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Can someone explain or point me to an article that explains how to use an SPL meter to measure hiss from a speaker?

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I borrowed a friend's Radio Shack digital SPL meter, and I'm having a hard time figuring out how to use it to measure hiss from my active speakers. It simple says "LOW" no matter what the range or weighting is set to. I obviously need to set it to a much quieter range and am not sure if that's even possible for SPLs as low as speaker hiss, or how to do it if its. I Googled but couldn't find anything particular to measuring such low levels.
 
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The lowest it can measure is 50db. If it does not measure above 50db 1cm from the tweeter, forget it, And select C weigthing

Got it, thanks. I guess I'd need something else to measure hiss.
 

MakeMineVinyl

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Got it, thanks. I guess I'd need something else to measure hiss.
You need to measure the electrical signal going to the speaker terminals, and even then, you will need a relatively sensitive meter. As a general rule, if you can hear distracting hiss at your listening position, then it is too much. Typically you shouldn't hear hiss farther than a foot or two from the tweeter, and ideally very little with your ear directly over the tweeter.
 

sergeauckland

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An inexpensive SPL like the Radio Shack just isn't sensitive enough. You need either a 'Pro' meter, which is a lot more expensive, or you can use a measuring microphone and some software like REW. Even then, you'll be limited both by the inherent noise of the microphone amplifier, and more so by the room's ambient noise. Good active loudspeakers have a noise level of some 10-15dB SPL whilst even a good studio let alone a home, will have a noise level of 18-20dB unless very well insulated and with excellent quiet aircon.

Probably the best way is to measure close to the 'speaker, say 10cm or so, then scale the noise to the more or less standard 1m distance.

S
 
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An inexpensive SPL like the Radio Shack just isn't sensitive enough. You need either a 'Pro' meter, which is a lot more expensive, or you can use a measuring microphone and some software like REW. Even then, you'll be limited both by the inherent noise of the microphone amplifier, and more so by the room's ambient noise. Good active loudspeakers have a noise level of some 10-15dB SPL whilst even a good studio let alone a home, will have a noise level of 18-20dB unless very well insulated and with excellent quiet aircon.

Probably the best way is to measure close to the 'speaker, say 10cm or so, then scale the noise to the more or less standard 1m distance.

S

Awesome, thank you.
 
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An inexpensive SPL like the Radio Shack just isn't sensitive enough. You need either a 'Pro' meter, which is a lot more expensive, or you can use a measuring microphone and some software like REW. Even then, you'll be limited both by the inherent noise of the microphone amplifier, and more so by the room's ambient noise. Good active loudspeakers have a noise level of some 10-15dB SPL whilst even a good studio let alone a home, will have a noise level of 18-20dB unless very well insulated and with excellent quiet aircon.

Probably the best way is to measure close to the 'speaker, say 10cm or so, then scale the noise to the more or less standard 1m distance.

S

These active Dynaudios are definitely louder than that. :-/ I can clearly hear the speaker noise (self-noise -- it happens even without cables plugged in) above the room tone here in my studio (which is not well insulated from noise), at proper listening distance of 1.5 m and even 2m or more.
 

MakeMineVinyl

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These active Dynaudios are definitely louder than that. :-/ I can clearly hear the speaker noise (self-noise -- it happens even without cables plugged in) above the room tone here in my studio (which is not well insulated from noise), at proper listening distance of 1.5 m and even 2m or more.
Do your speakers have input level controls? If so, does turning them down alter the noise?
 
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Do your speakers have input level controls? If so, does turning them down alter the noise?

They do, yes. They're already set to the lowest level -- I'm driving them in a +4 setup.
 

MakeMineVinyl

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They do, yes. They're already set to the lowest level -- I'm driving them in a +4 setup.
And if they have -10db / +4db switches, the position makes no difference?
 
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And if they have -10db / +4db switches, the position makes no difference?

It doesn't make a difference, no. I've since read many reports of the Dynaudios having a pretty loud hiss, unfortunately.
 

MakeMineVinyl

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DVDdoug

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I'm going to guess you can't measure it over the room noise even if you can hear it over the room noise. :(

You might be able to calibrate your regular microphone... I assume you have a mic and an interface and some digital recording software that can give you digital levels... Run some white noise and get an SPL reading and a digital dBFS reading at the same time. Then for example, if the SPL reading drops by 6dB the digital level will also drop by 6dB.

