I wonder if 5-ish kHz dip is endemic to these tweeters or an artifact of the test.
I wondered about that. Moving the microphone closer or farther away did not get rid of the 5 kHz dip. The FR plot below is of my SDA SRS 1.2TLs in the same room. There is a small dip in the response at 5 kHz, but nothing close to what is shown in the tweeter response plots.
Figure 19. Room response of SDA SRS 1.2TLs in tweeter testing room.
The SDA CRS+s in my office at work do show a dip at 3.5 kHz and at 5 kHz.
Figure 20. Room response of SDA CRS+s in office at work.
I did a search on "tweeter dip at 5 kHz" and found that some speakers have a dip at 5 kHz to improve the smoothness and midrange "presence" of the speaker.
@KennethSwauger would you ask Stu if these tweeters are supposed to have a dip at 5 kHz?
"So hot it burnsMice!"~DK
"Polk SDA-SRSs are hopelessly out of date both sonically and technologically... I see no value whatsoever in older SDA speakers."~Audio Asylum Member
"Knowledge, without understanding, is a path to failure."~DK
"Those who irrationally rail against something or someone that is no threat to them, actually desire (or desire to be like) the thing or person they are railing against."~DK
After further study and experimentation, the previous near-field frequency response measurements were redone. The previous measurements were taken at a distance of 9 inches. The new measurements were taken at a distance of 2 inches, with the microphone pointing at the exact center of the tweeter dome.
The following quote is taken from a white paper by Jeff Bagby, "How to Achieve Accurate In-Room Quasi-Anechoic Free-Field Frequency Response Measurements Down to 10 Hz":
"To begin with we need to understand what a far-field response really is. To be in the far-field is not as far as you may think. You are effectively in the far-field when your microphone is at a distance that is 3-5 times the radiating diameter of the driver."
Therefore, for a near field measurement for a 1" tweeter, the microphone should have been no further than 3 to 5 inches away. At the prior 9 inch microphone distance, room effects were coming into play.
Also from Bagby, "...the usable upper limit of the near field response is defined as
Fmax = 4311/ radiating diameter (in inches). Below this frequency the near-field response will be accurate and free of room and cabinet diffraction effects, above this frequency the near-field data is less reliable and less accurate."
Another rule for near-field measurement is that the microphone needs to be spaced from the center of the driver approximately 0.10 times the effective radiating radius of the driver. In the case of a 1" tweeter, this distance would have been 1/20th (0.05"). This was impractical in my case due to reflections from the tripod holding the microphone. A distance of 2 inches from the center of the tweeter domes resulted in smooth response curves without any dips due to room effects.
SDA Tweeter Frequency Response Measurements - Two Inch Distance
Figure 21. SL1000 frequency response.
Figure 22. SL2000 frequency response.
Figure 23. SL2500 frequency response.
Figure 24. SL3000 frequency response.
Figure 25. RD0194 frequency response.
Figure 26. RD0198 frequency response.
Figure 27. Composite plot of all six tweeters. Black line: RD0194. Red line: RD0198. Light blue line: SL1000. Green line: SL2000. Purple line: SL2500. Dark blue line: SL3000.
Figure 28. Comparison of RD0194 and SL2000 frequency response.
Figure 29. Comparison of RD0194 and SL1000 frequency response.
Figure 30. Comparison of RD0198 and SL2500 frequency response.
Figure 31. Comparison of RD0198 and SL3000 frequency response.
SDA Tweeter Harmonic Distortion Analysis - Two Inch Distance
In order of least harmonic distortion to most, the tweeters are: RD0198, RD0194, SL3000, SL1000, SL2500, SL2000.
The legend for the harmonic distortion plots is as follows:
Black line at top - frequency response.
Dark blue line second from top - summation of 2nd - 5th harmonics.
Light blue line - 5th harmonic.
Green line - 4th harmonic.
Purple line - 3rd harmonic.
Red line - 2nd harmonic.
Figure 32. SL1000 harmonic distortion analysis.
Figure 33. SL2000 harmonic distortion analysis.
Figure 34. SL2500 harmonic distortion analysis.
Figure 35. SL3000 harmonic distortion analysis.
Figure 36. RD0194 harmonic distortion analysis.
Figure 37. RD0198 harmonic distortion analysis.
References
1. Jeff Bagby, "How to Achieve Accurate In-Room Quasi-Anechoic Free-Field Frequency Response Measurements Down to 10 Hz", white paper, January 3, 2014, presented at Loudspeaker Design Workshop”, Kokomo, IN, December 14, 2013.
2. Christopher J. Struck, Steve F. Temme, " Simulated Free Field Measurements", Journal of the Audio Engineering Society, Vol. 42, No.6, June 1994.
"So hot it burnsMice!"~DK
"Polk SDA-SRSs are hopelessly out of date both sonically and technologically... I see no value whatsoever in older SDA speakers."~Audio Asylum Member
"Knowledge, without understanding, is a path to failure."~DK
"Those who irrationally rail against something or someone that is no threat to them, actually desire (or desire to be like) the thing or person they are railing against."~DK
Throughout the years it has been said that the SL2000 was the worst performing/worst sounding of the SDA tweeters. The quantitative measurements and physical inspections done in this study seem to support that. The SL2000 rated at the bottom in terms of build quality, balanced frequency response, and harmonic distortion among the six tweeters tested.
