My REW journey

[badbunny]

Hi,

some quick background, my system is:
- Denon AVR-X4000 with Audyssey MultEQ-XT32
- 5.1 speaker setup - Kef T301 front left/right, Kef T301c centre, Kef T101 surround left/right.
- subwoofer was an SVS PC-13 ultra which has recently died, so I've reverted to using the small Kef T2 subwoofer that came with the satellite speaker set

for testing I have a laptop setup with REW and the following test gear:
- minidsp UMIK-1
- HDMI connection from laptop to receier

I've attached a picture showing my lounge layout with the wall mounted satellites and the small subwoofer "lounge layout.jpg". I've put on dimensions of the room. The Kef sub is in the front left position currently.

After the SVS died I've decided to spend some time understanding my room behaviour and subwoofer positions before deciding whether to repair (If I make a 25mm thick adaptor plate the new SLEDGE 1200 amp will fit it) or replace the SVS (probably with a SVS SB2000 pro, or PC2000 pro).
The SVS is in the corner next to the small Kef subwoofer but not shown on that picture. I didn't know about REW or this type of testing before so the position it was in was arbitrary.

I've read getting started guides and watched a few youtube videos on REW, and today have had a crack at generating some plots. The test procedure was as follows:
- set the UMIK-1 on a tripod at my listening position (and did not move this during the tests)
- carry out audyssey setup with subwoofer (this has an issue in that audyssey complains that the subwoofer is too loud ~85dB but I can't do anything about that as the sub has no volume control)
- disable audyssey EQ in the denon setup menus (which retains speaker distance and level settings)
- modify the sub level from the -12dB audyssey has set it to, back up to 0dB
- set receiver volume to give SPL reading of ~75dB in REW with full range pink noise (my laptop is connected via HDMI to the receiver for the input signal generation)
- carry out REW sweeps in the five positions shown on the lounge image
- the front left seemed best to me so I then did a sweep with Audyssey enabled in that position, and then fiddled with the crossover settings to see if that made any difference.

I've attached the REW plots for these tests:
- "2020-08-08 rew 001a - room positions - full range.jpg" This shows the sweeps with Audyssey disabled at the five test positions I used. Full range meaning the full frequency range 10Hz-20kHz
- "2020-08-08 rew 001b - room positions - sub range.jpg" same as previous but frequency range 10-200Hz.
- "2020-08-08 rew 002a - front left with audyssey - full range.jpg" comparison sweep at front left without and with default audyssey over range 10-20kHz.
- "2020-08-08 rew 002b - front left with audyssey - sub range.jpg" same as previous but 10-200Hz.
- "2020-08-08 rew 003a - front left audyssey with phase - full range.jpg" just the default audyssey sweep but with the phase plot too, over 10-20kHz.
- "2020-08-08 rew 003b - front left audyssey with phase - sub range.jpg" same as previous but 10-200Hz.

For info, the sub doesn't go very low - I found a Kef T2 response on the soundandvision website (cant post a link as the forum software tells me the message has spam like content if I include the link!). I've attached their graph - the sub goes down to about 30Hz (the blue plot).

Having done these tests, I think the front left looks like the best position. I also suspect my room has bad behaviour.
However I don't totally understand what these plots are telling me or what I should do next and would be very grateful for any help.

In hindsight I also think I may have messed up by not rerunning the audyssey calibration for the sub in each position as the sub distance will have been set to the front left distance for all tests.

Thanks,
Pete (from UK).

 

[John Mulcahy]

Very thorough job, looks like you have got to grips with everything well. The front right position looks a little more even. Not sure how that 2 kHz dip and the raised area the follows it will sound, but perhaps Audyssey will level that out a bit. All rooms have modal resonances and reflections, your responses look fairly typical.

 

[DanDan]

Be sure to say more than say 2Metres away from the mic when sweeping.

 

[badbunny]

Hi,

I thought I would keep updating this thread as I do different things so that other people can learn from what I've done.

After spending some time with my small Kef T2 subwoofer (10" driver, 250W, sealed box) doing room sweeps in various positions around my room, I had learned several important things:

• the sub position around the room had a massive affect on the listening position sound response
• from these tests I decided that the sub needed to be on the front wall somewhere mid to right under the TV (there is another position that might be more optimal but our dog will not like it next to his bed!)
• from the room sweeps I did I know that I get significant low frequency room gain, so having a ported sub was not necessary for me
• The position limitation meant I needed a sub that was less than about 16" tall so my centre speaker had a reasonable clearance above the sub to allow me maximum flexibility to try different positions along the front wall.

So based on these things I learnt from using a small lowish powered sub I decided to buy a SVS SB3000, which arrived yesterday and I've put it in exactly the same place (the front centres of the drivers) as the Kef T2 was previously.

Having run one audyssey calibration with the SB3000 I am really pleased with the results. There are about four narrowband dips between about 90-130Hz but I'm not sure if they are important. I will also play around with fine tuning the sub position to see if they can be improved. These attached images show the SB3000 response (with default audyssey settings except for the AVR +6dB boost plot):

• 2020-08-22 SB3000 10-200Hz.jpg
• 2020-08-22 SB3000 20-20kHz.jpg

The graphs show the red line with default audyssey settings. The other two lines show a comparison of applying a +6dB sub level boost on the AVR or a +6dB boost on the sub. I had read things on various forums saying that the gain needed to be edited on the AVR otherwise the DEQ isn't applied correctly. To my eyes/ears I can't see/hear any significant difference so I think that may be an urban myth and that applying a sub boost on the AVR or sub after audyssey calibration gives the same result.

I've also attached two other images showing a comparison of the Kef T2 (10" driver, 250W, sealed box) and SB3000 (13" driver, 800W, sealed box) at the same position. These were on different days so there might be some small differences between the tests (both with the audyssey mic positions used for the audyssey calibrations and the UMIK1 position for the REW tests). However there is a striking similarity between the two responses in the sub range above 45Hz, below which the SB3000 continues strongly down to 10Hz. Note that my crossovers are set at 150 front, 120 centre, 200 surround, so there is a large range of sub response comparison there. Again these are with default audyssey settings.

• 2020-08-22 kef t2 vs sb3000 10-200Hz.jpg
• 2020-08-22 kef t2 vs sb3000 20-20kHz.jpg

The points I take away from this comparison are:

• the room position for a sub is more important than the sub itself
• you can use a small lower powered sub to investigate how the position of the (any?) sub will respond at your listening position (at least with the two sealed subs i compared, not sure if a ported one would introduce another complexity). You could even borrow one from a friend to do this with about 3 hours of playing if you don't yet have one.
• from the tests you do with your existing/borrowed sub you can figure out the best positions and find the best compromise of sub position and the sub size/shape that will fit in those positions

Hope these thoughts help someone trying to decide whether to upgrade/buy a sub, which one to buy, and where to put it.
I will update further as I fine tune the position along with any other observations I make. I would also be grateful for any other observations on the graphs as well as suggestions for useful things I can do with REW that I haven't yet got my head around (eg waterfall plots?).

Thanks,
Pete.