S&V Calibration Disk and Sub Xover Setting

kberg

Hey All,

The S&V calibration disk "recommends" that if you are going to set the receiver to "do the work" on subwoofer xover, then crank the xover frequency all the way clockwise on the sub. However, I was under the impression that if the receiver xover is set to 80Hz, for example, the setting on the sub should also be set to 80Hz or slightly higher.

If the receiver setting is set to 80Hz, and is truly "doing the work" on crossover, does it really matter where the sub xover is set?

Thanks,

Kevin

Dr. Spec

kberg:

Does your Infinity sub have a dedicated LFE (unfiltered) input?

Or, do you have a crossover disable or bypass switch?

If the receiver is doing the filtering at 80 Hz, you do not want the sub to also filter at 80 Hz. This double trouble is referred to as "double filtering" and is bad news.

Normally, if you filter at the receiver, then you should plug the sub cable into the LFE (Unfiltered) port on the sub. This input bypasses the filter control on the sub amp, which is what you want ideally. This is why this input is often labeled "Unfiltered".

If your sub has no Unfiltered LFE input, and there is no filter bypass or defeat switch, then - yes - you have to crank the filter control on the sub all the way to the highest value to avoid double filtering.

scottvamp

If the receiver is doing the filtering at 80 Hz, you do not want the sub to also filter at 80 Hz. This double trouble is referred to as "double filtering" and is bad news.

Dr. Spec you must understand that the whole unfiltered input on subs - is something that has just barely started in the industry.
I would say that as of 2002 95% of all subs on the market do not have an unfiltered input. And the debate over the past year has made many speaker makers bow there heads and say "ohh $hit we screwed up". DD says that its lfe is sent out at 80hz. I believe that an unfiltered will give you more control over frequency but having a "normal" sub hooked up to the LFE necessarly means "bad news". I for one have never had an issue.
But I would really like to set two identical subs together and one filtered and one un and hear just what a difference it would make. IMHO both setup "correctly" - very little.

kberg

...and the Spec-Man comes through again! Thanks for your reply.

Looks like I only have low level inputs/outputs for speakers, and a L/R low level input (which is currently used to connect to my sub out on my Onkyo with a "Y" connector).

I see no dedicated LFE (unfiltered) input, or crossover disable or bypass switch. So, by cranking up the frequency all the way to 200 Hz, this will eliminate double filtering, yes?

Is this sub inferior in any way or does it present limitations in its ability to function better because of its features, or lack thereof?

As usual, thanks!

Kevin

kberg

scottvamp,

Thanks for your input as well!

Let the debate begin! :-)

Dr. Spec

Yes, cranking it up to 200 Hz will avoid double filtering. And no, your sub is not inferior in any way. You just need to be aware of and avoid double filtering.

Scott - I never said hooking up an LFE output to a sub that is not equipped with an Unfiltered LFE input was bad news.

I said allowing the receiver and the sub to both filter at 80 Hz was bad news.

If the filter cannot be bypassed or disabled on a sub with low level inputs, then it must be cranked all the way up if you are using the receiver to filter the signal at 80 Hz (i.e., speaks set to small).

Scott: I agree - if the filter control is set all the way up, the two subs would sound identical. But if the filter is set at 80 Hz, the signal will be double filtered and there will be a huge depression in the FR at 80 Hz.

Sumflow

Originally posted by scottvamp
the whole unfiltered input on subs - is something that has just barely started in the industry.

95% of all subs on the market do not have an unfiltered input.

I believe that an unfiltered (Input)will give you more control over frequency

Thanks again Tony!

scottvamp

Dr. Spec - so what your saying is I should have both my subs with the frequency cranked all the way. What frequency would that give me exactly? Asumming that my lfe is at 80 hz. What is the lowest I should have it set to? Just picking your brain. Give me some input.

Dr. Spec

Originally posted by scottvamp
Dr. Spec - so what your saying is I should have both my subs with the frequency cranked all the way. What frequency would that give me exactly? Asumming that my lfe is at 80 hz. What is the lowest I should have it set to? Just picking your brain. Give me some input.

Your receiver LFE jack is low-pass filtered. That means there is a filter that blocks signals above a given frequency (80 Hz for you) from out the LFE jack. It redirects these signals to whatever speakers you have set to small.

All filters have a slope, called a filter rate - audio filters are rated in dB/octave. Your low-pass LFE filter is probably sloped pretty sharply - maybe 24 dB/ocatve.

That means the sub will see a full strength signal right up to 80 Hz, and the speakers you have set to small will see a full strength signal right down to 80 Hz. At one octave BELOW 80 Hz, the signal to the speakers you have set to small will be 24 dB weaker. Conversely, at one octave ABOVE 80 Hz, the signal to the signal to the subwoofer will be 24 dB weaker.

So you can see that the sub will still play a little bit above 80 Hz, and the speaks set to small will still play a little below 80 Hz - both on a 24 dB/octave diminishing slope.

So since filters are not "brick walls", and do let signals pass on a sloping rate in both directions, you need to make sure the filter on your subwoofer is set as high as possible to minimize its effect on the LFE input signal. The closer you move the subwoofer filter to 80 Hz, the more of a negative effect it will start to have on the FR at 80 Hz.

If your subs don't have unfiltered inputs, and your filter controls are set to 80 Hz, then you undoubtedly have a large depression in your FR at 80 Hz. If you doubt this, run a signal sweep and measure with your SPL and prove it to yourself.

Here's what a double filtered LFE input signal looks like at 100 Hz - notice the large depression in the FR at the filter point. That's because both the receiver and the sub are filtering the signal at the same time.

Hope this helps.

Doc

scottvamp

Thanks - I understand now!!!!!!:)

Dr. Spec

Originally posted by scottvamp
Thanks - I understand now!!!!!!:)

Scott:

Have your tried this at home, and if so did you hear a difference?

I was actually tempted to run a FR sweep with my sub filter enabled and set to 80 Hz and plot the results for myself, but I have thus far resisted the temptation in deference to watching movies and having sex. BUT, with that said, I'll do it and email the result to you if you want.