Forums

Use of DSP Technology to filter ambient noise

Started by parallel54 June 9, 2009
On 9 Jun, 13:38, "parallel54" <t...@newmediaintelligence.com> wrote:
> Hi there, > > I am interested in using DSP technology to filter ambient noise. That is > not just headphone noise cancellation but to reduce noise in an external > area. So for example to use a technology to "block" / "reduce" the noise of > an aircraft/train in the garden area of a restaurant. > > So the device would project the inverse of the background noise and so > reduce it within the given area. Does anyone know of any systems that > currently do this?? Very interested in the group's thoughts on this.
Active noise control, which is what you are talking about, would only work in small target volumes, like sizes comparable to the human head. Such systems are used mainly in situations where humans are sitting still in noisy environments, like drivers in noisy machinery or aircraft passengers. In these situations the system would consist of microphones and speakers near the headrest of each seat, that are tuned to create a quiet zone just around the ears of the occupant. To reduce noise in a larger out-door area use shields against the sources if you can, and use scattering and absorbing materials around the area. There are companies who specialize in these types of designs. Check out your local Yellow Pages.
parallel54 wrote:
> Hi there, > > I am interested in using DSP technology to filter ambient noise. That is > not just headphone noise cancellation but to reduce noise in an external > area. So for example to use a technology to "block" / "reduce" the noise of > an aircraft/train in the garden area of a restaurant. > > So the device would project the inverse of the background noise and so > reduce it within the given area. Does anyone know of any systems that > currently do this?? Very interested in the group's thoughts on this. > > Thanks > > TIM > >
Hi, I agree with the other posters on the difficulty of cancelling noise over a wide area, but how about masking the noise instead, to reduce its annoyance factor? Injecting some white audio noise into the area would seem to be the obvious way to go, but it occurs to me that some 'intelligence' could be added to the process to improve the masking effect. A FT could be performed on the unwanted signal and the resulting spectrum used to modify the spectrum of the white noise. In effect we would want to attenuate the white noise in those frequency regions that correspond to peaks in the spectrum of the incoming unwanted signal. The resulting "signal + noise" heard by the listener would then have a reasonably flat spectrum and may sound more like white noise than 'unwanted signal' (Or it may not. This is pure speculation on my part.) The above obviously would not work if the unwanted signal was narrow-band (e.g. a train whistle) because you would not want to use white noise levels that gave a comparable spectral density. It may be practical with a reasonably wide range of unwanted signals such as tyre noise from cars on a nearby road that have much broader spectral peaks. Regards, John
Sorry for late reply only just got time to catch-up with the thread - it
sounds like noise deflection/ shielding (via vegetation etc) is a much more
practical alternative.

Thanks - but thought it was worth exploring - you never know!

TIM
Eric Jacobsen wrote:
> On 6/9/2009 4:38 AM, parallel54 wrote: >> Hi there, >> >> I am interested in using DSP technology to filter ambient noise. That is >> not just headphone noise cancellation but to reduce noise in an external >> area. So for example to use a technology to "block" / "reduce" the >> noise of >> an aircraft/train in the garden area of a restaurant. >> >> So the device would project the inverse of the background noise and so >> reduce it within the given area. Does anyone know of any systems that >> currently do this?? Very interested in the group's thoughts on this. >> >> Thanks >> >> TIM >> > > As others have mentioned, it's tough to noise cancel over a large area. > > You might look into shrubbery/vegetation around the garden (tall stuff) > that can reflect the noise away from the garden. Some well-placed heavy > reflectors (I see them curved a lot) may work well, too, depending on > how localized the noise source(s) are. That sort of thing combined with > low level music/noise/sound generators can often do wonders.
I spent last night in a motel room near Providence, RI that overlooked the airport. Conversation was quite difficult with the window ajar, but the room was quiet when it was closed. I thought it remarkable. One system that had limited but inadequate success canceled fan noise emanating from a small register, using small speakers surrounding the register. I was called in to improve the suppression, which I did by lining the last 20 feet of duct with felt and removing the speakers. Jerry -- Engineering is the art of making what you want from things you can get. &#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;
On 19 Jun, 20:30, Jerry Avins <j...@ieee.org> wrote:

