Hi John
“Oh Tom, now you have gone and done it. It was hard enough with out considering losses and the effect of source area on radiation resistance”
Haha, well it seemed like the gears needed more sand
Hi willray
“Unless the impedance changes for the slot case by a factor of 2 (and I don't understand acoustical impedance well enough to know whether this is true) this leaves us, for the slot case, with 4x the watts per square meter, distributed over 1/2 the area, resulting in 2x the total energy.”
As Frank Zappa once said, "the crux of the biscuit is the apostrophe" while i am not sure why that popped into my head this might help;
Here is a graph of the chunk you didn’t find, the acoustic radiation resistance plotted as a function of the radiator size in wavelengths;
http://www.fonema.se/mouthcorr/Image3s.GIF
As one can see, the slot or even a typical woofer cone in the bass range is well to the left of the graph and so one finds that going from a cone radiator to a smaller slot, one has moved further to the left and as a result is a less efficient radiator.
A horn (in a perfect world and ideal size etc) connects the radiation resistance of the flat portion of the curve (coupled at the big end of the horn) to the radiator (at the small end) which would otherwise occupy a place on the graph to the left where there is much less radiation loading.
What can also be inferred is the reason woofers (to have a flat response as infinitely baffled direct radiator) must have 4 times the excursion as the frequency falls an octave.
If the radiation resistance were constant, then increasing the time period by 2 only increases the travel by 2. Instead, as the frequency falls, the radiator is smaller compared to the wavelength and so is moved to the left and that loss of radiation resistance means the cone must travel 4 times further to offset that reduction.
This is accomplished by having enough moving mass and a weak enough motor to make the system acceleration based instead of constant velocity.
This mass governed operation is how / why one can add a ring of solder or other weight to the voice coil of a woofer and NOT effect it’s high frequency or transient response (but you do lower the sensitivity and LF corner) .
In the (ideal) horn, one finds that if the mouth is large enough to reach the flat portion of it’s curve, that it will automatically be “large enough” at any frequency above that.
Hope that helps
Tom
“Oh Tom, now you have gone and done it. It was hard enough with out considering losses and the effect of source area on radiation resistance”
Haha, well it seemed like the gears needed more sand
Hi willray
“Unless the impedance changes for the slot case by a factor of 2 (and I don't understand acoustical impedance well enough to know whether this is true) this leaves us, for the slot case, with 4x the watts per square meter, distributed over 1/2 the area, resulting in 2x the total energy.”
As Frank Zappa once said, "the crux of the biscuit is the apostrophe" while i am not sure why that popped into my head this might help;
Here is a graph of the chunk you didn’t find, the acoustic radiation resistance plotted as a function of the radiator size in wavelengths;
http://www.fonema.se/mouthcorr/Image3s.GIF
As one can see, the slot or even a typical woofer cone in the bass range is well to the left of the graph and so one finds that going from a cone radiator to a smaller slot, one has moved further to the left and as a result is a less efficient radiator.
A horn (in a perfect world and ideal size etc) connects the radiation resistance of the flat portion of the curve (coupled at the big end of the horn) to the radiator (at the small end) which would otherwise occupy a place on the graph to the left where there is much less radiation loading.
What can also be inferred is the reason woofers (to have a flat response as infinitely baffled direct radiator) must have 4 times the excursion as the frequency falls an octave.
If the radiation resistance were constant, then increasing the time period by 2 only increases the travel by 2. Instead, as the frequency falls, the radiator is smaller compared to the wavelength and so is moved to the left and that loss of radiation resistance means the cone must travel 4 times further to offset that reduction.
This is accomplished by having enough moving mass and a weak enough motor to make the system acceleration based instead of constant velocity.
This mass governed operation is how / why one can add a ring of solder or other weight to the voice coil of a woofer and NOT effect it’s high frequency or transient response (but you do lower the sensitivity and LF corner) .
In the (ideal) horn, one finds that if the mouth is large enough to reach the flat portion of it’s curve, that it will automatically be “large enough” at any frequency above that.
Hope that helps
Tom
If Nelson Pass and Tom Danley drop into a thread I started, I will just feel blessed.
Thanks for dropping in.
Thanks for dropping in.
Hi,
That is pure and utter nonsense because your physics are just wrong.
Some 2.5 ways were implemented by adding a lump of mass
to the centre of the "bass" unit, of two identical drivers.
Why I'll leave you to work out and understand.
rgds, sreten.
Last edited:
“That is pure and utter nonsense because your physics are just wrong.
Why I'll leave you to work out and understand.”
I have even glued a lead ring to a woofer voice coil and then measured this to confirm this to a skeptic once so perhaps your physics is wrong, or, perhaps you meant to say the added mass to the radiator body which can alter it’s hf behavior.
In any case, if you doubt this, do the homework, do what I said and measure it.
“The OP asked for some sanity, not irrelevant showing off.”
You reminded me how much DIY forums have changed and why I rarely post here anymore.
You do not have two times the total energy, you have two times the kinetic energy. Smoothly accelerating air in the slot will lower the air pressure relative to that at the driver in order to maintain a constant total pressure. You can equate the total pressure, p + 0.5*rho*U*U, at the driver and the slot exit to find the relative change in pressure. Rho is the density of the air.
