Speakerplans.com Homepage
Forum Home Forum Home > General > General Forum
  New Posts New Posts RSS Feed - Skram vs. C2E - Subwoofers info research
  FAQ FAQ  Forum Search   Events   Register Register  Login Login

Skram vs. C2E - Subwoofers info research

 Post Reply Post Reply Page  123 6>
Author
Message
sushi View Drop Down
Registered User
Registered User


Joined: 27 March 2012
Location: Milan
Status: Offline
Points: 80
Post Options Post Options   Thanks (0) Thanks(0)   Quote sushi Quote  Post ReplyReply Direct Link To This Post Topic: Skram vs. C2E - Subwoofers info research
    Posted: 17 January 2022 at 10:12am
Hello! Lately i've been doing some research for sub designs, looking for a single driver/ high efficiency/ loud and deep sounding cab to build in the future.. two designs fashinated me the most: Ricci's Skram (a ported horn with 21' woofer) and HOQWS's C2E (a Paraflex, kind of compound horn with a high tuned resonator combined with a low tuned folded path) which has 18' and 21' versions available.. Sinai had the 21s built recently.
Both the designs seem to be really loud and clear sounding, in the words of the builders/owners, and it seems they can go fairly low.
I've been looking around for graphs and measurements but since they are both recent designs, not so many people built them yet and fewer measured or even compared them.
Can anyone here give some direct feedback on these 2 subs? Some real life outdoor measuraments would be nice to see too
I would like to be sure before i pick one, and spend money on drivers and plywood. I'd like to get more output than my ESW1018 give, a deeper bass (let's say 30hz f6, f3 if possible), all-around versatile and possibly suitable to music as well to outdoor cinema.. demanding a lot, i admit.
If somebody has heard, tested, or measured, one of these 2 designs and would like to share his knowledge, i would be grateful!

Cheers!
Back to Top
sushi View Drop Down
Registered User
Registered User


Joined: 27 March 2012
Location: Milan
Status: Offline
Points: 80
Post Options Post Options   Thanks (0) Thanks(0)   Quote sushi Quote  Post ReplyReply Direct Link To This Post Posted: 18 January 2022 at 6:04pm
I managed to get some info on HOQWS fb page: aparently, somebody did test all these subs, but measurements were unfortunately taken in different locations.. for what i've been told, 18' C2E golden formula was taken in free field, 21'C2E silver formula was in a backyard (no specification about significant boundaries around), and Skram was taken indoors at Motion Lab, Berlin (no obstacles in a 5m radius). This is quite invalidating for the comparison between them imho.. anyway, here's the graph i've been provided

Edit: basic data i forgot to mention! C2E gf was loaded with B&C 18DS115-4, C2E sf was loaded with 21NWL9001, Skram had SAN215.30 in them.

Edited by sushi - 18 January 2022 at 6:18pm
Back to Top
bob4 View Drop Down
Old Croc
Old Croc
Avatar

Joined: 29 February 2004
Location: Finland/Germany
Status: Offline
Points: 1676
Post Options Post Options   Thanks (0) Thanks(0)   Quote bob4 Quote  Post ReplyReply Direct Link To This Post Posted: 18 January 2022 at 7:02pm
Originally posted by sushi sushi wrote:


I've been looking around for graphs and measurements but since they are both recent designs, not so many people built them yet and fewer measured or even compared them.
Can anyone here give some direct feedback on these 2 subs? Some real life outdoor measuraments would be nice to see too

The SKRAM was published almost three years ago, and there is active discussion going on. Many successful builds and feedback there. why don't you ask the designer himself?  He seems very accommodating.......

Back to Top
toastyghost View Drop Down
The 10,000 Points Club
The 10,000 Points Club
Avatar

Joined: 09 January 2007
Location: Manchester
Status: Offline
Points: 10646
Post Options Post Options   Thanks (0) Thanks(0)   Quote toastyghost Quote  Post ReplyReply Direct Link To This Post Posted: 18 January 2022 at 7:56pm
I take it there’s also no information regarding the stimulus level, calibration process, mic distance, and atmospheric parameters with those REW plots? Have they been calculated back to a common distance?

