I'm designing a little two-way speaker for surround sound use, what are your thoughts on the design so far?

[abstract]

I say just go for 2 'subs' so you can make it a 2 way without all the compromises. I've tried the "magic trick" of satellites with mystery bass, and the execution can be tricky...

I had 15L boxes for the the satellites and the baffle step went up to 700Hz approx.

Even 24dB/oct crossovers let through muffled voices and other such sounds that gave away the sub's position. A 7th order Bessel filter finally nailed it, but then I didn't know how to sum the L+R channels "correctly" - because there is no right answer! You either get amplitude summing (pure mono) or power summing (stereo), and it changes from one to the other, depending on how apart the satellites are spaced. Not to mention occasional fun signals that deliberately switch polarity between left and right, which a mono sub won't reproduce.

As for the Alu boxes, I say try and make them resemble a stereotypical raindrop or heart shape, with the pointy end stretched back for good diffraction. A sphere is not so great for diffraction because of how the wave converges back in on itself.

 

[Dameo182]

In general, there is no point to high pass lows as there is rarely enough 🙂 except on a tuned system. The thing is, a bass reflex box port output is in phase with driver output around tuning frequency, hense we get bass boost around tuning frequency. Purpose of the port is to provide resonance to the system which then makes some extra boost to SPL output that the driver would output on its own, in a closed box for example. But, soon below the tuning frequency output of the port gets out of phase compared to driver output and they cancel each other out. Also, the box and port do not provide any acoustic loading to the driver below tuning frequency, the driver is able to move freely as there is no pressure constricting in the box/system. This means that the driver would happily flap around when you feed 20Hz to it, but there would be no audible output, only huge excursion. This excursion will cause distortion on all the driver bandwidth though! Basically, all bass reflex box would need high pass filter to keep excessive distortion out. On a two way box this affects performance of the whole mid range!

Compare to closed box, pressure inside the box is not leaked anywhere so it acts on the cone all the way down to few Hz and prevents high excursion. Also, there is no out of phase output to cancel sound. This means closed box can be run without high pass filter just fine, without distortion penalty, and even the 20Hz would have some "audible" output. Well, most likely not audible still if small woofer.

Best way to high pass is to no high pass! just make system that requires no high pass filter and doesn't sacrifice mid range performance and is still capable of good enough bass output 😉 This could mean closed box, or just big high sensitivity system with reflex box so that excursion is minimal even below system tuning. If you need to have small reflex speaker you could use any kind of high pass filter, like output transformer on a tube amplifier. Or line level filter somewhere inside the amp or before it. Amplifiers have some (high) input impedance so (small) capacitor in series with input would make simple line level high pass filter.

An old trick: use closed box and current output amplifier, driver resonance is not damped electrically because high series impedance in the circuit so you'd get some boost from that, no need for bass reflex box to do resonance and boost. With voltage output amplifier, that have very low output impedance by definition, one can increase impedance in the circuit by adding (big) series capacitor. This would also let the woofer resonance run free and make some bass boost.

Thanks for the info, I think I'll probably go with the inline filter before the amp if I do use them as a stereo setup, seems like the easiest option for me, mostly be used on the reciever anyway though I imagine

 

[Surtsey]

I don't have the technical nous of the others but as as stand-alones I feel these speakers will disappoint. I've owned many pairs: from JBL Control 1 to Wharfedale Diamond V but I've never owned a set of small speakers that could satisfactorily fill a room. The Dayton's a SPL of 82dB is not a promising start.
I'm thinking even the Monacor may model better.

 

[Dameo182]

I say just go for 2 'subs' so you can make it a 2 way without all the compromises. I've tried the "magic trick" of satellites with mystery bass, and the execution can be tricky...

I had 15L boxes for the the satellites and the baffle step went up to 700Hz approx.

Even 24dB/oct crossovers let through muffled voices and other such sounds that gave away the sub's position. A 7th order Bessel filter finally nailed it, but then I didn't know how to sum the L+R channels "correctly" - because there is no right answer! You either get amplitude summing (pure mono) or power summing (stereo), and it changes from one to the other, depending on how apart the satellites are spaced. Not to mention occasional fun signals that deliberately switch polarity between left and right, which a mono sub won't reproduce.

As for the Alu boxes, I say try and make them resemble a stereotypical raindrop or heart shape, with the pointy end stretched back for good diffraction. A sphere is not so great for diffraction because of how the wave converges back in on itself.

I probably will go for two small subs, it all depends on if I can find the space, and I would have liked to give the box more of a shape but I'm limited from it's small size and the needed width at the back for the port, for this little speaker I'm not too bothered for now, once I've done the measurements I'll be able to see if it's causing any problems and if so I can adjust from there, but I get what you mean about making it more 'streamlined' if possible.

 

[Dameo182]

I don't have the technical nous of the others but as as stand-alones I feel these speakers will disappoint. I've owned many pairs: from JBL Control 1 to Wharfedale Diamond V but I've never owned a set of small speakers that could satisfactorily fill a room. The Dayton's a SPL of 82dB is not a promising start.
I'm thinking even the Monacor may model better.

Yeah I did have the same concern at first, but in winisd with 24watts signal power it's showing an spl of 95db, and tbh I bet I don't listen past 85db most of the time. The speaker I posted on the first page uses the nd65 which has a sensitivity of 83db, and that speaker is pretty loud with good bass, granted theres two of them and it's 4ohm but if these manage to get close to how that sounds I'd be fine with that, and bear in mind the room this is going in is 4.2 metres square so it is tiny. Typical terraced house dimensions 😂