Home Forums DIY Speakers and Subwoofers Need some help with diy bluetooth speaker Reply To: RE: Need some help with diy bluetooth speaker

  • 123toid

    Administrator
    August 31, 2020 at 6:50 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. 



    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. 

    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. 

    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. 


    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). 


    Reply To: RE: Need some help with diy bluetooth speaker