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Old 28th June 2002, 11:40 PM   #11
sam9 is offline sam9  United States
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Default That's Right

Don't ask me the physics of it, but it's supossed to be the case. It's called resonance respricosity or something. With the sub where you will listen, the loudest spot in the room will be the place where if you move thwe sub there that will be the location that gives your listening position the loudest level. Only glitch- loudest may not be the best since you are trying to blend in the sub with the other speakers. However, it is worthwhile undertaking to at least get started.
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Old 29th June 2002, 12:23 AM   #12
Bose(o) is offline Bose(o)  Canada
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Quote:
Originally posted by e96mlo
I have heard that you should place the sub at your listening position and then walk around and listen. The place where it sounds loudest is where you finally should have the sub.

Any comments on this?

/Marcus
Sure, if you can get a computer to simulate what will happen acoustically you are saving a lot of time. For Engineers and alike you also go for the numbers, proving that your placement works-and not relying on your ears. If I'm setting up a system for myself well, fire up my test CDs or DVDs and listen away! If anyone can find such software than please tell me.

I do know that if you are trying to 'blend' in the sub with the mid/high freqs. then placing the subwoofer above the mid/high freq. devices will do the job. There are more probs. associated with this though, such as resonance that carries into other rooms because the ceiling in your target room travels through doorways and in between walls unless acoustic dampening is used (doubt wife will like that . I also know that THX calls for the sub to be placed up front and away from corners so that the bass is still powerful yet, is more articulated than if it were in a corner. If your seating is close enough, I'd go with any side of the wall because low-freqs are omni-directional. And, yes it does get louder in some spots. Essentially, this louder effect is lessened once your sub is placed up front. My sub is up front and beside the left speaker, with proper volume adjustment and cross over adjustment the sound volume is pretty darn even.
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Old 29th June 2002, 01:21 AM   #13
sam9 is offline sam9  United States
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Default Bass

The last time a saw such software for sale it was beyond my means. The few fre-shareware thingd I've seen assume a standard rectangular room.

The cheapest "instrumentation" availacle is Radio Shacks analog SPL meter coupled with a test disk. Not super precise but it identifies the grosser anomolies.

I've found the trouble with corner placement to be that it reinforces the level so much that slight changes to the sub's level control result in big changes in volume making it hard to adjust well.

There is a placement that I've heard recomended but has never been feasible for me - place it right next to your listening postion. The direct, unreflected energy will dominate so you can pretty much ignore the room effects. It may sound terrible for anyone else in the room but you, of course.
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Old 29th June 2002, 01:41 AM   #14
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Quote:
I have heard that you should place the sub at your listening position and then walk around and listen. The place where it sounds loudest is where you finally should have the sub.
While doing so very probably You`ll end up with 2 places where the sub is loudest:

1.)In the center of the room where the second lowest room modes corresponding the 3 widest room dimensions make a big bump. Obviously not only from the visual view this is not a comfortable position though the lowest room modes could be avoided to a big extend.
2.) In the corners of the room as all kind of room modes have their max. pressure level there. This place too should be avoided by all means. Otherwise the sub will best stimulate all these room modes to maximum and will cause bad ringing on them.

I don`t think this is a suitable method to figure out the best position for a sub but consider this rather a method which positions to avoid.

Though a couple of simulation software exist for this purpose, I doubt there are affordable ones which unless simple room dimensions are able to take in account properly all the other specific room properties as stiffness of walls, ceiling, floor, windows, doors etc. and their individual damping properties.

Therefore I guess still the best (and worth the money though not the cheapest as simple trial and error) method would be playing pink noise through the speakers and to use a narrow band (at least 1/3 octave) Real Time Analyzer (RTA) to find out the most even frequency response for different sub/listener positions. As due to lack of room space and other restrictions (for example as mentioned already visual acceptability) the positions mostly are predetermined to some extend this should not take too much time also.

I t is not very likely that there is a position which is optimal in every respect (as always, there is no free launch). Eventually remaining peaks can only be flattenend either acoustically (acoustic traps, big and expensive) or electronically with special designed equalizer circuits (parametric equalizers, small and cheap if DIY and flexible). For those having some reservations about additonal electronic circuity in the signal path, the electronic solution is particular useful with active fired subs where it has less to none bad influence on the upper frequency range.


to core:
I know all this does not bring You any further with YOUR sub-location problem (though might be useful information for others ).
I took a look at Your photos and so far I can judge this at all, I fear that it does not make make much difference where You locate the sub inbetween the possibilties that are left (which does not mean that the result have to be bad).
By all means You should take care about what said planet 10 about rainbow and the CRT-screen.
But as You plan to make the sub with its own amp., maybe what I said about electronic equalization maybe become useful at some time when You intend to tweak Your system.

P.S: I know from own experience that it is very troublesome to impossible to find the optimal place or setup via hearing music only. It is simply not possible to judge all the variations by ears only correctly. Besides this one always tend to trade one disadvantage against another without ever encountering what would be possible actually with some help of test equipment.
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Old 29th June 2002, 02:01 AM   #15
sam9 is offline sam9  United States
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Default Bass optimization still in process

I had the good fortune to grab a pro level spectrum anayzer off e-bay about a year ago for a very reasonable price. It was one of the best buys I've made. It did two things - it made the locating and setting up my sub much easier and with better results and it let me evaluate and decide on accoustic treatment for my room.

I still have some additions to make as my budget permits. I need to add at least one more quarter round bass trap and absorption at a couple of other spots. Following that, I be looking at Behringer DSP8024. One realization I've come two is that EQ and acoustic treatment are not alternative approaches but complementary ones that -- each adds to trhe effectiveness of the other. EQ can only affect what comes out of the speakers while acoustic treatment affect what happens after that. My personal theory is the goal of accoustic treatment with regard to bass response is to reduce the spatial variations in the room, so that the bass comes closer to sounding the same everwhere, while EQ can then smooth out the response curve not just at my personal listen position by for a much larger area of the room.
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