Crossovers, db levels, what does it all mean?

[tommyb1]

Trying to use Audessey to set some levels on my Onkyo 875 and Quad L-ite speakers. I'm not convinced as to how well it's doing it though.

With respect to db - why is setting some as + and some as -? is this simply 'volume'?

In relation to each other, which speakers should have the highest db levels? Centre, Fronts etc is there a certain order - ie centre highest etc, and how do they all relate to the sub?

How should crossovers work? should the frequency set for the speakers be lower than that set for the sub?

Sorry for the sheer basic level of my questions but totally confused by it all.

[stuman]

ok, acoustic science 101

Db can be rated as + or - because it is a oscillating wave, ie. goes above and below the 0Db mark to create sound. Its just another way of rating it. dont worry about the symbol. the numbers are exactly the same.

as to setting Db levels there should be no lower or higher Db levels in a perfect world where you sit all levels should read the exact same.

to set the
Db levels you need a sound meter. you play a white noise from each speaker independently then take a reading then as you read each Db reading adjust the Db level on the amp to compensate.

as for crossover frequencies depending on what speakers you have you will need to select a freq' that will get the widest band of freq' to the speakers so if you have small bookshelf speakers then you will need to set it to quite a high setting, 100 - 120Hz. if they are slightly larger then you can get away with lower ie. 50 - 80 hz, you'll have to have a look through the manual or you could always just have a listen and decide what you think is the best!!

hope this clears some questions up for yah...

stu

[Cynar]

Originally Posted by tommyb1

With respect to db - why is setting some as + and some as -? is this simply 'volume'?

Yes it is simply volume and it's just trying to get them all to be at the same volume at the measurement/listening position. Think of 0 as the starting point for all the speakers.
If when they're set to 0, one sounds louder at the listening position than the others, the receiver will reduce the volume on that channel to make it sound the same and it will have a -. Conversely if one is quieter, it will increase the volume and it will have a +.
It doesn't really matter whether they're +, - or 0 as long as the end result is that they're all the same volume at the listening point.

In relation to each other, which speakers should have the highest db levels? Centre, Fronts etc is there a certain order - ie centre highest etc, and how do they all relate to the sub?

As I said above, they should all be at the same level at the listening point and to achieve this the receiver will vary the settings. There is no set order for this as it depends on many different factors such as distance, differences between speakers, room acoustics etc etc. The sub is no different than the other speakers in this respect and should also be at the same volume as the other speakers.

How should crossovers work? should the frequency set for the speakers be lower than that set for the sub?

The crossover is the frequency at which the receiver starts to divert the sound away from the speakers and to the sub and vice versa. It's not a brick wall though, more of a gradual transition from one to the other, so some frequencies above the crossover will still go to the sub and some below will still go to the speakers. This means there's an overlap where the sub and speakers are both sharing the job of producing some frequencies. For that reason, you should set the crossover a little way above the lowest frequency your speakers can produce.
I'm not sure why the Onkyo's have the sub setting. Many receivers don't have that feature at all. I would set it to as high a level as you can.

[Mark.Yudkin]

dB is deciBels that is 0.1 Bels. A Bel is a logarithmic measurement of sound pressure, which roughly corresponds to perceived volume. An increase of 1 Bel means 10 times as loud, so 3dB is roughly twice as loud (10**0.3 = 1.995). As a result, an increase of 10dB, meaning 10 times as loud, means you need 10 time the power from your amp.

Subs have a different issue. Many dts soundtracks on DVDs, and most DVD-A's require a boost of 10 dB to the LFE track. However this is ludicrously inconsistent and there is no encoding to let you know whether you do or don't need the boost, other than your ears. Your Onkyo should have a button or setting for this.

Crossovers are about when to stop trying to get bass from the speakers and redirecting it to your subwoofer (the crossover frequency is not a rigid bound). Basically, smaller speakers equates to higher crossover frequency. However as the frequency increases, your ability to determine a sound's source improves. The THX norm therefore states 80Hz as the crossover. With your Quad L-ites, you will probably want to set the crossover to 120Hz, details are in the manual. Since you're doing the bass management in the Onyko, you do not need to do it in the L-ites - again, the Quad manual has a decent explanation.

