Which way to face subwoofer

 

Silver Member
Username: Bvan

Cape Town, Copenhagen,...

Post Number: 281
Registered: Jun-05
I've read countless pages on subwoofer setup but dont recall ever having seen this answered, so forgive me if it's been dealt with here before.

I've got stereo dipole subs sitting each side of my mains the go down to 30hz and now have a 3rd sub(sealed) that I want to place in the rear corner to fill in 20-30hz. I'll have it eq'd flat for music and have a bit of a house curve for movies.

The little I've read on the matter suggests firing the sub towards the listener will give a more accurate output and firing it into the wall will produce more output but make it sound boomy. I'm wondering though if more output might not always be better provided one has an equalizer to make sure it still measures flat? The other thing that occurs to me is that Rel, who make very musical subs, fire there's into the floor which to me seems no different from firing into a wall at an inch or two's distance.

Any input here greatly appreciated,

B.
 

Platinum Member
Username: Jan_b_vigne

Dallas, TX

Post Number: 10325
Registered: May-04
.

"I'm wondering though if more output might not always be better provided one has an equalizer to make sure it still measures flat?"


A plot of frequency response alone will never indicate how good the sound quality is. The speaker can measure flat but still sound boomy or thin or just bad. Unless you have a method which measures the in room "Q" of the expressed signal at a specific frequency and at a specific location (and you can correct for specific frequency anomalies), you should ignore the most specific frequency response measurements and concentrate on how the system sounds.





"The other thing that occurs to me is that Rel, who make very musical subs, fire there's into the floor which to me seems no different from firing into a wall at an inch or two's distance."




Low bass frequencies are generally considered omni-directional. The placement of the driver (and enclosure in most cases), in relation to the room surfaces determines the working relationship of the driver, or the Pi of the system. What's your question? Or is there one?


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Silver Member
Username: Bvan

Cape Town, Copenhagen,...

Post Number: 282
Registered: Jun-05
Thanks Jan. Didnt know that about Q.

My questions is whether I should fire is into the wall or towards me. I can of course try both but it takes a fair deal of time to eq them flat at each position.

I was thinking that firing into a wall should be as good as toward the middle of the room, and mentioned the Rel in support of this belief, hoping for further comment and maybe a theory about why Rel would choose to fire their subwoofers strait into a floor/wall if it muddies the sound.

B.
 

Platinum Member
Username: Jan_b_vigne

Dallas, TX

Post Number: 10327
Registered: May-04
.

I can envision no benefit and several downsides to misplacing a driver. REL takes advantage of a known driver position. Unless you intentionally misdirect the REL driver, the system will always begin working into the same Pi space. The variable would be how close to a wall or walls you might place the enclosure. I don't know if REL gives specifics for such placement or not. But a downfiring woofer is taking advantage of what is called "The Allison Effect".

http://www.stereophile.com/interviews/105villchur/index2.html


Allison is not the only designer to have taken advantage of the benefits provided by defining the placement of the low frequency driver within a room but he is most famous for exploiting the technique and built his speaker line around the principle, hence the name.


I can't provide specifics for where or how your sub should be placed within your room, excellent bass response is too complicated for that to be done over a forum. Read the interview and you should gain some insight into low frequency wave propogation into a room. As to boomy sound when firing into a wall, it will depend on the driver and the designer's goals. If the designer envisions a placement more suited to a typical home theater, the sound might turn boomy due to uneven frequency response boosts and dips. You might be able to balance these out with your EQ but it seems to be adding too much hassle when there are better alternatives.


Here's what I would do in your situation. Turn off the two other subs and set this unit up for best overall sound. I wouldn't worry about doing any EQ on the sub as you do basic set up. It either works in the position you choose or that's not the right position. When you find the position that works, turn the enclosure any which way you choose and listen for changes, the difference in overall frequency response is not going to change so significantly that you have to worry about EQ just for trial purposes, listen only for quality of sound. Once you have found a position that seems to suit this subwoofer, add the second and then the third, listening for quality as you go along. EQ the system after you've set up room position with all three subs working together.


As an aside, I've set up my second system sub sitting high off the floor (about one third the distance from floor to ceiling) and in a corner, firing across the longest diagonal of the room. To my ear, with the material I play on this system, the room and the sub, this off the floor position provides cleaner response than any other I've tried. Whether this would work for your sub, you'll have to try.


.
 

Platinum Member
Username: Jan_b_vigne

Dallas, TX

Post Number: 10328
Registered: May-04
.


http://www.stereophile.com/reference/706deep/index.html
 

Platinum Member
Username: Jan_b_vigne

Dallas, TX

Post Number: 10329
Registered: May-04
.


http://www.stereophile.com/historical/138/index.html
 

Silver Member
Username: Bvan

Cape Town, Copenhagen,...

Post Number: 283
Registered: Jun-05
Thanks again Jan. You must have a large and well archived library of articles on your pc.

As often it seems there's no way to get around the hard work of listening. Nothing in this hobby is as simple as I wish it would be. For example I still dont have a good feel for what Q is aside from how it relates to FR. Off topic but I found Allisons idea of realism vs pinpoint imaging quite relevant to my efforts to understand the appeal of the open baffles I'm currently living with.

Happened upon the Vandersteen website yesterday and there was some relevant stuff there but not in enough detail. An interesting theory I had not hear before, he reckons that even if you equalize away the effects of the room, that the brain can still distinguish the speakers contribution(which would now be anything but flat) from the rooms contribution. But he concedes the benefits of EQ bellow 200hz outweigh this negative.

Just had some phase plugs arrive this afternoon so I'll start operating on my drivers before I get to playing with the subs.

cheers

Bevan
 

Platinum Member
Username: Jan_b_vigne

Dallas, TX

Post Number: 10332
Registered: May-04
.

