What intrigues me, is that that the behaviour of the spider, to me, seems to be extremely crucial to the performance of the driver. Yet, it is barely mentioned - it's a by-the-way element in most discussions - is it a bit like the "electrical parts not in the direct signal path are not important" type of thing?
The heat can't be instantaneously be removed from the voice coil. If you run x watts through the voice coil, you've still got x watts in that voice coil and it's not dissipated instantly. Now your cones don't have much in the way of thermal mass and their surface area isn't all that great so I doubt they make a huge difference compared to using cones which don't have much in the way of thermal conductivity.
So let's do a little math.
Let's say we use a driver that on its own has a sensitivity 6dB greater than one of yours. And wire four of those parallel/series, giving another 6dB, while retaining the same impedance.
Now if I'm able to get the level I want with 5 watts, you would have to pump 80 watts into one of yours to achieve the same level. And of course that 5 watts is spread across 4 drivers so you're only looking at each driver having to deal with 1.25 watts.
1.25 watts vs 80 watts.
Whatever additional help the aluminum cones may add, it's not even remotely close to 1.25 watts on a driver with insulative cones, like paper.
This thread is pretty much about whatever people want to talk about, save for politics and religion.
se
This seems a good rundown on some important factors - http://www.klippel.de/pubs/Klippel papers/Diagnosis_and_remedy_of_Nonlinearities_00.pdf
I could be way off base here, but in my experience, high efficiency speakers just seem to have a certain "presence" and just sound more dynamic than I've ecperienced with much less efficient speakers being driven by a lot more power. I've just chalked this up to reduced thermal compression.
se
S.E,
You are correct that by the time the heat can transfer to the cone it would be to late to prevent power compression. At the same time that really isn't much of an issue when your not running a high efficiency driver like you would in Pro-Audio an are pushing those voicecoils close to the thermal limits of the polyimide coated wire. Another thing that you have to consider is the former material. I use Kapton that is wrapped with a material called Tufquin to dampen the sound of that Kapton. So your heat path through the formet is really made up of some very good insulating materials and most high quality speakers use that type of material in the former. Unless you are using an aluminum former I don't think you have much chance of moving heat out through that path. Most of the heat is lost to the surrounding metal through radiation and a small amount through air conduction. I would not use aluminum as a former, it is again a noise contributor in exactly a place I don't think you want it to be directly coupled to the cone.
Frank,
Wow I am answering a question from you, I took you off my ignore list a couple days ago. You are correct that the spider is a major contributor to unwanted noise, the smaller the diameter or surface area the better but that does not necessarily relate to having the most linear suspension so it is a trade off. There have been speakers built that are called spiderless but that just introduces many other problems with the cone rocking about its axis and that can be a very destructive situation if the coil ever rubs on any surface. I have tried to discuss with some other speaker designer about the noises coming off many surrounds and the usual response is that isn't important. If they would just move the microphone over very close to the surround and measure the noise coming off a rubber surround I think they would change that opinion. Surrounds can be a major contributor of noise and if you consider the large surface area of the surround you see it really is something to consider. Just changing the surround material and the adhesive used at the surround cone junction changes so much it isn't funny, it is a real issue. Many speaker builders use Cyano-acrylic adhesives at this junction because of its speed to cure along a production line and this is a serious mistake. Each and every joint has to be looked at in isolation and the purpose of the joint. You wouldn't want to use the same adhesive at the former cone connection as you do at the surround cone junction but it is done every day. Dust caps are another area of noise if not attached correctly.
You are correct that by the time the heat can transfer to the cone it would be to late to prevent power compression. At the same time that really isn't much of an issue when your not running a high efficiency driver like you would in Pro-Audio an are pushing those voicecoils close to the thermal limits of the polyimide coated wire. Another thing that you have to consider is the former material. I use Kapton that is wrapped with a material called Tufquin to dampen the sound of that Kapton. So your heat path through the formet is really made up of some very good insulating materials and most high quality speakers use that type of material in the former. Unless you are using an aluminum former I don't think you have much chance of moving heat out through that path. Most of the heat is lost to the surrounding metal through radiation and a small amount through air conduction. I would not use aluminum as a former, it is again a noise contributor in exactly a place I don't think you want it to be directly coupled to the cone.
