Free air resonance

Hah, thanks @mahgister - the free air resonance is not, by itself, the most important thing in determining the use of a ported enclosure or not, and certainly nearly useless in determining in-room performance.

The questions of whether this is best as a ported or sealed cabinet is a different question than "what would work well in my room."

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

I think this is not the right way to think about it. The question is driver to cabinet matching and then matching the total speaker (driver in a specific cabinet) to the room. There’s no best answer based on resonant frequency alone.

These questions are best asked in DIYaudio but you can also read the last paragraph here:

https://eminence.com/blogs/blog/sealed-vs-ported-enclosures

@unreceivedogma , Boy are you making like complicated.

The free air resonance of a driver is determined mostly by the mass of the construct (cone, suspension, voice coil and former) and the stiffness of the entire suspension. I doubt you will hear any difference between the drivers. Try them both. 

As for the enclosures, each surface has a resonance frequency. Every enclosure is a symphony of resonances. If you stiffen the walls by doubling up on the plywood you will raise the frequency of those resonances. There is no way to know if that will be better or worse than what you have now. Certainly a very stiff, heavy baffle (the surface to which the woofer is attached) is beneficial. It will limit the transfer of energy to the rest of the enclosure. I think I would leave everything else alone. 

If you really want to make them sing get another subwoofer and a two way crossover. Cross at 100 Hz or even higher. The woofers in that speaker carry a significant portion of the midrange which is being Doppler distorted by bass below 100 Hz. Taking those frequencies away from the Altecs will clean them up  noticeably, very noticeably at higher volumes. 

I was right about you  ... 😊

Your answer make sense for me and help me thanks... I hope it will helpful fot the OP...

Hah, thanks @mahgister - the free air resonance is not, by itself, the most important thing in determining the use of a ported enclosure or not, and certainly nearly useless in determining in-room performance.

The questions of whether this is best as a ported or sealed cabinet is a different question than "what would work well in my room."

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

I think this is not the right way to think about it. The question is driver to cabinet matching and then matching the total speaker (driver in a specific cabinet) to the room. There’s no best answer based on resonant frequency alone.

 

These questions are best asked in DIYaudio but you can also read the last paragraph here:

 

https://eminence.com/blogs/blog/sealed-vs-ported-enclosures

@erik_squires

thank you Eric.

I am working on finishing the room.
All the walls are 5” rock wool.
The gable ceiling is 12” rock wool.
All covered with fire resistant burlap instead of sheet rock.
The floor is hard wood.

Essentially, a semi-anechoic room. Very dead: the difference in sound quality is immediately perceptible as you climb the stairs into the room.

I was told by the guy who built my Futterman OTL3s that stiffening lowers the resonant frequency, but he was also quick to offer that speaker cabinet design is not his area of expertise. What you said about stiffening the baffle only makes good sense, as I would like to decrease the energy flowing through the cabinet walls. 

I think you are really getting confused about how the resonant frequency of a speaker driver (a good thing) works and mixing it up with how cabinet panels resonate (which is completely undesirable). The resonant frequency of a driver is used to model the bass performance in a cabinet in terms of the -3dB point as well as the slope and optimal flatness (Q) of the low end. It has nothing to do with distortion introduced due to imperfect cabinet materials. Along with Qts, and equivalent air mass and other parameters the resonant frequency is something you plug into your cabinet design software.

Driver resonance frequency has zero to do with the materials used or bracing methods used to construct the cabinet itself. The driver resonant frequency also has zero to do with driver value or quality but it is an indicator of the type of driver you have on your hands. A driver with a resonant frequency of 300 Hz is probably not going to go lower than a midrange for instance.

Also, you want diffusion between and directly to the sides and often behind the speakers and listening area. Anything truly anechoic is going to sound too dead, and lack imaging and space.