Steve:
The port tunes the 9 liter box to 34 Hz. The size of the port does not matter, as long as it tunes the box to 34 Hz.
Since the Bandors, (understandably, considering their 2" size), have a high Fs, the graph should not surprise us. When Fb gets very low, the box output, impedance curve, etc. begins to resemble a closed box. Here, there is some difference in the outputs, but it is minor. F3 for the closed box is 80 Hz, for the vented box is 70 Hz.
The vented box does NOT show any effects the Quarter Wave action of the Port, (Line), which might well be there. Win ISD, (free version), does not chart or deal with Quarter Wave action.
The port tunes the 9 liter box to 34 Hz. The size of the port does not matter, as long as it tunes the box to 34 Hz.
Since the Bandors, (understandably, considering their 2" size), have a high Fs, the graph should not surprise us. When Fb gets very low, the box output, impedance curve, etc. begins to resemble a closed box. Here, there is some difference in the outputs, but it is minor. F3 for the closed box is 80 Hz, for the vented box is 70 Hz.
The vented box does NOT show any effects the Quarter Wave action of the Port, (Line), which might well be there. Win ISD, (free version), does not chart or deal with Quarter Wave action.
Attachments
Steve:
Can't help but notice that in the System IV's, the pipe resonance is about the same distance above Fb as it was in the Focal Dalines-about half an octave.
The Focal Dalines had a Line with a cross section about 1.7 times the cone area of the driver. The System IV's had a cross section about equal, according to Steve.
The Focal Daline has huge "dip" if you model it like a reflex and ignore any output increase from the Line. The System IV's seem to have a decent curve if you model it like reflex. That might be a big difference.
The Focal Daline might need a Line with a big cross section relative to the driver Sd in order to provide the extra "oomph" in the "dip" region around 40-250 Hz or so.
The System IV's have no such "dip" region. Perhaps that is why they can get away with a Line with a cross section that is comparatively smaller, (relative to the driver), than the Focal Dalines.
Just speculating here, folks.
I am going to try to locate some freeware that models pipe resonances. I think LspCAD for Adire might do it. If so, I will try to setup some modifications on Adire drivers, (they have a crossover modeling section) to see if I can finagle an Adire driver down to similar Qts's as the Focal Daline driver and the Bandor 2". If I can, then I can just scale the Vas's etc to get an equivalent.
Can't help but notice that in the System IV's, the pipe resonance is about the same distance above Fb as it was in the Focal Dalines-about half an octave.
The Focal Dalines had a Line with a cross section about 1.7 times the cone area of the driver. The System IV's had a cross section about equal, according to Steve.
The Focal Daline has huge "dip" if you model it like a reflex and ignore any output increase from the Line. The System IV's seem to have a decent curve if you model it like reflex. That might be a big difference.
The Focal Daline might need a Line with a big cross section relative to the driver Sd in order to provide the extra "oomph" in the "dip" region around 40-250 Hz or so.
The System IV's have no such "dip" region. Perhaps that is why they can get away with a Line with a cross section that is comparatively smaller, (relative to the driver), than the Focal Dalines.
Just speculating here, folks.
I am going to try to locate some freeware that models pipe resonances. I think LspCAD for Adire might do it. If so, I will try to setup some modifications on Adire drivers, (they have a crossover modeling section) to see if I can finagle an Adire driver down to similar Qts's as the Focal Daline driver and the Bandor 2". If I can, then I can just scale the Vas's etc to get an equivalent.
BAM said:
Bam:
Was that with one NSB or two? Actually, the box is so much bigger than the Vas of the speaker it probably does not matter.
Actually, Bam, your Qtc in the box is going to unaffected by the box volume much. So your Qtc ought to be close to the Qts of your NSB, wihich is 0.79. Tha Qtc for the top chamber of the System IV was 0.83,(very close), so you should be right on.
Also, Steve's Fs of the Bandor driver was 65 Hz. The Fc of his top chamber, (if it were sealed), would be around 97 Hz. Your Fc should be about 105 Hz, which is your Fs.
