Aside from some opinions to the contrary, I wish to explore the use of a low Qts driver in a TL design. I solved the equations in the MJK's classic alignment tables document using the TS parameters for the Great Plains Audio 604H driver and here are the details:
So = 3.15 which makes the cross sectional area approximately 550 sq in. I also detuned from the driver resonance of 30Hz to 40Hz (I think I read somewhere that shifting the TL tuning 5-10 Hz smooths the response ripples?) to shorten the line to a little over 7 feet. I think the TL pipe volume is around 33 cu ft. How much different will this sound from a ~9 cu ft BR cabinet?
A 24" sonotube gives me about 450 sq in cross section so I have thought about using some. If I use the sonotube, will the 20% reduction in CSA adversely affect the system performance? The alternative is a box cab approx 18 x 29 x TL length (height).
What happens if I close down the open end some with a vent? Does this make it a 'mass loaded' TL? I gather there are some fuzzy differences between traditional BR cabs and MLTL designs. I have never seen many specifics regarding all the TL design variations.
I've seen the design on 6moons.com for the same speaker and it is much smaller than the solution I derived from the tables. I don't want to make the speaker any smaller unless it makes no difference.
Does this sound like a viable method to utilize this speaker?
So = 3.15 which makes the cross sectional area approximately 550 sq in. I also detuned from the driver resonance of 30Hz to 40Hz (I think I read somewhere that shifting the TL tuning 5-10 Hz smooths the response ripples?) to shorten the line to a little over 7 feet. I think the TL pipe volume is around 33 cu ft. How much different will this sound from a ~9 cu ft BR cabinet?
A 24" sonotube gives me about 450 sq in cross section so I have thought about using some. If I use the sonotube, will the 20% reduction in CSA adversely affect the system performance? The alternative is a box cab approx 18 x 29 x TL length (height).
What happens if I close down the open end some with a vent? Does this make it a 'mass loaded' TL? I gather there are some fuzzy differences between traditional BR cabs and MLTL designs. I have never seen many specifics regarding all the TL design variations.
I've seen the design on 6moons.com for the same speaker and it is much smaller than the solution I derived from the tables. I don't want to make the speaker any smaller unless it makes no difference.
Does this sound like a viable method to utilize this speaker?
Greets!
Well, it shifts them lower, so they are for a longer period, ergo requires more damping to quell, which I guess can be construed as to equate to smoother.
TLs are much more highly damped with a more IB-like response than BRs.
Reducing a TL's Vb just means it will have a higher F3 and lower Q roll off below it.
There's two ways to make a MLTL (aka tower or column speaker), either by sticking a vent in the terminus or using a high aspect ratio TQWT (aka TQWP) to 'neck' it down to the vent area.
A bit more than 'fuzzy'. A BR alignment assumes the internal air mass has a uniform particle density, but it morphs to a 1/4 WL resonator with increasing height to CSA (cross sectional area = width x depth) ratio.
The 6moons speaker is a MLTL designed to be flush with a rear wall and is a truncated version of the much larger floor standing one I normally recommend. As such it needs the wall/floor boundary gain to somewhat offset the loss of LF gain BW and driven with a high output impedance to round it out. IOW a classic vintage alignment. What was once old is yet new again.
Anyway, the beauty of a low Fs, Qts driver is its tuning flexibility for a wide range of alignments, so what are your performance goals and how big can you tolerate?
GM
Well, it shifts them lower, so they are for a longer period, ergo requires more damping to quell, which I guess can be construed as to equate to smoother.
TLs are much more highly damped with a more IB-like response than BRs.
Reducing a TL's Vb just means it will have a higher F3 and lower Q roll off below it.
There's two ways to make a MLTL (aka tower or column speaker), either by sticking a vent in the terminus or using a high aspect ratio TQWT (aka TQWP) to 'neck' it down to the vent area.
A bit more than 'fuzzy'.
A BR alignment assumes the internal air mass has a uniform particle density, but it morphs to a 1/4 WL resonator with increasing height to CSA (cross sectional area = width x depth) ratio. The 6moons speaker is a MLTL designed to be flush with a rear wall and is a truncated version of the much larger floor standing one I normally recommend. As such it needs the wall/floor boundary gain to somewhat offset the loss of LF gain BW and driven with a high output impedance to round it out. IOW a classic vintage alignment. What was once old is yet new again.
Anyway, the beauty of a low Fs, Qts driver is its tuning flexibility for a wide range of alignments, so what are your performance goals and how big can you tolerate?
GM
Thanks for the reply, GM. I want maximum performance and I am fortunate to be able to accomodate something sick in size. I recently bought Mathcad and have Martin's worksheets and have discovered the original So figure I came up with a little off. I used one of the worksheet to calculate BI based on other TS parameters and came up with a slightly revised figure. As it turns out, the cross section of the 24" sonotube is exactly (to 1 cm^) the value of So*Sd so that alone is driving me towards the ML TQWT design using the 24"sonotube. Not to mention the quest for real bass.
The 30Hz tube length (112" less 5") models response out to 20Hz but it is a little bumpy (+/- 2.5db) around 80 - 200 Hz. I then shortened the tube to 60" for a 50Hz tuning and it goes to 30Hz and is pretty smooth through the intended range (<1500Hz). The TL impedance curve (2 peaks at resonance) straddle the IB impedance curve pretty evenly with the 50Hz pipe. With the 30Hz line, the higher TL resonance lines up almost evenly with the IB peak. Shouldn't the IB peak bisect the TL peaks? I think I have noticed other designs meeting this condition.
As far as the bumpy response region for the 30Hz pipe, I suppose I could tweak the driver placement and maybe play around with the port dimensions to fix the response. I achieved a better curve, albeit not going as low, by de-tuning the pipe a little upward in frequency. I would like to keep experimentation confined to the simulations and do the build once right the first time.
