Speakers distortion

[Blumlein 88]

I've been meaning to take my lsr 305s outside for some measures.

 

[Thomas Savage]

I actually find it relevant to measure speakers in the very environment I'm listeing to them. That way you see which figures actually matter and whcih don't.



I see no reason to do that for home speakers of all sizes.

Will I guess the reasoning will be to try and create a consistent environment or set of parameters so our results are relevant to all across the board rather then just being a resource purely for ourselves as individuals.

 

[Krunok]

I've been meaning to take my lsr 305s outside for some measures.

Well, I believe the right thing to do is to measure speakers in their working environment which means measuring them while they're sitting in my room and mic being in an area around my head at my LP, as that is how I listen to them.

 

[Blumlein 88]

Is there a way you could average multiple sweeps in REW? I was thinking there is.

 

[sergeauckland]

You don't think measurements made at home with REW are precise enough for the speakers to be compared distortion wise?

To answer your question directly, no I don't consider measurements done at home to be anything other than indicative of whether anything is seriously wrong. REW is great software, and if used rigorously I'm confident it can produce good repeatable results, but as used here, with different microphones, with more or less accurate calibration files, in different rooms, at different distances makes it very difficult to have confidence in the interoperability of results.

I have exactly the same issues when I measure amplifiers, something I do more regularly than loudspeakers. I am confident my measurements are good enough to tell whether there's anything wrong with an amplifier, but I wouldn't want to make any claims for overall accuracy. Firstly, I don't have AP measuring kit, just an assortment of old analogue instruments supplemented by software and a half-decent sound card (Lexicon). Secondly, the results I get depend very much on local conditions. Just one example, when an amplifier is measured, how accurate is the mains voltage? Unless an amplifier has a stabilised power supply, the available power depends entirely on the local mains voltage. An amplifier rated at 100 watts with a 240v power supply will give only 91 watts with a 220v supply, all other things being equal.

A THD+N figure depends as much on the 'N' as the 'D' and if, for example, there's some hum being introduced, the THD+N figure will be a lot higher than it needs to be unless suitably qualified.

What I'm saying, is that how something is measured affects what results one gets.

In the case of loudspeaker measurements, I applied as much rigour as I could when I set up my 801s for on-axis pseudo-anechoic frequency response, as I wanted to achieve a +-1dB variation above 200Hz, which is the lower limit of my measuring capability. I'm reasonably satisfied I did that correctly, but much less confident in the distortion figures I measured as they were totally dependent on room gain as a 3dB boost or cut at any one frequency will double or halve the measured distortion , and 3dB variations in room gain are fairly normal, few domestic rooms have a smoother response than that, but nevertheless, my measurements indicate that there's nothing wrong with what I have.

In general, that's what I'm trying to achieve with home measurements, confirmation that the equipment is working correctly, and not to worry if the distortion is 0.025% when the spec is 0.01%. Neither are audible, so why care? Ditto with output power on amplifiers, If the spec is 150 watts for 1% THD and I measure 130 watts at the onset of clipping, do I care? No, because even 130 watts is more than enough, and 1% THD is very visible on a 'scope and I measure power before any visible clipping.

I'm all in favour of people making measurements as it helps them to understand both what the measurements mean and what their equipment is doing, but as part of that understanding, to understand the limitations in accuracy, and how different conditions result in different numbers.

S.

 

[Blumlein 88]

I know you can open up multiple measures and add them in the window.

 

[Krunok]

Will I guess the reasoning will be to try and create a consistent environment or set of parameters so our results are relevant to all across the board rather then just being a resource purely for ourselves as individuals.

By all means!

One thing I have learned so far is if I measure frequency response of my speakers while moving mic relative to my head at my LP left and right for 0.5m, up and down for 20cm and forward and backward for 30cm I get very consistent results. When I did speakers response correction based on those measurements I can measure again and see that reponse has flattened, and I can also hear it sounds better. If I repeat that measurements few days after I get the same results, which is how it needs to be. I believe everybody can do the same and have similar results.

