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Considerations when plugging ports — what else happens beyond bass response?

nothingman

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I’m considering plugging the port of my LS50 Metas and wondered if there are other considerations than simple bass response.

See Amir’s review measurement below, where I circled the port resonance in the midrange.

E2C0CE02-B8EA-4EC5-9958-6804D7594680.jpeg


This measurement got me thinking I would achieve more midrange clarity if I plugged the port, and I assume it would lower overall group delay in the bass as well.

What I’m wondering is what else does plugging the ports do? Am I messing up how the mid-driver performs elsewhere in the frequency response? Is plugging a port known to introduce new resonances or breakup of a mid-driver, or create distortion or limit the SPL or anything? Does it mess with the impulse response or phase? Or does plugging the port only help everything about the speaker performance except for the low bass? I haven’t seen this answered.

Background:

I’m using a miniDSP SHD with Dirac and a single KC62 sub.

Per the standard instructions, first I tested and implemented the high-pass and low-pass filters and then used REW acoustic timing reference to time-align the sub with L+R and got the sub volume level in the ballpark then I ran Dirac measurements and filters.

HPF for the LS50 is set to 100hz BW 2nd order (12db/oct)
LPF for the KC62 is set to 80hz LR 4th order (24db/oct)

Plugging the port would of course come at expense of raw bass output from the port, but I think my KC62 and room gain in the region can mitigate that fine. That said, if I try plugging the ports I would start the whole integration process from the beginning and experiment with dropping the BW2 HPF down to 90 or 80hz but no lower.
 
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fpitas

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A lot of people plug reflex ports, usually because room gain or modes are making the speaker boomy, or they just prefer the sound of sealed. The midrange should be more or less unaffected. Sometimes you can get a good compromise with some absorber in the port. Some Acousta-Stuf for example might absorb the mdrange you circled while not eliminating the bass output entirely.

Be aware though, if you EQ the bass up after sealing the port, the resulting extra cone motion might become audible as intermod. With a sub though, you should be OK.
 
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nothingman

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Except the LS50 is a two-way bookshelf and there are no cabinet separations. It’s a hollowed out 5.25” driver with the surface area of something more like a 4” conventional driver, but it’s the only thing producing bass with the port.

The speakers come with fairly malleable foam plugs, so that’s what I would use.
 

fpitas

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Except the LS50 is a two-way bookshelf and there are no cabinet separations. It’s a hollowed out 5.25” driver with the surface area of something more like a 4” conventional driver, but it’s the only thing producing bass with the port.

The speakers come with fairly malleable foam plugs, so that’s what I would use.
Yeah, I fixed that. Thought we were talking about Blades for some reason.
 

fpitas

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nothingman

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Yeah, I fixed that. Thought we were talking about Blades for some reason.

Gotcha. I should have quoted your original text, just so people could see for context (the gist is that it was suggested that the mid-driver is in a separate internal enclosure than the port, which isn’t the case for a two-way like LS50).

Wish I had Blades!!! Best speaker I’ve ever heard.

Be aware though, if you EQ the bass up after sealing the port, the resulting extra cone motion might become audible as intermod. With a sub though, you should be OK.

That’s exactly the sort of consideration I’m asking about, thanks. I agree I would have to be careful I’m not giving back anything gained by lower port resonance by pushing the mid harder and thus increasing IMD from the coax design. That may be hard to control given the layers of filters and with Dirac not being aware it’s actually EQing L+R+Mono Sub instead of three separate units. Really wish miniDSP would tell us if Dirac Live Bass Control is possible for the SHD series. That would make all the difference here.
 

fpitas

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Gotcha. I should have quoted your original text, just so people could see for context (the gist is that it was suggested that the mid-driver is in a separate internal enclosure than the port, which isn’t the case for a two-way like LS50).

Wish I had Blades!!! Best speaker I’ve ever heard.



That’s exactly the sort of consideration I’m asking about, thanks. I agree I would have to be careful I’m not giving back anything gained by lower port resonance by pushing the mid harder and thus increasing IMD from the coax design. That may be hard to control given the layers of filters and with Dirac not being aware it’s actually EQing L+R+Mono Sub instead of three separate units. Really wish miniDSP would tell us if Dirac Live Bass Control is possible for the SHD series. That would make all the difference here.
As long as your sub goes up to (say) 100Hz, I think you'll be fine.
 

thewas

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When you anyway use a subwoofer and highpass your loudspeakers it is usually advantageous to close the ports as you reduce the mid noise coming out of them and usually you make the dropping slope more continuous and easier to match to the subwoofer slope. Personally I have closed all ports of both my subs and my two LS50 and LS50 Meta setups.
 

Holdt

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Gotcha. I should have quoted your original text, just so people could see for context (the gist is that it was suggested that the mid-driver is in a separate internal enclosure than the port, which isn’t the case for a two-way like LS50).

Wish I had Blades!!! Best speaker I’ve ever heard.



