[santosh.s]

Originally Posted by DerAlte

Your lunch must have really disagreed with you, as must have mine with me. Both of us are making fundamental mistakes!
Oy, shorter waves (higher frequencies) attenuate lesser, travel further. True for all frequencies from audio to light, no? That's why you need to push more power into the subs (and Xmax matters) than into the tweeters, no? And a whistle is heard farther than a bellow? And the crack of a cracker heard farther than the boom?

No... there is no fundamental mistake. Higher frequencies attenuate more than lower frequencies, in general. Lower frequencies are capable of traveling farther. That applies to audio as well as electromagnetic waves. Otherwise it would have been difficult to absorb treble than bass, sub would be mounted on A pillars and tweeters hidden down in doors. Why high frequencies are used in communication has many other reasons, like their interaction with earth, atmosphere around it, interference from outside space, reliability. There are some basic reasons as well, like-
1. The size of transmitting antenna, lower frequencies need very big antennae. In audio it is size of sub versus tweeters.
2. Low frequencies need to operate at high power levels, again same as in audio. I don't know the exact reason, but I feel that for an efficient receiver, you should have equally big antennae but that is not the case. Imagine AM radio with a 100 meter antenna. In case of audio too, microphones that I know of are in generally small... including our holy pair of ears!

When you compare different sounds, it depends on not only the power level, but the psychoacoustics as well (equal loudness contours) and what power low and high frequencies have to begin with. If you measure db level of two frequencies at different distances, roll off of higher frequency with distance will be more.

You have described the ultimate bionic audiophile!!!

Imagine that the audiophile happens to be Navin-ji... guess each member of his family would have his/her own pair of customized/tweaked voice coils

That way, a bad HT woofer would be a great car sub practically? Or am I missing something?

I believe you are not completely wrong. Room gain will kick in at lower frequencies as compared to cabin gain, so car is going to be an easier job for a typical subwoofer.

[navin]

Originally Posted by DerAlte

True for all frequencies from audio to light, no? That's why you need to push more power into the subs (and Xmax matters) than into the tweeters, no?

Car Gain is not the only component of the Transfer Function, and nor is apparent loudness in 2 different environments!

1. the primary reason why we need more power at lower freq. is beucase the human ear is not a linear device. it is more sensitive in the miiddle and less sensitive in the low bass (sub 100Hz) and treble (10k+). This is espeicailly true of the bass. See Fletcher Munsson curves.

2. Car Gain / Room Gain is nodal. These gains are not like LPFs.

The gain is peaky and is dependant on

the size of the room/cabin,

absorbtion/diffusion/dispersion characteristics of the cabin/room,

the placement of the speakers within the room (the speakers will excite the nodes diffrently when placed at different locations; the nodal freqencies do not change just the level of their excitment)

and remember all this can mean different things for different people a lot depends on the music you are listening to. Baroque music for example will make for a very different expereince than Trance.

[navin]

Originally Posted by santosh.s

Higher frequencies attenuate more than lower frequencies, in general. Lower frequencies are capable of traveling farther. That applies to audio as well as electromagnetic waves. Otherwise it would have been difficult to absorb treble than bass, sub would be mounted on A pillars and tweeters hidden down in doors.

I believe you are not completely wrong. Room gain will kick in at lower frequencies as compared to cabin gain, so car is going to be an easier job for a typical subwoofer.

higher freqnuecies are also more directional and that is why your tweeters are as close to your ear's listening axis and the subwofoers are behind your seat.

Like I have said beofre Room/Cabin Gain is not like a LPF. Just becuase a cabin has a 6db boost at 60Hz it wont nesscarily have a 12db boos at 30Hz.

[santosh.s]

Originally Posted by navin

higher freqnuecies are also more directional and that is why your tweeters are as close to your ear's listening axis and the subwofoers are behind your seat.

Yes, of course, this is probably the primary reason. But I think the word "also" is important here, because attenuation of high frequency is not any less important a reason. Assume that you were listening to mono recordings (no spatial information) and the tweeters were also omnidirectional (no directivity), even then I don't think we can mount the tweeter in boot behind thick cushion of seats. It wouldn't help since major portion of highs would get absorbed, right?

Like I have said beofre Room/Cabin Gain is not like a LPF. Just becuase a cabin has a 6db boost at 60Hz it wont nesscarily have a 12db boos at 30Hz.

I hope I understand whatever you have said about gain- being "nodal" and "not like LPF", you need to "excite" those modes which vastly depends upon "positioning" etc. That is why I had said- it is "chaotic" to say the least. I am sure that these room modes spoil the SQ, and also makes it dependent upon the listener position (sweet spot).

Buttttt.......

