The Oldest problem in hi-fi: Ported, PR, Sealed Box or OB ?

[Xaborus]

I find room gain tends to increase bottom end at 3-6 dB/octave below about 120ish Hz so I like tuning at frequencies seemingly too low for the box, which rolls off the response considerably higher than the usual case. It does rob a bit of sensitivity in the lower midbass but around 20 Hz and lower are improved. Pipe organs are great fun.

The curves below show this in action: the green line shows my default cabinet and the yellow line shows what happens when I stuff a sock in one of the two ports. The first case sounded a bit lumpy in the bottom end, with not much articulation between bass and drums. The second case, while not as immediate with WOW!ful bass, feels more transparent as bass and drums are now distinct entities. It's not exactly shy with bottom end either: both woofers turned up can rattle various bits of the house. Add in a 16 Hz highpass to keep the cones from sailing across the room, along with a touch of Linkwitz Transform, and the world is my oyster.

View attachment 836453

I was wondering how people were tuning their potted cabinets for room gain. Thanks!!

 

[camplo]

A constant CSA TL stuffed till backwaved is muted...has no box issues...but you dismissed it?

1.

I don't see how the resonances problem would be fixed with a tapered TL or similar.

Tapered will shorten the design...longer paths eat more backwave (via damping material) so if you find tricks to shorten the line length ( taper/mass loading) you have to compensate by increasing damping material density...

Passive radiator is a waste isn’t it? What is accomplished by a passive radiator that cant be accomplished better by adding an active radiator instead?

As for ported tuning I created a post on tuning for SQ that was controversial, I suggested tuning to half of cutoff just like any other horn I mean vented I mean ported I mean...

 

[Bill poster]

Havent read thread but decided to go sealed on latest build. Modern amps are much more efficient, which negates one drawback. With BR's, bass control with any woofer tuned above say, 32hz. It's going to flap around with sub 30hz bass. I realised after listening to a vintage pair of sealed Linn's that I much preferred the sealed sound. Plus with room gain, there is adequate bass output below 40hz or so, without that drop off a cliff response

 

[JonBocani]

No problem JonBocani!

The BondedLogic product has the highest NRC profile of any product I've seen on the market. Its normal house insulation, so it should very readily available. And kid-friendly too!

If you find a project that you want to do this on, but cant fit the 3.5" bonded logic or your 3" rockwool, this is the highest performance 2" product I've found.

https://www.soundproofcow.com/skin/common_files/pdf/echo_absorber_acoustic_panel_pds.pdf

Even better, thank you!
2'' thickness ... NRC 1.32 @ 500hz...

I consider testing combinations of different materials on each enclosure's walls, to control different frequencies.

 

[ErnieM]

I use bonded logic for absorbing the backwave of my open baffles. Works great.

Didn't know about soundproofcow. Thanks!

 

[DSP_Geek]

I was wondering how people were tuning their potted cabinets for room gain. Thanks!!

Well... this isn't the usual way vented boxes are tuned. Most examples I've seen tend to go for maximally flat Butterworth-ish type tunings, but IMHO those only sound good in large rooms. I did have a woofer designed to reproduce blue whale songs for an art exhibit, flat to 17 Hz; even with a couple hundred watts it rattled a DIYAudio fest some. 😀

I think another reason some folks prefer sealed boxes is their more gradual rolloff at 12 dB/octave, whereas vented are fourth order systems so the rolloff tends to 24 dB/oct below Fb. Now why might this matter? Imagine you're listening to music, and the bass notes go lower, lower, then right when the deepest should be vibrating your very soul the fundamental suddenly drops 6 dB when notes a third up were still full. It's a disappointment. However, by tuning the system rolloff so you don't have a sharp corner as you might with 4th order Qtc >= 0.707 then the contrast isn't so drastic so the ear will be more forgiving, and as a side benefit you get the advantage we discussed earlier of a better interface between box and room for flatter actual response.

 

[weltersys]

You can measure the sound coming back through the cone from reflections inside the cabinet. I did this using a function generator, a microphone and a scope.
Brian

Brian,

The reflected sound energy in your pictorial appears to be attenuated from the inverse distance as well as the cone blockage.

What was measured level difference in dB between the direct vs the reflected?

Art

 

[DSP_Geek]

Experimenting with this wasn't exactly high tech. My current woofers were tuned for Fb = 28Hz Qtc = 0.55 but the bottom felt lumpy to me, so I retuned the system to fB = 19 Hz Qtc = 0.35ish as shown in the graphs earlier.

Some might think this entailed a new box. I got there by the High Technology expedient of jamming a sock in one of the two ports. Worked okay. 😛

 

[DSP_Geek]

Havent read thread but decided to go sealed on latest build. Modern amps are much more efficient, which negates one drawback. With BR's, bass control with any woofer tuned above say, 32hz. It's going to flap around with sub 30hz bass. I realised after listening to a vintage pair of sealed Linn's that I much preferred the sealed sound. Plus with room gain, there is adequate bass output below 40hz or so, without that drop off a cliff response

Hey, I like vented boxes, but I hear you completely. Have fun storming the castle!

 

[brig001]

Brian,

The reflected sound energy in your pictorial appears to be attenuated from the inverse distance as well as the cone blockage.

What was measured level difference in dB between the direct vs the reflected?

Art

Hello Art, I’m sorry, I can’t remember exactly and can’t find the photo now. I seem to remember it was about 1/10 on the scope. so about -20dB without any treatment to the magnet or cabinet. I got it so I couldn’t measure either on the scope, but the clicks were driving me mad at that point as I didn’t have a storage scope

Brian