PD158 with copper sleeve
Hi Tinitus,
Yes indeed... but this might be a good thing!
I suspect that the real benefit of lowering inductance is the lowering of distortion, not the extended high frequency response.
Lowest possible Le is not at the top of my priority list when choosing a driver to test in a speaker design, but I do think that lowering distortion can’t be a bad thing!
On the other hand lowering the type of distortion caused by flux variations when the voice coil is travelling backwards and forwards in its tunnel of love ( sorry magnetic field ! ) is IMO, nowhere near as important as ( a) minimising thermal compression, ( b ) having a well designed linen surround and non- resonant spider and last but not least (c) a low Mms to Bl ratio i.e. low Mms with high Bl.
Plus good old paper cones not alloy, titanium, bell metal or unobtainium coated with diamond and a drizzle of snake oil...
Cheers
Derek.
Hi Tinitus,
Yes indeed... but this might be a good thing!
I suspect that the real benefit of lowering inductance is the lowering of distortion, not the extended high frequency response.
Lowest possible Le is not at the top of my priority list when choosing a driver to test in a speaker design, but I do think that lowering distortion can’t be a bad thing!
On the other hand lowering the type of distortion caused by flux variations when the voice coil is travelling backwards and forwards in its tunnel of love ( sorry magnetic field ! ) is IMO, nowhere near as important as ( a) minimising thermal compression, ( b ) having a well designed linen surround and non- resonant spider and last but not least (c) a low Mms to Bl ratio i.e. low Mms with high Bl.
Plus good old paper cones not alloy, titanium, bell metal or unobtainium coated with diamond and a drizzle of snake oil...
Cheers
Derek.
Thats very theoretical
IMO the best way to reduce distortion is to reduce Xmax and cone breakup
Hey, I just thought it could be fun with a customised DIY Audiocom driver
But probably impossible😀
btw John, I once mailed about having the TD15M with underhung motor, lower Fs, medium Qts and Xmax
Tho I suggested to pay in advance, never got a reply
And now they claim that Lynn Olson got a similar driver built
IMO the best way to reduce distortion is to reduce Xmax and cone breakup
Hey, I just thought it could be fun with a customised DIY Audiocom driver
But probably impossible😀
btw John, I once mailed about having the TD15M with underhung motor, lower Fs, medium Qts and Xmax
Tho I suggested to pay in advance, never got a reply
And now they claim that Lynn Olson got a similar driver built
Reduce driver travel not XMax!
Hi Tinitus,
I think you might mean reduce driver travel NOT reduce Xmax...!
I ( and many others ) have been doing this for years, i.e. using a Beyma 12 LX60 to cross over to the Manger at 300Hz to 500Hz when the Manger family and all the DIY "sheep " were gushing over their dinky little 6 inch ceramic coned incense holders ( sorry Accuton !) or Scan Speak 7 inch vibrators ( really sorry Scan Speak !! ) but just go and listen to a well designed Pro driver Vs a HiFi marketing toy.
As my infamous article ( attached for your amusement!) states, : ALL so called " pistonic drivers "are so fundamentally flawed it’s a complete bare faced lie to market them as " pistonic drivers " . They are all out of control " mass on a spring " jello systems, the lack of cone break up at certain frequencies is a pure and utter RED HERRING which all driver manufactures hide behind!
So if you are in fact saying reduce driver cone travel and this will massively reduce the insidious time domain ( ghost echoes which " fry " ear / brain functions ) distortion then boy oh boy are you preaching to the converted....!
Cheers
Derek.
Hi Tinitus,
I think you might mean reduce driver travel NOT reduce Xmax...!
I ( and many others ) have been doing this for years, i.e. using a Beyma 12 LX60 to cross over to the Manger at 300Hz to 500Hz when the Manger family and all the DIY "sheep " were gushing over their dinky little 6 inch ceramic coned incense holders ( sorry Accuton !) or Scan Speak 7 inch vibrators ( really sorry Scan Speak !! ) but just go and listen to a well designed Pro driver Vs a HiFi marketing toy.
