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Ricci's Skhorn Subwoofer & Files

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Just completed the Skhorn and just want to say thanks to @Ricci 

Never had so much fun firing it up for the first time. Everything in the house shaking and my 10 year old saying his chest "feels weird" :)

Don't have much of a reference to compare to, only had two 15s before this. To say this is a giant leap forward, would be an understatement. 

Very impressed with the sound sonically, it's pounds, I have the volume at 50% with one bridged side of my inuke nu4. I had to back off or I start breaking my wifes stuff. Can't imagine how it performs with a great amp. 

Thanks again for making this available! 

 

 

 

 

 

IMG_20180806_210930.jpg

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Great. What drivers Are you using? Are you going to paint it? I see you have wires running out the port. Do you plan to add a speakon terminal?

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I have 21DS115 on it. went with 8ohms,  thinking my inuke would blow up with 2ohm loads. It's ugly now, but it will be painted and speakon-ed.. Just couldn't wait to fire it up. 

Wife is told it's only the left side, I need one for the right side. After her jaw dropped, she just said, OK sell your other speakers and you can build another sub. Wohooo :)

 

 

 

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It took awhile, made a couple of mistakes, a bit messy but mission accomplished. I'm very happy with the subs performance. Perfect Match for the SH50. Next one should go a lot faster and smoother. 

Thank you Josh

0_IMG_20180707_124750.jpg

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That room looks small.  Are you in an apartment?  And you're planning on building a second horn?  Wow!

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With people building their own versions of this design, I thought I'd chime in with a few points.

The long, flared front horn gives a lot of sensitivity above 100hz, where it isn't needed or wanted. That means that we've spent cab volume for no good. In my simulations I've seen that by using a shorter straight horn, I can keep the sensitivity below 90hz unchanged while greatly reducing the sensitivity above 90hz, reducing the volume of the design by 10%, simplifying the build by removing the angled cuts, further force cancel the drivers by placing them absolutely parallel, and at the same time reduce the weight of the build, in part because of the fewer parts needed, and in part because of the actual lower design volume. Simpler, smaller, lighter, more force cancelled - why not?

While we're at it with force cancelled drivers in a large front chamber... why not invert the mounting of one driver to further reduce the distortion? Free decreased distortion - why not?

Why not place all the ports in the center of the front baffle instead of along the edges? The increased boundary coupling that this gives would give us another 0,25db down by 30hz, rising to 1db by 100hz, given that the baffle sizes are the same. Free increased sound pressure - why not? 

The exit for the front part of the design would be as a slot in the center of the baffle, with the ports exiting as slots above and below the front part's slot.

These few changes would make the Skhorn smaller, lighter, easier to build, louder, and it would have less distortion. What's not to love? 

Here are the inputs that I'm using: (These are meant to imitate the Skhorn as closely as possible below 90hz)

1628971720_Skhornedit.jpg.e3346a72dcc10d49eb21977fea3912e7.jpg

Although, I'd prefer these inputs even more: (Flatter response, bigger port for less compression)1259763420_Skhornedit2.jpg.8dc22609249deb94f5798907f6dfb11d.jpg

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Awesome stuff Jesal. Sh50's I've heard a time or 2. That should be a great combo. 

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MOAR! 

Only 1 person has built a modified version which is Paul. He scaled it up. Mine is intentionally very dense. I think you'll find it is way easier to do a 5min sim in HR that "beats" something else. Once it comes time to design the finished product is where the rubber meets the road. There are reasons I didn't do many of the items you mention and I wouldn't make most of those changes if starting from scratch for various reasons, but I've already looked at all of this during multiple designs. At the end of the day there are a lot of considerations in cab design that have nothing to do with the acoustic sims. It would be interesting if you designed the cab and built it. 

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1 hour ago, Ricci said:

There are reasons I didn't do many of the items you mention and I wouldn't make most of those changes if starting from scratch for various reasons...

I am bringing some fair points to the table, but I'm happy to hear what points are more important than my mentioned ones when it comes to going with one solution over the other.