I doubt the first one is truly done in free field conditions unless someone shoved it 10 metres up on a crane...

If the sweeps are not taken in the far-field of the cabinet, then the data can’t be trusted even if they’ve measured and documented the amp output with a TrueRMS voltmeter and 50 Hz sine. Up close, the radiation versus frequency will be inconsistent and won’t necessarily obey inverse distance law.

This is worth a read - you can do ultra near-field and scale the IR by a/2r for low frequency measurements, but you also have to merge the ultra near-field data from all radiating surfaces, ports and the like first. https://www.artalabs.hr/AppNotes/AN4-FreeField-Rev03eng.pdf

That said, the overall plots look as I'd expect from listening to and simulating a few Paraflex cabinets in Akabak BEM. You've got some 20+ dB of gain above 60 Hz relative to the low corner around 30 Hz. Since this design type is a variation on a tapped horn and similar quarter-wave air column resonators, you can't expect the same 'flattening' of response that results as multiples of FLH designs with compromised mouth areas are stacked together.

Judging by that, I'd personally much prefer the SKRAM's more linear response.

Edited by toastyghost - 18 January 2022 at 8:02pm
Back to Top
sushi View Drop Down
Registered User
Registered User


Joined: 27 March 2012
Location: Milan
Status: Offline
Points: 80
Post Options Post Options   Thanks (0) Thanks(0)   Quote sushi Quote  Post ReplyReply Direct Link To This Post Posted: 19 January 2022 at 2:54pm
Thanks for the answers!
Bob, i've red that topic months ago but it looked like most links and pics were unavailable.. opened it today on my laptop and they work, so probably my phone was the problem then..
Defo reading it once again, thanks!
Toastyghost, the only other info given to me was they were all 1w/1m measurements, can't assure if mic had been freshly calibrated or if a truerms multimeter was used to set power.. i just don't know, and wouldn't even ask again since the test wasn't really a fair comparison between the 3 cabs. Testing one of the subs indoors makes no sense to me in the first place, moreover no info was given about room's size, shape, impulse response, so.. kinda worthless!
Like you said, me too think the Skram would have a more linear response than the C2E which is also tuned a bit higher (35 vs. 30, iirc) and drops rapidly below fs, while Skram seems to drop more gradually.
I admit the Skram seems to me a really versatile cab: even response, wide usable band, compact size, multiple tunings available.. Wins for now!
Back to Top
snowflake View Drop Down
Old Croc
Old Croc


Joined: 29 December 2004
Location: Bristol
Status: Online
Points: 2876
Post Options Post Options   Thanks (0) Thanks(0)   Quote snowflake Quote  Post ReplyReply Direct Link To This Post Posted: 19 January 2022 at 6:01pm
it's amazing how many paraflex seem to have been built without anyone doing a proper measurement.
Back to Top
bee View Drop Down
Old Croc
Old Croc
Avatar

Joined: 14 June 2011
Location: Middlesex
Status: Offline
Points: 4553
Post Options Post Options   Thanks (0) Thanks(0)   Quote bee Quote  Post ReplyReply Direct Link To This Post Posted: 31 January 2022 at 9:10pm
first post in many years, Plenty of Rta measurments of the paraflex cabs have been done. Any that have been published with the plans, were taken 1w at 1m out doors. set a 1khz. All the guys on the design team working in the back ground all measure to the same standards, so we can compare data ect. The free field was measured in a field. the back yard was done outside his workshop, there was walls on both sides near by. 

