Well Excuuuuuuse Us....
Bobken:
It is good to stick up for the facts, but it is so much better to present the facts and let them speak for themselves, rather than to regard all doubters, even those who are mistaken, as vicious assailants upon all that is Good and Holy.
I had read of the "lowest frequency for a specific size room" theory discussed, both pro and con, in very general terms. I had begun to lean against it, because subjectively, it seemed to me that the "bottom" of the music was there in a car when the theory seemed to indicate it would not be.
In your original post on this matter, you said:
At this point, we should bring up the question of the word "cutoff". In most audio situations, your "cutoff" will be 12 dB/octave or more. Yes, a single element crossover will have a cutoff slope of 6 dB, but that is perhaps the one common case where we see this. Closed box speakers have a low cutoff at 12 dB/octave. Ported speakers cut off at 24 dB. Woofers with a smooth rolloff at the high end cut off at 12 dB/octave. While 6 dB/octave crossovers do have a substantial following, there is a movement toward 18 dB, 24 dB and even higher slope crossovers gaining momentum.
Given these facts, is it not fair to say that a member who reads about a "cutoff" below a wavelength of 8 feet would interpret that as meaning, "there is not much usable output below 140 Hz"? Yet in most cars, even small ones, there definitely is good, solid output below that. So, I voiced these doubts.
Your reaction?
You continue:
In fact, a home system with a cutoff of 42 Hz would fill the bill for good sound in many people's opinion. Although getting a sub eventually would be a good idea.
Second, we arrive at the crux of the matter. If the rolloff starts around 140 Hz and the response is only 7 or 8 dB down at 40 Hz, that has got to be the most gradual rolloff rate I have ever seen in audio. Since 40 Hz is 1.8 octaves underneath 140 Hz, the rate is a scant 4 dB per octave!!
Moreover, 110 cu ft of space is a rather small passenger compartment. If the longest dimension is 8 feet, then the height and width are only 3.7 feet each. Tight squeeze. For larger cars, the rolloff would start later, which means that the response might only be 5 or 6 dB down at 40 Hz.
I willingly accept your evidence, including your own measurements on your house and car, and now realize that there is indeed an attenuation of bass frequencies in an automobile, although the attenuation rate appears to be so gradual that it is not huge at the 40 Hz mark.
Without that further explanation on your part, however, it seemed for all the world that you were saying that there is little to hear in a car below 140 Hz, which is rather bass shy. I might not have the keenest ear in the world, but I think I can tell if a system is putting out below 140 Hz, and in many cars, the sound system does.
If you had offered your data and explanation without snide comment, I for one would have accepted it without a problem. Instead, in the very same post where you offer the important explanatory information, we are treated to such gems as:
Your comments might have made sense if someone had posted something like, "Bobken continues to pollute these pages with still more ill-conceived drivel based upon frauds like Dickason and his own inability to read an SPL meter". However, nobody said anything like that. Even Pinkmouse's "this is a case of people confusing the thought model with reality" is nowhere near a broadside attack.
Bob, you have already added much to this forum and I certainly hope you will add more. However, can you make it a policy to allow other members to look at your proof and full explanation of something before blasting them for not accepting it? Give the facts a chance to speak for themselves first. Most of the time, people do accept the facts, if they are presented in a calm and reasoned way.
Bobken:
It is good to stick up for the facts, but it is so much better to present the facts and let them speak for themselves, rather than to regard all doubters, even those who are mistaken, as vicious assailants upon all that is Good and Holy.
I had read of the "lowest frequency for a specific size room" theory discussed, both pro and con, in very general terms. I had begun to lean against it, because subjectively, it seemed to me that the "bottom" of the music was there in a car when the theory seemed to indicate it would not be.
In your original post on this matter, you said:
From the above, is it not fair to assume that the reader will believe that the sound will cut off below the frequency that correspnds to the longest dimension of the listening space? And if the longest dimension is 8 feet, then the cutoff frequency is 140 Hz.
At this point, we should bring up the question of the word "cutoff". In most audio situations, your "cutoff" will be 12 dB/octave or more. Yes, a single element crossover will have a cutoff slope of 6 dB, but that is perhaps the one common case where we see this. Closed box speakers have a low cutoff at 12 dB/octave. Ported speakers cut off at 24 dB. Woofers with a smooth rolloff at the high end cut off at 12 dB/octave. While 6 dB/octave crossovers do have a substantial following, there is a movement toward 18 dB, 24 dB and even higher slope crossovers gaining momentum.
