Very nice!! The TD12M doesnt go low at all. I have TD12S drivers too so I could build again just like yours. I like that horn, Was it custom built? Do you have a build thread?
But did you see the rising HD towards the LF (<100Hz) of the underhung TD15LO?
OTOH, the overhung motors show more consistent results. This is the HD of Eminence Kappalite 3012HO, (pretty good I guess):
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Hi CLS,
I believe the TD15LO is designed as a 15" midbass to be used down to 100-200Hz as a special build for Lynn Olsen. Lynn liked the sound of the Altec underhung motor and wanted to see if a Lambda could surpass the simplier Altec motors. It has the TD15_Dipole underhung motor and short voice coil, with the TD15M pleated surround cone. For this design, the rising HD under 100Hz would be expected.
Even the TD15M with a overhung motor is designed to be used in a 3-way. Sometimes over the new 18" woofer.
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Hi Doug, a friend and I designed and built them. They are Tractrix flairs driven by JBL 2445 compression drivers with TrueXtent barrilyum (S) diaphragms. The whole speaker is flat from 25hz or so to 20khz. The lambda in the ones in the pix are TD15X which go lower than the Ms and are 3db less effiencent. I am still on the fence about using the M or X, but I have great subwoofers so I don't need to go that low.
Don't get me wrong. I admire AE's drivers very much and appreciate their effort in making good quality dirvers. It's now the underhang motor confuses me.
And I'm not convinced a 15" driver with Xmax of 9mm should be used above 100Hz. It's t/s is specified here:
AE Speakers LO15 4ohm (drivervault)
Under test, the HD is 37% when the excursion reaches 8mm:
Xmax (drivervault)
(in the first 3mm, the growth is almost exponential)
It just so confusing. It's a common 'cognition' that an underhung motor gives very flat BL within its Xmax, thus a very low distortion -- or it's what I've been told, or taught by various books. But why are these test numbers?
I'm wondering if the Dipole15 (with 12mm Xmax and half-roll surround) would be any better...
A midbass with midrange detail is my focus. Several new high end midrange speakers use underhung motors. The Tang Band uses ferrite magnets, the Illuminator has a more favorable compact NdFeb structure.
Several years ago Sigfied Linkwitz tested the TD15Dipole for the Orion. Nick at Lambda posted this note on the test:
"Hi Folks, I got the Dipole results from Seigfried.
He found the 2nd harmonic and aerodynamic noise to be very low, but found
the 3rd harmonic to be higher because of the underhung geometry of the
design. This is something I was afraid of to be honest. At 25Hz and above
(the Fs of the driver) the 2nd harmonic was 5.8% maximum, 3rd harmonic was
7.2% maximum with the driver pushed to 0.5" P-P. When the driver was
pushed to xmax at 25Hz and above (1" P-P), the 2nd harmonic rose to 7.8%
maximum, and the 3rd harmonic grew quickly to 29.5% (30Hz), which quickly
shows the problem with underhung drivers, distortion brick wall rises when
the coil is at xmax.
Below 25Hz the distortion was much higher, in some part to operating below
the natural Fs I think, there was no testing above 50Hz, so there is no
information above 50Hz to utilize.
Thus for his design since 2 drivers are used push-pull lowering the 2nd
harmonic, and output above ~100Hz is not a consideration, the Peerless XLS
is a better choice especially considering the price (I did not send him a
standard TD for testing).
For those looking at using their woofers on a flat baffle with a higher
xover point (vast majority of you), I don't know how much of this means
anything as I don't know what the Peerless does above 50Hz, I know the
Lambda works very good above 50Hz. Most of you that are using B&G ribbons
or electrostatics (and a couple of Unity folks) and want ~300Hz xover
points, with a clean bandwidth of 25hz~600Hz, we covered that well, but it
is up to you to decide if it would work for you.
I can forward an XLS spreadsheet of the distortion test to those interested.
Nick"
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Thanks Doug. I'd not gotten that far in my research. I'd hate to screw with the upper mid bass as that is where they shine.
I think it's more useful to look at the HD sweeps. I had the same concerns with the TD12M's Xmax numbers but I realized that the HD rises rapidly below 80 Hz. Brandon's Xmax test is done at Fs where the distortion is quite high even with small signals. Use them above 80 Hz as they are intended and both the M series and the LO series are excellent performers.
