KEF B200 SP 1014 (high MMs and high Q)
KEF B200 SP1014
This is how it looks and how it measures. The Q might appear high but this is an effect of 35 years of aging that have made the suspension less supple. If the Fr could be dropped from 40 to 25 Hz the Q would drop from 0.8 to 0.5. That would be in line with KEFs data sheet.
This is the impedance of SP1014 in Decca placed in corner and reverse wall (driver facing forward).
The left graph in post 12 of the B200 in a voigt pipe of different dimensions than the Decca show some features to note.
Driver NF: the driver has a substantial peak just above the dip of the fundamental.
Pipe NF: there is a mismatch of peak output from pipe and the tuning frequency. At tuning frequency the pipe output is several dB below the peak output.
Time to look at how the KEF works in the Decca.
Driver Near Field: The KEF is in red and the black trace is the Philips 9710 as a reference. (I had to increase the KEF by 10 dB to match it to the 9710). The B200 has this +5dB hump at 65 Hz, the 9710 while not a real low Q driver still is flatter than the KEF.
Pipe output: Above 80 Hz there is no difference really between the red KEF and the black Philips. Below 80 Hz the Philips is within +/- 2 dB from 33 to 80 Hz relative to 92 dB. If I use the same reference level for the KEF it peaks at 10 dB at 58 Hz.
The B200 SP1014 regardless of other qualities is not a good driver for tuned pipes. The fact that measurements 38 years apart on two different pipes gives so similar results suggest that the finding is general. I also have the feeling that the 9710 works but is marginal in tuned pipes but the high frequency lift is good in orientation with the driver facing the back wall or corner.
KEF B200 SP1014
This is how it looks and how it measures. The Q might appear high but this is an effect of 35 years of aging that have made the suspension less supple. If the Fr could be dropped from 40 to 25 Hz the Q would drop from 0.8 to 0.5. That would be in line with KEFs data sheet.
This is the impedance of SP1014 in Decca placed in corner and reverse wall (driver facing forward).
The left graph in post 12 of the B200 in a voigt pipe of different dimensions than the Decca show some features to note.
Driver NF: the driver has a substantial peak just above the dip of the fundamental.
Pipe NF: there is a mismatch of peak output from pipe and the tuning frequency. At tuning frequency the pipe output is several dB below the peak output.
Time to look at how the KEF works in the Decca.
Driver Near Field: The KEF is in red and the black trace is the Philips 9710 as a reference. (I had to increase the KEF by 10 dB to match it to the 9710). The B200 has this +5dB hump at 65 Hz, the 9710 while not a real low Q driver still is flatter than the KEF.
Pipe output: Above 80 Hz there is no difference really between the red KEF and the black Philips. Below 80 Hz the Philips is within +/- 2 dB from 33 to 80 Hz relative to 92 dB. If I use the same reference level for the KEF it peaks at 10 dB at 58 Hz.
The B200 SP1014 regardless of other qualities is not a good driver for tuned pipes. The fact that measurements 38 years apart on two different pipes gives so similar results suggest that the finding is general. I also have the feeling that the 9710 works but is marginal in tuned pipes but the high frequency lift is good in orientation with the driver facing the back wall or corner.
This is a crazy candidate a Pioneer TSE20 Car speaker. They fit the cutout and the Q is lower than the previous two tested drivers. I usually measure MMs and Vas by adding a roll of masking tape to the cone but the way this one looks it can not be done. My guess is that it is high mass low Vas driver.
Partial Thile Small
In the pipe, hard do see any impedance peaks at the harmonics.
Now for the response curves. I have adjusted them to equal output disregarding differences in surface area.
Pipe output is really flat +/- 1dB from 40 to 70 Hz, good match between peak pipe output and the dip in driver response centered at 45-50 Hz.
Now I am really out of drivers that fit that 190mm cutout, I think at least...
Partial Thile Small
In the pipe, hard do see any impedance peaks at the harmonics.
Now for the response curves. I have adjusted them to equal output disregarding differences in surface area.
Pipe output is really flat +/- 1dB from 40 to 70 Hz, good match between peak pipe output and the dip in driver response centered at 45-50 Hz.
Now I am really out of drivers that fit that 190mm cutout, I think at least...
Added a 16mm MDF subbaffle to fit standard cutout 8" drivers, that I have a few of. First in line is a Peerless 831862. Polypropylene cone, foam surround, Low Q a typical modern bass reflex driver.
