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RCF LF15 vs Eminence Kappa 15LF

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ringo34 View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote ringo34 Quote  Post ReplyReply Direct Link To This Post Posted: 05 March 2022 at 11:20am
I tried to simulate this driver yesterday in UniBox program, which I really like.
Simple and easy to use. Though excel based.

I received some weird results. I am not sure that my box physical size is correct, and also I did receive some very long port length.

Could anyone try also that driver for optimum bass reflex system.
What box size, tuning freq and also port dimensions you get?

Here are T/S parameters:
Resonant frequencyfS34Hz
Electrical QQES0.30
Mechanical QQMS7.60
Total Q factorQTS0.29
Suspension equivalent air volumeVAS146litres
DC resistanceRE5.5Ω
Minimum impedanceZmin6.0Ω
Voice coil inductanceLE1.3mH
Sdmm2900
Xmaxmm12

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MarjanM View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote MarjanM Quote  Post ReplyReply Direct Link To This Post Posted: 05 March 2022 at 12:34pm
Originally posted by ringo34 ringo34 wrote:

Hi
I will go ahead with those RCF LF15X401 drivers. As they dont cost too much and I think they will cover my excpectations.
http://www.loudspeakerdatabase.com/RCF/LF15X401

I have two a littlebit different box design in mind. They just look enough good to me.
Which one should I prefer? What is main difference?


And what simulation program do you suggest me to use to model these boxes. Because I dont have any idea how to get those internal dimensions of box (also port sizes etc, all those angles). I am familiar with Bassbox pro program (I used it for home speakers). But thats my first PA project, so many questions and not knowing details for me.

Thank you for help.

You need to stop watching those videos from Indonesia. They have no idea what they are doing overthere. Get some plans that are actually tested and proven.
Marjan Milosevic
MM-Acoustics
www.mm-acoustics.com
https://www.facebook.com/pages/MM-Acoustics/608901282527713
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DMorison View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote DMorison Quote  Post ReplyReply Direct Link To This Post Posted: 05 March 2022 at 3:26pm
Originally posted by ringo34 ringo34 wrote:

I tried to simulate this driver yesterday in UniBox program, which I really like.
Simple and easy to use. Though excel based.

I received some weird results. I am not sure that my box physical size is correct, and also I did receive some very long port length.

Could anyone try also that driver for optimum bass reflex system.
What box size, tuning freq and also port dimensions you get?

For the range you want to cover and the target size, try 100litres net tuned around 36-37Hz.
If building a rectangular "shelf" vent as shown in the images you shared earlier, be aware that it will tune the box lower than the simple predictions from software like WinISD, which is what I use.
That is because this software, and many others, assume the back end of the port is well away from the walls of the cabinet.
When built in as a shelf, the opposite is true, with 3 out of the 4 walls of the port being a lot longer than the shelf itself, so some of the air immediately around the back end of the port behaves as if it's part of the port rather than part of the cabinet volume. One way of approximating this change is to manually calculate the required vent length, with a different end correction value, rather than using the length predicted by the modelling software. (If Unibox allows you to change the end correction value, try increasing it to 2.227 instead of the default. This will get you back to a manageable port length.)

Remember also that you will need a crossover from your sub to your mains, and a High Pass Filter to protect the drivers from over excursion - WinISD allows us to model the effects of those on excursion and vent air speed, I'm not sure if Unibox does or not.

Here's a few graphs.
The white line on the SPL graph is a target curve for the crossover, I've used 100Hz LR24 for that.
I've calculated Xmax as 11.25mm for this sim, based on the stated 30mm voicecoil and 15mm gap.
The SPL, Excursion and Airspeed shown are all modelled at an input of 86V, which equates to an amp of 925W at 8Ω. Your CS800 would be approximately 6dB quieter, but vent airspeed and distortion from excursion would therefore be lower too.
The 2 vents would be 198mm wide x 88mm tall, with one central divider, allowing for a 450mm external cabinet width using 18mm timber. Height & depth of the cabinet would be 615mm, allowing ~7l for bracing, handles etc as well as the driver, giving 170litres overall size.




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ringo34 View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote ringo34 Quote  Post ReplyReply Direct Link To This Post Posted: 06 March 2022 at 2:24pm
Oh yeah!
There is a lot of good input for me. Appreciated!
I simulated again that driver in Unibox, there is also port end correction option, which is set to 2.224.
I wasnt aware that impact at all, but to think about, there is definately physical impact what shape and location port have. Again something new for me.

Here are some german layout also from ports end correction:
https://posts.org/ -


I read some german sites, where people got good results of 120 L net and tuning of 40Hz and it was sounding very good.

Though this setup of 100L net for driver, tuning 37Hz looks even better for me. My main question right now is port design, to make sure all comes together correct way. Simulation suggest min 15cm diameter ports (2x), but length comes then 40 cm. Which is quite long, so I have then free space ca 20cm from back wall to port beginning. This looks enough space, I guess. Do you get same results for port length? 

if I lower port diameter to 12cm (eg. equal surface area for rectangular) I get higher port air velocity and it will reach close to 40m/s. Though simulation suggest not to use less than 15cm diameter port.

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DMorison View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote DMorison Quote  Post ReplyReply Direct Link To This Post Posted: 06 March 2022 at 6:05pm
Yeah, that's the same info about end correction I was working from, so we're on the same page there.

