DIY - 212 cabinet - help with ports calculation

[ThisBass]

I really do suspect that dollars does figure into it. After you've spent $10-20K on a power amp, it might be hard to justify spending another bunch of bucks on another one. Spending mega-bucks on the most pristine signal path, but then pushing the final signal through a passive crossover, no matter how exquisitely designed, just doesn't add up for me. It's kind of like putting Firestones on your Ferrari. On the other hand, for my ordinary plebian listening environment at home, passive crossovers are good enough...at least as far as the trade-off of the additional complexity goes. Plus the old Spouse Approval Factor starts to figure in.

Now I guess I'll pull on the old flame suit for when the Firestone tire aficionados start in on me.

Uhm, in this case I'd also question if it makes anyway sense to power any loudspeaker.
The signal chain (and power amp) might be suitable to "reinforce" the "bang" of an exploding ballon but, no cab device will ever "accurately" push this sound into the room. I don't think a passive crossover does noticable "hurt" the inappropriate speaker quality a lot.
Filter properties are valid for any filters which in practice addresses to either passive or active filters.
Of course there is a difference regarding losses but, even in this case its possible to "overthink" the filter math beyond comprehension.

 

[Redbrangus]

Filter properties are valid for any filters which in practice addresses to either passive or active filters.

It's true of the mathematics, I guess. But one can build a filter with an IC op-amp and a handful of cheap passive components that will exhibit markedly better linearity, etc. than the finest, most expensive passive one. Or at least I think so...am I mistaken?

 

[Redbrangus]

Phase shift is kinda most overthinked issue with filters and I think very often poorly understood even by engineers.

I mostly agree with this, especially the part about it being poorly understood. BUT...when digital signal processing came into the sound reinforcement world and it became possible to electrically time-align all the drivers in a speaker system, it made a very audible difference in the end product. I had always presumed that was because of the improved phase coherence. Or am I perceiving some other effect?

 

[ThisBass]

It's true of the mathematics, I guess. But one can build a filter with an IC op-amp and a handful of cheap passive components that will exhibit markedly better linearity, etc. than the finest, most expensive passive one. Or at least I think so...am I mistaken?

If you keep a close look to the non linearities of a generic loudspeaker you may notice that rather smallish non linearities of a passive crossover does not change tons on the total performance.

I'm not sure if a low current (low power) OP amp really provides better tonal results versus a passive crossover.
If in doubt I'd prefer passive crossover versus low power OP amp "active" crossover cause too many OP amps "color" the sound at some content more or less

 

[Redbrangus]

I guess I never looked at it that way; that some op-amps sound bad, so all circuits containing op-amps have inferior performance.

But at any rate, all I did was offer an opinion on what I felt was a better alternative to the circuit the OP was proposing, while still being something fairly easy to design and build...I wasn't intending to get into a p*ssing-match with anyone about it. No hard feelings intended, but I never did actually get what your point is, other than higher-order filters are superior to lower-order ones, and that--mathematically--filters are filters, regardless of whether they are realized in a low-power circuit or a high-power one. If you've got an actual alternative suggestion for the OP, I'm sure it will get respectful consideration here, but if you don't, don't just sit on the sidelines and snipe...any jackass can kick down a barn. Just saying.

​

My apologies to all for the rant. Hopefully, we can now return to our regularly scheduled programming. Good day.

​

 

[agedhorse]

The largest improvements due to active crossovers are IMO lower insertion losses and much improved filter response because the filters aren't driving a wildly varying impedance.

 

[ThisBass]

I guess I never looked at it that way; that some op-amps sound bad, so all circuits containing op-amps have inferior performance.

I wouldn't call it bad but some do sound different.
In my experience the ones which draw lots of current sound better than "low power" op amps.
There is this triangular relationship of
current draw
noise floor
slew rate
which roughly "trades off" op amp properties versus desiered application properties.

Basically the schematic design of an op amp equals very much the design of an power amplifier.
It makes no wonder that different op amp design may color the sound in a different way.
Old school TL072 sounds different versus old school low power TL062.

So why not do just the same job with simple passive L and C instead of a complex linear chip.

The OP intends to crossover a HT device to a woofer.
I think we should keep the things as simple as possible in this regard.

 

[agedhorse]

So why not do just the same job with simple passive L and C instead of a complex linear chip.

Because it's generally not the device that causes the coloration as much as the interface of the passive L & C driving a complex load. This means that the active filters driving restive are almost always many times more linear and well behaved than with a passive crossover driving a reactive load.

 

[Redbrangus]

So why not do just the same job with simple passive L and C instead of a complex linear chip.

In my world it's because we're dealing with dozens of speaker systems at a time dissipating thousands of watts, among other reasons. Plus, we really do benefit from being able to manipulate the various pass-bands in the time domain. But, as I said, I'm fine with passive crossovers for my own home listening environment, I just don't understand why in the audiophile world--you know, where the lunatics roam--they don't embrace active crossovers more enthusiastically. I mean, if they're willing to spend fabulous amounts of money to squeeze the last ounce of performance out of their systems, that seems like a logical place to begin...not trading in their $8K preamp with .0001% harmonic distortion for a $12K one with half as much distortion, or upgrading from $500 cables to $700 ones. If I understand what you're saying, the passive crossover doesn't contribute as much non-linearity as the loudspeaker components themselves, so it really doesn't matter that much. I'm not sure I agree with that if one is trying to build an Uber-system, which is what the lunatic fringe guys are doing.