Comments graciously accepted.
The 30Hz tube length (112" less 5") models response out to 20Hz but it is a little bumpy (+/- 2.5db) around 80 - 200 Hz. I then shortened the tube to 60" for a 50Hz tuning and it goes to 30Hz and is pretty smooth through the intended range (<1500Hz). The TL impedance curve (2 peaks at resonance) straddle the IB impedance curve pretty evenly with the 50Hz pipe. With the 30Hz line, the higher TL resonance lines up almost evenly with the IB peak. Shouldn't the IB peak bisect the TL peaks? I think I have noticed other designs meeting this condition.
As far as the bumpy response region for the 30Hz pipe, I suppose I could tweak the driver placement and maybe play around with the port dimensions to fix the response. I achieved a better curve, albeit not going as low, by de-tuning the pipe a little upward in frequency. I would like to keep experimentation confined to the simulations and do the build once right the first time.
Comments graciously accepted.
Greets!
You're welcome!
Hmm, apparently we're working with different specs since using Altec's I get a ~540.639"^2 SO/SL (~26.237" diameter) for a 30 Hz Fp. Even with GPA's series II specs I get ~489.402"^2/24.962", so are you using measured specs? Regardless, I'm curious how you plan to adapt a Sonotube to an offset driver layout or why you would even want to.
The theoretical ideal is to ~completely damp the driver's Fs peak, so Fp = Fs/Qts in a heavily stuffed end loaded pipe, ergo with a low Fs, Qts driver this limits it to a mid-bass alignment. For tuning around Fs, it doesn't matter whether you damp the impedance peak or not with a very low output impedance, but with a high output impedance you typically want the Fs peak to damp the upper TL or MLTL peak, so that the amp 'feels' the twin peaks for best LF gain and why a low power SET tube amp can to some extent perform like a much more powerful SS amp.
Anyway, most folks seem to prefer speakers with plenty of mid-bass 'slam', so short of building a large BLH, this means either a high Fb (Fp) or an under-damped alignment. Some of us prefer a more IB-like response except with gain, so a tuning at/below Fs in a MLTL or TQWT cab that has at least a Vb = Vas since this is what the driver wants to 'feel', then use selective damping to quell any Fb (Fp) peaking.
Bottom line, unless you know exactly how the driver will perform in various alignments in your room and how it should look in a sim, you may not be able to 'build once right the first time'.
GM
You're welcome!
Hmm, apparently we're working with different specs since using Altec's I get a ~540.639"^2 SO/SL (~26.237" diameter) for a 30 Hz Fp. Even with GPA's series II specs I get ~489.402"^2/24.962", so are you using measured specs? Regardless, I'm curious how you plan to adapt a Sonotube to an offset driver layout or why you would even want to.
The theoretical ideal is to ~completely damp the driver's Fs peak, so Fp = Fs/Qts in a heavily stuffed end loaded pipe, ergo with a low Fs, Qts driver this limits it to a mid-bass alignment. For tuning around Fs, it doesn't matter whether you damp the impedance peak or not with a very low output impedance, but with a high output impedance you typically want the Fs peak to damp the upper TL or MLTL peak, so that the amp 'feels' the twin peaks for best LF gain and why a low power SET tube amp can to some extent perform like a much more powerful SS amp.
Anyway, most folks seem to prefer speakers with plenty of mid-bass 'slam', so short of building a large BLH, this means either a high Fb (Fp) or an under-damped alignment. Some of us prefer a more IB-like response except with gain, so a tuning at/below Fs in a MLTL or TQWT cab that has at least a Vb = Vas since this is what the driver wants to 'feel', then use selective damping to quell any Fb (Fp) peaking.
Bottom line, unless you know exactly how the driver will perform in various alignments in your room and how it should look in a sim, you may not be able to 'build once right the first time'.
GM
I am using the provided TS parameters from GPA. I didn't have a BI parameter and took a stab at it using an Altec figure, around 16 or so. Thats where I came up with the original 550 sq in So. I used the TS consistency check BI worksheet to derive the BI parameter from the others. Here are the driver parameters I am using:
Re = 6.8 Ohms
Qmd = 8.49
Qed = .270
Qtd = .262
Vad = 16.35 cu ft
Vd = 19.20 cu in
Fs = 30Hz
Sd = .113 cu meter (~175 cu in)
Those are all the parameters I have for the GPA driver. Using those parameters with the consistency worksheet, I came up with a value of 23.171 for BI. This made the So figure more like 452 sq in.
I imagine the actual measured driver parameters would probably be a little different and would be more suitable for inclusion in the models. Assuming the parameters solve the CSA larger than the 24" sonotube, scrap the idea? What if somehow the CSA does work for the sonotube, scrap anyway? What are the problems you see with using the sonotube?
The sonotube seemed like a good idea based on some other designs I have run across. I was going to mount the driver on a baffle/coupler into the side of the tube at a suitable offset. I suppose I need to be careful about any transitional CS from the driver baffle/coupler to the pipe. I guess there is only one way to find out. Also I was thinking of turning the whole thing 'upside down' with the vent at the top of the pipe and the driver situated at about 35" off the floor. I don't see a problem with this except I loose the port coupling with the floor. A sonotube seems like a ready-made enclosure of the proper dimensions and is relatively inexpensive. A similar wooden cabinet would be much more complicated for a test of the design. I would like to prove/disprove the concept before moving too far ahead.
If I am reading you right I shouldn't tune the line higher than Fs of the driver but right at or below Fs. Is this right?