There are a couple of issues with that - When you measure the real hiss the levels will be very low and those may be swamped by preamp noise and/or room noise. (Of course you'll have to amplify digitally but as long as you know how much you are amplifying you can stay calibrated.)

And your microphone-digital readings are not weighted. That might not be a big deal since hiss is similar to white noise, or you could high-pass filter your generated white noise to better-approximate the characteristics of the hiss from the tweeter.



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...I've got an older analog Radio Shack SPL meter with a dial with a few ranges to choose from, but I'm pretty sure it also couldn't measure that low-level hiss. I just ordered a cheap ~$100 SPL calibrator for it because I've read that electret condenser mics loose their sensitivity over time (like old people :D ). I could have bought a new cheap SPL meter but I thought it would be more fun to have the calibrator. They claim it's accurate to 0.3dB (at 1kHz and 94dB SPL) but at that price it's not certified or calibrated by an independent lab so I don't really believe it.
 

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An inexpensive SPL like the Radio Shack just isn't sensitive enough. You need either a 'Pro' meter, which is a lot more expensive, or you can use a measuring microphone and some software like REW. Even then, you'll be limited both by the inherent noise of the microphone amplifier, and more so by the room's ambient noise.


Measuring the "hiss" of a JBL LSR 308 with a UMIK-1 feeding REW:

microphone 1" from the tweeter:


index.php



And with the speaker powered off:


index.php


Looks to me like a broad area - starting about 1kHz - that is higher than ambient/measurement noise, with a more pronounced area from 12 to 20kHz or so.

The difference is about 10dB mostly, but, not detectable from the listening position.

https://www.audiosciencereview.com/forum/index.php?threads/jbl-lsr-308-in-the-house.1066/#post-27832
 
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Measuring the "hiss" of a JBL LSR 308 with a UMIK-1 feeding REW:

microphone 1" from the tweeter:


index.php



And with the speaker powered off:


index.php


Looks to me like a broad area - starting about 1kHz - that is higher than ambient/measurement noise, with a more pronounced area from 12 to 20kHz or so.

The difference is about 10dB mostly, but, not detectable from the listening position.

https://www.audiosciencereview.com/forum/index.php?threads/jbl-lsr-308-in-the-house.1066/#post-27832

What sound did you use for the measurement -- the REW sine sweep?
 

MakeMineVinyl

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What sound did you use for the measurement -- the REW sine sweep?
Those graphs are using the RTA function in REW - the button is at the top to access it. No signal source necessary.
 
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Those graphs are using the RTA function in REW - the button is at the top to access it. No signal source necessary.

Do you know of a step-by-step instruction somewhere on how to do this for the measurement we're talking about here? I don't quite understand from what I've been reading.
 

MakeMineVinyl

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Do you know of a step-by-step instruction somewhere on how to do this for the measurement we're talking about here? I don't quite understand from what I've been reading.
The REW online help might shed some light, but my experience is that this help is not all that helpful in some instances. Ideally you are using a microphone calibration file (such as the one which is included with MiniDSP measurement microphones), so the absolute SPL numbers match reality. But in any case the RTA function allows a real-time observation of the noise coming from the tweeter if the microphone is situated right in front of it. Turning the speaker off will show the relative amount of noise coming from the speaker verses general room noise. That's what the above plots are showing. Doing some math can interpolate the noise at the listening position, but I think the bottom line is that if you can hear the noise and it bothers you, its too much.
 
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The REW online help might shed some light, but my experience is that this help is not all that helpful in some instances. Ideally you are using a microphone calibration file (such as the one which is included with MiniDSP measurement microphones), so the absolute SPL numbers match reality. But in any case the RTA function allows a real-time observation of the noise coming from the tweeter if the microphone is situated right in front of it. Turning the speaker off will show the relative amount of noise coming from the speaker verses general room noise. That's what the above plots are showing. Doing some math can interpolate the noise at the listening position, but I think the bottom line is that if you can hear the noise and it bothers you, its too much.

Great, thanks again. The purpose of the measurement in this case is to send to Dynaudio to see if they're faulty units, or if they all have this level of noise.
 
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