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Post by aaks38 on Nov 28, 2007 19:10:19 GMT -7
Im not sure if this has been covered yet, but im trying to decide between these 2 drivers. Im planning on getting 4 of them.
My rear room (backside for the subs in the manifold) is roughly 1200 cu ft, so im thinking the AE with its larger Vas would be better, however i noticed it has 18mm of xmas vs the FIs 22 xmax.
The FI seems to have 3db more on sensitivity but slightly higher Le. The AE has lower distortion and Fs, which suggests it might be the cleaner and lower extension driver.
I guess in one sense, im trying to figure out what should i specifically focus in on to make the right choice for my application.
Thanks Cal
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Post by ThomasW on Nov 28, 2007 23:49:12 GMT -7
Your rear room is big enough the drivers Vas differences are irrelevant.
Pick the AE of you want a cleaner driver, pick the Fi if you want higher SPL.
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Post by aaks38 on Nov 30, 2007 10:01:49 GMT -7
On a different note, ive noticed many of the IB drivers lack a rubber surround and use foam. I suppose this is due to cost, but rubber is obviously the better material. I am curious though..
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Post by aespeakers on Nov 30, 2007 11:37:26 GMT -7
On a different note, ive noticed many of the IB drivers lack a rubber surround and use foam. I suppose this is due to cost, but rubber is obviously the better material. I am curious though.. Saying rubber is a better material is really misleading. There are many types of rubber. They all have different characteristics. One of the biggest issues with most rubber surrounds is that in order to make them strong enough they get pretty thick. Rubber surrounds are much heavier than foam surrounds. As a result compliance goes up and you have stiffer suspension. This is not what you want in an IB as you don't want to have to apply more power to move the driver the same distance. Rubber surrounds in general also have much more resonance than foam surrounds. Depending on the size of the surround and the bandwidth used, this may be an issue. This is one of the main reasons we don't use any type of rubber as our woofers can play upwards of 500hz and in some cases are called on to do so. There are also different kinds of foam. Polyester is the old type of foam. Think of old polyester clothes. The other is Polyether which is a newer material with more longevity. However, the older polyester foam is more flexible, less expensive, and also more well damped. It just needs a little help to be an ideal surround material. We use the polyester for it's better damping properties and flexibility. We we hand seal and coat both sides of the surround with a damping compound that further damps any resonance and also protects from moisture and UV rays. In the end it is probably more expensive than going with a different material due to the labor factor, but the results are well worth it. If treated properly the surround will last for 25 yrs or more and have no detectable resonance allowing for much higher bandwidth. Comparing the Fi to our IB15 in terms of displacement will show you this. The AEIB15 will displace 3.07L at 18.5mm Xmax. Suspension travel is good to 25mm in these. They are impossible to bottom the coil and by 25mm Bl had decreased enough that you can't physically tear apart the suspension. The Fi has 22mm Xmax but smaller Sd giving 3.56L displacement at 22mm Xmax. This is where the suspension limits the travel according to the post on this forum, but Xmag is 24mm. In this case you have to be careful as you have enough force out at 22mm to push the driver to 24mm or more. As the suspension can't handle it, you can risk damaging the drivers. IMO and most others who design woofers, you always need more suspension travel than Xmax or you will tear apart a lot of drivers. Keep in mind in an IB there is no additional compliance from the enclosure to stop the movement. Relying strictly on the suspension to stop the momentum of the coil is not usually a good idea. To strictly compare output at a given frequency based at Xmax use this formula: 20 log (Vd * F^2) + 48.4 = 1/2 space SPL So say you pick 20hz. The AEIB15 will be capable of 110.2dB. The Fi is capable of 111.4dB, a difference of only 1.2dB. Then keep in mind that while the Fi is suspension limited at that point, the AE suspension can still move another 5+ mm. John
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Post by aaks38 on Dec 1, 2007 23:02:23 GMT -7
Thanks for the explanation John. I had just thought that rubber was more stronger then foam. I remember back in the days when it was common to see cracked and torn foam surrounds and i dont think ive ever seen a cracked rubber surround.
One thing im trying to understand about your drivers is that are you saying after 18.5mm of xmas, does the driver then enter a power compression region and can mechanically go up to 25mm of xmax without any added spl output?
Thanks Cal
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Post by aespeakers on Dec 2, 2007 13:35:23 GMT -7
Thanks for the explanation John. I had just thought that rubber was more stronger then foam. I remember back in the days when it was common to see cracked and torn foam surrounds and i dont think ive ever seen a cracked rubber surround. One thing im trying to understand about your drivers is that are you saying after 18.5mm of xmas, does the driver then enter a power compression region and can mechanically go up to 25mm of xmax without any added spl output? Thanks Cal Yes, the old foams did have a tendency to rot out and crack. Most of that is due to moisture issues and UV rays deteriorating the foam over time. Sealing both sides and coating them to avoid the UV rays gets rid of the issues. Natural rubbers also tend to dry rot. Just like car tires. With most any driver, your force becomes less the farther you are away from center. As the coil is centered it has 100% of the specified Bl to move the coil. Xmag is rated as the point where the Bl drops to 70%. This is usually considered the useable range for most drivers. After that point, Bl generally drops off more quickly. At the suspension limits there is maybe 20% of the motor strength left. If you push the driver to 25mm you'll get more output as you are moving more air than at 18.5mm. The issue is that you do have less force now applied for the power input. So as an example say it takes 150W to move it the first 18.5mm. It may then take another 150W to move the driver the next 6.5mm instead of moving another 18.5mm. It can be looked at as compression, but not like a hard limiting. John
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Post by txsmoke on Dec 4, 2007 9:12:45 GMT -7
Thanks from me, too, John. That's one of the best explanations of foam vs. rubber. Now, if we could get a counterpoint from a rubber guy, that'd really be great.
Thanks again, Mike
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Post by aespeakers on Dec 4, 2007 12:17:42 GMT -7
Thanks from me, too, John. That's one of the best explanations of foam vs. rubber. Now, if we could get a counterpoint from a rubber guy, that'd really be great. Thanks again, Mike We do use rubber too for some things. Our AV series use santoprene which is a butyl/poly mixture in a specified ratio. They have a few different durometers. For drivers where you don't need the soft suspension and don't need to go up higher in frequency the santoprene works well. It is more resistive to temperature changes in vehicle applications, etc. Santoprene is also the most well damped of all the speaker surround rubbers and has the largest temperature range. The brittle point is -60F I believe. It's all really just a matter of using the right material for the application not that any material is best for all applications. John
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Post by ficaraudio on Dec 6, 2007 16:35:05 GMT -7
As John mentioned, foam has come a long way. I use foam for most of the subs we build, although I do have OEM clients that request rubber and its variants.
For the Fi IB, the suspension doesnt lock up at that... that is the Xsus which is the linear limit of the suspension. Itll throw further, just not at what is considered "linear". So given that, the sub is Xmax limited via the suspension and not the coil. It still has more movement to it, I choose to just post the lienar nature of the sub and not the absolute Xmech.
Thanks, Scott
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