Sealed Loudspeakers and Ported Subwoofers?

[Folsom]

IIRC you didn't quiet love the price tag though!

They sure are Beasts.

 

[Ron Resnick]

I want to spend a good year or so “hatching” the system and understanding it and fine-tuning it.

By then maybe some demo pair or something of Subsonics will become available. . .

I already bought a used pair of Parasound JC1s just in case. The new Wilson Audio active crossover obviates the need for two Watch Controllers.

The only thing is that with the Wilson system there is no speaker-level input, so one cannot use the REL system of tapping off of the outputs of the power amplifiers driving the main speakers. And I like the REL speaker-level system to drive the subwoofer amplifiers so the subwoofer amplifiers are infused with the sonic character of the amplifiers driving the main speakers.

 

[ack]

Explain "phase issues" please.

when the sub runs into the main speakers' range, then the port's output is out of phase with the mains, at various degrees. The result is audibly muddied bass in that region, and dependent on a system's resolution, it is easily audible. Magico solves this in two ways: sealed, plus software-controlled cutoff (not crossover per se) at a certain frequency. Simply brilliant.

Finally, ported designs - main or sbs - always measure with a big hump at the port's resonant frequency, and that fundamentally bothers me.

 

[jeff1225]

Most companies do as it is a cheaper way to get "full range" sound. And as long as you have a big enough room, you can get away with the phase anomalies and some of the challenges in terms of speakers placement to avoid room modes.

Ported designs are not "cheap" by any means, they are just another design strategy.

 

[Ron Resnick]

when the sub runs into the main speakers' range, then the port's output is out of phase with the mains, at various degrees. The result is audibly muddied bass in that region, and dependent on a system's resolution, it is easily audible. . . .

Is this true even if the sealed main speakers are playing down to 20Hz or 25Hz or so, and the ported subwoofers are low-passed to start at 20Hz or 25Hz or so?

 

[ack]

Is this true even if the sealed main speakers are playing down to 20Hz or 25Hz or so, and the ported subwoofers are low-passed to start at 20Hz or 25Hz or so?

It's a similar situation, and it would depend on the crossover slopes. But if you main speakers go down that low, then do you really need a sub. In general, I would say, use ported subs with ported main speakers from the same manufacturer (a la Wilson) who knows what he's doing and makes an effort to design with integration in mind; or go sealed all around, and avoid too much overlap. This mixing that I see many doing - including myself - is really tough to marry.

 

[ack]

I was just reading the Stereophile Magico M2 review https://absolutehiend.com/media/wysiwyg/pdf/MagicoM2Stereophile.pdf and on page 2, Wolf/JA describe the differences between ported and sealed designs really well - one of many such references - especially with respect to the Fletcher-Munson curves, though they don't discuss sub integration.

 

[Folsom]

when the sub runs into the main speakers' range, then the port's output is out of phase with the mains, at various degrees. The result is audibly muddied bass in that region, and dependent on a system's resolution, it is easily audible. Magico solves this in two ways: sealed, plus software-controlled cutoff (not crossover per se) at a certain frequency. Simply brilliant.

Finally, ported designs - main or sbs - always measure with a big hump at the port's resonant frequency, and that fundamentally bothers me.

I admit half baiting you into this question because I wasn't expecting an answer that would be legit.

This isn't true in the way you think it would be. Ports are slightly out of phase with the driver that is feeding them to begin with. Can you hear it? Actually no, you hear numerous things but not the phase part. First you must understand that a driver is out of phase with itself constantly. Every frequency moves the driver a different amount because the size of the frequency is different. Because of this the frequencies cannot have the exact same phase, since the sound is originating from different points. To listen to a speaker of any kind is to hear varying phase.

What you're hearing is modes, caused by overlapping phase, but you aren't actually hearing the phase itself - you may be hearing the character of the ported subwoofer as well. This will happen with any subwoofer. Obviously using a crossover to reduce the overlap helps but this isn't specific to ported or any other form, it's source/amplifier dependent. When you adjust a subwoofer's phase (amp/preamp/crossover) you aren't perfectly aligning it to the mains to have same phase (no such thing), not in any way what-so-ever, you're simply getting to a mode/node point that is least offensive so that it sounds right.

