Fi 18's vs AE 15

[moonfly]

As per title really. I'm currently trying to decide if I should go with 2 Fi 18's or 4 15" IB drivers from AE.

Does anyone have any input on this? I'll hold of on anything Ive looked into till I get some thoughts from you guys.

Cheers

[jman]

Two 18's is better because you have the option of going to four later. With 4 15's the (usual) manifold is full.

Are you worried about 18's being too "slow" or "sloppy"?

[moonfly]

In either case, I will be placing the drivers in 2 places to get a kind of stereo setup (although the same mono signal will be sent to them).

I will either have 2 single drivers, or 2 dual driver manifolds. In either case both will allow for the addition of further drivers.

I'm not worried about the 18's sounding sloppy at all. In fact after looking at the sims I actually favoured the 18's, but a recent conversation with John from AE is changing my mind.

[chrisbee]

Oct 19, 2010 9:29:40 GMT -7 moonfly said:

In either case, I will be placing the drivers in 2 places to get a kind of stereo setup (although the same mono signal will be sent to them).

I will either have 2 single drivers, or 2 dual driver manifolds. In either case both will allow for the addition of further drivers.

I'm not worried about the 18's sounding sloppy at all. In fact after looking at the sims I actually favoured the 18's, but a recent conversation with John from AE is changing my mind.

Are AE now making IB15s again? There was a long hiatus due to a lack of surrounds according to the AE forum and silence on the issue when questioned about progress.

AE claim lower distortion than the Fi drivers. The question is whether the margin of distortion between the two is audible.

A pair of IB318s have marginally greater displacement than four AEIB15s. In my own experience four AEIB15s can just about run out of excursion during some VLF film effect peaks at high levels. Electronic music, with hidden depths, can often produce remarkable cone excursions on only four 15" drivers. Any turntable system capable of reproducing record warp or footfalls can easily find the cones flapping wildly unless a high pass filter is introduced. Whether the extra displacement of the two 18"s is worth having under these circumstances I can't say.

Despite having double the displacement the IB318s can use a smaller enclosure than the AEIB15s if this is an important factor for you.

---------------------------------------------------

I wouldn't waste the opportunity to run a pair of separated IB subs in stereo. It is usually considered that the locatory information, contained in the stereo channels, is irrelevant at sub-80Hz frequencies. The wavelengths are so long a that any wave front delays in reaching each ear from separated stereo transducers cannot be reliably detected.

However, the amplitude content of each stereo channel is certainly not the same as each other. There are noticeable amplitude differences between stereo channels. This is easily seen when glancing at the dancing LED level bars of the BFD under stereo music reproduction.

The stereo loudspeakers do indeed steer the apparent location of bass sources in the soundfield. Though the clues offered by the differential output between two well separated IBs may still be worth having.

Delay differences do exist between separated L&R stereo IBs and the opposing R&L speakers. In dual mono this may cause soundfield confusion for the listener. Not to mention the phase related FR anomalies of wide separation when reproducing the same frequency. These problems may be minimised by a lower output from the guilty IB thanks to the stereo amplitude imbalance between one IB and the opposite channel speaker. i.e. Left IB and R speaker. Right IB and Left speaker.

Remember that all sounds (no matter their dominant fundamental) begin as transients with a bandwidth equal to the entire FR of the subwoofer/speaker system. This suggests that the VLF component of the leading edge should remain within its intended stereo channel structure, within the soundfield, to be reproduced as faithfully as possible.

I still run my system in stereo, even for films. So I can directly relate to the differences between having a single offset IB and two, stereo subwoofers.

It is quite impossible to locate the bass as coming from the left even in a very lop-sided arrangement like mine. (IB in the left wall) However, the introduction of another, smaller subwoofer over on the right, to balance the existing IB on the left, was very noticeable when each was fed their correct stereo signal. Had I had another IB, over on the right, I am sure the beneficial audible effects would have been even greater.

Far more to think about than you asked for but worthy of consideration in your planning, I hope.

[moonfly]

John had this to say on the subject.

The thing you are missing is that the goal is not to "take" large amounts of power. You want the driver to move to high excursions with as little power as possible. This is a good thing. Now from a price only standpoint the IB318 will give you more output per dollar. The IB15 gives 2.98L peak-peak displacement at 18mm Xmax. This is $41.83 per L of displacement when purchased in a group of 4 drivers. The IB318 gives $30.30 per L of displacement. This is however not at all the full story.

The IB15's are designed specifically to not need EQ to boost the low end response. In an IB they have an F3 point of around 16.8hz. This means you need no EQ to flatten the response down to 16hz in room. The IB318 has an F3 of about 29hz and by 16Hz is -9dB. You're most likely going to need EQ to boost the low end response if you want to get to 16Hz or lower. If you wanted to go as low as 10hz, the IB15 response is 6dB higher at that point than the IB318. EQ is going to cost you something.

