Ricci's Skram Subwoofer & Files

[Domme]

@Ricci I think the stacking problem of your initial post has not been solved yet and I was just searching for corner protection and stumbled upon those

https://www.thomann.de/de/adam_hall_4071_cabinet_corner_plastic.htm

Me and my slight OCD find them much more elegant than trying to make stacking edges because they look much less asymmetrical, but if you want to go for them it should work as long as two neighboring edges have negative patterns, even if you rotate them. Just take a look at this very professional diagram that I made to understand the principle of those corners because my brain somehow refuses to think in transformation matrices.



 I hope  it will work without math but I hereby declare that I won't take any responsibility for resulting damages 😂

[jngggggggg]

hey everyone, new to thread but have been silently following along and inching my way towards build 4 skrams for my system as well. the latest rabbit hole i've found myself stuck in is whether b&c 21sw152 in either 4ohm or 8ohm impedence would be best in my unique situation (power limitations). i was hoping all your fine folks could help me make a decision. much appreciated.

the near term plan is 4 skrams (2 amps on subs so one per channel) but that number will eventually grow to 6 skrams where i would likely run all 6 off the same 2 amps (2 in parallel on one channel and 1 single on the other channel). amp specs would be
2ohm  7530w
4ohm  5380w
8ohm  3160w

A few questions i have hoping to get some clarity on:
i had initially set my eyes on 21sw152-4ohm. if i plan to set RMS limit to 50% of continuous power handling (1000w), it appears that its generally easier to find amps that better power match the 21sw152 4ohm rather than the 8ohm version (i am targeting 6 to 9dB headroom before clip). based on the above, it seems like there aren't many (affordable) amps that can properly power the 8ohm drivers. to achieve similar SPL between 4 or 8ohm during operation, would it simply come down to adjusting the amplifier's line sensitivity (higher for the 8ohm) to compensate for the higher load? ie: 63vrms into 4ohm vs 89vrms into 8ohm - both yielding 1000w). spec sheet's sensitivity between the two versions appears to indicate so.

conversely, although 8ohm offers higher damping factor, there is supposed to be another benefit of allowing a given amp to power more skrams down the road if the system grows (ie: hang more higher impedence drivers in parallel etc). HOWEVER, is this really the case:
1. if the amplifier of choice doesn't have enough power to properly drive anymore than 2 skrams per channel anyway.
2. if 99% of venues have limited ac power supply (120v 15a service only but with multiple independent receptacles). 

i found some of the responses to Domme's question regarding the Eminence NSW operating at 6ohm driver quite helpful and somewhat relatable but am wondering if the recommendation changes given the power supply constraint?  damping factor sounds like a serious consideration but given how difficult (read expensive) it is to power these 21sw152s at 8ohm, i suspect 4ohm may make more sense for my application?

[SME]

On 2/26/2022 at 9:14 PM, jngggggggg said:

[...]

damping factor sounds like a serious consideration but given how difficult (read expensive) it is to power these 21sw152s at 8ohm, i suspect 4ohm may make more sense for my application?

Don't worry about damping factor, but do keep in mind that many amps are not designed to power subs unless they are used in their bridged mode, in which the amps for two channels work together to power the load.  The bridged mode typically doubles the impedance requirement, so an amp rated into 4 ohm loads will typically require an 8 ohm load when bridged.  You could use this to power a single 8 ohm sub (with a lot of power and one amp per sub), or you could connect pairs of 4 ohm subs in series and run each pair off a bridged amp.

[Ricci]

As far as damping factor goes...This really only becomes an issue under extreme circumstances with low impedances and long cable runs. Use heavy gauge wire and avoid long runs from the amp when possible. This also avoids voltage losses as much as possible. Bridging amps for subs is also good advice. 

Typically in a sub system there will be multiple drivers in multiple cabs. This opens up many wiring possibilities and different impedances. In some cases the 8 ohm driver might be a better fit than the 4ohm or vice versa. The 4 ohm 21SW152 is a bit more efficient than the 8 ohm, but otherwise they perform similarly. Which makes more sense depends on how many drivers you plan to use and your amplification. 

[Ricci]

Also does anyone around here have a Skram or 2 they would be willing to sell me, or build me? 