Compared to wall the corner postion lowers the tuning and also the lower impedance peak hight.
.
Instead of a hump at 70 Hz as the KEF there gentle slope from 130 to 70 Hz.
I also tried to measure in the corner but despite being very close to the cone the walls close by totaly mess up the response curves.
With this driver I can hear more of a boxy coloration than what I heard with the Philips 9710, at least I think I do. The relevant comparison would be to listen to the same driver in a welldamped box.
I saw someone using a constriction baffle in a tapped horn to reduce harmonics. Has onyone done this in Voigt pipes? I am thinking about trying to reduce that pesky 5th harmonic.
Compared to wall the corner postion lowers the tuning and also the lower impedance peak hight.
.Instead of a hump at 70 Hz as the KEF there gentle slope from 130 to 70 Hz.
I also tried to measure in the corner but despite being very close to the cone the walls close by totaly mess up the response curves.
With this driver I can hear more of a boxy coloration than what I heard with the Philips 9710, at least I think I do. The relevant comparison would be to listen to the same driver in a welldamped box.
I saw someone using a constriction baffle in a tapped horn to reduce harmonics. Has onyone done this in Voigt pipes? I am thinking about trying to reduce that pesky 5th harmonic.
An other Peerless PP cone driver, this one with inverted PP dome and rubber surround.
* Manufacturer: Peerless
* Model: 850126
* Piston Diameter = 175.0 mm
* f(s)= 48.45 Hz
* R(e)= 6.00 Ohms
* Z(max)= 58.76 Ohms
* Q(ms)= 4.488
* Q(es)= 0.511
* Q(ts)= 0.459
* V(as)= 43.160 liters (1.524 cubic feet)
* L(e)= 1.91 mH
* n(0)= 0.92 %
* SPL= 91.72 1W/1m
* M(ms)= 20.31 grams
* C(ms)= 0.53 mm/N
* BL= 8.52
The response is quite similar to the other Peerless driver
* Manufacturer: Peerless
* Model: 850126
* Piston Diameter = 175.0 mm
* f(s)= 48.45 Hz
* R(e)= 6.00 Ohms
* Z(max)= 58.76 Ohms
* Q(ms)= 4.488
* Q(es)= 0.511
* Q(ts)= 0.459
* V(as)= 43.160 liters (1.524 cubic feet)
* L(e)= 1.91 mH
* n(0)= 0.92 %
* SPL= 91.72 1W/1m
* M(ms)= 20.31 grams
* C(ms)= 0.53 mm/N
* BL= 8.52
The response is quite similar to the other Peerless driver
A high efficiency paper cone driver salvaged from Audio Pro 4-40 dipole speakers from the late 70s. Corrugated paper sorround coated with some sticky green stuff. The frame look like the Peerless did in the 1970s.
* Piston Diameter = 170.0 mm
* f(s)= 47.10 Hz
* R(e)= 6.65 Ohms
* Z(max)= 34.26 Ohms
* Q(ms)= 1.575
* Q(es)= 0.379
* Q(ts)= 0.306
* V(as)= 59.860 liters (2.114 cubic feet)
* L(e)= 0.93 mH
* n(0)= 1.57 %
* SPL= 94.07 1W/1m
* M(ms)= 13.81 grams
* C(ms)= 0.83 mm/N
* BL= 8.47
Note the impedance peaks at the harmonics. Compare that to the lack of impedance peaks for drivers like the Pioneer one. However, in frequency response they both have output peaks at the harmonics. So when comparing different drivers those impedance peaks say little if anything about the harmonics.
Compare these curves to the one in post #12 the set to the right with that gentle slope below 200 Hz. Pretty similar, so I assume that that Peerless driver had a light cone and low Q as this driver has.
* Piston Diameter = 170.0 mm
* f(s)= 47.10 Hz
* R(e)= 6.65 Ohms
* Z(max)= 34.26 Ohms
* Q(ms)= 1.575
* Q(es)= 0.379
* Q(ts)= 0.306
* V(as)= 59.860 liters (2.114 cubic feet)
* L(e)= 0.93 mH
* n(0)= 1.57 %
* SPL= 94.07 1W/1m
* M(ms)= 13.81 grams
* C(ms)= 0.83 mm/N
* BL= 8.47
Note the impedance peaks at the harmonics. Compare that to the lack of impedance peaks for drivers like the Pioneer one. However, in frequency response they both have output peaks at the harmonics. So when comparing different drivers those impedance peaks say little if anything about the harmonics.
