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Has any fine folks on this thread had the chance to run impedence measurements on the skram? I thought about using the skhorn measurements as a close approximation if none were available but it would really help me for sizing up the right amplifier.

I am looking to run two Eminence NSW6021 (nominal 6 ohm) per amplifier and an considering two options:

1. operating a 2 channel amplifier in bridge mode with 2 drivers hung in parallel (net 3ohm). However, this would theoretically put a 1.5ohm load per channel (which is below the rated 2ohm minimum per channel) - that is unless the cabinet loading (acoustic impedance) raises the effective impedance to something more tolerable for the amplifier. 

2. Purchasing a 4 channel amplifier and also running it in (dual) bridge mode. Here I would hang one driver off each 'stereo bridged channel' and therefore only impose a 6 ohm load per bridged channel (ie: 3ohm spread across 4 channels which is more tolerable for the amplifier). +whatever cabinet effects may impart on the impedance the 'amplifier sees' 

First option is a bit more budget friendly so that would be my first pick. 

Amplifier is Wasi W15K or W15K4 respectively 

has any builder attempted to update the skram plans to factor in rebates for all the panels? I was watching a video of a boxman in the UK who was a strong advocate of this from a woodworking standpoint as you would create significantly more contact area between each panel resulting in much sturdier connections and a better build - at a price of course.

Just unsure if it's actually necessarily or just an overkill? As it'll be complicated (without having SolidWorks) to modify the existing cut sheets to factor in these additional dimensions. The guy recommended 3mm recesses which can definitely cause issues if not taken into account.

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?

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?