So this guy had it right way back at the beginning....
As to adding mass, I would agree that moderate additions of mass have no influence on bandwidth. You can apply heavy coatings on cones and see the sensitivity drop with no change in HF response. Ditto with mass rings. Of course if you take it too far then you may change the cone modes or get into decoupling effects, otherwise HF rolloff of a woofer comes from impedance curve, modal effects and the radiation resistance flattening out at ka = 1.
As to theoretical pontificating, we are just comparing empirical science to theoretical science and seeing the pitfalls of each. With empirical science you may measure pressure at a slot and say "aha, 9 dB louder", ignoring the far field effect (or lack). With theoretical science you may get hung up on energy without considering the total model (radiation resistence). In the end, the theorizing about what is going on, and then confirming it with experiment gets you to the answer.
I was convinced when John put his slot loaded device into the sealed cabinet and got the same LF level.
David S.
Well you know what Feynmen said. Doesn't matter how eloquent your theory is. If it doesn't match experiment it's useless. Anyway, yes you get higher SPL in the plan of the slot in a near field measurement, just as you get higher SPL in the plan of a ported speaker. And what do you do when you want to sum the port response to the driver response to get an idea of the net SPL? You scale the port SPL down by the ration of port area to Sd. The slot is the same thing. Am I repeating myself here? Furthermore, the slot, mathematically, is really no different than a TL or a ported box. All have an source of energy, the driver, a capacitive element, the volume of air, and an inductive element, the mass of the air.
Same here Tom, but I got sucked back into this one.
Aww, come on! Wasn't Churchill that said "Never has so few destroyed for so many"
You'll let the lesser social skilled people win!! Most of what you write fly over my head but slowly some sort of "knowledge" is building up in my some what mushy-sorry-excuse-of a brain.
Keep posting and use "ignore button"
You'll let the lesser social skilled people win!! Most of what you write fly over my head but slowly some sort of "knowledge" is building up in my some what mushy-sorry-excuse-of a brain.
Keep posting and use "ignore button"
I am /really, really/ sorry I've catalyzed an argument amongst the lot of you.
It most certainly wasn't my intent, and post John K's first reply to my original question, I'm /still/ only trying to understand what I'm doing wrong with the math, that's letting it come up with values that can't be normalized by the port area.
It most certainly wasn't my intent, and post John K's first reply to my original question, I'm /still/ only trying to understand what I'm doing wrong with the math, that's letting it come up with values that can't be normalized by the port area.
Hi guys,
Sorry I don't have time to read all of these great posts so I'm going to jump in at my own risk of repeating what might have been said.
I'm using two AE IB15s per manifold per channel (4) mounted behind the front corners of a 12 by 18 by 7 foot basement room. They're powered with a Crest CA12 amplifier and a variable crossover.
Wide open they measure very well below 20hz to 50hz and rise a bit up to 120hz and down fast at 225hz. I dial in the crossover to roll off at 90hz. I can go a little higher but sonics start to degrade.
SBL wise they come in at about 2db less than the AE TD15S that sit in from so I'd say 90db for the pair. I tried a straight out IB single 15 mounted in the wall and it shook the wall creating a lot of distortion. The PPSL doesn't do that, no secondary reactive mechanical "hit" against the wall.
Some interesting observations are that putting ones hand in front of the manifold one can feel a definite air flow, more like a bass port than like a cone. So I think there air is accelerated out of the manifold. When a 40hz tone is played it is 4db lower in the back room than front. Also when visitors walk back to see the woofers they are amazed at how quiet they are compared to the listening position.
Bass sounds like its unlimited. On Pink Floyd's SACD of "Time" The bass cord just after the drums start moves your hair. On modern CDs bass sounds like it's enveloping your body and is felt by you entire body. On three occasions people had to leave the room to use the bathroom. It can be exhilarating and at times unnerving. Reactions in the rest of the house are unpredictable. My daughter’s second floor bedroom walls shake. Pictures downstairs have fallen off of walls. Nick knacks in the dining room rattled off shelves.
Woofer Xmax is no ware near their limits, +- ¼” maybe more on some material.
My recommendation for those who don’t want that kind of output is to use typical 10” subwoofer drives with FS in mid 20s Qts above .4 in the smallest manifold possible and cross as high as it sounds good. “Hit” and “punch” are very good with this design but coloration has to be considered. A 200hz crossover would be great. This would give a modern (twisted) adaptation on Allison’s work.
Sorry I don't have time to read all of these great posts so I'm going to jump in at my own risk of repeating what might have been said.
I'm using two AE IB15s per manifold per channel (4) mounted behind the front corners of a 12 by 18 by 7 foot basement room. They're powered with a Crest CA12 amplifier and a variable crossover.
Wide open they measure very well below 20hz to 50hz and rise a bit up to 120hz and down fast at 225hz. I dial in the crossover to roll off at 90hz. I can go a little higher but sonics start to degrade.
