EQ'ing my new IB - Page 8 - Home Theater Forum and Systems - HomeTheaterShack.com

Old 11-29-06, 11:19 AM
Elite Shackster
brucek

Join Date: Apr 2006
Posts: 7,514
Re: EQ'ing my new IB

Quote:
Why not turn down the input level and use some boost, since the only time we are using the full capability of the BFD is when those thunderous scenes are playing
I will try and attack this from another angle.

The BFD is a digital device that accepts analog signals at its input and produces analog signals at its output. A fact.

The BFD digitizes the analog signals, passes them through a DSP, and then undigitizes those signals. The best signal to noise ratio, distortion and dynamic range are enjoyed when the analog signal at the BFD's input (when at its highest expected level) is at a maximum allowed to avoid clipping. A fact.

The maximum input level is +2dBV. The maximum output level is +2dBV. A fact.

The analog signal sent to the BFD is stochastic and non-deterministic and as such can be represented by sinusoidal signals at all frequencies of interest. That is to say, as an example, I may send the BFD several movie selections where at any frequency there may be +2dBV signal feeding the BFD at the highest expected volume selected on your receiver. We don't just play one movie with a loud noise at one frequency forever. We must assume the input will receive maximum input level for all frequencies at some time.
The concern is not about the level of specific frequencies entering the BFD - assume all frequencies entering the BFD are at one time or the other at a maximum level. The concern for specific frequencies are a matter of how the speaker reacts with the room and what frequency specific voltage modifications must be made to the subwoofer input to compensate.

An example.

Assume the speaker / room interaction causes +15dB peaks at 20, 30, 40, 50, 60 Hz.

You have the option of:

1) Setting the input level of the BFD at maximum and cutting the areas at the peaks. This results in the output of the BFD being at +2dBV for those areas between the peak frequencies.

2) Setting the BFD input level of the BFD down -15dB and boosting the areas between the peaks. This results in the output of the BFD being at +2dBV for those areas between the peak frequencies.

The output signal level of the BFD is identical for both scenarios and will be for all scenarios. The #2 option results in a worse noise floor, less meaningful bits sent to the DSP for processing, and worse dynamic range.

Which option do you choose? You've indicated you prefer #2.

brucek
brucek is offline

Old 11-29-06, 01:37 PM Thread Starter
Shackster
Pete

Join Date: Sep 2006
Posts: 96
Re: EQ'ing my new IB

That all makes sense.

My only counter-argument would be that maybe the other components in my system produce more noise right now than the BFD would if I use some boost. In other words, maybe boosting the BFD output somewhat, which I think would allow me to lower my receiver volume (which is way up there right now at -10 dB on a -80 to +10 dB scale), and lower my sub amp volume, will result in my overall system (receiver - BFD - proamp) having less noise.

Possible?

I don't know if this is true, but I guess I will try it and see how things sound. Also, I will look at a 60Hz crossover and check my 80Hz crossover numbers.

OT - I heard that the 1124 is now discontinued (though there are many left in the supply chain). Here's hoping to an alternative with the same flexibility and nice price that incorporates an independant output level control and/or better dynamic range and/or anti-clipping technology...

Edit - Maybe I should just get a bigger amp like an EP2500 for my sub...

Thanks,
Pete

Last edited by PeteD; 11-29-06 at 01:46 PM.
PeteD is offline
Old 11-29-06, 02:06 PM
Elite Shackster
brucek

Join Date: Apr 2006
Posts: 7,514
Re: EQ'ing my new IB

Quote:
Also, I will look at a 60Hz crossover and check my 80Hz crossover numbers.
Yeah, you should really look into this and figure out why your raw measurement appears to not have a low pass filter applied to it from the reciever.

Quote:
which is way up there right now at -10 dB on a -80 to +10 dB scale

Quote:
Possible?
I would say no. Your problem really seems to come down to the massive amount of filtering you're doing because your raw measurement is wacky for some reason. No amount of messing around with input levels to the BFD will correct that problem.

brucek
brucek is offline
Old 11-29-06, 02:16 PM Thread Starter
Shackster
Pete

Join Date: Sep 2006
Posts: 96
Re: EQ'ing my new IB

Quote:
brucek wrote: View Post
That is the master volume. I have run the sub at +10, and the mains as low as -10, to allow me to turn down the pro-amp. H/K AVR235.
PeteD is offline
Old 11-29-06, 03:00 PM
Elite Shackster
brucek

Join Date: Apr 2006
Posts: 7,514
Re: EQ'ing my new IB

Quote:
I have run the sub at +10, and the mains as low as -10, to allow me to turn down the pro-amp. H/K AVR235.
Yeah, I wish I could help you more, but I guess we'd be going in circles. Fact is, the H/K AVR235 is a standard consumer item that outputs standard levels from the pre-out jacks and should easily satisfy the BFD input levels. That level should be fine for your sub amp that we already looked at, but could be increased with the line amp you bought if needed.

