Do ported tower speakers match well with sealed subs?

[girtab]

Hello ASR,

I've heard that integrating ported subs is very difficult due to increased group delay and phase rotation compared to a sealed design. Also the ported design makes roll off sharper in order to achieve the lowest usable output for less excursion and power

My question is what kind of sub to get for listening to music with deep bass if you already have ported towers that extend to about 35hz in room without compromising on timing/phase accuracy. Another important aspect is having multiple subs since that is required to avoid nulls and boomyness, so how does that come into play when deciding what kind of subs to get for the most amount of extension with the most amount of headroom for a certain budget.

Also, is there any guide on how to set up parameters for integrating subs for optimal phase linearity/ crossover frequency/ etc

Thanks in advance!

 

[LTig]

First of all I'm sceptical that ported subs are more problematic as sealed subs, since they are the majority, by large.

That said: If you use a high pass filter on the satellites so that they no longer play deep frequencies the port cannot have much influence on the sound. It could still leak higher resonances but in this case you could just close it without any negative influence on sound quality.

 

[wwenze]

Why not?

The amount of time it takes for the air to do its first "phase rotation" is much less than the amount of time it takes to hit the walls of your room and bounce back.

Second, ported designs roll off sharper below the tuning frequency. Sealed is -12dB per octave, ported is -24dB. Nothing to do with "in order to blah blah". We use port because it gives us more bass at tuning frequency at the expense of steeper rolloff below tuning frequency. Excursion is higher, while power needed per SPL is reduced.
When it goes below 20Hz or below -10dB, it no longer matters anyway.

Subs are good for
1) When your ported towers have high distortion by playing lower frequencies loud, sub takes over hence increasing maximum output volume
2) Sub covers the final lowest octave

 

[thcdru2k]

I think ported vs sealed is overstated for subwoofers but you could experiment with damping or sealing your towers. I seal my towers because I was getting excess decay in 60-90hz area.

 

[girtab]

ported designs roll off sharper below the tuning frequency. Sealed is -12dB per octave, ported is -24dB

That basically what I said? “roll off sharper in order to achieve the lowest usable output”

I know subs are good for covering the last octaves, my point was if a sealed or a ported enclosure would make more sense in such a scenario

Sorry if that wasn’t clear in my original post

 

[girtab]

use a high pass filter on the satellites so that they no longer play deep frequencies the port cannot have much influence on the sound

That was also my speculation, thanks for your input

 

[girtab]

I think ported vs sealed is overstated for subwoofers but you could experiment with damping or sealing your towers. I seal my towers because I was getting excess decay in 60-90hz area.

Does high passing it also have the same effect as sealing it?

 

[thcdru2k]

They will measure differently because DSP high passing is more precise. Technically mine are not sealed more like damp because its just a foam plug. I measured with REW and liked what I saw so I keep mine damped. With towers there are a lot of factors including distance from walls and room interaction so I would say case by case situation; so I just test different things and measure.

 

[somebodyelse]

Does high passing it also have the same effect as sealing it?

Not quite, depending on the details. Sealing it changes the mechanical tuning at the bottom end. This generally makes it roll off at at a higher frequency but more slowly, but could also cause some peaking before it rolls off - depending on the specifics of the speaker. The frequency where it rolls of isn't in your control. High passing gives you control over the frequency and won't cause a peak. What happens with the speed of roll-off depends on the filter you picked, and how far above the natural roll-off your chosen filter frequency is.

The aim is to pick the high pass for the mains and the low pass for the sub(s) to form an effective crossover, matching frequency, slope and phase at the listening position. How well you can do this depends on the controls at your disposal. With the limited controls on cheaper subs it may be impossible to get a good match. Use the same sub with a DSP based crossover and you should have enough control to get a good result - if you know what you're doing, or have good software to automate it.

 

[LTig]

Does high passing it also have the same effect as sealing it?

No:

• Sealing the port changes the speaker into a sealed one, which it is not designed for. Chances are that you get a bump at the resonance frequency of the woofer (depends on the Thiele-Small parameters of the woofer and the volume of the housing).
• High passing cuts off the low frequencies. Only then you can seal the port without influence on sound quality as the signals which trigger the resonance of the woofer are cut off.