Edited by bee - 31 January 2022 at 9:15pm
https://www.elements-audio.com
Back to Top
toastyghost View Drop Down
The 10,000 Points Club
The 10,000 Points Club
Avatar

Joined: 09 January 2007
Location: Manchester
Status: Offline
Points: 10646
Post Options Post Options   Thanks (0) Thanks(0)   Quote toastyghost Quote  Post ReplyReply Direct Link To This Post Posted: 01 February 2022 at 9:20am
It’s a shame that measuring a sub like that doesn’t produce valid data. You need to be in the acoustic far-field and should be using a much lower frequency for calibration of voltage to accommodate for the limited range of validity on cheaper DMMs. Typically, 50 Hz or 60 Hz allows the use of cheap multimeters, and 2.83 V is easy to get a stable result for.

Measuring in the near field produces much higher sound pressure levels and a response curve that is not representative of real listening, as the radiation conditions do not follow the inverse distance rule.

Ideally, ten metres is the best position for subs as it is easy to calculate back. Using 28.3 V is also a more realistic drive level, which is a benefit. Otherwise, if you’re not able to get that far out, at least 4 times the diagonal dimension of the mouth area is the rule of thumb. Just reduce the voltage, or calculate back by reducing the measured by the factor difference until you’re at 1 metre.

You should also document the electrical impedance versus frequency, so that the data can be properly scaled for comparison to other boxes. Easily done with REW, and a known resistor value. Using the driver’s free air nominal value isn’t really good enough. You’re in the same boat as most manufacturers in that, though.

While you’re at it, seems it would be good to do the CEA 2010 test built into REW, or do the M-Noise Linear LPeak test?

Unfortunately the poor or complete lack of labeling and documentation of test conditions, and all of the data I’ve seen needs to be taken with a large pinch of salt. I’m afraid that goes for your own massive design too.

Edited by toastyghost - 01 February 2022 at 9:57am
Back to Top
Sinai Sound View Drop Down
Young Croc
Young Croc
Avatar

Joined: 09 November 2009
Location: Sheffield
Status: Offline
Points: 591
Post Options Post Options   Thanks (0) Thanks(0)   Quote Sinai Sound Quote  Post ReplyReply Direct Link To This Post Posted: 01 February 2022 at 1:22pm
Originally posted by toastyghost toastyghost wrote:

It’s a shame that measuring a sub like that doesn’t produce valid data. You need to be in the acoustic far-field and should be using a much lower frequency for calibration of voltage to accommodate for the limited range of validity on cheaper DMMs. Typically, 50 Hz or 60 Hz allows the use of cheap multimeters, and 2.83 V is easy to get a stable result for.

Measuring in the near field produces much higher sound pressure levels and a response curve that is not representative of real listening, as the radiation conditions do not follow the inverse distance rule.

Ideally, ten metres is the best position for subs as it is easy to calculate back. Using 28.3 V is also a more realistic drive level, which is a benefit. Otherwise, if you’re not able to get that far out, at least 4 times the diagonal dimension of the mouth area is the rule of thumb. Just reduce the voltage, or calculate back by reducing the measured by the factor difference until you’re at 1 metre.

You should also document the electrical impedance versus frequency, so that the data can be properly scaled for comparison to other boxes. Easily done with REW, and a known resistor value. Using the driver’s free air nominal value isn’t really good enough. You’re in the same boat as most manufacturers in that, though.

While you’re at it, seems it would be good to do the CEA 2010 test built into REW, or do the M-Noise Linear LPeak test?

Unfortunately the poor or complete lack of labeling and documentation of test conditions, and all of the data I’ve seen needs to be taken with a large pinch of salt. I’m afraid that goes for your own massive design too.

How much to just live in your brain for a bit please
Back to Top
smitske96 View Drop Down
Young Croc
Young Croc


Joined: 16 February 2016
Location: The Netherlands
Status: Offline
Points: 864
Post Options Post Options   Thanks (0) Thanks(0)   Quote smitske96 Quote  Post ReplyReply Direct Link To This Post Posted: 01 February 2022 at 1:39pm
@toasty

I once opted for CE2010 tests in the paraflex fb group, and most where not fond of it. While it is one of the methods to see what is going on at higher levels and show the absolute limits compared to other designs. Just saying it is loud would not do it for me, because that observation can be influenced by several factors. 

