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Skram vs. C2E - Subwoofers info research

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Ricci View Drop Down
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Post Options Post Options   Thanks (1) Thanks(1)   Quote Ricci Quote  Post ReplyReply Direct Link To This Post Posted: 01 February 2022 at 8:43pm
I was informed of this GTG at Motion Labs a few weeks before it took place. I was told there was going to be a comparison of a few subs with measurements and someone would be building a Skram and was asked if the 21NTLW5000 was a match. It's not ideal for the Skram due to slightly lower motor force than the cab was designed to work with (NSW6021, etc...) and I said as much, but told them it would be serviceable. As far as I was aware all of the other subs were the paraflex type that suddenly seems to be the popular flavor in DIY subs. Unfortunately I never saw any good measurements or data come from this meeting and the only thing I was told is that the Skram was placed differently, built very quickly and barely listened to at all at the gathering because it wasn't as "exciting" as the much larger, I believe pairs of paraflex subs. Not very confidence inspiring for a fair or scientific comparison. I'm not sure what driver, amp, settings were used for the subs and I don't think it was level matched. 

The Skram is a 30Hz tuned 450L net cabinet with a lot of effort put into balancing: Smooth linear response, output capability, low distortion, tuning flexibility to work in multiple applications and manageable size / weight. Scaling the system with multiple cabs to fulfill the output requirements of the app is intended. I intentionally choose not to tune any higher than about 30Hz on any of my subs. I know this gives up some loudness to achieve this type of extension. It'd be easy to tune it to 35 or even 40Hz and gain some sensitivity and loudness in the 40-100Hz bandwidth but it's a tradeoff that I choose to make for being able to really hit that 25-30Hz content when it does show up. I design for the top tier drivers because the extra xmax and power handling can help make up some of the deficit from tuning lower and/or being smaller than a lot of other subs. It's not a philosophy that fits or is cost effective for everyone and that's ok. There are a lot of ways to skin the cat. 

The 21" paraflex appears to be 2X the size at 900L net and with a higher 35Hz corner. 
900L is a huge cabinet. My Skhorn 2x 21" is quite a bit smaller at 680L net.  As we all know bass efficiency is all about air volume / size balanced against extension. Is a 21" paraflex going to be more sensitive and louder than a Skram that is half the size and tuned lower? Yes.
I'd be very interested to see a fair comparison with 2 Skrams since the dual cabs take up the same volume as the 21" paraflex. With equally good amplification, proper level matching, processing, etc... 

+1 on pretty much everything TG has posted in here. We need data!

I'm a hard data kind of guy. Hence my website...
It's crucial to understanding the behavior of a system and understanding the causes of the difference in sound between designs. Part of the qualification / improvement process if you will. I don't put much value on subjective reviews/opinion especially from people who have built the cabinet they are evaluating. 

 I'll eventually get around to testing Skram and Ckram subs. I should've done it long ago but I took a hiatus from DB testing. I'd really like to see an equivalent ground-plane measurement workup on a few of the paraflex designs considered to be the most refined. I'd like to see some popular scoops done as well. Impedance and 1w sensitivity measurements are a start but the interesting bits are what happens with compression, thermal shifting of output and distortion at war volume. CEA style short term SPL capability. Etc. Most designs look great at a few volts. What happens at 50 volts? 100? I want to see where things start to degrade and fall apart. 
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Post Options Post Options   Thanks (1) Thanks(1)   Quote Ricci Quote  Post ReplyReply Direct Link To This Post Posted: 01 February 2022 at 9:04pm
Toasty,

Hell of a post you made there. Thanks for the Ted Talk. LOL
I can tell you put a fair amount of time into looking at that. 

A couple short observations if I may...
You are dead on that the low end response will droop by a couple of dB when measuring a front firing sub of this size at 1m vs 10m. These are big subs with a very large frontal area. At minimum a 4m ground-plane measurement would be advisable if 10m isn't possible. Or use the 10m measurement for a cal file on the shorter distance. 