I would do rectangular ports, if you want to build it 450mm wide overall using 18mm plywood you'd have 198mm wide for each port, 88mm high and 431mm long to get the modelled airspeed.

If you went with 15mm plywood, which is probably OK if you're mostly using it in your garage & it's well braced, then you'd have 202.5mm wide x 86mm high by 431mm long, for the same vent airspeed.

Here's what the 15mm option would look like, it comes out to 600mm deep and high, the end of the vent is ~120mm from the back wall so probably just about OK, but I wouldn't want it any closer than that. You could build a box a couple of cm deeper and take the same off the height if you want to be safe on that aspect though.


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Post Options Post Options   Thanks (0) Thanks(0)   Quote ringo34 Quote  Post ReplyReply Direct Link To This Post Posted: 06 March 2022 at 11:27pm
Evening!
You have been great help. For this setup I think I have a full plan now.
Btw-does wider speaker enclosures produce more SPL, due baffle step? I mean if front baffle is wider, baffle step point is lower and more energy is directed to the listeners? Energy cant go so easily around the edge of baffle. This one I am going to build is quite narrow compared driver.

Just for curiousity:
In german forum I found totally different design also for that driver. It looks then horn type, I guess.
Do you have any idea, what could be advantages of such a design?
https://posts.org/ -


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Post Options Post Options   Thanks (0) Thanks(0)   Quote DMorison Quote  Post ReplyReply Direct Link To This Post Posted: 07 March 2022 at 9:01am
Hi Ringo,
For a sub, we're mostly operating below the frequency at which the bafflestep has effect, so it won't really change much. It is far more relevant for full range type speakers.
Even then, the low frequency part of the speaker's response is still likely the same for different baffle widths, so we'd end up pulling the mids back to match that anyway.

The other design you posted is what's known as a scoop, or sometimes back loaded horn. It will be more efficient, at least over part of it's bandwidth, but may also have a more coloured sound. They also tend to have a distinct notch in their frequency response that limits how high they can usefully play as the sound from the horn part is out of phase with the direct sound from the driver.

There is a dedicated scoop sub-forum on this site if you haven't yet found it.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote ringo34 Quote  Post ReplyReply Direct Link To This Post Posted: 14 March 2022 at 12:09pm
I already made some plans for enclosures. Your plan and dimensions were nice help. I try to make front baffle maybe even from 24mm plywood, other walls probably from 21/18mm.


But I came up with one question, when I checked driver Xmax in enclosure. It is exceeding slightly 11.5 around 50Hz.


Could this be a problem for me? Should I lower Vb to get it under 11.5 mm?
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Post Options Post Options   Thanks (0) Thanks(0)   Quote DMorison Quote  Post ReplyReply Direct Link To This Post Posted: 14 March 2022 at 2:45pm
That sim does not look like it includes the effect of the Crossover & EQ filters I modelled, which is probably enough to explain the difference of the basic box volume & tuning are the same. If you were going to use the same filters I included, you therefore wouldn't need to worry about it at all. If you were for example going to use a higher frequency crossover to your main speakers, that might allow a bit more excursion around 50Hz.
Simply not turning it up quite so loud would be all you need to manage that if it were a problem - the difference between 13mm in your model and 11.25 in mine is only 1.25dB, and I'm quite sure none of your audience will complain about a difference that small. 

Also, Pretty sure that 21 & 24mm timber are overkill for a box this size, if well braced.
By all means do it if it makes you feel better, as long as you're OK with lifting the extra 8-10kg every time you move it Wink

You'd need to adjust all the dimensions to keep the net internal volume, vent cross sectional area and vent length the same as well; I can't see if you've done that already as postimage has shrunk your pic so much it's unreadable, sorry.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote ringo34 Quote  Post ReplyReply Direct Link To This Post Posted: 15 March 2022 at 9:23am
Ok, then i dont worry about Xmax. Probably they do not get very loud use at all, just bass extension for my main and mostly listen background music when I work outside of garage.

Yes, my simulation does not include crossover. Btw does your WinISD also provide that schematic for me?
LR24 it was if I remember correctly. I am good in wood working, but not so much deep technical stuff. So if you have also schematic for that specific LP filer, I would build that also.

It was just to show you that I am working already with plan. I will add higher resolution pic also. I havent jet added final internal measurements, maybe couple of cm here to there I will adjust. But overall I get ca 118-120 L total enclosure (100 for driver, ca 4-5 for driver physical, 5 for bracing and ca 9 for port). I will go then 21 for baffle and other walls 18, maybe bracing even 15 as they do not bend. They provide across strength.

Here one pic from my first and only home main speaker. I built it long time as this time I didnt have much tools and place where to work. Real piano poly laquer btw.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote DMorison Quote  Post ReplyReply Direct Link To This Post Posted: 15 March 2022 at 7:44pm
That LR24 crossover filter is best applied to the signal before your amp rather than passively within the sub itself. That's because the component values required to make a passive filter at that frequency result in them being big, expensive and still they eat up a bit more of your amp power than is worth it.
Behringer DCX2496 is the king of entry level Digital Signal Processors for applying crossover filters, EQ etc, but there are certainly several others worth a look too depending on your needs.

Your plan looks good, BTW, good luck with the build!
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