The dustcap seems to be an eyesore, but is not the weakest link. There is a gigantic peak just from the straight-walled cone, even when the dustcap and whizzer is gone (pictured).
I note that Lowthers also have straight-walled cones, and similar FR plots.
That might work with some drivers, but not these. I tried the usual gentle dissections (phase plug, basket tweaks, fuzz, dammar) before going full abattoir.
Even with irreversible and very heavy cone treatments, these straight-walled cones seem to be bad for use above ~2kHz.
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Yes. As I say, I'm not convinced about the idea myself.
Still, a lot apparently do like them, & I've never heard them so can't comment other than saying fair play to them.
Note that Lowthers, and, I believe the Wharfedale were never actually designed or intended to be used as direct radiators. They were meant for indirect radiation, where the excess of output through the mid-treble compensated for the losses you would expect to find; they also date from a time where the limitations of the contemporary carrier mediums meant that the lack of extreme HF was essentially a non-issue.
My own suspicion is that Lowther are to a point prisoners of their own history. Their drivers started to be used as direct radiators, gained a following, the indirect designs died away in general from the '50s, and they've not been able to change the drivers for fear of losing their particular market niche. They can play with motors, diffusers / central plugs, suspensions -but the cones? Not as much. They do smooth out a bit after a long while, as the cone seems to soften. Not to my taste, but I respect them -any small company that keeps going as long as they have is clearly doing something right.
My own suspicion is that Lowther are to a point prisoners of their own history. Their drivers started to be used as direct radiators, gained a following, the indirect designs died away in general from the '50s, and they've not been able to change the drivers for fear of losing their particular market niche. They can play with motors, diffusers / central plugs, suspensions -but the cones? Not as much. They do smooth out a bit after a long while, as the cone seems to soften. Not to my taste, but I respect them -any small company that keeps going as long as they have is clearly doing something right.
Yes!
I just completed the test enclosure and experimented a little using vertical, triangle-shaped "phase-rods" with the tip pointing to the driver on-axis and had great results. Probably 10cm/4inch distance.
I want wide dispersion of highs. So far it worked very good.
Now the question is what width works best.
So far I used a width close to voice coil diameter.
Maybe it should have a little more width.
What would you do to them also?
Cool info!
For the lowther, it seems not easy to find another driver that is close enough to 100dB efficiency, QTS of approx 0.2X, Vas 50-90L.
Actual Lowthers measured here:
Preliminary Measurements of the Lowther DX Series of Drivers
Note (1) a lot of the efficiency "appears to be a very directional SPL response due to whizzer cone resonances". The very low Qts of the DX4 gives only a 2.7dB bump, which is trifling compared to that 10dB HF hump.
Note (2) the Fs of 60Hz is a lot higher than the advertised numbers.
For a midrange with equivalent specs (95-97dB and low Qts):
B&C are well regarded, and have several 8" drivers that have similar numbers. They cost about 20% as much as a hacked up Lowther, and don't have a 15dB peak at ~3kHz.
Faital Pro: ditto, e.g. the 8PR200 looks like a good mid. I have some of their 12" drivers, and mine measure just as flat as the spec sheet.
The 18 Sound 6ND410 looks like another contender.
Actually, almost any good pro driver manufacturer has an equivalent.
Measuring the Dx4 with added mass (CLIO Pocket) I got these values:
MANUFACTURER: Lowther MODEL: DX4 Fs 57.86 Hz Re 12.40 Ω Sd 210.0000 cm² Qms 4.23 Qes 0.25 Qts 0.23 Cms 0.9207 mm/N Mms 8.2180 g Rms 0.71 Ωm Bl 12.21 N/A dBspl 98.48 VAS 56.6937 L Zmin 13.51 Ω L1kHz 0.00 mH L10kHz 0.04 mH
Since I would need an 8" I looked at the 18Sound 8NMB420 and the spec mentions 95dB (3dB less) and the Qts 0.28 is higher but not extremely.