[peniku8]

15 hours ago, SME said:

Don't worry about damping factor, but do keep in mind that many amps are not designed to power subs unless they are used in their bridged mode, in which the amps for two channels work together to power the load.  The bridged mode typically doubles the impedance requirement, so an amp rated into 4 ohm loads will typically require an 8 ohm load when bridged.  You could use this to power a single 8 ohm sub (with a lot of power and one amp per sub), or you could connect pairs of 4 ohm subs in series and run each pair off a bridged amp.

From what I gathered, this can be an issue which is relatively easy to avoid.

It mostly only becomes an issue when you load channels asymmetrically, i.e. subs on one and tops on the other. In this case you amp might power cycle at worst (I suppose no proper amp will die from that). To improve stability, just run channel pairs that can be bridged with the same signals.
To further enhance stability and/or amp performance, reverse the phase on one channel input and reverse the wiring on its output. This won't affect the subs, since it's a double polarity swap coming back full circle, but the amp will run a mirrored config internally, which is actually what most modern amps do already. An amp that bridges from 1+ to 2- should be running this config. Brian from Speakerpower posted about this on AVS some time ago, when he was still working there.

Despite this advice, I've been running my system on TopL(A) SubL(B) TopR(C) SubR(D), since my amp's 4pin speakons are wired for A+B and C+D, so I'd have to use a breakout cable to change this, which isn't very convenient. I would, if I had issues, but never did, so I just left it at that. Been pushing 4R 21ds115's quite heavily with no issues.

Oh and just to throw it out there, there is a 16R variant of the 21sw152. It's probably 50MOQ and only directly from B&C, but hey, it exists, just like the 2R IPAL

[SME]

6 hours ago, peniku8 said:

From what I gathered, this can be an issue which is relatively easy to avoid.

It mostly only becomes an issue when you load channels asymmetrically, i.e. subs on one and tops on the other. In this case you amp might power cycle at worst (I suppose no proper amp will die from that). To improve stability, just run channel pairs that can be bridged with the same signals.
To further enhance stability and/or amp performance, reverse the phase on one channel input and reverse the wiring on its output. This won't affect the subs, since it's a double polarity swap coming back full circle, but the amp will run a mirrored config internally, which is actually what most modern amps do already. An amp that bridges from 1+ to 2- should be running this config. Brian from Speakerpower posted about this on AVS some time ago, when he was still working there.

The way I read this, your described workaround is functionally the same as just engaging "bridge mode" in the first place.  This makes perfect sense, especially if the loads on each channel share a common ground.  Which is to say that one should just enable bridge mode anyway because it's easier.

But this does not necessarily allow for *asymmetric* loads across multiple channels, which is basically the point of having multiple channels in the first place.  Asymmetric loading between different subs can be useful in some situations, but not all amps can reliably do this if subs are involved.

And I would say the "worst case scenario" isn't having the amp shut down.  The "worst case scenario" is designing with an amp that is not adequate.  OP is wise to carefully choose the impedance to match the intended driver and amp configuration.  And as noted by others above, damping factor is not a problem with proper matched wiring.

[peniku8]

15 hours ago, SME said:

The way I read this, your described workaround is functionally the same as just engaging "bridge mode" in the first place.  This makes perfect sense, especially if the loads on each channel share a common ground.  Which is to say that one should just enable bridge mode anyway because it's easier.

But this does not necessarily allow for *asymmetric* loads across multiple channels, which is basically the point of having multiple channels in the first place.  Asymmetric loading between different subs can be useful in some situations, but not all amps can reliably do this if subs are involved.

And I would say the "worst case scenario" isn't having the amp shut down.  The "worst case scenario" is designing with an amp that is not adequate.  OP is wise to carefully choose the impedance to match the intended driver and amp configuration.  And as noted by others above, damping factor is not a problem with proper matched wiring.

No, with my workaround you still have two independent channels, but internally it will appear as if they are bridged. You leave channel A alone and swap polarity of both the input and the output signal on channel B. You use both channels separately. If you now tied A+ and B+ together, your amp is running bridged, but instead you connect your channels to separate subs. B+ connects to Sub- to have all speakers running in phase.