SBL wise they come in at about 2db less than the AE TD15S that sit in from so I'd say 90db for the pair. I tried a straight out IB single 15 mounted in the wall and it shook the wall creating a lot of distortion. The PPSL doesn't do that, no secondary reactive mechanical "hit" against the wall.
Some interesting observations are that putting ones hand in front of the manifold one can feel a definite air flow, more like a bass port than like a cone. So I think there air is accelerated out of the manifold. When a 40hz tone is played it is 4db lower in the back room than front. Also when visitors walk back to see the woofers they are amazed at how quiet they are compared to the listening position.
Bass sounds like its unlimited. On Pink Floyd's SACD of "Time" The bass cord just after the drums start moves your hair. On modern CDs bass sounds like it's enveloping your body and is felt by you entire body. On three occasions people had to leave the room to use the bathroom. It can be exhilarating and at times unnerving. Reactions in the rest of the house are unpredictable. My daughter’s second floor bedroom walls shake. Pictures downstairs have fallen off of walls. Nick knacks in the dining room rattled off shelves.
Woofer Xmax is no ware near their limits, +- ¼” maybe more on some material.
My recommendation for those who don’t want that kind of output is to use typical 10” subwoofer drives with FS in mid 20s Qts above .4 in the smallest manifold possible and cross as high as it sounds good. “Hit” and “punch” are very good with this design but coloration has to be considered. A 200hz crossover would be great. This would give a modern (twisted) adaptation on Allison’s work.
You do not seem to be doing anything wrong with the maths but you do seem to be holding onto assumptions about what is physically important even after your own analysis has shown them not to be. What is it that is stopping you trusting your own workings?
You should not need to apologise for asking why and persisting until the penny drops. Why seems to be a fairly rare question around here and it probably shouldn't be. It is a lot easier to talk about what.
My post was not aimed at you! I have not seen any abrasive in your replies
)Cheers,
Peter
Please ignore him Tom, the rest of us do.
Your posts, as well as Nelson, Dave, and John's posts are greatly appreciated here.
Last edited:
I appreciate your perspective sir, and I wish a larger fraction of the world shared it.
I just dislike causing a fracas unnecessarily. In my own domains I end up stirring the pot rather frequently, as I'm not much for worshipping sacred cows without careful examination, but it's kind of disturbing to see that I'm causing similar polarization even when that /wasn't/ my intent.
I'm not /aware/ of holding any particular assumptions regarding what's physically important. The only assumption that I'm aware that I'm making, is that I should be able to work the problem starting from area and particle velocity forward through volume velocity to sound pressure, and from those same values backwards through sound intensity to sound pressure, and get the same result.
I guess I'm also making the assumption that volume velocity is conserved (more or less) over time in a propagating wave. I have to think about that - I'm not sure I see an excuse for why that would necessarily be true.
Of course, if I'm making other implicit assumptions, I'm likely to be blind to what they are.
Partly it's because I don't yet have an intuitive grasp of how the physical properties fit together, so when the math says something weird, I don't know whether it's because I've applied it wrong, or because I've asked it the wrong question in the first place.
Partly it's because there appear to be at least 3 different opinions as to what's physically happening, and possibly even more about what I'm doing wrong in the analysis, all from people who I expect know far more about this than I. This is making it a bit difficult to isolate the fault in my thinking or application.
Honestly, this question is making me feel absolutely dimwitted. I am used to being able to reliably get from first principles, to practically any analysis I need, in just about any science or math domain. I have an audio question, stumble into an arena where real live experts are still willing to rub shoulders with the masses, and all I can do is start an argument by trying to understand what should be a fairly simple topic.
Apologies necessary or not, this does not seem a particularly auspicious beginning
In aid of experimental results:
About 40 years ago, I built a 3-way system around a slot-loaded 12". The mid/tweeter box was spaced over the 12" firing upwards, with the slot all around. In extensive listening tests, we had the same bass no matter if the slot was 1", 6", or the top box was removed.
About 42 years ago, when I was building Infinity 1001s, we actually did some measurements, noting a rather nasty cone breakup at 1200 Hz. Since we had lots or "Permagum" we used to add mass to the woofers anyway, we thought, "hey, what if we damp the whole cone?". No change in cone breakup, no change in HF output, other than efficiency.
About 40 years ago, I built a 3-way system around a slot-loaded 12". The mid/tweeter box was spaced over the 12" firing upwards, with the slot all around. In extensive listening tests, we had the same bass no matter if the slot was 1", 6", or the top box was removed.
About 42 years ago, when I was building Infinity 1001s, we actually did some measurements, noting a rather nasty cone breakup at 1200 Hz. Since we had lots or "Permagum" we used to add mass to the woofers anyway, we thought, "hey, what if we damp the whole cone?". No change in cone breakup, no change in HF output, other than efficiency.
I.B. "the real deal"
Earlier in this thread, I shared my experiences with a similar setup using the same drivers.Thanks for sharing yours as well. We both seem to love our I.B. systems, but this thread somehow got into something else.
Earlier in this thread, I shared my experiences with a similar setup using the same drivers.Thanks for sharing yours as well. We both seem to love our I.B. systems, but this thread somehow got into something else.
- Status
- This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.