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Why Do TEF Systems read 3-5 dB high ?
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<blockquote data-quote="Art Welter" data-source="post: 24296" data-attributes="member: 52"><p>Re: Why Do TEF Systems read 3-5 dB high ?</p><p></p><p></p><p>Ivan,</p><p></p><p>Thank you for the quick reply. Looking at two traces makes the comparison much easier to see.</p><p></p><p>After a close look at the 2007 NYC results, deducting the 3 dB advantage the four ohm EV2181 has over the eight ohm TH-115, and looking at relative levels, both the EV and the DSL are quite close in response shape to the published spec sheets, other than the obvious room influence on both cabinets.</p><p></p><p>The EV spec sheet chart has a very small frequency axis compared to the DSL charts, which makes the EV look “peaky”, and the DSL “smooth”. When you compare the actual SPL levels, the TH falls off below the LF corner with a steeper slope than the BR cabinet, as it does in the NYC chart.</p><p></p><p>The TH-115 spec sheet chart, compared to the EV2181, both measured in half space are shown below the 2007 NYC chart .</p><p></p><p>Since the scaling (and cabinet impedance) difference of the charts makes visual comparison difficult, I have “done the math”, using the charts blown up large so that small differences are visible.</p><p>I could not find a chart for the eight ohm TH-115, so the TH-115-4 chart has the dB scale lowered by 3 dB since it was tested at 28.3 v rather than 20 v. </p><p></p><p>The EV2181, being a 4 ohm cabinet, should be 3 dB louder when driven at 2.83V than 2V (as it was at the NYC test) is shown in the “2183+3” column.</p><p></p><p>The difference between the TH-115 and the EV2181 spec sheets with 3 dB added ot the 2181 is shown in the “diff.SS” column.</p><p></p><p>The difference measured at the 2007 NYC test is shown in the “Diff.NYC” column using the measured difference and subtracting 3 dB.</p><p></p><p>The levels from the charts are rounded to the nearest dB. </p><p></p><p>The difference in the spec sheets totals 16 dB/9 =1.77 dB, if the spec sheets are correct, the 2181 would average 1.77 dB more sensitive than the TH-115 (average 98.888 dB at 2.83V to 100.666 dB at 2V from 20-100 Hz).</p><p></p><p>The difference in the 2007 NYC results total 43/9=4.77 dB, exactly 3 dB more than the spec sheets would indicate, the DSL spec sheet high by 3 dB from the comparative measured results.</p><p></p><p>If the TH-115-4 is not a full 3 dB more sensitive than the TH-115-8 (my guess is it is not, IIRC the B&C 15TBX100-8 is not double the impedance of the 15TBX100-4 ), the DSL TEF sensitivity (and max output) specs would be off by more than 3 dB.</p></blockquote><p></p>
[QUOTE="Art Welter, post: 24296, member: 52"] Re: Why Do TEF Systems read 3-5 dB high ? Ivan, Thank you for the quick reply. Looking at two traces makes the comparison much easier to see. After a close look at the 2007 NYC results, deducting the 3 dB advantage the four ohm EV2181 has over the eight ohm TH-115, and looking at relative levels, both the EV and the DSL are quite close in response shape to the published spec sheets, other than the obvious room influence on both cabinets. The EV spec sheet chart has a very small frequency axis compared to the DSL charts, which makes the EV look “peaky”, and the DSL “smooth”. When you compare the actual SPL levels, the TH falls off below the LF corner with a steeper slope than the BR cabinet, as it does in the NYC chart. The TH-115 spec sheet chart, compared to the EV2181, both measured in half space are shown below the 2007 NYC chart . Since the scaling (and cabinet impedance) difference of the charts makes visual comparison difficult, I have “done the math”, using the charts blown up large so that small differences are visible. I could not find a chart for the eight ohm TH-115, so the TH-115-4 chart has the dB scale lowered by 3 dB since it was tested at 28.3 v rather than 20 v. The EV2181, being a 4 ohm cabinet, should be 3 dB louder when driven at 2.83V than 2V (as it was at the NYC test) is shown in the “2183+3” column. The difference between the TH-115 and the EV2181 spec sheets with 3 dB added ot the 2181 is shown in the “diff.SS” column. The difference measured at the 2007 NYC test is shown in the “Diff.NYC” column using the measured difference and subtracting 3 dB. The levels from the charts are rounded to the nearest dB. The difference in the spec sheets totals 16 dB/9 =1.77 dB, if the spec sheets are correct, the 2181 would average 1.77 dB more sensitive than the TH-115 (average 98.888 dB at 2.83V to 100.666 dB at 2V from 20-100 Hz). The difference in the 2007 NYC results total 43/9=4.77 dB, exactly 3 dB more than the spec sheets would indicate, the DSL spec sheet high by 3 dB from the comparative measured results. If the TH-115-4 is not a full 3 dB more sensitive than the TH-115-8 (my guess is it is not, IIRC the B&C 15TBX100-8 is not double the impedance of the 15TBX100-4 ), the DSL TEF sensitivity (and max output) specs would be off by more than 3 dB. [/QUOTE]
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