# dB and Hz clarifications

#### BassOdyssey

##### Auditioning
Hi, Im just looking for a better understanding of dB VS Volume and how Hz plays a factor in HT and speaker ratings.

On my sub, what would be the difference in output from my sub if I turned the knob on the back of the unit from 0 dB to +6 dB. How does this differ from turning up the volume on the unit.

Also could someone give me a good explanation of Hz rating and what it means. I have a very limited understanding of how it plays a role in my subs setup.

~Chris

#### Wayne A. Pflughaupt

Moderator
If by “Hz rating” you mean the sub’s frequency response -the lower it goes, the better. 30 Hz would be a so-so sub, 20 Hz or lower is outstanding. Most knowledgeable home theater buffs agree that 25 Hz is minimal for an acceptable sub for home theater.

Regards,
Wayne A. Pflughaupt [/size][/font]

#### JohnRice

##### Bounded In a Nutshell
Supporter
Senior HTF Member
I get the feeling Chriis is looking for a more fundamental explanation of dB and Hz, so...

Hz, is a measure of frequency. Essentially, sound is vibrations and the number of Hz is the number of vibrations per second. "Standard" sound range is typically defined in the 20-20,000 Hz range, however, essentially nobody can actually hear up to 20,000 Hz. Usually about 17,000 Hz is about the maximum of human hearing, though it can be lower, depending on the age of the individual and a bunch of other factors. Also, frequencies below around 80Hz aren't technically heard, so much as felt, though there is a gradual shift between the two senses.

dB is simply a unit of measurement to guage the volume of sound. Objectively, an increase of 3dB is considered to be "twice as loud" but in the real world and in the perception of listeners, that doesn't usually work out that way.

Increasing the volume on your sub is different than just turning up the volume on your receiver, because it changes the ratio of the volume between the sub and the rest of the speakers. If you turn up the volume on the receiver, all speakers get louder in proportion. When you turn up the volume on the sub, only the sub gets louder.

The real wild card is that none of this actually explains anything, since perception is such a major factor and manufacturers lie as far as the day is long about the specs of their equipment. They want consumers to purchase based on numbers, which invariably have nothing to do with the real world.

#### BassOdyssey

##### Auditioning
Hi John,

Thanks for taking the time to reply to my question. I guess my question is now, is it better to increase the dB or the volume on my Sub If I want more Bass? Is one tighter then the other? Safer then the other? Also what is the significance of setting the cutoff frequency any where from 35 Hz - 150 Hz ?

Thanks again.

#### Seth=L

##### Screenwriter
Lets make a hypothetical system. I will make it a simple system to make it easier on me.

Lets say you have Denon surround sound receiver but you have chosen to use it for stereo for the time being. You also have in this hypothetical system a pair of Bookself speakers and a hefty subwoofer.

Lets say the bookshelf speakers have an average frequency range of 60Hz-20Khz (20KHz is 20,000 Hertz). The sub has a frequency range of 20Hz-200Hz due to the intentions of the x-over design to keep any high frequencies out of the sub.

To make a seamless integration of the speakers and the sub you must set the x-over on the sub to, in theory, around 60hz. This allows the sub to pick up the lower bass the bookself speakers are unable to produce. The gain AKA volume or Db level will increase how much bass you have.

Now, if you set the x-over to high on the subwoofer it could result in cancelation of bass or exagerated or boomy bass depending on the acoustic environment and location of each component.

Idealy you would set the receiver to not allow any frequencies lower than 80 or 100 hz to go to the bookselfs. Doing this allows you to reduce demands on the receiver's amplifiers, because deeper bass requires more power. Then you would set the sub to what ever frequency cut off you chose for the receiver. Say you set the receiver to only allow the bookshelfs to go to 80Hz, you would then set the sub x-over frequency to 80Hz.

#### JohnRice

##### Bounded In a Nutshell
Supporter
Senior HTF Member

You're still having a fundamental misunderstanding of the terms, at least from how I am interpreting the question. dB and volume are connected. If you increase the volume, you increase the output, which is measured in dB. And, yes, you increase the volume on the sub if you want more bass in reference to the other speakers. This does not mean you will get deeper bass.

