Sealed vs Ported Subwoofers

A ported enclosure can be 3dB more efficient at the same size or play a quarter octave lower at the same efficiency.

The same driver excursion will net you perhaps an extra 1/3 octave of extension with a ported speaker.

You'll have higher excursion limited output in the bottom of a ported design's pass-band so you can use smaller + less expensive drivers.

Distortion will also be lower in the bottom of the speaker's pass-band with the port because of the reduced excursion.

Ported enclosure+driver combinations have four poles in their high-pass function for an eventual 24dB/octave roll-off function while sealed ones have just two for 12dB/octave. With sufficiently shallow roll-off room gain (12dB/octave in an infinitely rigid room below its fundamental resonance at 1130 / 2 / the longest dimension) can keep the speaker flat below its roll-off.

Ported enclosures do not load the driver once you get below the port tune, with excursion increasing to what it would be in free air. Where too much low frequency energy is present below the speaker's pass-band you'll have distortion (including midrange IM distortion on 2-way speakers) and may even run the drivers into their mechanical limits resulting in damage (some very nice drivers will bottom the voice coils on the back plate). For a given input level sealed speaker excursion remains constant with decreasing frequency.

Drew,

Your comments remind me of the experience I had with a pair of Tannoy 15 inch Dual Concentrics I bought in 1956. They were $159 each new, whew! I put them in Hartley Boffle enclosures I built, who remembers what they were?

I drove them with Marantz model 2 amps and the voice coils bottomed out on the back plate continually. I sold them to a friend in 1962 after I built a pair of Electro Voice Patricians that rattled all the windows in my parents home. He kept them until a few years ago when he sold them; I wish I could've bought them back!

A great loudspeaker is like a great woman; If you find one, don't let her go as you may never find another.

Ken

Bob, You are correct, sealed woofers do roll off @ 12db per octave. My fingers are faster than my head. Everything else is accurate. I have built several woofers in my time. The best we did back in my old SpeakerCraft/Marcof days was a woofer facing up in a encloser that had 4 ports also facing up, it had an identical section with a woofer firing down. The four ports on both sections were joined by PVC, so the top & bottom chambers were ported into each other. There was about a one inch gap between them. We made these to look like an end table, they had the benefits of a ported system, kinda like a passive radiator, yet still rolled @ 12db per octave. I haven't seen this done anywhere else. Ed Martin designed this and it was very good indeed.
If a driver has enough LINEAR excursion, I still prefer a sealed system, but I have zero issue sitting down to a good ported design anyday.

Thanks everyone for taking the time to reply to my post. I still have to get my head around some of the information. I'll wait until my basement is finished and I have time to enjoy my system before I make any decisions.

Cheers

Jim