What I want from whatever design I end up with is a cabinet that extracts every bit of performance possible from the driver. I like my bass clean and tight and real. I don't want 2nd harmonics 'masquerading' as fundamental frequencies.
I have some UREI 809 12" coaxial monitors and they sound excellent except they are missing the lowest octave, at least. They are the baby to the 813 monitor which used some additional 15" woofers to help out the low end, all in a 10 cu ft or so BR cab. I would do a BR but I've heard that TL is the way to go for better transient response and so on.
What would you do to best accomodate these drivers? Why or why not sonotube? A wooden cabinet 104 inches tall? Scaled down? I thought I was on to something.
Re = 6.8 Ohms
Qmd = 8.49
Qed = .270
Qtd = .262
Vad = 16.35 cu ft
Vd = 19.20 cu in
Fs = 30Hz
Sd = .113 cu meter (~175 cu in)
Those are all the parameters I have for the GPA driver. Using those parameters with the consistency worksheet, I came up with a value of 23.171 for BI. This made the So figure more like 452 sq in.
I imagine the actual measured driver parameters would probably be a little different and would be more suitable for inclusion in the models. Assuming the parameters solve the CSA larger than the 24" sonotube, scrap the idea? What if somehow the CSA does work for the sonotube, scrap anyway? What are the problems you see with using the sonotube?
The sonotube seemed like a good idea based on some other designs I have run across. I was going to mount the driver on a baffle/coupler into the side of the tube at a suitable offset. I suppose I need to be careful about any transitional CS from the driver baffle/coupler to the pipe. I guess there is only one way to find out. Also I was thinking of turning the whole thing 'upside down' with the vent at the top of the pipe and the driver situated at about 35" off the floor. I don't see a problem with this except I loose the port coupling with the floor. A sonotube seems like a ready-made enclosure of the proper dimensions and is relatively inexpensive. A similar wooden cabinet would be much more complicated for a test of the design. I would like to prove/disprove the concept before moving too far ahead.
If I am reading you right I shouldn't tune the line higher than Fs of the driver but right at or below Fs. Is this right?
What I want from whatever design I end up with is a cabinet that extracts every bit of performance possible from the driver. I like my bass clean and tight and real. I don't want 2nd harmonics 'masquerading' as fundamental frequencies.
I have some UREI 809 12" coaxial monitors and they sound excellent except they are missing the lowest octave, at least. They are the baby to the 813 monitor which used some additional 15" woofers to help out the low end, all in a 10 cu ft or so BR cab. I would do a BR but I've heard that TL is the way to go for better transient response and so on.
What would you do to best accomodate these drivers? Why or why not sonotube? A wooden cabinet 104 inches tall? Scaled down? I thought I was on to something.
I forgot to mention that I have built some Linkwitz Phoenix speakers recently and they sound very good. I am most impressed with the low end and smooth, no holes response. They seem quite accurate and I am pretty well satisfied, but there is something missing. It doesn't quite have the life-like quality coming from them as the UREI's being driven with Transcendent Sound's Beast OTL amplifiers. The UREI's driven with an SS amp is good, but nothing like the OTL tubes. I haven't tried the Phoenix panel with the OTL as I only have two channels (two monoblocks). I don't think that would get me there.
This UREI-TS combo reproduces the timbre of instruments and voices so realistically it is startling. I am not quite sure what it is but I like it. You know it when you hear it. Over the last 35 years or so I've listened to Altec, JBL, Klipsch, Advent, Martin Logan, Tannoy (not co-ax) in short a lot of speakers. I like the sound of a coaxial driver. Whatever other problems they may have, phase coherency and 'imaging' isn't one of them.
This is why I want to build something around the 604 coaxial driver and I would like to keep the design to just the single 604 per side and no subs, etc. Fewer problems. Given I am using the sole 15" driver, I am trying to squeeze every drop of bass performance possible.
What say you?
This UREI-TS combo reproduces the timbre of instruments and voices so realistically it is startling. I am not quite sure what it is but I like it. You know it when you hear it. Over the last 35 years or so I've listened to Altec, JBL, Klipsch, Advent, Martin Logan, Tannoy (not co-ax) in short a lot of speakers. I like the sound of a coaxial driver. Whatever other problems they may have, phase coherency and 'imaging' isn't one of them.
This is why I want to build something around the 604 coaxial driver and I would like to keep the design to just the single 604 per side and no subs, etc. Fewer problems. Given I am using the sole 15" driver, I am trying to squeeze every drop of bass performance possible.
What say you?
Greets!
When the info is available, Sd can be accurately calc'd by Vd/Xmax = 19.2"^3/0.2 = 96"^2 (~619.354 cm^2), then:
B*L = 0.0001*SQRT((rho*(c*0.0001)^2*Sd^2*Re)/((2*PI*Fs)*(Vas*0.001)*Qes))
where:
rho = 1.21 kg/m^3
c = 342 m/sec
Sd = cm^2
Vas = liters
B*L = 12.333 N/A
Otherwise, you estimate Sd as best you can, then:
Cms = Vas/(Sd^2*rho*c^2)
where:
Vas is in m^3 (liters*0.001)
Sd is in cm^2
c is in meters/sec*0.0001 to get Cms in mm/N
then:
Mms = 1/((2*pi*Fs)^2*Cms)
BL = SQRT((2*Pi*Fs*Re*Mms)/Qes)
GM
When the info is available, Sd can be accurately calc'd by Vd/Xmax = 19.2"^3/0.2 = 96"^2 (~619.354 cm^2), then:
B*L = 0.0001*SQRT((rho*(c*0.0001)^2*Sd^2*Re)/((2*PI*Fs)*(Vas*0.001)*Qes))
where:
rho = 1.21 kg/m^3
c = 342 m/sec
Sd = cm^2
Vas = liters
B*L = 12.333 N/A
Otherwise, you estimate Sd as best you can, then:
Cms = Vas/(Sd^2*rho*c^2)
where:
Vas is in m^3 (liters*0.001)
Sd is in cm^2
c is in meters/sec*0.0001 to get Cms in mm/N
then:
Mms = 1/((2*pi*Fs)^2*Cms)
BL = SQRT((2*Pi*Fs*Re*Mms)/Qes)
GM
GM, I get a little confused sometimes with the nomenclature, i.e. Mathcad vs traditional. Sd as I mean to communicate it is the surface area of the driver cone, not the displacement. I think GPA specifies the displacement with the term Vd. My bad with respect to specifying cu in.
