Re: Why Do TEF Systems read 3-5 dB high ?
Quote Originally Posted by drew gandy
This thread is a little old now and my comment is a little bit ancillary but I still want to bring it up while thinking about it. Please be aware that the 8 ohm and 4 ohm versions of the B&C woofers are not necessarily identical except for the "ohmage". I've done some modeling with the B&C specs for the 4 ohm and 8 ohm versions of the 12TBX100 driver. The 4 ohm is actually somewhere between 4 and 8 ohms based on dcr alone and although very similar in it's overall behavior I don't get 3 db more sensitivity out of it compared to the 8 ohm version. A similar thing exists with the 8 and 16 ohm versions of some of the compression drivers. What I've heard is that instead of changing the total number of windings (which would change the moving mass among other things) they actually use a different kind of wire that has a different resistance.
Besides this, I too have been baffled at the high sensitivity of the DSL graphs compared to rough models I've worked on. I have mostly assumed that it's my models that are inaccurate. Although, Tom measured a box of mine once with his TEF and it seemed to match up pretty well with my own measures and models of the box. Maybe I need to dig that graph out again and make sure I'm not imagining this.
-drew
What is "sad but true" is most of the number chasing in this post stems from the fact that though the TH-18 using the 18Sound 18NLW9600-4 (2.5 ohm Re) was tested for impedance, sensitivity, and frequency response, when the higher impedance BC18SW115-4 (3.3 ohm Re) replaced the 18Sound three years ago DSL did not update the TH-118 specifications.
I had assumed DSL had published the specifications for the higher impedance, lower sensitivity B&C driver used in the TH-118, but recently discovered that was not the case.
http://soundforums.net/basement/7757-4-july-hi-fi.html#post61388
Same appears to apply to the DBH-218, assuming it does not currently use the 18NLW9600-4.
Mystery solved, only took two years...
