sorry if I am repeating myself...
I think that the infra bass is not to difficult to explain. The heart of the system is the duct or pipe. A conventional reflex vent has very narrow band resonance centred upon the frequency of the combined driver and box resonance frequency. This reflex action is for the most part a mass related resonance (air mass in the vent).
The infra bass design uses a pipe rather than a vent so as to achieve a wider band of resonance (multiple peaks). The two vent sections (in the infra bass) acoustically couple to form a single pipe. That pipe will have a series of resonances which you design by the choice of pipe length so as to have its modes centred in the band of interest.
The resonant pipe is coupled to the large cavity of air (Helmholtz resonator) which needs to be tuned to the centre frequency of the modes of the pipe. The Q of the cavity resonance will be higher than the Q of the pipe resonancesas a result of its larger volume. When you combine the two sets of overlapping resonances (pipe and box) you achieve increased output.
The lower the response of the driver the better able it will be to excite the system resonances. The larger the driver the better as a greater volume of air will be displaced and the volume of the air in the system will be increased (more air mass = more output). If you use a driver with a somewhat higher Qts then you can also boost your response at roll off. A guess would be to keep max driver Qts around 0.5 to 0.8..
The resonant frequency of the large cavity is important to system efficiency and needs to be as close to the centre frequency of the pipe modes as is possible.
When generating such low frequencies I don't think that the location of the cabinet in room should make much difference. That said though the room volume (openings) will likely have an impact as there is not a lot of air being moved with this system at these frequencies to begin with.
I would appreciate any and all correcions to my discription of this cabinet design. I may have missed some important factors but I think that this is a fair explaination of the infra bass design.
I think that the infra bass is not to difficult to explain. The heart of the system is the duct or pipe. A conventional reflex vent has very narrow band resonance centred upon the frequency of the combined driver and box resonance frequency. This reflex action is for the most part a mass related resonance (air mass in the vent).
The infra bass design uses a pipe rather than a vent so as to achieve a wider band of resonance (multiple peaks). The two vent sections (in the infra bass) acoustically couple to form a single pipe. That pipe will have a series of resonances which you design by the choice of pipe length so as to have its modes centred in the band of interest.
The resonant pipe is coupled to the large cavity of air (Helmholtz resonator) which needs to be tuned to the centre frequency of the modes of the pipe. The Q of the cavity resonance will be higher than the Q of the pipe resonancesas a result of its larger volume. When you combine the two sets of overlapping resonances (pipe and box) you achieve increased output.
The lower the response of the driver the better able it will be to excite the system resonances. The larger the driver the better as a greater volume of air will be displaced and the volume of the air in the system will be increased (more air mass = more output). If you use a driver with a somewhat higher Qts then you can also boost your response at roll off. A guess would be to keep max driver Qts around 0.5 to 0.8..
The resonant frequency of the large cavity is important to system efficiency and needs to be as close to the centre frequency of the pipe modes as is possible.
When generating such low frequencies I don't think that the location of the cabinet in room should make much difference. That said though the room volume (openings) will likely have an impact as there is not a lot of air being moved with this system at these frequencies to begin with.
I would appreciate any and all correcions to my discription of this cabinet design. I may have missed some important factors but I think that this is a fair explaination of the infra bass design.
Sorry about the lack of formatting. It was a Word .doc originally but it had to be changed to .txt to upload, as the forum will not accept a .doc attachment. I copied the text into Notepad (with word wrap on) and saved it, then uploaded it and what you see is what you get, sorry.
I am not suggesting that I am emphatically correct, however I do not agree with a lot of your theory. Remember that this design can use ports, tapered ports, or passive radiators to achieve it's output section. If a passive radiator is used instead of the Holliman ports as shown in the plans, your theory does not make sense to me. Passive radiators cannot have multiple resonant peaks. I still contend that this box only has one resonant peak and that resonance covers a large bandwidth.
Furthermore, the helmholtz resonator is definitely not tuned to the center frequencies of the modes of the pipe. Again, replace the Holliman ports with passive radiators and there can be no pipe modes.
