Integrating subs with Minidsp SHD, should you block main speaker ports?

[Rockdog]

I'm moving to a digital front end with a Minidsp SHD. I have 228be's with front ports, mating with two sealed JL subs. Before digital I used a JL CR-1 crossover. In discussing integration with the JL rep of that time, he was adamant that I needed to plug the main speaker ports in order to have a coherent integration, because the port added a 180 degree phase difference into an already challenging task getting timings correct. ... or something like that. I did manage to do a nice sounding integration, but as he explained, because the sub has inherent delay anyway, the best hope was to have a half or full cycle delay from the subs at the listening position, which has a pleasant "fattening" of low bass. Open ports would hopelessly confound that.

I've read a couple of informative threads here on setting delays with subs and will keep experimenting and seeking advice on that as well, but what about plugging ports?

The SHD has Dirac but I'd like to get as good of integration as possible before applying correction.

Thanks!

 

[RPG]

I'm moving to a digital front end with a Minidsp SHD. I have 228be's with front ports, mating with two sealed JL subs. Before digital I used a JL CR-1 crossover. In discussing integration with the JL rep of that time, he was adamant that I needed to plug the main speaker ports in order to have a coherent integration, because the port added a 180 degree phase difference into an already challenging task getting timings correct. ... or something like that. I did manage to do a nice sounding integration, but as he explained, because the sub has inherent delay anyway, the best hope was to have a half or full cycle delay from the subs at the listening position, which has a pleasant "fattening" of low bass. Open ports would hopelessly confound that.

I've read a couple of informative threads here on setting delays with subs and will keep experimenting and seeking advice on that as well, but what about plugging ports?

The SHD has Dirac but I'd like to get as good of integration as possible before applying correction.

Thanks!

I'm interested in this question, myself, as I'll take delivery of two new subs in a month or so. Like you, my mains speakers are front ported. Seems to be lots of opinions on this. In my reading explorations, I found one guy (no idea whether he's legit or not, so I don't vouch for him) who agrees with plugging the main speaker ports in relation to integrating subs. Don't know if you saw this or not, but you can find his opinion/explanation about 1/2 way down the page here:

The Soundoctor™ - Test CD

Also, not about mains, specifically, but I found it interesting that SVS subs have an option in their app to configure some of their ported subs into "sealed mode" by changing some internal processing parameters and then physically plugging the subs' ports. Their explanation is this:

Sealed Mode:

• All ports plugged.
• Subwoofer Tune menu set to Sealed.
• The Sealed mode has the best transient characteristics, and is the preferred choice for a primarily music application. While Sealed mode does roll-off earlier, the roll-off slope is shallower than the vented modes, and therefore takes the best advantage of available room gain. This can result in extremely deep extension when the subwoofer is placed in a smaller enclosed listening space.

 

[Rockdog]

I'm interested in this question, myself, as I'll take delivery of two new subs in a month or so. Like you, my mains speakers are front ported. Seems to be lots of opinions on this. In my reading explorations, I found one guy (no idea whether he's legit or not, so I don't vouch for him) who agrees with plugging the main speaker ports in relation to integrating subs. Don't know if you saw this or not, but you can find his opinion/explanation about 1/2 way down the page here:

The Soundoctor™ - Test CD

Also, not about mains, specifically, but I found it interesting that SVS subs have an option in their app to configure some of their ported subs into "sealed mode" by changing some internal processing parameters and then physically plugging the subs' ports. Their explanation is this:

Sealed Mode:

• All ports plugged.
• Subwoofer Tune menu set to Sealed.
• The Sealed mode has the best transient characteristics, and is the preferred choice for a primarily music application. While Sealed mode does roll-off earlier, the roll-off slope is shallower than the vented modes, and therefore takes the best advantage of available room gain. This can result in extremely deep extension when the subwoofer is placed in a smaller enclosed listening space.

Bingo! Exactly the concept I was presented.

