inertial said:I understand your point but agreed only partial.
If you are familiar with room's simulators ( yes you have said this previously) you sure know that floor is not the only issue.
There are six walls, you can virtually add one at time and see the difference in your listening position. A caos!
When you have added all the six walls, the influence of the only floor
is not so rilevant .
I am referring at european rooms, not very large, very solid walls and
listen triangle about 2 metres.
In this scenario, i always see peaks and dips in the midbass zone and basic measurement semms comfirmate this. Problems in the 80-300Hz zone. ( of course there are big problem also below 80 Hz)
It is easy listenable with normally a lack of punch, no body, no weight , very bad sound .
This is a very typicall performance in our "small" european rooms ( to say 20-25 square meters), not sure how much different can be in yours americans rooms .
I know simulators makes big simplifications respect real conditions, but something is interesting to my eyes .
So the question remain IMHO, who takes care of the 80-300Hz?
Yes, you're right. The solid boundaries of European homes are much more problematic than the framed drywall construction common in North America. Many European flats have concrete and solid plaster, very little damping. You might add false walls that act as dampers.
I'm talking about floor bounce in the 100Hz to 200Hz range. I see it pretty frequently in mini-monitors on stands and towers. Its frequency is dependent on height, and changes slightly with respect to listener position because it is caused by the path length difference between the direct sound and the floor reflection. You never see it in vertical line arrays, because of the dense interference in the vertical plane. I have also found 2.5-ways and low-crossed mids that overlap with woofers mitigate the notch. Same with a sub that is used fairly high, overlapped with the mains. Again, the problem that can come up is localization, if the sound sources are too far apart.
Re: Re: Re: Multiple Small Subs - Geddes Approach
Two subs placed on opposing walls will cancel the first standing wave that will be there when any of the two subs are operated alone. Using three or four subs on the right locations will cancel many of the standing waves leading to smoother in room response of the speaker system.
Viewed in isolation a pair of main speakers (decently designed)will have less groupdelay than a sub+sat combo. However again, using several subs will decrease the level of the standing waves in the room which totally swamps the fine GD performance of the main speaker used alone. So what I'm saying is a main speaker crossed to several subs will likely sound much better than a main speaker in a non treated room. In a treated room the differences get smaller but will still be there. But as you seem to imply, various kinds of 2.5 way systems where the mains and "subs" work together works fine as well. Of course, depending on the "x-over" there's only so much you have to play with regarding placement of the added "fill-in" drivers.
Sure, active basabsorbers can be used either fed by a mic or placed at the wall opposite to the main speaker wall and DSP controlled to "make the wall dissapear" but that will be more expensive and that money and those active correction speakers can be used on more subs instead that will increase output and decrease nonlinear distortion and thermal compression.
That's true (or rather the focus and localization suffers) and multiple subs, bassabsorbers, DSP and dipoles are different ways of dealing with this
/Peter
soongsc said:
I'll take two.
The main issue with multiple subs is that you excite multiple room modes. This translates to the muddiness that Cal is referring to because now the low frequency energy cannot decay fast enough.
Two subs placed on opposing walls will cancel the first standing wave that will be there when any of the two subs are operated alone. Using three or four subs on the right locations will cancel many of the standing waves leading to smoother in room response of the speaker system.
Viewed in isolation a pair of main speakers (decently designed)will have less groupdelay than a sub+sat combo. However again, using several subs will decrease the level of the standing waves in the room which totally swamps the fine GD performance of the main speaker used alone. So what I'm saying is a main speaker crossed to several subs will likely sound much better than a main speaker in a non treated room. In a treated room the differences get smaller but will still be there. But as you seem to imply, various kinds of 2.5 way systems where the mains and "subs" work together works fine as well. Of course, depending on the "x-over" there's only so much you have to play with regarding placement of the added "fill-in" drivers.
Sure, active basabsorbers can be used either fed by a mic or placed at the wall opposite to the main speaker wall and DSP controlled to "make the wall dissapear" but that will be more expensive and that money and those active correction speakers can be used on more subs instead that will increase output and decrease nonlinear distortion and thermal compression.
That's true (or rather the focus and localization suffers) and multiple subs, bassabsorbers, DSP and dipoles are different ways of dealing with this
/Peter
Re: Re: Re: Re: Re: Re: Re: Re: Multiple Small Subs - Geddes Approach
Multiple subs decrease the decay time of the room resonances. It's not strictly correct to talk about reverberation time in the modal range of small rooms but when the frequency response is improved (flattened) the decay time and thereby transient response is improved as well. AFAIK standing waves are more or less minimum-phase phenomena.
Three is still better than two and four is even better. There are more than a few that ended up on four as the most sensible compromise betweeen cost, performance and "practicallity".
/Peter
markus76 said:
The preference to have huge level variations (±15dB) at low frequencies?