My guess would be to make a port, (Line) that is 56 inches long, (1/4 wave of 60 Hz), that tunes the line to 40 Hz. That would be my guesstimate.
Don't get nasty if comes out lousy. I am just trying to figure out by suppositions here.
Remember, the wavelength of 1 Hz = 13,500 inches. To find the Quarter Wavelength of 60 Hz, we go:
13,500 in ÷ 60 Hz ÷ 4 = 56.25 inches.
System IV measurements
I've managed to find some near-field measurement graphs of the System IV, which I've attached below.
The first graph is a near-field measurement of the System IV enclosure as a closed box.
The second graph is a near-field measurement of the System IV enclosure with the line open. The near-field measurement of the output from the line end has been added to this graph (although not summed because of the phase differences).
The reasons that there are discrepencies between these actual measurements and kelticwizard's calculations are:
1. I mistakenly stated the volume of the top chamber as 9 litres. In fact it was nearer 10 litres.
2. The driver specifications were for the latest Bandor 8 ohm drivers. There have been some changes and the specifications of the drivers used on the System IVs were slightly different.
As a result, it can be seen that the Qtc is somewhat lower than the 0.83 quoted by kelticwizard although perhaps not as low as the 0.6 that I had assumed.
Sorry for any confusion caused. I'm afraid that the 13 year gap has somewhat blunted my memory.
I've managed to find some near-field measurement graphs of the System IV, which I've attached below.
The first graph is a near-field measurement of the System IV enclosure as a closed box.
The second graph is a near-field measurement of the System IV enclosure with the line open. The near-field measurement of the output from the line end has been added to this graph (although not summed because of the phase differences).
The reasons that there are discrepencies between these actual measurements and kelticwizard's calculations are:
1. I mistakenly stated the volume of the top chamber as 9 litres. In fact it was nearer 10 litres.
2. The driver specifications were for the latest Bandor 8 ohm drivers. There have been some changes and the specifications of the drivers used on the System IVs were slightly different.
As a result, it can be seen that the Qtc is somewhat lower than the 0.83 quoted by kelticwizard although perhaps not as low as the 0.6 that I had assumed.
Sorry for any confusion caused. I'm afraid that the 13 year gap has somewhat blunted my memory.
Attachments
Steve:
The differences you mentioned probably do not amount to that much.
Checking Bandor's site, I see that you gave me the specs for the Type - 50AFSW/8. That is okay-I can work with that.
I have a different program to run these on. It is freeware, written by F4ier, a member here. It is Subwoofer Simulator, and it models many more curves. It is exact enough of a program, for instance, that it calculated the Bl prduct of the Bandor as being something less than 3, based on it's SPL.
http://www.geocities.com/f4ier/speaker.htm
One question: you don't have a frequency response chart for the System IV working together, do you? Like the typical SPL @ 1W/1M? It might not be entirely necessary, because I can get much info from your charts compared to Subwoofer Simulator, but it would be nice.
The differences you mentioned probably do not amount to that much.
Checking Bandor's site, I see that you gave me the specs for the Type - 50AFSW/8. That is okay-I can work with that.
I have a different program to run these on. It is freeware, written by F4ier, a member here. It is Subwoofer Simulator, and it models many more curves. It is exact enough of a program, for instance, that it calculated the Bl prduct of the Bandor as being something less than 3, based on it's SPL.
http://www.geocities.com/f4ier/speaker.htm
One question: you don't have a frequency response chart for the System IV working together, do you? Like the typical SPL @ 1W/1M? It might not be entirely necessary, because I can get much info from your charts compared to Subwoofer Simulator, but it would be nice.
So, I can model a ported box with a 56" line/port tuning the box to 40 Hz, with the quarter-wave action happening at 60 Hz or something like that, and probably get a decent result?
Or was that a sealed box with a Qtc generally around 0.8 and the 56" line stuck on that ? A 1.5 cubic-foot box yields a Qtc of exactly 0.8, and a 0.75 cubic foot box yields a Qtc of about 0.84.
