Room Sim and Bass Management issue?

[SubViking]

I have used REW extensively for setting up my room and have had great results and I have been very impressed with the way the simulations made before placing the speakers have matched measurements taken after moving them into place.
Today while fooling around with simulations with the third sub added to the setup and adjusting the bass management crossover and the -3dB freq. of the main speakers I noticed that even though the crossover is set at 80Hz incrementally changing the -3dB of the main speakers from 39Hz to ie 32Hz shows up in the simulation with quite dramatic results. But that seems odd as their contributions in the 30Hz region must be minute when the crossover is set at 80 Hz. Actually this has been confirmed by the measurements - they have very, very little output below 45Hz.

Perhaps the slope is steeper on my Yamaha than what is assumed in the simulations?
Or am I missing something?

On the same subject: In the help section: roomeqwizard.com/help/help_en-GB/html/modalsim.html
there's a sentence that I can't make sense of:
"Note that the simulation automatically level aligns sources to the main listening position, but that all the simulated subwoofers generate signals at the same level - this is necessary if they are arranged symmetrically to minimise modal excitation and reduce seat-to-seat variation."
I assume it is supposed to mean that level is aligned at the listening position but that the subs do NOT generate signals at the same level (ie if measured at 1 meter) or???

The reason this is important is, that I I will try to integrate the three subs though the 3rd is capable of a somewhat lower max. SPL compared to the other two it does provide useful output below 30Hz and could be positioned closer to the main listening position if needed.

 

[John Mulcahy]

I have used REW extensively for setting up my room and have had great results and I have been very impressed with the way the simulations made before placing the speakers have matched measurements taken after moving them into place.
Today while fooling around with simulations with the third sub added to the setup and adjusting the bass management crossover and the -3dB freq. of the main speakers I noticed that even though the crossover is set at 80Hz incrementally changing the -3dB of the main speakers from 39Hz to ie 32Hz shows up in the simulation with quite dramatic results. But that seems odd as their contributions in the 30Hz region must be minute when the crossover is set at 80 Hz. Actually this has been confirmed by the measurements - they have very, very little output below 45Hz.

Perhaps the slope is steeper on my Yamaha than what is assumed in the simulations?
Or am I missing something?

Measurements of your speakers aren't really relevant here, they may have no output below 45 Hz but you are telling the simulator the mains are only 3 dB down at 32 Hz. An 80 Hz bass management crossover is usually 2nd order, at 32 Hz it attenuates by about 16 dB.

On the same subject: In the help section: roomeqwizard.com/help/help_en-GB/html/modalsim.html
there's a sentence that I can't make sense of:
"Note that the simulation automatically level aligns sources to the main listening position, but that all the simulated subwoofers generate signals at the same level - this is necessary if they are arranged symmetrically to minimise modal excitation and reduce seat-to-seat variation."
I assume it is supposed to mean that level is aligned at the listening position but that the subs do NOT generate signals at the same level (ie if measured at 1 meter) or???

The reason this is important is, that I I will try to integrate the three subs though the 3rd is capable of a somewhat lower max. SPL compared to the other two it does provide useful output below 30Hz and could be positioned closer to the main listening position if needed.

If multiple subwoofers are arranged in a symmetrical arrangement to cancel resonances (a sub in each corner for example, or at the mid point of each wall) the cancellation will only work if each subwoofer is producing the same level at the sub position. If the sub levels were adjusted so they were the same at the listening position the differences in their individual outputs mean they would no longer be able to cancel the modal resonances. That isn't relevant if the arrangement isn't attempting modal cancellation in that way, but changing individual sub levels will still affect how they interact so it wouldn't be appropriate for REW to impose a level alignment on them.

 

[SubViking]

Measurements of your speakers aren't really relevant here, they may have no output below 45 Hz but you are telling the simulator the mains are only 3 dB down at 32 Hz. An 80 Hz bass management crossover is usually 2nd order, at 32 Hz it attenuates by about 16 dB.

If multiple subwoofers are arranged in a symmetrical arrangement to cancel resonances (a sub in each corner for example, or at the mid point of each wall) the cancellation will only work if each subwoofer is producing the same level at the sub position. If the sub levels were adjusted so they were the same at the listening position the differences in their individual outputs mean they would no longer be able to cancel the modal resonances. That isn't relevant if the arrangement isn't attempting modal cancellation in that way, but changing individual sub levels will still affect how they interact so it wouldn't be appropriate for REW to impose a level alignment on them.

Thanks a million for the explanations. I stupidly missed the significance of the distinguishing between "sources" and "subwoofers".
Regarding the response with different -3dB points it still baffles me that small changes in the 30 Hz region attenuated almost 20 dB affects deep some of the dips between 120 and 200 Hz. But for now that is all theoretical as I do not have the money needed to upgrade the main speakers. I just wanted to play with the idea :-)

The simulation and the measurements have been extremely helpful both in getting a decent result from playing across the rectangular room instead of along the longest axis. My living room was not in any way designed for audio reproduction so not only am I forced to place the main speakers on the long side of the room my main listening position is also way to close to the wall behind me, so simulations and measurements have improved the sound enormously.

Also a huge thank you for the REW itself: What a gargantuan achievement

 

[lemania]

Measurements of your speakers aren't really relevant here, they may have no output below 45 Hz but you are telling the simulator the mains are only 3 dB down at 32 Hz. An 80 Hz bass management crossover is usually 2nd order, at 32 Hz it attenuates by about 16 dB.

If multiple subwoofers are arranged in a symmetrical arrangement to cancel resonances (a sub in each corner for example, or at the mid point of each wall) the cancellation will only work if each subwoofer is producing the same level at the sub position. If the sub levels were adjusted so they were the same at the listening position the differences in their individual outputs mean they would no longer be able to cancel the modal resonances. That isn't relevant if the arrangement isn't attempting modal cancellation in that way, but changing individual sub levels will still affect how they interact so it wouldn't be appropriate for REW to impose a level alignment on them.

Hello John,
Is it meanwhile possible to simulate Dipole woofers in REW Room Simulation? Or is there a plan to do so in future?
Best regards
Michael

 

[John Mulcahy]

Is it meanwhile possible to simulate Dipole woofers in REW Room Simulation?

You can do that by adding a second, inverted source at the distance corresponding to the woofer separation.

 

[lemania]

Hello John,
Thank you...this was a fast response:-)
This is what I did by now.
But as I have two 2m high dipole Subs, I´m not shure if 8 subs in your simulation are enough to simulate both subs in full height. So by now I take two subs (one inverted) at position 0.5m in height and two subs (one inverted) in height 1.5m. What do you think, or would you place the pairs at bottom and top?
Best regards
Michael

 

[John Mulcahy]

So by now I take two subs (one inverted) at position 0.5m in height and two subs (one inverted) in height 1.5m

That sounds like a sensible approach. You could try simulating a single sub with 4 drivers and with 8 drivers and see what difference it makes.

 

[lemania]

thanks again - good idea