DIY - 212 cabinet - help with ports calculation

[seamonkey]

Another vote for Bill Fitzmaurice Simplex
The corner ports help brace the cab. Low level of complexity.

There is no perfect single driver, so there is room in the simplex to add a mid/tweeter if you find you need one.

If not, then at least build a prototype from MDF, test, measure, recalculate, adjust, then maybe build the finale. There is always some surprise and it will be like you'll always hear what you got wrong unless you have a chance to try and correct it.

 

[ThisBass]

Ok so having two ports I can make two separate baffles?
Also what about air velocity? For 2 ports WinISD shows 24 m/s quite a lot! That's why I would stay with 3 ports I think.

Also can I find somwhere BCH file for faital 12pr300 8hm?

With three ports the front of the cap looks very impressive.

At the other hand side two narrow "stacked" 110mm diameter ports placed on the right bottom corner helps to prevent from resonancies inside the chamber. That's how I was told back in the days by a pro German cab builder with very good reputation.

 

[KoziejMaclowski]

With three ports the front of the cap looks very impressive.

At the other hand side two narrow "stacked" 110mm diameter ports placed on the right bottom corner helps to prevent from resonancies inside the chamber. That's how I was told back in the days by a pro German cab builder with very good reputation.

You're convincing me to build two different panels for ports I think I will make two different panels and test it!

You can lead a horse to water.........

BTW @KoziejMaclowski welcome to Talk Bass.

Hey thank you!

 

[ThisBass]

Some considerations regarding (theoretical) air velocity 24 m/sec

You'd have to push 600 Watt at ~50Hz with sunusoidal waveform to reach 24 m/sec.
In real pratice the total power spreads along a broadband bandwidth with distinct "power density" rather than (theoretical) power at a distinct frequency point.
For bass guitar power density is quite high at the lows but as long as you don't play sine waves you will not be able to reach 24 m/sec at 50Hz.

A bass guitar in real practice can't push all the amplifier power into a singular frequency point.

 

[KoziejMaclowski]

Some considerations regarding (theoretical) air velocity 24 m/sec

You'd have to push 600 Watt at ~50Hz with sunusoidal waveform to reach 24 m/sec.
In real pratice the total power spreads along a broadband bandwidth with distinct "power density" rather than (theoretical) power at a distinct frequency point.
For bass guitar power density is quite high at the lows but as long as you don't play sine waves you will not be able to reach 24 m/sec at 50Hz.

A bass guitar in real practice can't push all the amplifier power into a singular frequency point.

Well explained! Which one? And making separately baffles is a good idea?

 

[ThisBass]

Thought issue on my side.

@KoziejMaclowski

With two ports you will miss the possibility to tune the cab to your needs with the easy adjustable length of the Monacor ports cause port length will be too small

Furthermore the two "seperated" chambers for ports and drivers should aready help to prevent resonance inside the chamber.

So in total I'd give a go for the "three ports" design.

 

[KoziejMaclowski]

Thought issue on my side.

@KoziejMaclowski

With two ports you will miss the possibility to tune the cab to your needs with the easy adjustable length of the Monacor ports cause port length will be too small

Furthermore the two "seperated" chambers for ports and drivers should aready help to prevent resonance inside the chamber.

So in total I'd give a go for the "three ports" design.

I'm not sure how monacor is assembled. Maybe some small modification will provide adjust between 5-10 cm

 

[ThisBass]

Well explained! Which one? And making separately baffles is a good idea?
View attachment 3440826 View attachment 3440827

With two ports I'd narrow "stack" the ports like shown in pic #1 but place both ports at the bottom like shown for the bottom port in pic #2.

While others may argue that a bottom and upper port like shown in pic #2 helps to improve thermal handling due to improved interchange of air.

 

[ThisBass]

I'm not sure how monacor is assembled. Maybe some small modification will provide adjust between 5-10 cm

Ports are anyway cheap.
You may start at 55Hz tuning and evaluate the tonal outcome with the bass guitar.
In the second step you may want replace the ports with ports of some different port lenght to get either higher or lower tuning and again evaluate the outcome.
Its a good idea to "evaluate" the sound performance as well with the band playing (for example at rehearsal).

 

[KoziejMaclowski]

Ports are anyway cheap.
You may start at 55Hz tuning and evaluate the tonal outcome with the bass guitar.
In the second step you may want replace the ports with ports of some different port lenght to get either higher or lower tuning and again evaluate the outcome.
Its a good idea to "evaluate" the sound performance as well with the band playing (for example at rehearsal).

My worries are about having difference distances between drivers and ports. I know that bass cabs works more on preasure than wave peopagation, but I found somewhere that someone have built 212 and had higher extursion on driver one closer to port. But I can move upper driver to the right, spacing will be more similar, and I will get space for tweeter If I will need in future.