I won't be too sad if it comes out wrong, because the drivers are only a buck, and pretty expendable. The drivers themselves are designed for use in a television, but much experimentation by resourceful DIYers have revealed their remarkable sonic qualities (light and airy in the midrange), and their easy application in DIY speaker designs. I can always take them out if the project is a total bomb and reuse them, but if the project comes out well, then anyone interested in the NSBs will have a unique project option.
The last thing to be worked out about the NSB-Dalines is that wonky crossover issue with the tweeter and woofer's center-to-center spacing. I would be willing to settle for a crossover point of about 8,000 Hz, but the Onkyo-Buyout (another PE phenomenon) mylar semi-dome tweeter element only goes down to 6,000 Hz.
Also, what do you think of having the second crossoverless NSB that fires to the rear and upward? Do you think it would add any enhancement or just sound dumb? I know a similar concept was used on the BD-Pipes, and I have read some decent reviews of those. Where these speakers will be placed, people won't be very able to sit down and listen to them, but they will be up and moving around the room. That is why I want to have the added ambience of the reflecting driver.
Or was that a sealed box with a Qtc generally around 0.8 and the 56" line stuck on that ? A 1.5 cubic-foot box yields a Qtc of exactly 0.8, and a 0.75 cubic foot box yields a Qtc of about 0.84.
I won't be too sad if it comes out wrong, because the drivers are only a buck, and pretty expendable. The drivers themselves are designed for use in a television, but much experimentation by resourceful DIYers have revealed their remarkable sonic qualities (light and airy in the midrange), and their easy application in DIY speaker designs. I can always take them out if the project is a total bomb and reuse them, but if the project comes out well, then anyone interested in the NSBs will have a unique project option.
The last thing to be worked out about the NSB-Dalines is that wonky crossover issue with the tweeter and woofer's center-to-center spacing. I would be willing to settle for a crossover point of about 8,000 Hz, but the Onkyo-Buyout (another PE phenomenon) mylar semi-dome tweeter element only goes down to 6,000 Hz.
Also, what do you think of having the second crossoverless NSB that fires to the rear and upward? Do you think it would add any enhancement or just sound dumb? I know a similar concept was used on the BD-Pipes, and I have read some decent reviews of those. Where these speakers will be placed, people won't be very able to sit down and listen to them, but they will be up and moving around the room. That is why I want to have the added ambience of the reflecting driver.
BAM:
I won't be able to model the pipe resonance part of the curve. My software only models the output due to the cone and the bass reflex action. As the Focal Daline kit 044 shows, under some circumstances the output from the pipe resonance can be substantial. To be commercially successful, the response curve on the Focal Daline has to be reasonably flat, and it is not-IF only the bass reflex action is modelled. The difference has to be the pipe resonance which I am unable to show. That is why the port in a Daline takes up more than half the internal volume!
As for the speaker on the back of the encloure pointed back and up-I say, "Why not?". With the output of the NSB going up fairly high, you won't miss the high range much. I do believe I have seen commercially produced speakers do the same thing. It is essentially a bipolar speaker, and those are highly rated.
I won't be able to model the pipe resonance part of the curve. My software only models the output due to the cone and the bass reflex action. As the Focal Daline kit 044 shows, under some circumstances the output from the pipe resonance can be substantial. To be commercially successful, the response curve on the Focal Daline has to be reasonably flat, and it is not-IF only the bass reflex action is modelled. The difference has to be the pipe resonance which I am unable to show. That is why the port in a Daline takes up more than half the internal volume!
As for the speaker on the back of the encloure pointed back and up-I say, "Why not?". With the output of the NSB going up fairly high, you won't miss the high range much. I do believe I have seen commercially produced speakers do the same thing. It is essentially a bipolar speaker, and those are highly rated.
Okay, guys, you are going to have to bear with me.
Subwoofer Simulator and the rest of the freeware normally does not model pipe resonances.
I am downloading Unibox. I am learning Unibox. Unibox might or might not model pipe resonances.
I am also thinking of downloading Martin King's Transmission Line program. The problem is finding a free version of MathCAD-he doesn't use Excel.