> One system that had limited but inadequate success canceled fan noise > emanating from a small register, using small speakers surrounding the > register. I was called in to improve the suppression, which I did by > lining the last 20 feet of duct with felt and removing the speakers.
Not a good solution: 1) The system's efficiency is affected 2) The felt traps moist and dust, where bacteria and fungii can grow. Rune
Rune Allnor wrote:
> On 19 Jun, 20:30, Jerry Avins <j...@ieee.org> wrote: > >> One system that had limited but inadequate success canceled fan noise >> emanating from a small register, using small speakers surrounding the >> register. I was called in to improve the suppression, which I did by >> lining the last 20 feet of duct with felt and removing the speakers. > > Not a good solution: > > 1) The system's efficiency is affected > 2) The felt traps moist and dust, where bacteria and fungii can grow.
1) The duct was a standard size, larger than needed for the register. 2) That was standard industry practice. The felt came from an HVAC shop. (My father designed and installed such systems.) Jerry -- Engineering is the art of making what you want from things you can get. &#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;
On 20 Jun, 22:33, Jerry Avins <j...@ieee.org> wrote:
> Rune Allnor wrote: > > On 19 Jun, 20:30, Jerry Avins <j...@ieee.org> wrote: > > >> One system that had limited but inadequate success canceled fan noise > >> emanating from a small register, using small speakers surrounding the > >> register. I was called in to improve the suppression, which I did by > >> lining the last 20 feet of duct with felt and removing the speakers. > > > Not a good solution:
> > 2) The felt traps moist and dust, where bacteria and fungii can grow.
> 2) That was standard industry practice. The felt came from an HVAC shop. > (My father designed and installed such systems.)
I don't say it was a wrong solution for its day; but it *is* a bad solution. There has been lots of fuzz (maybe a bit too literally) about ventilation systems in recent years. The general consensus seems to be that 1960-70's specs were way too feeble. Students in schools were seriously affected by poor ventilation - headaches, poor concentration, generally poor health. The factor that made the relevant institutions act to upgrade and replace vent systems, was that fungii were found in the dust in the ventilation ducts. The ducts hadn't been cleaned since they were installed, decades earlier. Once the fungii were discovered, it became a matter of the teachers' working conditions, and then all of a sudden the legal mechanisms regarding working environments kicked into action. As long as it was a 'mere' matter of kids, everything was allowed to go on as it had always done. Rune
Rune Allnor wrote:
> On 20 Jun, 22:33, Jerry Avins <j...@ieee.org> wrote: >> Rune Allnor wrote: >>> On 19 Jun, 20:30, Jerry Avins <j...@ieee.org> wrote: >>>> One system that had limited but inadequate success canceled fan noise >>>> emanating from a small register, using small speakers surrounding the >>>> register. I was called in to improve the suppression, which I did by >>>> lining the last 20 feet of duct with felt and removing the speakers. >>> Not a good solution: > >>> 2) The felt traps moist and dust, where bacteria and fungii can grow. > >> 2) That was standard industry practice. The felt came from an HVAC shop. >> (My father designed and installed such systems.) > > I don't say it was a wrong solution for its day; but it *is* > a bad solution. > > There has been lots of fuzz (maybe a bit too literally) about > ventilation systems in recent years. The general consensus seems > to be that 1960-70's specs were way too feeble. Students in > schools were seriously affected by poor ventilation - headaches, > poor concentration, generally poor health. > > The factor that made the relevant institutions act to upgrade > and replace vent systems, was that fungii were found in the > dust in the ventilation ducts. The ducts hadn't been cleaned > since they were installed, decades earlier. > > Once the fungii were discovered, it became a matter of the > teachers' working conditions, and then all of a sudden the > legal mechanisms regarding working environments kicked into > action. As long as it was a 'mere' matter of kids, everything > was allowed to go on as it had always done.
It's a shame when kids' welfare isn't given enough weight. In one instance here, A school play yard was closed when toxic soil was discovered in it, but parents weren't told. Remedial work was deferred to the summer, when there would be no concentration of students in the area. Word leaked out and there was an uproar from the parents. The school administration didn't trust the parents to keep cool, and the parents didn't trust the administration to protect the students. Perhaps both were right. Jerry -- Engineering is the art of making what you want from things you can get. &#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;
On 21 Jun, 15:08, Jerry Avins <j...@ieee.org> wrote:

> In one > instance here, A school play yard was closed when toxic soil was > discovered in it, but parents weren't told. Remedial work was deferred > to the summer, when there would be no concentration of students in the > area. Word leaked out and there was an uproar from the parents.
There is a similar thing going on here. A German U-boat was sunk somewhere off the coast in February, 1945. This particular U-boat carried tens of tonnes of mercury: http://www.kjemi.com/artikkel/2159/kvikksolvet-i-ubaten-ved-fedje/ The question is what to do with the wreck: - Locals and fishermen want the wreck and mercury removed from the area - Professionals claim that there are more dangers associated with messing with the wreckage, than with leaving it in place. The above link is from a professional associasion of chemistry engineers, and raises the question about exactly how the mercury might react with surroundings. From the ingress: "Pr&#2013266168;ver av bunndyr og fisk rundt ub&#2013265925;ten har ikke gitt overbevisende holdepunkter for at organismene rundt vraket inneholder h&#2013266168;yere konsentrasjoner av kvikks&#2013266168;lv enn en normalt observerer langs norskekysten." "Samples from [organisms] around the wreckage have given no convincing evidence that [they] contain more mercury than [is usual for wildlife] along the Norwegian coast." The author then argues that the chemical and physical properties of Mercury indicate that it represents no particular dangers if left in place: The reactants that are known to interact with disturb mercury are just not present at the site of the wreck. The arguemnt is that there is no particular dagers associated with leaving the wreck in sity, and covering it with sand and gravel. The alternative, recovering a 70-year-old wreck, is far more worrying. When (not if) it disintegrates, the mercury is free to mix with waters that actually do contain reactants that bind to mercury. But of course, when politicians are involved, rasional evaluations of arguments has no further place in the discussions. A decision was made to leave the wreck. Two months later, somebody had written a contract with a salvage company, 'to have at hand when the decision is altered.' Oh well. Rune
Rune Allnor wrote:
> On 21 Jun, 15:08, Jerry Avins <j...@ieee.org> wrote: > >> In one >> instance here, A school play yard was closed when toxic soil was >> discovered in it, but parents weren't told. Remedial work was deferred >> to the summer, when there would be no concentration of students in the >> area. Word leaked out and there was an uproar from the parents. > > There is a similar thing going on here. A German U-boat was sunk > somewhere off the coast in February, 1945. This particular U-boat > carried tens of tonnes of mercury: > > http://www.kjemi.com/artikkel/2159/kvikksolvet-i-ubaten-ved-fedje/ > > The question is what to do with the wreck: > > - Locals and fishermen want the wreck and mercury removed > from the area > - Professionals claim that there are more dangers associated > with messing with the wreckage, than with leaving it in place. > > The above link is from a professional associasion of chemistry > engineers, and raises the question about exactly how the mercury > might react with surroundings. From the ingress: > > "Pr&#2013266168;ver av bunndyr og fisk rundt ub&#2013265925;ten har ikke gitt > overbevisende holdepunkter for at organismene rundt > vraket inneholder h&#2013266168;yere konsentrasjoner av kvikks&#2013266168;lv > enn en normalt observerer langs norskekysten." > > "Samples from [organisms] around the wreckage have given > no convincing evidence that [they] contain more mercury > than [is usual for wildlife] along the Norwegian coast." > > The author then argues that the chemical and physical > properties of Mercury indicate that it represents no > particular dangers if left in place: The reactants that > are known to interact with disturb mercury are just not > present at the site of the wreck. > > The arguemnt is that there is no particular dagers > associated with leaving the wreck in sity, and covering > it with sand and gravel. > > The alternative, recovering a 70-year-old wreck, is far > more worrying. When (not if) it disintegrates, the > mercury is free to mix with waters that actually do > contain reactants that bind to mercury. > > But of course, when politicians are involved, rasional > evaluations of arguments has no further place in the > discussions. A decision was made to leave the wreck. > Two months later, somebody had written a contract > with a salvage company, 'to have at hand when the > decision is altered.'
I was once part of a conspiracy to hide the presence of PCBs in the sediment under a major supply of drinking water. The D&R canal was once an important route for transporting coal barges from Pennsylvania coal mines to New York City. Now it carries water from Trenton on the Delaware River to New Brunswick on the Raritan River. It is the spine of a long park. People canoe on it and communities along the way tap it for drinking water. In years long past, industries along the way used it to carry away waste, and an analysis showed that high concentrations of PCBs were sequestered in the sediment. When I learned through my connection with the sewerage authority that there might be a problem, I was alarmed and asked a member of the Canal Commission if it were true and if true, wht wasn't the public informed. He calmed me down. There was, as I said, no measurable concentration in the water, but dredging the sediment would change that. A public announcement would almost undoubtedly create counterproductive panic. What to do? They started upstream, at Trenton, where the concentration was highest. They built two dams about a mile apart, connected by a pipe to bypass the dammed-off section, then cleaned it out and rebuilt the riprap lining. When it was clean, they moved the upstream dam two miles downstream and repeated the process. At the end, the canal was not only free of silt and contamination, it was refurbished and much of the towpath restored. I and probably some others had agreed to keep silent as long as the work diligently progressed. It did. Jerry -- Engineering is the art of making what you want from things you can get. &#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;&#2013266095;