Given these facts, is it not fair to say that a member who reads about a "cutoff" below a wavelength of 8 feet would interpret that as meaning, "there is not much usable output below 140 Hz"? Yet in most cars, even small ones, there definitely is good, solid output below that. So, I voiced these doubts.
Your reaction?
On the contrary, on the basis of your post I figured out the frequency which has a wavelength of 8 feet and arrived at 140 Hz as the "cutoff frequency". Not a sign of somebody who didn't read your post carefully.
You continue:
Nobody is trying to defy nature, we are just trying to understand why we can hear notes substantially beneath 140 Hz in a car when your post tended to indicate that we would not.
First, I would argue somewhat with the characterization of 40 Hz as being "not very low". The lowest note of the bass guitar-often the lowest note on a popular record-is 42 Hz. I haven't seen Audio magazine for awhile, but as of a few years ago they were reviewing many a floorstanding loudspeaker with an F3 of 40 Hz or so. These speakers sold for several thousand dollars a pair. I realize that Velodyne, Definitive and other companies produce products that plumb much lower depths than 42 Hz, but I have always felt that if you can get a system in your car producing hearable and feelable bass down to the lowest note of the bass guitar, you really have all the bass you need. I think most would agree. Most cars don't have room for a Velodyne sized enclosure, though I am sure people have done it.
In fact, a home system with a cutoff of 42 Hz would fill the bill for good sound in many people's opinion. Although getting a sub eventually would be a good idea.
Second, we arrive at the crux of the matter. If the rolloff starts around 140 Hz and the response is only 7 or 8 dB down at 40 Hz, that has got to be the most gradual rolloff rate I have ever seen in audio. Since 40 Hz is 1.8 octaves underneath 140 Hz, the rate is a scant 4 dB per octave!!
Moreover, 110 cu ft of space is a rather small passenger compartment. If the longest dimension is 8 feet, then the height and width are only 3.7 feet each. Tight squeeze. For larger cars, the rolloff would start later, which means that the response might only be 5 or 6 dB down at 40 Hz.
I willingly accept your evidence, including your own measurements on your house and car, and now realize that there is indeed an attenuation of bass frequencies in an automobile, although the attenuation rate appears to be so gradual that it is not huge at the 40 Hz mark.
Without that further explanation on your part, however, it seemed for all the world that you were saying that there is little to hear in a car below 140 Hz, which is rather bass shy. I might not have the keenest ear in the world, but I think I can tell if a system is putting out below 140 Hz, and in many cars, the sound system does.
If you had offered your data and explanation without snide comment, I for one would have accepted it without a problem. Instead, in the very same post where you offer the important explanatory information, we are treated to such gems as:
Heck, Bob, in light of your data, we would have been glad to recognize the difference if you had given us the chance to before "going ballistic" on us.
Uh, Bob, nobody is complaining about your data. The problem is that you vent your anger at us for not accepting your data in the same post that you reveal this data to us for the very first time.
I happily accept your proof and explanation at face value. A statement that appears to indicate that I am hearing nothing good in my car under 140 Hz I reserve the right to question. However, your proof and explanation arrived in the same post that you bitterly criticized everyone for not accepting your proof and explanation-even though we clearly had no opportunity to tell you that we had indeed accepted it.
Your comments might have made sense if someone had posted something like, "Bobken continues to pollute these pages with still more ill-conceived drivel based upon frauds like Dickason and his own inability to read an SPL meter". However, nobody said anything like that. Even Pinkmouse's "this is a case of people confusing the thought model with reality" is nowhere near a broadside attack.
Bob, you have already added much to this forum and I certainly hope you will add more. However, can you make it a policy to allow other members to look at your proof and full explanation of something before blasting them for not accepting it? Give the facts a chance to speak for themselves first. Most of the time, people do accept the facts, if they are presented in a calm and reasoned way.
To this discussion, I have a simple thought experiment to propose.
If we follow the reasoning of bobken with regards to the propagation of sound waves in an acoustic environment smaller than the wavelength we're trying to produce:
What would the theoretical cutoff frequency be for a pair of headphones, which have a standard loudspeaker driver (albeit small) in a small closed chamber, firing into an acoustic environment (for all intents and purposes, the same as the "room" or "car" whose largest dimension is an inch or two?
