Variac said:
I had the Bandor 100 rattling around in the back of my mind for a future project, but with the pathetic Australian dollar travelling at about three dollars per British pound, I guess that's the end of that.
S3:
You mentioned that you wanted the midrange driver in a sealed enclosure for smoothest response-reflex is too rough.
Have you considered putting the midrange driver in a transmission line enclosure?
There are two types of transmission line, apparently. One type gives substantial output-as high as 6 dB-out the port. The other type apparently has little output from the port. I have not built a TL, so I am just going by what I have read.
Even the type with substantial port output, I understand, has a rolloff of 12 dB/octave-just like a sealed speaker.
If so, is not reasonable to assume that such things as distortion, overhang, etc. are similar in a transmission line and a sealed box?
Perhaps our transmission line experts can answer that question. I just threw it out because it seems to be a reasonable assumption.
If the line has 6 dB output, that means the speaker only has to move half as far at 70 Hz as it would in a sealed box. This will greatly help to make the midrange uncolored.
If you increase the area of the diaphragm by using an oval speaker, you get the dispersion of the narrow dimension while having twice the cone area. Twice the cone area means half the excursion.
So if you put an oval speaker, (assuming you can find a suitable one), in a transmission line enclosure, you save 3/4 of your excursion at low fequencies, and half your excursion the rest of the way up. Just a suggestion for you to consider-I personally have not built a transmission line.
In my opinion, cone excursion is the biggest enemy in this type of project.
PS: If you do go this route, you will have the additional satisfaction of executing a unique solution that is probably not commerically available at any price.
You mentioned that you wanted the midrange driver in a sealed enclosure for smoothest response-reflex is too rough.
Have you considered putting the midrange driver in a transmission line enclosure?
There are two types of transmission line, apparently. One type gives substantial output-as high as 6 dB-out the port. The other type apparently has little output from the port. I have not built a TL, so I am just going by what I have read.
Even the type with substantial port output, I understand, has a rolloff of 12 dB/octave-just like a sealed speaker.
If so, is not reasonable to assume that such things as distortion, overhang, etc. are similar in a transmission line and a sealed box?
Perhaps our transmission line experts can answer that question. I just threw it out because it seems to be a reasonable assumption.
If the line has 6 dB output, that means the speaker only has to move half as far at 70 Hz as it would in a sealed box. This will greatly help to make the midrange uncolored.
If you increase the area of the diaphragm by using an oval speaker, you get the dispersion of the narrow dimension while having twice the cone area. Twice the cone area means half the excursion.
So if you put an oval speaker, (assuming you can find a suitable one), in a transmission line enclosure, you save 3/4 of your excursion at low fequencies, and half your excursion the rest of the way up. Just a suggestion for you to consider-I personally have not built a transmission line.
In my opinion, cone excursion is the biggest enemy in this type of project.
PS: If you do go this route, you will have the additional satisfaction of executing a unique solution that is probably not commerically available at any price.
kelticwizard said:
An excellent solution
It is more like there are 2 ends of a spectrum. On one end is the line that is stuffed just enuff to kill most of the ripple & maximize terminus output (requires geometry to help with the low pass function of the terminus) and on the other end the heavily stuffed, essentially aperiodic line with minimal terminus output.
The 1st exhibits a double saddle impedance curve and a 24 dB/octave roll-off. the former, done well, has almost no impedance peak and a 12 db/octave roll-off. There is a continuum in-between.
dave
Planet 10,
My drivers are actually quite a motley bunch. I quite a few that are(were) made by Rola here in Australia. Rola have very small enclosed magnets, but are very well made, very neat and tidy construction. Can be found in a lot of consoles and speakers with the names MK and Kreisler on them. Actually they sound quite good also. I have a set with a 6.5" and 8" full-ranges running in parallel in a ported 25 liter box with the 6.5" bleed off with a 1mF? cap. The boxes are junk, but they still manage to sound very good indeed.
The rest of my drivers are old Pioneer, Sharp, RCA, Philips, and some no names.
