Hi Claudio,
I'm not at home at the moment so can't give a page number but it is in Dicaksons Loudspeaker Design Cookbook 6th edition. it is in the section where he talks about the different methods of measuring, ie nearfield, groundplane, gated etc. I don't remember him saying it differed with cone diameter......
I've observed the same sort of rolloff from 200Hz up with both my Vifa M26WR09-08's and my Morel MW144's when I first did the vifa's I thought it was probably the drivers, but when I got an almost identical effect with the MW144's (5" vs 10") I figured it was the effect dickason was talking about.
Tony.
I'm not at home at the moment so can't give a page number but it is in Dicaksons Loudspeaker Design Cookbook 6th edition. it is in the section where he talks about the different methods of measuring, ie nearfield, groundplane, gated etc. I don't remember him saying it differed with cone diameter......
I've observed the same sort of rolloff from 200Hz up with both my Vifa M26WR09-08's and my Morel MW144's when I first did the vifa's I thought it was probably the drivers, but when I got an almost identical effect with the MW144's (5" vs 10") I figured it was the effect dickason was talking about.
Tony.
Here is a sw graph of my MW144's in MTM config... blue graph is gated measurement black is nearfield smoothed 1/8th octave.
the two plots seem to be correlate only between about 200 and 375Hz (as far as SPL level goes). resolution of the nearfield data is much higher than that of the gated due to limited gate time due because of room relfections.
Note that my rolloff isn't as steep as Vikash's but this could be due to mic placement or other factors, I have had measurements which looked closer to Vikash's, but at that stage I wasn't writing down all of the conditions of the test
I now measure with mic about 3-4mm from the center of the cone for nearfield, with quite low drive level.... I think the drive level is what affects this particular effect the most (from memory).
Tony.
the two plots seem to be correlate only between about 200 and 375Hz (as far as SPL level goes). resolution of the nearfield data is much higher than that of the gated due to limited gate time due because of room relfections.
Note that my rolloff isn't as steep as Vikash's but this could be due to mic placement or other factors, I have had measurements which looked closer to Vikash's, but at that stage I wasn't writing down all of the conditions of the test
I now measure with mic about 3-4mm from the center of the cone for nearfield, with quite low drive level.... I think the drive level is what affects this particular effect the most (from memory).Tony.
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Vikash said:My neighbour breeds pigeons in his garden sheds. Enough said. By all means you're welcome to come around with your pelet guns to afford me the peace of measuring outside
Ugh! Stinking pidgeons!
The ones we have up north are really crazy, I've seen one eat a fag butt before. Like I said they are scruffy things.
after reading that section of Dickason I almost gave up but I decided to forge ahead and just not think of any measurements I did as being authoritative
I'm going to have to get a copy of Joe D'appolito's Testing Loudspeakers..... I think SY considers it mandatory
Tony.
edit: on the rats with wings a particular councilor near me in Sydney got into hot water after saying that about the local pidgeons, and suggesting that they should all be exterminated..... apparently he views them as the rats (of black plauge status) with regards to bird flu....
but I decided to forge ahead and just not think of any measurements I did as being authoritative I'm going to have to get a copy of Joe D'appolito's Testing Loudspeakers..... I think SY considers it mandatory
Tony.
edit: on the rats with wings a particular councilor near me in Sydney got into hot water after saying that about the local pidgeons, and suggesting that they should all be exterminated..... apparently he views them as the rats (of black plauge status) with regards to bird flu....
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