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Ricci's Skhorn Subwoofer & Files

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https://www.facebook.com/groups/733449990043427/?ref=group_header

This is an awesome group on Facebook and I've been posting there for a while. Some of my measurements can be found over there and many other discussions mostly for pro audio.

You can find manufacturers there , like Brandon Heinz (from Renkus Heinz) Dave Millard, representative from full far audio, Sean Hennessey and some others.

Please, feel free to join!

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23 hours ago, radulescu_paul_mircea said:

@Ricci yes I am using ABEC 3 but barely. It is way to complicated for now and I don't pretend I am getting any easy progress. I have an Akabak script on my older laptop (it doesn't run on Windows 10)  that I could copy and post or send to PM. It is not very detailed but with the additions I managed to get a higher Directivity and a closer response.

  

Don't worry I'm in much the same boat. I've been avoiding using it for a long time. 

I'd love to see a few of the measurements. 

I also needed this handy directivity calculator in my toolbox. I've done some checking and it matches up very well with my measurements. What I've found is that even relatively small baffles like 20x20" have effects down to 40-50Hz and lower. There isn't a whole lot of change from there until the baffle size gets truly large. I believe the enclosure used for the SI 24" testing and the DTS-10 were the biggest frontal areas I've had. If I recall they were providing 1dB of lift way down at 30Hz if not a bit lower. 

I've subtracted out the directivity lift for the Skhorn calculated by Edge and the results are pretty close. I'm working on tweaking the sim a bit closer in HR based on this. The main thing I'm seeing is there is still a moderate 1-2dB lift in the 50-80Hz region that I cannot seem to get in HR. I'll post a revised HR input when I'm done. 

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I'm glad that I could be of great help here! :)

Playing around with Edge, you'll find that you get more baffle gain if the source is located more towards the middle than the edges of the baffle (or more towards the middle and then the floor for a sub, because of the "mirrored sub below the floor" in a half space scenario).

I've been fiddling around with hornresp to come up with a cab that is smaller than the 21ipal loaded Skhorn (which is rather huge unless you're a rental company with big trucks and a range of smaller subs than the Skhorn for the times where it's size and power will be too much), that has more frontal area relative to the depth of the cab and the source located at the bottom of the cab (to be able to get more baffle gain both in singles and in multiples), that extends as deep as the Skhorn(for comparisons and good extensions sake), that is easier to build, is cheaper to build(the 21IPAL sure is pricey), that is preferably as powerful(because power), and that rolls off above 100-120hz(to roll off distortion).

I've kept the 6th order concept. It really is a power dense and good sounding design if done right. I've split the cab in half, ie, one 21" per cab, and therefore and for the prices sake I've gone with the 21sw152-4 instead. That is one great driver in price/performance, performance/weight ratios, in (Bl2/Re)/(Le/Re), and it's also 4ohm so they can be run in singles, and wired in parallel with two per amp channel if needed. For comparisons sake I've kept the volume per driver identical.
I've straightened out the 'horn' part of the Skhorn, because I often find in my simulations that keeping ducts straight is more space efficient than flaring them. They're also easier to build.

So, what I've come up with is a regular bandpass cab with a great driver lol. Pretty simple really, but with complex reasoning behind, as usual with us nerds.

Hornresp inputs: (I simply selected quarter space instead of selecting 2 speakers all the time in the tools menu.)

5a8327af0e358_hrinputs.jpg.0f0f3adaeb1971bbfd04d77dfb99534d.jpg

The form factor of the cab I have in mind would be 24" deep, 25,5" wide and about 34" tall. Slot port at the bottom, driver vertically mounted pointing forward in the cab, the hf sections slot port would be just above the lf sections slot port. Two cabs next to each other simulated in Edge would look like this, my cabs in red and a Skhorn, laying vertically, simulated in blue:5a8324bf66710_Edgebaffles.thumb.jpg.323f80522dbd122b4e60ff71c9460797.jpg
Despite having the exact same total volume, my cabs have just shy of 1db more baffle gain down by 40hz, rising to just shy of 2db by 100hz.

In the sims I've tried to subtract the baffle gain from the hornresp response both with the cab design and the filters used. If you add the baffle gain back you'll get a flat response with a high pass at ~100hz. And oh yeah, unless I want to see the raw response to look for warning signs, I always simulate with the filters in effect and try to go for a flat response(if the baffle gain would have been added back) with only the filters in use. The cabs will always be used with filters anyways so it makes most sense to sim it like that, I think.

21ipal Skhorn in black, 2 of my cabs with the 21sw152-4 in grey. Both have 12db/oct hpf and 24db/oct lpf, set at different points to adapt to the different responses, excursion behaviors, and so on.

responses.jpg.ca8f87fe22d445131574935ef1794ffe.jpg

So, yeah, about the same difference as in the Edge simulation, but inverted. The two responses should match up very well with the baffle gain added.