They range in size from set of 2" cone tweeters to a bunch of 6"-8" FR to 8", 10", 12" woofers.
Of course I am always doing drive-by's, Goodwills, and dumpster diving, so my collection is getting bigger, much to the dismay of my better half.
Lynn aka Surf, Sun & Sound
My drivers are actually quite a motley bunch. I quite a few that are(were) made by Rola here in Australia. Rola have very small enclosed magnets, but are very well made, very neat and tidy construction. Can be found in a lot of consoles and speakers with the names MK and Kreisler on them. Actually they sound quite good also. I have a set with a 6.5" and 8" full-ranges running in parallel in a ported 25 liter box with the 6.5" bleed off with a 1mF? cap. The boxes are junk, but they still manage to sound very good indeed.
The rest of my drivers are old Pioneer, Sharp, RCA, Philips, and some no names.
They range in size from set of 2" cone tweeters to a bunch of 6"-8" FR to 8", 10", 12" woofers.
Of course I am always doing drive-by's, Goodwills, and dumpster diving, so my collection is getting bigger, much to the dismay of my better half.
Lynn aka Surf, Sun & Sound
Kelticwizard;
I just want to start actually exploring this configuration, with the limited fund and resources that I have on hand. I have not made my mind up about the drivers I am going to use for the final speakers, so keep the suggestions coming.
It never crossed my mind to use ovals. I will look into this possibility. I will cover more points about my final driver of choice in another post, which will be more of a rant than anything. So get ready.
Lynn aka Surf, Sun, Sound
I just want to start actually exploring this configuration, with the limited fund and resources that I have on hand. I have not made my mind up about the drivers I am going to use for the final speakers, so keep the suggestions coming.
It never crossed my mind to use ovals. I will look into this possibility. I will cover more points about my final driver of choice in another post, which will be more of a rant than anything. So get ready.
Lynn aka Surf, Sun, Sound
Navin
I am going to say this a politely as possible, you have missed the plot, with your 4-way have a crossover smack in the middle of the music scale.
I am not flaming you, just please reread all my posted in this thread, and you will see what I am aiming for -
A Full Range driver that just needs reinforcement on both extreme ends.
I do value your ideas and input, so keep you thinking cap on.
Lynn aka Surf, Sun & Sound
I am going to say this a politely as possible, you have missed the plot, with your 4-way have a crossover smack in the middle of the music scale.
I am not flaming you, just please reread all my posted in this thread, and you will see what I am aiming for -
A Full Range driver that just needs reinforcement on both extreme ends.
I do value your ideas and input, so keep you thinking cap on.
Lynn aka Surf, Sun & Sound
surf said:
Sounds like more than a few of these should be alnico. And i'm surprised you haven't turned up any ovals.
Alnico magnets don't need to be nearly as big as ceramic, and some of those drivers do amazing thru the midrange. You might well find that some of that "junk" actually ends up being suitable.
I'm off to the lab to finish up my alnico Frugal-phile(tm) midi-monitors so that i can give them a listen before i pack the NAIM up to get it ready for its new home... and some pictures for all here.
dave
Jordan, Bandor and most drivers
Let's revisit some of the original parameters for our "mid-range driver -
Must be flat from 75Hz to 4000Hz+
Must have good off-axis response
Must be efficient enough to be driven by a tube or low power Class-A to 100db+
Kelticwizard was exactly right, the biggest problem with all the drivers I have plotted so far, which include drivers from Jordan, Bandor, Tagband, Vifa, Scanspeak, pretty much everything on the market, is cone overexcursion. Sure you can get a 5"- 6" driver to meet this frequency range pretty well, but off-axis response is terrible. So smaller drivers that claim to meet this requirement actually when plotted run out of linear excursion very quickly, which is big trouble.
So it looks like we again must compromise, or must we?
Well, revisit this thread for my rant post where I am going to break all the rules and describe my ultimate driver and how I think it can be done. Also I will be putting forth some other radical ideas and thoughts.
Blame it on the medication!!!
Lynn
PS. It may be well for everyone to reread this thread, so you can get the angle I will be coming from. It will be several hours in the making so be patient.
