Free air resonance

Very complex question i am not competent to answer...

I did not need to study this question because i dont have a sub...

But the answer is there...

https://rmsacoustics.nl/papers/whitepaperbassreflex.pdf

@unreceivedogma , 1+ @mahgister  Subwoofer drivers have a long list of characteristics that defines the size and type of enclosure. Both of your drivers might be usable in sealed enclosures and ported enclosures or only in one or the other. Read this https://en.wikipedia.org/wiki/Thiele/Small_parameters.

Having said all this and just having finished the construction of a new set of subwoofers, you can pick a driver suited to small sealed enclosures with as low an Fs as possible and with a lot of power and digital signal processing make it do whatever you want. A large B X L product ( above 25 T.m) helps a lot. You can push a sealed enclosure lower than a ported one. The ported one will go lower before rolling off but then drops off like a cliff. The sealed sub will start rolling off earlier but will continue to have useful output down lower.  This is a very cursory explanation of a complicated design process. I hate math. 

Thanks mijostyn.

I never think about that because i never need a sub or i did not want to bother me with one...

 But bass frequencies are necessary...For sure... My headphone deep bass is enough for me now...

@unreceivedogma , 1+ @mahgister  Subwoofer drivers have a long list of characteristics that defines the size and type of enclosure. Both of your drivers might be usable in sealed enclosures and ported enclosures or only in one or the other. Read this https://en.wikipedia.org/wiki/Thiele/Small_parameters.

Thank you @mijostyn ​​​​@mahgister

This is not about a subwoofer.

The reason I ask is that I have a pair of Altec Lansing 604Cs and I now, as of last night, was able to get a 604D to match the 604D that I already have.

I am currently using the 604Cs. The D was a backup in case one blew. Now that I have two D’s, should I switch?

As far as I can tell, however, the ONLY difference in the specs is the free air resonance.

I will be putting the cabinets on rubber feet designed to isolate them from the wood plank floor so that the building doesn’t become a de-facto loudspeaker. I’d like to close the port so as to make the midrange more detailed. This entails losing some bass, but …

I use a Velodyne ULD15, with an active crossover at 60hz for the bottom.

I’m thinking that a speaker with lower resonant frequency will sound better than the one with a higher resonant frequency.

But is the difference too small to even matter, or are the numbers a logarithmic progression instead of arithmetic and thus the difference bigger than one might think? And, does having an active sub crossover at 60hz make this question moot?

one other question: the cabinets are DIY, made of 3/4 ply with a veneer, geometry and materials to Altec specs standard in the day (1950s/60s). Would the bass benefit by stiffening them with another 3/4 layer of ply or solid wood on the interior? If so, do I stiffen all 6 sides, or would just the 4 perimeter sides (not front and back) suffice?

Also, someone told me that one mechanical difference between the two is that the stock C used a paper surround and the stock D used an accordion surround. As Cs are today almost always reconed with the accordion surround (mine are), and as the materials of the cone help determine the free air resonance, simply reconing the C allegedly makes it a D.

And yes, while I did once have a high math aptitude I’m these days inclined to look for layman’s answers to these questions, or as simple as possible.  

Thoughts?

Thank you again.

Ask erik_squires he is very helpful...

He know basic acoustic ...

He know a lot about speakers design, he created some,  and i know nothing useful for you  for this complex problem solution  ...

Thank you @mijostyn ​​​​@mahgister

This is not about a subwoofer.

The reason I ask is that I have a pair of Altec Lansing 604Cs and I now, as of last night, was able to get a 604D to match the 604D that I already have.

I am currently using the 604Cs. The D was a backup in case one blew. Now that I have two D’s, should I switch?

As far as I can tell, however, the ONLY difference in the specs is the free air resonance.

I will be putting the cabinets on rubber feet designed to isolate them from the wood plank floor so that the building doesn’t become a de-facto loudspeaker. I’d like to close the port so as to make the midrange more detailed. This entails losing some bass, but …

I use a Velodyne ULD15, with an active crossover at 60hz for the bottom.

I’m thinking that a speaker with lower resonant frequency will sound better than the one with a higher resonant frequency.

But is the difference too small to even matter, or are the numbers a logarithmic progression instead of arithmetic and thus the difference bigger than one might think? And, does having an active sub crossover at 60hz make this question moot?

one other question: the cabinets are DIY, made of 3/4 ply with a veneer, geometry and materials to Altec specs standard in the day (1950s/60s). Would the bass benefit by stiffening them with another 3/4 layer of ply or solid wood on the interior? If so, do I stiffen all 6 sides, or would just the 4 perimeter sides (not front and back) suffice?

Also, someone told me that one mechanical difference between the two is that the stock C used a paper surround and the stock D used an accordion surround. As Cs are today almost always reconed with the accordion surround (mine are), and as the materials of the cone help determine the free air resonance, simply reconing the C allegedly makes it a D.

And yes, while I did once have a high math aptitude I’m these days inclined to look for layman’s answers to these questions, or as simple as possible.

Thoughts?

Thank you again.