As my infamous article ( attached for your amusement!) states, : ALL so called " pistonic drivers "are so fundamentally flawed it’s a complete bare faced lie to market them as " pistonic drivers " . They are all out of control " mass on a spring " jello systems, the lack of cone break up at certain frequencies is a pure and utter RED HERRING which all driver manufactures hide behind!
So if you are in fact saying reduce driver cone travel and this will massively reduce the insidious time domain ( ghost echoes which " fry " ear / brain functions ) distortion then boy oh boy are you preaching to the converted....!
Cheers
Derek.
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both 😉
But I never play loud, so we may have very different goal, or different means to use 😕
The copper sleeve makes a impedance compensation less necessary. It also keeps the crossover functioning properly at all excursions. Quite simply there is much more to the issues caused by inductive variation than just the distortion in the driver. The biggest issue is how that driver functions as part of a system. Variation in inductance has severe issues one driver is mated to another.
Take a hypothetical driver that has the standard S shaped Le(x) curve. At rest we will say inductance is 1mH. At the forward stroke it may drop to .25mH and the inward stroke may increase to 2mH. It's all about how much iron is in the core. So you design your crossover assuming 1mH inductance and measuring the small signal response curve. The crossover looks good. Smooth response, good phase coherency, everything looks good... until the driver starts moving.
Once it moves, the only time the crossover is correct is when the driver comes back through the rest position. On the inward stroke the upper response tapers off more with the higher inductance. On the outward stroke the upper response extends as inductance lowers. This difference between the inward and outward stroke is a very audible phenomenon. Not only does it present a difference in the response magnitude there are also differences in phase. This throws off the phase at the crossover point so you may no longer have flat response and things just sound off. The variation in inductance changes the amount of current applied and it also changes things in the time domain. IMO you want no variation in the inductance of the driver for at least two octaves above the crossover point to make sure that there are none of these issues as levels are increased.
This is where the TD woofers excel, not only in low distortion, but in implementation in a system. Take a look at the TD12M Le(x) measured here. At 7mm you can see no change all the way out to 20KHz. This means the coil is acting as an air core throughout it's entire travel. The crossover designed based on small signal measurements will remain valid at higher excursions.
Le(x) (drivervault)
Compare that to something like the GPA414. Look at 1KHz and you can see impedance varies from 15 ohm on the outward stroke to 25ohm on the inward stroke. At 2KHz it varies from 20ohm on the outward stroke to 40ohm on the inward stroke. If you had planned to take this 12" driver to 1KHz, this would surely have significant effects.
Le(x) (drivervault)
While linear inductance lowers the driver distortion, that may not even be the biggest benefit. The benefits in how that driver can be implemented in a system are even larger.
John
Just a word on my xmax testing: when looking at the %HD remember that the room totally dominates the response at these frequencies. Because of that these vlaues are not absolutely correct (they are inflated), I would need an anechoic chamber for that. So the LO15 is not producing 37% distortion at 8mm. The value in the measurements though is that they are relatively correct between drivers.
Le and crossovers
Hi John,
You make some very good points regarding the benefits of a low and stable Le value when it comes to passive crossover design and the driver matching.
Again I am not an expert with passive crossovers but for any and all passive systems your argument really makes sense to me.
BUT.... Don’t ya just hate that word!
The obvious solution is go active and all these issues go away, plus a whole lot of other issues that passive crossovers or " frequency dependant energy storage devices with heat related variable resistance " as I like to call them, bring to the party.
High quality DIY power amps are easy and cheap to build ( especially with Li Po4 battery power now available ) and good analog active crossovers or DSP based crossovers are again perfect for DIY battery power projects.