And ported speakers don't always have a bump, but you do see it often. There is no specific reason why they would have to have a bump - I've seen lots that roll of very gradual.

Is this true even if the sealed main speakers are playing down to 20Hz or 25Hz or so, and the ported subwoofers are low-passed to start at 20Hz or 25Hz or so?

Well, it's not true so...

 

[ack]

What you're hearing is modes, caused by overlapping phase, but you aren't actually hearing the phase itself - you may be hearing the character of the ported subwoofer as well. This will happen with any subwoofer.

Well, yes, you are hearing the effects of the phase interactions, not the phase itself; root cause is still the phase, which is more egregious with ported designs. And yes, I agree, even a sealed design may have phase issues with the main speakers, depending on its position.

Don't know what the bait was, but it was tasty

 

[Duke LeJeune]

...frankly, I no longer see the point of the ported subwoofer concept - why!

In general I prefer sealed subs, but I make ported subs. The reason is, I can get closer to my "target response" with a ported sub than I can with a sealed sub.

The reason I normally prefer sealed subs is this: We never hear the subwoofer without the room, so we are always hearing subwoofer + room. And typically the room's boundaries are reinforcing the low end. Ported subs tend to stay "flat" down to a lower frequency before they start rolling off, while sealed subs start rolling off higher but do so much more gradually. Unfortunately for most ported subs, "flat" + room = boomy. So, at the risk over-generalizing, sealed sub + room tends to sound better than ported sub + room.

(The room being the deciding factor is somewhat counter-intuitive, but if we take both subs outdoors, the ported sub which sounded "boomy" in our room now sounds "tight", while our previously "tight" sealed sub now sounds "thin"... so it WAS the room making the difference.)

Ported box design has more degrees of freedom, which can be used to compensate for room gain from boundary reinforcement. Typical room gain is approximately 3 dB per octave usually starting somewhere below 100 Hz, and its inverse (-3 dB per octave rolloff about 100 Hz on down) is easier to achieve with a ported box, using a somewhat unorthodox tuning. Achieving the same end result with a sealed box calls for EQ, which is not a bad thing, but if we keep the box sizes and -3 dB points identical, the sealed box solution calls for twice the excursion and four times the power (and four times the power handling).

Note that the specs on the Wilson Subsonic include this wording: "10 Hz to 150 Hz. +0, -3 dB Room Average Response". Imo this implies Wilson is taking anticipated room gain into account. And by using the word "average", I think they are acknowledging that the real-world in-room response will have room-induced peaks and dips which will stray outside that +0, -3 dB window.

So the main reason I use ported subs - and I THINK the main reason Wilson uses ported subs - is so that we can do a better job of compensating for the room's anticipated effects.

 

[Ron Resnick]

Thank you very much, Duke, for this clear and understandable post!

 

[Folsom]

Note that the specs on the Wilson Subsonic include this wording: "10 Hz to 150 Hz. +0, -3 dB Room Average Response". Imo this implies Wilson is taking anticipated room gain into account. And by using the word "average", I think they are acknowledging that the real-world in-room response will have room-induced peaks and dips which will stray outside that +0, -3 dB window.

So the main reason I use ported subs - and I THINK the main reason Wilson uses ported subs - is so that we can do a better job of compensating for the room's anticipated effects.

That or Wilson expects the people buying them will primarily have large rooms to fit those monsters.

 

[Duke LeJeune]

The only thing is that with the Wilson system there is no speaker-level input, so one cannot use the REL system of tapping off of the outputs of the power amplifiers driving the main speakers. And I like the REL speaker-level system to drive the subwoofer amplifiers so the subwoofer amplifiers are infused with the sonic character of the amplifiers driving the main speakers.