The IB15's are also designed to make very efficient use of Xmax. At 16hz it takes only about 100W to get to the 18mm Xmax point. This is ideal as the more power is input, the more thermal issues you have to deal with, both distortion and power compression. The idea is to get as much excursion with the least amount of power possible. On the other side, the IB318 requires around 600W to get to it's 30mm Xmax at 16hz. This is just past the rated power handling of the driver. At 600W input you have a LOT of current through the VC. This means a lot of heat. You will lose a lot of output to power compression and distortion skyrockets. This high amount of current running through the coil also leads to the next issue of flux modulation.

The IB318 does not use shorting rings to keep the flux fixed in the gap. This is the single more overlooked issue in drivers today and is the biggest cause of distortion. Look at the corner of the Klippel Non-linear distortion poster. You will see that the various types of distortions are defined and it shows their effects. Look at Le(i).



Le(i) or flux modulation is responsible for the most types of distortion. Not only that but current HD and IMD are noted as saying "provides unique symptoms which are sufficient for identification of the nonlinearity." Meaning, they are significant an easily audible effects. When the coil is energized it becomes an electromagnet. When this electromagnet moves through the gap it moves the permanent magnetic field around. The permanent field is no longer where it is supposed to be and the driver can no longer properly control the position of the coil. The more current you put in, the stronger the electromagnet and the more significant the effects. This is why it is important to have the smallest amount of power required to move the driver the farthest distance. As the IB318 requires about 6x the power to reach Xmax as the IB15, distortion will then be significantly higher. In addition to that you have issues with Le(x) related distortions as nothing is done in the IB318 to handle this. The IB15 has a full copper sleeve over the pole. This means that Le(x) stays perfect at all excursion levels and this distortion is completely eliminated. Le(i) or flux modulation is also nearly eliminated due to the shorting ring.

The goals of the IB15 and the IB318 are totally different. The IB318 is just designed with the brute force method in mind. Apply a lot of power to a driver with high Xmax in order to get loud. The IB15's are designed to be able to play loud also, but the main priority is on accuracy. There is not an IB driver anywhere that can compare to the clean low distortion output that you can get from the IB15's.

John

Would you care to have any thoughts on any of that? I dont know how audible any of that might be either, I know the Fi's do sound good. Ive also asked questions with regards your other points, mainly focused on cab size, higher system Q from the AE's and the results derived from the AE's hitting xmax while the Fi's would be a couple mm clear of that target.

As for a true stereo setup, well that would require running the speakers full range in a kind of high level type connection, and I'm not sure I want to pursue that route. Its something to keep in mind, but honestly, I will try the traditional way first and see if I am happy with that initially.

Ive spoke to AE and the roll surround issue plaguing the AV's were supposed to be sorted by the beginning of this month. Ive asked for a quote and spoke to John about ordering, and havent been met with any additional warning on the matter.

[ThomasW]

John had this to say on the subject.

The IB15's are designed specifically to not need EQ to boost the low end response.

Whether drivers need EQ or how much EQ is needed is much more a function of room-gain than a super low Fs. To date I've never seen an IB built that didn't benefit from the judicious use of EQ

The IB318 does not use shorting rings to keep the flux fixed in the gap. This is the single more overlooked issue in drivers today and is the biggest cause of distortion.

I guess John's never seen a Fi driver. No they don't use a full copper sleeve, they do use copper shorting rings

The goals of the IB15 and the IB318 are totally different.

That's one man's opinion

The drivers from both companies are very good. I see them occupying different sectors of the market

[chrisbee]

Hi Dan

Interesting stuff. As the owner of eight IB15 I have no complaints about SQ. Particularly from the newer, paper-coned drivers which provide an amazingly flat response to sub-10Hz without EQ in my room.

And they were almost to T/S spec at Fs = 13Hz. They were a "free" gift from John to compensate for my totally off-spec, Fs 32Hz, incredibly badly made, vinyl-coned originals. The one's which need +16dB (max BFD boost) at 20Hz to function as subwoofers and they still roll off from 30hz. The ones I paid for dearly once. Then again and again over a couple of years of frustration at their inability to perform as claimed.

I paid the freight charges on the new drivers, the import taxes and Schenker's outrageous charges for clearing the paperwork for collection from the nearest airfield. Which amounted, in total, to more than the full American retail price of the drivers. I never mentioned any of this before because I was so grateful to finally have some drivers I could use as intended. I felt exposed on the Cult, in my endless build thread and on my blog. Nobody wants to look like an idiot so publicly for being taken for a ride.

Perhaps the question of which is the best driver between AE and Fi is purely academic? My reservations about John@AE are his reliability of delivery, matching his claimed T/S parameters and his incredibly poor communication skills with his paying customers. This despite having direct access to them through his various forums. (No criticism of Simon is intended. He does a great job. Though I still have absolutely no idea of his job description)

You are keen to buy IB15s? Who can tell you when they will be despatched? Who can tell you whether they will be all silver, all black or with diamond turned highlights? Will they be to their claimed T/S parameters? Have the new, in-house surrounds rolled off the production line on-spec yet? Are baskets finally available for IB5s? Who knows?

As a paying customer shouldn't you be told up front if there is yet another shortage of vital components in one of the simplest, man-made constructions available as regards total component count? Has anybody told you anything? Or is it a given that you will receive the same standard of service as going to Fi?