I suspect that the response differences between your sim and the provided measurement are primarily due to a different driver being used in the measurement. Perhaps a 21NTLW5000. I could be wrong but that'd be my quick guess. Also some of the extra upper end response in the measurement would be from cab diffraction. That's a good sized frontal area. You may have taken this into account already and I missed it, 3dB extra gain by 100Hz already wouldn't be out of the question. Combine those 2 possibilities and it may close the gap between the measurement and sim considerably. 


Edit to add a Skram FR measurement. This was taken by a user Jay Michael outdoors at 1m GP in his backyard. Driver is the B&C 21SW152-4. This is the most trustworthy FR measurement of one I've seen yet. I don't trust the SPL calibration of the measurement but the overall FR shape should be close. 





Edited by Ricci - 01 February 2022 at 9:18pm
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Post Options Post Options   Thanks (0) Thanks(0)   Quote citizensc Quote  Post ReplyReply Direct Link To This Post Posted: 02 February 2022 at 6:37am
Originally posted by Ricci Ricci wrote:

I'd be very interested to see a fair comparison with 2 Skrams since the dual cabs take up the same volume as the 21" paraflex. 


A 900L volume and 800 euro driver budget opens up a lot of options. To be honest, I would like to see it compared to a couple of simple 21 inch reflex with something like the 21PW1400Fe.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote kipman725 Quote  Post ReplyReply Direct Link To This Post Posted: 02 February 2022 at 2:10pm
Thanks for doing all that sim work Kyle, I had suspected all the talk about rear rejection was incorrect as I couldn't think of a physical mechanism beyond the frontal area.  The HOQWs in general is lacking in test data, its disappointing that ASFIK the only people doing proper testing are data-bass and production partner.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote sushi Quote  Post ReplyReply Direct Link To This Post Posted: 02 February 2022 at 2:26pm
Gentlemen, thank you all for you answers and for the data provided. I may not perfectly understand some of those, being me a newbie for what regards audio measurements, but this is for me a big motivation to learn more and achieve a deeper understanding of this matter.
Ricci, thanks for showing up, as well for sharing your good work! I'm currently re-reading the Skram topic on data-bass, couldn't see pics the first time i read it.. that measurement taken by Jay might not be good for a proper and complete review of your sub, but it shows a smooth and even response which is really promising.. i definitely could be building a pair of Skrams in the future, as they seem to well fit my requirements for now.
As regards the paraflex subs, i really like they are "free" plans and get constantly improved through shared knowledge, but i find nowadays some people are kinda taking them for "the best subs ever - period" and contribute to fuel a hype that could illude some non-expert users (like me) that they are just as good as one could dream a sub to sound. A badass look makes things worse..
Pay attention! I'm not saying C2E are not good! I believe they must sound loud and clear since lots of people are happy with them, and i'm really looking forward to hear one personally. But if the outdoor measurements are correct, then 30hz 15db down from 60hz seems no such dream performance for a sub, also that big.. it has a powerful overall bass response indeed, but the graph also suggests the low end is not so loud. It could maybe get better with some eq lowering that large peak around 65hz but, again.. we don't know cause no detailed eq setting are posted with the plans on the fb page, neither real life measuraments, sometimes not even simulations.. I understand many just want to build and play, but that doesn't work for me. I think it would work better if common half-space test setting standards had been given to the builders, and the resultant measurements and eq tips had been posted with the designs. This way it would really be society work, as people could give something back while sharing their own experience. That said, i reckon admins and designers are quite helpful when asked.

Edited by sushi - 02 February 2022 at 2:32pm
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Post Options Post Options   Thanks (1) Thanks(1)   Quote toastyghost Quote  Post ReplyReply Direct Link To This Post Posted: 02 February 2022 at 3:07pm
I actually wanted to do one of the C2E since the size is way more practical for most people, but I was quite put off by the fact that the pinned post on the group had 3 ‘drawings’, all with different dimensions, and the lack of any apparent measurements for comparison or validation.

One thing to consider for anyone interested in measuring subwoofers is that you can actually get useful data even if you’re stuck indoors. Using the principle of superposition, if the sub’s mouth is placed at the very centre of a room, then putting the mic’s capsule right into one of the corners where the walls meet the floor gives you the fewest reflections possible in that space.