"So hot it burnsMice!"~DK
"Polk SDA-SRSs are hopelessly out of date both sonically and technologically... I see no value whatsoever in older SDA speakers."~Audio Asylum Member
"Knowledge, without understanding, is a path to failure."~DK
"Those who irrationally rail against something or someone that is no threat to them, actually desire (or desire to be like) the thing or person they are railing against."~DK
Throughout the years it has been said that the SL2000 was the worst performing/worst sounding of the SDA tweeters. The quantitative measurements and physical inspections done in this study seem to support that. The SL2000 rated at the bottom in terms of build quality, balanced frequency response, and harmonic distortion among the six tweeters tested.
"So hot it burnsMice!"~DK
"Polk SDA-SRSs are hopelessly out of date both sonically and technologically... I see no value whatsoever in older SDA speakers."~Audio Asylum Member
"Knowledge, without understanding, is a path to failure."~DK
"Those who irrationally rail against something or someone that is no threat to them, actually desire (or desire to be like) the thing or person they are railing against."~DK
I said I've heard over the years there was a rise in amplitude around the 5khz. region.
Is my memory wrong about the all the discussions about why the SL2000 sounds so bad most of the time?
The 5Khz region is where I was concentrating my curiosity at in the graphs. As you can see and.
Prior to your comment, I had never heard any mention of an amplitude rise in the 5 kHz region. All the discussions I know about were concerning the 5 dB rise in the 13 kHz region.
With the tweeters mounted in "Free Space" with no speaker baffle, you are seeing the effects of Baffle edge diffraction taking place at a higher frequency, than when mounted in the speaker.
The small dimensions of the face plate create a ripple effect when frequencies are a wavelength of the dimensions radiating from the tweeter dome.
In this case, it is approximately 4.5" wide, and there for a null around approximetly 5000hz and a resultant rise at about 10khz and about 2.5 khz.
Since the height dimension is smaller, diffraction will occur at a different frequency and help mask some of the ripple of up and down levels with rising frequency.
Comments
I have tested several copies of each tweeter, including brand new copies of the RD0194 and RD0198, and the 5 kHz dip still appears.
I wondered about that. Moving the microphone closer or farther away did not get rid of the 5 kHz dip. The FR plot below is of my SDA SRS 1.2TLs in the same room. There is a small dip in the response at 5 kHz, but nothing close to what is shown in the tweeter response plots.
Figure 19. Room response of SDA SRS 1.2TLs in tweeter testing room.
The SDA CRS+s in my office at work do show a dip at 3.5 kHz and at 5 kHz.
Figure 20. Room response of SDA CRS+s in office at work.
I did a search on "tweeter dip at 5 kHz" and found that some speakers have a dip at 5 kHz to improve the smoothness and midrange "presence" of the speaker.
@KennethSwauger would you ask Stu if these tweeters are supposed to have a dip at 5 kHz?
"Polk SDA-SRSs are hopelessly out of date both sonically and technologically... I see no value whatsoever in older SDA speakers."~Audio Asylum Member
"Knowledge, without understanding, is a path to failure."~DK
"Those who irrationally rail against something or someone that is no threat to them, actually desire (or desire to be like) the thing or person they are railing against."~DK
After further study and experimentation, the previous near-field frequency response measurements were redone. The previous measurements were taken at a distance of 9 inches. The new measurements were taken at a distance of 2 inches, with the microphone pointing at the exact center of the tweeter dome.
The following quote is taken from a white paper by Jeff Bagby, "How to Achieve Accurate In-Room Quasi-Anechoic Free-Field Frequency Response Measurements Down to 10 Hz":
"To begin with we need to understand what a far-field response really is. To be in the far-field is not as far as you may think. You are effectively in the far-field when your microphone is at a distance that is 3-5 times the radiating diameter of the driver."
Therefore, for a near field measurement for a 1" tweeter, the microphone should have been no further than 3 to 5 inches away. At the prior 9 inch microphone distance, room effects were coming into play.
Also from Bagby, "...the usable upper limit of the near field response is defined as
Fmax = 4311/ radiating diameter (in inches). Below this frequency the near-field response will be accurate and free of room and cabinet diffraction effects, above this frequency the near-field data is less reliable and less accurate."
Another rule for near-field measurement is that the microphone needs to be spaced from the center of the driver approximately 0.10 times the effective radiating radius of the driver. In the case of a 1" tweeter, this distance would have been 1/20th (0.05"). This was impractical in my case due to reflections from the tripod holding the microphone. A distance of 2 inches from the center of the tweeter domes resulted in smooth response curves without any dips due to room effects.
SDA Tweeter Frequency Response Measurements - Two Inch Distance
Figure 21. SL1000 frequency response.
Figure 22. SL2000 frequency response.
Figure 23. SL2500 frequency response.
Figure 24. SL3000 frequency response.
Figure 25. RD0194 frequency response.