There's just something not right, and I really have no clue what it is...... you need to do some more investigation. Could be as simple as a bad cable.

brucek
brucek is offline
Old 11-29-06, 03:15 PM Thread Starter
Shackster
Pete

Join Date: Sep 2006
Posts: 96
Re: EQ'ing my new IB

I will start back at new raw measurements of the sub only using crossovers of 60 and 80Hz and post those when I have them.

Pete
PeteD is offline
Old 11-30-06, 12:01 AM Thread Starter
Shackster
Pete

Join Date: Sep 2006
Posts: 96
Re: EQ'ing my new IB

OK, I have two pieces of information. This curve is correct for my sub only crossed at 80 Hz. Actually, the curve is exactly the same for 100 Hz crossover also, which seems a little strange to me:

I will post a 60 Hz cross tomorrow, but I quickly tested that it will draw it down at the higher frequencies.

One question I have is can I get away with a 60 Hz crossover? Here is the response of my mains by themselves. The response falls away quickly below 45 Hz.
PeteD is offline
Old 11-30-06, 07:44 AM
Elite Shackster
brucek

Join Date: Apr 2006
Posts: 7,514
Re: EQ'ing my new IB

Quote:
One question I have is can I get away with a 60 Hz crossover?
With the amount of gain you must be getting from the room (evidenced by that raw sub graph), I can't see that you'd have any trouble.

Quote:
Actually, the curve is exactly the same for 100 Hz crossover also, which seems a little strange to me:
Yeah, seems strange to me to. I'd sure like to see the 60Hz raw graph (and the 40Hz too)...

brucek
brucek is offline
Old 11-30-06, 09:35 AM Thread Starter
Shackster
Pete

Join Date: Sep 2006
Posts: 96
Re: EQ'ing my new IB

Actually, something weird may be going on with my receiver - I may reset the whole processor and start over. The sub is getting signals based on the crossover of my rear surrounds in a certain mode, when it should be getting them from the front - I have checked the manual and settings many times and the OSD looks a little funky - doesn't quite match the manual.

Do you take the readings in stereo mode (with sub enabled) or in a surround mode?

Also, when doing manual readings, does it matter if I determine the master volume setting (scale in dB) to bring a certain frequency to a given decibal level (i.e. how much power to reach 75 dB) or leave the master volume in one spot and take actual dB readings of the room. I have done both with the same results, but I want to make sure I am doing things right.

Which method does REW use?

A potential "fly in the ointment" of using a lower crossover (i.e. 60Hz):
What do I do with my surrounds/center? They need support below 100Hz. If I cal the sub with 60Hz crossover with my mains in stereo, but feed the sub up to 100Hz material from my center and four surrounds, won't I create a huge hump in my surround mode response and maybe clip the BFD? I realize this is a problem for everyone, but I was bascially using the BFD as part of my crossover before to tame the response from 60 to 100Hz. No perfect answer, I guess...

Thanks,
Pete
PeteD is offline
Old 11-30-06, 09:54 AM
Elite Shackster
brucek

Join Date: Apr 2006
Posts: 7,514
Re: EQ'ing my new IB

Quote:
Do you take the readings in stereo mode (with sub enabled) or in a surround mode?
Stereo.

Quote:
Also, when doing manual readings, does it matter if I determine the master volume setting (scale in dB) to bring a certain frequency to a given decibal level (i.e. how much power to reach 75 dB) or leave the master volume in one spot and take actual dB readings of the room. I have done both with the same results, but I want to make sure I am doing things right.
Best to set the master volume to bring a certain frequency to a 75dB level using the SPL meter (with correction), and then leave the volume there for the entire set of measurements.

You can pick any frequency you want for that initial setting, but you may have to redo the whole thing if you picked a frequency that was a peak. I think you get what I mean..

Quote:
Which method does REW use?
REW sets the initial level with a type of pink noise. No big deal. If you're not using REW (and you should), then using a single frequency or a selection of a couple frequencies to get the starting master volume level is fine. Just don't touch the volume once you start measuring. If you do, start over.

Quote:
What do I do with my surrounds/center? They need support below 100Hz.
Not much you can do there. I'm actually more interested in seeing the 60Hz and 40Hz raw setting graph just to try and establish what the is wrong with your system.......

brucek
brucek is offline

 Bookmarks

 Tags eqing , ib

Message:
Options

## Register Now

Random Question
Random Question #2

User Name:
OR

## Log-in

Human Verification

In order to verify that you are a human and not a spam bot, please enter the answer into the following box below based on the instructions contained in the graphic.