Multiple subs do nothing to the low frequency reverberation time, that's true. Only active (not available as a product) or passive absorption can help. But what multiple subs do is to smooth the frequency response in a way it can't be done with any other method (I know of). That IS the number one goal for low frequency reproduction.
Multiple subs decrease the decay time of the room resonances. It's not strictly correct to talk about reverberation time in the modal range of small rooms but when the frequency response is improved (flattened) the decay time and thereby transient response is improved as well. AFAIK standing waves are more or less minimum-phase phenomena.
Three is still better than two and four is even better. There are more than a few that ended up on four as the most sensible compromise betweeen cost, performance and "practicallity".
/Peter
How should multiple subs decrease the decay time? They don't change a room's modal field and they don't dissipate energy. They only work as active absorption as long as they radiate energy.
And it's correct to talk about reverberation time because resonances are always part of the reverberation time. If reverberation time says anything useful is another question but reverberation time includes room resonances.
I don't know what others have achieved with 4 subs but the 3 subs setup I use now is lightyears better than what I've achieved with 4 subs.
And it's correct to talk about reverberation time because resonances are always part of the reverberation time. If reverberation time says anything useful is another question but reverberation time includes room resonances.
I don't know what others have achieved with 4 subs but the 3 subs setup I use now is lightyears better than what I've achieved with 4 subs.
markus76 said:
And if the listening room is the control room, what is the original then?
It's true that a stero set up has its limitations but the frontal wave, the direct sound of a recording is not the weakest point. What I'm saying is that the direct sound from a source can be captured and played back with great accuracy even if the ambience is missing or is distorted.
I'm not surprised that soongsc objects to linear distortion on taiko or timpani since the reproduction of those have shown to have demand high performance in the upper bass. Excessive GD of the speaker and excessive room modes will decrease the fidelity greatly.. even though a lot of the energy is in the midrange. A drum transient is a wide bandwith signal.
And the speakers can not and should not only reproduce what was heard in a control room (stictly speaking they can not reproduce a side chain), they should reproduce the captured signals from the mic's, with or without spices (and sometimes electronic non-acoustical sounds of course) added post recording.
Sure there are recordings that can be said to be created in the studio, but many are created live in a hall or some other venue.
/Peter
Then you're lucky and you hear the original.
That doesn't change the fact that 99% of all recordings, broadcasts and movies available today were created in a studio. And it doesn't change the fact that live recordings are never mixed and mastered at the location of the original venues (use of headphones excluded - but then again the original would be what was heard with the headphones).
When you look at loudspeakers as instruments then sound reproduction becomes arbitrary.
markus76 said:
By avoiding the excitation of the resonance the time/transient behaviour is improved. In a minimum phase system frequency and phase goes hand in hand.
I seem to remember that measuring and calculating reverberation time demands/assumes diffuse field and a discrete resonance/standing wave is not a diffuse field phenomena. Only above the Schroeder frequency we can talk about reverberation time. I may remember wrong though and the important thing is of course not what it is called (though it makes conversation easier
but to understand the underlaying phenomena.I have achieved better subjective and measured results with four subs. The more subs the better you can fight the excitation of the room resonances. The people at Harman and also people here in Sweden have ended up at four as a good compromise.
/Peter
markus76 said:
Is this a misprint? Did you mean to say what you've done with three subs is light-years better than what you've done with one sub?
I wouldn't expect a huge improvement going from three to four, but I wouldn't expect performance to go down either. If nothing else, you could put two subs in the same place and you should expect parity with the three-sub setup. Move it around, in the right spot, it just about can't help but smooth the sound field further. The question of adding subs isn't whether it will smooth the field, it is by how much. There comes a point of diminishing returns.
Pan said:I seem to remember that measuring and calculating reverberation time demands/assumes diffuse field and a discrete resonance/standing wave is not a diffuse field phenomena. Only above the Schroeder frequency we can talk about reverberation time. I may remember wrong though and the important thing is of course not what it is called (though it makes conversation easier
If you're talking about RT60 then a diffuse field is assumed. A real diffuse field (isotropic and homogeneous) exists only in theory. But it works accurate enough for large spaces. In small spaces reverberation time can only be a measure to do comparative studies because the sound field is highly directional.
markus76 said:
And you're as charming as usual.
I don't have to show data as physics dictates these things.
I have shared lots of information and experience that has helped many people, wihtout showing data. I know you think everything I say and do is useless you don't have to say it. I'm not here for you but for people willing to learn and who appreciate when people take the time to explain things.
You know, an alternative to your rudeness would be something that a person with normal social skills might have said instead, like "oh interesting, did you save some graphs that you'd like to share?"
It's not like your pisspoor attitude inspires to go search for information and post it here for your benefit.
You are wrong and you make yourself look bad.
Know what, where's YOUR data?? Are you allowed to do things that other are not allowed to do?
Grow up will you!
If you do not realize that you can place several sources that avoids excitation of a standing wave you need to be a little more humble and go study basics.
/Peter