As far as cutoff goes, it is best to bypass the cutoff on the sub and let the receiver handle that, if your components have the capability.

You have no idea how complex the questions you are asking are. There absolutely are no correct answers to them particularly with so little information provided. If you want to learn this stuff, you need to do a lot of reading first. Look around HTF and plan on taking quite some time to soak it all in before it starts making sense. If you continue with the questions you are asking, you will only end up more confused, because no reliable answers can be given without a LOT more information being provided first.

#### JeremyErwin

Senior HTF Member

What an odd technical definition. Of course it's heard. You can't localize it, but the ears are picking it up. Have you no access to a pair of headphones and a tone generator?

#### JohnRice

##### Bounded In a Nutshell
Supporter
Senior HTF Member
Whatever Jeremy. Maybe it is a bit lower than 80 Hz, but pretty close to that area you no longer hear frequencies. It's called subsonic radiation, subsonic meaning below sonic frequencies, meaning below the ability to hear. The headphone analogy has no bearing. Headphones can also be capable of reproducing subsonic frequencies. They transmit them directly to your skull as vibrations. The "nondirectional" aspect is just another characteristic of low frequency "audio" radiation.

#### JeremyErwin

Senior HTF Member
Sounds lower than the lower limit of human hearing (20Hz) are infrasonic (not subsonic). Some of those can be felt. The 80 Hz crossover is a compromise, and has as much to do with making speaker setup easier as anything else.
And no, it's not an analogy. It's an experiment.

#### JohnRice

##### Bounded In a Nutshell
Supporter
Senior HTF Member
All quite helpful to the questions posed in the thread. No doubt pointing out that infrasonic is technically the correct term, and various bits of (somewhat incorrect) nitpicking will go a long way to clearing up the confusion of the thread creator. Productivity at its best.

Try to give some constructive help, and someone has to come in and show their vast knowledge, while likely causing more confusion. My obvious mistake for trying to interject some "plain language" to make some broad strokes and reduce some confusion. Now I remember why I started steering clear of the hardware sections several years ago.

#### JeremyErwin

Senior HTF Member
Ah, instead of reaching into the web for a Physiological Reviews article on the "Mechanics of the mammalian cochlea", I'll just go with the following observations.

1. Humans can hear frequencies between 20 Hz and 20 kHz, with substantial erosion of the high frequencies by adulthood.
2. They can feel infrasonic sounds, provided that such 'sounds' are loud enough.
3. A human can also "feel" low octave sounds, and up to perhaps 25 -- 40 Hz, this is important.

4. At the same time, human hearing is less sensitive to the lowest frequencies. There's a threshold of audibility: if a 23 Hz frequency s reproduced at less than 75 decibels, it won't be heard or felt. 20 Hz has an audibility threshold of about 82 dB; 15 Hz, about 90 dB. This part of the reason why movies have a Low Frequency effects channel-- while the main speakers have an upper limit of 105 dB, the LFE is calibrated to reproduce sounds as loud as 115 dB. All of this, of course, is dependent on whether the amplifiers can supply enough power.

5. A subwoofer that cannot reproduce sound below 30 Hz or so won't provide the same visceral impact as one that can hit 25 Hz or below. And so on, and so forth.

Sound pressure levels (among other things) are measured in decibels. Decibels are logarithmic--

85 dB is twice as loud as 82 dB, which is twice as loud as 79 dB. Conveniently, a loudspeaker requires twice as much power to generate a 3dB louder sound.

In short, if you want to hear the lowest notes of the movie, turn up the system volume. If you prefer to listen at lower volumes, you could always run the subwoofer turned up, although this could result in a bassy sound. The gain on the subwoofer and in the receiver do approximately the same thing.

And, now, back to the equivalent of rec.audio.opion with me.

#### Ryan-T

##### Auditioning
It sounds to me like the OP has a bass boost in his sub amp that is switchable( 0db=off, 6db=boost).

Is there any Hz numbers printed next to the 0-6 dial? Possibly 30Hz?
Bass boost is used to increase output at certain frequencies (Hz) usually in a sub that doesn't have a very good low end.