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My point was when you are satisfied that you have the best simulation for the goals, design the finished speaker. You may find that what seems good in theory isn't practical to implement when it comes time to fit everything in the box. 

 I considered everything mentioned during design and decided they weren't worth the effort, were impractical or overly complicated to fit in the cab dimensions, or came with other compromises that outweighed any potential benefit. In my opinion of course. With a clean slate and a different cabinet shape or dimensions who knows...Someone else may prioritize entirely differently. 

BTW I'm not saying these are bad ideas. They are worth considering. It is difficult to get everything you want into the final product sometimes. That old issue with compromises needing to be made. Etc...

 

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Ok, so I finally got some time to reply.

On 8/10/2018 at 5:53 AM, Ricci said:

You may find that what seems good in theory isn't practical to implement when it comes time to fit everything in the box. 

2021454751_databass.jpg2.jpg.bdb33a7da344af09b91a93932991cab5.jpg

Ok, so I drew out a quick sketch by hand. This would be the layout. I don't see how anything doesn't fit in there.

In the above drawing, I took the same design volume as in the Skhorn sims and drew it into the same final design volume that the actual Skhorn is. Now, the sim volume and the actual volume within the actual Skhorn differ by some 65l, according to your numbers (18.35ft3(519,6L)vs584,3L) but for comparisons sake I've done as I have.

I've also skipped the one inverted driver in the above drawing, for fear of getting a drink accidentally tossed into the front chamber, sploshing about around the driver motor. *shivers down my spine*

Here are the inputs of the design that I've drawn:

867380411_databass3.jpg.5c0e59d734ba5fdd77e73dba61802cc3.jpg

Try to put these inputs in HR, put a 27hz 3rd order low pass and a 70hz 3rd order high pass on it, and compare it to the regular Skhorn sims with a 25hz 4th order low pass and a 68hz 3rd order highpass on it, with a 197hz 3q -10db EQ on it to pull that peak down.
One will find that the two designs are incredibly close as far as phase, group delay, excursion and driver power goes. The inputs above has a slight output edge near 35hz in the sims, otherwise the response is identical. The efficiency shows that the design above doesn't emphasize output around and above 100hz as much, and that it emphasizes 25-40hz more instead. 
As far as the points above goes, would it be worth it to redo the whole design because of them? Hell no. 
Where it gets interesting is in the points below though:
It has less output above 100hz, so it rolls of the response where the bulk of the distortion is , it's an easier build (no angled cuts), it's better boundary coupled (0,25-1db more output forward and hence also less backwards), it's a bit more force cancelled, and it's got bigger ports for less compression and less vent noise (20% less port particle velocity).
All in all, it should make for a design that fits well within the size of the cab, is a bit louder, a bit cleaner, and a bit easier to build. All in all, I think it's a good idea for a slight development of a design that people clearly have a VERY good time with! 

Now, again, I don't mean to crap all over your work, Josh. I am an extremely analytical mind with a huge passion for both live sound and hi-fi, and to design the holy graal of bass designs has been the goal ever since I wasn't satisfied with the FLH subs that I built almost 15 years ago. The Skhorn is incredibly potent in many ways for good reasons, and, if it weren't, you wouldn't have designed and built it. I know that I've introduced Edge, the baffle gain sim program, into your set of tools, so it's not like I haven't brought something useful to this forum, and I know that my mind can do more good around here, among you other analytical, geeky and passionate minds. 

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On 8/7/2018 at 10:39 AM, Jesal said:

Wife is told it's only the left side, I need one for the right side. After her jaw dropped, she just said, OK sell your other speakers and you can build another sub. Wohooo :)

 

 

 

Well played:)

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On ‎8‎/‎14‎/‎2018 at 2:18 PM, Moar!! said:

Ok, so I finally got some time to reply.

2021454751_databass.jpg2.jpg.bdb33a7da344af09b91a93932991cab5.jpg

Ok, so I drew out a quick sketch by hand. This would be the layout. I don't see how anything doesn't fit in there.

