High Pass, Low Pass Touchdown!!!

[dhead1]

I have read a lot on the Forums and plenty of Articles in the "Need Basic Advice? Check Here First" Area. I guess that it will take some time before I understand enough to benifit more. But for now, can an one help me with these questions?

I set all my speakers to small and have determined just from reading here (starting point mind you) to set my crossover at 60hz, but what do I set the rest of the setting at?


1: Crossover ( I set it to 60hz i octave higher than my -3db lower limit on my mains (30hz))
2: High Pass ( I set it to the defalt 12.0 db THX)
3 Low pass (I set it to the defalt 24.0 db THX)

4: LFE Level (I set it to the defalt 0.0 db THX)

I am running a B&K Ref 50 with a Rotel 1095 amp.

All my speakers are polks...

Main Towers Rti12 Overall Freq= 18hz-27khz, -3db Limits= 30hz-26khz

Center one CSi5 Overall Freq= 45hz-27khz, -3db Limits= 55hz-26khz

Surrounds FXi5 Overall Freq= 45hz-27khz, -3db Limits= 55hz-26khz

Sub PSW505 Overall Freq= 23hz-160hz, -3db Limits= 28hz-125hz

Next question.

What is and how do I relate it to my amp/Processor "speaker efficiency"

Main Towers Rti12 90db (1M,1W)
Center one CSi5 90DB (1M,2.83VRMS)
Surrounds FXi5 89DB (1M,1W)

Thanks
Duane

 

[MDS]

Speaker efficiency (more correctly - 'sensitivity') is a measure of how much output sound pressure level is created from a given amount of input power. The usual measurement is 2.83 Volts (1 watt if 8 ohm speakers) input power and the SPL is measured 1 meter from the speaker.

You may see the sensitivity rating listed as 90 dB/1W/1M which means that the speaker will produce 90 dB SPL 1 meter from the speaker when you feed it 1 watt of input power. Higher sensitivies mean less amplifier power is required to achieve high SPL, but don't tell you anything about 'sound quality'.

 

[dhead1]

MSD,Thank you for the explanation on speaker sensitivity.

Can you or anyone explain the "low pass,high pass and LFE level" settings and what I should set them to on my system. (taking in to consideration the specs I layed out in my first post)

Thanks,
Duane

 

[MDS]

Your settings from the first post are correct but here's a brief explanation of what they mean:

1. xover: The frequency where the bass will start to be redirected away from the Small speakers and sent to the sub. It is not an exact cut-off at that frequency but rather depends on the 'slope' of the xover and that is where the high-pass and low-pass comes into play.

2. High-pass : A filter that lets the highs pass; it attenuates (reduces) the level of frequencies below the xover. The default setting of 12 dB per octave is known as '2nd order' slope. The high pass starts working below the xover frequency so with 60 Hz as the xover, the high pass will reduce 30 Hz by 12 dB and less so on up to 60 Hz so that the level at 60 Hz is roughly unchanged.

Many receivers don't let you set the high-pass but it is fixed at 12 dB/octave because that is the standard. You'd only need to change it if your speakers didn't also use 12 dB/octave.

3. Low-pass: A filter that lets the lows pass. It starts working above the xover frequency and the default slope of 24 dB/octave is '4th order'. So it will reduce 120 Hz by 24 dB and less so down to 60 Hz.

The point of the high and low pass and their slopes is to blend the sound at the xover point so that the sub sees roughly 60 Hz and below and the other speakers only see 60 Hz and above.

4. LFE level: This is an extra control to allow you to increase or decrease the level of the LFE. The default is 0 dB (unchanged) because it is rarely needed. The receiver/processor increases the level of the LFE by 10 dB automatically but if the level of the LFE on the disc is already higher than the other channels, adding the 10 dB boost makes it too boomy so you can use the lfe level setting to compensate for that.

It isn't much of an issue anymore because mastering engineers know that the processor will add the boost and they no longer (incorrectly) master the lfe track hotter than the other channels.

 

[dhead1]

MDS,

Believe it or not, I understand. You explained it very well. I have plenty to learn, but I think it will gradually sink in.

Thanks
Duane