Compare these curves to the one in post #12 the set to the right with that gentle slope below 200 Hz. Pretty similar, so I assume that that Peerless driver had a light cone and low Q as this driver has.
Dr Boar,
As always, you continue to amaze us with your thoroughness in studying this cabinet. Nice work! Is it my correct understanding that the ideal driver for this horn is a low Qts variety? The Pioneer car audio one seems very good but I think car door panel speakers are generally high Qts. I have often wondered about using a Pioneer 6.5 in coaxial on "fullrangedriver" type cabinets.
As always, you continue to amaze us with your thoroughness in studying this cabinet. Nice work! Is it my correct understanding that the ideal driver for this horn is a low Qts variety? The Pioneer car audio one seems very good but I think car door panel speakers are generally high Qts. I have often wondered about using a Pioneer 6.5 in coaxial on "fullrangedriver" type cabinets.
xrk971,
So far it looks like the medium to low Q drivers works better than the high Q driver I have tested so far. But as I have only tested one high Q driver so far (KEF B200 SP 1014) I have to test other high Q drivers (in the pipeline!).
Low Q is not the only thing, my guess is two drivers with Q of 0.3 with one having a Fr of 20 Hz and one 80 Hz might behave differently in the Decca Pipe.
So far it looks like the medium to low Q drivers works better than the high Q driver I have tested so far. But as I have only tested one high Q driver so far (KEF B200 SP 1014) I have to test other high Q drivers (in the pipeline!).
Low Q is not the only thing, my guess is two drivers with Q of 0.3 with one having a Fr of 20 Hz and one 80 Hz might behave differently in the Decca Pipe.
High Q (1) low mass 8gram and high Fr (63 Hz) and impressive power handling of 12 Watt American rating, the more modest UK rating is 6W.
BTW I was belting out some loud rock music with the Peerless 850126, I felt the vibrations in the hardwood floor, then the vibrations in the lower part of the front is substantial and quite a lot in the backside below the driver and surprisingly in the top. The flat and angled sides as well as the driver baffle fares much better.
I front mounted it, sealed as best as I could, but it really should be rear mounted.
The driver has some resonances as can be seen at the impedance and phase curves.
In the pipe the lower resonance peak is lower than upper one, that seems to be the case with drivers that has an Fr above tuning frequency.
The output does not look good the driver has a peak around 100 Hz and the pipe maximal output is above the tuning frequency.
The Axiette could be used on open baffle at low levels or in a closed box/ box with resistive damping. But pipes and horns is not were it works well.
BTW I was belting out some loud rock music with the Peerless 850126, I felt the vibrations in the hardwood floor, then the vibrations in the lower part of the front is substantial and quite a lot in the backside below the driver and surprisingly in the top. The flat and angled sides as well as the driver baffle fares much better.
I front mounted it, sealed as best as I could, but it really should be rear mounted.
The driver has some resonances as can be seen at the impedance and phase curves.
In the pipe the lower resonance peak is lower than upper one, that seems to be the case with drivers that has an Fr above tuning frequency.
The output does not look good the driver has a peak around 100 Hz and the pipe maximal output is above the tuning frequency.
The Axiette could be used on open baffle at low levels or in a closed box/ box with resistive damping. But pipes and horns is not were it works well.
A third high Q driver this time the Philips AD8061W4, a very common driver here in Europe in its day, in run of the mill HiFi setups.
Despite being a budget driver they show little variations between samples.
