With the summer finaly coming to a close, I thought I do some work outside before the rain and cold sets in.
The square cuts from the lumber yard.
I then followed the buildning instructions in the HFN &RR article as refered to in prevous posts. Adding some guide rails in softwood for on the sides
I then seald the corners with a latex. Many small corner fillets were added after the latex sealing.
Finaly the dividing panel was glued, screwed and sealed in place. Some of the other panels were cut to shape and some oddly shaped braces were made.
Now the whole thing will sit over night and set glue and sealant. I will have to make some 45degree edges things I have not done before. So I think I call it a day and rehydrate myselft with a beer
I think it will give some horrible resonances as is is totaly devoid of any damping material, but it will be fun trying to tame it, I hope!
The square cuts from the lumber yard.
I then followed the buildning instructions in the HFN &RR article as refered to in prevous posts. Adding some guide rails in softwood for on the sides
I then seald the corners with a latex. Many small corner fillets were added after the latex sealing.
Finaly the dividing panel was glued, screwed and sealed in place. Some of the other panels were cut to shape and some oddly shaped braces were made.
Now the whole thing will sit over night and set glue and sealant. I will have to make some 45degree edges things I have not done before. So I think I call it a day and rehydrate myselft with a beer
I think it will give some horrible resonances as is is totaly devoid of any damping material, but it will be fun trying to tame it, I hope!
9710 for sure, some car triaxial, some Peerless bass reflex driver, perhaps also Fane 8M Studio, KEF B200 to get both drivers that should work and those that should not. Beech Plywood is six times the price of OSB. I think OSB is closer structure wise to Plywood than MDF is. If I ever build a real pair I would, at least now, think that I would do them in MDF 12 or 16mm and then have a nice front cover, be it a mirror or plywood.
More braces than a group of teenagers
The Philips 9710 and the cutouts for the driver, including the one to clear the magnet
This is a size comparison with a large TLS. Weigth wise the Decca is a comfortable one arm lift the TLS is not!
I was worried that the slot in the bottom would be affected by the floor so I measured the impedance on hardwood floor, concrete floor and a thick rug on top of hardwood floor. Not much of a difference. The pipe is tuned to 50 Hz and the harmonics peaks seem to be quite small.
The right way around for some music
Hardly an ideal setup but here I go.
Way more sensitive than TLS, the bottom octave is missing when I compare with the Tyrland with a fundamental resonance at 20-25 Hz.
With the pipe totaly empty and with such thin walls I expected a lot of boxy colorations. It sounds really good! what is going on here? Playing loud bass and moving my hand over the various surfaces there is not much vibrations apart from the lower third of the front.
That small IMF folded TLS I built using a modern very good Peerless PP cone driver sounded horrible with empty pipe. This one with a shouty 9710 sounds really nice.
The Philips 9710 and the cutouts for the driver, including the one to clear the magnet
This is a size comparison with a large TLS. Weigth wise the Decca is a comfortable one arm lift the TLS is not!
I was worried that the slot in the bottom would be affected by the floor so I measured the impedance on hardwood floor, concrete floor and a thick rug on top of hardwood floor. Not much of a difference. The pipe is tuned to 50 Hz and the harmonics peaks seem to be quite small.
The right way around for some music
Hardly an ideal setup but here I go.
Way more sensitive than TLS, the bottom octave is missing when I compare with the Tyrland with a fundamental resonance at 20-25 Hz.
With the pipe totaly empty and with such thin walls I expected a lot of boxy colorations. It sounds really good! what is going on here? Playing loud bass and moving my hand over the various surfaces there is not much vibrations apart from the lower third of the front.
That small IMF folded TLS I built using a modern very good Peerless PP cone driver sounded horrible with empty pipe. This one with a shouty 9710 sounds really nice.
Nice work Dr Boar. Sometimes a big empty box can sound nice. 
the shoutyness is reduced by back firing driver. The large surface area and high volume serve as built in damping? If you can get me the detailed CSA vs distance data I can model it for you and we can try to see what is going on. Very cool.
the shoutyness is reduced by back firing driver. The large surface area and high volume serve as built in damping? If you can get me the detailed CSA vs distance data I can model it for you and we can try to see what is going on. Very cool. 
Hi,
My first speaker many years ago was the real Decca. No internal damping.
Driven by a Tripletone mono small valve amp of probably high impedance.