What about the other questions?
What about the other questions?
Greets part deux!
Well, 'Sd' is the driver's *effective* piston area, which is much reduced in a coax, particularly a horn loaded one. 'Vd' is the driver's swept volume displacement at Xmax, both being standard nomenclature/definitions that pre-date T/S, though not common in the DIY community's lexicon before then AFAIK.
I'm working on it, I just copied this info from one of my previous posts on the subject to give you something to work with in the meantime. I do what I can when I can and if I'm not fast enough, then feel free to search all the forums that me, MJK, Scott, Bob Brines and others have helped folks with pipe, etc. design on.
GM
Well, 'Sd' is the driver's *effective* piston area, which is much reduced in a coax, particularly a horn loaded one. 'Vd' is the driver's swept volume displacement at Xmax, both being standard nomenclature/definitions that pre-date T/S, though not common in the DIY community's lexicon before then AFAIK.
I'm working on it, I just copied this info from one of my previous posts on the subject to give you something to work with in the meantime. I do what I can when I can and if I'm not fast enough, then feel free to search all the forums that me, MJK, Scott, Bob Brines and others have helped folks with pipe, etc. design on.
GM
I didn't intend to sound impatient. I am grateful that you are taking time to work on some of my questions for me.
With respect to cone area in the coax, I understand that the HF horn on the front side will cause some stopping down of the open piston area, but isn't the back of the cone pretty much like any other speaker? I suppose whatever is 'loading' the front transfers to some degree to the back as it is just two opposite sides of the same membrane.
Thanks for your replies.
With respect to cone area in the coax, I understand that the HF horn on the front side will cause some stopping down of the open piston area, but isn't the back of the cone pretty much like any other speaker? I suppose whatever is 'loading' the front transfers to some degree to the back as it is just two opposite sides of the same membrane.
Thanks for your replies.
Greets part tres!
Yeah, measured specs will be different, but manufacturer's specs tend to be much more accurate than they once were and since you're not trying to see how small a cab you can get away with, the variance should be swamped by the cab's Vb.
Sonotubes are fine for end loaded subs where you have end plates and you could of course build an adapter or short square box to mount the tubes to, ditto for the bend, but they work best in compression, so you'll need to run some all-thread to tension them. Keep in mind the driver's weight too, 34 lbs is a lot to hang off the side of even a tensioned 24" dia. Sonotube. To me, a basic rectangular wooden tube divided by an internal baffle/brace (IOW folded) is by far the easiest to construct and considering the cost of 24" Sonotube, probably cheaper to boot assuming you already have the basic woodworking tools.
At/below Fs tuning is my preference for MLTLs, MLhorns, TQWTs for most drivers. For TLs, it depends on the driver, app.
To get the max out of this driver requires a BLH so large it's not really viable for a stereo pair in a typical room, but if you're fortunate enough to have a small theater.......... Otherwise, at this point you're better off putting it in a relatively small sealed cab and XO it to a mono woofer horn that can be folded up to load from floor to ceiling between the mains.
Assuming no room this large, a low tuned MLTL or MLhorn has the best trade-offs IMO, though with such a low Qts some form of EQ is required if not corner loaded, otherwise the higher harmonics will be as loud or louder than the fundamental, though the sound will be very 'tight' (over-damped) rather than the 'boomy' mid-bass of a too small cab (under-damped).
GM
Yeah, measured specs will be different, but manufacturer's specs tend to be much more accurate than they once were and since you're not trying to see how small a cab you can get away with, the variance should be swamped by the cab's Vb.
Sonotubes are fine for end loaded subs where you have end plates and you could of course build an adapter or short square box to mount the tubes to, ditto for the bend, but they work best in compression, so you'll need to run some all-thread to tension them. Keep in mind the driver's weight too, 34 lbs is a lot to hang off the side of even a tensioned 24" dia. Sonotube. To me, a basic rectangular wooden tube divided by an internal baffle/brace (IOW folded) is by far the easiest to construct and considering the cost of 24" Sonotube, probably cheaper to boot assuming you already have the basic woodworking tools.
At/below Fs tuning is my preference for MLTLs, MLhorns, TQWTs for most drivers. For TLs, it depends on the driver, app.
To get the max out of this driver requires a BLH so large it's not really viable for a stereo pair in a typical room, but if you're fortunate enough to have a small theater..........
Otherwise, at this point you're better off putting it in a relatively small sealed cab and XO it to a mono woofer horn that can be folded up to load from floor to ceiling between the mains. Assuming no room this large, a low tuned MLTL or MLhorn has the best trade-offs IMO, though with such a low Qts some form of EQ is required if not corner loaded, otherwise the higher harmonics will be as loud or louder than the fundamental, though the sound will be very 'tight' (over-damped) rather than the 'boomy' mid-bass of a too small cab (under-damped).
GM
cesout said:
Greets!
Understood, though a properly aligned two way will sound like a co-ax if you have a large enough room to sit outside its near-field. A larger horn in the 604 to get the XO point lower is the best of both worlds IMO, but goes well beyond the casual DIYer's knowledge/skill/tools and of course voids any driver warranty.
