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D2U
 D2U
(@d2u)
New Member Registered
Joined: 2 months ago
Posts: 4
30/08/2020 10:58 am  

Hello there,

I have a couple questions about winisd. I am currently modeling multiple types of enclosure's for two dayton audio rs180p-4 7" drivers. And I have a few questions about them.

First a little bit of context. I'm building a high power bluetooth speaker. It has to be able to play low. You could put it in the category of 123Toids portable Dinas which is an epic project btw :D, props to toid. However, differing of this project I want to build an active 2-way stereo bluetooth speaker with DSP. The dayton drivers will take 50 watts rms each and i want the enclosure to play low bass(as in down to 40ish) without any compromises.

 

Currently I have two designs for the enclosure.

- Enclosure A has an f3 at 35 hz, a volume of 60.86 liters and a tuning frequency of 37.1 hz.

- Enclosure B has an f3 at 30.9 hz, a volume of 86.34 liters and a tuning frequency of 33.73 hz.

Both are modeled sub-chebyshev and with a 4 inch port.

Now the first thing to look at with these models was the air velocity. With a 4 inch port, both of them have a higher peak velocity than in recommended. Instead of the 17m/s model A shows a peak velocity of 20.24 m/s and model B even higher at 24.35 m removed link However, I plan on using the precision sound 4 inch flared port which gives a little bit extra headroom. Although, I do have my doubts about it holding up with speeds of 24.35 m removed link If anyone has any experience with flared ports and has any tips or tricks, by all means please share them :D.     (PS. I could go with a slot port, but i want the speakers to play loud and be efficient. Since a round port is as efficient as it gets, I want to use this instead.)

The second thing I checked was the excursion plot and herein lies one of my questions. In both of the models the excursion exceeded the maximum excursion of the driver. I'm not able to post pictures yet but if you model the enclosures yourself you will be able to see what I am talking about. In short, both models show an increase after the tuning frequency that is above the maximum of 6 mm(A peaks around 8.3mm and B around 9.5). What should I think of this? I mean obviously the mechanical limits are to be reached at this point, but is there any solution? And does this simulation of winsid translate well into the real world? If I lower the (combined) signal power to 53 watts(A)(42 watts for B) the excursion graph is completely under the 6 mm maximum. Does this mean I can't run them at 50 watts a piece?

 

That's about it. Btw, I'm totally new to designing with winisd. I have been tinkering quite a bit, but if i made any newbie mistakes or just didnot take something into account, feel free to fully roast me(preferably in a constructive way :D). In the end I'm leaning to enclosure A, because it's more flat and has a lower airspeed and the excursion is a bit more neat. It can't play as low as enclosure B, but i might be able to fix this with the help of DSP. Anyways all tips and tricks are welcome 🙂

 


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123Toid
(@123toid)
Illustrious Member Admin
Joined: 3 years ago
Posts: 980
31/08/2020 2:50 am  

@d2u

 

First of all excellent driver choice!  I modeled both of these scenarios and will post pictures along with some answers.  But before I go threre, it does appear you are putting both drivers in one enclosure.  I am guilty of doing this myself, but for this build, you would probably be better off putting a small 1/2" partition in and porting each side seperately.  

First let's start out with pictures. I have 37.1 tuning green and 30.9 tuning red.  If I understood you correctly, here are the graphs.  This is at full rms power of 120watts combined. 

tfm
rpv
ce

You already have noticed the big issue, which s your cone excursion.  You can take care of this one of two ways.  The first is limit it with your dsp program.  This can be down in multiple ways, but is an option.  THe second, I beleive better option, is to just limit the power.  There is a false misunderstanding of RMS power.  RMS power is the continuous power of a driver, but that is dependent of the box that you put it in.  Both of these would be damaged by running full power to them.  A graph that is very useful to determine the power you should run to it, is maximum power. 