Figure 26. RD0198 frequency response.
Figure 27. Composite plot of all six tweeters. Black line: RD0194. Red line: RD0198. Light blue line: SL1000. Green line: SL2000. Purple line: SL2500. Dark blue line: SL3000.
Figure 28. Comparison of RD0194 and SL2000 frequency response.
Figure 29. Comparison of RD0194 and SL1000 frequency response.
Figure 30. Comparison of RD0198 and SL2500 frequency response.
Figure 31. Comparison of RD0198 and SL3000 frequency response.
SDA Tweeter Harmonic Distortion Analysis - Two Inch Distance
In order of least harmonic distortion to most, the tweeters are: RD0198, RD0194, SL3000, SL1000, SL2500, SL2000.
The legend for the harmonic distortion plots is as follows:
Black line at top - frequency response.
Dark blue line second from top - summation of 2nd - 5th harmonics.
Light blue line - 5th harmonic.
Green line - 4th harmonic.
Purple line - 3rd harmonic.
Red line - 2nd harmonic.
Figure 32. SL1000 harmonic distortion analysis.
Figure 33. SL2000 harmonic distortion analysis.
Figure 34. SL2500 harmonic distortion analysis.
Figure 35. SL3000 harmonic distortion analysis.
Figure 36. RD0194 harmonic distortion analysis.
Figure 37. RD0198 harmonic distortion analysis.
References
1. Jeff Bagby, "How to Achieve Accurate In-Room Quasi-Anechoic Free-Field Frequency Response Measurements Down to 10 Hz", white paper, January 3, 2014, presented at Loudspeaker Design Workshop”, Kokomo, IN, December 14, 2013.
2. Christopher J. Struck, Steve F. Temme, " Simulated Free Field Measurements", Journal of the Audio Engineering Society, Vol. 42, No.6, June 1994.
3. Michael LaLena, "Speaker Testing and Analysis", https://www.diyaudioandvideo.com/Tutorial/SpeakerResponseTesting/
"Polk SDA-SRSs are hopelessly out of date both sonically and technologically... I see no value whatsoever in older SDA speakers."~Audio Asylum Member
"Knowledge, without understanding, is a path to failure."~DK
"Those who irrationally rail against something or someone that is no threat to them, actually desire (or desire to be like) the thing or person they are railing against."~DK
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Throughout the years it has been said that the SL2000 was the worst performing/worst sounding of the SDA tweeters. The quantitative measurements and physical inspections done in this study seem to support that. The SL2000 rated at the bottom in terms of build quality, balanced frequency response, and harmonic distortion among the six tweeters tested.
Build Quality
1. RD0198
2. RD0194
3. SL3000
4. SL2500
5. SL1000
6. SL2000
Frequency Response
1. RD0198
2. RD0194
3. SL3000
4. SL2500
5. SL1000
6. SL2000
Harmonic Distortion
1. RD0198
2. RD0194
3. SL3000
4. SL1000
5. SL2500
6. SL2000
"Polk SDA-SRSs are hopelessly out of date both sonically and technologically... I see no value whatsoever in older SDA speakers."~Audio Asylum Member
"Knowledge, without understanding, is a path to failure."~DK
"Those who irrationally rail against something or someone that is no threat to them, actually desire (or desire to be like) the thing or person they are railing against."~DK
Sounds about right.
By the way, did you ever get around to doing the Frequency Response of the MW mentioned earlier??
B+W-Sold
Epos-Now gone
Infinity-Sold
Advent-Now gone
Yamaha A-S801
Yamaha RX-V377
Yamaha RX-A860
Yamaha RX-A3060
Harman Kardon Hk-350i
Harman Kardon Hk-........
Harman Kardon PM-665
Harman Kardon HK-775
Pioneer.......Stereo Receiver
"Polk SDA-SRSs are hopelessly out of date both sonically and technologically... I see no value whatsoever in older SDA speakers."~Audio Asylum Member
"Knowledge, without understanding, is a path to failure."~DK
"Those who irrationally rail against something or someone that is no threat to them, actually desire (or desire to be like) the thing or person they are railing against."~DK
With the tweeters mounted in "Free Space" with no speaker baffle, you are seeing the effects of Baffle edge diffraction taking place at a higher frequency, than when mounted in the speaker.
http://www.linkwitzlab.com/diffraction.htm
http://ampslab.com/blog/2017/09/06/dome-tweeters/
The small dimensions of the face plate create a ripple effect when frequencies are a wavelength of the dimensions radiating from the tweeter dome.
In this case, it is approximately 4.5" wide, and there for a null around approximetly 5000hz and a resultant rise at about 10khz and about 2.5 khz.
Since the height dimension is smaller, diffraction will occur at a different frequency and help mask some of the ripple of up and down levels with rising frequency.
B+W-Sold
Epos-Now gone
Infinity-Sold
Advent-Now gone
Yamaha A-S801
Yamaha RX-V377
Yamaha RX-A860
Yamaha RX-A3060
Harman Kardon Hk-350i
Harman Kardon Hk-........
Harman Kardon PM-665
Harman Kardon HK-775
Pioneer.......Stereo Receiver