Still, if you don't have rigid corners and plenty of room gain down low to help with the near IB response of a low tuned MLTL, etc., either a much higher tuned TL (no bass of note) or adding a helper woofer rolled off as needed is required otherwise it will sound even 'thinner' overall than the short TL.
GM
You put a little work in to your responses and I appreciate that very much. I'm with you on the sonotube though it seemed like a viable option at the time. I have some experience with wooden cabinet construction so I'll go with that.
So you are saying put it in a closed box? What do you consider to be the best damping/alignment? .5? .7? I have also considered a large open baffle 48" wide x 80" tall and sacrifice some bass for the sonics of OB design. So much to consider.
So you are saying put it in a closed box? What do you consider to be the best damping/alignment? .5? .7? I have also considered a large open baffle 48" wide x 80" tall and sacrifice some bass for the sonics of OB design. So much to consider.
OK. Lets just say I have a theater sized room and space is not a consideration. Let's say there are 18 foot ceilings and the overall room dimensions are 75 x 60. What size TL (or variant) would you consider adequate for these drivers? If driver Fs is 30 Hz, what F should the TL be tuned? 25? 20? Is there a particular offset from Fs that works best? I suppose to design the entire system not only do the box characteristics need to be sympathetic to the driver, but the box/driver combo should be sympathetic to the room as well. Obviously a commerical venture cannot build speakers according to each particular room they will be in, but as a DIY'er I can do that.
I still like the idea of doing some kind of TL for this speaker as it seems to provide the low end characteristics I want (I think). A friend of mine mentioned the BIB design and from what I can tell is a folded transmission line with an expanding cross section from throat to the mouth. Does this also qualify as a BLH design? Where does one draw the line when many are hybrid designs?
Anyway, the BIB has a 1.414:1 depth to width ratio and the cabinet hieght is 1/2 times the 1/4 wavelength of choice. Playing with some numbers a cabinet tuned to 20 Hz makes it a little over 7 feet tall. It makes for a fairly good sized box, overall. These will easily fit in the space I have. Anecdotal commentary indicates they "seem to work well, albeit not sure how or why". Huh?
I have been proportioning dimensions and driver placement based on the 'golden' ratio of 1.618 or .618 for my designs. I notice some designs using other ratios that are different. An example is an open baffle design with a 1:0.8181 ratio. The IEC standard baffle is based on this ratio. I have played around with the OB worksheets and by altering baffle size, dimension ratios, and driver placement I can get some wildly different response curves. Certain ratios clearly work better than others. I fully appreciate the concept of spreading the 'nasties' around rather than allowing them to clump together. One iteration caused about a 12db dip around 700Hz and by moving the driver placement it completely disappeared. I am grateful for simulation software but maybe not as grateful as a test pilot would be.
All that is leading to this question: Is the 1.414 ratio in the BIB design integral to it's performance or might some improvement be made by altering this? I'm making the assumption that the ratios at the turn (a=b=c=D/2) remain the same. I don't think the MJK worksheets model the CSA dimensional ratios (if at all) in the same way as it does the CSA expansion along the line length. Alterations to these dimensions cause no changes in response curves as long as the CSA is the same (at least to my recollection).
I'm going back to mathcad to model that closed box you mentioned...
I still like the idea of doing some kind of TL for this speaker as it seems to provide the low end characteristics I want (I think). A friend of mine mentioned the BIB design and from what I can tell is a folded transmission line with an expanding cross section from throat to the mouth. Does this also qualify as a BLH design? Where does one draw the line when many are hybrid designs?
Anyway, the BIB has a 1.414:1 depth to width ratio and the cabinet hieght is 1/2 times the 1/4 wavelength of choice. Playing with some numbers a cabinet tuned to 20 Hz makes it a little over 7 feet tall. It makes for a fairly good sized box, overall. These will easily fit in the space I have. Anecdotal commentary indicates they "seem to work well, albeit not sure how or why". Huh?
I have been proportioning dimensions and driver placement based on the 'golden' ratio of 1.618 or .618 for my designs. I notice some designs using other ratios that are different. An example is an open baffle design with a 1:0.8181 ratio. The IEC standard baffle is based on this ratio. I have played around with the OB worksheets and by altering baffle size, dimension ratios, and driver placement I can get some wildly different response curves. Certain ratios clearly work better than others. I fully appreciate the concept of spreading the 'nasties' around rather than allowing them to clump together. One iteration caused about a 12db dip around 700Hz and by moving the driver placement it completely disappeared. I am grateful for simulation software but maybe not as grateful as a test pilot would be.
All that is leading to this question: Is the 1.414 ratio in the BIB design integral to it's performance or might some improvement be made by altering this? I'm making the assumption that the ratios at the turn (a=b=c=D/2) remain the same. I don't think the MJK worksheets model the CSA dimensional ratios (if at all) in the same way as it does the CSA expansion along the line length. Alterations to these dimensions cause no changes in response curves as long as the CSA is the same (at least to my recollection).
I'm going back to mathcad to model that closed box you mentioned...
Greets!
You're welcome! More than a little actually, but the extra effort is mostly due to my abysmal short term memory.
Sealed is one option. 'Best' alignment depends on the XO point/slope used, but if you put it in a ~3 ft^3 or less cab no high pass is required, improving transient response, though large OB is probably a better option overall. It looks like it only needs to be ~2000"^2 if sitting on and perpendicular to a rigid floor as either alignment will definitely need a sub system to realize all the 604's lower mids - up performance.
GM
You're welcome! More than a little actually, but the extra effort is mostly due to my abysmal short term memory.