Non-linear Distortion (drivervault)
Edit: Brandon measures distortion at 100 dB / 30 inches and the LO15 is somewhere on the order of .1%-.3% from 80-1500 Hz so I think we can say that's pretty good.
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Precision Devices 15' bass
Hi all,
I have not had a chance to listen to any of the AE drivers in my own system yet but I really like the look of the 15M on paper.
What I can tell you for sure is that the bass performance from the PD 1550 and the mid bass / low midrange performance of the PD 158 drivers is the best I have experienced.
On the spec front it’s very difficult, sometimes impossible to draw meaningful comparisons between different manufacturers data sheets and / or different independent testers results.
For example the 2nd and 3rd harmonic distortion of the 1550 is quoted as
" below 1% " but that is at OVER 117dB at 1 m...! Or 60 watts i.e. 10% of AES rated power.
Also worthy of note is that very few manufacturers ( Precision Devices are one of the few ) who adhere to the demanding AES reference measurement practices. Many drivers which boast " huge spec " crumble when asked to meet the AES standard....
Cheers
Derek.
Hi all,
I have not had a chance to listen to any of the AE drivers in my own system yet but I really like the look of the 15M on paper.
What I can tell you for sure is that the bass performance from the PD 1550 and the mid bass / low midrange performance of the PD 158 drivers is the best I have experienced.
On the spec front it’s very difficult, sometimes impossible to draw meaningful comparisons between different manufacturers data sheets and / or different independent testers results.
For example the 2nd and 3rd harmonic distortion of the 1550 is quoted as
" below 1% " but that is at OVER 117dB at 1 m...! Or 60 watts i.e. 10% of AES rated power.
Also worthy of note is that very few manufacturers ( Precision Devices are one of the few ) who adhere to the demanding AES reference measurement practices. Many drivers which boast " huge spec " crumble when asked to meet the AES standard....
Cheers
Derek.
I have no experience with the PD1550 or PD158 personally. Both of these drivers have substantially higher inductance than the TD15M though. The PD158 is about 10x the TD15 and the PD1550 doesn't list an Le spec but you can see that by 1KHz it is already over 20ohm. If you plan to use the driver up to over about 250hz, the variation of Le with respect to excursion will cause significant issues with how the crossover functions at this point. Also it appears nothing is done to reduce flux modulation. This is a huge issue in terms of how accurate a driver can be, and as we mention it is ignored by 99% of all woofers out there. I'd be willing to compare the TD15's to them at any time.
In terms of measured data, I agree that it is nearly impossible to draw any meaningful conclusions about how drivers compare. That is one of the reasons I just don't have the time to spend hours and hours doing tests on drivers. Yes, I can easily do tests that will make the drivers look good, but unless there are tests that allow for meaningful comparisons I just don't see the point. Most people like to do their own measurements. The likes of Seaton Sound, Salk Sound, Evolution Acoustics, The Lotus Group, etc who have done the direct comparisons with other drivers and settled upon our drivers based on those comparisions. Obviously they don't publish their data, but their results have shown the superiority of the products in their applications.
John
In terms of measured data, I agree that it is nearly impossible to draw any meaningful conclusions about how drivers compare. That is one of the reasons I just don't have the time to spend hours and hours doing tests on drivers. Yes, I can easily do tests that will make the drivers look good, but unless there are tests that allow for meaningful comparisons I just don't see the point. Most people like to do their own measurements. The likes of Seaton Sound, Salk Sound, Evolution Acoustics, The Lotus Group, etc who have done the direct comparisons with other drivers and settled upon our drivers based on those comparisions. Obviously they don't publish their data, but their results have shown the superiority of the products in their applications.
John
quote from PD1550
Research has resulted in the development of an advanced magnetic assembly which incorporates a composite alloy and steel pole piece giving a uniform and stable magnetic field, improving linear excursion and providing an efficient thermal path to dissipate the heat produced by the voice coil. The motor assembly generates a BL product of 26T/M which is exceptional for a transducer of this type. It is this approach which contributes to the speed, accuracy and fidelity of the unit and maintains control of the cone under the most demanding operating conditions.