Frank,
Wow I am answering a question from you, I took you off my ignore list a couple days ago. You are correct that the spider is a major contributor to unwanted noise, the smaller the diameter or surface area the better but that does not necessarily relate to having the most linear suspension so it is a trade off. There have been speakers built that are called spiderless but that just introduces many other problems with the cone rocking about its axis and that can be a very destructive situation if the coil ever rubs on any surface. I have tried to discuss with some other speaker designer about the noises coming off many surrounds and the usual response is that isn't important. If they would just move the microphone over very close to the surround and measure the noise coming off a rubber surround I think they would change that opinion. Surrounds can be a major contributor of noise and if you consider the large surface area of the surround you see it really is something to consider. Just changing the surround material and the adhesive used at the surround cone junction changes so much it isn't funny, it is a real issue. Many speaker builders use Cyano-acrylic adhesives at this junction because of its speed to cure along a production line and this is a serious mistake. Each and every joint has to be looked at in isolation and the purpose of the joint. You wouldn't want to use the same adhesive at the former cone connection as you do at the surround cone junction but it is done every day. Dust caps are another area of noise if not attached correctly.
Yes, I agree with the "certain presence and just sound more dynamic" element in the sound - this to me is crucial ... but, IME the "less efficient driven by more power" often fails because that nominally greater power is not clean power. I've done the experiment many times where the quality of the higher power delivered to the speakers is improved, and the result is always, always very significant gains in "presence" and "more dynamic". If the speaker was at fault, this just would not happen.
John,
With a good high power amp and I would include your designs in that group I do think we can trade some efficiency in a speaker for more power in the amp. Obviously it is an exponential power problem with the need for so much more power to drive the speaker but when we aren't worried about power compression, limited power output and clipping in a usable range I think you can make the argument that it isn't as important in a home environment. I wouldn't think that way in a live sound application but in a house with a limited space and much less demand for high SPL I will take that tradeoff in specific applications.
With a good high power amp and I would include your designs in that group I do think we can trade some efficiency in a speaker for more power in the amp. Obviously it is an exponential power problem with the need for so much more power to drive the speaker but when we aren't worried about power compression, limited power output and clipping in a usable range I think you can make the argument that it isn't as important in a home environment. I wouldn't think that way in a live sound application but in a house with a limited space and much less demand for high SPL I will take that tradeoff in specific applications.
This driver, Lorenz S-888 Loudspeaker Measurements and Information, impressed me because the cone and surround are common - and, it appears to do many things that are right ...
You really don't think thermal compression is an issue until you're about to cause the polyamide to fail?
I did the same. Couldn't believe it.
se
It's so nice to feel worthy ...
At least I didn't put you on an ignore list. I just scroll past.
se
SE,
I guess that was a poor way to say that. I just believe that you are indeed getting up into the range of melting the binder or at least pushing the coil fairly hard by the time that compression is audible at least by most. I think you would see more problem from a clipped amp than you are going to have to deal with power compression in a normal home environment unless you are listening at levels that most people would run out of the room. I qualify that with it depends on the wire size, amount of metal around the coil and how long the peak power is being applied. Not so sure that very short transients are going to be audible by the average listener.
I guess that was a poor way to say that. I just believe that you are indeed getting up into the range of melting the binder or at least pushing the coil fairly hard by the time that compression is audible at least by most. I think you would see more problem from a clipped amp than you are going to have to deal with power compression in a normal home environment unless you are listening at levels that most people would run out of the room. I qualify that with it depends on the wire size, amount of metal around the coil and how long the peak power is being applied. Not so sure that very short transients are going to be audible by the average listener.
My hypothesis is that its down to normal amps (even more so higher powered amps) having too much noise(*) on their output. High efficiency drivers are less taxing on res cap banks.
(*) Not noise that can be measured when no signal is playing, noise whose amplitude is modulated by the envelope of the signal.
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Could be. Like I said, it's not anything I have any sort of firm opinion on. I just find higher efficiency loudspeakers to be more pleasing to listen to.
se
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