Can't we produce clean bass in a car's cabin?

[santosh.s]

Originally Posted by DerAlte

(OEO = O Enlightened One!

Not yet enlightened... none of the answers explain what makes car subs more suitable to acoustics of a car's cabin!

Some more background on my questions- I knew that in any room, above certain frequency (corresponding to the lowest room mode), there is this unavoidable problem of reflections and standing waves. And it is "chaotic" to say the least. But leaving that part aside, I had little or no information on what happens below the lowest room mode frequency. The mouthshut debate was based on what I had learnt from an article on Rod Elliot's page (see section on wave versus pressure-mode propagation of sound):
The Subwoofer Conundrum

Today I saw another passing comment about this on Linkwidtz Lab site (see section "C2- Sound waves in a rectangular, rigid room"):
Room Acoustics

However, both these articles cover the point superficially, thereby leaving it unclear. Both of them seem to imply that at very low frequencies (low being defined by the size of room or cabin), pressure-mode dominates over soundwaves. And that the "pressure-mode" leads to improved acoustic response for subwoofers, popularly known as room or cabin gain. The first one says that sealed subs perform "better" than ported ones under such circumstances, whereas the second one says this gain is 12dB/octave for "sealed" subs (no mention of ported subs here!).

The last point about sealed versus ported can actually be a good sub-topic for this thread

[Sahil]

I love the bass that was put out in my mercedes. Was very clean and crisp as opposed to hard and loud when you use a sub woofer.
Havent been able to achieve such bass from other speakers that i have ever fitted in any of my cars.
I am yet to find speakers that can give such bass in standard fitment.

[navin]

Originally Posted by DerAlte

I was talking about what happened after that: OEO asked "how is a car sub different from home sub (Ignoring all electrical or environmental factors)": sub as a component. .

Oops. Ok most car subs do not make good home subs. Most home subs wont survive too long in a car.

I have used home subs in a car (4 8" 8N515 Focals becuase I had them lying around and the install in my nephew's car called for a small sub so I built him a pair of isobarik 4th order bass reflex). The sounded good while they lasted but I guess Mumbai's heat and humidity got to them before too long.

There are a few home subs that look good as car subs. Many of these have heavy cones, huge surrounds, and huge Xmax and low Sensitivity. They are meant to be driven with big Class D amps and while they can pump out prodigious ammounts of bass in the home or in a car the bass is not of very good quality.

I feel that most car subs if used at home will need proper placement to produce decent bass and even then might end up sounding a bit lumpy. I have never used car subs at home (as usually I have more home speakers lying around than car speakers) but Vivek Phadnis is working on such a design. We will see what happens when he is done.

[mithun]

The length of the average car interior (including trunk) is in the 12 ft range the 40 Hz note will be longer then the car's interior. This is why notes below 70-90 Hz (depending on the vehicle) will have a greater output than the rest of the frequencies. Once this magic frequency is reached, bass output will increase by about 12 dB/octave below that frequency. This phenomenon is called cabin gain or "transfer function". So a smaller vehicle will have a greater cabin gain and should be able to have greater low bass than a larger vehicle. This is true for identical subwoofer systems with identical power.

Because there is so little space in a car the bass notes (which are long waves) build up inside the passenger area. Hope that may be the reason why we can't produce clean bass in a car's cabin.

[santosh.s]

Originally Posted by mithun

Because there is so little space in a car the bass notes (which are long waves) build up inside the passenger area. Hope that may be the reason why we can't produce clean bass in a car's cabin.

You mean to say as you go on reducing the cabin size, more and more "clarity" will be compromised. Think of headphones- there is very tiny space between them and ears. However, they are very good at producing "clean" bass (Not only they are supposed to be free from room modes, they are also able to provide stereo bass). How do you explain that?

Originally Posted by navin

Like I said earlier the reason we are able to produce bass that is lower than the wavelengths supported by the boundaries (in a car or in a home) is that we are
1. able to damp all resonance nodes and their overtones sufficiently enough for these low frequencies to be heard

-Resonance modes occur at frequencies above the one that corresponds to twice the maximum dimension of the room, not below that. Since car cabin's max (internal) dimension is quite low the first room mode itself should be quite high in frequency. Say it is 5-6 feet, then there should not be any resonance mode below wavelength of 10-12 feet, which is about 100Hz, and it covers pretty much the whole "bass" range! Does that mean that bass in fact may be cleaner in cars as compared to typical homes?

