The physics and understanding of low frequencies - Page 5

Originally Posted by Bone215

I think there is a very serious language barrier here.

By the way, I asked how old you were to determine your age, period, don't worry about what I was assuming, I was just asking.

You seem to be a person whose natural first language is not English. If that is true, I think that is contributing to some of the confusion.

The other possibility is, well unkind and I won't say it. Good luck.

Originally Posted by ccotenj

^^^

dude, there's no "excuse" for your disagreement... you simply are wrong... you can restate your points over and over again, but it's not going to change anything...

you can choose to accept that and learn from what people are trying to tell you, or you can beat your head up against the wall... it won't take much longer for people to lose interest in trying to educate you...

did you buy "the master handbook of acoustics" yet?

Originally Posted by jwickers

I am surprised you can actually compare a flat TV speakers to floorstanding speakers, but i guess it depends what kind of tower you actually had in what condition they were.

But in general flat TVs are very poor on the sound side, which is why manufacturers try to push "sound bars" as upgrades. For example i had a samsung LCD C6500 i think, it had one driver on the back, the sound was horrible for anything either a bit loud or the lower frequencies. Even man voices sounded bad.

The speaker is so bad that you have to play it loud just to be able to understand what people are saying, and that cause the speaker to saturate and make the TV plastic back to vibrate. Of course that the speaker was firing at the back of the TV did not help.

So when you say "loud enough to be unpleasant and vibrates the tv like crazy" i guess you are talking about the same thing, very early saturation.

With a good speaker at least you can clearly understand voice so that you can play them at low volume without losing clarity.
And a good speaker can play very loud without being unpleasant (if you stay within reasonable SPL of course), if at a given volume the sound seems unpleasant, saturated, you are either at the limit of the speaker of the speaker is just poor and high volume amplifies the weaknesses.

But then not all TVs are the same, you can have decent sound for TV watching, but nothing approaching the dynamic of a real sound system.

Originally Posted by DanLW

Ah, now we're getting somewhere, to the genesis of the issue.

Do you have any idea what towers those were? 3" drivers isn't all that large. 5" is usually standard for bookshelves.

The TV can be loud enough to be unpleasant and vibrate like crazy because distortion sounds "loud". What is the make/model of your TV?

Here's what happens when you give speakers more power than they can handle. They start distorting, maybe even clipping. When clipping happens, your THD goes through the roof because a clipped waveform generates harmonics like crazy.

For example, here is a spectrum of a 60Hz sine wave vs a 60Hz square wave (full clipping)



In this picture, for the sine wave (top) we see a small harmonic at 120Hz, and another at 240Hz. Ignore the peak at 190Hz as that is not a harmonic. That's fan noise from the room I am in.

On the bottom of this picture, the square wave is generating strong harmonics at 180, 300, and 420Hz. But it's actually worse. I widened the spectrum out a bit...



Going all the way out to 2KHz, we can clearly see the first 16 odd harmonics of this clipped 60Hz waveform! So not only are we getting 60Hz, we are also getting sound output at 180, 300, 420, 540, 660, 780, 900, 1020,1140, 1260, 1380, 1500, 1620, 1740, 1860, and 1980Hz!

This is where bigger speakers come into play. If you drive small speakers into clipping, they will sound much louder, and much more annoying, because of the distortion. Recall that a complex sinewave has many, many different frequencies in it. If you clip all those, you are going to get hundreds if not thousands of odd harmonics coming through the speakers. That turns sound into noise.

Bigger speakers can handle much more power than the small ones. So you can have them louder without them being noisier.

Another advantage of separate speakers is the wider you can space them apart, the larger your "soundstage" will be. So your stereo effects will be much ore enveloping.

Your room also can play a part in how speakers sound. If you have hardwood floors with no carpet, and a vaulted ceiling, most any sound system will sound bad. This is because as the room echoes, those echoes become noise. So carpet and furniture in general can help.


Out of curiosity, what is your native language? I moved to Germany and got a basic understanding of the German language, but I can't imagine being able to carry on a conversation as complex as audio theory with a native German speaker. So you're doing better than I am!

Originally Posted by DanLW

Oh, dang, I'm sorry! I misread your statement a few posts back...

Originally Posted by DanLW

Yeah, the typo was what caused my misunderstanding.

Moving on...

Looks like the speakers in your TV are 10W speakers. So their sensitivity is likely at best 85db, meaning they will generate 85db of sound with 1 watt of power at 1 meter. Sound pressure decreases by 3db per doubling of distance in most rooms, so at 2 meters, it will be 82db, 4 meters 79db. Not sure how far away from your TV you sit, but we'll say 2 meters, about 6 feet, for the sake of argument. So at the listening position you will hear 82db with 1 watt going to the speakers. Now, the loudest you will hear is 92db if the speakers received a full 10W of power, assuming the amp in the TV can provide a full 10 watts per channel (and I don't see why it wouldn't) So, when you watch a movie, you will have to watch at least 13db below reference (reference being 105db peaks). So while most of a movie may sound good, once the action starts, you will probably not be getting near as good sound quality as with your towers.

Also, the tower's ability to play lower frequencies is a good thing. Ideally you want to cross your sub over to your main speakers no higher than 80Hz. This is because below 80Hz (60hz by some accounts) sound loses directionality. So if a sub is only playing 80Hz or lower, you won't be able to tell the sound is coming from the subs location. But if you have to cross it over at 120Hz in order to meet up with your TV speakers, you will be able to tell that the lows (80-120hz) are coming from the sub.

So external speakers would be good, if nothing more than for their lower frequency response. How much you spend is up to your own personal preference and budget.

Originally Posted by goneten

A bigger room will naturally have a lower resonating frequency. In the size space of the Imax theater it might be 10 Hz. Good luck achieving any kind of boost down there. At the end of the day in order to perceive a low frequency you need displacement and lots of it. To achieve clean 20 Hz output at levels you can perceive in a massive space like an Imax requires lots and lots of woofers with clean linear excursion and massive amounts of power.

One can't say that the Imax didn't thrill them simply because they couldn't detect 20 Hz. Either the content had sub-20 Hz information recorded in the soundtrack or it did not. At the end of the day, whether the content has the low frequencies recorded is irrelevant if the system is still incapable of shifting the required amount of air at those frequencies which is the most important criteria for determining whether you will or won't experience those frequencies.

Originally Posted by JHAz

You can hear the fundamental of the bottom piano note (27 Hz) in a large concert hall. "pressurizing" the room, while I kind of understand it, sometimes seems to me to equate to "make it like my car." Well, most of the sounds we're reproducing aren't like what occurs inside a car, so folks who seek the car experience in their homes are looking for something other than accurate reproduction, in my view, assuming I understand what folks seem to be saying. My little 10 inch sub will play 20 Hz loudly enough te be heard, but it's closer to flat only down to 25 Hz (and only if I don't get too loud. There is no reason at all that theaters cannot play down into the 20s, and in fact movies are mixed in theater sized rooms that have systems that are flat to below 20 Hz. It is neither necessary (in my view) nor possible once you exceed some specific room dimensions to create the kind of pressurization that easily occurs in cars, and that many can achieve in their home systems, in more manageable size (ie dimensions less than the wavelength of the bass frequencies). I'm not saying it isn't fun, just that it isn't necessary to "pressurize" a home theater room to play low.

Originally Posted by bfreedma

I think it has more to do with the ability to keep bass in one theater from interfering with others in a multiplex. You would need some serious soundproofing in the common walls to contain output below 40hz or so.