Since some amps (like lab gruppen and I suppose most other tour grade amps as well) already do this internally, B- will actually be carrying the hot signal and B+ is ground. This is because the wiring has been reversed internally to change back the polarity to normal (0°). If you feed both channels the same signal, you should be able to run it bridged via A+ and B- without engaging the 'bridge' switch.

Some people call this running your amp 'half-bridged', but I don't think that's an appropriate description. It's just using one of the steps, you need to do to bridge your amp, for something else, so it's like saying the workbench you built is half-subwoofer, just because you built it out of plywood.

[klipsch]

On 3/1/2022 at 10:09 AM, Ricci said:

Also does anyone around here have a Skram or 2 they would be willing to sell me, or build me? 

If/when BB comes down in price, I would like to help. 

[jngggggggg]

On 3/1/2022 at 2:52 AM, SME said:

Don't worry about damping factor, but do keep in mind that many amps are not designed to power subs unless they are used in their bridged mode, in which the amps for two channels work together to power the load.  The bridged mode typically doubles the impedance requirement, so an amp rated into 4 ohm loads will typically require an 8 ohm load when bridged.  You could use this to power a single 8 ohm sub (with a lot of power and one amp per sub), or you could connect pairs of 4 ohm subs in series and run each pair off a bridged amp.

in my sound reinforcement handbook, it claims that series connections 'tend to have more interaction between functioning loudspeaker which can cause distortion'. it also goes on to say how damping factor is 'severely degraded in series connections which may have an adverse effect on low frequency reproduction'. i am by FARRR an expert on amps and am unsure how series connections impact damping factor in a mathematic sense as i have reviewed the previously posted literature, but it seems to make sense intuitively. to me anyway....

for example - if the voltage drop of the amplifier is shared (which is the case when 2 speakers are wired in series) and the amp is driven to the point that voltage begins to sag and amp begins to behave non-linearly?

[SME]

On 3/5/2022 at 6:19 PM, jngggggggg said:

in my sound reinforcement handbook, it claims that series connections 'tend to have more interaction between functioning loudspeaker which can cause distortion'. it also goes on to say how damping factor is 'severely degraded in series connections which may have an adverse effect on low frequency reproduction'. i am by FARRR an expert on amps and am unsure how series connections impact damping factor in a mathematic sense as i have reviewed the previously posted literature, but it seems to make sense intuitively. to me anyway....

for example - if the voltage drop of the amplifier is shared (which is the case when 2 speakers are wired in series) and the amp is driven to the point that voltage begins to sag and amp begins to behave non-linearly?

Drivers in series have higher impedance, which means that yes, they share voltage drop.  And an amp in bridge mode typically grants 2X the voltage compared to each single channel alone, so it all balances out.

Damping factor is kind of an anachronistic term from when amps (made of tubes) had non-negligible output impedance, so damping factor was high enough to significantly alter the bass response in ways that varied depending on pairing of driver and amp.  I don't know if I'd call this "distortion" though, in that in audio distortion usually implies non-linear distortion whereas increased "damping factor" looks a lot like a shift in T/S parameters.  It's likely something that can be completely corrected with EQ (except for the lost power, of course).

The other thing is that more than 2 drivers in series may behave sub-optimally if they are different or if their specs are not very similar.  However, I don't think I've heard of this being a problem in practice.

[peniku8]

7 hours ago, SME said:

Damping factor is kind of an anachronistic term from when amps (made of tubes) had non-negligible output impedance, so damping factor was high enough to significantly alter the bass response in ways that varied depending on pairing of driver and amp.  I don't know if I'd call this "distortion" though, in that in audio distortion usually implies non-linear distortion whereas increased "damping factor" looks a lot like a shift in T/S parameters.  It's likely something that can be completely corrected with EQ (except for the lost power, of course).

I think we'll have to differentiate between three effects of damping factor.

-power loss (negligible for sound quality if you don't clip your amps)
-response shift (neglegible if you use EQ to compensate imo, which is also the point you addressed)
-lack in physical driver damping

The last point apparently only becomes an issue once the damping factor gets really bad, like single digits, but from what I understand, shorting rings in your drivers achieve that on their own already, so it might not be much of an issue at all anymore. Would be interesting if someone with more knowledge on this could chime in, maybe I'll send Bennett a mail.