In the above drawing, I took the same design volume as in the Skhorn sims and drew it into the same final design volume that the actual Skhorn is. Now, the sim volume and the actual volume within the actual Skhorn differ by some 65l, according to your numbers (18.35ft3(519,6L)vs584,3L) but for comparisons sake I've done as I have.

I've also skipped the one inverted driver in the above drawing, for fear of getting a drink accidentally tossed into the front chamber, sploshing about around the driver motor. *shivers down my spine*

Here are the inputs of the design that I've drawn:

867380411_databass3.jpg.5c0e59d734ba5fdd77e73dba61802cc3.jpg

Try to put these inputs in HR, put a 27hz 3rd order low pass and a 70hz 3rd order high pass on it, and compare it to the regular Skhorn sims with a 25hz 4th order low pass and a 68hz 3rd order highpass on it, with a 197hz 3q -10db EQ on it to pull that peak down.
One will find that the two designs are incredibly close as far as phase, group delay, excursion and driver power goes. The inputs above has a slight output edge near 35hz in the sims, otherwise the response is identical. The efficiency shows that the design above doesn't emphasize output around and above 100hz as much, and that it emphasizes 25-40hz more instead. 
As far as the points above goes, would it be worth it to redo the whole design because of them? Hell no. 
Where it gets interesting is in the points below though:
It has less output above 100hz, so it rolls of the response where the bulk of the distortion is , it's an easier build (no angled cuts), it's better boundary coupled (0,25-1db more output forward and hence also less backwards), it's a bit more force cancelled, and it's got bigger ports for less compression and less vent noise (20% less port particle velocity).
All in all, it should make for a design that fits well within the size of the cab, is a bit louder, a bit cleaner, and a bit easier to build. All in all, I think it's a good idea for a slight development of a design that people clearly have a VERY good time with! 

I looked at the sim and it is quite close below 80Hz.

This one should have less efficiency and less output above 40Hz on paper. It should have a bit more output near tuning. I'd say the original sims as being the slightly bit louder cab overall for music apps or live sound (kick drum, percussion fundamentals, most of the content being above 40Hz etc.).

I've found over the years I like smoother responding wider bandwidth systems vs systems optimized for more sensitivity over a narrower band of operation. This is part of the reason I decided not to do a straight slot. I wanted extra upper bass output and extension well beyond 100Hz as part of the design goal. Often times you'll see guys using subs for 30-70Hz and another set of kick bins for 70-140Hz or whatever. Usually due to sub bins with degraded upper range behavior or just not enough output. I'm not a fan of that approach. I'd much rather have one cab that can handle everything. I think the sim you proposed would be fine. I tried to get the top end as extended as possible on this one.

Another reason I didn't choose a large straight slot was to more fully enclose the drivers inside the cab. Most of the time I notice non harmonic mechanical and operational noises before HD gets to be offensive. The acoustic roll off of the slot above 100Hz should help lower HD a bit, but with the driver cone edge only 10" from the end of a large slot with line of sight to the outside world I'd expect there to be more operational noise leakage, though HR doesn't show too much of a difference. I'd like to see that tested actually. Also the drivers would be a little more susceptible to rain or a drink spill, but either arrangement is safer than a direct radiator cab!

I didn't go with a push pull driver arrangement due to the minimum clearances needed for the drivers  (10.5" driver depth + a large dustcap and +40mm excursion worst case scenario minus some for the baffle thicknesses and depth to the dustcap below the frame plane) and the fact that most high excursion sub drivers make quite a racket from the motor and suspension when pushed hard. Even more of a reason was the uneven loading it would present on the drivers. It would be much more involved and difficult to design the cab to evenly load the drivers with one inverted. Not impossible but it would complicate things. I'd give a rough guess that there would be about a 25-30L difference in the vented air volumes seen by the drivers. Tuning would be slightly different unless compensated for and the throat area would be a concern. I know this has been done in plenty of cabs before but I don't know if I trust it with the kinds of pressures that can be developed inside something like these. I didn't think the potential lowered even order distortion outweighed the concerns with uneven loading and possible mechanical noise from the inverted driver motor. The forces inside these can be pretty ridiculous.