 

[Duke]

I've heard that integrating ported subs is very difficult due to increased group delay and phase rotation compared to a sealed design. Also the ported design makes roll off sharper in order to achieve the lowest usable output for less excursion and power.

My question is what kind of sub to get for listening to music with deep bass if you already have ported towers that extend to about 35hz in room without compromising on timing/phase accuracy.

How, and how well, the subs blend with the mains is not much influenced by whether the subs are ported or sealed. The rapid phase rotation and associated group delay peak are happening at the very bottom end of the subwoofer's range, while the blending with the mains is happening at the upper end of the subwoofer's range.

Imo when it comes to blending sub(s) and mains, the specifics matter, and sometimes they matter a lot.

Another important aspect is having multiple subs since that is required to avoid nulls and boomyness, so how does that come into play when deciding what kind of subs to get for the most amount of extension with the most amount of headroom for a certain budget.

I have some experience in this area, having manufactured dedicated multi-sub systems for about twenty years. My individual subs are ported but the ports can be plugged, converting them into low-Qtc sealed boxes.

If you place a high priority on maximizing extension and headroom within a certain budget, ported subs theoretically offer 6 dB of "free" increased output at the port tuning frequency. To match that extension, an equivalent sealed box would need 6 dB of bass boost, potentially calling for four times as much wattage, and correspondingly producing more heat.

There are of course arguments that favor sealed subs, but "most headroom and most extension for a certain budget" points towards ported subs, unless said budget is pretty big.

Also, is there any guide on how to set up parameters for integrating subs for optimal phase linearity/ crossover frequency/ etc

The devils are in the details. For instance, whether or not it is feasible to plug the ports on your towers can make a difference. Are you comfortable posting what they are?

Anyway, here are some generalities: Good in-room frequency response is what matters the most, by a large margin. First set the gain for the subwoofers; next set the crossover frequency (and slope if available); and last set the phase control (if the subs have them). Then go back through that sequence several times, fine-tuning. Gain-crossover-phase; gain-crossover-phase. The gain setting for the subs matters the most; the crossover next; and the phase matters the least. You may end up tweaking the gain setting over the course of several days, as that's the most difficult one to get exactly "right".

Sealing the port changes the speaker into a sealed one, which it is not designed for. Chances are that you get a bump at the resonance frequency of the woofer (depends on the Thiele-Small parameters of the woofer and the volume of the housing).

Imo "getting a bump at the resonance frequency" from plugging the port(s) would be unusual. Typically woofers used in vented boxes have considerably lower Qes values than woofers used in sealed boxes, in which case the net result from plugging the port(s) is likely to be a low-Q sealed box... so, quite possibly -6 dB at system resonance, and rolling off gently from there on down.

 

[girtab]

The gain setting for the subs matters the most; the crossover next; and the phase matters the least

But how do I know what the best crossover frequency is? That’s what I’m wondering. Like does higher/lower crossover affect headroom in a way maybe? Should I pick one that high passes the towers or do I let them dig as deep as they can?

Are you comfortable posting what they are?

Of course, Polk R700

There are of course arguments that favor sealed subs

Which ones? Group delay?

Thanks for the insights by the way!

 

[girtab]

The aim is to pick the high pass for the mains and the low pass for the sub(s) to form an effective crossover, matching frequency, slope and phase at the listening position

this is also what I’ve been imagining. If for example the mains have a large trough at 40hz, then that would make for a good crossover region, right?

 

[LTig]

But how do I know what the best crossover frequency is? That’s what I’m wondering. Like does higher/lower crossover affect headroom in a way maybe? Should I pick one that high passes the towers or do I let them dig as deep as they can?

As a rule of tumb go as high as possible, but not so high that you can identify the position of the sub. A higher xover frequency increases headroom for the satellites and gives the sub a wider frequency range to fix room modes.

 

[pablolie]

I personally prefer sealed subs indeed.

But as in all things audio, generalizations are a perfect way to end up with an indefensible argument.

 

[thcdru2k]

I think there are tradeoffs rather than one universally ideal crossover. I usually end up measuring multiple crossover points in REW and choose whichever gives the best combination of smooth summation, decay, and passes the sounds good to the wife test.

 

[Duke]

But how do I know what the best crossover frequency is? That’s what I’m wondering. Like does higher/lower crossover affect headroom in a way maybe? Should I pick one that high passes the towers or do I let them dig as deep as they can?