 

[Rockdog]

Bump?

 

[theyellowspecial]

Measure your integration results before applying correction.

 

[Pdxwayne]

In my living room and family room, I have found that I like the sound of stuffed port better. I have front ported speakers and back ported speakers and in both cases, I like my port stuffed.

But, your room may be different than mine.
You can try this song to judge how your speakers sound in your room, port open vs stuffed.

In my rooms, with port open, I found the double bass too muddy. Closing the port made it cleaner.

 

[digitalfrost]

I would simply test it by ear and see what you like best. You could also confirm with measurements. The bass-reflex tuning will help with bass output and also limit excursion, so it's good to have it (especially for 2 way speakers where the woofer also is the midrange). The only thing you should not do, is boost a bass-reflex speaker below tuning frequency, as the enclosure is acoustically open at that point.

So the lowest highpass frequency should be at br tuning (could be 60hz for a bookshelf...) but more realistically higher than that (twice should be 100% on the safe side).

When I added subs to my KEF LS50, I liked them better with the BR ports open. I would not worry so much about theory, because at these frequency points, the room is main player anyway.

 

[Rockdog]

In my living room and family room, I have found that I like the sound of stuffed port better. I have front ported speakers and back ported speakers and in both cases, I like my port stuffed.

But, your room may be different than mine.
You can try this song to judge how your speakers sound in your room, port open vs stuffed.

In my rooms, with port open, I found the double bass too muddy. Closing the port made it cleaner.

If I hear that song one more time!! No, it's my go to song for bass response and imaging checks. She has a great voice and I like some of her other stuff, but it's about time she figured out the damn horse didn't really run away!

I've been experimenting each evening and I think I like the sound of the ports blocked with the subs crossed at 80 or 90. There is some debate about how important time alignment is, but with the capability to set delays it seems worth trying. My analogue setup was phase aligned but one full cycle late. Still sounded "tight" to me though, but maybe a little muddy on deep acoustic bass. Pretty new to REW but will measure individual step responses and try to align that way. There seems no simple way to do it, or at least not a widely accepted way that I can glean from lots of reading here. Audiolense gets high praise for time alignment, but I can't afford another software.

Thanks!

 

[Pdxwayne]

If I hear that song one more time!! No, it's my go to song for bass response and imaging checks. She has a great voice and I like some of her other stuff, but it's about time she figured out the damn horse didn't really run away!

I've been experimenting each evening and I think I like the sound of the ports blocked with the subs crossed at 80 or 90. There is some debate about how important time alignment is, but with the capability to set delays it seems worth trying. My analogue setup was phase aligned but one full cycle late. Still sounded "tight" to me though, but maybe a little muddy on deep acoustic bass. Pretty new to REW but will measure individual step responses and try to align that way. There seems no simple way to do it, or at least not a widely accepted way that I can glean from lots of reading here. Audiolense gets high praise for time alignment, but I can't afford another software.

Thanks!

I tried REW a short while ago and it was eyes opening experience. I tried to match right sub to right speaker and left sub to left speakers (I am not using high pass for speakers). I found out that I had the subs crossed too high previously and it negatively effected higher up bass tones . I ended up using the lowest crossover point of my subs and used opposite phase setting for the subs (one at 0 and the other at 180) to get best looking REW graphs for right and left side. It ended up still sound great and actually sounded a bit cleaner.

 

[theyellowspecial]

Dirac has a trial if you want to test a professional solution.

 

[Senior NEET Engineer]

Plugging the port will EQ down the bass response and increase harmonic distortion.

 

[RPG]

Plugging the port will EQ down the bass response and increase harmonic distortion.

This seems to run a bit counter to what I've been reading, albeit which I could certainly have misunderstood.

My very basic understanding is this:

1. At least below the port tuning frequency in a ported speaker or sub, plugging the port (or, alternatively, a sealed sub design) results in less, not more, distortion in the lower bass frequencies vs. open ported subs or speakers.