mp

From this graph we can see that the drivers can handle 120watts RMS, until about 92watts.  Then it starts to drop off a cliff.  The 37.1 can really only handle a maximum of 45w while the 30.9 can only handle 36watts.  Now this really isn't as big of any issue as you would think, sinc eyou can limit power.  Most people would be concerned with losing SPL, but you are only losing about 4db in spl @ 3 feet by going from 120w down to 45w.  That is not bad at all.  A good graph to check this out is SPL (you can also mark in advanced to makes the SPL graph xmax limited).   Now keep in mind, changing the pwoer output will drastically change your port air velocity. 

spl

You can take care of the cone excursion after 30hz with a high pass on your dsp board.  Let's see what that looks like. We will jsut navigate to filters and add a highpass.  I added a4th order LR highpass at 27hz.  This will protect your driver and once again affect your port air velocity in a positive way. Let's see what it did. 

cehp
rpvhp

You now have your drivers completely protected and your port air velocity is no longer an issue. You don't need the precision port, in fact, you could jsut as easily use a cheap grey pvc conduit you can pick up at your local hardware store.  If you do want to flare both ends, you could go with a 3in.  Keep in mind that with both ends flared you can possibly go up to 30 m/s.  In this case would only need a 2.5" port.  But if you can fit bigger, you might as well. 

As far as which enclosure I would build.  I would choose the first one.  It has better power handling, smaller box and still fits your criteria of playing low.  I wouldn't fix it via boost with DSP, you will just create more excursion problems.  You would have to tune everything else down, which would give you less max SPL.  Personally, I don't think it is necessary.  38hz f3 is plenty good enough.  HEck it is practically the Dinas (35hz). 


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D2U
 D2U
(@d2u)
New Member Registered
Joined: 2 months ago
Posts: 4
01/09/2020 12:53 pm  

@123toid

First of all, thanks a lot for the feedback 😀 it really helps a lot. I now understand that these drivers will not be able to run on 50 watts rms in this configuration. I was planning on using Daytons kab-250v3 combined with the dspb-250. I suppose, I could fix the gain at a lower level in order to not damage the drivers. However, I do really want the speaker to fully utilize the capabilities of the amplifier boards and since the tweeters will take the full 50 watts a piece(as in they will be ok mechanically), I'm not too sure this is the right driver for this build. So yesterday evening I got back to modelling and with the help and further understanding I gained from your feedback I was able to come up with the following. 

Instead of the rs180p-4 I'll be using the rs225-4 which is essentially the 8 inch variant of the rs180p-4, but is has a higher rms power rating and it can play lower. The box I currently have modeled for a single driver has an f3 at 35 Hz which should play at 104db@50watts rms without any mechanical limiting after adding two high-pass filters(4th order RL@20 Hz and a 2nd order butterworth@27.5 Hz). Compared to the 100db@25watt rms the rs180p-4 could maximally produce it would be a huge gain. Since in theory, it will easily be twice as loud. And I won't have to limit the gain or find a different amplifier with dsp.

image
image
image

The box parameters are the following:

- Volume = 50L

- Tuning frequency = 35Hz

- Port diameter = 80mm

 

Furthermore, the air velocity is well below the 17 meter a second.

image

So now the challenging part begins which is trying to make the enclosure as small as possible well maintaining this response :b. If its not possible I'll accept the fact that it is huge :D. There is no wife acceptance factor for me yet so I think I'll be gucci for now ;).

Nevertheless, I do still have a couple questions :). The graph from maximum SPL shows some weird type of caving after 40 Hz with the lowest at 50 hz. Why is this the case? Is it, because the driver has an impedance peak at 50 hz? Furthermore, why does the impedance graph show two impedance peaks. The first one could be explained by the Fs, but the 2nd one makes no sense to me. Is it some type of effect? Or should i just ignore it?

image
image

Lastly, in the following picture it says 1st port resonance. Online there is a lot of talk that one should crossover before this resonance. However, I could only find this in threads that were about subwoofers. Does it matter in my case? If so what does this resonance create? An other peak in ouitput? Can this be countered by using dsp or any other way? I plan on crossing over between 1.6 and 2 kHz. And I'm using the peerless NE19VTS-04 as my tweeters. I also plan on making the cabinets front ported since I want to be able to put the speaker in any corner and not have it sound boomy. Thanks a lot for the help 😀

image

 


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