Yet another question about a subject that has been beat to death...ATTN Dr. Spec

nellis8166 · February 2003

Ok...I know this subject has been beat to death, but I have to ask this question as it pretains to my rig.
I have a HK 525 receiver. My sub is connected to the sub pre out on the amp. The manual states that you are to use l and r line level inputs for this connection. There are also 8 channel direct inputs which I assume is the LFE out.
When using the normal sub pre-out I still filter at the receiver, both crossovers for the amp and the sub are set at 80hrz. Is this still being double filtered even though it is a non lfe connection(I think???)
If I continue to use this connection should I crank the crossover all the way clockwise to avoid double filtering??? Which has the final say in the point at which the signal is sent to the sub with this setup, the receiver or sub???
Again sorry about the redundancy here. This is the one part of home theater that I really do not know anything about. Thanks in advance for your help.

Regards,
Nat

Dr. Spec · February 2003

From the H/K 525 owner's manual:

"4. Subwoofer Output: Connect this jack to the line level input of a powered subwoofer. If an external subwoofer amplifier is used, connect this jack to the subwoofer amplifier input."

I see no reference to requiring both L/R line level inputs. In addition, the 8 jacks you are referring to are for SACD and DVDA INPUTS, not outputs.

Regardless, if you set your speakers to small, you ARE filtering at the receiver. The manual clearly states setting the speaks to small will redirect the bass from the surround channels to the LFE channel.

So your subwoofer pre-out will send a signal to the subwoofer which contains the LFE channel, and all surround bass below 80 Hz.

Since this signal is already eletronically filtered, there is no need to do so again at the subwoofer. So you select the LFE (Unfiltered) input jack. If the sub lacks an unfiltered LFE input, then connect to a L or R (or both L & R it doesn't matter) line level inputs and crank the filter all the way to its highest setting and be done with it.

When you connect to both the L & the R line level inputs, you are essentially doubling the strength of the input signal and the sub volume will increase 3 dB. That's all it does. The same can be accomplished by connecting to one line level (L or R) and turning up the plate amp sub volume.

The sub only has so much dynamic range and volume capability. You can tap into it with the plate amp, or with the LFE signal, but you are not magically gaining "missing" or "hidden" volume by connecting to both L & R line level inputs. Volume is volume.

With that said, keep the LFE volume at the receiver at a little less than the midpoint of the adjustment range. The reason you do this is to keep the tiny sub out pre-amp from clipping its signal and sending a distorted signal to the sub. This can happen if you set your sub volume to +10 (on a scale of -10 to +10). Since the LFE signal is so extraordinarily dynamic, it's best to give the pre-amp a lot of voltage headroom and increase bass volume at the sub, not the receiver.

Hope this helps!

Doc

kberg · February 2003

Originally posted by Dr. Spec
From the H/K 525 owner's manual:
With that said, keep the LFE volume at the receiver at a little less than the midpoint of the adjustment range. The reason you do this is to keep the tiny sub out pre-amp from clipping its signal and sending a distorted signal to the sub.

Doc, I don't recall ever seeing the *reason* for setting the sub volume at the receiver less than the midpoint, so thanks for providing it.

nellis8166 · February 2003

Doc,
You are truely an asset to this forum we have here, you really are. You couldn't have been more clear on your explanation. My thanks to you sir.

Regards,
Nat

Dr. Spec · February 2003

Originally posted by nellis8166
Doc,
You are truely an asset to this forum we have here, you really are. You couldn't have been more clear on your explanation. My thanks to you sir.

Regards,
Nat

Thanks, Nat. We accumulate knowledge, we check each other to make sure it's correct and good advice, and then we pass it on. That's what Club Polk is all about, and that's what this hobby is all about.

You never did say what type of sub you are running and if it does or does not have an LFE (unfiltered) input jack.

Doc

nellis8166 · February 2003

Doc,
I have a Velodyne CHT 10. It does have an unfiltered input where the sub crossover is disabled. Have not tested anything yet but I plan on filtering at the receiver and using the direct LFE input on the sub. From what I have read here this is the best way to go. Thanks again for your help Doc.
Regards,
Nat

nellis8166 · February 2003

Doc,
I messed around with setting last night and came to the following conclusion:
Using the unfiltered input on the sub sounds great for movies, but for music it is very weak. I know this is a common problem and that cd's just don't have the capacity that DVD's do.
I then tried hooking it up to the line level input, still filtering at the receiver and cranking the crossover on the sub all the way clockwise to avoid double filtering. For all purposes this sounds best to me.
I would say that I use my rig 70% of the time for music and 30% for movies. With that being said I think this is the most logical choice.
Any comments, suggestions????
Thanks Doc.

Regards,
Nat

11Bravo · February 2003

Damn Doc!

Back to re-wiring my system again! Excellent writing.

Dr. Spec · February 2003

Originally posted by nellis8166
Doc,
I messed around with setting last night and came to the following conclusion:
Using the unfiltered input on the sub sounds great for movies, but for music it is very weak. I know this is a common problem and that cd's just don't have the capacity that DVD's do.
I then tried hooking it up to the line level input, still filtering at the receiver and cranking the crossover on the sub all the way clockwise to avoid double filtering. For all purposes this sounds best to me.
I would say that I use my rig 70% of the time for music and 30% for movies. With that being said I think this is the most logical choice.
Any comments, suggestions????
Thanks Doc.

Regards,
Nat

Did you hook up BOTH L/R line level?

If so, it should play louder than the LFE input by 3 dB and this may be the reason it sounds "better" on music. You are correct, most music is less powerful and dynamic in the bass department than the hot action DVDs.

Truth be told, the two methods should sound exactly the same, unless you connected both L/R line level.

Purely from a technical standpoint, the LFE input is the best choice, and the filtered line level with the sub filter cranked all the way up is the next best thing and really only approximates what you can already do with the unfiltered LFE input.

If you listen to music/HT 70/30, what I recommend is using the LFE input and setting the receiver sub volume level to 0 (midpoint) and adjusting the plate amp volume to where you like it for music.

If I'm reading you right, the correct music setting will then be too hot for movies, so you can simply and easily electronically lower the sub volume at the receiver ( to -3 or -4) and probably work out just fine for HT.

This is a common problem BTW with music and HT being at different bass levels. It's a minor PITA, but I don't see the big deal in altering the sub volume at the receiver when switching source material.

Yet another question about a subject that has been beat to death...ATTN Dr. Spec

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