Let's revisit some of the original parameters for our "mid-range driver -
Must be flat from 75Hz to 4000Hz+
Must have good off-axis response
Must be efficient enough to be driven by a tube or low power Class-A to 100db+
Kelticwizard was exactly right, the biggest problem with all the drivers I have plotted so far, which include drivers from Jordan, Bandor, Tagband, Vifa, Scanspeak, pretty much everything on the market, is cone overexcursion. Sure you can get a 5"- 6" driver to meet this frequency range pretty well, but off-axis response is terrible. So smaller drivers that claim to meet this requirement actually when plotted run out of linear excursion very quickly, which is big trouble.
So it looks like we again must compromise, or must we?
Well, revisit this thread for my rant post where I am going to break all the rules and describe my ultimate driver and how I think it can be done. Also I will be putting forth some other radical ideas and thoughts.
Blame it on the medication!!!
Lynn
PS. It may be well for everyone to reread this thread, so you can get the angle I will be coming from. It will be several hours in the making so be patient.
S3:
Before you make up your mind, I think you should know that there is a little known enclosure type which might suit your needs. I have not found a suitable 4" for it. However, I found at least a couple of 5 inchers that would work with it-and I didn't even look that hard.
Will post details tomorrow.
Before you make up your mind, I think you should know that there is a little known enclosure type which might suit your needs. I have not found a suitable 4" for it. However, I found at least a couple of 5 inchers that would work with it-and I didn't even look that hard.
Will post details tomorrow.
lynn, relax i got a tough hide.
the only reason i mentioned this was i am also trying to do what you want to do but cant find a driver that will give me adequate SPL at 70Hz and not break up at 4000Hz.
my needs for SPL are quite limited 105db at 70Hz.
i am now sreiouly considering dave suggestion of a TL (heavily damped, aperiodic version).
my initial idea was a TL bass with a ESL top end.
then i figured an all dynamic system might be easier so i hoped to build a TL bass up to 250Hz, a open back mid from 250-4k and a tweeter.
however after looking at your researrch on low freq. i decided the mid speaker would have to cover 70-4k none even the Focal ^W would do this in an open box at 105db.
i know the idea runs counter to your single driver concept but i was just thorwing in out there maye we can use 2 drivers (over the 70-4k range) with a large over lap and a 6db XO. say a 6" to cover 70-300 and a 4" to cover 300-4k. the idea is if you cant find one driver to do the job use 2 and make the XO as transparent as possible. maybe a series XO with a zeta of 1.2 or so would suffice.
BTW which part of Oz are you in?
the only reason i mentioned this was i am also trying to do what you want to do but cant find a driver that will give me adequate SPL at 70Hz and not break up at 4000Hz.
my needs for SPL are quite limited 105db at 70Hz.
i am now sreiouly considering dave suggestion of a TL (heavily damped, aperiodic version).
my initial idea was a TL bass with a ESL top end.
then i figured an all dynamic system might be easier so i hoped to build a TL bass up to 250Hz, a open back mid from 250-4k and a tweeter.
however after looking at your researrch on low freq. i decided the mid speaker would have to cover 70-4k none even the Focal ^W would do this in an open box at 105db.
i know the idea runs counter to your single driver concept but i was just thorwing in out there maye we can use 2 drivers (over the 70-4k range) with a large over lap and a 6db XO. say a 6" to cover 70-300 and a 4" to cover 300-4k. the idea is if you cant find one driver to do the job use 2 and make the XO as transparent as possible. maybe a series XO with a zeta of 1.2 or so would suffice.
BTW which part of Oz are you in?
S3:
Here is the enclosure I was talking about. It is designed to, among other things, enable a speaker to experience considerable augmentation from the enclosure-thereby cutting down on cone excursion by 3/4 at the cutoff frequency-but also to roll off around 12 dB/octave, just like a sealed design.
I saw it in a 2 part article in the Journal of The Audio Engineering Society, by Thomas L. Clarke.
It is the Augmented Passive Radiator, and I haven't built one yet, but think maybe you might want to try. There are many different alignments.