From the patent:
"The system does not in fact have to be entirely 'Port-loaded', either port X or port X', or even both X and X', can be replaced by other types of mass loading... tapered port, (or horn in its extreme form). Auxiliary Bass Radiator, slot radiator, or even (a) further powered units could be used." Don't forget the ports can be replaced with a passive radiator. This means that any theory regarding pipe resonances is out, at least in my opinion.
"Consider diagram C. The resonant frequency is determined by X and V as before, but it can be instantaneously changed to a lower frequency by the closure of the flap F, which introduces an extra length of port, X'. Now consider diagram D., in which the flap F has been replaced by a speaker drive unit. If the speaker is in phase with the resonance (X:V) it acts as an open flap, in which case the rest of the port, X', takes no part in the resonance, and the unit tries to resonate at the frequency determined by X and V. As resonance starts to build up, the resonant Amplitude increases beyond that of the unit driving it. The excess air motion can not pass through the cone and therefore it oscillates along port X'." This is my basis for claiming that the frequency of resonance of the helmholtz resonator alone is the high cutoff point, the frequency of resonance of the resonator with the ports (or passive radiators) combined is the low cutoff frequency. Everything in between is a broad range of fairly flat resonance.
I am not suggesting that I am emphatically correct, however I do not agree with a lot of your theory. Remember that this design can use ports, tapered ports, or passive radiators to achieve it's output section. If a passive radiator is used instead of the Holliman ports as shown in the plans, your theory does not make sense to me. Passive radiators cannot have multiple resonant peaks. I still contend that this box only has one resonant peak and that resonance covers a large bandwidth.
Furthermore, the helmholtz resonator is definitely not tuned to the center frequencies of the modes of the pipe. Again, replace the Holliman ports with passive radiators and there can be no pipe modes.
From the patent:
"The system does not in fact have to be entirely 'Port-loaded', either port X or port X', or even both X and X', can be replaced by other types of mass loading... tapered port, (or horn in its extreme form). Auxiliary Bass Radiator, slot radiator, or even (a) further powered units could be used." Don't forget the ports can be replaced with a passive radiator. This means that any theory regarding pipe resonances is out, at least in my opinion.
"Consider diagram C. The resonant frequency is determined by X and V as before, but it can be instantaneously changed to a lower frequency by the closure of the flap F, which introduces an extra length of port, X'. Now consider diagram D., in which the flap F has been replaced by a speaker drive unit. If the speaker is in phase with the resonance (X:V) it acts as an open flap, in which case the rest of the port, X', takes no part in the resonance, and the unit tries to resonate at the frequency determined by X and V. As resonance starts to build up, the resonant Amplitude increases beyond that of the unit driving it. The excess air motion can not pass through the cone and therefore it oscillates along port X'." This is my basis for claiming that the frequency of resonance of the helmholtz resonator alone is the high cutoff point, the frequency of resonance of the resonator with the ports (or passive radiators) combined is the low cutoff frequency. Everything in between is a broad range of fairly flat resonance.
passive radiators and ports amout to exactly the same thing they are just slightly different ways of doing the same job. Think of them both as a preset mass that is able to bounce upon the air in a box.
There are lots of variations that can be made in any design that will work. What I am suggesting is what I think would be the optimum arrangement. Given the drivers of the day the infra bass used what was available and met the kind of cost budget the designer probably had in mind and would get the job done. A driver with an Fs of 30 Hz will still have output well below that but the output will be very much reduced. So it would make sence that the Fs of the driver that you wanted to use to excite very low frequencies in a system like this should have its Fs as low as possible. The lower the driver Fs and the higher the drivers xmax the higher the system's efficiency will be.
What I have suggested is a pipe that is tuned to the driver so that it will produce a series of strong resonances which are as low in frequency as possible. Those resonant nodes will bump or boost the output of the system. Then the pipe is coupled to the large air cavity which should have a larger Q resonance to further bump the output of the pipes resonant nodes. This effect will be maximized when the cavity rsonance is exactly centred upon the multiple resonences of the pipe. I am not saying that that is what Holliman did or tried to do but rather that is what I see as making the most sence to achieve the maximun Q of the resonance of the system.