"Q" is nothing more than the rise and fall of a signal.

Basically.

If the signal has a rapid attack and short sustain, it would be considered a high Q signal. If the attack is slower and the sustain is longer, the Q is low. How the Q is affecting the signal will predominantly vary with the attack of the signal. Fast atack and long sustain are generally still considered a high Q since it will typically excite stronger resonances than a short or long duration attack. There are no hard and fast rules I'm aware of that say this is this and that is not this since the result of the signal is what you are considering in most instances.


EQ's have high and low Q's around their frequency centers. While most graphic EQ's are constructed with a partially fixed Q for every slider, or center frequency, parametric EQ's allow the user to adjust the Q to high or low value or somewhere between.


You will also see "Q" discussed as a "system Q" when designing or reviewing loudspeakers. In this case Q begins as a reference to the driver's ability to start and stop, which will be influenced by its mechanical structure and this value will be used by the designer to narrow choices when considering a particular driver for a distinct enclosure. Sealed boxes will normally employ high Q drivers in the low frequency region while vented boxes are going to exploit the advantages of a low Q driver. After the design is completed, the system of drivers and enclosure will have a "system Q" which attempts to describe the relative speed of the system and it's rather generic response. Qtc and Qts are also used in speaker design. When measuring the contribution of the cabinet to the overall sound, signals of various Q factors are fed to the speaker in order to excite the Q of the enclosure surfaces.


Simple, huh?


.
 

Platinum Member
Username: Jan_b_vigne

Dallas, TX

Post Number: 10333
Registered: May-04
.

"Allisons idea of realism vs pinpoint imaging"


While I tend to agree with Allison for the most part regarding what people actually hear in a live performance against what they desire from their systems, I have to keep in mind this is a bit self serving of Allison. Since his speakers were intended for corner placement, they were quite often much farther apart than many conventional speaker set up guides would allow. Even considering the toe in of the corner placement, images were never going to coalesce as they do with most audiophile speakers placed six to nine feet apart. On "naturally" mic'd recordings, this will not present much of a problem to the experienced listener of live unamplified music unless the room conditions and configuration betray the speakers. However, when fed material that is predominantly of the studio production variety, where "images" can tend to be more localized in many instances, the Allison presentation oftens fails to satisfy the unwitting consumer.


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Silver Member
Username: Bvan

Cape Town, Copenhagen,...

Post Number: 284
Registered: Jun-05
I still like sharp images though. Even though you dont get sharp in a live performance I think the at home it is a sort of substitute for the visual sharpness you would get live. I'm quite visual when I listen to music at home and tend to look at the images between the speakers rather than shut my eyes as some do.

Regarding Q, why is it that Q=5 or the 'critically dampened' speaker not held as an ideal. Shurely if it starts and stops quicker it is more accurate, If the note has a long decay and it is on the recording you will still hear it?

My sub is Q=0.5 and sounds pretty accurate to my ear. My dipole mains are higher q but this I understand is needed to achieve bass. But I wonder if because I have equalized my sub have I changes its Qts?

cheers

Bevan
 

Platinum Member
Username: Jan_b_vigne

Dallas, TX

Post Number: 10339
Registered: May-04
.

" ... why is it that Q=5 or the 'critically dampened' speaker not held as an ideal."


First, I assume you mean the system Qtc of 0.5.



Then the easy answer to your question is ... sales!

Beyond that this will require some links.



http://diyaudio.dyndns.org/about_sealed_enclosures.html


http://www.stereophile.com/standloudspeakers/171advent/index2.html


As you can see "critically damped" is merely a variation on ways to make a speaker sound different. The sound of a "critically damped" speaker will appeal to some people but not all. So the "Q" of the system is a designer's choice for what they think is either natural to their ear or will sell to an unwitting customer. Since "Q" is a variable that can be manipulated to achieve lower bass response, higher efficiency, smaller enclosure or overall sound quality, Qtc is what the designer aims for and then adjusts to make the system sound balanced. That you might prefer a Q of 0.5 is not relevant to the sales of speakers to others. You can find the system which performs to your taste and others will reject what you prefer.



Making a critically damped speaker system the norm would tend to make overall system pairing more complicated unless we could get all amplifier manufacturers to settle on a single output impedance. Partially allowing different speaker Q's will broaden the market for mating components. As speaker designers cannot guess whether the speaker might be paired with a tube or solid state amp, or a receiver rather than a single ended amplifier, they are typically trying to reach the broadest audience possible. Designing only critically damped speaker sytems would discount their value to many potential buyers. The overall market currently demands something with more weight and power than a critically damped system is likely to produce. More so now that before the coming of home theater. You can have crunch or you can have finesse. Which is more likely to sell in the average audio showroom?



Remember also that critically damped speakers will sound good when the system sound is balanced to the two frequency extremes. A critically damped speaker will have fairly "light and tight" bass response for most enclosures. If the designer wishes to have an extended high frequency response in the final system sound, light and tight will probably cause the speaker to sound thin and top heavy. So, balancing the alignment of the enclosure to gain overall system balance is typically the designer's goal. As with the LS3/5a, where the system Q is rather high, the alignment was chosen to provide the extra bump in the bass response that gives the speaker some Oommph which balances the high frequencies required of a monitor type design. This sort of frequency tailoring has become more popular with speaker designers following the lead of Holt's article "Down With Flat".


Since equalization should not affect either the amplifier's output resistance, the electrical or mechanical resistance of the driver, I can't see how you could have altered the sub's Qts or Qtc.


.
 

Silver Member
Username: Bvan

Cape Town, Copenhagen,...

Post Number: 285
Registered: Jun-05
quick thanks. will get on the links this weekend.

b.
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