Sorry if I expressed myself wrong
I meant to say that I would buy AE woofers solely because of the specs, not because Im impressed by the build quality
Those specs would be Fs, Qts, and Xmax
I strongly believe that the major part of the wanted bass quality comes from the complete design, box and all, crossovers and amps, etc
And ofcourse not to forget, good assembling with consistent quality
Midrange is a quite different matter
But no, Im not a particular fan of double magnets
Or the use of double poleplates glued together, as seen elsewhere
But ofcourse results in a "cost effective" design
Please dont think Im negative
Not at all
As said, I too would buy AE, if it wasnt for the taxes and shipping
I only try to be realistic
Yes, this is typical with every driver. Most companies use words like "advanced magnetic assembly", "composite alloy", "optimized with FEA Analysis", etc but they really don't mean much. Using FEA to get a symmetric BL curve is of course something that is important most every driver is going to be designed with some kind of optimization to the motor assembly to give more symmetry to the Bl curve. The linearity of inductance is a whole separate issue though and reducing the Le(x) and Le(i) related distortions. Unless you drastically reduce the electrical conductivity (permendur pole) or completely remove all electrical conductivity(powdered iron) to the pole, you'll need to use shorting rings to address this issue. Quite simply you need to keep the "core" of the inductor from changing. Forcing the VC to operate as an air core inductor is IMO the best way to do this. Proper placement of the shorting ring is also critical. I've seen many drivers with massive shorting rings that are completely ineffective at reducing distortion or inductance.
John
No
Its only stated for 4 of their more expencive woofers, the 50 series, 1550, 1850, 2150, 2450
Their other models are "ordinary" magnet design, and cheaper
btw, Audio Technology(Skaaning) have used full copper sleeve for decades (SD patent?)
PD 1550 Le observations
Hi John,
As the PD 1550 really is a pure bass driver it should never really be crossed over above 150Hz in my opinion. I have run it up to 300Hz with a very steep ( 60 dB /octave DSP crossover ) but it starts to lose its magic when pushed too high. As a bass driver it’s a real party animal! You can ram it with 600 watts plus heavy EQ and get still maintain real Tymp drum dynamics combined with delicate texture and decay on low end Steinway.
I am not technically qualified to comment on the "air cored inductor idea " but my gut feel ( plus a little bit of research....! ) tells me you are on to something with this when it comes to the 200Hz to 600 Hz band ( above 600Hz its always Manger or a Radian 1.4 inch compression driver for me ) and my dream driver is to combine your full sleeve shorting rings with a PD 158....
Regarding the PD 158 it sounds just beautiful between 100Hz and 600Hz run in a VPL open baffle.
Here I am not sure if the lowest possible Le is the holy grail of spec, i.e. a big heavy rubber surround will destroy the low midrange performance ( sound quality, not necessarily measured performance, as most folks are still measuring the wrong spec...) of any driver, Precision Devices, AE or any other top brand.
So maybe one day if I get the time to launch Rainforest Audio I will have to buy a pair of 15 inch TD M drivers and have a " wee shoot out " !!!
All the best
Derek.
Hi John,
As the PD 1550 really is a pure bass driver it should never really be crossed over above 150Hz in my opinion. I have run it up to 300Hz with a very steep ( 60 dB /octave DSP crossover ) but it starts to lose its magic when pushed too high. As a bass driver it’s a real party animal! You can ram it with 600 watts plus heavy EQ and get still maintain real Tymp drum dynamics combined with delicate texture and decay on low end Steinway.
I am not technically qualified to comment on the "air cored inductor idea " but my gut feel ( plus a little bit of research....! ) tells me you are on to something with this when it comes to the 200Hz to 600 Hz band ( above 600Hz its always Manger or a Radian 1.4 inch compression driver for me ) and my dream driver is to combine your full sleeve shorting rings with a PD 158....
Regarding the PD 158 it sounds just beautiful between 100Hz and 600Hz run in a VPL open baffle.
Here I am not sure if the lowest possible Le is the holy grail of spec, i.e. a big heavy rubber surround will destroy the low midrange performance ( sound quality, not necessarily measured performance, as most folks are still measuring the wrong spec...) of any driver, Precision Devices, AE or any other top brand.
So maybe one day if I get the time to launch Rainforest Audio I will have to buy a pair of 15 inch TD M drivers and have a " wee shoot out " !!!
All the best
Derek.
Then you will get a quite different FR response, and not the smooth falling response you like so much now
http://www.precision-devices.com/asps/uploads/super/48.pdf
btw, my master once said that the copper sleeve makes a crossover paralel zobel(cap/resistor) less effective, but he still recommended it (SD)
I still wonder what makes so many people love dirt cheap woofers like the Alpha15
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