This whole design is not about building a speaker with flat response. This design is about making a woofer generate resonant output at frequencies well below its normal pass band. I am not really all that interested in what Holliman says in the patent. Patents are most often intensionally vague and or written at a time when the inventor has limited experience and understanding of a design. Sometimes they are a best guess and can be totally wrong. The fact that this design patent has gone unused for such a long time in the public domain says that it is probably not a useful discription of what the inventor thought was happening. Others trying to follow the inventors directions probably got lost in a mess that did not work properly.
I am just giving you my best guess here. I have not built one of these cabinets and I don't think I would build one. I might be interested to experiment with the ideas that I have put forward as they make some sence to me. I am however not saying that I am correct in my assumptions.
As I said before I would be interested in comments from those here with enough technical background in the physics of such systems. I may well be all wrong in my assesment of how these things work. I have no way to prove or to disprove what I have said . This is a discussion of ideas. It is up to other interested readers with more experience to provide some direction at this point as I am just repeating myself. Regards Moray James.
There are lots of variations that can be made in any design that will work. What I am suggesting is what I think would be the optimum arrangement. Given the drivers of the day the infra bass used what was available and met the kind of cost budget the designer probably had in mind and would get the job done. A driver with an Fs of 30 Hz will still have output well below that but the output will be very much reduced. So it would make sence that the Fs of the driver that you wanted to use to excite very low frequencies in a system like this should have its Fs as low as possible. The lower the driver Fs and the higher the drivers xmax the higher the system's efficiency will be.
What I have suggested is a pipe that is tuned to the driver so that it will produce a series of strong resonances which are as low in frequency as possible. Those resonant nodes will bump or boost the output of the system. Then the pipe is coupled to the large air cavity which should have a larger Q resonance to further bump the output of the pipes resonant nodes. This effect will be maximized when the cavity rsonance is exactly centred upon the multiple resonences of the pipe. I am not saying that that is what Holliman did or tried to do but rather that is what I see as making the most sence to achieve the maximun Q of the resonance of the system.
This whole design is not about building a speaker with flat response. This design is about making a woofer generate resonant output at frequencies well below its normal pass band. I am not really all that interested in what Holliman says in the patent. Patents are most often intensionally vague and or written at a time when the inventor has limited experience and understanding of a design. Sometimes they are a best guess and can be totally wrong. The fact that this design patent has gone unused for such a long time in the public domain says that it is probably not a useful discription of what the inventor thought was happening. Others trying to follow the inventors directions probably got lost in a mess that did not work properly.
I am just giving you my best guess here. I have not built one of these cabinets and I don't think I would build one. I might be interested to experiment with the ideas that I have put forward as they make some sence to me. I am however not saying that I am correct in my assumptions.
As I said before I would be interested in comments from those here with enough technical background in the physics of such systems. I may well be all wrong in my assesment of how these things work. I have no way to prove or to disprove what I have said . This is a discussion of ideas. It is up to other interested readers with more experience to provide some direction at this point as I am just repeating myself. Regards Moray James.
Moray, I appreciate your interest in this subject, and anyone else who has commented. I too was hoping for some insight from some of the experts here that can intuitively see how things work. I don't have enough math or science and I am at least years of speaker building away from such an intuitive understanding of how things work.
For now we can agree to disagree (can't we?) because I'm not buying your theories and you aren't sold on mine. Maybe we are both completely wrong.
The whole point of this thread was to try to identify any possible problems, tweakable areas, etc before I build, just in case it doesn't work as planned. Since I found the forum post that I attached with my last attachment (on the second page of this thread) I am much less worried. The guy says the bass gets louder as it gets lower and plays 5 - 25 hz with great sensitivity. That is exactly what I am looking for and I am no longer scared to build. Also, if it still does not turn out right I feel confident that I know enough about the design to tweak it to personal taste.
Since we have both been repeating ourselves over and over without presenting anything new I am bowing out of this for now until and unless someone either pops in that can at least try to confirm or deny ANY of the theories presented so far or can maybe come up with something different. With roughly 900 hits on this thread so far I KNOW some of the world's best minds have read it, probably chuckling all the while at how naive I am. Or maybe the expert consensus is that this design is not worth the time and money to even experiment with. I guess I won't know until I build it and listen.
For now we can agree to disagree (can't we?) because I'm not buying your theories and you aren't sold on mine. Maybe we are both completely wrong.
