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Old 26th June 2008, 12:58 AM   #11
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Quote:
Originally posted by swak
I have been thinking about my OB project and I had come to some conclusions which are pretty similar to the ones Magnetar arrived at for his project.

It would be a three way OB on a relatively small baffle. There is a paper (which I can link as I am home) which shows the maximal baffle width should at the most be 2.2 times the effective cone diameter. The baffle width D would be set by the effective diameter of the 10" mid. The same paper shows that with this baffle the mid driver could be able to reproduce frequencies down to 114 Hz.

Now, the mid should have highish Q and the highest sensitivity possible, so perhaps a very light cone is mandatory. The driver would cover up to 1.5-1.8 kHz. An AE driver inspired the EV SRO Mag. raves about would be great. The existing 10" has probably more xmax as necessary for this application.

Another possibility is to have a 12-13" mid driver that could reproduce the human voice range, 80-1200Hz, flat and with excellent fall off on the higher end.

Regarding the range above ~1.2-1.8K I would use a fullrange driver with a very light paper membrane (like the Fe108 Sigma). They are not very expensive, easy to implement and have very nice highs.

The lowest range would be done actively and eq'd with a high Q 15-18 inch driver.

This setup might lack in the lower range specially in large rooms, but permits something more decor friendly, and in smallish rooms as mine should be enough.

If AE comes with such a mid (and perhaps a dedicated LF unit) I would be in for a pair.
Just wandering through and pokin' my nose in...

Most of my product work boils down to finding a simplest solution or direct path to the desired end. I can't help but read along and wonder if less complicated solutions within existing capabilities are being overlooked for unwarranted reasons...

Given what Nick and John have noted about the sound qualities of the TD-15 (particularly the M), and my own brief encounters with the TD15, it seems that for a crossover in the 900-1400Hz range, most 10" drivers don't offer much improvement without significant departure or improvements from commonly available examples. Many audiophiles seem quite happy with the Emerald Physics CS2 which uses nothing more than an Eminence Alpha 15A...

Methinks the implementation and suitability of a given driver matters as much or more than how ideal it is. I did a few quick models for comparison, and it strikes me that something reasonably close to what is being asked for is right under our proverbial noses...

It would seem that a TD15M is already 2-5dB more efficient than say the Alpha15 >100Hz. It also appears that a much stiffer suspension which would raise both Fs and Q would provide a gain of 1-2.5dB near the lower corner (~80-200Hz) over the standard TD15M. With 6mm of travel each way on the 15" cone, there is plenty of headroom and power handling for a wide range of crossover points to some bass drivers of choice. Considering that Nick and John have repeatedly noted that the 15" has an extremely well behaved upper frequency response, and provides one of the best subjective sounds of the bunch, why fight what's already working?

There are all a few things which could be tried in the name of making the TD15M design more dipole-friendly, but it's quite hard to not loose sensitivity above 300Hz in the process, and all of those efforts are unknowns that take time and money. This is a rather plausible adjustment that will give some impressive sensitivity. If you get a little creative with a passive crossover and are a little looser with the impedance min, you can probably get the sensitivity to tickle 100dB @ 2.8V/1m.

There very well may be some practical hurdles to such an alteration, but I have to think that the TD15M or a dipole midrange derivative would be worth looking into. Besides, then you could call it the TD15 MD.
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Old 26th June 2008, 02:07 AM   #12
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Hi Nick,

My goal is getting the best design for 80-1,500Hz human voice on one speaker in a high efficiency (95+ db/watt) dipole design. For good off-axis response, a 10" seems best, but a 12" with a clever cone profile might also show good 30 degree off axis response. Linkwitz uses an 8" midrange over 120-1,400 in his 90 db/watt Orion, and Magnetar has converted from midrange horns to one 100 db/watt EV SRO 12" 120-1,500Hz dipole midrange. With a 1,500Hz xover, the tweeter could be a waveguide +compression driver, dome tweeter, or (dipole) ribbon. Pro audio midranges often have rising SPL for horn loading and focus more on efficiency over small room vocal quality. So, it looks like there could be a home audio market for a wide bandwidth high efficiency midrange.