Looks like a nice one otherwise
8NMB420
MANUFACTURER: Lowther MODEL: DX4 Fs 57.86 Hz Re 12.40 Ω Sd 210.0000 cm² Qms 4.23 Qes 0.25 Qts 0.23 Cms 0.9207 mm/N Mms 8.2180 g Rms 0.71 Ωm Bl 12.21 N/A dBspl 98.48 VAS 56.6937 L Zmin 13.51 Ω L1kHz 0.00 mH L10kHz 0.04 mH
Since I would need an 8" I looked at the 18Sound 8NMB420 and the spec mentions 95dB (3dB less) and the Qts 0.28 is higher but not extremely.
Looks like a nice one otherwise
8NMB420
Good to see the consistency with Martin King's numbers.
Is the 3dB a big deal? If you measure the Lowther as a direct radiator on a 'normal' sized baffle, where does it fall to -3dB? 400Hz? 200Hz?
I note that Martin King's Lowther design was 90-95dB after eq.
The 18 Sound - 8M400 looks like a good pro 8" if you want a more efficient mid: 98dB, with a bit of on-axis rise, no huge peaks. Available for a little over $100.
In the 8" full range whizzer cone drivers I've measured and tweaked, most (and in some cases depending on the driver) all of the major resonances in the upper midrange attributed to the whizzer are actually due to the response of the main cone not the whizzer.
This is especially the case on my Coral Flat 8 II's which have exponential (trumpet shaped) whizzer cones - the whizzer itself on these is exceptionally clean up into the treble region but there is a small amount of breakup from the edge of the main cone around 3-5Khz, and some breakup of the aluminium dustcap around 10Khz.
And yes, I've de-whizzered a Coral Flat 8A years ago to confirm this - one with a really stiff surround that wasn't much use for anything other than midrange as it could barely move for bass - taking measurements before and after, and then re-gluing the whizzer later!
)To solve the cone breakup of the main cone on these and tailor the response from 3-4Khz I use an empirically derived pattern of small self adhesive foam strips on the rear of the cone in the outer 20% of the cone diameter - this eliminates all traces of the "random cone breakup" sound normally associated with this size of full range driver, making it sound extremely clean, and both the radial and circumferential modes of the driver's main cone can be nearly eliminated achieving a much flatter response.
I've also tried the same modification on some Fostex FE207's without much success. No matter what pattern of foam strips I used some severe upper midrange resonances still remained, especially around 2.5Khz that this model of driver is known for.
I believe this is down to the conical whizzer used in the FE207 which has a poor stiffness to weight ratio compared to the exponential whizzer on the Coral driver. Although the Fostex whizzer has the edge folded to try to improve the stiffness the rest of the cone is still weak as it is conical.
The compound curve of the exponential whizzer in the Coral driver is inherently superior and performs vastly better than a conical type.
So my conclusions after experimenting with a few different whizzer cone drivers are:
a) Conical whizzer cones will always be compromised and suffer from resonances, however an exponential (trumpet) whizzer cone with a compound curve (especially when made from multiple laminated layers as the Coral ones are) can be made to be very clean and free from resonances at least through the upper midrange and up into the low treble.
b) Both types of drivers will still have cone resonances on the main cone, and for an 8" driver these will fall at around 2Khz and 4Khz. And for an exponential whizzer design the main cone breakup resonances probably predominate.
c) These main cone resonances can often be controlled with patterns of damping strips near the edge of the cone, and far more completely than just trying to make the surround heavily damped.
d) Whizzer cones don't just increase high frequency extension, done right they also increase dispersion at lower frequencies by acting as a phase plug for the main cone. They also increase treble response by horn loading the dust cap radiation.
On my de-whizzered Coral driver I did on axis, 15, 30 and 45 degree off axis measurements with and without whizzer.