-Room modes or standing waves are a result of reflection from rigid boundaries. In case of car the tin walls are far from being rigid for acoustics. I believe they vibrate themselves so much and a lot of sound is transmitted outside, especially at bass frequencies. That is probably why people hear that thump from a passing by car. And AFAIK, the damping material applied in car walls helps more to tame its own vibrations (ringing) than helping in reducing the reflected sound. And in any case, damping materials don't help much for reflections at bass frequencies, right?

[tsk1979]

There is a wrong assumption here, i.e. the car is an enclosed space.
Its not. Its only a partially enclosed space.
A car may be 12 feet long but how thick is the steel?
We can safely say atmost 2 sheets totalling about 1 inch.
Also car doors or glass do not have vaccum, right?
So the "sound energy" is not enclosed, but can be easily transmitted outside.
If you take car which has sound proof glass, i.e. vaccum or air filled double layer glass, then you will get more.
Now if your wavelength is 12 feet, and your car has 6 feet of space, that will lead to a standing wave.
In a car like environment, which is not "opaque" bass energy can be dissipated easily, so no issue of energy buildup in normal cars.
To have a good Bass response, the interior of a car should be such that it does not reflect sound.
Why do you think Cinema halls have all those thick curtains, so that no reflections are there.
As long as the level of reflections in a car is kept to minimum, the Bass will be clean.

[low_bass_makker]

Originally Posted by santosh.s

You mean to say as you go on reducing the cabin size, more and more "clarity" will be compromised. Think of headphones- there is very tiny space between them and ears. However, they are very good at producing "clean" bass (Not only they are supposed to be free from room modes, they are also able to provide stereo bass). How do you explain that?

Sir in a headphone it is a case of IB install with on side of the driver is cover directly over the ear and the other side is open, the work done is by the air trapped between the ear and the driver.

[santosh.s]

Originally Posted by tsk1979

There is a wrong assumption here, i.e. the car is an enclosed space.
Its not. Its only a partially enclosed space.

As always, nothing is perfect in practice, so yes it can not be considered as infinitely rigid enclosed space. But on the other extreme, it is not fully transparent (acoustically) also, which would be as good as open air- cabin boundaries would be no issue at all, in this case. It has to be somewhere in between these two. As compared to cement-concrete rooms that most of us live in, car is much more transparent and I had mentioned this point.

A car may be 12 feet long but how thick is the steel?
We can safely say atmost 2 sheets totalling about 1 inch.

if you are referring to metal sheets used to make the body, it is far less than 1 inch.

Also car doors or glass do not have vaccum, right?

I believe glass is much more opaque (rigid) than metal/plastic doors (although for sound, not light!)

If you take car which has sound proof glass, i.e. vaccum or air filled double layer glass, then you will get more.

You are referring to techniques to make it more sound proof, but as I said above solid glass itself is pretty much sound proof and it causes significant reflection of sound. Glass walls are a major problem in room acoustics (though, in spite of this fact, you may find many "demo" rooms with glass walls all around!)

Why do you think Cinema halls have all those thick curtains, so that no reflections are there.

Well, I know why curtains are there, but do you know that they are good at high frequencies and that for bass they provide little or no benefit?

[santosh.s]

Originally Posted by low_bass_makker

Sir in a headphone it is a case of IB install with on side of the driver is cover directly over the ear and the other side is open, the work done is by the air trapped between the ear and the driver.

Exactly, so I was thinking that the air trapped in the cabin may be doing some similar job. Though it is not as "trapped" as in headphone because of its size is relatively bigger. As the size becomes very big, there is no "trapping" as such and it would become more of "free" air. Does it make sense?

[navin]

guys mithun does have a point.

All cars have a transfer function and part of that transfer function is a roll off in the low bass (below 60Hz). Car subs are designed to compenate for this roll off by having a rising response.

Like I said it is not diffcult to produce bass in a car but dont expect a home sub to do the job satisfactorily.

The gauge of steel in a car is 18GA or at best 16GA. Even with damping it does resonate some. Almost every door panel resonates. If one built a car that was really sound proof one would nee a 400 cu in block to move it and it would give 4 mpg.

[santosh.s]

Originally Posted by navin

part of that transfer function is a roll off in the low bass (below 60Hz). Car subs are designed to compenate for this roll off by having a rising response.

I guess you have said it the other way round, by mistake. There is a "gain" at lower frequencies and subs have to be "roll off"

[DerAlte]

Originally Posted by santosh.s

it would become more of "free" air. Does it make sense?

Not entirely. "Free air", as the term is used, is absence of interplay, i.e. absence of a "transfer function". Headphone "trapped air" does have a transfer function, so it is not also "free air". Canal buds, or in-ear EPs are the closest, where the "free air" is a few cc with no interplay (other than the hair in the canal). Capisce?