First here is an illustration. It seems to me the 2-part passive radiator that is at the heart of this could just be two flat syrofoam pieces with two homemade surrounds. Saves money and enclosure space. But if you cusomarily collect speakers from vintage radio, you probably have cones on hand that you can use.
Anyway, the picture:
Here is the enclosure I was talking about. It is designed to, among other things, enable a speaker to experience considerable augmentation from the enclosure-thereby cutting down on cone excursion by 3/4 at the cutoff frequency-but also to roll off around 12 dB/octave, just like a sealed design.
I saw it in a 2 part article in the Journal of The Audio Engineering Society, by Thomas L. Clarke.
It is the Augmented Passive Radiator, and I haven't built one yet, but think maybe you might want to try. There are many different alignments.
First here is an illustration. It seems to me the 2-part passive radiator that is at the heart of this could just be two flat syrofoam pieces with two homemade surrounds. Saves money and enclosure space. But if you cusomarily collect speakers from vintage radio, you probably have cones on hand that you can use.
Anyway, the picture:
Attachments
Before I explain the importance of the size relation of the two PR's that are attached to each other, I just thought I would post one of the curves suitable for your project. Remember, Greek "a" = (Vas/Vb (total enclosure). This would involve "a" = 3, that is, the volume of the entire box would be equal to one third of the speaker's Vas.
From what I can see, the response appears to be 2 dB down at 2 Fb, and 15 dB down at Fb. This is just going by sight. I think that is 13 dB/octave rolloff, though it might be considered 18. Don't know-but it sure is less than the traditional 24 dB/octave rolloff of the normal reflex.
Anyway, I highlighted the appropriate curve in red.
From what I can see, the response appears to be 2 dB down at 2 Fb, and 15 dB down at Fb. This is just going by sight. I think that is 13 dB/octave rolloff, though it might be considered 18. Don't know-but it sure is less than the traditional 24 dB/octave rolloff of the normal reflex.
Anyway, I highlighted the appropriate curve in red.
Attachments
Articles I have read have said that transient response, overhang, etc., are all related to rollof rate. From this, I can gather that speakers with similar rolloff rates will have similar results in the other characteristics. So therefore, this enclosure type should yield the benefits of very muc lessened cone excursion with advantages of a gradual cutoff slope.
This enclosrue type might be of interest to TL fans also, since one of the major attractions of the Transmission Line design is transient response. Could the Augmented Passive Radiator design be a worthy alternative? I guess we will find out when somebody on the forum builds and tests one.
Also, this enclosre looks like a good choice for someone who wants to build a reflex box, but his driver's Qts is too low for the size box he needs to build in order to achieve a low F3.
Anyway, here is a chart for this type of Augmented Passive Radiator alignment. It seems for your purposes, it seems to require a speaker with a Qts of .21, (I think we can settle for anything in the low .20s), and an Fs of 40 or so. this will give an F3 of 70 Hz or so.
Happily, there are at least three drivers that I quickly found that meet the requirements. I have not checked the response curve for the full range use-just throwing them out there for now. They are all 5 inchers-not too much bigger than the 4 inchers you were looking for.
VersaTronics EOB 130R FGC18, and EOB 130R WCC. Both are available at Speaker City, which ships internationally.
www.speakercity.com
http://www.speakercity.com/specs/versatron_ts.shtml
Also the Focal 5N412DBL, available many places.
I am sure there are others.
By the way, Greek "y" means the relationship of the outer passive radiator area-always the larger one-to the inner passive radiator area. So if a 12 inch cone of 86 sq in, facing out into the room, is connected to an 8 inch of 32 sp in connected to the interior chamber, you have "y" = 2.7.
Greek "e" means the relationship of the chamber in which the speaker is located to the entire enclosure. So if the speaker chamber takes up 3/4 of the entire enclosure volume, "e" would equal .75.
I wouldn't worry about the tuning ratio of the passive radiator. I would think you would just add wieght until you get the right response.
