So.. I have this idea that keeps tickling the back of my mind about making a customised speaker driver and offering it for the DIY market. I think I can see a little niche, but do not want to blab about it yet when I have not even done a prototype. Please bare with me!
To do this I would need to create my own surround for the cone and I was wondering what the differences are between foam and rubber? Anyone got experience with driver design?
Perhaps does foam hit its excursion limits more gently than rubber, my assumption is that it can stretch a little more?
It might be my imagination but I feel I've seen more foam surrounds used in car audio and probably more in subs than midrange for example?
What do you know? 🙂
To do this I would need to create my own surround for the cone and I was wondering what the differences are between foam and rubber? Anyone got experience with driver design?
Perhaps does foam hit its excursion limits more gently than rubber, my assumption is that it can stretch a little more?
It might be my imagination but I feel I've seen more foam surrounds used in car audio and probably more in subs than midrange for example?
What do you know? 🙂
Hi. Have you considered the profile also, be it flat, domed or concertina etc? Do you think that the surround also serves to locate the cone? Dome surrounds, to me at least seem to allows itself to "roll" and pivot as it extends whilst flat ones seem to need to stretch to function. Concertina, though I could be wrong on this extend in a more "straight line" sort of way, bending at the fixture points. Material type used, stiffness, profile, and dimensions to me would possibly mean that there is a fairly big overlap in performance of different configurations. Hope this has helped and not just distracted from your initial question.
Good luck.
Good luck.
The focus will be midrange performance over all else and I was looking at the old Audax PR17 drivers as the closest equivalent to what I'm aiming for, even though the end goal is rather different. These drivers have an almost flat surround that is made from foam and a very minimal xmax of +/- 0.5mm.
So perhaps I should re-frame my question and ask the gurus here, why does the Audax PR17 use a foam surround rather than rubber?
Yes the profile will also matter a lot. I'm wondering about making a prototype using 3D printing and create a press mold for PU flexable resin. I might not have access to fancy FEA analysis, but I can re-iterate and test! (Yes I'm aware of Polymate 3D printing TPU surrounds directly on a 3D printer)
So perhaps I should re-frame my question and ask the gurus here, why does the Audax PR17 use a foam surround rather than rubber?
Yes the profile will also matter a lot. I'm wondering about making a prototype using 3D printing and create a press mold for PU flexable resin. I might not have access to fancy FEA analysis, but I can re-iterate and test! (Yes I'm aware of Polymate 3D printing TPU surrounds directly on a 3D printer)
Foam is lighter and more flexible.
Rubber gives better damping to cone resonances, more robust and usually lasts longer.
Rubber gives better damping to cone resonances, more robust and usually lasts longer.
I was meaning acoustical simulation, rather than mechanical. Something like this - www.plm.automation.siemens.com/global/en/products/simulation-test/acoustic-simulation.html
You can get some trials but I imagine learning this type of thing would take longer than 90 days!
That said You got me to search a little more and OpenBEM seems interesting. Wonder how difficult it is to learn 🤔
There are so many different degrees of freedom with a surround let alone a driver, one has to look at everything and know the tradeoffs to get the target result.
dave
dave
100% of rubber surround Rola drivers in Hammond organs from 1955 to 1970 that I've heard, worked. I own 4 such organs. 100% of rubber surrounds in drivers in Wurlizer organs from 1958 to 1966 work. I own 2.
0% of foam surrounds in top speakers from Allen organ from 1980 worked properly. Sounded like **** and when you took the cover off, surrounds were visibly torn. Only reason they didn't launch the cones into space, the amps were down to 2 watts.
0% of foam surrounds in top speakers from Allen organ from 1980 worked properly. Sounded like **** and when you took the cover off, surrounds were visibly torn. Only reason they didn't launch the cones into space, the amps were down to 2 watts.
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Old foam will rot. Manufacturers are mking much different foam surrounds in terms of longevity now. Trying to compare 50-60 year old tech to today’s is fraught with peril.
dave
dave
The EDF FEM code I linked to can be used for linear acoustics. It doesn't have BEM that I am aware of but in the past I have used it to perform modal analyses of vibrating cabinets and then taken the surface velocities as boundary conditions for the acousto BEM code to get the radiated sound field. The attraction of the EDF code is that it is a freely available industrial code rather than a university research code.
If you are familiar with FEA/CFD/CAA/BEM/... numerical analysis then picking up new codes takes little time. If not then how long it takes to become effective will depend on how much of the basics you need to learn. The mechanics of getting data in and out of a program should take no more than a few days to learn even for software with a poor user interface. What does take a long time to learn though is the the relevant physics, maths, computer science,... and that depends on ones background. For example, if you have an engineering degree it shouldn't be a struggle but it might be for other backgrounds.
OpenBEM depends on matlab and is not open despite the name given you have to write to get a copy. Acousto, BEM++, and a few others are open and probably better options for a quick dip to see how you get on. They are research codes though and not industrial codes which means they have minimal support and will be a bit awkward to use.
