From my experience asking questions, the port just creates one more complexity in phase. If LF extension is challenging excursion then add more woofers. Don't forget also, fixing Group Delay with DSP, adds more delay to the whole signal.
I would appreciate if somebody could answer point by point for better understanding.
Thanks and Regards,
WonderfulAudio
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Having spatial diversity in that dimension is what gives you control over those modes. People speak of leaving certain things to chance. Who knows, you might get lucky. Go ahead anyway, do some measuring and see how it goes.
The original Summa had ports. But after I went with multiple subs I realized that at best porting was not necessary and it could also be detrimental because of the total lack of cone control below tuning. So I just deleted them. All my subs are closed box.
The bass was clean, cleaner than most monopoles, but still not as good as multiple subs.
I think that it should be advantageous, but not critical. Only one of my subs is a few feet off the floor.
We can, but I am not sure why one would want to do that. In my room, the first mode is at about 22 Hz. Not much point in trying to go lower than that.
You could never do that. One cannot control the phase difference (180 degrees) between the cone and the port with DSP so below tuning the two are just cancelling each other out - no sound to EQ - and trying to do so would just add a lot of excursion with no gain in output.
Hi Earl (@gedlee)
1)Can the corner sub be the one that is lifted? It could be aesthetically more acceptable, the other two subs not so.
2)The multi sub article at https://mehlau.net/audio/multisub_geddes/ recommends adding delay, but you have told delay is not a good idea, am I understanding right?
Thank you,
Warm Regards,
WonderfulAudio
Hi Earl,
Few more relevant questions came to my mind, hope you find time to answer them.
3) It seems like each additional sub we are adding contribute less and less spl, then can we optimize by having 1st sub 12 inch driver, 2nd sub 10 inch and third sub 8 inch driver, each tuned to 25hz (with PRs) just to avoid loss of loading at low frequencies. I am just thinking of saving some real estate if it works. In the city where I live rooms are typically small 🙁
4) If after multi sub approach we move the listening position, the sofa a foot ahead or back(for cleaning the room), do we need to do multi sub tuning again or should the sofa be at exact the same place that we better mark its position on the floor and always keep it there?
5) The multi sub article at https://mehlau.net/audio/multisub_geddes/ uses mp3 for whitenoise, doesn't MP3 format remove quite a lot of frequencies that are required for this multi sub technique?
6) Can we use frequency stepped sweep (from lets say freeware Arta-Steps) instead of whitenoise for this technique? If yes, then is 1/6th octave between 25Hz and 200Hz good enough? We could take just one measurement with linear mic array instead of rotating the mic by hand. There are 2 feet and 4 feet versions available at https://www.shure.com/en-IN/products/microphones/mxa710?variant=MXA710AL-2FT%20
7) Is first room mode always a peak or a null or could be anything?
8) If this technique was done with door closed (almost sealed room) and we then open the door then should this technique be done all over again?
Thank you,
Warm Regards,
WonderfulAudio
Few more relevant questions came to my mind, hope you find time to answer them.
3) It seems like each additional sub we are adding contribute less and less spl, then can we optimize by having 1st sub 12 inch driver, 2nd sub 10 inch and third sub 8 inch driver, each tuned to 25hz (with PRs) just to avoid loss of loading at low frequencies. I am just thinking of saving some real estate if it works. In the city where I live rooms are typically small 🙁
4) If after multi sub approach we move the listening position, the sofa a foot ahead or back(for cleaning the room), do we need to do multi sub tuning again or should the sofa be at exact the same place that we better mark its position on the floor and always keep it there?
5) The multi sub article at https://mehlau.net/audio/multisub_geddes/ uses mp3 for whitenoise, doesn't MP3 format remove quite a lot of frequencies that are required for this multi sub technique?
6) Can we use frequency stepped sweep (from lets say freeware Arta-Steps) instead of whitenoise for this technique? If yes, then is 1/6th octave between 25Hz and 200Hz good enough? We could take just one measurement with linear mic array instead of rotating the mic by hand. There are 2 feet and 4 feet versions available at https://www.shure.com/en-IN/products/microphones/mxa710?variant=MXA710AL-2FT%20
7) Is first room mode always a peak or a null or could be anything?
8) If this technique was done with door closed (almost sealed room) and we then open the door then should this technique be done all over again?
Thank you,
Warm Regards,
WonderfulAudio
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For those that dont know, REW has a nice Room Simulation tab. I guess 8 subwoofer + Main Left and Main Right is sufficient to most.
I dont know how accurate it is, but it is really easy to try ideas and theory from the couch 🙂
For example my room. I like to keep my mains rather close to backwall:
Only mains:
Adding one sub at backwall at midpoint (huge dip at 50 hz is gone)
Adding 3 ms delay (delay added is the same as if plateamp had phase turning knob - Took me some time to realize that):
Adding third sub:
I dont know how accurate it is, but it is really easy to try ideas and theory from the couch 🙂
For example my room. I like to keep my mains rather close to backwall:
Only mains:
Adding one sub at backwall at midpoint (huge dip at 50 hz is gone)
Adding 3 ms delay (delay added is the same as if plateamp had phase turning knob - Took me some time to realize that):
Adding third sub:
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It is educational. However straight simulations (in general) tend to give tall peaks calculating on point placement, and real subs can give different results even when you rotate a sub in the same position.