I have both parts of the article EXCEPT two pages inexplicably lost. I am thinking of sending away for that first article from the Journal Of The Audio Engineering Society. Will send what pages I have, if you are interested.
This enclosrue type might be of interest to TL fans also, since one of the major attractions of the Transmission Line design is transient response. Could the Augmented Passive Radiator design be a worthy alternative? I guess we will find out when somebody on the forum builds and tests one.
Also, this enclosre looks like a good choice for someone who wants to build a reflex box, but his driver's Qts is too low for the size box he needs to build in order to achieve a low F3.
Anyway, here is a chart for this type of Augmented Passive Radiator alignment. It seems for your purposes, it seems to require a speaker with a Qts of .21, (I think we can settle for anything in the low .20s), and an Fs of 40 or so. this will give an F3 of 70 Hz or so.
Happily, there are at least three drivers that I quickly found that meet the requirements. I have not checked the response curve for the full range use-just throwing them out there for now. They are all 5 inchers-not too much bigger than the 4 inchers you were looking for.
VersaTronics EOB 130R FGC18, and EOB 130R WCC. Both are available at Speaker City, which ships internationally.
www.speakercity.com
http://www.speakercity.com/specs/versatron_ts.shtml
Also the Focal 5N412DBL, available many places.
I am sure there are others.
By the way, Greek "y" means the relationship of the outer passive radiator area-always the larger one-to the inner passive radiator area. So if a 12 inch cone of 86 sq in, facing out into the room, is connected to an 8 inch of 32 sp in connected to the interior chamber, you have "y" = 2.7.
Greek "e" means the relationship of the chamber in which the speaker is located to the entire enclosure. So if the speaker chamber takes up 3/4 of the entire enclosure volume, "e" would equal .75.
I wouldn't worry about the tuning ratio of the passive radiator. I would think you would just add wieght until you get the right response.
I have both parts of the article EXCEPT two pages inexplicably lost. I am thinking of sending away for that first article from the Journal Of The Audio Engineering Society. Will send what pages I have, if you are interested.
Attachments
S3:
After examining Thomas L. Clarke's paper, I realize that the Augmented Passive Radiator enclosure can be adapted in the same way as a ported or conventional drone cone. Values of "a" less than 3-say 2 or 1.5-will not yield that big an increase in the rolloff rate. Therefore, the should yield transient and phase responses roughly similar to sealed boxes with the same rollof rates.
Incidentally, in this alignment, the rolloff rate of "a=3" is about the same as a sealed box with a Qtc of 1. Values of "a=1.5" look just a little steeper in the rolloff rate.
I have a couple of recommendations for 5 inch speakers that most likely could be made to fit into an Augmented Passive Radiator system, albeit with a few modifications in the alignment.
One is the Peerless 850108, (CSX line). This has a natural high rolloff that is 3 dB down at 5K Hz. The other is the Peerless 850488, (HDS line). This has a natural rolloff that is 3 dB down at 6K Hz. I do not know if that is high enough for you. With a 5 incher you might consider taking the crossover point down a notch than with a 4 incher.
Response curves for both can be seen at
http://www.d-s-t.com/peerless/index.htm
I certainly hope I have not killed this thread with this new enclosure type. It is just a suggestion for you to consider or reject as you see fit. Just thought I would throw it out there. I will post no more about it unless I am specifically asked
If anyone else wishes to come up with suggestions in a different direction, please jump right in. And I hope S3 keeps us posted about what he is currently thinking or decided as regards this project. 🙂
After examining Thomas L. Clarke's paper, I realize that the Augmented Passive Radiator enclosure can be adapted in the same way as a ported or conventional drone cone. Values of "a" less than 3-say 2 or 1.5-will not yield that big an increase in the rolloff rate. Therefore, the should yield transient and phase responses roughly similar to sealed boxes with the same rollof rates.
Incidentally, in this alignment, the rolloff rate of "a=3" is about the same as a sealed box with a Qtc of 1. Values of "a=1.5" look just a little steeper in the rolloff rate.
I have a couple of recommendations for 5 inch speakers that most likely could be made to fit into an Augmented Passive Radiator system, albeit with a few modifications in the alignment.