To some perspective on this, going active with a good battery powered crossover and two ( bi-amp ) or 3 ( tri-amp ) power amps will be a huge upgrade and dwarf any difference between Beyma, 18 Sound, Precision Devices, Focal, Volt, ATC, and AE drivers.
Going active is the be all and end all of upgrades. Full stop.....!
Of course you will still get further smaller upgrades by using better drivers in an active system, but all passive crossovers are the " Elephant in the room "
All the best
Derek.
PS the crazy prices being charged for copper and silver foil inductors, oily paper mushy capacitors and holy water resistors is (a) a sad reflection on the audio business and (b) makes them way MORE EXPENSIVE than going active...!
Hi John,
You make some very good points regarding the benefits of a low and stable Le value when it comes to passive crossover design and the driver matching.
Again I am not an expert with passive crossovers but for any and all passive systems your argument really makes sense to me.
BUT.... Don’t ya just hate that word!
The obvious solution is go active and all these issues go away, plus a whole lot of other issues that passive crossovers or " frequency dependant energy storage devices with heat related variable resistance " as I like to call them, bring to the party.
High quality DIY power amps are easy and cheap to build ( especially with Li Po4 battery power now available ) and good analog active crossovers or DSP based crossovers are again perfect for DIY battery power projects.
To some perspective on this, going active with a good battery powered crossover and two ( bi-amp ) or 3 ( tri-amp ) power amps will be a huge upgrade and dwarf any difference between Beyma, 18 Sound, Precision Devices, Focal, Volt, ATC, and AE drivers.
Going active is the be all and end all of upgrades. Full stop.....!
Of course you will still get further smaller upgrades by using better drivers in an active system, but all passive crossovers are the " Elephant in the room "
All the best
Derek.
PS the crazy prices being charged for copper and silver foil inductors, oily paper mushy capacitors and holy water resistors is (a) a sad reflection on the audio business and (b) makes them way MORE EXPENSIVE than going active...!
Of course that's your opinion, and in almost everything it seems to be right. I would say the challenge here is, for every good designer, to make a (very) good passive system. A lot of people are not satisfied with their active systems, from what I've been reading, along the years, unless it already changed (or depending on the applications).
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Now that is just an opinion 😉
Many, many people enjoy active systems day after day. I would never go back to a passive setup because they are simply inferior.
Many, many people enjoy active systems day after day. I would never go back to a passive setup because they are simply inferior.
Thanks but Im still going to pick the AESpeaker drivers overall all other choices because they are simply better drivers.
AE Vs PD
Hi Doug,
The AE drivers certainly look great on paper, also they have a large and dedicated " fan base " who have obviously tried and tested them in comparison to a broad range of other top drivers and choose to buy AE. That speaks volumes.
Its only the high cost of shipping, insurance, import duty and then 17.5% VAT tax on top of the retail price that stops me ( and most UK / European ) from taking the plunge.
Do you happen to know of anyone who has compared the 15 TDM against the Precision Devices 158 or 1550... preferably in a high resolution active system using open baffle cabinets...?
Cheers
Derek.
Hi Doug,
The AE drivers certainly look great on paper, also they have a large and dedicated " fan base " who have obviously tried and tested them in comparison to a broad range of other top drivers and choose to buy AE. That speaks volumes.
Its only the high cost of shipping, insurance, import duty and then 17.5% VAT tax on top of the retail price that stops me ( and most UK / European ) from taking the plunge.
Do you happen to know of anyone who has compared the 15 TDM against the Precision Devices 158 or 1550... preferably in a high resolution active system using open baffle cabinets...?
Cheers
Derek.