I have yet to see if I can make consistent distortion measurement in that same manner. Althoug, ot be honest, that is less important than frequency response as you can't correct distortion. But it can still be of great help when choosing new speakers.

 

[RayDunzl]

Is there a way you could average multiple sweeps in REW? I was thinking there is.

That might be a question for @JohnPM

Nope, I had to RTFM.

 

[Thomas Savage]

By all means!

One thing I have learned so far is if I measure frequency response of my speakers while moving mic relative to my head at my LP left and right for 0.5m, up and down for 20cm and forward and backward for 30cm I get very consistent results. When I did speakers response correction based on those measurements I can measure again and see that reponse has flattened, and I can also hear it sounds better. If I repeat that measurements few days after I get the same results, which is how it needs to be. I believe everybody can do the same and have similar results.

I have yet to see if I can make consistent distortion measurement in that same manner. Althoug, ot be honest, that is less important than frequency response as you can't correct distortion. But it can still be of great help when choosing new speakers.

Yeah I guess I was just thinking about measuring speakers as speakers rather than measuring speakers plus room.

All measuring fun is encouraged here though as long as it doesn't involve me lol

 

[Krunok]

Is there a way you could average multiple sweeps in REW? I was thinking there is.

Sure there is - go to "All SPL" tab, make sure all the sweep measurements you want to average are ticked and press "average the responses" in the lower left corner of the window and averaged response will be generated as a new measurement. That is how it works when you measure frequency response with sweeps.

 

[RayDunzl]

@Cosmik might argue measuring the speaker itself is all that is important.

I prefer to play with in-room and single-point at the listening position, because that's where I listen, I'm not building speakers, I get to to do whatever stupid stuff I want here at Neverland East, and so on...

 

[Krunok]

Yeah I guess I was just thinking about measuring speakers as speakers rather than measuring speakers plus room.

All measuring fun is encouraged here though as long as it doesn't involve me lol

Oh no, you won't give up that easilly! You will measure and correct your speakers and trust me, you will be pleasantly surprised with the results!

 

[RayDunzl]

That is how it works when you measure frequency response with sweeps.

Yes, but you don't get many (or all) of the additional calculations available to a single sweep measurement (though that "single" measurement can have multiple sweeps). No distortion or impulse, etc., just averaged SPL.

 

[Krunok]

QUOTE="RayDunzl, post: 133532, member: 33"]
I prefer to play with in-room and single-point at the listening position, because that's where I listen, I'm not building speakers, I get to to do whatever stupid stuff I want here at Neverland East, and so on...[/QUOTE]

I agree with you, but a single point measurement doesn't really give you a meaningfull pciture so you have to widen it a little and use RTA while you are moving your mic. It's all explained [URL='http://www.ohl.to/audio/downloads/MMM-moving-mic-measurement.pdf']here[/URL] in detail!

 

[Krunok]

Yes, but you don't get many (or all) of the additional calculations available to a single sweep measurement (though that "single" measurement can have multiple sweeps). No distortion or impulse, etc., just averaged SPL.

That's true, you can't get impulse that way, but you do get very reliable frequency response measurement.

I don't see a reason why it couldn't work with distortion as well but REW doesn't seem to support it. For that reason I will try to move mic while doing single tone RTA distortion measurement and see if that will be more consistent.

 

[RayDunzl]

Single-point listening gives me a meaningful picture.

 

[RayDunzl]

That's true, you can't get impulse that way, but you do get very reliable frequency response measurement.

You get an average.

Remember, the average person has one ball and one tit.

 

[Krunok]

@pos , how about giving me a little help here? You're the expert in this field and making living on this, not me..

 

[Krunok]

Single-point listening gives me a meaningful picture.

Yes, but if you move mic only 10cm in any direction you will get another picture. Try to read that pdf I posted, it is all desribed there much better than I can do it here.

 

[Blumlein 88]

There's benefits to measuring in situ and outdoors. Being indoors isn't increasing distortion from the speaker. So if indoors distortion is higher it's a measurement artifact or error.