It does of course produce a massive boost to the overall response since you’re in 1/8th space, so you have to manually adjust the measured response down by approximately 9 dB for that, as well as adjusting for the distance offset.

The room still has to be quite large, and ideally square, and have solid, dense walls on all sides to ensure that there’s an even distribution of reflections and a relatively easy calculation of the modal response. However, if you can get a distance of >8 metres from the sub’s mouth to the nearest boundary, then you should push the reflection down to well below 30 Hz. Any peaks in the data can be compared to the calculated modes, to see if they can be ignored.

You can also make a simple sealed subwoofer, and measure this to create an inverse calibration curve including the modal response. That can then be applied to any future measurements in that space.

I'm pretty sure most folk have access to a reasonably sized warehouse or barn. You could also try this outdoors, if your nearest car park or yard isn't massive...

The same principle applies when looking for the best subwoofer placement in your house or a venue too. Stick the speaker where you'd normally have your ears, and move the mic to the various positions where you could reasonably put the speaker. Far less effort than shifting the heavy box around!

It is however essential that the charts are labelled properly, and are accompanied by photos or text explaining what you did, what kit was used, how cold and humid it was, etc etc. The boring part where you document the method is as important as the actual process of gathering the data for any acoustical measurement - and a foundation of scientific process, regardless of field.

Funnily enough, this sort of thing is documented as part of the CEA 2010 process

Edited by toastyghost - 02 February 2022 at 3:11pm
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Post Options Post Options   Thanks (0) Thanks(0)   Quote snowflake Quote  Post ReplyReply Direct Link To This Post Posted: 02 February 2022 at 5:03pm
any measurements or model of second and third harmonic distortion in paraflex? this could account for perceived loudness and directivity...

Edited by snowflake - 02 February 2022 at 5:03pm
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Ricci Quote  Post ReplyReply Direct Link To This Post Posted: 02 February 2022 at 8:49pm
It would be great to have a few more outlets of in depth performance evaluation style testing of "pro"  subs and speakers, but I can understand why there are not. It is tedious, time consuming and requires a healthy dose of grunt work. It's really only the last 15 years that has seen this type of measurements enter into the mainstream. I find it slightly amusing that the home audio segment appears to be adopting objective data like spinorama and CEA-2010 testing more rapidly than the professional market. 

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Post Options Post Options   Thanks (0) Thanks(0)   Quote toastyghost Quote  Post ReplyReply Direct Link To This Post Posted: 02 February 2022 at 9:48pm
Originally posted by snowflake snowflake wrote:

any measurements or model of second and third harmonic distortion in paraflex? this could account for perceived loudness and directivity...


Unfortunately, if the measurement process isn’t correct for magnitude, the harmonic data produced from the Farina sweep method is also questionable. Especially at low drive levels.

In modeling terms, it is possible to derive an estimation of the lower order linear harmonic distortion components from FEA or BEM models, but you need to integrate over a lot of finely spaced data points along a line from the driver to the far field.

There are also time-dependent solvers which can be used to simulate nonlinear acoustics in the newer versions of COMSOL, but I tried to run the example model of a simple, axisymmetric horn (https://www.comsol.com/blogs/simulating-nonlinear-sound-propagation-in-an-acoustic-horn/) and I don't think my desktop PC has forgiven me since.

It is a shame there's not more quantified, repeatable data shared publicly in the pro audio world. My cynical side says that's at least partly intentional, but then I also see the variety of standards and understand a little why practitioners are less likely to pick up a book or paper, let alone a microphone. The folk in the actual engineering jobs seem to understand this stuff pretty well, though.