* Manufacturer: Philips
* Model: 8061W4
* Piston Diameter = 170.0 mm
* f(s)= 64.60 Hz
* R(e)= 4.17 Ohms
* Z(max)= 18.45 Ohms
* Q(ms)= 4.564
* Q(es)= 1.333
* Q(ts)= 1.032
* V(as)= 32.260 liters (1.139 cubic feet)
* L(e)= 0.80 mH
* n(0)= 0.62 %
* SPL= 90.04 1W/1m
* M(ms)= 13.62 grams
* C(ms)= 0.45 mm/N
* BL= 4.16
* Manufacturer: Philips
* Model: 8061W4
* Piston Diameter = 170.0 mm
* f(s)= 61.91 Hz
* R(e)= 4.16 Ohms
* Z(max)= 17.88 Ohms
* Q(ms)= 4.480
* Q(es)= 1.358
* Q(ts)= 1.042
* V(as)= 38.530 liters (1.361 cubic feet)
* L(e)= 0.76 mH
* n(0)= 0.64 %
* SPL= 90.18 1W/1m
* M(ms)= 12.41 grams
* C(ms)= 0.53 mm/N
* BL= 3.85
And then the response ( Pipe output lowered 5 dB)
Driver peak +4dB above midrange levels from 75 to 100 Hz, pipe output is from 35 Hz and upwards. They sound quite good if you like a fat bass pounding away, I think this is reflection of the good midrange with a fall above 3 kHz without any nasty peaks.
Despite being a budget driver they show little variations between samples.
* Manufacturer: Philips
* Model: 8061W4
* Piston Diameter = 170.0 mm
* f(s)= 64.60 Hz
* R(e)= 4.17 Ohms
* Z(max)= 18.45 Ohms
* Q(ms)= 4.564
* Q(es)= 1.333
* Q(ts)= 1.032
* V(as)= 32.260 liters (1.139 cubic feet)
* L(e)= 0.80 mH
* n(0)= 0.62 %
* SPL= 90.04 1W/1m
* M(ms)= 13.62 grams
* C(ms)= 0.45 mm/N
* BL= 4.16
* Manufacturer: Philips
* Model: 8061W4
* Piston Diameter = 170.0 mm
* f(s)= 61.91 Hz
* R(e)= 4.16 Ohms
* Z(max)= 17.88 Ohms
* Q(ms)= 4.480
* Q(es)= 1.358
* Q(ts)= 1.042
* V(as)= 38.530 liters (1.361 cubic feet)
* L(e)= 0.76 mH
* n(0)= 0.64 %
* SPL= 90.18 1W/1m
* M(ms)= 12.41 grams
* C(ms)= 0.53 mm/N
* BL= 3.85
And then the response ( Pipe output lowered 5 dB)
Driver peak +4dB above midrange levels from 75 to 100 Hz, pipe output is from 35 Hz and upwards. They sound quite good if you like a fat bass pounding away, I think this is reflection of the good midrange with a fall above 3 kHz without any nasty peaks.
The 4th high Q driver: Something similar from Seas but with a paper surround, the Seas 21F-GW. On top it is Seas to the left and Philips 8061 to the right.
* Manufacturer: Seas
* Model: 21F-GW
* Piston Diameter = 175.0 mm
* f(s)= 57.87 Hz
* R(e)= 4.76 Ohms
* Z(max)= 15.09 Ohms
* Q(ms)= 2.971
* Q(es)= 1.369
* Q(ts)= 0.937
* V(as)= 42.030 liters (1.484 cubic feet)
* L(e)= 0.70 mH
* n(0)= 0.57 %
* SPL= 89.64 1W/1m
* M(ms)= 14.62 grams
* C(ms)= 0.52 mm/N
* BL= 4.30
The sound is OK but not more than that.
* Manufacturer: Seas
* Model: 21F-GW
* Piston Diameter = 175.0 mm
* f(s)= 57.87 Hz
* R(e)= 4.76 Ohms
* Z(max)= 15.09 Ohms
* Q(ms)= 2.971
* Q(es)= 1.369
* Q(ts)= 0.937
* V(as)= 42.030 liters (1.484 cubic feet)
* L(e)= 0.70 mH
* n(0)= 0.57 %
* SPL= 89.64 1W/1m
* M(ms)= 14.62 grams
* C(ms)= 0.52 mm/N
* BL= 4.30
The sound is OK but not more than that.
And how long have you been collecting them? If one wanted to use a modern commercially available driver in the Decca which one tops your list?
The 5th driver with high Q (0.7) Seas 21TV-EW. High cone mass 28 g and a rather low Fr of 35 Hz.
* Manufacturer: Seas
* Model: 21TV-EW
* Piston Diameter = 170.0 mm
* f(s)= 34.99 Hz
* R(e)= 5.99 Ohms
* Z(max)= 70.15 Ohms
* Q(ms)= 7.519
* Q(es)= 0.702
* Q(ts)= 0.642
* V(as)= 52.260 liters (1.845 cubic feet)
* L(e)= 1.88 mH
* n(0)= 0.30 %
* SPL= 86.93 1W/1m
* M(ms)= 28.65 grams
* C(ms)= 0.72 mm/N
* BL= 7.33
.