The whole point of this thread was to try to identify any possible problems, tweakable areas, etc before I build, just in case it doesn't work as planned. Since I found the forum post that I attached with my last attachment (on the second page of this thread) I am much less worried. The guy says the bass gets louder as it gets lower and plays 5 - 25 hz with great sensitivity. That is exactly what I am looking for and I am no longer scared to build. Also, if it still does not turn out right I feel confident that I know enough about the design to tweak it to personal taste.
Since we have both been repeating ourselves over and over without presenting anything new I am bowing out of this for now until and unless someone either pops in that can at least try to confirm or deny ANY of the theories presented so far or can maybe come up with something different. With roughly 900 hits on this thread so far I KNOW some of the world's best minds have read it, probably chuckling all the while at how naive I am. Or maybe the expert consensus is that this design is not worth the time and money to even experiment with. I guess I won't know until I build it and listen.
Agree...
I would be very interested to know how your project works out. I am sure as you have noted that there are probably many others that would also be interested. I also agree with you in that the guys that know how to fly all the math have looked and not seen much merrit in the design. I think that the design probably works but just does nor offer anywhere near enough gain in anything but closed room conditions to be practicle. I think that the fact that we have had reports confirming this issue backs that up. so it would seem to me that larger would be better and that one would want to design a system that has as high a Q as possible to insure the maximum output.
If you read through the thread on the "Acoustic Cannon" you will see that that system is capable of yielding a gain of 6db. I wonder if such a configuration could be further boosted by the addition of a resonator cavity as in the Holliman design? My concerns would be two fold, 1) that the necessary volume would have to be very large (confining the design to built in applications) and 2) that positioning the driver at a point on the pipe where ther is not a natural acoustical null (at the fundamental) might cause the driver to be driven well beyond its mechanical limits. The Holliman design while using what appears to be two ducts has the two duct section coupled at the centre point where the driver is mounted so that amounts to the middle of a single length of pipe which is where the null of the fundamental will occur. Best regards Moray James.
I would be very interested to know how your project works out. I am sure as you have noted that there are probably many others that would also be interested. I also agree with you in that the guys that know how to fly all the math have looked and not seen much merrit in the design. I think that the design probably works but just does nor offer anywhere near enough gain in anything but closed room conditions to be practicle. I think that the fact that we have had reports confirming this issue backs that up. so it would seem to me that larger would be better and that one would want to design a system that has as high a Q as possible to insure the maximum output.
If you read through the thread on the "Acoustic Cannon" you will see that that system is capable of yielding a gain of 6db. I wonder if such a configuration could be further boosted by the addition of a resonator cavity as in the Holliman design? My concerns would be two fold, 1) that the necessary volume would have to be very large (confining the design to built in applications) and 2) that positioning the driver at a point on the pipe where ther is not a natural acoustical null (at the fundamental) might cause the driver to be driven well beyond its mechanical limits. The Holliman design while using what appears to be two ducts has the two duct section coupled at the centre point where the driver is mounted so that amounts to the middle of a single length of pipe which is where the null of the fundamental will occur. Best regards Moray James.
just a guy said:
my experience when having still been working on ported boxes, in emperical, observational terms, is that the angle cut at 45 degrees became the center point of the tube length measurement. This becomes a lower, wider 'q' of the resonance of the port. It tends to be notably more effective in trapping (more properly:defeating) internal box resonance modes, or removing them from being issues. This, concerning standing waves that may evolve in the box. The orientation can also be used to deal with pressure issues in the box, due to port proximity to box walls, bracing, etc. Very much a subtle audiophile thing, but it is observable/hearable. it can and does, at times (in car audio) make the difference between blown and working sub drivers. Along with other things that can be done, of course. One small part of an overall recipe. One of my favorite parts, was to take a box where the idiot owner kept blowing drivers (wrong box! wrong driver!)...and put a thin film of resistant material over the inner end of the port. They were so thankful!!
I played with porting extensively while being the 'braintrust -sub box developer' at a car audio shop. It gave me the opportunity to make a painless costless..and near priceless analysis of just about every concievable combination and paramater known to or speculated by mankind, concerning bass and ported boxes. It was fun.