Sealed is one option. 'Best' alignment depends on the XO point/slope used, but if you put it in a ~3 ft^3 or less cab no high pass is required, improving transient response, though large OB is probably a better option overall. It looks like it only needs to be ~2000"^2 if sitting on and perpendicular to a rigid floor as either alignment will definitely need a sub system to realize all the 604's lower mids - up performance.
GM
Thanks for the reply.
I played around with some closed box designs and now I am making the connection between box alignment and box size based on driver parameters. A box with a Q of .5 works out to about 2.85 cu ft which is much smaller than I would have expected. This driver is bordering on being an acoustic suspension speaker, huh? The air is providing more spring than the driver suspension. You are absolutely correct that the closed box design will keep the driver 'between the ditches' and actually produces the best overall characteristics vs the other options. That is except the OB design. The box beats it in the low end by a few Hz and a few db but in either case some additional low frequency augmentation is clearly in order. The benefits of (large) OB vs the minimal tradeoff in low end make OB a no brainer to me.
The older Altec cabinets intended for this driver were around 9-10 cu ft and used a reflex vent. I've modled the same type of box with these drivers and it is ugly. I suspect the Qts of the earlier drivers were significantly higher? I don't have an old system I can reverse engineer. The UREI 811 used a single 15" in a vented box of about 5-6 cu ft. So it would appear there were significant variation between drivers, or they just willy-nilly slapped some stuff together.
I guess I'll make the OB panels and get it all set up in the room and make some measurements to figure out the low end fix. I don't need sound effects but I would like to reproduce pipe organ, piano, and double bass fundamentals.
BTW, you mentioned a smaller panel (2000 in^2) doing the job and I derived a 57x35 panel. I'll see how that compares to the larger one in the model. What is your basis for this suggestion? I would situate the larger one exactly as you indicated. I so happen to have some 3/4 13 ply BB plywood that is 60"x60" and would work nicely if the smaller panel does the job.
I'm going to use a passive crossover design specific to the drivers for now. There were several iterations of crossover for this driver, but as the years went on they got better. The UREI's incorporated the 'Time Aligned' crossover which corrected the phase differences to the extent the speaker could accurately reproduce square waves. Not an easy feat. This crossover is phase corrected and should work just fine. If I decide to bi-amp at some point I'll need more amplifiers (Beast OTL), and discrete tube crossover. $Ouch$.
Since the sub needs to cover only about two octaves, a higher Qts driver seems to make sense. A narrow bandpass filter, basically. I seems like a good design would create the optimum bandpass acoustically, if possible. Then again, a tuned (resonant) design may introduce some phase and transient response issues I would rather avoid. I want the extreme low end to be as accurate as possible as well.
I like the way a dipole sub (Linkwitz Phoenix as example) works in a room, fewer interactions and smoother overall response. I may need to create a W frame sub 'stack' (quad 18" or 21" - lets move some air). If the single sub driver is 10db less sensitive than 604, I just use 4 in parallel which should give me 12 db more output. Something like that. Of course I'll sum LR and correct 6db otv slope before hitting the (2KW ?) amp. I'll most likely situate the sub between the OB panels.
I'm going to test some ideas about the sub cabinet options with the models and see what I come up with.
I think I may be getting somewhere.
I played around with some closed box designs and now I am making the connection between box alignment and box size based on driver parameters. A box with a Q of .5 works out to about 2.85 cu ft which is much smaller than I would have expected. This driver is bordering on being an acoustic suspension speaker, huh? The air is providing more spring than the driver suspension. You are absolutely correct that the closed box design will keep the driver 'between the ditches' and actually produces the best overall characteristics vs the other options. That is except the OB design. The box beats it in the low end by a few Hz and a few db but in either case some additional low frequency augmentation is clearly in order. The benefits of (large) OB vs the minimal tradeoff in low end make OB a no brainer to me.
The older Altec cabinets intended for this driver were around 9-10 cu ft and used a reflex vent. I've modled the same type of box with these drivers and it is ugly. I suspect the Qts of the earlier drivers were significantly higher? I don't have an old system I can reverse engineer. The UREI 811 used a single 15" in a vented box of about 5-6 cu ft. So it would appear there were significant variation between drivers, or they just willy-nilly slapped some stuff together.
I guess I'll make the OB panels and get it all set up in the room and make some measurements to figure out the low end fix. I don't need sound effects but I would like to reproduce pipe organ, piano, and double bass fundamentals.
BTW, you mentioned a smaller panel (2000 in^2) doing the job and I derived a 57x35 panel. I'll see how that compares to the larger one in the model. What is your basis for this suggestion? I would situate the larger one exactly as you indicated. I so happen to have some 3/4 13 ply BB plywood that is 60"x60" and would work nicely if the smaller panel does the job.
I'm going to use a passive crossover design specific to the drivers for now. There were several iterations of crossover for this driver, but as the years went on they got better. The UREI's incorporated the 'Time Aligned' crossover which corrected the phase differences to the extent the speaker could accurately reproduce square waves. Not an easy feat. This crossover is phase corrected and should work just fine. If I decide to bi-amp at some point I'll need more amplifiers (Beast OTL), and discrete tube crossover. $Ouch$.
Since the sub needs to cover only about two octaves, a higher Qts driver seems to make sense. A narrow bandpass filter, basically. I seems like a good design would create the optimum bandpass acoustically, if possible. Then again, a tuned (resonant) design may introduce some phase and transient response issues I would rather avoid. I want the extreme low end to be as accurate as possible as well.
I like the way a dipole sub (Linkwitz Phoenix as example) works in a room, fewer interactions and smoother overall response. I may need to create a W frame sub 'stack' (quad 18" or 21" - lets move some air). If the single sub driver is 10db less sensitive than 604, I just use 4 in parallel which should give me 12 db more output. Something like that. Of course I'll sum LR and correct 6db otv slope before hitting the (2KW ?) amp. I'll most likely situate the sub between the OB panels.