2. Yes, a ported sub, or speaker will have somewhat better spl, prior to their roll-off, but their roll-off is quite a bit sharper than a sealed sub or speaker. Due to this, a well-designed sealed (or plugged port) sub will actually have higher spl than the open ported in the very low bass frequencies.

Feel free to correct me if I've got this wrong.......

 

[digitalfrost]

1. Theoretically yes, but br tunings are usually set so the usable output is increased. Most music does not have content below 50hz, a lot is rolled off in the bass. The theoretical advantage below the tuning frequency is almost never there in practice. I don't know any speaker that has the tuning so high that it would become a problem with normal material. Electronic music might be something else. But even then, if you go with a subwoofer and can select a high-pass for the satellites you can easily prevent this becoming an issue. BR will almost always lower distortion in the usable band.

2. Again theoretically yes, but given large enough enclosure size or simply using a passive membrane you can tune bass reflex really low if you want to. The lowest wanted frequency should be considered when buying a sub. In fact, I'd rather have a closed sub and waste efficiency than a closed speaker, because a closed sub you can always push with DSP where you want it to be. A sub with too high of a tuning frequency is a hopeless case if you want output below that. The highest tuning frequency for a sub should be 40hz IMHO, because that is a realistic worst case scenario with music. For movies, it should be even lower.

If you take any simulation software and compare the same driver in closed box and bass reflex, you will easily see what I'm saying here. Well designed bassreflex will almost always have benefits. That said, given that we have DSP and amplifier power for cheap nowadays, I think closed box speaker/sub can be much easier gotten to where you want it to be.

For retail speakers, the price of a hole in the box and a tube is so low that using BR is a nobrainer. Also I should probably mention I'm sitting here with closed box speakers and subs , but without DSP the bass qualities really are not satisfying. I'm simply solving the problem with a lot of speaker chassis and amplifier power.

 

[Another Bob]

First, and most importantly, use REW to make your decisions. Proper sub integration without it is strictly hit-or-miss. Experiment with several configurations, and don't cling too tightly to rules of thumb. If your chosen crossover frequency is close (less than an octave) to the cutoff frequency of either your mains or your subwoofer, you may need different high pass and low pass slopes in your SHD, because the effective crossover slope will be the combination of what you program into the SHD and what the speakers are doing. Again, experiment and measure, and when the response is smooth at the crossover frequency, you've got it right.

As far as port stuffing, you generally cannot have a driver/box configuration that is optimal for both sealed and vented use. On my JBL Studio 590's (which has 2x8" woofers like your 228's and a similar tuning frequency), stuffing the ports caused the speakers to start rolling off around 90Hz. There was more output below 30Hz, but that's where the subs are taking care of business.

 

[RPG]

I think both the O.P. and I would appreciate some learned commentary/opinion on these statements excerpted and quoted, in the context of sub and mains integration, from Barry Ober (Soundoctor). Personally, I am not knowledgeable enough to judge what he says, so I am a neutral observer here.....

"Lets examine ported speakers. We'll start with the worst case, the port in the front. At mid bass frequencies, say 50-80 Hz, the LF driver moves IN the cabinet, the air in the cabinet is elastic, and the port air moves out of the cabinet. Because of the frequency at which the cone is moving, by the time the cone moves out (forward) again, the port air is now moving out, so in front of the cabinet the two air pressure sources sum together and you get a fake bass "bump" or "boost".

As you go lower and lower in frequency, at some low frequency the air pressure from the LF driver and the air pressure from the port are exactly opposite each other, so they cancel, and there is no more audio at that frequency: it disappears.

When the manufacturer of a speaker cabinet defines the frequency response (i.e., 37 Hz - 20kHz +/- 3dB) this is what is defined by the entire arrangement of the port and the air in the cabinet and the driver. At some low frequency the port air is exactly out of phase with the driver air pressure and since they cancel, there is NO output from the cabinet into the room. Therefore with a ported cabinet, the entire sloppy concept is this juggling game between the response of the drivers under air pressure, the passive crossover inside the box, the port size and placement.

