New speaker (sub) project

edited January 3 in DIY
This is to go with my current main DIY speakers.
My intention was to add a dedicated bass speaker to each of the stereo speakers, crossing over somewhere below 100Hz. I had a look at cross over value options and the simplest I could work out crossed over at 75Hz. I bought the necessary capacitors and inductors for each.
But I'm so happy with the DIY Monacors as they are I don't think that an additional bass section for each is necessary, or desirable, in my lounge.
However, as I say, I'd already bought some of the components for the crossover. And who doesn't want the option of occasional extra bass...?

So I have decided to have a complete experiment and build a single subwoofer.

I chose a driver with a double voice coil so that it can be fed directly (though via suitable crossovers) by both channels of my One4 amp.
Also, as the pricey caps and inductors I already had were chosen on the basis of my using 8 ohm drivers, my options were a little limited (most dual voice coil subs are 4 ohms per coil). To the rescue Dayton Audio's SD315A-88 12 inch DVC subwoofer.


I'm currently awaiting its delivery from the US.

In the meantime on with the crossovers.
Check out those enormous inductors! (Ignore the shabby MDF cases. Shameful.)



The red and black cables will feed the sub. The other sets will go to the inputs of the 2 stereo Monacor speakers.

Also, have got busy with the cabinet.
Now I'm hoping this will be interesting. Possibly laughable.

There was a thread on here recently about using a sandwich approach to cabinet walls. Two 9mm sheets of ply separated by a layer of some sort of squishy glue. I wanted to try that using the workshop available at art college. But, due to the necessary covid restrictions there I have deferred my 2nd year. I don't have the tools at home for complicated carpentry.
I am able to build a basic (but carefully calculated) cab using MDF. Which I have done.
But I liked the idea of trying sandwich cabinet walls.
And, I was happy with the effects of painting the inside walls of my DIY Monacor cabs with bitumen paint.
So a new idea has been hatched...
I am pouring a 2mm depth of bitumen paint on to the inside walls of the cabinet as the sandwich filling. Easy enough. (I knew that old turntable spirit level would come in handy!) It is taking ages to dry. But I'm in no rush.
I'll need to fix the front baffle before adding the bitumen to any of the other inner surfaces.



Of course, once dry I am going to need to add the second, inner piece of bread of the sandwich.
Not ply or MDF though. Oh no.
Instead, I am going to pour in 3mm of floor self-levelling compound over the bitumen to act as the inner bread.
I've used floor leveller before in its more conventional application. It's e easy to use, very good at self-levelling, fast setting and extremely durable (down to 3mm depth). This may be quite a heavy piece!

Comments

  • Bonkers! Or so it seems to the minimally DIY-inclined Dave  :)
    I'll be glued to developments (pun intended).
  • edited January 3
    May be slow progress, but obviously will delight in keeping you posted!
    I'm interested to see how the sensitivity of the sub driver will play out. Specs say it's a few dBs down on the Monacors. But the Moncaors are about 70cm off the floor whereas the Dayton sub driver will be only a few inches off the ground, so will be reinforced there.
    Only one way to find out!
  • Any thoughts of building in an adjustable crossover point for fine tuning and maybe another pot to adjust volume.

    I always found having the crossover point as low as possible and the the volume set to discrete i.e. less than the main, always helped with integration.

    I know it makes things more complicated but bound to give more desireable results.

    Orrrrrrrrrr, replace the dust cap with an SDS bit, whack up the amp and dig up the kitchen floor....
  • cj66 said:
    Any thoughts of building in an adjustable crossover point for fine tuning and maybe another pot to adjust volume.

    I always found having the crossover point as low as possible and the the volume set to discrete i.e. less than the main, always helped with integration.

    I know it makes things more complicated but bound to give more desireable results.

    Orrrrrrrrrr, replace the dust cap with an SDS bit, whack up the amp and dig up the kitchen floor....
    All good thoughts!
    May well try these things CJ!
    I will get the basic build done and see how it sounds.
    Should be easy enough to add and tweak things accordingly. :-)
  • edited January 4
    Hi Ben
    I have bought some of this kit to maybe try inside my speaker cabinets.
    https://www.deadening.co.uk/collections/dynamat - used mainly for car stereos 
    More expensive than your bitumen but not so nasty to use I suspect. 
    Still mulling over whether to apply it as it is apparently a bugger to get off and may actually overdampen the acoustics.

  • But Merv, why would I want to use something less messy...?!

    It's a tricky one if a tweak isn't easily reversed isn't it?
    Personally I have never introduced a brace or some dampening to any or my diy efforts that has made things sound worse. But maybe I just haven't gone far enough!
  • I'm always fascinated by speaker modding/building threads.
    It's the one area where I have barely DIY'd.
    My limit is a xover converted to biwire, another converted to biamp and my pinnacle was making completely new, higher specified, xovers for another.

    Bit of a black art for me, mucho respeto a todos que pueden!
  • cj66 said:
    I'm always fascinated by speaker modding/building threads.
    It's the one area where I have barely DIY'd.
    My limit is a xover converted to biwire, another converted to biamp and my pinnacle was making completely new, higher specified, xovers for another.
    Hardly meagre achievements, Sir!
  • edited January 12
    Update...
    Bitumen has dried on the first internal face to be coated. It took about a week to be stable enough.
    The driver has arrived from the States.
    But I'm still waiting on the oversized aeroport (10cm diameter, approx 30cm length) that I ordered from Germany at the end of last year.



    I've contacted the seller and have been informed that Brexit is causing significant delays to surface deliveries to the UK. Approx 2-3 weeks. Bloody Brexit...

    The wait has complicated things a bit as to pour the bitumen on to any of the remaining 5 internal faces I need the final panel to be glued and screwed into place to contain the bitumen, and I can't do that easily until I've fixed in the aeroport inside the cabinet.

    However, I'm impatient so have constructed a bit of a work-around to allow me to crack on with bitumening the next internal face. I decided to fit a small mdf lip (about 5x5mm) along the open edge of one of the internal faces. This acts as a dam (in-lieu of the currently missing panel) to hold back the bitumen.



    I could have made a better job of fixing the damn in place. As can be seen, there was some seepage, but nothing drastic.

    I'm hoping that by the weekend the aeroport will have arrived so that I can fit it before sealing the cabinet with the front panel and move on to bitumening the next internal face. (Obviously I'll still be able to access the inside of the cabinet via the hole for the driver.)

  • edited January 13
    The aeroport has finally made it through the Brexit backlog!
    Chose this one as it's big and has flaring at both ends.
    The wider the diameter the openings of a port the less prone it is to chuffing, but also the longer the port needs to be (hence the benefits of flared ends).
    To achieve the right frequency for the speaker - cabinet combo, this port will need to be 30.2cm. So I'll be trimming down the central tube to achieve that.



    I have made a bit of compromise in the design.
    I've read that ideally the port's opening should be the same distance away from all walls as the port's own diameter. For various reasons i decided on a placement that does not achieve that internally (the internal port opening will be <10cm away from the cab's top panel, and there's a brace <10cm below it), but I'm hoping it doesn't make an enormous distance. Fingers crossed!




  • You'll be doing this for money soon, Ben!
  • Dave, what wouldn't I...?
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