Very low Mms and a low distortion linear gap flux seem to point to an underhung motor with a high flux to minimize voice coil wire weight. Mms ~ 30 grams for a 10" and ~40 grams for a 12" seem possible goals, as does about 8mm Xmax

FEMM model of Lambda TD15_Dipole motor
Estimated from measuring speaker exterior

Ceramic_5 0.18 T in center of gap
NdFeB_37 0.47 T in center of gap

bottom plate saturates first


Seas W22 Magnesium midrange 220 sq cm
Mms = 29 grams
SPL = 90.5 db/watt
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Old 26th June 2008, 03:33 AM   #13
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Underhung and high flux in the gap is a tough combination to achieve at a cost people are willing to pay. I hear enough complaints about the current pricing and John is looking at having to raise prices (his current pricing is about the same as what Lambda charged 8 years ago even though the raw materials are much more expensive now).

I am considering an underhung for this, question at the moment is how much power handling is really needed as the smaller the coil the lower the mass and the lower the inductance. However we also run into the lower the motor strength at the same time.

What will probably happen is a field coil version will be needed for those that want crazy high sensitivity. Especially if we do this with an ultra small voice coil. Field coils solve a lot of issues with magnet strength requirements. For the normal folks the ceramic or Alnico versions would be fine.

Mark - issue with any large driver above 300Hz or so is the "cone cry" or sonic signature the cone has as it goes into its many breakups. Also the shape is significant, I am going to do some serious testing with small coil motors (like 6mm voice coils in our 18mm gap motor) with some different 10" cone shapes and materials to see what if anything can be learned. I will admit that it will be directly compared against the 15M version as that is the best one IMHO.
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Old 26th June 2008, 04:53 AM   #14
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Quote:
Originally posted by nickmckinney
I am considering an underhung for this, question at the moment is how much power handling is really needed as the smaller the coil the lower the mass and the lower the inductance.
Nick,

There is a recent thread discussing SPL requirements for home audio that covers most viewpoints. I typically listen at 70-75 db at my 12' away couch seat and find 85 db loud. The SPL thread had some agreement that an extra 10 db of transient headroom was required over the average SPL. I design my speakers for reliable continuous operation at 115 db @1m. The SPL thread authors might be closer to asking for 120 db @1m max. Commercial customers might also demand the 120 db to meet marketing demands.

Increasing the efficiency will reduce continuous power requirements. Magnetar's EV SRO 12" speaker with 100+ db/watt allows cool jamming.

db watts
95 1
98 2
101 4
104 8
107 16
110 32
113 64
116 128
119 256

db watts
100 1
103 2
106 4
109 8
112 16
115 32
118 64
121 128
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Old 26th June 2008, 05:09 AM   #15
agent.5 is offline agent.5  United States
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Quote:
question at the moment is how much power handling is really needed

probably just a few watts, as most will probably use a SET amp.
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Old 26th June 2008, 06:03 AM   #16
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Quote:
Originally posted by LineSource
My goal is getting the best design for 80-1,500Hz human voice on one speaker in a high efficiency (95+ db/watt) dipole design. For good off-axis response, a 10" seems best, but a 12" with a clever cone profile might also show good 30 degree off axis response. Linkwitz uses an 8" midrange over 120-1,400 in his 90 db/watt Orion, and Magnetar has converted from midrange horns to one 100 db/watt EV SRO 12" 120-1,500Hz dipole midrange. With a 1,500Hz xover, the tweeter could be a waveguide +compression driver, dome tweeter, or (dipole) ribbon. Pro audio midranges often have rising SPL for horn loading and focus more on efficiency over small room vocal quality. So, it looks like there could be a home audio market for a wide bandwidth high efficiency midrange.