Delay:

delays.jpg.f80167a724bbc5fb6efc2d3d2c95a256.jpg

Phase:

Phases.jpg.0722ee23c15c5200378602afe3d66854.jpg

Efficiency:

efficiencies.jpg.cf7a79a4a9c2fef8f017c4625fb45849.jpg

Excursion:

excursions.jpg.352797d5d928e541fcb181de2bbba4fd.jpg

All in check so far. By all accounts, everything so far is pretty much the same. Response, phase, delay and efficiency is pretty much exactly the same. The excursion differs, but they are both in check. What differs is the power per driver:
5a832b102c403_driverpowers.jpg.f490ce8f1ef274ba1feb59d6e9bc2111.jpg

The Skhorn seems to need about 40% more power to get the same job done. Now, in my book, that's a huge difference. Especially considering that the drivers in the Skhorn are about 75% more expensive and the Skhorn has to be brought in in one piece whereas half of my option can be left at home if one would want to. My design has no angled pieces, so it's a bit easier to build. It rolls off fast above 120hz to roll off distortion, as shown below:

5a832d90281fa_rawresponses.jpg.3b74ad22e34865784dfd7b824d6410cc.jpg

Now, could the 21ipal be used the same way and reap the same benefits as my cab loaded with the 21sw152? IMO, not practically so. One driver per cab loads the amp with too low of an impedance, so a pair is pretty much the only viable option. Would you like a double loaded cab that is 24" deep, 36" tall and 48" wide? I don't know. I wouldn't. I like to have a bit of scalability.

Areas where my design can't beat the Skhorn is the force cancelling mounting and how deep inside the cab the drivers are buried. I think less power needed, cheaper amps, more scalability, cheaper builds and easier builds outweighs the cons by a pretty good margin though.

 

Now, I don't mean to take a crap on Ricci's work. The importance of the work he/you have done can't be overstated. I just wish to contribute with my .02$ and to shed some light over this whole directivity deal, and show an example of how one can use it to one's advantage.

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That's a lot to respond to.

Couple of things I noticed.

You shouldn't use 1pi as an approximation for 2 cabs. It's better to cut the Skhorn in half or double the inputs for your single driver simulation. Also I noticed some of your inputs for the 21SW152-4 are off. Re should be 3.4. Also the original Skhorn sim isn't as close as it could be. The original inputs were as best I could guess at it feeding inputs from the cab design back into HR during the design phase, prior to building and measuring. I never went back and fit it better to the real result. I'm lazy!

I do have some preliminary target sims for my single driver, half size Skhorn cab, but I've not had time to get so far as to design the cab. The final cab design process takes about 100X longer than and always modifies the simple HR sims. That's why I haven't gotten it done yet. 

That looks like a lot larger boost than I would guess off of such a minor difference in frontal area. 

Hopefully I'll get time to look at some of it more in depth. 

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On 2/12/2018 at 5:23 PM, radulescu_paul_mircea said:

https://www.facebook.com/groups/733449990043427/?ref=group_header

This is an awesome group on Facebook and I've been posting there for a while. Some of my measurements can be found over there and many other discussions mostly for pro audio.

You can find manufacturers there , like Brandon Heinz (from Renkus Heinz) Dave Millard, representative from full far audio, Sean Hennessey and some others.

Please, feel free to join!

I've never been on social media. I need another time sink like a hole in the head. 

  • Haha 2

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Hopefully your single version takes advantage of being a single driver version and perhaps a slightly larger version also.

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10 hours ago, Ricci said:

You shouldn't use 1pi as an approximation for 2 cabs.

I know. The only thing that differs though is the impedance, which I knew would be in check and quite similar between the two designs, so I just saved myself some time instead. Half of the times that I want to go into the filter wizard or the multiple speaker tool I end up going into the other instead, which is mildly irritating at times, so I end up saving myself from some blood pressure rise too lol.

10 hours ago, Ricci said:

Also I noticed some of your inputs for the 21SW152-4 are off. Re should be 3.4.

True. I corrected that, increased the input by one volt and it was all identical again.

10 hours ago, Ricci said:

Also the original Skhorn sim isn't as close as it could be. The original inputs were as best I could guess at it feeding inputs from the cab design back into HR during the design phase, prior to building and measuring. I never went back and fit it better to the real result. I'm lazy!

The thing is though that I matched the volume of the two designs within half a liter of each other, so even if the Skhorn sim doesn't match real world to 100%, it should still be a very fair comparison in the simulations. Of course, correcting the sim will give and take a tad here and there in the response, shift the impedance somewhat, etc, but that 40% gap in power will still be there, although the peaks in the power demand will probably shift a little so that they will be a tad lower up top and higher down low, or vice versa.

10 hours ago, Ricci said:

That looks like a lot larger boost than I would guess off of such a minor difference in frontal area. 

It is. The contributor to that boost is not only the frontal area though, it's also where the source is located on the baffle, as I mentioned in the first section of my last post. Centering the source on the baffle or the stack gives you a good deal of extra baffle gain. Danley's BC218 is named like that because it's built around the baffle gain phenomenon - BC stands for 'boundary coupled'.


Again, I don't mean to be rude or anything, posting like this. I have an enormous amount of respect for what you've done and created here on data-bass. I simply wish to be of good use, and to exchange a thought or two:)

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11 hours ago, Ricci said:

I've never been on social media. I need another time sink like a hole in the head. 

Haha. Yeah, that group can be a time black hole. But lots of good stuff overall, even though like any other forum or group there is some background noise. 

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For anyone who wants to see the measurements for the directivity of 1,2 and 4 single 18" subwoofers in different configurations, on and off axys, you can access my Drive account and download the zip with REW measurements. Where there is a V, it means vertical possition

You would need to change the Impulse response windowing to Left Window Tukey 0.25 400 ms, Right Window Blackman-Harris 7- 150 ms and Ref. T is left in place for each sweep.

https://drive.google.com/open?id=15MmO5qj9v1RLZfO1_BYkUIAf6MDLi8M2

I hope it works.

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