Denon crossovers not working

[Zedly]

I am using a Denon X3600H for 5.2.4 Atmos setup. My two subwoofers are connected to a miniDSP 2x4 HD, which is then connected to the Subwoofer 1 output of the Denon. I was trying to check the crossover frequencies and looking at the results in REW. It appears that the crossover is not happening. No matter how I set the crossover point, the frequency response is the same, except that dB level is lower for higher crossover points.

I have Audyssey disabled, and all my speakers are set to small, so the mains shouldn't be playing the low frequencies. Yet REW shows that they are producting output at all the frequencies below the crossover point. In the REW output, the top line is the response with the subwoofers enabled. The other lines are the responses with the subwoofer muted (in miniDSP). The top green line is 80 Hz, and the bottom green line is 250 Hz.

What is going on here?

 

[Pogre]

When using a crossover the signal doesn't just drop off a cliff. It rolls off like a slope.

You need to explain this a little bit better. You have several unlabeled sweeps that look like different Offset Level settings in DEQ. I don't know what you're measuring or what your expectations are? You're measuring your speakers with the subs muted for..? On, off, disabled... how did you disable Audyssey? What are you trying to do? Why do you have 2 subs connected to only output 1? Audyssey XT32 SubEQ (which the 3600 is equipped with) will set the levels and timing for each one separately. I have a Mini and used REW to dial my subs in too, but what you're describing sounds far more complicated than what I did.

 

[Zedly]

Thanks for the reply. I will try to explain better. I measured with my subwoofers muted because I wanted to see how much output the mains were producing at frequencies below the crossover point. I have both subs connected to one output because I am using miniDSP to align and equalize my subs. The Audyssey and MultiEQ XT32 settings are grayed-out in my menus, which I believe indicates that they are disabled.

The graph shows the frequency response of a sweep from 20 Hz to 250 Hz at different crossover settings (I think the drop at 70 Hz is due to a room mode). The top blue line is the response when my subs are enabled and the crossover is set to 80 Hz. The top green line is the response with the subs turned off and the crossover set at 80 Hz. The yellow line is the response with the crossover set to 100 Hz. The bottom green line is the response with the crossover set to 250 Hz. I'm attaching a new graph with labels and without the subs.

I understand that the signal rolls off instead of plummeting, but I had thought that the roll-off would be steeper than I am seeing. For instance, in my graph, the top green line is 100 dB at 85 Hz, but it is still close to 100 at 45 Hz, which is not what I expected. Shouldn't the drop be much steeper? I had thought that, with a crossover set to 80 Hz, the mains would be producing very little at 45 Hz. That expectation was set by charts like the one below. Have my expectations been unreasonable? Is this really how the crossover is supposed to look?

 

[Pogre]

How are you disabling Audyssey? Are you in pure/direct? Is GEQ on or off?

If I get this correctly, you're just playing around and found something you weren't expecting then? Okay. Well... there are many, many variables running from mic positions and calibration files used when you took measurements to the settings in your AVR. Starting with how did you "disable" Audyssey?

 

[William Lemmerhirt]

That’s weird. It looks like amplitude changes only. Dumb question. In the minidsp did you set the crossovers to off?

 

[Pogre]

That’s weird. It looks like amplitude changes only. Dumb question. In the minidsp did you set the crossovers to off?

If I read it right I think he muted the subs in the mini and measured his speakers only with the avr crossover on.

 

[William Lemmerhirt]

If I read it right I think he muted the subs in the mini and measured his speakers only with the avr crossover on.

Exactly how I understood too. The thing that’s weird is, at least to my eye, is the loudness or amplitude is the only thing changing. All the sweeps look the same, except they get higher in the chart. Louder.
The mains appear to roll off about 48hz. Can’t see much if any difference on the higher end.

 

[Zedly]

Yes, that's what I did. That's why I think it's weird and am wondering what is causing it (or whether I'm just misunderstanding.

 

[Zedly]

How are you disabling Audyssey? Are you in pure/direct? Is GEQ on or off?

If I get this correctly, you're just playing around and found something you weren't expecting then? Okay. Well... there are many, many variables running from mic positions and calibration files used when you took measurements to the settings in your AVR. Starting with how did you "disable" Audyssey?