They sound like they measure with strong bass lines regardless of the music. I do not mind some added bass but at this level it is irritating it is of that one note version also. If I play loud the cone starts to flap about quite a lot.
* Manufacturer: Seas
* Model: 21TV-EW
* Piston Diameter = 170.0 mm
* f(s)= 34.99 Hz
* R(e)= 5.99 Ohms
* Z(max)= 70.15 Ohms
* Q(ms)= 7.519
* Q(es)= 0.702
* Q(ts)= 0.642
* V(as)= 52.260 liters (1.845 cubic feet)
* L(e)= 1.88 mH
* n(0)= 0.30 %
* SPL= 86.93 1W/1m
* M(ms)= 28.65 grams
* C(ms)= 0.72 mm/N
* BL= 7.33
.They sound like they measure with strong bass lines regardless of the music. I do not mind some added bass but at this level it is irritating it is of that one note version also. If I play loud the cone starts to flap about quite a lot.
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The 6th and filal high Q driver is from Scanspeak (21W 4208 P2A SD), salvaged from an Ortophon speaker. Q is similar to the Seas but Fr is up 20 Hz to 55 Hz, paper cone and a surround of coated cloth roll.
* Manufacturer: Scanspeak
* Model: 21w 4208 p2a sd
* Piston Diameter = 170.0 mm
* f(s)= 55.85 Hz
* R(e)= 6.38 Ohms
* Z(max)= 21.66 Ohms
* Q(ms)= 2.378
* Q(es)= 0.992
* Q(ts)= 0.700
* V(as)= 32.020 liters (1.131 cubic feet)
* L(e)= 1.16 mH
* n(0)= 0.54 %
* SPL= 89.39 1W/1m
* M(ms)= 18.36 grams
* C(ms)= 0.44 mm/N
* BL= 6.43
Also this one has to much bass at least agains a concrete back wall, but it is less to much than the Seas 21TV-EW and a far more tuneful bass. If I play really loud the cone still do not flap around.
So to conclude (incuding a Fane Studio 8M that I will post later) the Peerless 850126 simply sounded the "most right/natrual" with the Peerless 83126 and the Pioneer car speaker not far behind. Worst is the Seas TV-EW or perhaps the KEF B200 SP-1014 followed by the Goodman Axiette.
* Manufacturer: Scanspeak
* Model: 21w 4208 p2a sd
* Piston Diameter = 170.0 mm
* f(s)= 55.85 Hz
* R(e)= 6.38 Ohms
* Z(max)= 21.66 Ohms
* Q(ms)= 2.378
* Q(es)= 0.992
* Q(ts)= 0.700
* V(as)= 32.020 liters (1.131 cubic feet)
* L(e)= 1.16 mH
* n(0)= 0.54 %
* SPL= 89.39 1W/1m
* M(ms)= 18.36 grams
* C(ms)= 0.44 mm/N
* BL= 6.43
Also this one has to much bass at least agains a concrete back wall, but it is less to much than the Seas 21TV-EW and a far more tuneful bass. If I play really loud the cone still do not flap around.
So to conclude (incuding a Fane Studio 8M that I will post later) the Peerless 850126 simply sounded the "most right/natrual" with the Peerless 83126 and the Pioneer car speaker not far behind. Worst is the Seas TV-EW or perhaps the KEF B200 SP-1014 followed by the Goodman Axiette.
I end with a monster from England
* Manufacturer: Fane
* Model: Studio 8M
* Piston Diameter = 168.0 mm
* f(s)= 108.30 Hz
* R(e)= 5.85 Ohms
* Z(max)= 79.01 Ohms
* Q(ms)= 7.661
* Q(es)= 0.613
* Q(ts)= 0.567
* V(as)= 13.390 liters (0.473 cubic feet)
* L(e)= 0.75 mH
* n(0)= 2.65 %
* SPL= 96.33 1W/1m
* M(ms)= 11.13 grams
* C(ms)= 0.19 mm/N
* BL= 8.50
The impedance peaks at 800Hz and 3 kHz are intrinsic to the driver.
