The coupling issues are a big issue. Two identical loudspeakers will give similar but not the same results. You can use two, three or even more transducers for calibration. The more the better.
The idea was that most folks try to use a small microphone capsule and hope it is flat enough.
But when you try it yourself even with small loose drivers you might just be surprised at how stupidly simple it can be with decent results!
The real issue is how to account for directivity.
Scott,
Sure. BUT, it can be quite good.
At AMR we devised a test for pair matching of speakers (or whole systems channel matching) that may be slightly unique (but I expect ten guys to jump out from behind the corner and say James Bollocks Lansing did that in 1871 already)...
It actually came from the running in process we use for speakers before final test.
We place the speakers face to face with a small gap (now standardised at 10mm) and feed them one of our test signals from our CD. That is pink noise mono, channels out of phase at a level that is near the clipping limit of our biggest amp...
The face to face placement and the out of phase part was simply acoustic self defence. When you have ten pairs playing at around 200W per speaker pink noise even the good pro earplugs are not enough.
We found however that it allows very quickly and easily to tell if anything is out with pair matching, because the depth of attenuation of the fact to face placement is directly proportional to to the matching at all frequencies...
If any pair is "loud" at any frequency or in generally we can tell instantly and pull them out of the series. Well, it is using your ears and what is between them...
Ciao T
Sure. BUT, it can be quite good.
At AMR we devised a test for pair matching of speakers (or whole systems channel matching) that may be slightly unique (but I expect ten guys to jump out from behind the corner and say James Bollocks Lansing did that in 1871 already)...
It actually came from the running in process we use for speakers before final test.
We place the speakers face to face with a small gap (now standardised at 10mm) and feed them one of our test signals from our CD. That is pink noise mono, channels out of phase at a level that is near the clipping limit of our biggest amp...
The face to face placement and the out of phase part was simply acoustic self defence. When you have ten pairs playing at around 200W per speaker pink noise even the good pro earplugs are not enough.
We found however that it allows very quickly and easily to tell if anything is out with pair matching, because the depth of attenuation of the fact to face placement is directly proportional to to the matching at all frequencies...
If any pair is "loud" at any frequency or in generally we can tell instantly and pull them out of the series. Well, it is using your ears and what is between them...
Ciao T
Last edited:
Scott,
Could be.
I like Infinon GHz Mixer Schottkys.
These give you distortion well into the lower GHz, must be heard to be believed... That is not just 11 on Spinal Tap, that is twelfe... You know, sometimes the kind of distortion you get at 11 is not enough and you want more, so mine goes to 12...
Ciao T
Could be.
I like Infinon GHz Mixer Schottkys.
These give you distortion well into the lower GHz, must be heard to be believed... That is not just 11 on Spinal Tap, that is twelfe... You know, sometimes the kind of distortion you get at 11 is not enough and you want more, so mine goes to 12...
Ciao T
That will be in part three of my article. It turns out in Zel'dovich, Ya. B. and Raizer, Yu. P. Physics of Shock Waves and High-Temperature Hydrodynamic Phenomena the exact spectra of a spark discharge is derived which makes possible an amazingly good relative calibration signal (barbeque grill starter).
The spark technique has been around since the second Sabine. In larger spaces the exploding wire works better.
That's a slightly different application, the reciprocity calibration is for absolute determination of the response of a mic to some absurd number like .005dB. A mic is sort of a "point" sampler of acoustic pressure, I presume the speaker equivalent would be a method for determining the frequency response at a given listening position.
Face to face coupling seems like a perfectly good way to do pairwise matching.
There are way too many issues involved in trying to get "flat" response in a real room at any distance. The idea is to be able to have a clue what your loudspeakers are actually producing.
On axis frequency response and actual energy response are a good starting point. I have sent out loudspeakers to have those measurements taken when needed. The quick and dirty of using IEC 1/3 octave filters and rotating the loudspeaker in a large space does give a decent approximation, but for real design use a fully detailed standard format file is much better.
You actually think I was unaware of that? There are very few references that obtain results that are particularly useful, in fact more than half of them don't even get into the fact that the spectra is that of a doublet not impulse but not quite because it's a shockwave followed by thermal relaxation. We will have to wait and see I have access to a B&K calibrated system and anechoic chamber (thanks to the MEMs mic folks) to compare to. My goal is <.5dB with things scavenged from the kitchen vs a B&K 4133.