All speakers should have the same level, however some people find that increasing the SPL on the centre helps dialogue comprehension, so you may need to experiment after calibration to find what suits you best.

[tommyb1]

Cheers guys - that's absolutely brilliant

Ok, so I'm thinking:

Set crossovers on Onkyo as follows - Satellites and Centre: 90; Sub 120 (max I can go to for sub)

Levels: I need to get the speakers to sound at the same volume in my listening position. I need an SPL meter to do this. Is it straightforward to use?

Should I start at 0db and work away from those points?

When setting the levels with Audyssey, or on my own with an SPL - what volume should I set the Sub at Low/mid/high? I know I should have the low pass filter set to off.

Audyssey - I liked the equaliser settings it set - the sound was nice. I wouldn't have liked to do these myself, not sure where to start. It also did a good job of detecting distances.

Should I run Audyssey first and let it set the equaliser, distances and delays, and then manually change the crossovers and levels myself?

Oh, and one final thing - is it that the closer to 0 the db level, then the more efficient/less power is needed to drive the speakers by the amp?

Thanks for your patience.

[Peter Galbavy]

Originally Posted by tommyb1

Should I run Audyssey first and let it set the equaliser, distances and delays, and then manually change the crossovers and levels myself?

Run Audyssey and then change the crossovers to suite. Don't change the speaker levels. Audyssey works by evaluating each speaker in your room in multiple locations and builds a set of freqency and time domain filters which are then applied when you listen to reverse the "bad" effects of your room. The crossovers and speaker size selection are based on these measurements, but as Chris from Audyssey has said on "another forum", these are simply based on the performance of your speakers at 80Hz - changing the crossovers and LFE/LFE+Main settings does not affect the correction of each speaker.

[tommyb1]

Oh ok, thats great thanks

I've never had to indicate what size of speakers I have on the Onkyo 875 - am I missing something?

Right, cool.

What do you guys think of this then?

1) Set sub to max Crossover on amp and to 3/4 volume (about 75)?
2) run Audyssey, - using 6 measurements?
3) save settings
4) alter crossovers - all 90 except sub which I'll set to 120
5) check the levels of each speaker - I suppose by ear is as good as anything?


After all - Audyssey multiEQ on the 875 should be pretty good shouldn't it!?!?!?!

[Alan Mac]

Originally Posted by Mark.Yudkin

An increase of 1 Bel means 10 times as loud, so 3dB is roughly twice as loud (10**0.3 = 1.995). As a result, an increase of 10dB, meaning 10 times as loud, means you need 10 time the power from your amp.

Mark,

An increase of 10 dB corresponds approximately to a doubling in the apparent loudness (not ten times as loud).

Alan

[cribeiro]

Originally Posted by stuman

ok, acoustic science 101

Db can be rated as + or - because it is a oscillating wave, ie. goes above and below the 0Db mark to create sound.

Sorry for , but that's not correct.

dB is a relative measure. Thus, 0 dB means reference loudness (not necessarily "reference level", but it should be so in the newest amps [referring to master volume, not to single speaker levels]). For example, the reference loudness of the SPL meters (sound level meter) is such that you can barely hear the sound (or so I believe, please correct me if I am wrong).
If you are in the "-" side, it means the volume is below that of the reference (whatever this is). If you are in the "+" side, it means you are above it.
It is like counting years: "355 BC" or "2008 AD". You just need a reference. Note that "D" and "C" in the example is the same Mysteries of religion

Originally Posted by stuman

as for crossover frequencies depending on what speakers you have you will need to select a freq' that will get the widest band of freq' to the speakers

It is a good effort, though
Actually, you want to set it high enough so that your loudspeakers are relieved from the low-bass duties, but not so high that you can tell where the bass is coming from. Depending on the qualities of your speakers and/or sub, you may want to go higher or lower. For example, if your speakers give better bass in the 80Hz region than your sub, you want to go below 80Hz with the crossover, to take advantage of it (assuming of course that your speakers can go down to 50 or 40Hz at least). There are many other considerations, and the right crossover depends in the end on your particular system, setup and ears.