I wonder, does Martin L. King's program contain a way of modelling a chamber on top of the Transmission Line? For that is what a Daline is-a chamber on top of a Transmission Line.
I shall try Martin L. King's site and see what happens.
Subwoofer Simulator and the rest of the freeware normally does not model pipe resonances.
I am downloading Unibox. I am learning Unibox. Unibox might or might not model pipe resonances.
I am also thinking of downloading Martin King's Transmission Line program. The problem is finding a free version of MathCAD-he doesn't use Excel.
I wonder, does Martin L. King's program contain a way of modelling a chamber on top of the Transmission Line? For that is what a Daline is-a chamber on top of a Transmission Line.
I shall try Martin L. King's site and see what happens.
kelticwizard said:
Mathcad explorer (12 MB download thou)
http://sliunix.lanecc.edu/~jamies/mcexp802.exe
Martins model handles a daline with no problem. You need to use the sevtions version of the worksheet.
Martin also has the 1st of his alignment tables (each table has to restrict the lines geometry to work), which can get you in the ballpark real quickly (daline isn't covered in these yet)
dave
Hmm, just looking at the dwg. and knowing that BH5 reduces the cab Vb some, I get a net Vb = ~.229ft^3. The vent's effective size would be a constant ~2.5" x 6", and its base length as measured down the middle comes to 73". This wouldn't be its total acoustic length though since the inside height of the cab must be factored in. This adds ~12" to the length, or 85". Then there's the end correction, or ~0.618*((2.5*6)/pi)^0.5 = ~1.35". ~(13560/4)/86.35 = ~39.25Hz, so let's just say it's tuned ~ to Fs.
It has two 0.5mH inductors in series, so figure ~0.7ohms of series resistance using a large gauge, upping Qts to ~0.332 using the 5NV4211DB's published specs.
Plugging all this into BoxPlot for a basic alignment yields a T/S max flat 0.28ft^3 Vb/48.6Hz Fb. Shrinking it to 0.229ft^3/40.4Hz Fb, the acoustic response is a nice smooth/well damped roll off (no underdamped dip in the FR or peaking at Fb) beginning around 125Hz, with an F3 in the high 40s. Factor in the pipe effects and based on experience a F3 shift to 40hz with a bit more midbass output seems reasonable. If you're curious you can model it in MJK's excellent MLTQWT spreadsheet for a more accurate sim. BH5 really damps well, so I suggest using 1.0lb/ft^3 as an approximation and the driver's position should be listed as L*0.0853 for this design, which is the driver's distance from the top of the cab divided by the pipe's physical length (~7.25/85).
Anyway, looks like whoever designed this did themselves proud with this one, and assuming you accept my analysis, should give you enough insight to adapt it to other drivers.
HTH,
GM
Well, phooey! Decided to input this into MLTQWT and noticed I'd used 0.3 instead of 0.23 for Qes, skewing everything, so ignore my previous post.
It has two 0.5mH inductors in series, so figure ~0.7ohms of series resistance using a large gauge, upping Qts to ~0.26 using the 5NV4211DB's published specs.
Anyway, looks like whoever designed this did themselves proud with this one, and assuming you accept my analysis, should give you enough insight to adapt it to other drivers.
HTH,
GM
Addendum: plugging the numbers into the MLTQWT spreadsheet shows a typical resonant pipe that would be less so with damping in the vent pipe per the spec, F3 = ~33Hz, Fb = ~28Hz. It appears that what I considered a worst case scenario for how much the BH5 affects the dims turned out to be not conservative enough if the published specs and my assumption as to how much series resistance there is ~accurate.
Anyway, eschewing all this and calculating a Daline my way using the 0.26Qts and Fb = Fs, taking the max flat 0.13Vb and increasing it 1.414x I get a rear chamber of ~0.1837ft^3, or a ~golden ratio 11.03"h x 6.82"w x 4.21"d.. Maintaining the same driver vertical spacing, the woofer is 7.25"/11.03" = ~0.6573*L.