The force cancelling works really well on it. It's not like the drivers are 90deg rotated from each other or even 45deg. It's only a 12deg offset and it's a 250+ lb sub. In use the cab has  no perceptible rocking from the driver operation. That small amount of offset from exact opposition plus the sheer size and mass just doesn't add up to any real rocking forces fore and aft. Technically I'd guess a perfect driver opposition would measure a bit lower with an accelerometer but in practice it worked like expected and it's a complete non issue. Regular old panel vibration and bracing is a much bigger concern. The Skhorn has been quite good as far as that is concerned when compared with most other large cabs, but this is always a battle on big subs with tons of output.

About Edge and directivity. Keep in mind that the math is simplified and goes back to the point source mic placement method. If the radiating points are spread on one sub and focused on another you can never truly get the same mic distance from the two. In practice there is a very large area that one is trying to cover usually inside of a room with boundaries. It's complicated. One sub is more diffuse but that's not necessarily always a bad thing. Edge is a good tool but I don't get too caught up in an apparent half dB advantage here or there. Most of that directivity happens above 80Hz unless the baffle area starts getting truly large.

One way I like to think about this is with 2 different philosophies. The first would be maximize the baffle area for the cabinet (think DTS-10 shape or similar) and get as much out in front of the cab with the drivers and design as possible. However at what point does this become impractical? Let's say the cab has a 60x60" baffle and is very shallow and gets some extra forward gain over a very similar design with the same driver which has a baffle of  30x30" but is much deeper. At some point you run into limitations in available depth to use and/or available baffle area. How many 60x60" baffle cabs are going to be able to be arranged? In a lot of cases not too many and eventually you just need more cabs and drivers. You could fit 4 of the 30x30 subs into the same baffle area as the 60x60 that would outperform it. The best case as far as potential output density per baffle area goes is that one entire face of the sub is radiating surface area. That's not going to be the best for directivity control though. You also end up with deeper cabs to get your cab volume. Tradeoffs.

Vent area is vent area I'll give you that as an advantage for sure. This is the #1 priority I would have when redesigning the Skhorn. Mostly to work better with the lowered tunings. I try to avoid turns in vents when possible though. The reduced area of the slot for the drivers would increase air velocity over the horn expansion type though. I have some new thoughts on designing vented subs that I haven't gone to far with yet but I'll share once I think it through a bit more.

Anyway that's part of the thinking behind not doing the straight slot or push pull drivers originally. It all comes down to tradeoffs and design choices. None of it is black and white it's all grey area and what makes sense for each case.

 

563442871_SkhornComp.png.365eb2c789449d477255ef1628049ab0.png

 

1464173626_SkhornCompefficiency.png.741693dce952be8344b50be29dcaf557.png

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7 hours ago, Ricci said:

[...]

I've found over the years I like smoother responding wider bandwidth systems vs systems optimized for more sensitivity over a narrower band of operation. This is part of the reason I decided not to do a straight slot. I wanted extra upper bass output and extension well beyond 100Hz as part of the design goal. Often times you'll see guys using subs for 30-70Hz and another set of kick bins for 70-140Hz or whatever. Usually due to sub bins with degraded upper range behavior or just not enough output. I'm not a fan of that approach. I'd much rather have one cab that can handle everything. I think the sim you proposed would be fine. I tried to get the top end as extended as possible on this one.

[...]

Thanks for this post!  It is excellent and gets to the heart of matter.  It's not necessarily that the sims are wrong but rather that they don't tell the whole story and miss important parts.

I especially concur with the quoted passage and agree that smooth operation over a wide bandwidth is a good idea.  Subs make plenty of sound above the XO point, and that sound can have a surprisingly big impact on overall quality.  Problems there can make distortion sound a lot worse.  For example, even fairly high harmonic distortion may go unnoticed by listeners if it is fairly uniform vs. frequency, but if certain notes have spikes in harmonic distortion due to horn resonances and whatnot, you'll get notes that tend to stand out, which is a lot more likely to be audible.

