New 15" Scanspeak Ellipticor

[mhardy6647]

You know Godzilla stomping around would generate all the bass. ALL the bass.

He was all about that bass...

 

[bigjacko]

I have a hard time comparing the ellipticor woofer with purifi woofer in erin's review. The L(x) is better on purifi but symmetry range for Bl and Kms seems worse. How do those things affect the woofer and which one is the better one? The distortion might be the ultimate goal for all those motor measurements, and the distortion on purifi in my opinion is a bit better. What do you guys think?

For most of people they want to use the woofer extend to subbass, why is that? For me I think get dedicated subwoofer not only reduce IMD and distortion, but also makes placing the sub according to room modes a bit easier. So if I want to get a woofer, I will get purifi woofer and just put it into closed box, make a crossover at 80 Hz and spend the rest of money to get subwoofer. Very easy to design and make, better distortion and better room mode treatment.

 

[andreasmaaan]

I have a hard time comparing the ellipticor woofer with purifi woofer in erin's review. The L(x) is better on purifi but symmetry range for Bl and Kms seems worse. How do those things affect the woofer and which one is the better one? The distortion might be the ultimate goal for all those motor measurements, and the distortion on purifi in my opinion is a bit better. What do you guys think?

For most of people they want to use the woofer extend to subbass, why is that? For me I think get dedicated subwoofer not only reduce IMD and distortion, but also makes placing the sub according to room modes a bit easier. So if I want to get a woofer, I will get purifi woofer and just put it into closed box, make a crossover at 80 Hz and spend the rest of money to get subwoofer. Very easy to design and make, better distortion and better room mode treatment.

Do you have a link to the Ellipticor review you're talking about, please? I can only find the Purifi measurements on Erin's website.

 

[bigjacko]

Do you have a link to the Ellipticor review you're talking about, please? I can only find the Purifi measurements on Erin's website.

The ellipticor measurement was from voice coil test bench, not from erin. They both use kllipel to measure the motor so I think we can compare their results.

 

[andreasmaaan]

The ellipticor measurement was from voice coil test bench, not from erin. They both use kllipel to measure the motor so I think we can compare their results.

Thanks. Yes, absolutely can be compared.

IMO, the Purifi measures significantly better (although the Scanspeak measures very well, too).

The Purifi's force factor and compliance remain significantly more linear out to greater displacement limits (the ratio is roughly 3:2 in favour of the Purifi).

Comparing the distortion measurements is a little more fraught, but to the extent that we can compare them, the Purifi also appears to have significantly lower H2 in the midrange. Below 500Hz, the two drivers are more similar at 94dB/1m, although presumably the Scanspeak's distortion would rise at increased SPLs before the Purifi's does, owing to the Scanspeak's less linear motor/suspension at greater displacements.

EDIT: should just clarify, as a general you can't necessarily directly compare displacement-limiting figures as I've done here, unless other attributes of the drivers are similar. In this case, the two drivers are similar enough to make these comparisons (more or less) possible.

 

[bigjacko]

Thanks for your input. I agree with you that distortion are quite similar except over 500Hz. One thing interesting is when ellipticor increases in 2nd harmonic, the 3rd harmonic decreases. That decrease is nice but increase in 2nd harmonic really makes it not as good as purifi.

 

[andreasmaaan]

Thanks for your input. I agree with you that distortion are quite similar except over 500Hz. One thing interesting is when ellipticor increases in 2nd harmonic, the 3rd harmonic decreases. That decrease is nice but increase in 2nd harmonic really makes it not as good as purifi.

TBH, I doubt that 2HD is going to be audible (firstly because our hearing systems mask 2HD until it gets extremely high, and secondly because IM distortion is unlikely to be high given that H3 and presumably higher-order harmonics are low in level).

However, the differences in displacement limits are real and are likely to manifest in the Scanspeak beginning to create high levels of distortion at lower SPLs than the Purifi does.