(Hint, a 7khz sinewave has a wavelength of roughly 2 inches)
If we follow the reasoning of bobken with regards to the propagation of sound waves in an acoustic environment smaller than the wavelength we're trying to produce:
What would the theoretical cutoff frequency be for a pair of headphones, which have a standard loudspeaker driver (albeit small) in a small closed chamber, firing into an acoustic environment (for all intents and purposes, the same as the "room" or "car" whose largest dimension is an inch or two?
(Hint, a 7khz sinewave has a wavelength of roughly 2 inches)
ThingyNess said:
Hi ThingyNess,
This is the most challenging (in thought) post on this thread for some time, and it is a very interesting point which you have raised here.
There is an equally interesting but rather involved answer, of course, but I am not going to post it all *directly* here as I don't want any more disagreements with anyone.
I will give you some clues, though, and I guess you will quite quickly reason it out for yourself.
When you are listening to some real bass through headphones, try moving the earpiece well away from your ear so that there is clear air space between your ear and the driver, and see what that does particularly to the lower frequencies.
In doing that, you will be losing any close-coupling effect and the attendant 'direct excitation' of the inner ear.
Remember, unless you poke something hard into your ears (not recommended!), the way that you *hear* things normally is via the air between the sound source and your eardrum etc., and this 'column' of air also has to vibrate in some fashion (in time) to the sound of the source, for this sound to be transferred.
Almost everything has a fundamental resonace below which it cannot normally be made to vibrate *properly* (i.e. in tune) and the greater the mass, the lower this fundamental resonance is.
Big ships pitch very slowly because of their huge mass, but rowing boats bob up and down quite quickly!
Air is quite light in weight (=low in mass), and to get some of it to vibrate (oscillate) at a very low frequency, you do need rather a lot of it!
This is the crux of the problem with propagating low bass in cars with loudspeakers. There simply isn't very much air in them because their maximum inside dimensions are so small!
However, very likely if you could somehow press the car speakers hard against your ears whilst listening, to avoid the intervening column of air, you would probably not have this same limitation.A while ago, before I had a stethoscope, I used to listen to car engines when diagnosing their problems, by placing a screwdriver handle hard against my outer ear and the blade against the engine block. This was very effective and is an example of 'direct excitation', which does not rely on any air at all for the sounds to be heard, and therefore it has *unlimited* downward extension in frequency.
I realise that this has not directly answered your point, but hopefully from what I have said, it will enable you satisfy yourself with regard to (some of) the differences which exist when dealing with headphones and in the ways sounds are propagated.
Basically, it is not correct to suggest that these rather different environments, with varying limitations, are the same, and comparing a pair of headphones with a room is therefore not really appropriate, even though it may be intuitive.
(I haven't said any of this, though)
Regards,
Hi Bob
Sorry it took so long to get back to you but I am very busy at the minute, ( so I will also have to be brief )
OK, what I see as the problem in the idea that a room has to be a wavelength or longer to support a frequency is this:
I assume you agree with me, that an inpulse from a driver moving can be carried in a very small space, due to it being a pressure wave travelling at the speed of sound, in fact in the space moved by the cone when it displaces.
This is pure transmission, and in effect is duplicating the signal as received by the driver from the amp. This is demonstrated in the open air, when there are no boundaries to support standing waves, or very close to a speaker, when boundaries will have no effect, ( this is similar to the technique used in measuring drivers with an impulse response test, where low frequencies are gated out).
Once you bring a room, (any size or shape) into the equation, you then have a reverberant space. This colours the speaker response in the same way that adding capacitances and inductances at random to a speaker cable would, not something that is desirable, I'm sure you would agree.
Therefore the theory that a room has to be big enough to support a particular frequency is only true if you want to add room reverb effects to the sound you get from a speaker. This may not be a bad thing, some people may like that effect, and as sound perception is a personal thing, no one can tell anyone else that their perception is wrong, especially not me
Sorry it took so long to get back to you but I am very busy at the minute, ( so I will also have to be brief
)OK, what I see as the problem in the idea that a room has to be a wavelength or longer to support a frequency is this:
I assume you agree with me, that an inpulse from a driver moving can be carried in a very small space, due to it being a pressure wave travelling at the speed of sound, in fact in the space moved by the cone when it displaces.