One is the Peerless 850108, (CSX line). This has a natural high rolloff that is 3 dB down at 5K Hz. The other is the Peerless 850488, (HDS line). This has a natural rolloff that is 3 dB down at 6K Hz. I do not know if that is high enough for you. With a 5 incher you might consider taking the crossover point down a notch than with a 4 incher.
Response curves for both can be seen at
http://www.d-s-t.com/peerless/index.htm
I certainly hope I have not killed this thread with this new enclosure type. It is just a suggestion for you to consider or reject as you see fit. Just thought I would throw it out there. I will post no more about it unless I am specifically asked
If anyone else wishes to come up with suggestions in a different direction, please jump right in. And I hope S3 keeps us posted about what he is currently thinking or decided as regards this project. 🙂
This is an interesting project and it would be interesting to see it to completion. Here is a bump, and another driver worth considering (maybe?) - bottlehead seems partial to MCM 5" drivers . Their current straight 8 drivers also look very similar to MCM drivers.
Sorry to leave everyone hanging!!!
To one and all;
I decided that discretion is the better part of valour in this case, and so before I post what appears to be a half-brained rant, I decided to do more research so I can at least present what appears to be a rational, if hair-brained and unsupported theory.
Also I have spent the last few days doing drive-bys, picking up more drivers. Here in Sydney, every 3 months, there is what is called a "clean-up" and everyone throws all their junk out on the side of the street for everyone to pick through and then a few days later the council comes along and hauls what is left to the landfill.
Dave aka Planet10, I have found some beauties this time. A pair of 2" cone tweeters with that crazy magnet structure, came out of a pair of Sanyo's and I am crying because I cannot find the mate to a Pioneer which had a 8" and a 3" with that magnet. I hate when I cannot find stuff in pairs. Anyway, such is life. I will get some more info on these drivers in a bit.
In all I added 14 more drivers to my collection along with a few transformers and lots of caps, transistors, and such.
Thanks to all for the continued interest in the crazy project.
Lynn aka 3S or Surf, Sun & Sound
To one and all;
I decided that discretion is the better part of valour in this case, and so before I post what appears to be a half-brained rant, I decided to do more research so I can at least present what appears to be a rational, if hair-brained and unsupported theory.
Also I have spent the last few days doing drive-bys, picking up more drivers. Here in Sydney, every 3 months, there is what is called a "clean-up" and everyone throws all their junk out on the side of the street for everyone to pick through and then a few days later the council comes along and hauls what is left to the landfill.
Dave aka Planet10, I have found some beauties this time. A pair of 2" cone tweeters with that crazy magnet structure, came out of a pair of Sanyo's and I am crying because I cannot find the mate to a Pioneer which had a 8" and a 3" with that magnet. I hate when I cannot find stuff in pairs. Anyway, such is life. I will get some more info on these drivers in a bit.
In all I added 14 more drivers to my collection along with a few transformers and lots of caps, transistors, and such.
Thanks to all for the continued interest in the crazy project.
Lynn aka 3S or Surf, Sun & Sound
Re: Sorry to leave everyone hanging!!!
The alpha version of my Single Driver Mating Service is done... i need to do some cosmetic upgrades and add a few drivers (i have probably 40-50 singles) and it can go beta.
dave
surf said:
The alpha version of my Single Driver Mating Service is done... i need to do some cosmetic upgrades and add a few drivers (i have probably 40-50 singles) and it can go beta.
dave
OK, my first hairbrained theory!!!
First and foremost, I want to say that I am not an expert or an authority on speaker or driver design. Far from it, what I am presenting here are only opinions and ideas formed from months of listening, reading and researching drivers and speakers. I stand to be corrected on all points, and will take any criticism with a smile hoping to learn more in the process. So let’s get started.
I am going to use several posts to present my thoughts, so that it does not get too long and unmanageable, and will be asking more questions than giving answers.