Below 2Khz removing the whizzer made no difference apart from a small change in overall driver sensitivity due to a change of mass.
From about 2.5Khz to 6Khz the whizzer cone being present increased the 30 degree off axis response by about 4dB and simultaneously decreased the on axis response by about 3dB, the fact that it reduced the on axis response clearly shows that it is acting like a phase plug at these frequencies where both cones are overlapping but working independently.
Above 6.5Khz the output from the main cone falls off rapidly, so nearly all output from about 6.5Khz to 10Khz is from the whizzer cone. From about 10Khz up the aluminium dust cap is acting as a horn loaded tweeter - when de-whizzered the treble above 10Khz also drops a lot due to loss of horn loading of the dust cap.
Separately on another Coral driver I have tried de-dust capping it while leaving the whizzer in place and confirmed that the dust cap starts producing the major output above about 10Khz with the whizzer falling off above about 12Khz. The dust cap extends the response to about 16Khz.
The de-whizzered Coral driver was still good up to about 6Khz but suffered from severe beaming above 2Khz, as you'd expect from an 8" driver. However with the whizzer cone in place the frequency where they start beaming was increased by at least an octave to about 4Khz.
There's a lot more to a full range whizzer cone drivers design than meets the eye....
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Anything you can imagine being done to a LOWTHER driver has been done.
I would think Mr. Pass was saying the large peak was the result of the removal.
Based upon an article in SOUND PRACTICES twenty years ago and due to the fact they are still around I would contact Audio Technik GmbH.
Mr. Kirchoff is who I suspect is the man with the answers regarding LOWTHER.
Just realized there was a second page and Mr. Pass made the clarification. (oops)
I would think Mr. Pass was saying the large peak was the result of the removal.
Based upon an article in SOUND PRACTICES twenty years ago and due to the fact they are still around I would contact Audio Technik GmbH.
Mr. Kirchoff is who I suspect is the man with the answers regarding LOWTHER.
Just realized there was a second page and Mr. Pass made the clarification. (oops)
In the 8" full range whizzer cone drivers I've measured and tweaked, most (and in some cases depending on the driver) all of the major resonances in the upper midrange attributed to the whizzer are actually due to the response of the main cone not the whizzer.
This is especially the case on my Coral Flat 8 II's which have exponential (trumpet shaped) whizzer cones - the whizzer itself on these is exceptionally clean up into the treble region but there is a small amount of breakup from the edge of the main cone around 3-5Khz, and some breakup of the aluminium dustcap around 10Khz.
And yes, I've de-whizzered a Coral Flat 8A years ago to confirm this - one with a really stiff surround that wasn't much use for anything other than midrange as it could barely move for bass - taking measurements before and after, and then re-gluing the whizzer later!
To solve the cone breakup of the main cone on these and tailor the response from 3-4Khz I use an empirically derived pattern of small self adhesive foam strips on the rear of the cone in the outer 20% of the cone diameter - this eliminates all traces of the "random cone breakup" sound normally associated with this size of full range driver, making it sound extremely clean, and both the radial and circumferential modes of the driver's main cone can be nearly eliminated achieving a much flatter response.
I've also tried the same modification on some Fostex FE207's without much success. No matter what pattern of foam strips I used some severe upper midrange resonances still remained, especially around 2.5Khz that this model of driver is known for.
I believe this is down to the conical whizzer used in the FE207 which has a poor stiffness to weight ratio compared to the exponential whizzer on the Coral driver. Although the Fostex whizzer has the edge folded to try to improve the stiffness the rest of the cone is still weak as it is conical.
The compound curve of the exponential whizzer in the Coral driver is inherently superior and performs vastly better than a conical type.