I disabled MultiEQ in the settings, then I set Manual Config in the Speakers menu. After I did that, the Audio section of the settings shows the Audysset and GEQ settings grayed out and unavailable. Am I wrong to think that that means they are disabled?

 

[Zedly]

I had expected the graph to look like this. Am I wrong to have expected this?

 

[Zedly]

I ran some more tests tonight. I thought the sound modes might be affecting the results. I ran two tests with my receiver in Direct mode (i.e. no processing). I expected that changing the crossover would not change the output since Direct mode even disables crossover processing. That is exactly what the measurements showed. The graphs with an 80 Hz and 250 Hz crossovers were identical

I then set the sound mode to Stereo and re-ran the tests (output from REW going to only the right speaker). This time, the responses looked the same, but the 250 Hz crossover curve was 15 dB below the 80 Hz curve, just like before. With an 80 Hz crossover, the output is 95 dB until around 60 Hz, when it starts rolling off.

To isolate my subs, I unplugged my right speaker and ran another sweep. Something unexpected happened. My sub swept up to around 100 Hz, and then my receiver shut off. When I restarted it, it told me that it shutdown because it detected that the right speaker was unplugged. I thought it was interesting that it didn't shutdown until 100 Hz. The output shows that my subs roll off very quickly after reaching the crossover point.

When I superimposed the sub response with the right speaker response, I think I might see what the receiver is trying to do. At 80 Hz, the subs are outputting about 88 dB. At the low and high ends, the subs and mains are outputting about 95 dB. The receiver seems to be keeping the response high all the way through the crossover range and not dropping until it is in the region where the sub is providing strong output. So this might be the receiver's way of trying to ensure a smooth transition during the crossover. Does this seem like a reasonable interpretation of the data? It would explain why the mains are reaching so far into the low frequencies. What do you think?

 

[TLS Guy]

Obviously after all these years I have wated my fingers on the key board.

The crossover is working as designed, intended, and the way it should.

If you set a crossover at 80 Hz second order which is what the high pass crossover is in a receiver, then the crossover will be 3 db down at 80 Hz. Now the crossover will slope at 12 db peroctave. However in most rooms there will be room gain and often some ripple at 80 Hz and a bit below.

Now the slope will be ultimately determined by the design of the speaker and its F3.

So if we exclude room gain which will exist, and for a lot of non custom rooms which will be around 60 Hz, if we take a speaker with an F3 of 45 Hz then the slope will be 12 db per octave until 45 Hz and then transition to 24 db per octave. Now the low pass crossover on the sub is 24 db. So at 80 Hz we have a 24 db per octave roll off with the sub at least 3 db down at 80 again excluding room gain. So the crossover is not correct and will not sound right.

Now I have been telling you for years that receiver and pre/pro bass management is a crock of you know what. The primary reason being because it is an off the shelf crossover and not custom. That is a bad engineering solution unless you really understand it.

The guys at THX who came up with this close to farcical scheme specified that the roll off of the main speakers be 12 db per octave. That means the speakers had to be sealed designs or TLs and you know how many of those are around these days?

So the idea was if you had a sealed speaker with an F3 of 80 Hz and set the crossover to 80 Hz you would have a perfect crossover with a 24 db LR composite crossover. However most rooms and locations muck this up mightily.

My recent experience.

As most of you know I designed and built an in wall 3.1 system with sealed mains and center with an F3 of 80 Hz and an in wall TL sub. Since it was an in wall no BSC was designed into the crossover.

So setting the crossover to 80 Hz should have been perfect. Well it did not turn out that way, bacause the reinforcement of the wall boosted the respoanse of the mains and center speakers below crossover. So by listening and measurement showed the correct crossover frequency to be 40 Hz.

This whole bass management issue needs to be totally rethought.

Most systems I have heard that use this type of bass mangement I have not thought to be very good.

I have said this before that in most systems I have set up LFE + main is the best setting with speakers set to large. The use the sub very subtely and at low volume to gently supplement the speakers starting somewhere between the F3 of the mains and F3 of the mains plus 50%. I have found that to give the best results by listening and measuremt.

For music there remains a very good case for extended range speakers and forget the subs.