More generally, I think people worry may too much about the sub range to the detriment of the higher bass frequencies.  Bass isn't something that only happens below 80 Hz.  Indeed, a lot of the sound of bass instruments including synths is in the low hundreds of Hz, and sound up to at least 4-500 Hz contributes to tactile sensation.  Hot subs sound much better when the rise in response is spread out across the mid/upper-bass and low-mid range.  Having augmented output capability up to something like 150 Hz rather than merely 80-100 Hz is probably nice to have in many situations.

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The specs on that Lavoce do look good. Mentions Klippel derived parameters, gap and coil dims look solid and a shorting ring in the motor. Price is lower than most other pro 21's with similar specs. I've never used a Lavoce product. 

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I’ve to and fro’ for the last few days , am caught in between Othorn & the Skhorn  , and what would be the next best driver, if we put 21Ipal aside ? I think I should start with the Sk cause as it is I have 8*21” ported Br of my own design that hit 28hz , I’l Find some pictures and upload them . 

And Thanks Ricci for the hard work 

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10 minutes ago, Father Francis said:

I’ve to and fro’ for the last few days , am caught in between Othorn & the Skhorn  , and what would be the next best driver, if we put 21Ipal aside ? I think I should start with the Sk cause as it is I have 8*21” ported Br of my own design that hit 28hz , I’l Find some pictures and upload them . 

And Thanks Ricci for the hard work 

Me thinks you’ll fit in just fine here.  Welcome.

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Quote

I looked at the sim and it is quite close below 80Hz.
This one should have less efficiency and less output above 40Hz on paper. It should have a bit more output near tuning. I'd say the original sims as being the slightly bit louder cab overall for music apps or live sound (kick drum, percussion fundamentals, most of the content being above 40Hz etc.).

563442871_SkhornComp.png.365eb2c789449d477255ef1628049ab0.png

You didn't compensate for "Lossy LE" in HR. When done the sims look like this:

144603677_databass4.jpg.43632d88bd4add332ce87c66ea8c8d1c.jpg

So, with the added baffle gain added in, the response will be quite similar between about 40hz and 110hz, with the grey line having more output below 40hz and less above 110hz.

On 8/16/2018 at 11:54 PM, Ricci said:

I've found over the years I like smoother responding wider bandwidth systems vs systems optimized for more sensitivity over a narrower band of operation. This is part of the reason I decided not to do a straight slot. I wanted extra upper bass output and extension well beyond 100Hz as part of the design goal. Often times you'll see guys using subs for 30-70Hz and another set of kick bins for 70-140Hz or whatever. Usually due to sub bins with degraded upper range behavior or just not enough output. I'm not a fan of that approach. I'd much rather have one cab that can handle everything. I think the sim you proposed would be fine. I tried to get the top end as extended as possible on this one.

This is an interesting topic. Now, my sim has good output to about 120-130hz, which should cover the demands of a sub in about 99% of the cases. But what is interesting is the topic of extension above 100hz... Now, the more 'orders' that one adds to a solution, the more the impulse response and the SQ typically worsens. So, my thinking is: If one has a design that already has a 2nd order roll off above ~110hz, and then adds a 4th order lowpass over that, don't we have a 6th order lowpass, which typically should sound worse? So, couldn't the solution with the SQ 'issue' with bandpass subs with a narrow band be to use less steep filters? The upside of this approach would of course be that the HD gets rolled off in a BP design. That HD won't get filtered away with a regular low pass filter. 
The above could also be part of the reason why you've found that you like the sound of subs with wider bandwidths more.

Quote

Another reason I didn't choose a large straight slot was to more fully enclose the drivers inside the cab. Most of the time I notice non harmonic mechanical and operational noises before HD gets to be offensive. The acoustic roll off of the slot above 100Hz should help lower HD a bit, but with the driver cone edge only 10" from the end of a large slot with line of sight to the outside world I'd expect there to be more operational noise leakage, though HR doesn't show too much of a difference. I'd like to see that tested actually. Also the drivers would be a little more susceptible to rain or a drink spill, but either arrangement is safer than a direct radiator cab!