It is not a matter of getting the widest band to the speakers, but rather a balance between speakers and subwoofer (and your ears ).

Sorry for the , but I think it is important, for the sake of newcomers. Of course, Russ.will won't take long to show up and me in exchange

[Cynar]

Originally Posted by tommyb1

Oh ok, thats great thanks

I've never had to indicate what size of speakers I have on the Onkyo 875 - am I missing something?

I don't think so - I think it's just the way the Onkyo setup works. With some amps you specify large or small and set the crossover seperately. I believe with the Onkyo when you set the crossover it automatically treats the speaker as small which is logical really.

Right, cool.

What do you guys think of this then?

1) Set sub to max Crossover on amp and to 3/4 volume (about 75)?
2) run Audyssey, - using 6 measurements?
3) save settings
4) alter crossovers - all 90 except sub which I'll set to 120
5) check the levels of each speaker - I suppose by ear is as good as anything?


After all - Audyssey multiEQ on the 875 should be pretty good shouldn't it!?!?!?!

That sounds like a good plan. Don't forget to turn the filter off on the sub and try it's different phase settings too.
To be sure your speaker levels are correct you really need an SPL as it's difficult to judge accurately by ear, particularly with the sub as the test tone sounds very different through it.
Having said that, as far as I'm aware Audyssey is pretty good at setting the levels so if they do sound similar they probably are.
I'd also have a fiddle with the subs volume control after the setup as you may find you prefer it turned up a bit more - especially for movies.

[tommyb1]

Looks like i've opened a can of worms wit the whole decibel question!

Ok, that's good to know that my plan is good. I'll just have t owait for my faulty amp and speaker to come back from the shop now so I can set it all up.

Thanks for all your help guys.

Must say - got the Quad's in Cherry - they look fantastic, classic styling but yet with a modern twist very very happy, and they sound amazing (which is more important), I'm so glad I came on this forum, I was all set to buy the Tannoy arena lites until I was convinced that would be a mistake and the Quads were just too good to miss!

[Mark.Yudkin]

An increase of 10 dB corresponds approximately to a doubling in the apparent loudness (not ten times as loud).

No, a 1 Bel increase corresponds to a factor of 10, not 2 (and not e!) . A Bel is a base 10 logarithm of power ratios.

A quick check under Definition on Wikipedia or any other elementary text book would have enabled you to verify the definition.

[Alan Mac]

Originally Posted by Mark.Yudkin

No, a 1 Bel increase corresponds to a factor of 10, not 2 (and not e!) . A Bel is a base 10 logarithm of power ratios.

A quick check under Definition on Wikipedia or any other elementary text book would have enabled you to verify the definition.

1 bel (or 10 dB) does indeed correspond to a power ratio of 10.

However, LOUDNESS is a term describing the subjective response to sound. Loudness is NOT directly proportional to sound power levels.

“For a sound to be perceived as twice as loud, the sound intensity must be increased by a factor of ten”.

(The sound intensity is sound power per unit area).

http://hyperphysics.phy-astr.gsu.edu...ound/loud.html


So to achieve 10 times the LOUDNESS, we must increase the power to the loudspeakers by about 33 dB (about 2000 times)


Alan

[Mark.Yudkin]

Things are actually more complicated when dealing with perceived "loudness". For example, loudness is also affected by frequency and duration (a longer sample will sound louder, up to about 1 second).

I suppose I was a bit sloppy in equating SPL with loudness (as well as power) without mentioning the issues of perceived loudness as a subjective measure and equal loudness contours. Or as the same web site puts it: Two different 60 decibel sounds will not in general have the same loudness).

In any case, we agree on front speakers!