This can be accomplished via something called a "voltage divider network", which derives a line-level signal from the speaker-level outputs on your power amps, with negligible effect on the amp/speaker interface. I presume the RELs incorporate a voltage divider network. Imo the maximum output voltage of the amp driving your mains, and the maximum input voltage of the Wilson active crossover, should be taken into account in designing the voltage divider network.

Thank you very much, Duke, for this clear and understandable post!

Thank you, Ron.

One of the implications of the higher power required to get equivalent SPL & -3 dB point out of a sealed box is, the amp and woofer have to work harder and correspondingly heat up more. A hot woofer motor + a hot amp + a compact enclosure can result in a short, exciting life for the amp.

 

[NorthStar]

A good informative educative article, in my opinion (on subs and their integration, and much more) ...
? https://www.widescreenreview.com/172subwoofer.pdf

 

[Ron Resnick]

This can be accomplished via something called a "voltage divider network", which derives a line-level signal from the speaker-level outputs on your power amps, with negligible effect on the amp/speaker interface. I presume the RELs incorporate a voltage divider network. Imo the maximum output voltage of the amp driving your mains, and the maximum input voltage of the Wilson active crossover, should be taken into account in designing the voltage divider network.



Thank you, Ron.

One of the implications of the higher power required to get equivalent SPL & -3 dB point out of a sealed box is, the amp and woofer have to work harder and correspondingly heat up more. A hot woofer motor + a hot amp + a compact enclosure can result in a short, exciting life for the amp.

“Voltage divider network” sounds like a fancy name for “potentiometer.”

 

[Duke LeJeune]

“Voltage divider network” sounds like a fancy name for “potentiometer.”

It looks like a fixed L-pad, but with something perhaps along the lines of 22k Ohms for the series resistance, and 1k ohms for the parallel resistance... these are values I have used for a 200 watt (40 volt) amp, deriving a lower-voltage signal for my subwoofer amp's 12K ohm input impedance. So the power amp sees 22k Ohms in parallel with the speaker's impedance curve. With other amp/line-level input impedance (and input sensitivity) combinations the values would change.

 

[Ron Resnick]

It looks like a fixed L-pad, but with something perhaps along the lines of 22k Ohms for the series resistance, and 1k ohms for the parallel resistance... these are values I have used for a 200 watt (40 volt) amp, deriving a lower-voltage signal for my subwoofer amp's 12K ohm input impedance. So the power amp sees 22k Ohms in parallel with the speaker's impedance curve. With other amp/line-level input impedance (and input sensitivity) combinations the values would change.

Interesting, thank you.

Whether attenuating a main amplifier speaker-level signal for a line-level subwoofer controller to infuse the subwoofer amplifier with the sonic character of the main speaker amplifier, or using a separate pair of line-stage preamplifier outputs to drive the subwoofer amplifier directly, achieves better sonic results may be one of those questions which is impossible to answer theoretically. I think I would have to try both methods and hear which sounds better.

Wilson, obviously, specifically does not like the REL method of tapping into the main speaker amplifier to feed the signal to the subwoofer amplifier driving its subwoofer.

 

[sbo6]

Ported designs are not "cheap" by any means, they are just another design strategy.

See acks' respons above, exactly correct. Which is why I plug the ports in my speakers and tune with multiple sealed subs in my moderate - sized room.

 

[sbo6]

Ported designs are not "cheap" by any means, they are just another design strategy.

It is a convenient way to get deeper bass while sacrificing bass linearity and injecting phase misalignment. To procure deeper bass in a sealed cabinet designs often require increasingly robust driver design and power to adequately for such drivers. See Magicos as an example.

 

[sbo6]

Ported designs are not "cheap" by any means, they are just another design strategy.

How many budget speakers do you know employ sealed cabinet designs? Customers love bass, everyone wants 'full range". Stick a port in the back (usually) at the most beneficial diameter and depth based on the speakers' design and you achieve another 10+ Hz of low frequency output. Sealed, not so easy.