This is also interesting. I too would see tests of this. Having a 10" slot should naturally be worse, but since it rolls of HD earlier, it should roll off those mechanical and operational noises earlier as well. This all depends on where the noises occur of course. Above 350hz the different designs have similar sensitivity, but my sim has less sensitivity between 120hz and 350hz. Above 350hz the wavelengths start to get relatively short... could a slight bit of damping in the front 'chamber' be the answer to decreasing the noises?
The front of the drivers would be a bit more susceptible to rain or drinks, but in the regular SKhorn, standing up, one can pour a beer straight into the motor of one of the drivers, through the middle part of the port.

Quote

I didn't go with a push pull driver arrangement due to the minimum clearances needed for the drivers  (10.5" driver depth + a large dustcap and +40mm excursion worst case scenario minus some for the baffle thicknesses and depth to the dustcap below the frame plane) and the fact that most high excursion sub drivers make quite a racket from the motor and suspension when pushed hard. Even more of a reason was the uneven loading it would present on the drivers. It would be much more involved and difficult to design the cab to evenly load the drivers with one inverted. Not impossible but it would complicate things. I'd give a rough guess that there would be about a 25-30L difference in the vented air volumes seen by the drivers. Tuning would be slightly different unless compensated for and the throat area would be a concern. I know this has been done in plenty of cabs before but I don't know if I trust it with the kinds of pressures that can be developed inside something like these. I didn't think the potential lowered even order distortion outweighed the concerns with uneven loading and possible mechanical noise from the inverted driver motor. The forces inside these can be pretty ridiculous.

Of course the volume differences would be accounted for in a push-pull scenario, which would be easier to do in a design that only has 90 degree bends, but since the push-pull scenario has been left behind for other reasons it's a bit of a non topic.

Quote

The force cancelling works really well on it. It's not like the drivers are 90deg rotated from each other or even 45deg. It's only a 12deg offset and it's a 250+ lb sub. In use the cab has  no perceptible rocking from the driver operation. That small amount of offset from exact opposition plus the sheer size and mass just doesn't add up to any real rocking forces fore and aft. Technically I'd guess a perfect driver opposition would measure a bit lower with an accelerometer but in practice it worked like expected and it's a complete non issue. Regular old panel vibration and bracing is a much bigger concern. The Skhorn has been quite good as far as that is concerned when compared with most other large cabs, but this is always a battle on big subs with tons of output.

Panel vibrations would be much worse, yeah. It would just be nice to know that one has done what one can to reduce the vibrations from the drivers themselves. 0 degrees would be nicer than 12 degrees, if all else is equal, but it's not like it's a make or break aspect of it all.

Quote

About Edge and directivity. Keep in mind that the math is simplified and goes back to the point source mic placement method. If the radiating points are spread on one sub and focused on another you can never truly get the same mic distance from the two. In practice there is a very large area that one is trying to cover usually inside of a room with boundaries. It's complicated. One sub is more diffuse but that's not necessarily always a bad thing. Edge is a good tool but I don't get too caught up in an apparent half dB advantage here or there. Most of that directivity happens above 80Hz unless the baffle area starts getting truly large.

That's why I've set the mic in Edge to measure the sound at 100000m(100km) out - to mask the difference in distance from sources on the baffle itself. If the mic is put 2-3m off of the dead center line so far out we can be sure that the sims will still be very fine.
In the second part of the above quote I suppose that you weigh 2 sources spread out by 45" against 1 source in a single location, and question which would be better. Me, I wouldn't put a Skhorn in my living room - I'd get a AE TD18H+, put it in a simple design, place it well, integrate it well, and be done with it, but that's me. 