I'm going to test some ideas about the sub cabinet options with the models and see what I come up with.
I think I may be getting somewhere.
Greets!
Gees, that's bigger than my house, garage, workshop and full length rear deck's gross square footage! Lucky you! Anyway, how far away you'll sit will determine bottom end requirements. Indeed, if you were to sit at the recommended ~2/3 room distance you'd need a front horn to load it enough to match the tweeter horn run WFO, which of course will require a similar efficiency system to fill in below it. For sure you'd want the system to go as low as the lowest frequency likely to need reproducing, so if you listen to organ symphonies it will need to be ~flat in-room to 16 Hz and with such a large space there won't be any room gain except for its reverb.
WRT Fs - Fp tuning offset, as I noted earlier:
"The theoretical ideal is to ~completely damp the driver's Fs peak, so Fp = Fs/Qts in a heavily stuffed end loaded pipe, ergo with a low Fs, Qts driver this limits it to a mid-bass alignment. For tuning around Fs, it doesn't matter whether you damp the impedance peak or not with a very low output impedance, but with a high output impedance you typically want the Fs peak to damp the upper TL or MLTL peak, so that the amp 'feels' the twin peaks for best LF gain and why a low power SET tube amp can to some extent perform like a much more powerful SS amp."
So with a high output impedance amp Fp = Fs*~1.6, but yours is a published 0.2 ohms, not enough to matter.
Yes, ideally the cab's roll off is the inverse of the room's gain curve so that the response is ~flat to near Dc.
No, this driver is a poor choice for a low tuned TL/TQWT due to its very low Qts unless a high output impedance and/or corner loading is used. That, or trade efficiency for gain BW by adding series resistance to flatten its response, not a good plan for such a large space though.
Yes, the BIB is a simple pipe horn and what I've wanted to suggest from the get-go, but your stated performance goals demand a very 'dry' presentation while the BIB is a very resonant ('rich') one. With such high ceilings though, it will have to be so tall that the higher harmonics will be audibly delayed, so floor loading may be the only option. A bi-amped, digitally time aligned OB loaded 604 with a ~optimum BL sub-horn OTOH could be a thing of beauty. Or large 604 BLH with a tapped sub-horn to fill in the bottom octave..............
Really, with this much space a large conical compression loaded multi-way is the 'hot ticket' IMO if you can sit back at least 25 ft, but this requires considerable tedious odd angles woodworking.
The BIB is ideally tuned to 1/2 WL of Fs, so is ~109" folded in half and puts the driver unacceptably high at ~62.4" off the floor if not either angled down or the listening distance is at least 25 ft away.
In a typical room they perform well because they're horns with enough gain to energize the room and have enough Vb for the driver to 'feel' a near IB response. IOW the diaphragm 'feels' ~the same air load on both sides for a much more linear, effortless presentation like you get with a high compression ratio (CR) horn, only without the high throat distortion that severely limits HF BW.
There are many acceptable ratios and due to us being amplitude oriented animals we ignore deep (high Q) notches, with the Q decreasing outside our acute hearing BW.
The BIB's 1.4142 ratio (where a-b-c/2) ~preserves the pipe's expansion through the bend, but many have been built using other ratios with apparently fine performance. Obviously, there's a point where the bend's constriction will audibly distort due to the acoustic impedance mis-match creating high amplitude harmonic reflections back to both the throat and mouth. Whether these added resonances degrades the perceived performance remains to be seen though as most folks like a lot of 'richness' in their systems to offset what gets lost in the recording 'mix' for a variety of reasons.
Right, MJK's WSs calcs based only on CSA.
GM
Gees, that's bigger than my house, garage, workshop and full length rear deck's gross square footage! Lucky you! Anyway, how far away you'll sit will determine bottom end requirements. Indeed, if you were to sit at the recommended ~2/3 room distance you'd need a front horn to load it enough to match the tweeter horn run WFO, which of course will require a similar efficiency system to fill in below it. For sure you'd want the system to go as low as the lowest frequency likely to need reproducing, so if you listen to organ symphonies it will need to be ~flat in-room to 16 Hz and with such a large space there won't be any room gain except for its reverb.
WRT Fs - Fp tuning offset, as I noted earlier:
"The theoretical ideal is to ~completely damp the driver's Fs peak, so Fp = Fs/Qts in a heavily stuffed end loaded pipe, ergo with a low Fs, Qts driver this limits it to a mid-bass alignment. For tuning around Fs, it doesn't matter whether you damp the impedance peak or not with a very low output impedance, but with a high output impedance you typically want the Fs peak to damp the upper TL or MLTL peak, so that the amp 'feels' the twin peaks for best LF gain and why a low power SET tube amp can to some extent perform like a much more powerful SS amp."
So with a high output impedance amp Fp = Fs*~1.6, but yours is a published 0.2 ohms, not enough to matter.
Yes, ideally the cab's roll off is the inverse of the room's gain curve so that the response is ~flat to near Dc.
No, this driver is a poor choice for a low tuned TL/TQWT due to its very low Qts unless a high output impedance and/or corner loading is used. That, or trade efficiency for gain BW by adding series resistance to flatten its response, not a good plan for such a large space though.
Yes, the BIB is a simple pipe horn and what I've wanted to suggest from the get-go, but your stated performance goals demand a very 'dry' presentation while the BIB is a very resonant ('rich') one. With such high ceilings though, it will have to be so tall that the higher harmonics will be audibly delayed, so floor loading may be the only option. A bi-amped, digitally time aligned OB loaded 604 with a ~optimum BL sub-horn OTOH could be a thing of beauty.