That means IF you were to simply put those same frequencies through the mains and the sub (that means with no crossover, and this is the mistake that nearly everyone makes) you would now have 3 sources of LF energy and differing phase: the 'main' LF driver, the port, and the sub, all fighting with each other in the time domain. A further corollary is that since the air inside the [mains] cabinet is elastic, the phase relationship of the port air to the driver air is also a sliding one; that means it's "out of phase" — and smearing — over a wider range of frequencies than you might think.

A ported sub for home use is even more wrong than ported mains. Now you would be attempting to acoustically add together in the room at least SIX low frequency sources with differing phase and frequency slope conditions: the LF drivers in your two mains, their ports, the sub driver, and its port.

If your speakers are ported, you SHOULD close (seal) the ports......What you are trying to accomplish is to NOT have multiple sources of differing phase relationships (the main driver, the port air, and the sub driver) at or near the crossover freq."

 

[Rockdog]

I think both the O.P. and I would appreciate some learned commentary/opinion on these statements excerpted and quoted, in the context of sub and mains integration, from Barry Ober (Soundoctor). Personally, I am not knowledgeable enough to judge what he says, so I am a neutral observer here.....

"Lets examine ported speakers. We'll start with the worst case, the port in the front. At mid bass frequencies, say 50-80 Hz, the LF driver moves IN the cabinet, the air in the cabinet is elastic, and the port air moves out of the cabinet. Because of the frequency at which the cone is moving, by the time the cone moves out (forward) again, the port air is now moving out, so in front of the cabinet the two air pressure sources sum together and you get a fake bass "bump" or "boost".

As you go lower and lower in frequency, at some low frequency the air pressure from the LF driver and the air pressure from the port are exactly opposite each other, so they cancel, and there is no more audio at that frequency: it disappears.

When the manufacturer of a speaker cabinet defines the frequency response (i.e., 37 Hz - 20kHz +/- 3dB) this is what is defined by the entire arrangement of the port and the air in the cabinet and the driver. At some low frequency the port air is exactly out of phase with the driver air pressure and since they cancel, there is NO output from the cabinet into the room. Therefore with a ported cabinet, the entire sloppy concept is this juggling game between the response of the drivers under air pressure, the passive crossover inside the box, the port size and placement.

That means IF you were to simply put those same frequencies through the mains and the sub (that means with no crossover, and this is the mistake that nearly everyone makes) you would now have 3 sources of LF energy and differing phase: the 'main' LF driver, the port, and the sub, all fighting with each other in the time domain. A further corollary is that since the air inside the [mains] cabinet is elastic, the phase relationship of the port air to the driver air is also a sliding one; that means it's "out of phase" — and smearing — over a wider range of frequencies than you might think.

A ported sub for home use is even more wrong than ported mains. Now you would be attempting to acoustically add together in the room at least SIX low frequency sources with differing phase and frequency slope conditions: the LF drivers in your two mains, their ports, the sub driver, and its port.

If your speakers are ported, you SHOULD close (seal) the ports......What you are trying to accomplish is to NOT have multiple sources of differing phase relationships (the main driver, the port air, and the sub driver) at or near the crossover freq."

This is really the crux of what I'd like to see debated, RPG. I had several long conversations with Barry Olber some 5 or 6 years ago. I believe he is retired but he was super generous with his time and a really fun and interesting person to work with. Pretty direct and as I say, adamant, about his method. Honestly, my integration sounded really good, in fact I chose a sealed main speaker at that time too, based on his advice. My system was all analog until it reached the subwoofer plate amp, which, he explained, was always delayed somewhat, so the closest time alignment was adjusting phase for one wave cycle late.