This is pure transmission, and in effect is duplicating the signal as received by the driver from the amp. This is demonstrated in the open air, when there are no boundaries to support standing waves, or very close to a speaker, when boundaries will have no effect, ( this is similar to the technique used in measuring drivers with an impulse response test, where low frequencies are gated out).
Once you bring a room, (any size or shape) into the equation, you then have a reverberant space. This colours the speaker response in the same way that adding capacitances and inductances at random to a speaker cable would, not something that is desirable, I'm sure you would agree.
Therefore the theory that a room has to be big enough to support a particular frequency is only true if you want to add room reverb effects to the sound you get from a speaker. This may not be a bad thing, some people may like that effect, and as sound perception is a personal thing, no one can tell anyone else that their perception is wrong, especially not me
pinkmouse said:Hi Bob
Sorry it took so long to get back to you but I am very busy at the minute, ( so I will also have to be brief
OK, what I see as the problem in the idea that a room has to be a wavelength or longer to support a frequency is this:
I assume you agree with me, that an inpulse from a driver moving can be carried in a very small space, due to it being a pressure wave travelling at the speed of sound, in fact in the space moved by the cone when it displaces.
This is pure transmission, and in effect is duplicating the signal as received by the driver from the amp. This is demonstrated in the open air, when there are no boundaries to support standing waves, or very close to a speaker, when boundaries will have no effect, ( this is similar to the technique used in measuring drivers with an impulse response test, where low frequencies are gated out).
Once you bring a room, (any size or shape) into the equation, you then have a reverberant space. This colours the speaker response in the same way that adding capacitances and inductances at random to a speaker cable would, not something that is desirable, I'm sure you would agree.
Therefore the theory that a room has to be big enough to support a particular frequency is only true if you want to add room reverb effects to the sound you get from a speaker. This may not be a bad thing, some people may like that effect, and as sound perception is a personal thing, no one can tell anyone else that their perception is wrong, especially not me
IMVHO nicely put
SkinnyBoy said:Just an update.. My Sproggy Powersupply can run my Celeron 466... It gets hot, but it runs.. Thats just the motherboard and graphics card, cpu and memory.. no HD or CD..
Do you have details of this power supply...? the HDD / CD-ROM are killers for power on spin-up, you would not want your PS voltage to 'sag' at these moments and cause an array of problems (sometimes not obvious but should be checked)
I was sort of thinking to make a comp. in 2U case (mostly because I have the bits kicking around spare) to make a MP3 jukebox (and do a few other bits and bobs). This would certainly not be the last word in sound reproduction quality, but there are some pieces of music I have on mp3 that I like but don't want to burn to CD, and background muzak for parties (planned or otherwise
).*ted*
I think a linear PS would be good (at least for the excuse of building it) . I do not plan on putting the mp3 player in the car.
Dear Bob,
OK there were some things kinda out of line (strong coffee probably and my rather mean attitude
lol), But.....
[playground] “Sir, sir, bobken started it!” [/playground]
And you still obviously want to continue arguing, which I am nearly (which I said earlier) tired of (but beats work).
TED
/
seek and find
OK there were some things kinda out of line (strong coffee probably and my rather mean attitude
lol), But.....[playground] “Sir, sir, bobken started it!” [/playground]
And you still obviously want to continue arguing, which I am nearly (which I said earlier) tired of (but beats work).
TED
/
seek and find
Bobken said:
..............
It is just a shame that we had to 'prod' you to get a more elaborate explanation". What am I, for goodness sake, merely a free service to satisfy everyone on the Forum who might enquire (or less politely, as was the case here, simply make some passing adverse comments) with some intrinsic obligation for me to patiently teach them, in one thread, all that I have taken 40 years to learn?
..............
Sort of,
When you post on a forum, you are bound to get a reply of some such and therefore should be aware that you may or may not be needed for an extended discussion/probing
Re: Re: SMART (*****)
I don’t think that this is the case within this topic at all...
We know :
Bobken = Bob
pinkmouse=Al
fdegrove=Frank
mrfeedback =Eric
helix=ted
christer=christer
we dont know:
skinnyboy
dhaen
kelticwizard
Personally I don't care if I know there real name or not, most of the time I forget it anyway (useless with names).