Or large 604 BLH with a tapped sub-horn to fill in the bottom octave..............Really, with this much space a large conical compression loaded multi-way is the 'hot ticket' IMO if you can sit back at least 25 ft, but this requires considerable tedious odd angles woodworking.
The BIB is ideally tuned to 1/2 WL of Fs, so is ~109" folded in half and puts the driver unacceptably high at ~62.4" off the floor if not either angled down or the listening distance is at least 25 ft away.
In a typical room they perform well because they're horns with enough gain to energize the room and have enough Vb for the driver to 'feel' a near IB response. IOW the diaphragm 'feels' ~the same air load on both sides for a much more linear, effortless presentation like you get with a high compression ratio (CR) horn, only without the high throat distortion that severely limits HF BW.
There are many acceptable ratios and due to us being amplitude oriented animals we ignore deep (high Q) notches, with the Q decreasing outside our acute hearing BW.
The BIB's 1.4142 ratio (where a-b-c/2) ~preserves the pipe's expansion through the bend, but many have been built using other ratios with apparently fine performance. Obviously, there's a point where the bend's constriction will audibly distort due to the acoustic impedance mis-match creating high amplitude harmonic reflections back to both the throat and mouth. Whether these added resonances degrades the perceived performance remains to be seen though as most folks like a lot of 'richness' in their systems to offset what gets lost in the recording 'mix' for a variety of reasons.
Right, MJK's WSs calcs based only on CSA
.GM
Hey GM.
Good feedback. I'm getting a much better feel for things now.
I started looking for some 'high' Qts drivers and came across a Fostex 31" woofer. Here is the 'low'down: Fs 18Hz, Qts=.69 and Vas=3201 liters! This thing models great (-3db at 15Hz) in a ---300+ cu ft closed box. The box Q is .8 and it doesn't hit .7 until about 3000 ft^3. It would probably be easier to mount them in the wall of the building, fer cryin' out loud. Sensitivity is 96db/watt (what frequency is that?) so two should fairly match level of one 604. If you think accomodating the box size for this thing is tough, try the $2.5K per price tag. Still, it would be fun to play around with this driver.
I'll keep looking.
Good feedback. I'm getting a much better feel for things now.
I started looking for some 'high' Qts drivers and came across a Fostex 31" woofer. Here is the 'low'down: Fs 18Hz, Qts=.69 and Vas=3201 liters! This thing models great (-3db at 15Hz) in a ---300+ cu ft closed box. The box Q is .8 and it doesn't hit .7 until about 3000 ft^3. It would probably be easier to mount them in the wall of the building, fer cryin' out loud. Sensitivity is 96db/watt (what frequency is that?) so two should fairly match level of one 604. If you think accomodating the box size for this thing is tough, try the $2.5K per price tag. Still, it would be fun to play around with this driver.
I'll keep looking.
Greets!
You're welcome!
These are essentially mid-bass horn drivers, so are way beyond the original definition of an acoustic suspension driver. To be AS you'd have to increase Qts to 0.38 and cab Vb to 0.33*Vas (alpha = 3). Nowadays though, any alignment < this is considered AS.
No, Qts has always been low because they have the most box design flexibility for dialing in bass EQ to ~'fit' the room/app and usually were coupled to high output impedance amps that could potentially nearly double the effective Qts, increasing the max flat alignment's Vb ~8x!, ergo why vintage cabs are typically quite large by today's standards.
I chose a baffle corner that would keep the driver from hitting Xmax and let a wide BW sub fill in the rest, so it will have to cover at least 3 octaves to get 'B' organ pipes.
I agree, you want a proper TD XO, though modded for driving the horn with a matching impedance SET for best performance.
While low Q dipole mid-bass systems are a good choice, true dipole subs are highly overrated IMO, wasting drivers and power down where our hearing acuity is pretty much limited to perceiving peak amplitude. Since you apparently can afford such a system, no reason not to, though I'd use more drivers, less power to get efficiency up to where amplitude modulation distortion (AMD) isn't an issue in the XO's HF BW. This allows for cheaper, higher Qts drivers, though the lower the Fs, the better. That, or mass load higher efficiency drivers to get both Fs down to ~16 Hz and Qts up to at least 0.5 Qts (my preference).
GM
You're welcome!
These are essentially mid-bass horn drivers, so are way beyond the original definition of an acoustic suspension driver. To be AS you'd have to increase Qts to 0.38 and cab Vb to 0.33*Vas (alpha = 3). Nowadays though, any alignment < this is considered AS.
No, Qts has always been low because they have the most box design flexibility for dialing in bass EQ to ~'fit' the room/app and usually were coupled to high output impedance amps that could potentially nearly double the effective Qts, increasing the max flat alignment's Vb ~8x!, ergo why vintage cabs are typically quite large by today's standards.
I chose a baffle corner that would keep the driver from hitting Xmax and let a wide BW sub fill in the rest, so it will have to cover at least 3 octaves to get 'B' organ pipes.
I agree, you want a proper TD XO, though modded for driving the horn with a matching impedance SET for best performance.
While low Q dipole mid-bass systems are a good choice, true dipole subs are highly overrated IMO, wasting drivers and power down where our hearing acuity is pretty much limited to perceiving peak amplitude. Since you apparently can afford such a system, no reason not to, though I'd use more drivers, less power to get efficiency up to where amplitude modulation distortion (AMD) isn't an issue in the XO's HF BW. This allows for cheaper, higher Qts drivers, though the lower the Fs, the better. That, or mass load higher efficiency drivers to get both Fs down to ~16 Hz and Qts up to at least 0.5 Qts (my preference).
GM
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