 

[bigjacko]

IM distortion is unlikely to be high given that H3 and presumably higher-order harmonics are low in level

Do you know what makes IMD? How does harmonic distortion relate to IMD? For example if we have a driver with higher 2nd HD and lower 3rd HD, how does the IMD compare to driver with lower 2nd HD and higher 3rd HD?

 

[andreasmaaan]

Do you know what makes IMD?

Basically, nonlinearities in the driver. These arise for various reasons. For example, as the voice coil moves back and forth through the gap, the force exerted on it by the motor varies (i.e tends to decrease with voice coil displacement). Similarly, as the cone moves back and forth the stiffness/compliance of the suspension varies. Another common source comes from voice coil inductance (particularly problematic at higher frequencies). There are of course many other possible sources of nonlinearity.

Interestingly in the context of the Ellipticor drivers, symmetrical nonlinearities generate odd-order distortion components (odd-order HD and odd-order IMD), while asymmetrical nonlinearities generate even-order components. This is one reason why 3rd-order HD is so much lower in this Ellipticor driver than 2nd-order HD: ellipses are not symmetrical.

How does harmonic distortion relate to IMD? For example if we have a driver with higher 2nd HD and lower 3rd HD, how does the IMD compare to driver with lower 2nd HD and higher 3rd HD?

I'm not at all well-versed in the signal theory that would be necessary to answer this question properly, so the version for dummies that I can give you is probably a massive oversimplification that can't be applied directly in practice.

Having said that, the essential relationship as I understand it is that the higher in order the harmonic, the higher in relative level the equivalent-order IM product will be.

In other words, if we have H2 and H3 at the same level, IM3 will be higher in level than IM2, etc. (I believe the simplified form of the relationship, not taking into account lots of very important factors, is: IM[n] = n*H[n], where IM[n] is the level in dB of IM of the nth product and H[n] is level in dB of the nth harmonic, but don't quote me on this.)

 

[MarsianC#]

ellipses are not symmetrical

Are they? A polygon with three cornes (Illuminati confirmed) would be a way to go. Or all low order uneven ones.

 

[bigjacko]

@andreasmaaan Wow thank you very much for the detailed explanation!!

 

[andreasmaaan]

Are they? A polygon with three cornes (Illuminati confirmed) would be a way to go. Or all low order uneven ones.

Well, ellipses are not rotationally symmetrical

 

[Zvu]

....

For most of people they want to use the woofer extend to subbass, why is that? For me I think get dedicated subwoofer not only reduce IMD and distortion, but also makes placing the sub according to room modes a bit easier. So if I want to get a woofer, I will get purifi woofer and just put it into closed box, make a crossover at 80 Hz and spend the rest of money to get subwoofer. Very easy to design and make, better distortion and better room mode treatment.

In my opinion, that would be wasting your hard earned money. If low distortion in that area is what you're after, check this out:



This is Purifi (390 euros per piece) vs SB17NBAC (75 euros per piece), both at about 100dB at 1m distance. If you are introducing sub to lower imd, then you don't need to spend 390 euros for midbas. 75 euros for 17NBAC will do. Use some waveguide loaded tweeter to cross it at 2kHz and you have saved yourself a lot of money without touching objective performance.

 

[bigjacko]

@Zvu Thanks, that price difference is huge.... Do you know other woofers that has the same low distortion above 80 Hz?

 

[ctrl]

Do you know other woofers that has the same low distortion above 80 Hz?

There is currently hardly anything better than what SBAcoustics offers in its top models.

Basically, all woofer/midwoofer without shorting rings/demodulating rings (or similar) should be inferior in terms of harmonic distortion.

Peerless offers very few drivers with shorting rings.
Peerless 830869 to 700Hz (crossover for lowest HD).