Originally Posted by navin

All cars have a transfer function and part of that transfer function is a roll off in the low bass (below 60Hz). Car subs are designed to compenate for this roll off by having a rising response.
Like I said it is not diffcult to produce bass in a car but dont expect a home sub to do the job satisfactorily.

Santosh, now THAT is the closest to enlightenment you can get on car subs v/s home subs.

Navin-ji, !!! Sorry, there was a problem with the decoders all this while, and it was going OHT.

Originally Posted by navin

The gauge of steel in a car is 18GA or at best 16GA. Even with damping it does resonate some. Almost every door panel resonates. If one built a car that was really sound proof one would nee a 400 cu in block to move it and it would give 4 mpg.

(Navin-ji, Metric units please, Imperial/US is confusing) Why *would* one want such a sound proof car? Talking of psycho-acoustics, don't forget the NVH distraction. From another viewpoint, if one can afford perfection, such a car and 4MPG are insignificant issues.

[santosh.s]

Originally Posted by DerAlte

Not entirely. "Free air", as the term is used, is absence of interplay, i.e. absence of a "transfer function". Headphone "trapped air" does have a transfer function, so it is not also "free air". Canal buds, or in-ear EPs are the closest, where the "free air" is a few cc with no interplay (other than the hair in the canal). Capisce?

I referred the term "free air" for two things-

1. Completely (acoustically) transparent boundaries, which is as good as having no boundaries.

2. "As the size becomes very big", here it is literally like free air.

Regarding transfer function, well free air is NOT neutral or "without interplay". It absorbs high frequency energy better than lower ones, that is why as you move further and further away from a sound source, you hear more of bass and less treble. In speaker enclosures, air does not compress linearly if the amount of compression is too much. That is why large throw (Xmax) woofers in relatively small enclosures suffer more from air-compression related distortion.

However, I tend to believe in whatever you have said about canal buds- that their transfer function comes (relatively) close to "no interplay". Because the only better method that I can think of is attaching the voice coil directly to ear drum

Santosh, now THAT is the closest to enlightenment you can get on car subs v/s home subs.

Navin-ji, !!! Sorry, there was a problem with the decoders all this while, and it was going OHT.

Are you serious here, or making fun of his typo??

If you go through the links that I have been posting, you know that I did have an idea about this "cabin gain" and I think most of us have. But that explains the "boom" factor, real enlightenment would be knowing what happens to SQ (our religion) or any additional gyan.

[clipto333]

Originally Posted by DerAlte

Even I am waiting for the gurus' knowledge and views on Subwoofer drivers (HT and ICE). Uee habh hard Nobhin-ji and LBM-da, now uee are oetting phor Gunobir and Clip-da and athars to shay shamtheeng. Hoeyar eej Sham?

did you mention my name deralte? was it by mistake? im not a guru, im shishya . also im not a home audio guy at all and i know little about ice.
im participating by reading this thread.

im really enjoying reading this thread. its giving my brain a good workout. i have never seen a thread in which one gets so much technical gyan. keep up the good work guys(gurus)

cheers
clip

[DerAlte]

Your lunch must have really disagreed with you, as must have mine with me. Both of us are making fundamental mistakes!

Originally Posted by santosh.s

It absorbs high frequency energy better than lower ones, that is why as you move further and further away from a sound source, you hear more of bass and less treble

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?

Originally Posted by santosh.s

Because the only better method that I can think of is attaching the voice coil directly to ear drum

You have described the ultimate bionic audiophile!!!

Originally Posted by santosh.s

Are you serious here, or making fun of his typo??
If you go through the links that I have been posting, you know that I did have an idea about this "cabin gain" and I think most of us have. But that explains the "boom" factor, real enlightenment would be knowing what happens to SQ (our religion) or any additional gyan.

Shantam papam, shantam papam! Car Gain is not the only component of the Transfer Function, and nor is apparent loudness in 2 different environments! Car Gain makes it sound louder than, say, your drawing room, but does not explain frequency response and roll-off. That way, a bad HT woofer would be a great car sub practically? Or am I missing something? You're the expert.

Originally Posted by clipto333

did you mention my name deralte? was it by mistake? im not a guru, im shishya . also im not a home audio guy at all and i know little about ice

Yes, I did, @clip. (Sorry, I forgot to include @B&T!). And no, it is not a mistake. A "guru" is by attitude, by thinking, not just knowledge. You have that, as does TEO - and that's what matters, bandhu.