It rocked, big time, even given my 16 year old sensibilities. The very
thin walls damped and resonated at the same time, pretty unusual.
As ever the driver ended up being blown, from about 5 distorted Watts
and being fairly clueless I never managed to fit a driver that got in any
real way close to the original 8" driver, but FWIW my opinion many
years later is the Visatoin B200 is your best bet for a Decca clone.
rgds, sreten.
later is the
My first speaker many years ago was the real Decca. No internal damping.
Driven by a Tripletone mono small valve amp of probably high impedance.
It rocked, big time, even given my 16 year old sensibilities. The very
thin walls damped and resonated at the same time, pretty unusual.
As ever the driver ended up being blown, from about 5 distorted Watts
and being fairly clueless I never managed to fit a driver that got in any
real way close to the original 8" driver, but FWIW my opinion many
years later is the Visatoin B200 is your best bet for a Decca clone.
rgds, sreten.
later is the
Hi,
My first speaker many years ago was the real Decca. No internal damping.
Driven by a Tripletone mono small valve amp of probably high impedance.
It rocked, big time, even given my 16 year old sensibilities. The very
thin walls damped and resonated at the same time, pretty unusual.
As ever the driver ended up being blown, from about 5 distorted Watts
and being fairly clueless I never managed to fit a driver that got in any
real way close to the original 8" driver, but FWIW my opinion many
years later is the Visaton B200 is your best bet for a Decca clone.
rgds, sreten.
My first speaker many years ago was the real Decca. No internal damping.
Driven by a Tripletone mono small valve amp of probably high impedance.
It rocked, big time, even given my 16 year old sensibilities. The very
thin walls damped and resonated at the same time, pretty unusual.
As ever the driver ended up being blown, from about 5 distorted Watts
and being fairly clueless I never managed to fit a driver that got in any
real way close to the original 8" driver, but FWIW my opinion many
years later is the Visaton B200 is your best bet for a Decca clone.
rgds, sreten.
Of 48 corners in the house only one is a proper horn corner.
I took a fast set of measurements with the Decca in the concrete corner (green) moving the Decca out on the floor Increase the impedance peaks as well as moving the tuning by 2 -3 Hz. The impedance peak at 180 Hz is moved up to 210 Hz.
Flipping the box over increass the tuning by 10 Hz from 45 to 55 Hz as judged by the zero phase transistions. The other peak is at 230 Hz or so.
When doing this measurements I listened to some music in the background. I got variations in the impedance curves, to verify the interaction I turned the volume up and sure enough the measurements with the decca in the corner whent haywire!
I took a fast set of measurements with the Decca in the concrete corner (green) moving the Decca out on the floor Increase the impedance peaks as well as moving the tuning by 2 -3 Hz. The impedance peak at 180 Hz is moved up to 210 Hz.
Flipping the box over increass the tuning by 10 Hz from 45 to 55 Hz as judged by the zero phase transistions. The other peak is at 230 Hz or so.
When doing this measurements I listened to some music in the background. I got variations in the impedance curves, to verify the interaction I turned the volume up and sure enough the measurements with the decca in the corner whent haywire!
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Some preliminary frequency response measurements. Made with a hand held mike perpendicular to the driver and the capusule just in front of the inner double cone. This was the only way I could do the measurement in the corner.
Black curve is with the pipe filled with damping material from the two crossbraces of the front to the open end of the pipe. It was hard getting rid of the lower impedance peak of the pipe, needed lots of stuffing.
Red it with empty pipe on floor There is a peak at 40 Hz messing up the fundamental dip. Now it looks to be at 50 Hz but it could be towards 45 Hz. There is major disturbance at 200 Hz and some minor ones at 120 and 300 Hz.
These pipe outputs were measured just inside the middle of the front shelf between the two feets
The black curve is the corner one that seems to do wonders for supression of 5th and 7th harmonics.
The red curve is in the room on hardwood floors brining up the harmonics by 10 B or so.
Brown curve is on thick carpet and that seem to attenuate the 40 Hz output by some few dB and then not doing anything until above 1 kHz that seems to be better than the hard floor.
The third harmonic seem to be well taken care of. If I by some gentle damping around the driver and in the first section could tame the higher harmonics.This is one interesting speaker.
Ralph West recomended the Lowther 6A, the Visaton B200 have the same frequency lift as Lowther and 9710 but the Qes is even higher than the 9710. It would be interesting to see how the Decca handle a modern bass driver with heavier cone and longer stroke but that will come at a later date.
