solution is to turn down the level, not to move the sub.
assuming you have parallel walls and ceiling/floor and no furniture in the room.
John,
Well, my measurements don't support your theory. When my VTF-3 was placed at a room corner, the room modes made a nice roller-coaster frequency response, with multiple >10dB humps/dips between 20-100Hz. With the sub relocated at the current position, the room modes have been quite well tamed, only with two 3-5dB humps at about 38Hz and 56Hz. These measurements are certainly corroborated by my listening assessments.
Anyway, where does that conspicuous number "~1.5 feet" come from?
It's roughly 1/10th of the 80hz crossover wavelength(for near maximum reinforcement)Masa; for lower frequencies the effect occurs at correspondingly greater distances.
This is interesting to me. Can you explain the logic behind it? In other words,
1. why 1/10th, and
2. why use the crossover frequency as a basis for that measurement?
hi mc1,for an oppinion on your tweeter height,i have always liked my tweeters at or as close to in height as possible,it seems to give a more seamless soundstage,higher tones are easier to localize so i like the tweeters to be about the same,try it ,it works for me..good luck....ron
Okay Peter, I'll give it a shot. I suppose that I learned this stuff as much as 20 years ago, a lot of it from articles in the late and lamented Audio magazine, which combined technical and non-technical approaches quite well. Although I also have enough technical training to be able to understand some of the stuff in technical journals, I prefer it when the math doesn't get much beyond 2+2.
This area involves two separate acoustical phenomena:1.standing waves(modes, resonances)which affect speakers placed close to room surfaces at frequencies in relation to the dimensions of the room in wavelengths; 2.boundary reinforcement(and cancellation)which affects all frequencies(not just the standing wave frequencies)where the speaker is "very close"(hence the 1/10th rule-of-thumb)to the room boundaries. As far as I know, the Audio material isn't available online. One thing I did find was
this somewhat awkward translation from the Swedish of a discussion of the two phenomena as they relate to sub placement.
Some of the Audio articles, which my library has, and which I suppose your library has or can get photocopies, etc. of if you're interested are : Weinberg and Ferstler,"Bass Versus Space", Audio,July/August 1999;Allison,"The Best Place For Your Speakers? Your Computer Knows!", Audio, August 1994; Noussaine,"Birth Of The Boom" Audio, June 1998,and also "2 subs in a corner beats 5 in The Round", Audio,June 1996, and still further "The Lowdown On Getting The Most Out Of Your Bass Box", Stereo Review, January 1995.
Much of this is based on research done almost 50 years ago by Waterhouse("Output of a Sound Source in a Reverberation Chamber and other Reflecting Environments",Journal of the Acoustical Society of America, Vol.30,No.1,January 1958). So this isn't just my theory, but it appears valid to me and the bass sounds good.
I just wanted to thank everyone for their informative responses. I've just received my Axioms and I'm waiting on my Pioneer receiver. Also, I'm having some walls constructed to enclose a room for home theater use. I'm excited to set it all up!
Thanks Again to all
John,
Obviously I haven't yet read any of the offline articles you cited. But I do have major objections to some of core assertions in the Swedish article:
The article states:
By choosing a corner placement you excite all existing resonances in the room and the frequency response will not become appreciable inferior compared to a completely free placement.
This will be the case ONLY IF you are lucky -- in that (1) you don't happen to have multiple different modes with resonance frequencies close to each other, which does occur commonly and will result in a big hump in that region; (2) the Q (quality factor) of every room mode is low enough so that they are all nicely tamed when overlapped with each other, without resulting in narrow humps/dips.
There is absolutely no guarantee that these conditions are met in YOUR room.
The article states:
An interesting side effect of placing the subwoofer in a corner is that the distortion is lowered significantly. The cause for this is that you get a reinforcement of fundamental tones from all the reflections in phase from the adjacent surfaces, while harmonics (which is distortion when it comes to a steeply low pass filtered subwoofer) are lacking the corner support, and become weaker in amplitude compared to the wanted fundamentals.
This completely self-contradicts the statement made earlier in the same article. You choose the corner placement with less than 1/8 - 1/10 wavelength distances from the three walls so that ALL frequencies in which the sub operates (e.g., 20-80Hz) get a boundary reinforcement. So, when the sub is playing, say, a ~20Hz fundamental, its 2nd, 3rd and 4th harmonics will all be similarly enhanced. In fact, if this isn't the case, you are in trouble because it means that you don't have a flat frequency response within the operating range.