I "believe" that this behavior happens above a certain frequency which is the lowest room mode, and its wavelength is twice the longest internal dimension of the room/cabin.

Real questions that I have are -I repeat it once again-
What happens to frequencies below the lowest (i.e. the first) room node?
-Is it as chaotic as explained above, and spoils SQ?
-Or is it more like a smoother, cleaner, LPF gain?
-Is that the reason why sealed boxes are better suited to cars, which have a natural roll-off of 12db/octave? This link tends to say that it should be so since the room gain experienced for sealed boxes is exactly equal to this- 12db/octave (it is a hyperlink in the previous link, named "below the lowest room resonance" :
http://www.linkwitzlab.com/images/gr...losure-spl.gif

I tend to think that at very low frequencies, it is more like a much cleaner, LPF kind of gain. Because I definitely don't hear room modes in case of headphones/ear buds/canal buds, and still enjoy very good bass....unlike home.

And then, I have another related questions as mentioned in post #16:
Are sealed subwoofers more suitable under such room gain conditions? Do ported ones show weired behavior (their problems getting aggravated or something)?

[navin]

Originally Posted by santosh.s

Real questions that I have are -I repeat it once again-
What happens to frequencies below the lowest (i.e. the first) room node?
-Is it as chaotic as explained above, and spoils SQ?
-Or is it more like a smoother, cleaner, LPF gain?
-Is that the reason why sealed boxes are better suited to cars, which have a natural roll-off of 12db/octave?

I tend to think that at very low frequencies, it is more like a much cleaner, LPF kind of gain.

And then, I have another related questions as mentioned in post #16:
Are sealed subwoofers more suitable under such room gain conditions? Do ported ones show weired behavior (their problems getting aggravated or something)?

Below the lowest room node the slope is about 12db/oct. The reason I say about is becuase all cabins/rooms are a bit leaky (more so in cars) and this can cause minor ripples is this response. The reason we dont hear these ripples is becuase they are -20db or more lower than the rest of the music and our ear is less sensitive in this area.

Sealed box woofers do have a roll off that is very much similar to room gain. Ported boxes rolll off 6db/oct after than sealed box woofers. Again one might not hear his difference (faster roll off) is one's music does not have significant information in the very low bass (sub 40Hz).

[DerAlte]

Originally Posted by santosh.s

No... there is no fundamental mistake. Higher frequencies attenuate more than lower frequencies, in general. Lower frequencies are capable of traveling farther.

Aah *hitting head*, OK, E = E0 * e^-alpha*z sin(omega*t - k*z)!!!

[santosh.s]

By now, I am pretty much enlightened

Navinji, the point taken about rooms/cabins being "leaky". Effect of leakiness is very apparent in case of ear-buds and headphones. Just a little loose and you miss a lot of bass, make it firm and bass is brought back to life. I think the effect is almost absent in case of big ear-cup type of headphones which remain sealed with cushion and firm enough around the ear, all by themselves.
BTW, once I lost a foam cap of my Nokia headset and I was desperate to get it back for the same reason. I thought shopkeepers would laugh at me if I asked for that tinny foam pad! So I just bought a Rs. 40/- ear-bud of similar size, took out their foams and stuck them permanently to the headset with Fevicol. Why not, I am a DIYer too

OK, open question now is about "ported subs operated below lowest room resonance". Let me be more precise about it:

Do ported subs have trouble with frequencies in this "gain" region? I know that if the frequency is below it's port tuning frequency, then it anyway has it's own trouble. And the gain can only make things worser. But the question is- that let us say the frequency is within the range it was designed for, but it falls in the gain region of the room/cabin- In this case, will it's sound be deteriorated as compared to what it would be in an anechoic chamber?

[navin]

Originally Posted by santosh.s

Do ported subs have trouble with frequencies in this "gain" region? I know that if the frequency is below it's port tuning frequency, then it anyway has it's own trouble. And the gain can only make things worser. But the question is- that let us say the frequency is within the range it was designed for, but it falls in the gain region of the room/cabin- In this case, will it's sound be deteriorated as compared to what it would be in an anechoic chamber?

I thought we were comparing a sealed sub to a ported sub. after all few of us live in anechoic chambers.

I have little knowledge about ahechoic chambers. I have only seen one twice.

[santosh.s]

Originally Posted by navin

I thought we were comparing a sealed sub to a ported sub. after all few of us live in anechoic chambers.

I have little knowledge about ahechoic chambers. I have only seen one twice.

And I haven't seen it even once! Not to mention, I am just asking these things for academic interests. I want to understand theoretical aspects to a reasonable extent, by that I mean- until it is fairly easy to deduce practical significance, without any contradictions/confusions.