Using a pipe area = ~Sd equates to 13.423in^2/6.82" w = ~1.97" d.. Actual pipe length = ~13560"/4/40.4Hz = ~83.91"- 11.03" - (13.423/pi)^0.5 = ~70.81".
This sims F3 = ~35Hz, Fb = ~32Hz. Works for me. To get an F3 = 40Hz required the pipe to be shortened to 55", or a ~50hz 1/4WL, showing how much the Vb damps the pipe action.
Decided to input this into MLTQWT and noticed I'd used 0.3 instead of 0.23 for Qes, skewing everything, so ignore my previous post.Hmm, just looking at the dwg. and knowing that BH5 reduces the cab Vb some, I get a net Vb = ~.229ft^3. The vent's effective size would be a constant ~2.5" x 6" (~2.1851" radius), and its base length as measured down the middle comes to 73". This wouldn't be its total acoustic length though since the inside height of the cab must be factored in. This adds ~11" to the length, or 84". Then there's the end correction, or ~0.618*((2.5*6)/pi)^0.5 = ~1.35". ~(13560/4)/85.35 = ~39.71Hz, so let's just say it's tuned ~ to Fs.
It has two 0.5mH inductors in series, so figure ~0.7ohms of series resistance using a large gauge, upping Qts to ~0.26 using the 5NV4211DB's published specs.
Plugging all this into BoxPlot for a basic alignment yields a T/S max flat 0.13ft^3 Vb/61.2Hz Fb. Expanding it to 0.229ft^3/40.4Hz Fb, the acoustic response is a nice smooth/well damped roll off (no underdamped dip in the FR or peaking at Fb) beginning around 225Hz, with an F3 of 50hz. Factor in the pipe effects and based on experience a F3 shift to 40hz with a bit more midbass output seems reasonable. If you're curious you can model it in MJK's excellent MLTQWT spreadsheet for a more accurate sim. BH5 really damps well, so I suggest using 1.0lb/ft^3 as an approximation and the driver's position should be listed as L*0.5682 for this design, which is the driver's distance from the top of the cab (minus 1" for the BH5) divided by the chamber's net length, or ~6.25"/11".
Anyway, looks like whoever designed this did themselves proud with this one, and assuming you accept my analysis, should give you enough insight to adapt it to other drivers.
HTH,
GM
Addendum: plugging the numbers into the MLTQWT spreadsheet shows a typical resonant pipe that would be less so with damping in the vent pipe per the spec, F3 = ~33Hz, Fb = ~28Hz. It appears that what I considered a worst case scenario for how much the BH5 affects the dims turned out to be not conservative enough if the published specs and my assumption as to how much series resistance there is ~accurate.
Anyway, eschewing all this and calculating a Daline my way using the 0.26Qts and Fb = Fs, taking the max flat 0.13Vb and increasing it 1.414x I get a rear chamber of ~0.1837ft^3, or a ~golden ratio 11.03"h x 6.82"w x 4.21"d.. Maintaining the same driver vertical spacing, the woofer is 7.25"/11.03" = ~0.6573*L.
Using a pipe area = ~Sd equates to 13.423in^2/6.82" w = ~1.97" d.. Actual pipe length = ~13560"/4/40.4Hz = ~83.91"- 11.03" - (13.423/pi)^0.5 = ~70.81".
This sims F3 = ~35Hz, Fb = ~32Hz. Works for me.
To get an F3 = 40Hz required the pipe to be shortened to 55", or a ~50hz 1/4WL, showing how much the Vb damps the pipe action.GM said:
When looking at another drawing not done as cleanly as the above, I arrive with a Vb of .229 Ft³ as well. However, it turned out that the black, shaded blocks were made not of wood, but of Black Hole 5, a substance with which I am not familiar.
I looked up Black Hole 5, and it turned out to be an expensive "viscoelastic" substance similar to Rubatex and other pipe coverings, only more sophisticated, in some way. I decided to treat Black Hole 5 according to author David Weems' rule for damping materials such as polyfill, wool, etc. That is, squeeze the material in your fingers, and see how far it compresses. The compressed volume is what you consider the actual thickness. Well, I have some Rubatex here, I squeezed it, (very soft), and I had no trouble compressing 90% or more. I assume Black Hole 5 is similar. So I considered the actual thickness of Black Hole 5 essentially negligible, as I would polyfill.