Oops...I thought I was done ranting. Apologies all...apologies most especially to you, @ThisBass.

 

[ThisBass]

Because it's generally not the device that causes the coloration as much as the interface of the passive L & C driving a complex load. This means that the active filters driving restive are almost always many times more linear and well behaved than with a passive crossover driving a reactive load.

I agree for power density at the lows or low mids around 800Hz.
The OP wants to crossover a HT device at highish mids where we do have only little stored reactive power.
At the high mids content in my experience swapping of OP amps may cause more deviation to the total sound vers the question if the signal path was crossovered active or passive.

 

[Redbrangus]

Because it's generally not the device that causes the coloration as much as the interface of the passive L & C driving a complex load. This means that the active filters driving restive are almost always many times more linear and well behaved than with a passive crossover driving a reactive load.

Plus, what he said.

 

[ThisBass]

In my world it's because we're dealing with dozens of speaker systems at a time dissipating thousands of watts,

While the OP still wants to build a 212 bass guitar cabinet and wants to have some extended top response.

 

[Redbrangus]

While the OP still wants to build a 212 bass guitar cabinet and wants to have some extended top response.

I didn't advise the OP to use an active crossover...I suggested a passive high-pass filter of a simplistic design. And I acknowledged that I don't know as much as I would like about passive filters because they never had much relevance in my (admittedly) narrow domain. They still don't, but I'm wanting to learn how to tweak some of the things I've got.

 

[ThisBass]

I didn't advise the OP to use an active crossover...I suggested a passive high-pass filter of a simplistic design. And I acknowledged that I don't know as much as I would like about passive filters because they never had much relevance in my (admittedly) narrow domain. They still don't, but I'm wanting to learn how to tweak some of the things I've got.

Same approach on my side because of,
he could start at around 3.5kHz with a Butterworth alignment and then decrease C to get higher crossover numbers to figure "sweet spot" for best personal taste.
Interestingly he would succesively graduate from Butterworth alignment to Linkwitz the more he was increasing the crossover point by decreasing the magnitude of C.

 

[JimChjones]

While the OP still wants...

It's a fascinating digression though - at least I find it so. Crossovers seem to be one of those subjects that are superficially very simple, but the more that I learn it's the less I seem to know...

 

[KoziejMaclowski]

Basicly my plan for now after building cab, is install woofers and HF, and measure separately them, and after that I will be able to do some more calculations about crossover. F Response vary depends on everything. Have some spare caps so I will be able do some initial tests.
I'm waiting for delivery MDF (front panel), and looking for baltic / polar brich.

I was thinking wave from tweeter will not diffract from left edge of panel, but since I going to instal wave guide it shouldn't. I hope so.

I think that's final design:

 

[bbh]

Very nice but it just looks sooo heavy.

 

[Redbrangus]

I heard that poplar wood is also recomended? Is that right?

Yes to birch plywood, no on the poplar. I've seen the guitar cab weirdos use poplar solid wood as a substitute for their beloved pine, but don't get me started about all that. Over here, true Baltic birch is kind of expensive and also getting more difficult to source. We have import stuff from China, derisively referred to as 'China birch' by cabinet-makers, that's cheaper, but it's not appropriate for our purposes--the outer faces look nice enough, but the inner veneers are horrible. We also have other imported products that are variously called Finnish birch or Russian birch, but it's not clear to me that those are anything different (inferior?) than products called Baltic birch...I mean, Finland and Russia are both "Baltic", aren't they? (I guess Russia only on a technicality) At any rate, given your closer proximity to where it's grown, I would think Baltic birch would easier to acquire, but it sounds like maybe not so much.

I glanced back through the thread but didn't see it...remind me of how thick your side and back panels are?

 

[KoziejMaclowski]

Yes to birch plywood, no on the poplar. I've seen the guitar cab weirdos use poplar solid wood as a substitute for their beloved pine, but don't get me started about all that. Over here, true Baltic birch is kind of expensive and also getting more difficult to source. We have import stuff from China, derisively referred to as 'China birch' by cabinet-makers, that's cheaper, but it's not appropriate for our purposes--the outer faces look nice enough, but the inner veneers are horrible. We also have other imported products that are variously called Finnish birch or Russian birch, but it's not clear to me that those are anything different (inferior?) than products called Baltic birch...I mean, Finland and Russia are both "Baltic", aren't they? (I guess Russia only on a technicality) At any rate, given your closer proximity to where it's grown, I would think Baltic birch would easier to acquire, but it sounds like maybe not so much.

I glanced back through the thread but didn't see it...remind me of how thick your side and back panels are?

18mm. Front 19mm

 

[Redbrangus]

Excellent. I guess I was thinking of a different thread where the builder was planning on using 8mm ply. (!) I understand people wanting to make lighter bass cabs, but one can go overboard.