Why has the “Hi-Fi powers that be” convinced us that we do not need to have a speaker that produces the last octave of music? I see it all the time, speakers, supposedly full-range with 2 or 3 way systems, that roll-off around 40Hz. Even some very highly acclaimed DIY designs, do not go below 40 – 50 Hz and the argument is that there not a lot of music down there. Well, there are no fundamental music notes above 8000Hz either, yes, there are plenty of harmonics that go well above the average human hearing but no written notes. But on the other hand, there are written music notes down to at least 27Hz since the bottom key of the piano keyboard is 27.5Hz. Now there are plenty of speakers that can brag flat response to 30kHz, but not flat to 25Hz.
It is my opinion, that it has been a result of a big push from speaker designers and manufacturers since it costs more to design and build a speaker flat to 30Hz than to it does to make it flat to 30kHz. In the scope of drivers, even the best tweeters are relatively cheap compared to big drivers needed to reach down to the last octave. It is a conspiracy, naawwww, just another casualty of economics.
Another casualty of economics is the large diameter woofer, capable of producing low distortion, low frequencies with reasonable amounts of power. Of course, the interior designers have to carry some of the blame since it is easier to integrate a bookshelf or tower speaker with a 6.5” driver than a floorstander with a 15” driver. There are things that a 15” driver can do that a 8” or 10” can only dream of.
Which brings me to my next heresy that I want to present. I am questioning the argument of the small woofer vs. the large woofer, which states that a smaller woofer is better because its lighter mass means it can stop and start easier. Hummm, yes, a 15” cone will have more mass than an 8”, but where do we consider the speed issue. Let me explain.
These are just theoretical numbers for discussion sake.
Frequency – 45Hz
15” cone – 100 grams
8” cone – 50 grams
Lets say to produce the same SPL at the same frequency, 45Hz, the 15” has a full excursion of 3mm, a full cycle of a wave, while the 8” has an excursion of 6mm. Now the frequency is the same, so both drivers are cycling the same rate, full length of the excursion in 1/45th of a second, but the 8” has to cover 6mm in that time while the 15” only has to cover 3mm.
According to my knowledge of such things, the 8” cone is travelling at twice the velocity of the 15”cone, and if my memory serves my correctly from ballistics, when you double the weight of a moving object you double the momentum, but if you double the velocity you also double the momentum. Since momentum equals mass times velocity, if the 15” cone weighs twice as much as the 8”, but is travelling at half the velocity, we arrive at the same momentum.
That is very simplistic, because I assume you will need to account for the force of the cone, when it is being decelerated at the end of an excursion, so if you factor in this element, you will find that doubling the weight only doubles the force, but double the velocity and you increase force by the square of the velocity. So if we go back to our illustration, if our cones were both travelling at the same velocity, the 15” would have double the force since it ways twice as much as the 8”, but since we have the 8” travelling at twice the speed we have twice the force of the 15”.
Here are my results –
15” – velocity of 135mm/sec – 100 grams – force of .0018225 Newtons
8” – velocity of 270mm/sec – 50 grams – force of .003645 Newtons
The 15” cone would have to weigh 4 times as much as the 8” cone to have equal force. I am not a physicist even in my wildest nightmares, so I am sure there will be some here to correct me on my observation, but it seems to me that we need to looks carefully how we look at our LF drivers. It would take about 3 ½-8” drivers to equal the area of a 15” and 2-8” do not quite equal a 12”. Have we again succumbed to a theory presented by manufacturers driven by cost and designers by aesthetics? I wonder…..
Of course, I have not covered all the factors involved, but I hopefully will have aroused someone’s attention that does know the factors involved in starting and stopping a cone.
That is all for now,
Lynn aka Surf, Sun & Sound
PS. Moderators, you are welcome to move this to a new thread if you deem it best.
First and foremost, I want to say that I am not an expert or an authority on speaker or driver design. Far from it, what I am presenting here are only opinions and ideas formed from months of listening, reading and researching drivers and speakers. I stand to be corrected on all points, and will take any criticism with a smile hoping to learn more in the process. So let’s get started.
I am going to use several posts to present my thoughts, so that it does not get too long and unmanageable, and will be asking more questions than giving answers.
