Subwoofer HF rolling off earlier than expected

ARNiTECT

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I have an SVS SB2000 sealed sub connected to an Audiolab 8200AP pre/pro.

I've been doing some Dirac measurements and the measured sub curve hovers flat at around 0dB until 80Hz then drops to -30dB by 200Hz.
I was expecting it to go higher ...at least stay flat'ish until 150Hz.
I found a graph of the SB2000 and I have drawn mine over this in dotted green.
1612110574760.png

Any ideas whats going on here?
My 8200AP is set to Large speakers for fronts, centre, surrounds and the rears are only able to be set at small.
There doesn't seem to be an option for HF roll off for the sub in the 8200AP.
My MiniDSP nanoAVR is set to bypass all filters, so no BM or Xover.
 
In the 8200AP, I set the speakers to Large where possible, so I hoped no BM is happening, the back pair might be affecting this though.
The fronts, centre & surrounds have the option of:
‘Large’ or
‘Small’ with a ‘Bass cut’ of 40-120Hz
The Back speakers only have an option for ‘None’, ‘1 Small’, ‘2 Small’ (Bass cut 100Hz)
Subwoofer: Yes/No
No option for a high level cut off, as I have seen in other AVRs, so I assumed there was none.
I can set distance and levels for the speakers and there is an option for: Bass Mgr: ‘Normal’, or ‘L+R to Sub’, but I understand this is for the stereo inputs (Normal = no sub if large, L+R = Large+Sub).

For the SVS SB2000 I use the LFE input and set the Low Pass Filter to LFE (assumed crossover disabled).

The miniDSP nanoAVR HD is set to purely bypass all filtering and crossovers and is only in the chain to fix a bug where the 8200AP mutes the test noise signal from nanoAVR DL if connected directly. After measurements, I put the HD upstream of the DL for BM and Xover etc.

The nanoAVR DL uses the Umik-1 for measurements, which seems fine for the other 7 speakers.

I might have to do some messing about with measuring using REW, swapping the sub to other connections and maybe trying a different sub.

I’m sure it’s a setting I’ve got wrong somewhere; the curve just seems to roll off like it has been filtered.
 
I set the speakers to Large where possible
Might that not cause what you are seeing, in that setting speakers to small would send a wider frequency range to your subwoofer I'd have thought?

I you're looking to test your sub over a wider frequency range for some reason, might it be possible to take the 8200AP out of the signal path and just use the nanoAVR connected to the sub?
 
Why would you not want bass management though? Set them to small, get it working properly even if you cross them over low.

Which speakers are they?
I do bass management downstream using the miniDSP nanoAVR HD so I would like to to disable BM in the 8200AP.

Equipment order >
Front: PMC Twenty5.26
Centre: PMC Twenty5.C
Surround: PMC DB1i
Power Amp: Bryston 9BSST (5ch) >​
Backs: Kef T101
Power Amp: Fosi Audio TDA7498E (2ch) >​
Sub: SVS SB2000 >
PrePro: Audiolab 8200AP (Set levels & distance from listening position)​
A. order for calibration:
miniDSP nanoAVR HD (Bypass all settings, removes bug)​
miniDSP nanoAVR DL (Dirac Live setup)​
B. order for use:
miniDSP nanoAVR DL (Dirac Live Presets)​
miniDSP nanoAVR HD (Base Management, Routing, Gains, Crossover)​
Source: Cambridge Audio CXUHD​
 
Does the nanoAVR not have level and delay adjustments? I'm not familiar with it but other miniDSP products do so I'd guess it does?
 
Might that not cause what you are seeing, in that setting speakers to small would send a wider frequency range to your subwoofer I'd have thought?
When I calibrate using the nanoAVR DL, it sends a full spectrum sweep from low to high to each speaker, including the sub. I want to measure & correct each speaker individually and do the bass management upstream after correction. Therefore I need the bass management disabled in the 8200AP.
I you're looking to test your sub over a wider frequency range for some reason, might it be possible to take the 8200AP out of the signal path and just use the nanoAVR connected to the sub?
The nanoAVRs have HDMI out only, but I have an 'HDMI audio extractor to stereo optical' device, I could plug into my stereo preamp/dac to test.
Does the nanoAVR not have level and delay adjustments? I'm not familiar with it but other miniDSP products do so I'd guess it does?
I do initial level and delay adjustments in the 8200AP to get it approximately correct, then nanoAVR DL does Dirac Live (Room EQ) for accuracy.
 
Last edited:
<Bit more Googling>

I see there are different nanoAVRs :). My picture is of the HDA whereas the HD and DL appear to not have analogue outputs :) .
 