Black curve is with the pipe filled with damping material from the two crossbraces of the front to the open end of the pipe. It was hard getting rid of the lower impedance peak of the pipe, needed lots of stuffing.
Red it with empty pipe on floor There is a peak at 40 Hz messing up the fundamental dip. Now it looks to be at 50 Hz but it could be towards 45 Hz. There is major disturbance at 200 Hz and some minor ones at 120 and 300 Hz.
These pipe outputs were measured just inside the middle of the front shelf between the two feets
The black curve is the corner one that seems to do wonders for supression of 5th and 7th harmonics.
The red curve is in the room on hardwood floors brining up the harmonics by 10 B or so.
Brown curve is on thick carpet and that seem to attenuate the 40 Hz output by some few dB and then not doing anything until above 1 kHz that seems to be better than the hard floor.
The third harmonic seem to be well taken care of. If I by some gentle damping around the driver and in the first section could tame the higher harmonics.This is one interesting speaker.
Ralph West recomended the Lowther 6A, the Visaton B200 have the same frequency lift as Lowther and 9710 but the Qes is even higher than the 9710. It would be interesting to see how the Decca handle a modern bass driver with heavier cone and longer stroke but that will come at a later date.
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Hi,
At one point I fitted a Fane 8" FR to the Decca cabinet. Not
particular efficient or particularly low Q. Pretty decent excursion
and fairly low Fs with a large rubber rolled surround.
Result : the worst one note bass I've ever heard .........
Full stuffing with fibreglass didn't help much .........
rgds, sreten.
At one point I fitted a Fane 8" FR to the Decca cabinet. Not
particular efficient or particularly low Q. Pretty decent excursion
and fairly low Fs with a large rubber rolled surround.
Result : the worst one note bass I've ever heard .........
Full stuffing with fibreglass didn't help much .........
rgds, sreten.
Bjarne Börja recomend low Q driver for pipes.
Below are two 8" units with the same Fr and Bl but the left one has a much heavier cone (higherQ) than the Peerless on the right. JBL 2110 was excellent but was deemed to expensive in this setting. Note the peak in driver response just above the fundamental of the pipe and the frequency missmatch of driver dip and pipe output.
Below are two 8" units with the same Fr and Bl but the left one has a much heavier cone (higherQ) than the Peerless on the right. JBL 2110 was excellent but was deemed to expensive in this setting. Note the peak in driver response just above the fundamental of the pipe and the frequency missmatch of driver dip and pipe output.
xrk971
http://www.diyaudio.com/forums/full-range/182858-anyone-built-decca-corner-horn-tqwp-3.html post 23 by Planet 10 has the original article as and PDF with all the measurements.
A more extended translation is on the way. The page is extracted from a series of articles about a Voigtpipe and I only translated what was pertinent to the task at hand, Decca drivers.
http://www.diyaudio.com/forums/full-range/182858-anyone-built-decca-corner-horn-tqwp-3.html post 23 by Planet 10 has the original article as and PDF with all the measurements.
A more extended translation is on the way. The page is extracted from a series of articles about a Voigtpipe and I only translated what was pertinent to the task at hand, Decca drivers.
Picking suitable drivers for the Voigt-horn
Historically the drivers resonance frequency was used to select suitable drivers. At a time when compliance and moving mass for any given driver size was small that could be done. But now when you can get a 15" and 5" driver with the same resonance frequency, it is not useful.
Drives for tuned pipes should have the same characteristics as drivers for horns. A low moving mass and a high BL factor relative their mass, that is a low Q.
Fig 4 and 5 show the frequency response for two different drivers with similar Fr and Bl but the fig 4 is a high mass/low compliance (I think it refers to KEF B200 one of the high Q versions)
In fig 5 Peerless KP 825 WF is used. Several important factors can be read from the curves
1. The fundamental resonance of the pipe is unchanged by the different Mms and is at 50 Hz.
2. The Q of the pipe output (that does not coincide with the50 Hz dip) is higher for the high mass driver in fig 4A. At 50 Hz output is 10 dB below peak output. Compare with 5B where the output at 50 Hz has only dropped 2dB compared to peak output, due to better match between pipe and driver. In fig 4A the bad matching of radiation resistance is clear. Just above the fundamental there is peak in driver output and damping can only be seen at the harmonics. Compare with 5A where the pipe damp the driver all the way up to 200 Hz (suppress output by increasing radiation resistance up to 200 Hz).