If you're using a highpass filter on the mains plus multiple subwoofers, I'd start with a crossover frequency around 80 Hz, preferably 4th order to rapidly roll off the upper-bass energy that might otherwise give away their locations. In general, much higher than that and it starts becoming more likely that you'll be able to hear where the subs are located, and much lower than that and you're not taking full advantage of the modal smoothing offered by a distributed multisub system.

If you're not highpass filtering the mains, then it's more a matter of trial-and-error to find the best lowpass filter frequency for the subs.

Of course, Polk R700

Thank you. It does not look to me like it would be easy to plug the R700's down-firing port - please correct me if I'm wrong about that! But if that's the case, then imo highpass-filtering the Polks up around 80 Hz makes sense. Sometimes subwoofer amps have a fixed 80-Hz highpass filter to protect the mains, and then the lowpass filter frequency for the subs is user-adjustable, in which case THAT is what you'd be adjusting for the "crossover frequency" adjustment.

Which ones? Group delay?

Sealed box subs will of course have less group delay. The Helmholtz resonance of a ported box introduces group delay. To a first approximation group delay starts to rise maybe an octave or so north of the port tuning frequency, and reaches its maximum near (but not necessarily precisely at) the port tuning frequency.

Not all vented boxes are the same when it comes to group delay. All else being equal, a bigger box results in more group delay, and a higher tuning frequency pushes north the frequency at which group delay starts to become audible. As a ballpark rule of thumb, in the bass region about 1/2 cycle of group delay is probably audible in a home audio setting, and about 1/4 cycle of group delay is the detection threshold under anechoic conditions. Unfortunately I don't think anybody publishes their group delay specs. In vented mode, my subs have 1/4 cycle or more of group delay at 37 Hz and below, and 1/2 cycle or more at 23 Hz and below, BUT I'm using a smaller-than-normal box with a lower-than-normal tuning frequency, so my group delay figures are probably not representative.

Imo what actually matters more than group delay is the in-room frequency response curve, which is the subwoofer's native response + its room interaction. Now room interaction varies greatly from one room to the next, and even from one location to another within a given room, but again to a ballpark first approximation in a modest size home listening room (not an "open floorplan" room), room "gain" from boundary reinforcement is often somewhere around 3 dB per octave as we go from 80 Hz to down to 20 Hz.

Now let's look at how this hypothetical "3 dB per octave" works with vented subs and with sealed subs:

Vented subs are usually optimized for deepest-and-loudest bass, and once that 3 dB-per-octave of boundary reinforcement is factored in, they often end up with TOO MUCH very low bass, making them prone to sounding boomy or slow or otherwise less "natural".

Sealed-box subs, and in particular low-Q sealed-box subs, have a natural roll-off characteristic that is a much better match for that 3-dB-per-octave room-induced bass boost, BUT if that boost isn't present (because the room is too big or it's an open floorplan), then a sealed sub may well sound inadequate without a considerable amount of EQ.

So imo an arguably cost-effective strategy would be to use multiple vented subs intelligently distributed and EQ them for good in-room reponse.

 

[girtab]

It does not look to me like it would be easy to plug the R700's down-firing port

thats correct but i think a high pass filter using my minidsp flex would be enough since the ports on the polks are well integrated and dont resonate or have chuffing

because the room is too big or it's an open floorplan

If I were to get subs then, should i rather stick to sealed since the room is a mid sized living room? I've personally been more keen on ported ones since to me they seemed like they actually make use of physics instead of brute forcing volume through excessive excursion.

Because the room is also not huge the maximum amount of subs i could add is 2

they often end up with TOO MUCH very low bass, making them prone to sounding boomy or slow or otherwise less "natural".

can't I EQ excess bass down?

 

[girtab]

I think there are tradeoffs rather than one universally ideal crossover. I usually end up measuring multiple crossover points in REW and choose whichever gives the best combination of smooth summation, decay, and passes the sounds good to the wife test.

I guess the key really is just trial and error

 

[tineared]

I personally prefer sealed subs indeed.

But as in all things audio, generalizations are a perfect way to end up with an indefensible argument.

Ha ha, myself included. All of my speakers (9) are sealed in addition to my 3 subs. I'm old school and have avoided ports on towers or subs.
I do have 2 pair of ported bookshelves though.