Acouple of things I want to add...
this forum represents a very small percentage of people who are into audio or who are audiophiles.. which that market is already small to begin with..
so as much as I preach the active and processing, as a mfg making speakers were passives still rule the land, AE goes above and beyond..
also, when a driver is that linear above 1k, it's that much more linear in the normal passband IMO..
and in regards to low inductance.. I have always found low inductance drivers along with low moving mass and great motor have an attack and decay unlike anything else.. sort of like having and internal servo...
this forum represents a very small percentage of people who are into audio or who are audiophiles.. which that market is already small to begin with..
so as much as I preach the active and processing, as a mfg making speakers were passives still rule the land, AE goes above and beyond..
also, when a driver is that linear above 1k, it's that much more linear in the normal passband IMO..
and in regards to low inductance.. I have always found low inductance drivers along with low moving mass and great motor have an attack and decay unlike anything else.. sort of like having and internal servo...
Yeah, definitely a cost to buying them internationally.
I have the TD12M, TD12S and the AV15X. I will be ordering the TD6 versions.
I have never heard of precisions devices 158 actually so I have no comment but now I have to go research them. EDIT: being that they are made in England, there is really no reason for you to consider American made drivers. Nice on axis response, any plots for off axis.
Im also not an open baffle guy at all, maybe some day but Im still enjoying sealed/ported boxes. Open baffle is very interesting but seems to be only popular in DIY or small custom ID designers. Its almost impossible to go listen to an open baffle design without going to RMAF or similar.
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Cost of Shipping
Thanks Doug,
Yes the international shipping and taxes are the problem....
Open baffle speakers are a very small % of all designs out there, but they are gaining in popularity all the time.
The acoustically transparent projector screens are great cause you can build the speakers 100% for sound quality and then hide the big ugly brutes behind the screen ( centre channel ) and some silk curtains ( Front L & R ).
Hi Trusound- The PD 158 Mms is 108g with a Bl of 27.3 so this gives ratio of 3.9, very fast! As you say this gives fast attack plus lifelike decay.
If you read my attachment in a reply to Tinitus a few posts ago you this explains why IMO low Mms high Bl are so important.
It all comes down to efficiency.
Look at compression drivers loaded with their horns / wave guides.
Nobody gets hung up over the tiny XMax of a compression driver, the whole beauty of them is how LITTLE they have to move at all.
A well designed horn sounds great, it simply reduces by an order of magnitude how far the driver cone has to move back and forth in order to produce any given SPL.
All the macho stuff about Xmax of 50mm / 2 inches is a load of hot steamy ****...! If you are listening to sounds from a cone moving plus / minus 20mm its already game over.
As a rough guide I aim for a absolute maximum of plus or minus 5mm for 18 inch or 15inch drivers covering 20Hz to 80Hz.
A Maximum of plus or minus 1mm for 12 inch or 15 inch drivers covering 80Hz to 600Hz band.
Usually its as simple as this, when the music is very loud ( 100dB at 1 meter ) if you can see ( with the naked eye ) ANY driver movement you need more Sd. This is a generalisation but its a very good rule of thumb. Sub 20 Hz home cinema is another story...!
Cheers
Derek.
Thanks Doug,
Yes the international shipping and taxes are the problem....
Open baffle speakers are a very small % of all designs out there, but they are gaining in popularity all the time.
The acoustically transparent projector screens are great cause you can build the speakers 100% for sound quality and then hide the big ugly brutes behind the screen ( centre channel ) and some silk curtains ( Front L & R ).
Hi Trusound- The PD 158 Mms is 108g with a Bl of 27.3 so this gives ratio of 3.9, very fast! As you say this gives fast attack plus lifelike decay.
If you read my attachment in a reply to Tinitus a few posts ago you this explains why IMO low Mms high Bl are so important.
It all comes down to efficiency.
Look at compression drivers loaded with their horns / wave guides.
Nobody gets hung up over the tiny XMax of a compression driver, the whole beauty of them is how LITTLE they have to move at all.
A well designed horn sounds great, it simply reduces by an order of magnitude how far the driver cone has to move back and forth in order to produce any given SPL.
All the macho stuff about Xmax of 50mm / 2 inches is a load of hot steamy ****...! If you are listening to sounds from a cone moving plus / minus 20mm its already game over.