Why has the “Hi-Fi powers that be” convinced us that we do not need to have a speaker that produces the last octave of music? I see it all the time, speakers, supposedly full-range with 2 or 3 way systems, that roll-off around 40Hz. Even some very highly acclaimed DIY designs, do not go below 40 – 50 Hz and the argument is that there not a lot of music down there. Well, there are no fundamental music notes above 8000Hz either, yes, there are plenty of harmonics that go well above the average human hearing but no written notes. But on the other hand, there are written music notes down to at least 27Hz since the bottom key of the piano keyboard is 27.5Hz. Now there are plenty of speakers that can brag flat response to 30kHz, but not flat to 25Hz.
It is my opinion, that it has been a result of a big push from speaker designers and manufacturers since it costs more to design and build a speaker flat to 30Hz than to it does to make it flat to 30kHz. In the scope of drivers, even the best tweeters are relatively cheap compared to big drivers needed to reach down to the last octave. It is a conspiracy, naawwww, just another casualty of economics.
Another casualty of economics is the large diameter woofer, capable of producing low distortion, low frequencies with reasonable amounts of power. Of course, the interior designers have to carry some of the blame since it is easier to integrate a bookshelf or tower speaker with a 6.5” driver than a floorstander with a 15” driver. There are things that a 15” driver can do that a 8” or 10” can only dream of.
Which brings me to my next heresy that I want to present. I am questioning the argument of the small woofer vs. the large woofer, which states that a smaller woofer is better because its lighter mass means it can stop and start easier. Hummm, yes, a 15” cone will have more mass than an 8”, but where do we consider the speed issue. Let me explain.
These are just theoretical numbers for discussion sake.
Frequency – 45Hz
15” cone – 100 grams
8” cone – 50 grams
Lets say to produce the same SPL at the same frequency, 45Hz, the 15” has a full excursion of 3mm, a full cycle of a wave, while the 8” has an excursion of 6mm. Now the frequency is the same, so both drivers are cycling the same rate, full length of the excursion in 1/45th of a second, but the 8” has to cover 6mm in that time while the 15” only has to cover 3mm.
According to my knowledge of such things, the 8” cone is travelling at twice the velocity of the 15”cone, and if my memory serves my correctly from ballistics, when you double the weight of a moving object you double the momentum, but if you double the velocity you also double the momentum. Since momentum equals mass times velocity, if the 15” cone weighs twice as much as the 8”, but is travelling at half the velocity, we arrive at the same momentum.
That is very simplistic, because I assume you will need to account for the force of the cone, when it is being decelerated at the end of an excursion, so if you factor in this element, you will find that doubling the weight only doubles the force, but double the velocity and you increase force by the square of the velocity. So if we go back to our illustration, if our cones were both travelling at the same velocity, the 15” would have double the force since it ways twice as much as the 8”, but since we have the 8” travelling at twice the speed we have twice the force of the 15”.
Here are my results –
15” – velocity of 135mm/sec – 100 grams – force of .0018225 Newtons
8” – velocity of 270mm/sec – 50 grams – force of .003645 Newtons
The 15” cone would have to weigh 4 times as much as the 8” cone to have equal force. I am not a physicist even in my wildest nightmares, so I am sure there will be some here to correct me on my observation, but it seems to me that we need to looks carefully how we look at our LF drivers. It would take about 3 ½-8” drivers to equal the area of a 15” and 2-8” do not quite equal a 12”. Have we again succumbed to a theory presented by manufacturers driven by cost and designers by aesthetics? I wonder…..
Of course, I have not covered all the factors involved, but I hopefully will have aroused someone’s attention that does know the factors involved in starting and stopping a cone.
That is all for now,
Lynn aka Surf, Sun & Sound
PS. Moderators, you are welcome to move this to a new thread if you deem it best.
On these pages, large pro type efficient woofers have generally been well accepted as a good thing. I think your point about multiple smaller woofers not nescessarily being better is also accepted by a lot of people on DiyAudio. So... you are in good company with these ideas.