The difference in sound quality is very clear at listening tests. With the loudspeaker fitted with the driver in fig 4 the bass is unclear with poor transient reproduction, high distortion and the driver tends to bottom out. On this star the KP825Wf was deemed suitable to be used to quite high standards in this construction. The driver in Fig4 was recommended in Seereo-HiFi nr 12 -75 and is a good driver but made for closed boxes.
JBL 2110 and LE8T were tried and gave far better results but due to cost reasons it was deemed less interesting for the general public so no further development was carried out. About 10 different drivers all with suitable characteristics were tried. finally the KP825WF was chosen due to low distortion, resistance to overload and low price.
The article series is about and update of an earlier construction. So "modern" driver is suggested, damping material and minor changes that could be introduced to an already built pipe and steps that does not require any measurement tools or more than two different kind of damping material.
As icing on the cake a TLS constructor well known in Sweden suggested that KEF B200 and filling the whole pipe with BAF was the way to go. The author B Börja disagreed and showd by measurements that that damping regime was not effective in reducing the 3rd harmonic and it also reduced the fundamental. Resulting in both a weak bass and boomy mid bass! A long exchange of letters to the magazine ensued…
Historically the drivers resonance frequency was used to select suitable drivers. At a time when compliance and moving mass for any given driver size was small that could be done. But now when you can get a 15" and 5" driver with the same resonance frequency, it is not useful.
Drives for tuned pipes should have the same characteristics as drivers for horns. A low moving mass and a high BL factor relative their mass, that is a low Q.
Fig 4 and 5 show the frequency response for two different drivers with similar Fr and Bl but the fig 4 is a high mass/low compliance (I think it refers to KEF B200 one of the high Q versions)
In fig 5 Peerless KP 825 WF is used. Several important factors can be read from the curves
1. The fundamental resonance of the pipe is unchanged by the different Mms and is at 50 Hz.
2. The Q of the pipe output (that does not coincide with the50 Hz dip) is higher for the high mass driver in fig 4A. At 50 Hz output is 10 dB below peak output. Compare with 5B where the output at 50 Hz has only dropped 2dB compared to peak output, due to better match between pipe and driver. In fig 4A the bad matching of radiation resistance is clear. Just above the fundamental there is peak in driver output and damping can only be seen at the harmonics. Compare with 5A where the pipe damp the driver all the way up to 200 Hz (suppress output by increasing radiation resistance up to 200 Hz).
The difference in sound quality is very clear at listening tests. With the loudspeaker fitted with the driver in fig 4 the bass is unclear with poor transient reproduction, high distortion and the driver tends to bottom out. On this star the KP825Wf was deemed suitable to be used to quite high standards in this construction. The driver in Fig4 was recommended in Seereo-HiFi nr 12 -75 and is a good driver but made for closed boxes.
JBL 2110 and LE8T were tried and gave far better results but due to cost reasons it was deemed less interesting for the general public so no further development was carried out. About 10 different drivers all with suitable characteristics were tried. finally the KP825WF was chosen due to low distortion, resistance to overload and low price.
The article series is about and update of an earlier construction. So "modern" driver is suggested, damping material and minor changes that could be introduced to an already built pipe and steps that does not require any measurement tools or more than two different kind of damping material.
As icing on the cake a TLS constructor well known in Sweden suggested that KEF B200 and filling the whole pipe with BAF was the way to go. The author B Börja disagreed and showd by measurements that that damping regime was not effective in reducing the 3rd harmonic and it also reduced the fundamental. Resulting in both a weak bass and boomy mid bass! A long exchange of letters to the magazine ensued…
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A new set of measurement of various pipe positions and parts of the pipe.
Black, brown and orange showes the Decca in a corner with the Microphone at the front, 10 cm inside the front and 10 cm inside the the side of the of the pipe. No difference between the microphone position. Green and Yellow is wall and floor position. +5dB at 3rd and 5th harmonics and +2-3 dB of 7th and 9th harmonic. So corner positions are good.
I then measured the response at 1 m distance at driver hight. Wall looks pretty good both with driver facing front and wall.
The corner measurement look the same but with a 5 dB lift below 300 Hz.