From Dayton there are some
RS180 to 1.2kHz (crossover for lowest HD).
RS225

When it comes to the most distortion-free reproduction of peak levels, one or the other PA chassis is the answer.
BMS 6S217
BMS 8S219 (used as BR, an 80Hz crossover should be possible)
I don't know independent HD measurements of these chassis. I have the BMS 6S217 here, but haven't measured it yet.

 

[Zvu]

Given how good Satori MW16P measures (disregarding 1.2kHz abberation due to paper cone), i expect that MW16TX will measure maybe even better than Purifi. It goes for 210€ on TLHP.

We'll have to wait for Yevgeniy from Hificompass to measure it.

 

[bigjacko]

Thank you guys so much. It is quite hard to dig out all those information, how did you guys get those information?

 

[carlosmante]

The two companies pursue very different strategies with these two model series.

Purifi's chassis is revolutionary in terms of the overall concept - very low HD, high linear excursion Xmax, high power handling.

In the case of the Ellipticor series, the revolutionary is quite obvious, elliptical shaped voice coil, magnet gap and dust cap, but also the damping of the chassis cone and surround.

The review of the 21WE/4542T00 (German Hobby Hifi 2019 No 5) I know shows very good measurements. The asymmetrical shape of the voice coil and dust cap, seems to suppress harmonic distortions of odd order extremely well.

In this review HD2@90dB is from 50Hz-9kHz at or below 0.32%. But the outstanding thing is that HD3 and HD5 are below 0.01% at 90dB in the frequency range 250-1600Hz, which is more than -80dB attenuation of the odd order HD.

For an 8.5'' chassis these are sensationally low HD3 and HD5 values - the concept seems to be, a bit more HD2, but extremely low HD3 and HD5 (significantly lower than what I would expect from an 8'' Purifi woofer in this frequency range).
Unfortunately, the price for the chassis is painfully high.

"The asymmetrical shape of the voice coil....."? An ellipse is NOT asymmetrical because an ellipse has 2 line of symmetry.

 

[carlosmante]

Basically, nonlinearities in the driver. These arise for various reasons. For example, as the voice coil moves back and forth through the gap, the force exerted on it by the motor varies (i.e tends to decrease with voice coil displacement). Similarly, as the cone moves back and forth the stiffness/compliance of the suspension varies. Another common source comes from voice coil inductance (particularly problematic at higher frequencies). There are of course many other possible sources of nonlinearity.

Interestingly in the context of the Ellipticor drivers, symmetrical nonlinearities generate odd-order distortion components (odd-order HD and odd-order IMD), while asymmetrical nonlinearities generate even-order components. This is one reason why 3rd-order HD is so much lower in this Ellipticor driver than 2nd-order HD: ellipses are not symmetrical.



I'm not at all well-versed in the signal theory that would be necessary to answer this question properly, so the version for dummies that I can give you is probably a massive oversimplification that can't be applied directly in practice.

Having said that, the essential relationship as I understand it is that the higher in order the harmonic, the higher in relative level the equivalent-order IM product will be.

In other words, if we have H2 and H3 at the same level, IM3 will be higher in level than IM2, etc. (I believe the simplified form of the relationship, not taking into account lots of very important factors, is: IM[n] = n*H[n], where IM[n] is the level in dB of IM of the nth product and H[n] is level in dB of the nth harmonic, but don't quote me on this.)

"...:ellipses are not symmetrical."? According to Geometry ellipses are symmetrical.

 

[ctrl]

"...:ellipses are not symmetrical."? According to Geometry ellipses are symmetrical.

As a non-native speaker it is not easy to put your own thoughts on paper. I'm not a loudspeaker chassis designer, so please take note of what I say with a grain of salt.

What was meant was that the elliptical shape of the voice coil and dust cap is "asymmetrical" to the circular cone, surround and circularly arranged magnets.
The result should be (as I understand it) that distortions of odd order are suppressed, at the price of a more distortion of even order, as asymmetrical nonlinearity generates high even order distortions.
For example when the cone or dust cap breaks up into partial oscillations.