It so loud! I can not really make any sound judgments on sound as the driver is installed rear end out. Sensitivity is very very high, bass is light, the brutal impact is there but not the weight.
This is the end of my stash unless I make adaptor plates and install 6.5" and 10" units then I have 5 more, but enough is enough.
* Manufacturer: Fane
* Model: Studio 8M
* Piston Diameter = 168.0 mm
* f(s)= 108.30 Hz
* R(e)= 5.85 Ohms
* Z(max)= 79.01 Ohms
* Q(ms)= 7.661
* Q(es)= 0.613
* Q(ts)= 0.567
* V(as)= 13.390 liters (0.473 cubic feet)
* L(e)= 0.75 mH
* n(0)= 2.65 %
* SPL= 96.33 1W/1m
* M(ms)= 11.13 grams
* C(ms)= 0.19 mm/N
* BL= 8.50
The impedance peaks at 800Hz and 3 kHz are intrinsic to the driver.
It so loud! I can not really make any sound judgments on sound as the driver is installed rear end out. Sensitivity is very very high, bass is light, the brutal impact is there but not the weight.
This is the end of my stash unless I make adaptor plates and install 6.5" and 10" units then I have 5 more, but enough is enough.
Regarding drivers:
The purist, fullrange and no tone controlls
Fostex, Tangband, Dayton
The semi-purist, fullrange and the option of tone control
Seas Prestige and perhaps MA Alpair 12P (if a 6.5" works)
With point source and "phase coherence" of fullrange drivers lost in a design were the driver is facing into a corner and we listen to the sound scatter. I would tend to go for a two way system.
The HiFi highway is paved with 8" units with Q close to 0.35 and Fr around 30-35 Hz. Armed with one of those and one or several high efficiency domes to get that lift in the high range the options are endless.
High efficiency two ways would be Eminence Beta 8A, Beyma SM 108, Beyma 8P300FE and some horn to top it of.
With Klipsch corner horns I lost 4-6 dB below 80Hz by having just one side wall of concrete (and the other plaster board) so my guess is that the pipe output of the Decca Corner Horn is substantially affected by the rigidity of the walls and floor.
By placement, damping material and perhaps constricting the pipe opening the system can be tuned to a range of combinations. Drivers with a Fr much lower than 30 Hz or well above 70 Hz will probably not fare well nor those with Q above 0.7 or below 0.2. In my room low Fr high Q driver (KEF B200 and Seas TV-EW) sound fare worse than drivers with similar higish Q but higher Fr like the Seas F-GW and the Philips 9710).
The purist, fullrange and no tone controlls
Fostex, Tangband, Dayton
The semi-purist, fullrange and the option of tone control
Seas Prestige and perhaps MA Alpair 12P (if a 6.5" works)
With point source and "phase coherence" of fullrange drivers lost in a design were the driver is facing into a corner and we listen to the sound scatter. I would tend to go for a two way system.
The HiFi highway is paved with 8" units with Q close to 0.35 and Fr around 30-35 Hz. Armed with one of those and one or several high efficiency domes to get that lift in the high range the options are endless.
High efficiency two ways would be Eminence Beta 8A, Beyma SM 108, Beyma 8P300FE and some horn to top it of.
With Klipsch corner horns I lost 4-6 dB below 80Hz by having just one side wall of concrete (and the other plaster board) so my guess is that the pipe output of the Decca Corner Horn is substantially affected by the rigidity of the walls and floor.
By placement, damping material and perhaps constricting the pipe opening the system can be tuned to a range of combinations. Drivers with a Fr much lower than 30 Hz or well above 70 Hz will probably not fare well nor those with Q above 0.7 or below 0.2. In my room low Fr high Q driver (KEF B200 and Seas TV-EW) sound fare worse than drivers with similar higish Q but higher Fr like the Seas F-GW and the Philips 9710).
Mick on a stick
I had this idea to measure what happens up the pipe so I took a stick marked it at 10 cm intervals and then used a rubber band to attach the microphone to the stick.
If the microphone is a pressure device so pressure minima is velocity maxima and good places for damping.
So this is from 0 cm at the pipe opening and at 10 cm increment to 90 cm into the pipe, basically just behind the driver. Getting into the pipe increase the pressure asymptyotically at the fundamental resonance and change the harmonics pressure.
If I normalize it at 50 Hz and delete the 10 and 80 cm to simplify the graph.