 

[JimChjones]

What about that?

It would worry me that someone would drop a mike stand or something and bang goes my cone. Having said that back in the 80s when we were really broke my band had a very budget monitor which was a cut down old 1*15. That had a wire shelf from an old cooker as a speaker protection grill and it did survive.

 

[ThisBass]

My worries are about having difference distances between drivers and ports. I know that bass cabs works more on preasure than wave peopagation, but I found somewhere that someone have built 212 and had higher extursion on driver one closer to port. But I can move upper driver to the right, spacing will be more similar, and I will get space for tweeter If I will need in future.

I don't think there was a noticeable preasure propagation delay due to some difference of "path length".
If there was ever any smallish propagation delay present the deviation was of no concern.

 

[ThisBass]

It would worry me that someone would drop a mike stand or something and bang goes my cone. Having said that back in the 80s when we were really broke my band had a very budget monitor which was a cut down old 1*15. That had a wire shelf from an old cooker as a speaker protection grill and it did survive.

Just this moment I'm trying to imagine a speaker grill that protects two drivers but lefts three(!) 110mm ports visible.
Sometimes cab design also includes design of art

 

[ThisBass]

Ok I will search how people deal with bending ports. Maybe hot air gun and slowly bend on a glass bottle?


I will have that in mind. That's a beautiful grill but will not do a job..
View attachment 3440554

Here are some renders (forget about screws, I think I will keep them only temporary for tuning):
View attachment 3440556
View attachment 3440557

Suggestion (mind thinking)
four chambers at the right column,
three chambers reserved for the ports and the top chamber in reserve to add a HT device.
The speaker grill might cover (resepectively protect) the 12" drivers while the ports column row remains visible.
The HT device (for example 6" driver) might be protected by a "smallish" ~110mm grill just to match in "visible" way the diameter of the ports

 

[Roxbororob]

View attachment 3440507

Something like that? Back to front but with big hole, so avoiding resonant cavities.

Also I have questnio... crucial for design. How short that distance can be? Comparing to overal baffle depth. (between bass reflex end - rear panel)

Yes, like that. Nice job you are doing.

Since you might be making a two piece baffle, maybe have the ported baffle 1/2" further foward than the speaker baffle. Speaker baffle could have a full length grill flush with the nude ported baffle (what do you think)?

 

[KoziejMaclowski]

Yes, like that. Nice job you are doing.

Since you might be making a two piece baffle, maybe have the ported baffle 1/2" further foward than the speaker baffle. Speaker baffle could have a full length grill flush with the nude ported baffle (what do you think)?

Thanks. I want keep overal design as simple as possible. I don't think i will gig with that speaker a lot, so so just like a nice furniture speaker.

Maybe some thing like that? But i will have to find a way for install that. Maybe these screws around front panel will do the job. I'm thinkging also about adding some faital tweeter with wg101

But not nure if I need it. I have allready put faital 12pr300 in some old cabinet and I dont't feel lack of high frequency.

 

[Redbrangus]

….But not nure if I need it. I have allready put faital 12pr300 in some old cabinet and I dont't feel lack of high frequency.

It's not necessarily the most popular position here at TB, but I'm with you in not needing an additional tweeter.

Even without a grill, I'd recess the baffle board a bit to protect the drivers...after all, they're going to be projecting out beyond the baffle. But it does seem like you're on your way to building a nice looking and good sounding box. Good luck with it...keep us posted when you get your build going.

 

[agedhorse]

Even without a grill, I'd recess the baffle board a bit to protect the drivers...after all, they're going to be projecting out beyond the baffle. But it does seem like you're on your way to building a nice looking and good sounding box. Good luck with it...keep us posted when you get your build going.

Absolutely, recessing is part of the finishing and that's how a typical grill is installed.

Why don't you look and see how other designers (successfully) do this? It seems like you are working really hard to reinvent the wheel, without realizing the the wheel has already been invented.

 

[ThisBass]

It's not necessarily the most popular position here at TB, but I'm with you in not needing an additional tweeter.

If necessary he wants to add a tweeter.

 

[fdeck]

Some considerations regarding (theoretical) air velocity 24 m/sec

You'd have to push 600 Watt at ~50Hz with sunusoidal waveform to reach 24 m/sec.
In real pratice the total power spreads along a broadband bandwidth with distinct "power density" rather than (theoretical) power at a distinct frequency point.
For bass guitar power density is quite high at the lows but as long as you don't play sine waves you will not be able to reach 24 m/sec at 50Hz.

A bass guitar in real practice can't push all the amplifier power into a singular frequency point.

You might be amused by my "waveform based" graphs, which are based on a simplistic model of a bass waveform. It illustrates exactly what you're saying:

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