|   Background noise... | Tom Bombadil
Jul 2, 2002 7:33 AM | | Do you measure for audible/palpable background noise and if there is enough what do you do before trying to measure the audible quality of whatever component you have in mind ? |
| re: Background noise... | skeptic
Jul 2, 2002 12:59 PM | | Residual noise is measured without an input signal and usually the input shorted. It is specified as a number of db below a reference signal and characterized by its spectrum spread, usually completely random. So for a preamplifier, it might be specified as say; better than 80 db below one volt output from 20 hz to 20 khz. Then when distortion measurements are made, it is combined with the noise. An example of an noise and distortion measurement for an amplifier might be something like; no more than .25% total noise and distortion at any power level up to rated power. This last part is important in an audio amplifier because harmonic distortion as a percentage of total signal could be much higher at low signal levels than at full power in a poorly designed or misadjusted class AB power amplifier. This was responsible for some of the harsh sound of early transisitor amplifiers. Many people believe that once noise and distortion are below a certain level, further improvements are inaudable and therefore of no value to the user. Hope that this explanation helps you understand what these measurements mean. |
| Noise outside of the Electronics... | Tom Bombadil
Jul 3, 2002 7:48 AM | | e.g. nearby highway noise contributing to increasing the noise floor...
If there is presence of such noise it seems reasonable that it may a) influence perception of music as well as b) need a higher playback volume from the system - thus adding more reflections ...
I dont have any calculations to present nor any measuring devices...was interested in knowing how people deal with this when doing listening tests. |
| Room acoustics and isolation | Warren Warren
Jul 2, 2002 1:16 PM | | Excellent point that you bring out, about background noise. I can only hope (rather than assume) that all of the yeahsayers and most of the naysayers have well designed listening rooms that not only work in concert with the audio system but also reduce the level of background noise to be as close to inaudible as possible. Not that I recommend building yourself an anechoic chamber for stereo listening (although for HT it is not a bad idea), but that you have followed some common sense construction practices such as staggered studs, screws rather than nails, insulated walls/floors/ceilings, etc. I have a whole list of things you can do to an existing room (or if you are planning new construction) to help minimize outside noise as well as take advantage of the geometry of the room to minimize/maximize unwanted/desired reflections, respectively. After your environment is properly tuned for listening, then it becomes much easier to evaluate audio components. |
| re: Background noise... | skeptic
Jul 3, 2002 7:52 AM | | Background acoustical noise as opposed to electrical noise in components is measured with a calibrated microphone (db meter) and is compared to AIA (American Institute of Architecture) Standards. The spectrum of the noise is also critical. There are at least two relevant considerations. The absolute noise level and the isolation between the room and the outside. The interior acoustics are completely independent of the isolation. For example, a very well isolated room could be acoustically live or dead or anything in between. So could a poorly isolated room. Good room isolation requires more than one layer of sheet rock on each side, acoustical batting such as fiberglass inside the wall and above the ceiling, a good sturdy floor, sealing of all of the cracks and crevices with caulking, a heavy door that makes a tight seal around the jamb. Isolation from outise low frequency disturbances is the hardest requiring that the room be floated on vibration absorbing material so that there is no direct transmission of vibratons through the walls or floor. The interior acoustics of the room depends on its size, geometry, and the relative absorption/reflection of the materials chosen and their distribution. With all the talk over the years about prefect room acoustic, live end/dead end rooms etc., I'm not so sure that the term perfect has any meaning for listening to stereo systems. Standing waves are bad. Other than that, it's safe to say the the acoustics of any home listening room is vastly different from the kind of spaces where live music is usually performed and heard. |
| Wow! | Warren Warren
Jul 3, 2002 1:44 PM | | For a man who doesn't know Pink Floyd, you actually do posess relevant knowledge and information, AND you presented it without being condescending or insulting. Of course, I still want to get my rub in, but good post!
WW |
| Wow! | JoeW
Jul 3, 2002 7:56 PM | | From my experience, I have to agree with everything said, as far as accoustical isolation. Interesting, it's also fire code from the BOCA Book, for multi-use buildings.
For those who want to take it a step further, home studio, say:
Use the 'hat channel' specified in the BOCA book for ceilings, for creating an air space between drywall layers.
Use solid core doors, and have them installed by a professional. Weather stripping can help greatly, if your need is to exclude outside sounds.
As was said before, it's really two separate issues. Accoustic isolation and echo control |
| Hey Warren | pctower
Jul 4, 2002 11:16 AM | | Haven't received the cables yet. If you have sent them, please email me at ptower@covad.net with a tracking number.
Sorry to communicate publicly, but I haven't been able to get an email through to you.
Thanks |
| Hey Phil! | Warren Warren
Jul 8, 2002 12:13 PM | | Sent the cables via USPS (snail mail), but Priority, last week. My ISP, netkonnect.net, is no more, and with it, my email. I guess they couldn't make enough money @ $5 a month to stay open. Please let me know if you still haven't received them. Sorry I've been away from the PC for a few days, but I mostly do this at work!
TTFN!
WW |
| Hey Phil! | mtrycrafts
Jul 8, 2002 5:59 PM | | b but I mostly do this at work!
:) Do they know :) |
| Do they know? | Warren Warren
Jul 8, 2002 7:13 PM | | I'm sure they do, as all internet usage here is monitored, for obvious reasons. Heck, I am more or less like a fireman here in any case. Most of the time I just sit here, and every once in a while I have to actually put out fires, so to speak. I don't exactly have a heavy workload working from 3 to 11, since most of the facility is empty by 5 or 6. I can't complain, in any case.
WW |
| Do they know? | mtrycrafts
Jul 8, 2002 10:08 PM | | b like a fireman here
:) |
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