Things to note in the mess:
Going up the pipe lowers the pressure of the 3rd harmonic note white line close to driver. So it is at a pressure minima as it should in a Voigt. For the 5th harmonic there seems to be a pressure minima for the green line at 50 cm.
So I added a roll of either 82 or 164 gram BAF at 50 cm into the pipe
The 164 g lowers the overall output to much. If I normalize the output to 50 Hz it looks like this.
The 164 g does not work, the 82 g might be OK. But stuffing in volume filling ways across a section seems to be a blunt tool. I might investigate if there is differences in how the fundamental and harmonics propagate in the pipe. That is how much in the geometric midline and along the surfaces and edges of the line.
I had this idea to measure what happens up the pipe so I took a stick marked it at 10 cm intervals and then used a rubber band to attach the microphone to the stick.
If the microphone is a pressure device so pressure minima is velocity maxima and good places for damping.
So this is from 0 cm at the pipe opening and at 10 cm increment to 90 cm into the pipe, basically just behind the driver. Getting into the pipe increase the pressure asymptyotically at the fundamental resonance and change the harmonics pressure.
If I normalize it at 50 Hz and delete the 10 and 80 cm to simplify the graph.
Things to note in the mess:
Going up the pipe lowers the pressure of the 3rd harmonic note white line close to driver. So it is at a pressure minima as it should in a Voigt. For the 5th harmonic there seems to be a pressure minima for the green line at 50 cm.
So I added a roll of either 82 or 164 gram BAF at 50 cm into the pipe
The 164 g lowers the overall output to much. If I normalize the output to 50 Hz it looks like this.
The 164 g does not work, the 82 g might be OK. But stuffing in volume filling ways across a section seems to be a blunt tool. I might investigate if there is differences in how the fundamental and harmonics propagate in the pipe. That is how much in the geometric midline and along the surfaces and edges of the line.
to self: never ever at the end of a long post change from simple to advanced post...
The aim is to find a way to reduce the 5th harmonics around 200 Hz.
Now I measuring in the start of the pipe and the annotation refer to distance from closed end of the pipe. This time I took the lazy way out and had the enclose laying flat on the front, so gravity sealed the driver. This does change the loading of the pipe as constriction at the open end is a part of the construction.
The results are quite similar at 0-10-20-30 cm from the closed en of the pipe at 40 & 50 cm (the 50 cm is more or less at the lower edge of the driver) the third harmonic pressure drops as it should.
But back to the range around 200 Hz and something seems to happen around 40cm so remeasure at 5 cm intervalls.
The results are quite consistent with previous set with a pressure minima of 200 Hz at 45 cm from the closed pipe. This should also be a velocity maxima that is good place to add damping.
I read that people buildning tapped horns have used internal constrictions to tame peaks in output. This is my bid at an constriction on a stick the 176 cm2 OSB plate has a screw at the middle that transect the stick so that the plate can be swiveled out to a perpendicular position to the stick (and the pipe) By drilling hole through the stick at 5cm intervalls I can try constricting the pipe at various lenths from the closed end.
Now the measurement microphone is at the open end of the pipe, as it unconstricted the output is quite different from the pattern at proper configuration. My expectation was that adding the baffle around 40-45 Hz should reduce output at 200 Hz.
To my surprise, the spice of life, nothing happend at all above 180 Hz regardless of baffle position! A baffle at 25 cm reduce the output 140-180 Hz by about 3 dB.
I am baffled in more ways than one
Has anyone else recently measured sounds inside resonant pipes?
The Decca Corner Horn is complex pipe with various positive and negative tapers a fold, constrictions and different cross section geometries at different parts of the pipe. Perhaps if I simplify the system as far as I can and measure that instead.
The aim is to find a way to reduce the 5th harmonics around 200 Hz.
Now I measuring in the start of the pipe and the annotation refer to distance from closed end of the pipe. This time I took the lazy way out and had the enclose laying flat on the front, so gravity sealed the driver. This does change the loading of the pipe as constriction at the open end is a part of the construction.
The results are quite similar at 0-10-20-30 cm from the closed en of the pipe at 40 & 50 cm (the 50 cm is more or less at the lower edge of the driver) the third harmonic pressure drops as it should.
But back to the range around 200 Hz and something seems to happen around 40cm so remeasure at 5 cm intervalls.