3D printing and moulding may work, (vacuuming the mix to remove air is possibly required) but if you don't intend on making the real thing in that way, it may just be giving false information. If your shape is flat, have you considered selecting various thicknesses, shore harnesses and types of flat materials and just cutting them out? Seems to me, an A4 sized piece may be enough for each trial. Samples might be available from some manufacturers for free. You may even be able to mould the sheet material into different shapes. Just thinking aloud. Good luck.
In the past foam surrounds degraded, especially in uv light, this puts me of using them; however as a previous poster stated they have improved so my misgivings may well be unfounded. I still avoid them though.
I bought some used JBL 8340a cinema surround speakers. One would suppose there is no damage from UV or overload in a commercial cinema. The foam surrounds just disappeared. Other than that, the speakers look good, so I got them for practice on how to install a new speaker surround.
On the other hand, my Lowther DX2 surround is still like new (and must be more than 10 years old).
On the other hand, my Lowther DX2 surround is still like new (and must be more than 10 years old).
Apart from the technical aspects:
Many people will not buy drivers with foam surrounds, because these have a bad reputation and cheap appearance.
Many people will not buy drivers with foam surrounds, because these have a bad reputation and cheap appearance.
The surround has a "compliance", just like the spider. It affects/contributes to the performance of the driver. The choice (by the designer) is part of the intended performance design.
Unfortunately, foam surrounds eventually deteriorate.
You are lumping all foam and all rubbers into only two pots. You are not considering ageing either.
Foam, made out of what? Aluminum? Corn protein? Buna N? Polyethene? Is it naturally compliant or infused with a plasticizer? What rubber? Thickness, cross section. profile.
Shape as well as material matters. The surround helps control teeter-totter, cone resonance reflections and cone resonance dampening.
How linear matters. How much it effects the Qms, and a host of other parameters. Do you want it compliant is all directions? Stretchable? or just flexable? Not to discourage you as you may have some really slick idea, but driver design is very hard and very complex.
If you idea is for a really flat, super low distortion, 4 inch midrange with high efficiency that can do 800 to 4K, with well behave out of band breakup, do let us know.
Foam, made out of what? Aluminum? Corn protein? Buna N? Polyethene? Is it naturally compliant or infused with a plasticizer? What rubber? Thickness, cross section. profile.
Shape as well as material matters. The surround helps control teeter-totter, cone resonance reflections and cone resonance dampening.
How linear matters. How much it effects the Qms, and a host of other parameters. Do you want it compliant is all directions? Stretchable? or just flexable? Not to discourage you as you may have some really slick idea, but driver design is very hard and very complex.
If you idea is for a really flat, super low distortion, 4 inch midrange with high efficiency that can do 800 to 4K, with well behave out of band breakup, do let us know.
For now, just BUY the rubber or foam edge, your choice.
I am a great believer (and doer!) of in-house making stuff, in fact, "anything" can be done, only limits are Market and $$$$$, lots of them.
Knowledge, which of course is most important, can be bought/hired. Again $$$$$$$
Practical advice from a raw frame speaker maker: buy whatever components you need until you need 5000 of anything.
We are talking processed stuff, which needs dies (injection - stamping - etc) which mean a huge chunk of money whose cost must be spread between finished parts.
Some machined parts, specially those which can be turned in a lathe, can be made in small quantities, say polepieces or magnet disks/plates, but anything else: spiders, cones, domes, edges, gaskets, terminals, are made in quantity using expensive dies mounted in VERY expensive machines, so .........
I am a great believer (and doer!) of in-house making stuff, in fact, "anything" can be done, only limits are Market and $$$$$, lots of them.
Knowledge, which of course is most important, can be bought/hired. Again $$$$$$$
Practical advice from a raw frame speaker maker: buy whatever components you need until you need 5000 of anything.
We are talking processed stuff, which needs dies (injection - stamping - etc) which mean a huge chunk of money whose cost must be spread between finished parts.
Some machined parts, specially those which can be turned in a lathe, can be made in small quantities, say polepieces or magnet disks/plates, but anything else: spiders, cones, domes, edges, gaskets, terminals, are made in quantity using expensive dies mounted in VERY expensive machines, so .........
I've been quoted for tooling and MOQ for a professionally produced surround to my specification and design. It seems within reach if I can entice a distributior or two.
The question is really about choosing the best material. I think the only answer is to try things and find out.
I think we are really lucky as DIYers these days to have such a vast array of methods to make things from 3d printing to CNC to resin rubber and foams and vacuum forming...
The question is really about choosing the best material. I think the only answer is to try things and find out.
I think we are really lucky as DIYers these days to have such a vast array of methods to make things from 3d printing to CNC to resin rubber and foams and vacuum forming...
For woofers installed in boxes, the behaviour of the surround to deal with the large pressure variations and excursions associated with low frequencies would be important. How is any surround deformation (billowing) with the pressure variations affecting compliance - is it modulating fs, for example?
For midranges, how well is the surround material terminating the cone to damp resonances within the cone?
For midwoofers, is it possible to satisfy both the above satisfactorily - or is it a compromise too far?
For midranges, how well is the surround material terminating the cone to damp resonances within the cone?
For midwoofers, is it possible to satisfy both the above satisfactorily - or is it a compromise too far?