Last edited:
Scott,
If the world were flat we would each be on opposite sides looking over a different edge and coming to contrary conclusions from the same observations. So what else is new?
ES
Hi,
You have access to way too many cool toys.
I have to take my speakers to the roof. place them on a large elevated flat surface, pointing at Jupiter (precisely) when it is in the zenith. If I wish to take off axis plots (which I very much do) I have to triangulate using tape measures to shift the mike and stand...
Maybe next time I just send the prototypes to you?
Ciao T
You have access to way too many cool toys.
I have to take my speakers to the roof. place them on a large elevated flat surface, pointing at Jupiter (precisely) when it is in the zenith. If I wish to take off axis plots (which I very much do) I have to triangulate using tape measures to shift the mike and stand...
Maybe next time I just send the prototypes to you?
Ciao T
John,
I don't see how eddy currents in the pole piece could enter into the VC and have an influence on the other John's measurement. It is only the wire moving to an magnetic field which induces a current.
vac
I thought I was the only one to use this trick to "break-in" speakers.
Indeed. While some speakers produce a superb null across most of the band, there are some where you get audible "hot spots." And with some pathological examples, this unmasks cabinet panel resonances.
John Atkinson
Editor, Stereophile
Thorsten, I will gladly take your advise and not react to your opinions any longer, even in case you contradict me with totally ludicrous beliefs.
vac
John,
I may have originally swiped this one off you TBH. Too long ago to remember.
When I still used to review stuff I had to wrap some speakers into thick blankets in addition to the face to face tango... They where that noisy. And they rarely improved matching after this.
No audible cab resonances with our current line (I'm sure piezo strip would find some low level modes though). But if a driver is about to hand in it's mess kit due to shoddy work at the OEM Factory you will hear it. Instantly.
Remember, we are driving around 500W peaks of pink noise into the speakers... If your null drops much it gets loud quickly. And it is no longer the speakers being tortured but you.
Ciao T
I thought I was the only one to use this trick to "break-in" speakers.
I may have originally swiped this one off you TBH. Too long ago to remember.
When I still used to review stuff I had to wrap some speakers into thick blankets in addition to the face to face tango... They where that noisy. And they rarely improved matching after this.
No audible cab resonances with our current line (I'm sure piezo strip would find some low level modes though). But if a driver is about to hand in it's mess kit due to shoddy work at the OEM Factory you will hear it. Instantly.
Remember, we are driving around 500W peaks of pink noise into the speakers... If your null drops much it gets loud quickly. And it is no longer the speakers being tortured but you.
Ciao T
When a wire carrying current is moved past a conductive material, it attempts to force change of flux in that material. The currents caused within that material tries to buck the field, trying to keep the field from penetrating.(Lenz effect). Since currents are flowing in the pole piece (eddy currents), there will be dissipation. That dissipation will be interpreted by a meter connected to the VC as dissipative loss that is, 90 degrees from the induced emf. It is a loss of energy in the system which is not related to emf, vc resistance, moving mass, nor conversion efficiency.
jn
Last edited:
I didn't know we were disagreeing on anything?? Ever since Earthworks claimed to use a "carefully" generated spark to measure their mics out to 100KHz+ I have looked in vain for a method that did any better than +- several dB and included a complete description of the apparatus. Maybe I missed it.
Last edited:
Hi,
Given that I am an Amateur who doesn't even know basic theory I doubt they will be any good...
They will probably be revoltingly bad.
But that is still a significant risk... All that fairy dust and snake oil we apply to the speakers is darn expensive.
I'll think about it.
What I hate about that "on the roof" gig is that one in three measurements is spoiled by passing trains, jets flying overhead and related annoyances. Where is that ruddy RPG when you need it to get some quiet?
Other than that the roof makes for a superb halve space anechoic measurement envoironment and it is basically for free...
Ciao T
Given that I am an Amateur who doesn't even know basic theory I doubt they will be any good...
They will probably be revoltingly bad.
But that is still a significant risk... All that fairy dust and snake oil we apply to the speakers is darn expensive.
I'll think about it.
What I hate about that "on the roof" gig is that one in three measurements is spoiled by passing trains, jets flying overhead and related annoyances. Where is that ruddy RPG when you need it to get some quiet?
Other than that the roof makes for a superb halve space anechoic measurement envoironment and it is basically for free...
Ciao T
- Status
- Not open for further replies.