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High Efficiency Speaker Asylum Need speakers that can rock with just one watt? You found da place. |
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In Reply to: Pi speaker design and measurement posted by laoye on September 29, 2002 at 17:23:27:
Ken,You know I actually attended the AES convention workshop where he delivered that paper. I even remember that statement. First off, you are taking him completely out of context. He is most definitely not agreeing with Wayne. He is emphasising the importance of measurement in the process of loudspeaker system design.
Regarding needing an anechoic room for low-frequency testing, if you asked him at the time why the same results couldn't be accomplished outdoors, I am pretty sure he would have said that they could, but it would be very inconvenient. If you are making hundreds of polar plot measurements every day it makes sense to invest in an anechoic chamber with an array of fixed test mics so you can do your measurements in parallel, rather than packing up your things, finding an empty parking lot, setting everything up, hoping it doesn't rain, or is too windy, doing polar plot measurements in series, packing up, going home...
For us DIYers who do this once every so often, there is no reason why we can't get equally good results out of doors--it just takes us a LOT longer to do it. The noise rejection properties of MLS and TDS are very good and you don't need to take my word on this, go and read some papers on MLS and TDS.
Floyde also brings up a good point that you need to do measurements over an entire sphere--it's not just on axis response you need to worry about. I've spent a lot of time with my system getting a flat on-axis response and a flat power response and I can attest to the importance of power response.
There is another issue here that published driver response data is generally taken in a "infinite" baffle, at least midrange and up. Once you put the driver in a box, your frequency response is going to be different, both because of diffraction and because of acoustic loading. In his talk, Floyd also addressed the issue of response anomolies due to resonances versus diffraction effects. I'll quote him as closely as can: "you want to equalize the resonances, but not the diffraction issues. The only way to separate the two is to look on and off-axis. Response anomolies that show up on and off axis are resonances. Response anomolies that change on and off axis are due to diffraction."
If Floyde were here participating in this forum, he would be the first to stress the importance of being able to measure what you are designing and if you asked him if you could design a world class speaker using only published on axis frequency response data, he would have the loudest laugh.
John
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Follow Ups
- Re: Pi speaker design and measurement - hancock 00:17:39 09/30/02 (5)
- Re: Pi speaker design and measurement - Wayne Parham 02:42:52 09/30/02 (4)
- Re: Pi speaker design and measurement - hancock 09:41:09 09/30/02 (2)
- Re: Pi speaker design and measurement - Wayne Parham 10:19:44 09/30/02 (0)
- "I haven't read the paper" "It is just amazing to me" - READ & LEARN - miro 09:58:05 09/30/02 (0)
- "that I interpreted from this document" You are in trouble man if this is Your interpretation - miro 09:11:45 09/30/02 (1)
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