So my conclusions after experimenting with a few different whizzer cone drivers are:
a) Conical whizzer cones will always be compromised and suffer from resonances, however an exponential (trumpet) whizzer cone with a compound curve (especially when made from multiple laminated layers as the Coral ones are) can be made to be very clean and free from resonances at least through the upper midrange and up into the low treble.
b) Both types of drivers will still have cone resonances on the main cone, and for an 8" driver these will fall at around 2Khz and 4Khz. And for an exponential whizzer design the main cone breakup resonances probably predominate.
c) These main cone resonances can often be controlled with patterns of damping strips near the edge of the cone, and far more completely than just trying to make the surround heavily damped.
d) Whizzer cones don't just increase high frequency extension, done right they also increase dispersion at lower frequencies by acting as a phase plug for the main cone. They also increase treble response by horn loading the dust cap radiation.
On my de-whizzered Coral driver I did on axis, 15, 30 and 45 degree off axis measurements with and without whizzer.
Below 2Khz removing the whizzer made no difference apart from a small change in overall driver sensitivity due to a change of mass.
From about 2.5Khz to 6Khz the whizzer cone increased the 30 degree off axis response by about 4dB and simultaneously decreased the on axis response by about 3dB, the fact that it reduced the on axis response clearly shows that it is acting like a phase plug at these frequencies where both cones are radiating.
Above 6.5Khz the output from the main cone falls off rapidly, so nearly all output from about 6.5Khz to 10Khz is from the whizzer cone. From about 10Khz up the aluminium dust cap is acting as a horn loaded tweeter - when de-whizzered the treble above 10Khz also drops a lot due to loss of horn loading of the dust cap.
Separately on another Coral driver I have tried de-dust capping it while leaving the whizzer in place and confirmed that the dust cap starts producing the major output above about 10Khz with the whizzer falling off above about 12Khz. The dust cap extends the response to about 16Khz.
The de-whizzered Coral driver was still good up to about 6Khz but suffered from severe beaming above 2Khz, as you'd expect from an 8" driver. However with the whizzer cone in place the frequency where they start beaming was increased by at least an octave to about 4Khz.
There's a lot more to a full range whizzer cone drivers design than meets the eye....
Thanks.
Interesting read.
My experience adds to this -
kHz resonances in full-range drivers are often from the area from 3/4 to full diameter of the main cone. These are hard to deal with, but efforts like Enabl and sticky glue on the back near the surround can help to some extent.
You can localise and confirm these active areas by using a signal generator and salt !
I don't think straight (conical) -coned drivers are always at fault. The Fostex FX120 is excellent in this regard, but lots of other Fostexes and Lowthers are very troublesome.
The AER Mk.1 is much better than the Lowthers by the way.
kHz resonances in full-range drivers are often from the area from 3/4 to full diameter of the main cone. These are hard to deal with, but efforts like Enabl and sticky glue on the back near the surround can help to some extent.
You can localise and confirm these active areas by using a signal generator and salt !
I don't think straight (conical) -coned drivers are always at fault. The Fostex FX120 is excellent in this regard, but lots of other Fostexes and Lowthers are very troublesome.
The AER Mk.1 is much better than the Lowthers by the way.
I should clarify that I'm specifically talking about the whizzer cone when I say conical cones are compromised compared to exponential.
The main cone on the Coral drivers is conical like most other drivers, however this can be dealt with by a combination of traditional edge termination damping from the surround and distributed damping strips placed in the correct pattern towards the edge of the cone as I described. (within about 2cm of the surround)
However the whizzer cone has no surround to terminate the edge and provide damping, nor does adding damping strips to the edge of the whizzer cone appear to provide any benefits. (I've tried that without success - part of the problem I think is they just add too much weight for a cone that needs to stay extremely light - any added weight on a whizzer cone almost invariably makes it perform worse)
So for a whizzer cone I still think exponential is inherently better than conical.
Thanks, dave. You were right.
I constructed 2 "phase-plugs" today for the Fane Sovereign 12-250TC.
Also I used a stripe of non-woven air permeable low-weight polyester to dampen highs a bit.
Now it is almost perfect with no EQ.
No need to rape it.
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