It seems intuitive that time aligning subs and mains would be nearly impossible with multiple ports as it would also seem that whatever was puffing out of a port would by definition be 180 degrees out of phase with the woofer driving it. (Has to be doesn't it?) I don't know if that's true, or if it even matters.

I have Dirac now, and the first attempt sound quite good. The room mode EQ is a whole other step forward, for sure. Dirac is vague about whether it can actually time align a sub integration, though it "kinda sorta" says it does.

Yeah, I know, just be happy and enjoy the music.. honestly I do that 90% of the time, but the hobby is a hobby.

Block ports on everything? Is time alignment really worth chasing. (My understanding, it is most important at crossover freq). Can Dirac truly set time alignment with adjusting delays between mains and subs? (I don't think it can, just adjust delays from main to main)

Thanks for all the thoughts, interesting and helpful.

 

[Rockdog]

Plugging the port will EQ down the bass response and increase harmonic distortion.

I understand it would roll bass off faster, but isn't one of the big challenges of port design in controlling inherent distortion of the port and box as a moving air dynamic? It would seem that anything outside of perfect cone movement linearity would add distortion and thus a port is a compromise of sorts compared to a larger driver and cabinet. Not that engineering hasn't accomplished great port design and very low distortion these days.

I really don't know that from any expertise so I could well be wrong.

 

[RPG]

I was doing some baseline speaker FR room measurements in advance of receiving new subs later this month. I measured the bass only (0-100hz) FR of both speakers (Revel F-208) together, no subs, from the MLP, calibrated mic on a boom stand, with the ports both plugged and both open. There was a difference. The affected frequencies were between 20 and 40hz.

When Stereophile measured these speakers they identified the port tuning frequency peak at about 27.3hz, with the ports crossing over with the woofers at around 40 hz. Not unexpectedly, with ports open I saw that there was a FR hump between about 27 and 40hz, peaking at about a +9db point at 28.8 hz in my measurements and gradually rolling off back to the approx. baseline (such as it is with bass) at 40hz.

With the ports plugged, the overall 20-40hz baseline was reduced by about 5db. The hump was still present, but there was only about +5db peak, thus leading to a shallower sloped roll-off back to baseline.

Overall, with the ports plugged I'd say the bass FR between 20 and 40hz appeared more linear, albeit about 5db lower. Intuitively (maybe a big mistake, heheh) it seems to me that, with the ports plugged, this would better lend itself to sub integration and/or EQ.

I wish I'd saved everything in order to post the comparison graph, but I was a bit rushed in order to complete everything before the missus returned home (she hates the sounds of the repeating sine sweeps) and neglected to do so. All I have is my notes.

 

[richard12511]

I understand it would roll bass off faster, but isn't one of the big challenges of port design in controlling inherent distortion of the port and box as a moving air dynamic? It would seem that anything outside of perfect cone movement linearity would add distortion and thus a port is a compromise of sorts compared to a larger driver and cabinet. Not that engineering hasn't accomplished great port design and very low distortion these days.

I really don't know that from any expertise so I could well be wrong.

By plugging the port, you are lowering the output at those frequencies above the port tuning(25Hz). You'll have to compensate for that decrease with EQ, which will increase distortion. The port gives you lower distortion above 25Hz, but increased distortion below 25Hz. Unless you're running them full range or crossing at 20Hz, plugging the port will increase distortion and limit headroom. It also depends on where your crossover is. If you're crossing at 40Hz, then plugging the port will increase distortion and limit headroom, but if you're crossing at 80 or 100Hz, it likely doesn't make much difference.

Badly designed ports can cause problems(ime), but the Revel ports are well designed and properly flared, so no problem.

 

[RPG]

As for my situation, which differs from Rockdog's to some extent, I will definitely be running speakers at full range and likely crossing them over w/new subs at between 50 and 80 hz......to be determined, of course, when subs arrive.

My theoretical plan was to keep the ports plugged, use the PEQ on my RME ADI-2 to flatten out the hump, and use the subs to compensate for the lowered output.