[zolthoff]

On 3/1/2022 at 9:09 AM, Ricci said:

Also does anyone around here have a Skram or 2 they would be willing to sell me, or build me? 

I have one in Iowa that I built that I'm not currently using (in favor of like 15 12"s), but I know that's like 8 hours away unless you wanted to try to make something work.  

[rolo95]

I just found this thread and get hooked in to it! , i have a couple of questions tough, 

is it possible to modify a little to fit 2 12" drivers or 4 8"? , take my questions

with a grain of salt or 2 i dont have any sub design knowledge

budget 18" drivers like the 18TBX100 possible ?

does anybody  had tested the clones like Sanway, sinbosen and CVR 

https://www.ebay.com/itm/275253000470?epid=12031073806&hash=item40165b7916:g:MHcAAOSwrY5iS0mr

Best.

Rolo.

[rolo95]

On 11/13/2021 at 12:51 PM, jay michael said:

Have a bit of an interesting field use report for my Skrams. I recently added new processing to my system using an XTA DPA 100. It’s a pretty interesting 4 channel amp, which I am using to bi-amp my Danley sh46 cabs. It also featured 4 channels of output control to add processing to my slave sub amplifiers. I used the information within this XTA/MC2 document on limiters to set up protection on my sub amps. 
 

https://audiocore.wpengine.com/wp-content/uploads/2018/05/XTA-Application-Note-DPA-Amps-Limiter-Settings.doc.pdf

using the chart within this document it says to set up the 21sw152 at 86.9 volts for limiting, minus 1db for safety margin. Having always been a little hesitant on knowing just how hard I can safely drive my Skrams I added a 2 wire thermocoupler temperature sensing system to 1 of the cabinets to monitor magnet temperature. 1 wire is mounted on the external circumference of the magnet, the other right next to the vent on the end of the magnet body. 
 

last night I provided sound for a local dubstep crew, 7 hours of continuous deep sine wave bass. Peak volume was held for about the 3 final hours of the night, at maximum I was running about 2db down from where limiting would engage.  Monitoring throughout the night, magnet temperature peaked at 44 degrees Celsius. This was also in a packed sweaty room that was raining condensation from the roof. 
 

pretty interesting to get some real Information about what the drivers are doing deep within the skram cabinets under real world conditions. I had previously come across a statement from Bennet Prescott who works with B&C saying that the 21sw152 can sustain 100 degrees magnet temperature without thermally damaging the coil. Previously I had been limiting these drivers to around 50 volts, it seems that in the Skram alignment we should be able to safely push them beyond that a bit without getting too much temperature build up. This of course may change for other types of music, I will continue to report back when I can speak to temps I’m seeing when doing other types of music shows. Data is beautiful. 
 

Always a pleasure getting to flex these cabinets, in a town where double 18’s rule,  the Skrams are raisins eyebrows and making lots of new fans. 

Thanks for sharing , that XTA pdf is pure gold!! never seen that detailed setup instructions for limiters, and btw, prices for drivers now are trough the roof, i wish have seen this thread in 2019

[jay michael]

16 hours ago, rolo95 said:

I just found this thread and get hooked in to it! , i have a couple of questions tough, 

is it possible to modify a little to fit 2 12" drivers or 4 8"? , take my questions

with a grain of salt or 2 i dont have any sub design knowledge

budget 18" drivers like the 18TBX100 possible ?

does anybody  had tested the clones like Sanway, sinbosen and CVR 

https://www.ebay.com/itm/275253000470?epid=12031073806&hash=item40165b7916:g:MHcAAOSwrY5iS0mr

Best.

Rolo.

I cant speak for the 18tbx100 option but I have some thoughts on the amplifiers you listed. I have powered my Skrams using the CVR's, a Powersoft K10, an Admark k420 and Wasi w15k's. All of these amps work great and will give similar results. I would rate the CVR, K10 and Wasi so close in performance I doubt you could tell the difference between them in a blind test. Some people have stated that they think the Admark may have a slight advantage over the cvr on tone but I haven't experienced any evidence to support this, but I have only played around with their 4 channel models vs their 2 channel models. I don't think you can go wrong with any of those options.

