Crossover's effect on LFE

adam2434

I posted this in another thread and thought it would be good to start a new one. I always thought that the LFE channel was not affected by the receiver/processor crossover setting. Apparently that's not the case. This may have you rethink the crossover you use for 5.1 material.

After a little research, looks like I'm wrong and that the receiver/processor crossover setting does affect the LFE channel for most equipment. I read this in a couple different places. According to the article below, a receiver/processor crossover setting below 120 Hz will theoretically truncate the LFE channel. However, most LFE content is below 80 Hz, so that's why 80 Hz is a good balance between LFE truncation and integration with the other speakers.

The whole article is good, but the "LFE Channel Integrity" section speaks to this issue:
http://www.hometheaterhifi.com/volume_9_3/feature-article-multiple-crossovers-9-2002.html

You learn something everyday! I'll start a new thread in the bass management forum on this.

Maestro

Very informative.

aaharvel

that's why i flip the switch to bypass when watching DVD's. Music I leave the crossover on, set to 60hz. Sometimes, I still prefer this setting when watching a dvd.

The LFE argument I can understand, even though for me LFE isn't a top priority as much as overall accurate bass is throughout the 25-62hz spectrum. Take music for example. The reason many people can't listen to music with the sub enabled is b/c when it's crossover is bypassed (aka running full range) it sounds like dogshit.

Excellent article btw Adam.

adam2434

That article explains some observations that I've made with my system, but for which I had some incorrect assumptions.

For example, I've always felt that running a 80 Hz crossover with my speakers set to small gave more bass impact than running a 50 Hz crossover for 5.1 material. I assumed this was completely due to the sub playing more bass from the channels set to small. However, this appears to be only part of the equation. The other factor is that the 80 Hz setting will not truncate the LFE channel as much as the 50 Hz setting.

Bottom line (assuming the article is right), for material with a LFE channel, you should set your receiver/processor crossover to at least 80 Hz to get the majority of what's in the LFE channel. A setting below that will truncate the LFE. This would be the case whether your speakers are set to large or small.

Depending on your L/R speakers' bass capabilities, for 2-ch listening of material without an LFE channel, I still think it makes sense to experiment with lower receiver/processor's crossover settings, although I don't personally use my sub for 2-ch.

Aaharvel, yes, I understand your music comments and I recall some other posts where you discussed this. I think this depends on the low pass slope in your receiver/processor. If it has a good, high slope (say 24 dB/octave), using the receiver/processor's crossover and keeping the sub's crossover bypassed may sound fine for music. If the receiver/processor's crossover slope is not as steep, you may benefit from using the sub's low pass crossover, assuming it is steeper. In any case, for music, you would want a high slope on the low pass to keep the sub from playing too much content above the crossover point.

Eric W

Yes this is correct. At a recent THX event, this was also brought up. The LFE soundtrack on a DVD disc is 20-120 Hz. If your receiver crossover is set to 80 Hz, the "sub out" channel is a mix of the material from *all* the channels around 80 Hz on down. The stuff from around 80-120 coming through the LFE channel "on the soundtrack* is lost. Apparently, not many people notice.

This is another reason why the "Polk method" in hooking up a subwoofer in a speaker system tends to sound a little fuller.

jrlouie

I mentioned this over on the Outlaw forum and heard differently. Maybe this is just how the Outlaw 990 does it, but they were saying the sub-out channel sees no crossover. So even if you have your crossover set to 40 Hz all around, a 66 Hz signal on the LFE track will still go to the sub.
The 40 Hz crossover is only a high-pass on the other 5 speakers adding anything below 40 Hz to the sub (along with the LFE).
I'm not an expert, so I'm not sure what the truth is. But I would like to know

vipari

jr louie..wanna buy your reciever..pm me.

adam2434

jrlouie wrote:

I mentioned this over on the Outlaw forum and heard differently. Maybe this is just how the Outlaw 990 does it, but they were saying the sub-out channel sees no crossover. So even if you have your crossover set to 40 Hz all around, a 66 Hz signal on the LFE track will still go to the sub.
The 40 Hz crossover is only a high-pass on the other 5 speakers adding anything below 40 Hz to the sub (along with the LFE).
I'm not an expert, so I'm not sure what the truth is. But I would like to know

The specs from Outlaw's 990 product page indicate a low pass for the subwoofer:

Bass Management
High-Pass Slope Crossover Frequency (Small Speaker Setting) (Adjustable 40/60/80/100/120/150/200Hz): 12 dB/octave (2nd order)
Low-Pass Slope (Subwoofer) 24 dB/octave (4th order): 40-200Hz as above

So, I'm wondering if those folks know something we don't know, or if they're making the same wrong assumption that some of us made.

jrlouie

I wonder if that low-pass is for the non-sub speakers and regarding the bass it directs away from them to the sub, rather than a low-pass on the LFE channel.

adam2434

I think the high pass determines what the non-sub speakers play, and the low pass determines what the sub plays, same as the low pass filter (crossover) on a sub's plate amp determines what the sub plays.

Maybe the Outlaw doesn't filter the LFE with the low pass - worth checking into with Outlaw.

danger boy

adam2434 wrote:

The specs from Outlaw's 990 product page indicate a low pass for the subwoofer:

Bass Management
High-Pass Slope Crossover Frequency (Small Speaker Setting) (Adjustable 40/60/80/100/120/150/200Hz): 12 dB/octave (2nd order)
Low-Pass Slope (Subwoofer) 24 dB/octave (4th order): 40-200Hz as above

So, I'm wondering if those folks know something we don't know, or if they're making the same wrong assumption that some of us made.

I don't think the subwoofer has any crossover setting(s) in the Outlaw 990 pre amp. I could be wrong.. but I have not found any. All other speakers do have crossover settings from 40 to 200Hz

adam2434

Low-Pass Slope (Subwoofer) 24 dB/octave (4th order): 40-200Hz as above

That spec implies that the 990 will apply a 24 dB/octave low pass filter on the subwoofer output at the selected crossover point.

Therefor, for any crossover point you select with speakers set to small, you will have a high pass filter on the speakers and a low pass filter on the sub out - that's how bass management blends the speakers and sub.

The issue I brought up in the first post (based on the article link) is that, apparently for the majority of receivers/processors, the low pass filter on the sub out is also applied to the LFE channel from a 5.1 source, effectively truncating a significant part of the LFE if you set the crossover lower than 80 Hz.

jrlouie

Yep, agree on the concept and agree about the spec. Just curious for sure if the 990 also applies it to the LFE channel from a 5.1 source. According to the Outlaw forum, it does not. I called Outlaw on my lunch break today, but had to leave a message as nobody answered. I'm waiting for their return call.

adam2434

jrlouie wrote:

Yep, agree on the concept and agree about the spec. Just curious for sure if the 990 also applies it to the LFE channel from a 5.1 source. According to the Outlaw forum, it does not. I called Outlaw on my lunch break today, but had to leave a message as nobody answered. I'm waiting for their return call.

Just curious, did Outlaw ever get back to you on this?

jrlouie

No, darn it. I'll have to call them back.

John K.

Yes, Outlaw's comment would be interesting(and hopefully correct). As the article states, most bass management low-passes everything on the sub out(including any LFE material)below the selected crossover frequency. However, since there's little or no LFE above 80Hz, although the channel theoretically extends to 120Hz, little or nothing is missing when the crossover is set at 80Hz.

A fair number of receivers(e.g. Denon 2807, etc., HK 635, etc., Onkyo 703, etc.)do have a separate setting for selecting a variable low-pass on the LFE alone, between 80-120Hz. The only reason for ever setting it lower than the 120Hz channel max appears to be that this sometimes can reduce noise level on the channel.

If, as JR was advised on the Outlaw board, the 990 applies no low pass to the LFE, this would partially excuse their manual saying nothing about it, but if true the manual still should have briefly noted the fact so that users would know.

jrlouie

Here is Outlaw's response for the 990...

The crossover points do not limit LFE channel information, they only
dictate the point at which information is directed away from small
speakers to the sub. Therefore, if all of your speakers are set to "small"
and all of their crossover points are set to 40 Hz. Information below
40Hz that was originally encoded for your speakers will be reproduced by
the sub. At the same time if there is an LFE signal of 65 Hz, your sub
will play it back as those signals are unaffected by the x-overs for
the other channels.

jrlouie

FYI...if in the 990 you use L/R+sub (rather than LFE only), they stated...

If, for example, the crossover point was 60 Hz the
main channels would continue to see the a full range front channel
signal while the sub would continue to see the LFE channel. In addition,
information from the main channels below 60Hz, would also be
duplicated/directed to the sub.