As a rough guide I aim for a absolute maximum of plus or minus 5mm for 18 inch or 15inch drivers covering 20Hz to 80Hz.
A Maximum of plus or minus 1mm for 12 inch or 15 inch drivers covering 80Hz to 600Hz band.
Usually its as simple as this, when the music is very loud ( 100dB at 1 meter ) if you can see ( with the naked eye ) ANY driver movement you need more Sd. This is a generalisation but its a very good rule of thumb. Sub 20 Hz home cinema is another story...!
Cheers
Derek.
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This is the first paper I point people to with the mms/bl ratio. Quite simply the ratio is absolutely meaningless and it drives me crazy to no end that year after year it keeps popping up. Without respect to Re, Bl means nothing. Force in a woofer = magnetic flux in gap ( B ) * Length of wire in gap ( l ) * current in the wire ( i ). Without applying current, the coil has no force. More current, more force. Higher inductance, less current and less force. "Speed" is directly related to the frequency being played. If you slow the "speed" you are playing a lower frequency. The "fastest" drivers are the ones that have the lowest inductance and can play the highest in frequency.
http://web.archive.org/web/20010810141852/lambdacoustics.com/library/whitepapers/bl_mms.htm
Again another paper by Adire showing the effects of adding mass to a driver. Added mass has NO effect in the time domain as seen in the impulse response. It only alters the magnitude. Adding inductance DOES change things in the time domain.
http://www.adireaudio.com/Files/WooferSpeed.pdf
That being said, the reason many "low mass" drivers sound good is that they have tiny VC's with naturally low inductance to begin with. It's not the amount of mass you have, but where it comes from that is the issue. 20 grams of added mass added to a cone will not affect the time domain, only the magnitude of the impulse response. Extra turns added to the VC to increase it by 20 grams adds both mass and increases the inductance. This will alter the time domain.
John
http://web.archive.org/web/20010810141852/lambdacoustics.com/library/whitepapers/bl_mms.htm
Again another paper by Adire showing the effects of adding mass to a driver. Added mass has NO effect in the time domain as seen in the impulse response. It only alters the magnitude. Adding inductance DOES change things in the time domain.
http://www.adireaudio.com/Files/WooferSpeed.pdf
That being said, the reason many "low mass" drivers sound good is that they have tiny VC's with naturally low inductance to begin with. It's not the amount of mass you have, but where it comes from that is the issue. 20 grams of added mass added to a cone will not affect the time domain, only the magnitude of the impulse response. Extra turns added to the VC to increase it by 20 grams adds both mass and increases the inductance. This will alter the time domain.
John
Unfortunately not all of the issues go away by going active. I'll give you an example of a 3way with 12" woofer. The image here shows an IDmax car woofer with about 1.5mH inductance but it could be any woofer in that range. Figure a 500hz crossover point. On the inward stroke inductance goes up. Outward it goes down. The top curve here illustrates the change in inductance at the extremes.
Now if you plan for a 500hz crossover, there is a 9dB difference in the response at that point from the inward stroke to the outward stroke! Regardless of having an active crossover, this is still a huge issue. Play a 20hz sine wave at high excursion then play a 500hz tone over it. You can hear the magnitude of the 500hz tone increase and decrease with every stroke in and out. Now to the same but play a vocal in that region and you hear the same issue. This is not accurate reproduction of the signal put in.
Also, see the paper i posted above and see the effects of inductance change on the impulse response. By the inductance varying, things are continually changing in the time domain with every stroke as well.
Now take a look at the AV12X which is the second 2 sets of curves. At 500hz there is NO change in the shape of the curve due to excursion. At 2KHz the change is only a little over 1dB. Going active does get rid of any issues with the driver inductance reacting with the passive component values. It doesn't however do anything to help with the response variations that this inductance change causes.
John
Sounds more like a sub to me
So, how does it look for a midbass with short Xmax and close to zero cone movement 😕
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