It is the only thing I sometimes dislike about the group, it is seen as the 'holy grail', with that its own following. Sure, it is a nice relatively new innovation in DIY etc, but its not the one go-to solution for all your needs.
Back to Top
toastyghost View Drop Down
The 10,000 Points Club
The 10,000 Points Club
Avatar

Joined: 09 January 2007
Location: Manchester
Status: Offline
Points: 10646
Post Options Post Options   Thanks (0) Thanks(0)   Quote toastyghost Quote  Post ReplyReply Direct Link To This Post Posted: 01 February 2022 at 2:55pm
That's a shame, since the point of the CEA-2010 process is to find the distortion-limited max output. That’s far more useful than a calculated value, even if you use the newer B variant of the test process which is supposed to be more psychoacoustically informed.

Of course to do it properly, you need to use a calibration measurement of a known sealed cabinet, even in most outdoor locations. Plus you have to also consider how to stay within the distortion limits of their microphone or audio interface, while maintaining sufficient signal to noise ratio for the data to be valid.

The CEA 2010 process is also more useful for comparing impulsive signals like a kick drum or an explosion sound effect for home theatre, and this can be easier for some boxes or designs than playing music content constantly.

The M-Noise process is a little more friendly to most practitioners, while also being more representative of long term signal drive levels. Your neighbours might not appreciate the noise running for the typical test lengths, though...

Both tests are very valid, especially for DIY boxes, and can be done at home by folk with a garden or access to a car park at their warehouse. It seems odd to be dismissive of them, since these procedures can easily highlight where a DIY design succeeds or fall short when compared to the 'industry standard' or professional cabinets.
Back to Top
toastyghost View Drop Down
The 10,000 Points Club
The 10,000 Points Club
Avatar

Joined: 09 January 2007
Location: Manchester
Status: Offline
Points: 10646
Post Options Post Options   Thanks (0) Thanks(0)   Quote toastyghost Quote  Post ReplyReply Direct Link To This Post Posted: 01 February 2022 at 5:03pm
Pictures tell a thousand words and all that... plus this has been floating about on my hard drive for a couple of months, so might as well share.



This is a coupled lumped element and boundary element model of the Paraflex C2A Golden 21" cabinet in AKABAK3. This is the largest and most performant design as I understand it, a no-compromise version of the loading with outer dimensions of 1.2 metres by 1.2 metres by 0.6 metres.

The PDF plans don't indicate what driver was used, but I believe it was the Eighteen Sound NLW9601-4, so my model uses that as well. The shared traces from CLIO Pocket on the first page are sadly super compressed as part of a single image. I did the best I could with curve tracing tools, to get comparison data.

The base CAD model was drawn by myself from the plans shared on the HOQWS group, using quarter-symmetry on the XY plane. Eight subdomains are used, with the interfaces between each subdomain being meshed at twice the element count of the subdomains on either side. The CAD model has been manually meshed using the Frontal-Delauney algorithm in Gmsh, using frequency-swept element length parameters based on the internal geometry - in particular, channel dimensions were considered versus the element size, to ensure there was no overlap between integration points across the boundaries.

Stuffing was modelled in the corner pieces of the driver's rear chamber, using a measured absorption coefficient curve for a densely compressed piece of dacron.

There are 4,319 elements per quadrant, and an Infinite Baffle plane is used to create half-space (2pi) radiation conditions.