[jay michael]

33 minutes ago, rolo95 said:

Thanks for sharing , that XTA pdf is pure gold!! never seen that detailed setup instructions for limiters, and btw, prices for drivers now are trough the roof, i wish have seen this thread in 2019

No problem, I agree that article really simplified things on my end. Following the recommendations within, I have a bunch of shows under the bridge at this point and between monitoring magnet temps or getting hands on drivers in my paraflex cabinets I feel confident my drivers are well protected and performing excellent at powers higher than I would have run them using many of the "rules of thumb" I had gathered in other resources. On that note, I am super happy with my XTA DPA100 amplifier. Its a bit spendy but considering the onboard dsp with 4 channels of dsp outputs for controlling of "slave amplifiers" I really think XTA hit a home run with these units. Great sound quality and easy to use software, lots of power onboard, highly recommended. I've done some smaller shows running my big Danley's plus 4 subs run entirely off the single Dpa100 on a single 15amp circuit with no problems. Nice and efficient power.

[Ricci]

19 hours ago, rolo95 said:

I just found this thread and get hooked in to it! , i have a couple of questions tough, 

is it possible to modify a little to fit 2 12" drivers or 4 8"? , take my questions

with a grain of salt or 2 i dont have any sub design knowledge

budget 18" drivers like the 18TBX100 possible ?

Best.

Rolo.

It's not impossible but I've not run across any 8", 10" 12" or more affordable 18's that make sense for this cabinet. 

This sub is natively tuned much lower than most. When you tune low you lose efficiency. It also requires much more displacement to produce the same output at lower frequencies. This is basic HIL in operation. 

This cab requires 3 things from the driver/s to perform the way I intended when I designed it. 

High efficiency

High power handling

Large displacement (Xmax x surface area)

It is very rare to find all 3 of these things in one driver. Even with unlimited budget.

The smaller 8 to 12" driver sizes can meet one or maybe 2 of these but not all 3. Generally you'll get really high displacement with abysmal efficiency and bad inductance issues, or high efficiency with very little displacement potential. Especially compared to the huge cone area of a 21. 

The 18's give up a lot of displacement to the 21's this cab was designed for. 

The lowest cost driver I can recommend for this cab is the Lavoce SAN214.50. It's a shame that prices are up so much. I remember when this driver could be had for about $475. 

If you are really on a budget and looking to try something the Dayton Audio PSS555-8 may be worth a shot. It'll give up some output and power handling to the SAN214.50 but it's $310

 

[peniku8]

iirc the LaVoces were in a parts express deal for 400 flat or something, 3 years ago.

I paid 410$ for my 21DS115's. Now they're around 650. That's up over 50%...

Imo it makes no sense to build the Skrams if you intend on putting non ideal drivers in it. A good subwoofer is a good subwoofer, but that's the entire system of driver+cabinet. Even if the cabinet design is stellar, it'll make a bad subwoofer if you don't put the right driver in it. That's also how DIY got a bad name over here. And just outright bad designs of course.
Build something else if you wanna use other drivers or design a simple vented cab if you have a specific driver in mind. Designing a vented cab with a slot port is really simple.

[rolo95]

On 4/13/2022 at 9:28 AM, jay michael said:

I cant speak for the 18tbx100 option but I have some thoughts on the amplifiers you listed. I have powered my Skrams using the CVR's, a Powersoft K10, an Admark k420 and Wasi w15k's. All of these amps work great and will give similar results. I would rate the CVR, K10 and Wasi so close in performance I doubt you could tell the difference between them in a blind test. Some people have stated that they think the Admark may have a slight advantage over the cvr on tone but I haven't experienced any evidence to support this, but I have only played around with their 4 channel models vs their 2 channel models. I don't think you can go wrong with any of those options.

Hey Jay,

thanks for the reply

do you have any experience with Sanway ?

and.. AYyyyy https://reverb.com/item/19924547-xta-dpa-100-dual-amplifier-with-xta-processing

those are not in my league for now, what would be a decent limiter, i have an old Driverack PA, not the PA2, not the 260, people say that the Ashly digital have a nice limiter, but they are around 999,

i was looking maybe at a MINIDSP, no matter that you need a PC to tweak it, once is set is set it and forget it

[rolo95]

On 4/13/2022 at 12:31 PM, Ricci said:

I

The lowest cost driver I can recommend for this cab is the Lavoce SAN214.50. It's a shame that prices are up so much. I remember when this driver could be had for about $475. 