Quote

One way I like to think about this is with 2 different philosophies. The first would be maximize the baffle area for the cabinet (think DTS-10 shape or similar) and get as much out in front of the cab with the drivers and design as possible. However at what point does this become impractical? Let's say the cab has a 60x60" baffle and is very shallow and gets some extra forward gain over a very similar design with the same driver which has a baffle of  30x30" but is much deeper. At some point you run into limitations in available depth to use and/or available baffle area. How many 60x60" baffle cabs are going to be able to be arranged? In a lot of cases not too many and eventually you just need more cabs and drivers. You could fit 4 of the 30x30 subs into the same baffle area as the 60x60 that would outperform it. The best case as far as potential output density per baffle area goes is that one entire face of the sub is radiating surface area. That's not going to be the best for directivity control though. You also end up with deeper cabs to get your cab volume. Tradeoffs.

I'd bone this all down to a relation between the depth of the stack and the height of the stack. Drunk people fall over and push each other around. To prevent them from knocking a sub over in their fall I guess that a depth about half of the height of the stack would be enough. 48" tall by 24" deep, for example. If taller than 48" one most likely does sound at an event that has a fence anyways, so stuff wouldn't get knocked over, and stacking would be safe even though the relative depth would get lower.

Quote

Vent area is vent area I'll give you that as an advantage for sure. This is the #1 priority I would have when redesigning the Skhorn. Mostly to work better with the lowered tunings. I try to avoid turns in vents when possible though. The reduced area of the slot for the drivers would increase air velocity over the horn expansion type though. I have some new thoughts on designing vented subs that I haven't gone to far with yet but I'll share once I think it through a bit more.

The reduced area of the front part would mean that the particle velocity would be brought up to about 30m/s (with filters in place), which is fine, and which is far from 45m/s of the particle velocity of the port, and 50-55m/s in the Skhorn.

 

Something that we haven't brought up yet is where the sensitivity is most needed. According to the Equal-Loudness contours ( https://en.wikipedia.org/wiki/Equal-loudness_contour ), for something to be perceived as being 100db, you actually have to reproduce a 100hz tone at about a 107db level, a 60hz tone at about a 112db level, and a 30hz tone at about a 122db(!) level. Now, that means that we have to send 10 times more energy to a tone at 30hz for it to be perceived as as loud as the tone at 60hz.

Let's say that we try to reproduce a perceived 100db signal with a speaker that has 100db sensitivity throughout our hearing range, 10m from the source (no reflections included in this example). This means that we have to send 100w to our speaker at 1000hz, we have to send 500w at 100hz, we have to send 1600w at 60hz and we have to send 16000w to 30hz, for it all to be percieved as as loud. Where does it make the most sense to increase the sensitivity by, let's say, 3db? At 100hz, where it we could cut the needed power by half, which would correspond to a decrease in needed power by 250w, or at 30 hz, where it would correspond to a decrease in needed power by 8000w? Of course the increased sensitivity would make the most good down by 30hz. Even if we increased the sensitivity at 60hz indefinitely and impossibly much, this would only correspond to a cut in power by 1600w - not a lot compared to a decrease by 8000w.

The above is why my sim has more sensitivity below 40hz than above 110hz. It's also why I've chosen a larger port. 1-1,5db extra sensitivity below 40hz, plus 0,25db extra baffle gain, plus about another db from the decreased port compression, that should all make for about 2-3db more maximum output, where it's sorely needed the most. 

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On 8/17/2018 at 7:39 AM, SME said:

Subs make plenty of sound above the XO point, and that sound can have a surprisingly big impact on overall quality.  Problems there can make distortion sound a lot worse.  For example, even fairly high harmonic distortion may go unnoticed by listeners if it is fairly uniform vs. frequency, but if certain notes have spikes in harmonic distortion due to horn resonances and whatnot, you'll get notes that tend to stand out, which is a lot more likely to be audible.

This has actually been a part of my concern with the response of the Skhorn. When looking at the HD, there seems to be a correlation between the 2nd and 3rd HD, and the response peak at 220hz.