Im sorry to ask such a stupid question, but what are you going to hear / feel between 5-25hz, Do you like the pipe organ? I know that that ocasionally has a 16hz response but really what else? Most instruments 40hz is the lowest point, by 25hz pretty much covers the rest, even the man made effects (ie not natural) sub bass found in cinema soundtracks.
Geoff in Auz made this point well...
I think it was in one of the other threads that there are in fact acoustic instruments that are capable of infra sonic reproduction. Then there are sound tracks with astoundingly low frequency information. So there is a reason to reproduce these frequencies. If it's there we should hear it and feel it to the fullest fidelity that we are capable of reproducing.
I think it was in one of the other threads that there are in fact acoustic instruments that are capable of infra sonic reproduction. Then there are sound tracks with astoundingly low frequency information. So there is a reason to reproduce these frequencies. If it's there we should hear it and feel it to the fullest fidelity that we are capable of reproducing.
Quite possibly...
there is a lot of spacial ambient information linked up to low frequency sounds. Highre frequency information gets carried around a room/venue on the back of low frequency waves. This is the same process that is used to carry AM radio signals as they travel on a low frequency carrier signal, that's how they transmit over distance. i have always maintained that people buy subs for the bass but fall in love with them for the space. Even with a mono sub (one channel) you get mor bass but people discover that the space and ambient information retriaval of thier systems is increased. Well mono subs combine left and right channel information so any common mode information is lost in the mix (equal but opposite phase information signals cancel out). When you move to stereo sube you maintain that previously lost spacial information. System spacial information is then increased.
there is a lot of spacial ambient information linked up to low frequency sounds. Highre frequency information gets carried around a room/venue on the back of low frequency waves. This is the same process that is used to carry AM radio signals as they travel on a low frequency carrier signal, that's how they transmit over distance. i have always maintained that people buy subs for the bass but fall in love with them for the space. Even with a mono sub (one channel) you get mor bass but people discover that the space and ambient information retriaval of thier systems is increased. Well mono subs combine left and right channel information so any common mode information is lost in the mix (equal but opposite phase information signals cancel out). When you move to stereo sube you maintain that previously lost spacial information. System spacial information is then increased.
if one's playing back lp without highpass filter, seems to me could be significant rumble, & stylus drag noise producing an arficial "ambiance-foundation" of sorts. (I highpass around 20-30 on transfer to hard drive)
how did some recordings even on cd reissue subjectively sound "so deep" such as Sinatra & Riddle's 1958 "Only For The Lonely" even with 50Hz cutoff speakers? (I like that sound)
how did some recordings even on cd reissue subjectively sound "so deep" such as Sinatra & Riddle's 1958 "Only For The Lonely" even with 50Hz cutoff speakers? (I like that sound)
Thank you very much for that. Wow, it really does not look all that complicated at all. What are the standing wave baffles that the South African from AVforums keeps talking about? The drawings show many different designs, I am unclear on which is the "best" one.
The wording of the description sounds a little egotistical to me "for years we've been trying" and the fact that he got a patent in the first place yet still no one really picked up on it makes it sound like maybe it's a little bit hype.
It is not indicated whether any of the sketches are to any kind of scale; by their roughness I am assuming they are not. Like this one that looks fairly simple to build:
Note that this is not the Graham Holliman velocity coupled......etc http://www.flickr.com/photos/rcadimensia/5916268941/sizes/l/in/photostream/
A lot of what threw me was the suggestion of using mica or something metalic for the baffle with the small hole located directly in front of the driver, also the specific angle of the X shaped part of the baffle with the small hole facing the driver.
The wording of the description sounds a little egotistical to me "for years we've been trying" and the fact that he got a patent in the first place yet still no one really picked up on it makes it sound like maybe it's a little bit hype.
It is not indicated whether any of the sketches are to any kind of scale; by their roughness I am assuming they are not. Like this one that looks fairly simple to build:
Note that this is not the Graham Holliman velocity coupled......etc http://www.flickr.com/photos/rcadimensia/5916268941/sizes/l/in/photostream/
A lot of what threw me was the suggestion of using mica or something metalic for the baffle with the small hole located directly in front of the driver, also the specific angle of the X shaped part of the baffle with the small hole facing the driver.
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You should read this short explanation of fundamental frequency and harmonics to learn more on this.
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