The recommended 21NLW9601-4 driver was modelled via the AKABAK voice coil model of complex, frequency-dependent inductance, using the driver-identification tool in the accompanying VACS software. For those who aren't familiar with this model, it uses exponential functions for resistance and reactance:
Zvc = Re(f) + j·Xe(f)
where
Re(f) = Re·(1 + f/fre)ExpoRe
and
Xe = (ω·Le)r
with
r = (1 + ExpoLe·q2)/(1 + q2)
q = ω·Le/Re

It is still a linear model overall, but this method produces a non-linear behaviour of Z(Le) as frequency increases.

Frequencies from 20 Hz to 250 Hz at 24 points per octave were calculated, for a total of 111 data points on each complex curve. Additionally, a 3-metre x 3-metre field across the ground plane was generated, with a resolution of 4 elements every 0.07 metres.

2V RMS driving level was used, based on the nominal impedance in pass-band being approximately 4 Ohm. This is equivalent to 1 Watt @ 1 metre distance, and matches the reported method on the plans.

Of interest to most people is the axial SPL, and electrical impedance, which I've shown compared to the measured data for qualification.


The electrical impedance tracks well, although it appears there is a slight shift down in tuning. Also, the upper response is reduced compared to measurement - this is likely caused by the lack of absorption from stuffing in the initial chambers of the model, and also the linear modelling method not including higher-order harmonic distortion components.

Another possible cause is that AKABAK3 is a BEM model in the physical domain, so does include effects of diffraction and wavefront distortion around bends and the like.

There's also a chance that the CLIO Pocket mic used for the original measurements was distorting, with the 3 dB crest factor of the log chirp (swept sine wave) stimulus and the CLIO Pocket mic's stated max peak SPL capability of 130 dB linear SPL at 1 kHz. The small plastic electret condensers typically perform worse at low frequencies, and I recently saw some strange behaviour at high signal levels when comparing two 'full-fat' CLIO mics to my own mics in a hemi-anechoic chamber.

If this wasn't just a 'bit of fun', and I had the cabinets to hand to experiment, I'd investigate further to determine what causes this discrepancy. As it is, close enough...


You can see that the electrical impedance dips to just under 3 Ohms at a couple of points between 30 Hz and 120 Hz, even in the measured data. As these are both small-signal data, it indicates that a 2 Ohm capable amplifier with one cabinet per channel would be a good idea for this box.

More importantly, you can see the problem of measuring at 1 metre. The light blue SPL trace tracks the 1-metre measurement very well, but the near-field condition provides an apparent +3 dB boost below 50 Hz when compared to a measurement taken in the far-field (green trace) and scaled back to 1 metre (purple trace). I don't know about you, but on my gigs and installs, only a tiny percentage of the punters are anywhere close to 1 metre away from the mouth of the boxes.


While we're here, one thing that is modelled well regardless of SPL discrepancies is cabinet diffraction. That is the primary effect on directivity, for low frequency enclosures. Since I've heard it said that Paraflex are supposedly very directional, that's worth a look at:


This is a broadband sum of all frequencies from 25 Hz to 125 Hz, looking from above the box at the 'ground'. The same pattern can be observed in the normalised horizontal polar plot - this is normalised relative to the axial response, so removes the SPL discrepancy between model and measurement from the equation:



It looks like there's little to no rear rejection - at least for a single cabinet - but there is a significant edge diffraction toward the lateral directions of +/-90 degrees, toward the rear cabinet corners.

One final bit of fun; stepping through the pressure response pattern from 10 Hz to 250 Hz, across that 3m x 3m plane. The meshing resolution of the observation field isn't high enough to show the entire internal path, so the 'gaps' are just where the cabinet walls are, but you can see the development of the pressure wavefront. That includes frequencies where the rearward radiation from the diaphragm is not in phase with that coming from the series resonant chambers.





Thanks for coming to my TED Talk
Back to Top
 Post Reply Post Reply Page  123 6>

Forum Jump Forum Permissions View Drop Down

Forum Software by Web Wiz Forums® version 12.05
Copyright ©2001-2022 Web Wiz Ltd.

This page was generated in 0.078 seconds.