If you are really on a budget and looking to try something the Dayton Audio PSS555-8 may be worth a shot. It'll give up some output and power handling to the SAN214.50 but it's $310

 

https://www.parts-express.com/LaVoce-SAN214.50-21-Neodymium-Subwoofer-8-Ohm-293-732

667 as of now to be exact, if if go with the LaVoce, what would be my  limiter settings, i saw a guy who put a 60hz signal in to it and with an RMS fluke AC meter , he adjusted until the voltage was what he want, then adjusted the limiter so no matter how much you raised the fader on the mixer mains, you never go above  whatever voltage you agree with.

[rolo95]

20 hours ago, peniku8 said:

iirc the LaVoces were in a parts express deal for 400 flat or something, 3 years ago.

I paid 410$ for my 21DS115's. Now they're around 650. That's up over 50%...

Imo it makes no sense to build the Skrams if you intend on putting non ideal drivers in it. A good subwoofer is a good subwoofer, but that's the entire system of driver+cabinet. Even if the cabinet design is stellar, it'll make a bad subwoofer if you don't put the right driver in it. That's also how DIY got a bad name over here. And just outright bad designs of course.
Build something else if you wanna use other drivers or design a simple vented cab if you have a specific driver in mind. Designing a vented cab with a slot port is really simple.

I guess, no wonder a danley TH118 are so expensive not to say we are paying the R&D but the 850USD drivers

Speaking of vented cabs, i was looking that the QSC driver in the 

• SP218
• SB7218
• WL218
• GP118W
• GP218SW

subs sells for 144

https://www.fullcompass.com/prod/594076-qsc-xd-000110-02-18-woofer-for-sp218-sb7218-wl218-gp118w-gp218sw

just to get the measurments of one of those boxes and make some   

 

[jay michael]

2 hours ago, rolo95 said:

Hey Jay,

thanks for the reply

do you have any experience with Sanway ?

and.. AYyyyy https://reverb.com/item/19924547-xta-dpa-100-dual-amplifier-with-xta-processing

those are not in my league for now, what would be a decent limiter, i have an old Driverack PA, not the PA2, not the 260, people say that the Ashly digital have a nice limiter, but they are around 999,

i was looking maybe at a MINIDSP, no matter that you need a PC to tweak it, once is set is set it and forget it

Sorry no experience with the Sanway stuff but there is a lot of info out there regarding their offerings. Those prices on reverb are pretty crazy, real world pricing from a rep should be about 50-60% of those listed prices.

 

[rolo95]

no worries man, 

my current lineup is 1 PLX 3002, 1 XLS 2500 and 1 XLS 2000 , on a dbx driverack pa ( the old one )

i read that even the behringer 2496 is better in the limiters than the dbx pa, what about the miniDSP

i have 4 b52  EV l36 clones that i need to get rid off, i got that from a guy who do not want to DJ anymore

and i get that around 2013, i did not know anything at the time, then start reading the DIY forums

and now i know that the dbx pa suck and the b52 subs suck more., lol. so i need to get something else

btw, the tops were some 80's jbl MR925's  4 of them, they are heavy as F... so i want to change that also

anyway... i need to start from somewhere , cant get rid of all and left without any workable rig

if i had the dough , i think i will get SH50's for tops and tell somebody to build 8 skrams 4 me

with Lab gruppen , for now CVR amplification lol when i swap the old amps

[jay michael]

While the limiters are basic on the dbx units I think they are enough to get by. I ran a Pa2 for probably close to 7 or 8 years and never burnt up any drivers. The venu360 is a big step up in functionality and sound quality but at that price there should be lots of good options out there. Personally I think if you are running your system into limit hard enough to think your limiter isn't up to the job the problem isn't your limiter, its that you don't have enough system for the job. I haven't needed to run my Skram's or my Danley's into limiting yet, if the day comes that it is required ill just start cutting up more wood