As a result of the uncertainty, any real fine tuning you'd do in a simulator is time better spent measuring.
This is just how SPL combines with ever-smaller increases in Vd. It is not because the additional subs are each moving less air.
Think about this way: adding a second, identical sub increases total Vd by 100%. A third sub 50%. A fourth only 33%. Etc. Turn those incremental changes into dB, and you see small gains after the first 2-3 subs.
All that said, if your room size & SPL needs are modest, then smaller subs can work. Or, if you're trying to improve a specific issue at ~60Hz, a smaller sub can do so without <40Hz extension.
Sure, whatever works.
Again, whatever works. Delay is nothing more than frequency dependent phase and of course phase makes a difference and so does delay, just in a different way - one may work better than the other. I've used both.
Then closed box, the smallest of the sub types is the obvious choice in your situation. As I have said before, there is no advantage to ported when one has DSP.
I highly doubt that. The convergence area will be about 1/4 lambda at the highest frequency that the subs run, typically not greater than 100 Hz. This means that moving 2-3 feet will not be a big deal and even five shouldn't be a disaster.
Not to my knowledge. LFs are easy for a coder. It's HFs that can get problematic.
Any reliable method of assessing FR differences will work just fine.
It depends on what one calls the first mode. There is a VLF mode of resonance between the outside of the room and the inside. This will be all over the map depending on how well sealed the room is - how it couples to the rest of the facility. But we mostly think of the longest parallel walls as representing the "first mode". This is the first one that I can measure in my room.
I doubt that this would have much of an effect - it moves the lowest resonance mode, but hardly changes any resonances based on reflective distances.
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As a general trend it is going to be OK. But there is a serious error in REWs room simulator that I have commented on before. That is it uses global damping and real mode shapes in the model which is not accurate when one has, for example, one wall much more damped than another. In this case the damping is strongly modal and the modes become mathematically complex (ie. have imaginary parts,) and a global damping assumption could be very wrong. If I hadn't of gotten so old, I at one time planned to create software that would allow for a small room with random wall impedances just to see how different the two approaches results are. Just not in the cards these days.
£2.2K for the 2ft version and £2.9K for the 4ft . . . I'd rather rotate my hand
Hi Earl (@gedlee ),
I understand that the relation of phase of active driver and port/PR phase stays same always, processing cant change that.
What I meant was: take the low tuned system (very low 25Hz PR or bass reflex ) as a whole system, take its phase response, probably it will look like an all-pass filter response and linearize it to flat. Does it have any sonic advantage?
If I vaguely remember correctly you were not happy with addition of delay in multi sub optimizer. Did you change your opinion on delay? While delay and phase can be interpreted same, but when delay is set too high, it may be multiple wavelengths, and that may not be good.
Thanks and Warm Regards,
WonderfulAudio
RE delay- a low pass filter is a delay in effect. A woofers output will be delayed by the crossover plus anything else. It the past I had best results with woofers on the floor in front of the main speakers by about 3 feet for a 100 Hz crossover. Today you can delay the main system in DSP to match the woofer. Precision is not that critical when the wavelength is 10' (100 Hz). but it does make a difference. With multiple woofers you would want their outputs to arrive at close to the same time to avoid unwanted cancellation. Its also the reason stereo bass or one channels bass tends to be better than summed bass. Music is not usually recorded with mikes that are close together to get stereo. The distance between them can lead to cancelling of LF content in mono. (Keith O. Johnson was who pointed this out to me and first demonstrated it).
Is the ear then sensitive to the absolute phase of the recorded signal. I would think that, at best, it is a very minor effect, if at all. I certainly have never worried about it.
I don't recall ever being against delay. Sure "multiple wavelengths" at say 50 Hz would be this would be on the order of 100's of ms. which is an enormous delay. I would think in terms of 10's of ms. being extreme. At typical delay at LFs, it only a small phase shift of the signals.
This has been argued for decades. Years ago we did a study of the LFs signals on recordings, at that time virtually 100% of them were mono at these frequencies. Hence "summed bass" is just fine except maybe for the rare event of stereo bass where the recordings are not well done. I don't think that this is a major concern.
Years ago we tried a very simple implementation of this idea. It was interesting and moving in the right direction, but needed more development.
I would think that it might reduce the demands on the number of subs, but spatial arraying is always going to be important. The idea is to decorrelate the subs output making them more independent, but numbers of subs will always be important as clearly just doing this to one sub isn't going to be very effective. Two more so and three even more so - diminishing returns, but where the significance cutoff is will be hard to determine.
I would think that it might reduce the demands on the number of subs, but spatial arraying is always going to be important. The idea is to decorrelate the subs output making them more independent, but numbers of subs will always be important as clearly just doing this to one sub isn't going to be very effective. Two more so and three even more so - diminishing returns, but where the significance cutoff is will be hard to determine.
This topic gets a lot of attention on ASR...how many recordings are mono bass vs stereo bass. Analysis of tracks, including older CD tracks, has been showing more is recorded in stereo than commonly presumed.
Maybe the old practice of needing to mono bass for vinyl, died off earlier and more prevalently than realized?
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