Very low Mms and a low distortion linear gap flux seem to point to an underhung motor with a high flux to minimize voice coil wire weight. Mms ~ 30 grams for a 10" and ~40 grams for a 12" seem possible goals, as does about 8mm Xmax

FEMM model of Lambda TD15_Dipole motor
Estimated from measuring speaker exterior

Ceramic_5 0.18 T in center of gap
NdFeB_37 0.47 T in center of gap

bottom plate saturates first


Seas W22 Magnesium midrange 220 sq cm
Mms = 29 grams
SPL = 90.5 db/watt

First, what are your off axis goals? I'll take some curves from a TD10M, 12M, and 15M as soon as I can and show you where things are at 1500hz and 30 degrees. I also have an 18sound 6ND410 here and I will do some curves of that at 30 degrees as well for comparison. As Mark pointed out, the TDM drivers with stiff suspension could be much more dipole friendly. As Nick mentions, the Dipole coil, about 12mm long in an 18mm gap would work pretty well. It would give about 3mm one way with near ruler flat BL curve and should get in the 95-96dB 1w/1m efficiency. As it is dual VC, about 6ohm DCR per coil, the 2.83V sensitivity with coils in parallel would come in at 99-100dB.

Now with the change to the acordian surround and slightly lighter cone instead of foam/thicker cone, we can take about 15grams off as well. This should put things at about 97dB 1w and 101dB 2.83V. Stiffening suspension up to CMS of .07 would bring Fs up to 69Hz and Qts up to .69. I'll put one of these together and see how close it gets as well.

Secondly in your model are you assuming the same size ndFeB+37 as the ceramic 5? If so, this is an extremely expensive piece of neo to start with. There are 2, maybe 3 magnetizers in all of the US that can magnetize a piece of neo this large. You're also modeling in 2d and not in 3d so you need to take into account the circular shape of the part and realize flux is much more concentrated towards the center. I use FEMM mainly to determine gap symmetry and BL curve shapes, but that is pretty much its extent. I'd love to have a full 3d FEA package, but can't afford $50,000 for a decent one. Luckily building and measuring is nowhere near as expensive. Based on a 3d model you'd expect to see the entire pole piece will also saturate nearly the same time as the back plate. I can saturate a 2" pole with ceramic magnets we currently stock. You can always thicken the back plate but once the pole saturates all you can do is increase the diameter or permeability.

John
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Old 26th June 2008, 04:56 PM   #17
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I am happy to see more of us are thinking about a similar setup and that AE speakers can come up with great drivers.

Nick:

What would the approx. price increase for a field coil motor be?

John

AE speakers could offer a kit or a completed design for DIYers that wouldn't like to mess with all the design complications or don't have the technical background. I think that would certainly help selling the drivers. An 18sound XT120 horn with a CD could cover the range above the two (midbass, bass) AE drivers, with the option of a supertweeter for the range above 12K.


PS: I would like to add that it could be very interesting for some if there would be drivers designed specifically for current drive amplifiers. Thorsten (Kuei) gave some points on this forum on needed motor/driver properties and advantages of current driven speakers versus traditional voltage drive, he even sketched a system with Seas drivers.
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Old 26th June 2008, 09:23 PM   #18
tinitus is offline tinitus  Europe
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67hz Fs, 100db, double 6ohm voicecoil, stiff surround, dipole, compression driver, waveguide ... now I am so confused I dont know what to say
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Old 26th June 2008, 10:10 PM   #19
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Quote:
Originally posted by John_E_Janowitz
I'll take some curves from a TD10M, 12M, and 15M as soon as I can and show you where things are at 1500hz and 30 degrees. John
John,

Eightsound seems to publish just 45 degree off axis data
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Old 26th June 2008, 10:13 PM   #20
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Quote:
Originally posted by LineSource


John,

Eightsound seems to publish just 45 degree off axis data
What would you want a 10db rising pattern?
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