The upcoming AES standardisation of the M-Noise process should go some way to knocking s few of those barriers down, at least in practical terms.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote bee Quote  Post ReplyReply Direct Link To This Post Posted: 07 February 2022 at 6:38pm
Wow some very good detail in that response. The driver tested was the 18 sound 21 9601c (carbon). The rear projection in all sims is on par with your findings, but in real would we are getting a massive 6 to 9 db drop off, behind, I would love to post why, in truth I have no idea.. a positive gain yes but why... I see your point re 10m distance readings. This can be done. Soon as weather gets a bit nicer, I'll get them back outside and measureLile alot of things, some of the designs are or where done by a few people all over the world, with different measuring kit ECT. The c2a golden was designed and prototyped in the UK, by my self and Mathew's assistance via video links ECT. The plotts need to be updated on the plan, as I did do a revised set, this included a few updates to the tuning of the front chamber. Plans show updates. I could possibly arrange to get some boxes to you, if you would like a play. 
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Post Options Post Options   Thanks (0) Thanks(0)   Quote T Willy Quote  Post ReplyReply Direct Link To This Post Posted: 07 February 2022 at 10:51pm
The reasoning behind the lack of data is due to the DIY nature of it. Some don't have the means or proper knowledge to take measurements. Some don't have the space to do it. Some don't have a working sample built to test. Everyone is at varying stages of knowledge, capabilities, and ability.
Granted there is always someone who has more knowledge and i would be glad to test anything with some guidance of the guru's.
For now, attached is the REW response taken at 1m/2.83v of the Paraflex C-2E Silver Formula loaded with SB Audience Nero 18SW1100d driver. UMIK1 was used as measurement mic. Overlay is the Hornresp model for same enclosure/driver combo using actual T/S parameters pulled from one of my nero drivers using DATS.
Take this data as you wish. Is it perfect or "uniform" test? No, but some of us are working on a knowledge and ability limited circumstance here.

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Edited by T Willy - 07 February 2022 at 10:55pm
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Jay michali Quote  Post ReplyReply Direct Link To This Post Posted: 08 February 2022 at 6:19am
Great conversations happening here, thanks everyone. I've built both Skram's as well as some smaller 15" Type A paraflex cabinets. They are both great sounding cabinets and honestly as far as sound character goes they are more similar than they are different in my opinion. I wont go any deeper with comparisons at this time as they aren't anywhere similar in size, tuning, or in driver used.

The Skram measurement Josh posted above is mine. I was very much a measurement noob at the time and I definitely didn't db calibrate my mic so take that with a grain of salt. The response shape however is truthful to more recent measurements I've taken. I have learned a lot about measurements since, and intend to do more complete and accurate measurements of both cabinets once the snow melts up here in Canada.

To the original poster. The Skram is a fantastic sounding cabinet when powered properly with the 21sw152, and I would imagine it would be even better with the new Eminence 21. With casters, or on a dolly, I can load them in and out of venues and my trailer with no issues on my own. I previously used some Othorns, and found them way more challenging to move around even though they are just slightly larger. I think the Skram hits a perfect balance of size, weight, output and low extension. A bank of 6 of them is really impressive, they really can haul ass all the way down to the mid 20's. We love them so much, there is going to be another 4 or 6 coming to our city real soon.

If you can tolerate larger cabinets, then that may change the game and other options might be more suitable for your purposes. If its just output you're looking for, you could just built more as Josh mentioned.

On the Type A's, for the size they are also really impressive. For a relatively small cabinet and a 15" driver they punch way above their weight. They excel with kick drum oriented music, and offer a cleaner and more dynamic sound than most subs I've heard. I like playing the track Invincible by Tool during sound checks with these subs, I've never heard a studio recording of a band sound as impressive through PA style subs, there really is some magic sauce happening with the design. My particular versions are tuned to 35hz, they can do a reasonably good job of deeper bass music but they are better suited for house and techno for sure. I haven't heard any larger paraflex's before so my opinion is limited to the type A's I've built.

Lastly to Toasty. Thanks for the Ted talk, lots of good pointers in regards to measurements, I've taken some notes. On the rear rejection topic I'd like to add something to the conversation. These type A's have a noticeable reduction in output behind them. I don't know anything about the software you are using to simulate with, but in my experience the rear cancellation is a real phenomenon. I will add this to my measurement to-do list and report back in a month or two when I can get back outside again. I made this measurement last summer, and again note that I was very much in measurement noob territory at the time. Perhaps it offers a glimpse into whats happening. Disregard the 2.83v@1meter, I believe it was at 6 feet, measured with a tape measure from the mouth, and from the back wall of the cabinet. The mic was not db calibrated at the time.








Edited by Jay michali - 08 February 2022 at 6:20am
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