The results are quite consistent with previous set with a pressure minima of 200 Hz at 45 cm from the closed pipe. This should also be a velocity maxima that is good place to add damping.
I read that people buildning tapped horns have used internal constrictions to tame peaks in output. This is my bid at an constriction on a stick the 176 cm2 OSB plate has a screw at the middle that transect the stick so that the plate can be swiveled out to a perpendicular position to the stick (and the pipe) By drilling hole through the stick at 5cm intervalls I can try constricting the pipe at various lenths from the closed end.
Now the measurement microphone is at the open end of the pipe, as it unconstricted the output is quite different from the pattern at proper configuration. My expectation was that adding the baffle around 40-45 Hz should reduce output at 200 Hz.
To my surprise, the spice of life, nothing happend at all above 180 Hz regardless of baffle position! A baffle at 25 cm reduce the output 140-180 Hz by about 3 dB.
I am baffled in more ways than one
Has anyone else recently measured sounds inside resonant pipes?
The Decca Corner Horn is complex pipe with various positive and negative tapers a fold, constrictions and different cross section geometries at different parts of the pipe. Perhaps if I simplify the system as far as I can and measure that instead.
I made a measurement of the nearfield dip with the DCH standing on a table in an other room and then I got a very clear symetric sharp dip at the tuning frequency. When I start to work with the damping where I will try to reduce the harmonics while at the same time maintaining as much radiation resistance at the fundental (the whole point of having a pipe in the first place) I think I go for a table.
Some damping of the walls in the top compartment behind the driver seem to be a minimum of required damping, I have 10mm thick felt, about 30mm thick foam and stiff BAF sheets also about 30 mm thick.
Some damping of the walls in the top compartment behind the driver seem to be a minimum of required damping, I have 10mm thick felt, about 30mm thick foam and stiff BAF sheets also about 30 mm thick.
The time domain plots clearly showed that getting some damping around the driver is a good thing. Also some vibrations in the OSB could benefit from damping. So I took 12mm bitumen impregnated softboard and glued 10mm felt to it. The sizes are 3 each of 400x120mm and 400x100mm. The final lenght of the boards were trimmed to size by 20-30 mm if needed.
One 100 wide board was glued to the cieling of the cabinet (I felt vibrations there before) The front wall was covered by one 100 and one 120mm piece ( seen far back in the picture below. One 100 wide pice was glued along the back of the closed end below the brace. Then two 120 mm wide pices was glued to the dividing baffle on the side facing the closed end. Finaly the top of the dividing baffle with the cutout was covered with a layer of felt. All gluing was done with silicone glue.
The nearfield response does not suggest any major changes perhaps a slight flattening of the dips at the harmonics.
At the pipe and large changes occur even with this very modest amount of damping material.
The sharp peak at 120 Hz is reduced by about 6 dB
The huge peak at 200 is marginaly affected
The peak at 350 Hz is reduced by 9 dB
The peak at 500 Hz is reduced by 4 dB.
I plan to add a large sheet of bitumen board to the front below the braces to see if I can gain any benefit from reducing the vibrations there (no felt lining)
The current opening is about 160cm2 I plan to block it and open a hole at the very back below the closed end. Hopefully this added 90 degree bend will reduce that 200 Hz peak... or not.
One 100 wide board was glued to the cieling of the cabinet (I felt vibrations there before) The front wall was covered by one 100 and one 120mm piece ( seen far back in the picture below. One 100 wide pice was glued along the back of the closed end below the brace. Then two 120 mm wide pices was glued to the dividing baffle on the side facing the closed end. Finaly the top of the dividing baffle with the cutout was covered with a layer of felt. All gluing was done with silicone glue.
The nearfield response does not suggest any major changes perhaps a slight flattening of the dips at the harmonics.
At the pipe and large changes occur even with this very modest amount of damping material.
The sharp peak at 120 Hz is reduced by about 6 dB
The huge peak at 200 is marginaly affected
The peak at 350 Hz is reduced by 9 dB
The peak at 500 Hz is reduced by 4 dB.
I plan to add a large sheet of bitumen board to the front below the braces to see if I can gain any benefit from reducing the vibrations there (no felt lining)
The current opening is about 160cm2 I plan to block it and open a hole at the very back below the closed end. Hopefully this added 90 degree bend will reduce that 200 Hz peak... or not.
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