I then wanted to explore the effect of damping material, So I took two rolls of BAF 60 cm long 82 grams each and stuffed down in the closed end of the pipe on opposite sides of the brace below the driver. Then I added 38 gBAF evenely spread out between the driver and the brace, finaly 82 gram BAF mat cut into 3 parts were used to cover the ceiling, sidewalls and the backwall opposite the driver. I expected this to kill the harmonics, but not so, it did smooth the response and took some few dB off so at least it does not seem to harm the pipe output.
Bass is not everything, damping material will affect higher frequencies as well. So I measured near field response at the center of the small cone. Both with empty cabinet and filled as described above. I got different top end response between the two measurements, small changes in position is quite tricky here.
With an empty pipe there is a lot of ringing but evenly distributed both plotted in time domain and as periods.
Adding the BAF reduces the ringing substantially getting close to the resonances intrinsic to the driver.
So conclusions so far
1. The Decca gives good response down to 40 Hz and even without any damping material the harmonics are benign.
2. For the sake of mid and high range resonances and reflections behind the driver some damping material will be good.
3. The closed end of the pipe can be filled with 200-300 g of BAF without any harm done to the fundamenal it seems but it does not eliminate the residual harmonics.
I will continue the investigation but at a slower pace
Black, brown and orange showes the Decca in a corner with the Microphone at the front, 10 cm inside the front and 10 cm inside the the side of the of the pipe. No difference between the microphone position. Green and Yellow is wall and floor position. +5dB at 3rd and 5th harmonics and +2-3 dB of 7th and 9th harmonic. So corner positions are good.
I then measured the response at 1 m distance at driver hight. Wall looks pretty good both with driver facing front and wall.
The corner measurement look the same but with a 5 dB lift below 300 Hz.
I then wanted to explore the effect of damping material, So I took two rolls of BAF 60 cm long 82 grams each and stuffed down in the closed end of the pipe on opposite sides of the brace below the driver. Then I added 38 gBAF evenely spread out between the driver and the brace, finaly 82 gram BAF mat cut into 3 parts were used to cover the ceiling, sidewalls and the backwall opposite the driver. I expected this to kill the harmonics, but not so, it did smooth the response and took some few dB off so at least it does not seem to harm the pipe output.
Bass is not everything, damping material will affect higher frequencies as well. So I measured near field response at the center of the small cone. Both with empty cabinet and filled as described above. I got different top end response between the two measurements, small changes in position is quite tricky here.
With an empty pipe there is a lot of ringing but evenly distributed both plotted in time domain and as periods.
Adding the BAF reduces the ringing substantially getting close to the resonances intrinsic to the driver.
So conclusions so far
1. The Decca gives good response down to 40 Hz and even without any damping material the harmonics are benign.
2. For the sake of mid and high range resonances and reflections behind the driver some damping material will be good.
3. The closed end of the pipe can be filled with 200-300 g of BAF without any harm done to the fundamenal it seems but it does not eliminate the residual harmonics.
I will continue the investigation but at a slower pace
Dr Boar,
Another excellent study of yet another BLH speaker, as usual from you. Very well done! This speaker looks on paper that it will sound good, and I think your listening impressions confirm this. Now if I can only get around to figuring out what the CSA's are from the drawings in that how to build a Decca horn article... Model to come as soon as I do that and we can hopefully see if effect of placement of damping material and wall vs corner positions agree with measurements. Thanks for doing this detailed study.
Regards,
X
Another excellent study of yet another BLH speaker, as usual from you. Very well done! This speaker looks on paper that it will sound good, and I think your listening impressions confirm this. Now if I can only get around to figuring out what the CSA's are from the drawings in that how to build a Decca horn article... Model to come as soon as I do that and we can hopefully see if effect of placement of damping material and wall vs corner positions agree with measurements. Thanks for doing this detailed study.
Regards,
X
Thanks for those kind words!
I plan to cut a hole for a 10" and then make a extra panel for 8" as the cutout for the 8.5" 9710 fit few other drivers. With 8" drivers I have collection of drivers so I can test how Q and Fr interact with the pipe.
I might try some smaller variations in panel damping but I will not bother with changing the taper or relocate the opening to the back panel as it works well as it is!
I plan to cut a hole for a 10" and then make a extra panel for 8" as the cutout for the 8.5" 9710 fit few other drivers. With 8" drivers I have collection of drivers so I can test how Q and Fr interact with the pipe.
I might try some smaller variations in panel damping but I will not bother with changing the taper or relocate the opening to the back panel as it works well as it is!
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