The harmonic and other distortions generated by the sub at above 80Hz is certainly a different story. But again, as the article itself says, the higher harmonics may be cancelled or enhanced, depending on specific frequencies they happen to be at. I would in fact even speculate that this modulation may well be one of the biggest culprits which make a corner-placed subwoofer sometimes very boomy (like my own case).
In the end, the article says after all the lengthy discussions:
"...then place the subwoofer, use a lot of experimenting." 
I wish that the AUDIO articles you cited are more coherent and convincing than this one at the very least.
[added in edit]
Oh, at least I now understand the "1/10 wavelength" recommendation. Thanks! Incidentally, I play flute, which is in fact the only orchestral woodwind instrument that acoustically behaves as a double open-ended, non-conical air column. Lo and behold, the mouth piece of a flute (where the "air reed" generates sound) is located at approximately 1/10 average air-column length from the top (left) end of the instrument.
Masa, I do believe that your flute has established yet another proof!! I would strongly urge you to prepare a paper for submission to the AES. The regional convention was in Tokyo this year, which would have been ideal,but it concluded yesterday, so don't rush. The relative proportions of your flute(incidentally, in an earlier life, clarinet here), presumably arrived at empirically, certainly are powerful data. To clinch the argument, I'd suggest that you add a temporary extension to the mouthpiece end and see if they don't start yelling that they can't hear you, play louder!
On the coincidence of room modes, if the room dimensions vary significantly, the resonances should be spread sufficiently so that the overall response is acceptable(at least the testing described in Audio and elsewhere appears to indicate this).
On the lower distortion point, I haven't really seen this discussed much as a significant advantage. I vaguely recall that it was pointed out in something I read that the lower overall volume required to be delivered by the sub amp and driver with corner reinforcement could be viewed as a minor plus.
On that note, I think when I get around to building my own house, I'll design the home theater to be a massive cylinder lying on its side. Then I'll place a 10' subwoofer driver 1/10th of the way out from the front wall. Not that will be some good bass! Let's just hope it doesn't cause me to spontaneously void my bowels...
You could put a toilet in the sweet spot.
Talking further about musical instruments and "one-tenth wavelength" rule:
- The hammers in the grand piano are placed to hit the strings at about 1/7 from one end.
- A violinist or cellist bows the string at around 1/10-1/7 from the bridge (in fact, the louder he wants it the closer to the bridge he bows).
- Organs have the reeds placed at about 1/8 from the bottom of each pipe.
[incidentally, in all cases the string/air-column lengths represent a half wavelengths]
Similarly on the guitar, you can isolate different harmonics of the fundamental tone by touching your fingers over the 12th, 7th, 5th, and 4th frets (to name the main ones) while plucking the string. These frets correspond to 1/2, 1/3, 1/4, and 1/5 the string lengths.
UPDATE: Just found out that, at least in the case of piano, positioning the hammer at ~1/7 string length has another specific purpose: To suppress the 7th harmonic resonance, which is significantly out of tune with the equal tempered scale.
My VCR blinks 1200 1200 1200... When this blinking is set to a 3/4 beat with a metronome, and the vcr is placed 1/10th of a cubit from the coffee maker, and one taps with your little finger on the table next to the vcr, my wife will walk over to me and tell me to take out the trash... !!?? Incredible, but true..
ROFLMAO! Thanks, Mikey, I needed that!!
And I think I can probably validate your research...
Nooo prob Tom...
Hey Alan !! Here we go again.. ROFLMAO ??
Tom, I have a hard nuff time keeping up with the 3 letter shortcuts.. But 7 ? Ouch.. My age is showing.. Again..
ROFLMAO?! Yikes! It's taken me ages to remember LOL (explained to me by my ex, probably on examining the monthly cheque I send North). I'm gonna consult my lexicon of terms that Amie sent me.
Regards,
Rolling On the Floor Laughing My Anatomy Off.
Sorry to be cryptic. I can only aspire to actual nerdhood.
Glad to know I am not alone in this..
Now, where did I put those car keys ???