When I write a message intended for 1 person I try to put my name at the bottom but I often forget, when I do a global or general question I normally don't bother. Most 'chat' things on the internet are pseudo named and I don’t expect DIYaudio to be different. Anyway what’s to say that if you enforce this rule that people don't just enter a pseudonym for there first name?
mrfeedback said:
I don’t think that this is the case within this topic at all...
We know :
Bobken = Bob
pinkmouse=Al
fdegrove=Frank
mrfeedback =Eric
helix=ted
christer=christer
we dont know:
skinnyboy
dhaen
kelticwizard
mrfeedback said:
Personally I don't care if I know there real name or not, most of the time I forget it anyway (useless with names).
When I write a message intended for 1 person I try to put my name at the bottom but I often forget, when I do a global or general question I normally don't bother. Most 'chat' things on the internet are pseudo named and I don’t expect DIYaudio to be different. Anyway what’s to say that if you enforce this rule that people don't just enter a pseudonym for there first name?
Helix said:
Do you have details of this power supply...? the HDD / CD-ROM are killers for power on spin-up, you would not want your PS voltage to 'sag' at these moments and cause an array of problems (sometimes not obvious but should be checked)
I was sort of thinking to make a comp. in 2U case (mostly because I have the bits kicking around spare) to make a MP3 jukebox (and do a few other bits and bobs). This would certainly not be the last word in sound reproduction quality, but there are some pieces of music I have on mp3 that I like but don't want to burn to CD, and background muzak for parties (planned or otherwise
*ted*
I think a linear PS would be good (at least for the excuse of building it) . I do not plan on putting the mp3 player in the car.
The "Sproggy" powersupply is DC-DC to run the computer in the car..
lol Can't help with details, sproggy's site seems to have gone..
HAVING THE LAST WORD.
Hi,
Thanks Eric, that is an accurate explanation.
Al,
When you look at what preceded this you may see that it was an attempt to make people realise that there is little point in continuing arguing a topic just for the sake of arguing, unwilling to see the other person's point of view.
If some people felt offended by it then I would like to apologise to them.
What bothers me most however, is that some people can be really offensive and rude to other members and get away with it.
Therefore a little moderator intervention wouldn't hurt at all, what is important though is to intervene at the right time and for the right reasons.
Like yourself, and no doubt many other members I would like to see a certain level of mutual courtesy and respect.
Nothing personal is meant by it, I fully understand that a moderator can't be omnipresent and no one expects perfection.
Anyway, I hope this settles the confusion,
Hi,
Thanks Eric, that is an accurate explanation.
Al,
When you look at what preceded this you may see that it was an attempt to make people realise that there is little point in continuing arguing a topic just for the sake of arguing, unwilling to see the other person's point of view.
If some people felt offended by it then I would like to apologise to them.
What bothers me most however, is that some people can be really offensive and rude to other members and get away with it.
Therefore a little moderator intervention wouldn't hurt at all, what is important though is to intervene at the right time and for the right reasons.
Like yourself, and no doubt many other members I would like to see a certain level of mutual courtesy and respect.
Nothing personal is meant by it, I fully understand that a moderator can't be omnipresent and no one expects perfection.
Anyway, I hope this settles the confusion,
If you are speaking audio electronics IQ count me an idiot. You have to start somewhere. On behalf of the idiots in the crowd I think the moderators do an impossible job tolerably well.
Here's to you Al (actually I like pinkmouse much better)
John Daniel? You must mean you don't know him?
He just started a website. http://www.dhaen.org.uk/valve.htm
Cheers
Craig Ryder
Re: Students Are Not All Idiots.
oh yes, so there are even less members here who "hide behind just about any kind of stupid pseudonym"
I think he is refering to me!
TED
Ryder said:
If you are speaking audio electronics IQ count me an idiot. You have to start somewhere. On behalf of the idiots in the crowd I think the moderators do an impossible job tolerably well.
Here's to you Al (actually I like pinkmouse much better)
John Daniel? You must mean you don't know him?
He just started a website. http://www.dhaen.org.uk/valve.htm
Cheers
Craig Ryder
oh yes, so there are even less members here who "hide behind just about any kind of stupid pseudonym"
mrfeedback said:
Hi Craig,
There are different kinds of idiots.
From what I have seen of your posts you are not the kind of idiot referred to.
Keep on learning and enjoy it.
Eric.
I think he is refering to me!
TED
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