Regardless of whether Black Hole 5 is like Rubatex or not, it is soft damping material and flexible. In your analysis, you are saying that two inches of Black Hole 5 on the walls is the same as 2 inches of wood. Without having used the product, I would tend to doubt that, although if that has been your experience with it, I wouldn't go against it. Similarly, using the same "Black Hole 5 = wood" principle, you reduced the line cross section from 3.5" x 5" to 2.5" x 5". Again, I cannot say with authority that is not the case, but I would like to know from someone who has used it that this soft, flexible rubber like product is to be treated the same as hard wood for the purpose of computing volume.
It seems to me that, on the Line/port, we are dealing with low frequencies, which have a penetrating power, and are much more likely to "see" a difference between a soft rubbery product and solid wood than higher frequencies will.
I measured the lengthof the Line in the following manner: When the Line came to a boundary and was about to do a 180º turn, I did not go all the way to the wall. Rather, I went halfway. For a 2.5" opening, I cut 1.25" off the length. Essentially, this is measuring down the middle. I have not built a Transmission Line, but certain books I have read on the matter said that is the way to go. Hence, my measurement will be shorter than yours. Again, if it has been your experience that to measure all the way to the end of the boundary, I won't oppose it. I just went by guidelines.
I don't see how Weems remark is valid WRT something like BH5, and I can only squeeze the foam portion enough to matter, so his 'test' for apparent density is way too 'flexible' to be of any use IMO. The BH5 I've used is 1.38" thick, and not knowing for sure how much to include as 'transparent' (I've only used it to damp metal panels in my convertible), took a 'leap of faith' that since the bends in the pipe were 2.5" in cross section that the 3.5" width with BH5 emulated this, so used 1" as an acoustic filler for all intent and purposes of calculating Vb. For sure, necking down the bends to create a series of shorter 1/4WL resonators would at best be a design of dubious tonal quality IMO, further 'proof' in my mind of the validity of my assumption.
One could argue that the rear chamber 'breathes' around Fb due to the sheer quantity used, making for a ~constant Vb regardless of pressure, but if it does, then the roll off would be more, further lowering the F3, and combined with the modest pressures the driver can generate, dismissed this as irrelevant for reverse engineering purposes. Same for the pipe since the BH5 'feels' the dominant pressure in shear, leaving the foam the major 'drag' on pipe action, with the balance of the BH5 damping the cab's construction.
Anyway, none of this was meant to imply that BH5 = wood.
WRT measuring a ~constant cross sectional area pipe, right, you measure down the middle, but I believe you forgot to include the bends in your calc..
GM
to be of any use IMO. The BH5 I've used is 1.38" thick, and not knowing for sure how much to include as 'transparent' (I've only used it to damp metal panels in my convertible), took a 'leap of faith' that since the bends in the pipe were 2.5" in cross section that the 3.5" width with BH5 emulated this, so used 1" as an acoustic filler for all intent and purposes of calculating Vb. For sure, necking down the bends to create a series of shorter 1/4WL resonators would at best be a design of dubious tonal quality IMO, further 'proof' in my mind of the validity of my assumption.One could argue that the rear chamber 'breathes' around Fb due to the sheer quantity used, making for a ~constant Vb regardless of pressure, but if it does, then the roll off would be more, further lowering the F3, and combined with the modest pressures the driver can generate, dismissed this as irrelevant for reverse engineering purposes. Same for the pipe since the BH5 'feels' the dominant pressure in shear, leaving the foam the major 'drag' on pipe action, with the balance of the BH5 damping the cab's construction.
Anyway, none of this was meant to imply that BH5 = wood.
WRT measuring a ~constant cross sectional area pipe, right, you measure down the middle, but I believe you forgot to include the bends in your calc..
GM
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