Reading the AE forums is an exercise in frustration on behalf of paying customers. Perhaps we only get to see the public failures to supply as promised. Not to mention the failures to communicate clearly about the months-long delays waiting for vital components for such an essentially simple product. Why not just state the true facts in the AE News forum?

On paper the IB15s are great drivers. I love the new ones. I wish John well and want him to succeed. But I really cannot recommend his drivers unreservedly from now on. Not without adding a list of caveats.

[moonfly]

Cheers for the candid response Nimby.

The points you raise are the very reasons I looked at Fi in the first place. I had 2 pr's arrive damaged (but they were replaced FoC) and had an issue with one of the 18 or so AV drivers Ive imported from them. The logistics of returning drivers means its a larger issue than would be usually.

They dont have the basket or surround issues now apparently, but a couple things have got me wandering. Beth has no gone and been replaced (why?), they are now not using DB Shenka (why?, unpaid bills?), and where does it leave me if there is an issue.

I really liked the AV woofers, but Ive seen a couple of Fi's products now and they seem just as well made (not quite as heavy though) and the SQ so far from them that Ive heard has been very good.

[newbieaudio]

I'm not sure whether this should be a new thread or not, so Thomas can move it if appropriate.

Many have commented about how sensational their IBs are, and they're using "IB" drivers with Q's of ~0.7.

I've read ThomasW recommendations about Q, and if cost were not a constraint, I would design for a critically damped system of 0.5, not 0.7. Cost is a constraint, and IB drivers are noticeabley less expensive than traditional low Q drivers.

Since I'll be buying (4) or (8) 15s, and I'll be making the purchase only once, I'm wondering whether it makes sense to spend extra money once for low Q drivers - if the expense is worthwhile. For a Q of 0.7, I'm considering either the AE IB15, or the Fi IB15. For a lower Q driver, I'm not sure what to do.

Has anyone heard both low Q and 0.7Q drivers in the same space to know whether difference is worth the additional cost of the low Q drivers?

My sense is that the large volume displacement in IB installations is the dominant factor in making bass so much better compared to boxed subs, and that having a lower Q driver while worthwhile, may be only a minor, and possibly insignificant improvement compared with the massive displacement improvement. I'm speculating about this, and that's why I'm asking for the opinion of people living with IBs.

I have an open house plan, and I'll be putting two manifolds in the crawl space. Chrisbee's comments about the dramatic improvements when he went from (4) to (8) IB15s have convinced me to use Thomas' recommendation about designing the manifolds to accommodate (4) 15s per manifold, but start by installing (2) 15" drivers per manifold. Then after adjustments and listening for a while, decide whether (4) more drivers would be necessary.

This will be for music, but possibly also for some HT.



Thanks,

Dave

[ThomasW]

Having proper acoustical room treatments is far more important than the difference between low or higher Q drivers

[moonfly]

I personally have no interest in a low Q system. Ive heard a couple low Q subs and the lack of upper bass meat just isnt for me. I would only use those kinds of subs to back up large speakers that themselves run pretty low.

IB drivers are designed with a higher Q for this very reason. System Q cannot drop below the drivers Q. As cab size increases, system Q drop until it reaches the drivers Q. An IB obviously has the largest cab, and in just about all circumstances the IB will have a system Q close to that of the drivers. If you wanted low Q drivers, you could just use standard drivers, but that would be expensive and Thomas will have a fit when he reads that too, arguing its not a true IB then. Most standard drivers have a Q under .5 as well, so you would either have to except that, or ensure the cab size was sufficiently small (or you had enough divers) to get the system Q back up to where you wanted it.

Some people argue that system Q just isnt important, and Thomas is probably one of those people, but personally I disagree with that notion having tried a few different examples for comparison. I also think the cleaner output of an IB lends itself to higher Qtc as the upper bass doesnt get muddied up the same. Ive only heard one IB, using the Fi 15's, but it sounded both plenty deep, and very clean, so I am happy with the system Q resulting from the use of those drivers personally.

One thing I do agree on though, is that the room is a very important factor in this, as a bad room will wreck the sound of even very high end systems.

[moonfly]

By the way, I got this reply back from AE, this snippet was attatched to the end of my quote:

However, I do want to let you know up front about the lead time on these. Normally, lead time for orders is about 2 to 3 weeks. However, we are waiting for some parts to come in for these, so lead time could be up to 2 months.

As much as I want to go with the AE drivers, they do seem to go out of their way to convince me otherwise. The Fi's will need a fair bit more power, and more EQ, but I am starting to think they are the safe choice when it comes to the logistics of getting hold of them. I too have started adding caveats to my recommendations of them.

[chrisbee]

Adding filters or EQ will probably raise system Q.

[FOH]

Yes, Thomas is right.
The speaker/room interface needs the attention, no need to split hairs wrt Q.

Enough drivers, ample displacement, plenty of power, shape the room response to provide whatever "meat" or characteristics one desires. Done

Focus on the room...huge gains to be had there.

My two cents

[newbieaudio]

Thanks to all for your advice concerning the Q of the driver in an IB.

Once I have the installation, then the fun will begin with room treatments and EQ.

Dave