That’s exactly the sort of consideration I’m asking about, thanks. I agree I would have to be careful I’m not giving back anything gained by lower port resonance by pushing the mid harder and thus increasing IMD from the coax design. That may be hard to control given the layers of filters and with Dirac not being aware it’s actually EQing L+R+Mono Sub instead of three separate units. Really wish miniDSP would tell us if Dirac Live Bass Control is possible for the SHD series. That would make all the difference here.
It's true that Dirac doesn't know there is a sub. But before you run Dirac you have setup your crossover, right? -So actually from crossover and below Dirac is in fact only measuring and EQ'ing the sub as it's the only driver responding to the low frequencies anyway.
 

solderdude

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Dirac doesn't know anything. It measures the response and produces data to alter the response of the signal to a set target at the point where the microphone is.
The response 1m away from that point may be very different.
 
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Tangband

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I’m considering plugging the port of my LS50 Metas and wondered if there are other considerations than simple bass response.

See Amir’s review measurement below, where I circled the port resonance in the midrange.

View attachment 242002

This measurement got me thinking I would achieve more midrange clarity if I plugged the port, and I assume it would lower overall group delay in the bass as well.

What I’m wondering is what else does plugging the ports do? Am I messing up how the mid-driver performs elsewhere in the frequency response? Is plugging a port known to introduce new resonances or breakup of a mid-driver, or create distortion or limit the SPL or anything? Does it mess with the impulse response or phase? Or does plugging the port only help everything about the speaker performance except for the low bass? I haven’t seen this answered.

Background:

I’m using a miniDSP SHD with Dirac and a single KC62 sub.

Per the standard instructions, first I tested and implemented the high-pass and low-pass filters and then used REW acoustic timing reference to time-align the sub with L+R and got the sub volume level in the ballpark then I ran Dirac measurements and filters.

HPF for the LS50 is set to 100hz BW 2nd order (12db/oct)
LPF for the KC62 is set to 80hz LR 4th order (24db/oct)

Plugging the port would of course come at expense of raw bass output from the port, but I think my KC62 and room gain in the region can mitigate that fine. That said, if I try plugging the ports I would start the whole integration process from the beginning and experiment with dropping the BW2 HPF down to 90 or 80hz but no lower.
A closed box falls in theory 12 dB/oct below the loudspeakers resonance frequency. A ported loudspeaker falls in theory 24 dB/ oct below the box resonance frequency.

If you use an AVR as a crossover, they are often 12 dB HP ( for main speakers ) and 24 dB LP ( subwoofer ) = THX standard . This demands closed main speakers ( plugged ) . The result will then be 24/24 acoustical for main speakers and subwoofer.

You can also get good results with 24/24 HP/LP crossovers with ported main loudspeakers, but all this depends on the flexibility of your dsp crossover. You might need to fine tune .

For a really good sound, one needs to get all those crossover topologies right before even thinking about using Dirac or other room correction software.
 
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nothingman

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This revived conversation is appreciated. However, I was hoping to hear more on what else plugging ports does beyond affecting the bass response slope. I have REW and can measure that just fine and overall I‘d say I have good integration to my single sub.

What I was wondering about was stuff I don’t know anything about, like resonances, woofer break-up, IMD, excursion considerations, maybe impedance, etc, etc, etc. I’m just throwing out stuff I figured might be affected, with the end result being, “your port plugs fixed one problem (the port resonance peak), but they caused X, Y, and Z problems in the process, so leave them be.”

Anywho, still very interesting!
 

ZolaIII

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Soniclife

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This revived conversation is appreciated. However, I was hoping to hear more on what else plugging ports does beyond affecting the bass response slope. I have REW and can measure that just fine and overall I‘d say I have good integration to my single sub.

What I was wondering about was stuff I don’t know anything about, like resonances, woofer break-up, IMD, excursion considerations, maybe impedance, etc, etc, etc. I’m just throwing out stuff I figured might be affected, with the end result being, “your port plugs fixed one problem (the port resonance peak), but they caused X, Y, and Z problems in the process, so leave them be.”

Anywho, still very interesting!
Did you see the following thread?
 

Soandso

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As I understand it from my old ASR notes: a port creates a relatively steeper octave cut-off at high dB listening levels inducing relatively increased phase shifts, which causes relatively more group delay resulting is musical transients sounding not quite as precise as otherwise. Whereas plugged ports mitigate those dynamics providing relatively greater sound articulation within an increased dynamic range
 

Tangband

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This revived conversation is appreciated. However, I was hoping to hear more on what else plugging ports does beyond affecting the bass response slope. I have REW and can measure that just fine and overall I‘d say I have good integration to my single sub.

What I was wondering about was stuff I don’t know anything about, like resonances, woofer break-up, IMD, excursion considerations, maybe impedance, etc, etc, etc. I’m just throwing out stuff I figured might be affected, with the end result being, “your port plugs fixed one problem (the port resonance peak), but they caused X, Y, and Z problems in the process, so leave them be.”

Anywho, still very interesting!
You can read about how ATC or Linn does it and about aperiodic bass tube loudspeakers with much damping material inside the box blocking the port from the inside. You get a behaviour much like a closed box but the advantage of higher spl/ cone damping just like a normal ported speaker. plugging the ports in your speaker with soft somewhat leaky materials ( socks ? ) will give you a similar response.

 

Rick Sykora

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See if this helps as I had modeled plugging the port on a small speaker based on the Purifi 6.5 woofer.

You can find it here.
 
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