[Build Log] High Quality PC Speakers Design and Build - Page 7

Thanks for the encouraging comments.

I have not made so much progress lately, but I have spent some time optimizing the crossover. Just a bit of fine tuning plus impedance correction for the tweeter resonance frequency peak.

I've also got the test enclosure resonances better under control with MDF on the inside of all surfaces. Now I'm very happy with the smooth sound of this little speaker, so I have ordered the correct components for a passive crossover. Then I will build the final boxes and move on to amplifier and pre-amplifier.

Finally had time for a bit of work on this project.

I've been experimenting a bit with the enclosures. The Acrylic with MDF on the inside is not bad at all, but it is time consuming to make.

So I had an idea, how about casting it from concrete. I have to admit I don't have that much experience with concrete, so I had to go through a learning curve, with several failed attempts, before getting something close to usable.

This is what I got so far, not perfect, but proving that it's doable:









The 6 holes on the front got nuts cast into the concrete so a front baffle can be easily screwed on. Still working on the front baffle, it's tricky and I'm not sure if I should make it out of wood, concrete or maybe thick acrylic.

Thanks, I think I took some pictures with my phone of the mold etc. I'll try see if I can find them.

The current mix I'm using is 1:1 cement and fine sharp sand (volume, not weight). It's important to use proper sharp sand to achieve strength. Then use as little water as possible. It should still be workable, but too much water will cause the mixture to shrink and crack during curing. I'll experiment with some more advanced additives, fibers, water reducers etc. A thick paste like consistency works well for me.

Another thing I found essential is to keep the mixture moist while it's curing. It takes at least a week to cure to good strength. If it's allowed to dry out within a day or two it looks fine, but the strength isn't good.

With little water usage it's important to work fast when filling the mold, it starts setting quickly.

Found the casting mold pictures on my phone, sorry about the poor quality.

This is the inside part:





And the outside:





Almost everything is just held together by tape in this mold (few pieces glued together on the inside part). Using just tape makes it easy to take apart when the curing is done. But I think I will make a bit more advanced mold that can be screwed together or something. It does take a lot of thinking when making the mold, everything has to be the opposite of what you want

I just fill up the outside part maybe 1/3 of the way with the mix, then squeeze in the inside part, complete the filling and tape it together. With some shaking during the filling to get rid of most air bubbles.

I'll try take some pictures during the process next time, but it's messy and has to be done quickly, so I'm not sure I'll have time.

Got some more crossover components as well, I believe I have everything I need now to complete these things:



Just need to make a test baffle for the cast enclosure, then I'll do a resonance analysis on them to see how good they perform. I hope using cast concrete will move the enclosure resonances so high in frequency that it will no longer have any effect on the sound quality.

Maybe a bit extreme to do this much work for a pair of small PC speakers, but I'm having fun

Yeah, I got a bit too many projects in progress, but I do try to get my project to at least some stage of completion, takes time but will get there

I did complete a test box for the second speakers and I am using them on a daily basis, but it's a bit messy with crossover lying on top etc. Anyway, this measurement is with enclosure (and the other measurements in thread following it) and it's quite good:



I have done some comparisons with a couple of smaller PSB speakers (I have a pair of Alpha B1 I use for surround). The small PSBs are still larger, so they can play louder and got deeper bass, but in areas like accuracy and imaging the little DIY PC speakers are, to me, much better. So if I had to choose one of those two pairs to live with, I would go with the DIY ones.

However, in general, I would not recommend starting out on a very expensive DIY project, if you'd like to build something, try something much smaller and less expensive first. Also I really would not recommend doing any DIY constructions at all, even well documented ones, without having at least a basic measurement microphone and some software available.

Even I've done many DIY speakers, I have to admit I've never done anything that could match my large PSB speakers, ok, they are ~$6K speakers and I have not tried doing DIY constructions that cost more than maybe $750. But commercial speakers above $5K are in a class where the manufacturer no longer tries to save money on drivers and crossover components, plus the finish and build quality is usually outstanding and they've put a lot of engineering effort into them.

In my experience buying speakers is a bit hit and miss, I believe it takes at least a month of listening to truly get to know a new pair of speakers, a session at a dealer will only give you a quick introduction, so by the time you really know their weaknesses and strengths it's usually too late to return them in case you are not 100% happy. I had a pair of Martin Logans before the PSBs, but I was never really satisfied with them, although I thought they sounded fantastic when I first got them.