Subwoofer setting

"How do you explain the stomach-churning bass able to be produced in some car installations?"

Don't confuse "pressure" with well-articulated sound at defined frequencies.

If you use a test disk with separate signals at various frequencies and a sound meter you can see for yourself if your car sub is producing "sound" at very low frequencies or just pressurizing the passenger compartment.

Now what you hear outside the car is a very different thing, because the "room" has no or very distant boundaries.

Halcro, you sort of answered your own question with the term "stomach churning" which indeed it is: ie. a mechanical vibration -- like SenSurround -- but not an acoustical vibration. And if anyone rolls down a window, the "room" becomes the "whole outdoors"!

A car interior can boost bass as much as 20db or more. But it is not always the deepest bass.

Thanks for clarifying that, Nsgarch. That's good info to know! -jz

"...for a 20Hz wave to form in the air, the largest dimension of the room must be at least 27.5 feet."
I've seen this argument before and also seen it refuted.
How do you explain the stomach-churning bass able to be produced in some car installations?

JZ -- Good question. Low bass disperses in all directions pretty quickly, so as long as the room is bigger than say 200 sq. ft., you can just set the sub on the floor at your LP, and you can stand normally when listening at different locations. When you are listening at a position near a wall (or in a corner) stay about 2 feet from the wall or corner to avoid the natural bass reinforcement that occurs when the wave hits the wall and reverses direction.

Again, I don't guarantee this method if your sub will be producing frequencies much over 80 - 100 Hz, but it's still worth a try.

Something many people don't realize is that for a 20Hz wave to form in the air, the largest dimension of the room must be at least 27.5 feet. This can be measured from a ceiling corner to the diagonally opposite floor corner. It's derived by dividing the speed of sound in the air (approx. 1100 ft/sec) by the freq. (20) which yields the full wavelength in the air for a 20Hz note (55 feet) and then you divide that by 2 (since a half-wave will do ;-) which gives you 27.5 feet. All dimensions increase a bit as you go higher than sea level ;-)) The moral of this story is: Even if your sub is making very low frequencies, your room might be too small to allow them to happen ;-)

Nsgarch - regarding your suggestion, I've seen this recommended before in print but they never say whether to place the sub on the floor at your listening position or up at ear level. By the same token, do you crawl around the room down low while listening for the best bass or walk around upright? Advise? -jz

Before auditioning different lo-freq cut-off points (I recommend the 50Hz also) you should find a reasonably intelligent location for the sub. . . . . .
Assuming you have only one sub (best IMO, as long as you can keep the x-over point below 100Hz) AND assuming the sub has no phase adjustment, the best method is to place the sub at your listening position, and then listen to program material from different locations in the room to find the best "final resting place" for the sub ;-) Try listening from these positions:

>Each corner of the room
>Smack between the main speakers
>Different positions along the four walls, but particularly the one behind the speakers.
>Right behind the listening position

One of them should provide the strongest and most seamless response in your room. Place the sub there.
.

If you adopt knownothings approach a good disk is the soundtrack from the movie SNEAKERS, in which a bass drum is struck repeatedly. Down load Sumiko's short sub set up guide from their website , I learned about this CD from it. It is available on Amazon at a reasonable price.

If you have some compulsive bones in your body, get an audio test disk from Stereophile, or Radioshack, or download one off the internet and get a cheap digital sound meter from Radioshack and test where your main speakers roll off in your room. Then set the sub's crossover to cut off at 50Hz and measure the roll off as you go up in frequencies with the sound meter. Then set the sub to 80Hz and do the same thing. See which setting best compliments the actual measured roll off of the speakers and leave it there for now.

Once you have decided on the crossover setting, now use the sound meter and the test disk to calibrate the volume setting on the subwoofer to match the output of your speakers and amplifier as best you can. You will undoubtedly have bumps and valleys at different frequencies in your listening space - but just do the best you can. Try to average output over several frequencies in the center of the subwoofer's range and set the volume level to match the output for the average of several frequencies in the center of the bass band on your main speakers (well above the cutoff).

Now that you know intellectually what cut off should sound best and have calibrated the output levels of the sub and speakers, listen to a few of your favorite bass heavy (not necessarily low bass) pieces of music with the sub set both at both 50Hz and 80Hz and then do what Zieman says above, leave it where it sounds best to you!

I find this method works pretty well, and if the sound I like ends up being "colored" in some way, at least I know how and why. In some systems "flat" sounds GOOD, and in other systems "flat" sounds just, well... FLAT.

50. The other settings are for home theater , as Alvin Gold recently pointed out " Do avoid the 80 HZ crossover point mandated by the world of home cinema-which completely spoils the chances of almost any subwoofer integrating as nature intended". The reason is simple, the crossover point is the frequency at which you began to roll off a sub. If the sub begins to roll off at 50 Hz and the main speakers are specified to 60 Hz there will still be considerable overlap in output between them. To raise the crossover point further is to further increase the frequency range in which both are playing. This is why Linn has 50 as the default.

AG, you asked two questions. Fortunately they both have the same answer. Use the crossover point that sounds the best to you. Because it sounds the best to you.

Yes, the in-room response is quite relevant but the vast majority of people have no way to measure that and must rely on the printed specs, if any.

Kal

As much a question as an attempt to add to the discussion, but doesn't the in room frequency response of the mains have something to do with the subwoofer crossover point? Or is that just considered a given?

I follow Kal's logic, but I would lean towards 80 or 50. 120 is way to easy to localize. I feel the lower the better unless you feel like you are missing something. Placement can also effect performance and volume. Placing speakers and sub equidistant to the listening position will ensure proper phase. Near walls and corners will increase volume. Many threads and opinions on this in the forums.

General rule is 1/2 or whole octave above the main speaker's -3dB point. Unfortunately, the spec you quote does not tell us that but, assuming 60Hz was the -3dB point, I would recommend 80 or 120Hz.

Kal

The 50 should be good since there will be some overlap as the low end of the mains rolls off, the sub will roll off in the opposite direction.