Last edited:
<Bit more Googling>
I see there are different nanoAVRs :). My picture is of the HDA whereas the HD and DL appear to not have analogue outputs :) .
Yep, thats the HDA :) I'd rather use the great dacs in my 8200AP.
 
I don't have much helpful to add I'm afraid but I'm curious, what's the reason for using two nanoavrs? Can the DL not do everything that the HD can but with the addition of Dirac?

I'd also be tempted to set all levels and distances in the 8200 to zero and just use it as a DAC. Dirac's going to do the level and distance setting anyway and it'll do it using phase and impulse rather than physical distance. I don't know it'll make any difference, but it might help to simplify the set-up.
 
Just to add, if you want to EQ just the subs, measure them on the LFE channel in REW, that'll give you a non-crossed-over response to work with.
 
I don't have much helpful to add I'm afraid but I'm curious, what's the reason for using two nanoavrs? Can the DL not do everything that the HD can but with the addition of Dirac?
The main reason I bought the HD is that there is a 'bug' in the 8200AP when the DL is directly connected during the calibration stage. The 8200AP automatically mutes the signal for any test tones except for front L&R. Apparently it's because the test tones are 20/24bit. After calibration I can remove the HD and the DL works fine in use connected directly.
The DL has a Dirac Live 1 interface, with no bass management. So I can either use the 8200AP for downstream BM (enabled prior to Dirac measurements), or the far more configurable HD upstream (enable after the measurements). This allows me to take individual measurements of the speakers with the DL and then in the HD play with the 'low pass filter', 'high pass filter', routing of the channels and much more.
I'd also be tempted to set all levels and distances in the 8200 to zero and just use it as a DAC. Dirac's going to do the level and distance setting anyway and it'll do it using phase and impulse rather than physical distance. I don't know it'll make any difference, but it might help to simplify the set-up.
I understood most Dirac systems require the levels to be set approximately before calibration, I'm not sure if this helps with dynamic range as the signal is kept digital from source to 8200AP dacs. I'll try it anyway. I have also read to set the distances in the AVR first, but not sure why, apart from it sounding ok when DL is not enabled for some reason. I could try zeroing the distances, as I plan on measuring from different listening positions anyway.
 
Just to add, if you want to EQ just the subs, measure them on the LFE channel in REW, that'll give you a non-crossed-over response to work with.
Yes, this is one of the things I want to try this evening:
  • Subwoofer to the Sub output from the 8200AP, REW test on LFE channel using HDMI from laptop
  • Subwoofer to the Front Right output from the 8200AP, REW test using 'HDMI>Optical' from laptop
  • Subwoofer to the Right channel of a stereo preamp, REW test using 'HDMI>Optical' from laptop
  • Try another subwoofer (my JL Audio or AVI sub)

This should help me narrow down the cause to the 8200AP, SB2000 or nanoAVRs.
 
It's the Audiolab 8200AP.

I measured the SB2000 with REW using a UMIK-1 and headphone out to the sub and the frequency range extended to about 200Hz before rolling off. I tried the sub's L+R inputs and then just the LFE input, there was 10dB difference, but same curve. So the SB2000 looks fine.

I measured again with the laptop headphone output into 8200AP analogue inputs, first AUX RCA input, then the Sub channel of the 8 channel RCA inputs. Again, this resulted in a similar curve extending to about 200Hz before rolling off.

I then tried going from laptop HDMI out into the 8200AP HDMI input. This resulted in the frequencies only extending to about 100Hz before rolling off.
I proceeded to change every setting in the 8200AP menus and the 100Hz high level cut off from HDMI remained. (Large/small, 2.1 to 7.1, sub on/off, removed levels & distances, tweaked other seaming unrelated settings just incase.)

I didn't try with the miniDSP nanoAVRs as the problem appears to be in the 8200AP.

Measurements below
  • Brown is analogue input into sub, or through analogue inputs of 8200AP (expected)
  • Purple is HDMI input (100Hz LPF that I cant disable)

REW_SB2000_8200AP_LFE.JPG


Not sure what to try next. I might reach out to other Audiolab 8200AP owners, if there are still any.


.
 
Last edited:
  • Purple is HDMI input (100Hz HPF that I cant disable)
Just to get the terminology right what you have there is a low-pass filter (LPF) not a high-pass filter (HPF).
 
Just to get the terminology right what you have there is a low-pass filter (LPF) not a high-pass filter (HPF).
Oops! Thanks, it was a late night.
 
I spoke to Audiolab and the sub's 100Hz LPF can't be disabled. Audiolab suggested maybe using RCA splitters between 8200AP and power amp out to sub, I'm not sure how this would work.

I could increase the volume of the subwoofer and use Dirac to correct it back again to get a bit more range out of the sub.
 

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