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Moar!!,

I used measured driver specs with complex inductance parameters. I have them so those are what I use.

Of course there is correlation between harmonic distortion and large spikes in response. This is a well known phenomenon affecting any speaker (vented resonances for example). In this case the 3rd harmonic isn't high enough to worry about. The second harmonic accounts for nearly all the THD 100-120Hz but it doesn't break 10% until it is producing 134-135dB at 2m outdoor ground-plane which is extremely loud. A typical low pass filter would decrease the output and power demands in that range quite a bit. I've not noticed it in use.

Low pass filtering does increase delay. However with less low pass filtering slope your putting more power into the cab at higher frequencies. The same holds true at lower frequencies as well.  I think the issue with many of the worst sounding bandpasses or higher order cabs is that as designed the bandwidth is extremely narrow, perhaps an octave or an octave and a half and they have ringing and other energy storage issues. You end up with what is described as the one note sound. Then you throw the filtering and other EQ on top of that and you end up with a smeared mess before you ever put them into a room, which further makes a huge mess. I've tried very hard with the Othorn and Skhorn to make subs that have an extended & smooth response over a large range and that have very well damped behavior.  They are not as absolutely loud as they could be because of it. However I think the tradeoff is worth it because they sound nothing like the typical higher order cabs I've had experience with. I think a lot of others would agree.

When I say "room" in this context I don't mean someone's living room. I mean everything from a church to a night club to an auditorium to a theater to a huge arena. Most of the time subs will not be operating outdoors or in a huge stadium or arena, but will be in some sort of small / medium venue. These are still rooms with boundaries. In a lot of cases the subs will be back up against a back wall or corner, under a stage, flanking the stage, part of the stage even, flown up near the ceiling, ground stacked etc. There's a lot of variation.

Vents and maximizing output at the low frequency corner...If you assume that we have enough upper and middle range output and efficiency and need the most output at the tuning area and follow this thought process you will end up with direct radiating vented subs. They will always have maximal use of cabinet volume for the vented chamber and maximum vent area versus an alignment which loads the front of the drivers. It should also be simpler. Assuming you keep the cabs the same total size of course. I thought the advantages of this alignment overall outweighed the slight loss in maximum output near the tuning frequency and the extra build complexity. If you want maximum vent loading and output near tune go standard vented.

ELC and is a whole other area of discussion that should probably be handled elsewhere. It's a study of how our hearing perception works not how we should be hearing things. We don't need to correct for it. 30Hz is not supposed to sound as loud as 500Hz. It's been covered in some good discussions on other forums like AVS and DIYaudio.

 

 

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I would add that the order of low pass / high pass filter at a XO isn't too important as long as they aren't too extreme.

The real problem with XOs is that the actual slopes you end up with never match any particular ideal.  For example, the Linkwitz Riley (LR) crossovers are quite good if the two sources are flat and phase-matched throughout the crossover region, but if one or both has any natural roll-off, the XO is not LR anymore.  The phases no longer match and one ends up with interference effects throughout the XO region and less output overall across the region.

Optimizing the XO can be a kind of dark art.  Setting sub delay is part of this, but delay can only fix the phase mis-match across different frequencies "on-average".  There will still be phase mis-match and a deficiency of energy.  A lot of systems would probably benefit from some low/moderate Q boost centered near the XO frequency, but getting it right is hard.

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Have you looked at the LaVoce 21" (soon to be carried by parts express) as a possible driver candidate for the SKhorn? I've heard comment that it is very similar to the B&C 21DS115. If it models well, it could be a great option, as it looks like it's going to sell for $150 cheaper than the 21DS115.

 

https://www.parts-express.com/lavoce-san21450-21-neodymium-subwoofer-8-ohm--293-732

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How does the time alignment work on a design like this?

Wouldn't the horn path delay the HF output longer than the LF output from the port?  

Or is it close enough to not matter much?

Or is that part of the design that needs to be factored in somehow during the design process?

I was considering an attempt to add a horn section onto an existing BR cab, but wasn't sure what all needed to be accounted for.  

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