What exactly happens if you seal a speaker which was specifically designed to be ported? KEF Reference 3 Meta

[ssashton]

that would be nice. Care to explain how plugging one port would lower the tubing frequency of the other port?

It changes the ratio of port area to length. Halve the port area is like doubling the length.

EDIT: This assumes the two ports share the same enclosure volume, there is no divider making the enclosure two separate volumes.

In my example above:

40Hz tuning = 50mm diameter 3.67cm length

30Hz tuning = 50mm diameter 9.39cm length

Final thought - if you have the option I'd get the Ref 1 and a sub or two.

 

[jonfitch]

I used port plugs on mine from my old Ascend speakers as I use my Kefs for nearfield and they are close to the wall. It doesn't affect bass extension much, but I don't run them very loud nearfield anyway. I would imagine it would limit SPLs to some extent and you would need subs to carry more of the load with a higher crossover if you are going to do this for a larger room setup.

 

[Heinrich]

that would be nice. Care to explain how plugging one port would lower the tubing frequency of the other port?

The resonance ist determined by volume and port area like Fr ~ sqrt(area/volume). Closing one of two would half the area, leading a shift to Fr(new) ~ 0,707 Fr(orig). Thing is, this would only work if the drivers operate in the same shared volume - I don't know if that's the case. Even if so, there could be some minor effects dpending which of the two to be closed.

You need a measurement equipment anyway. Such a device is, and with an appropriate equaliser at hand the more, the cheapest tuning for your listening experience imaginable. In regard to your questeion, the operations are easily learned. At least easier than sensible speculations over a hypothetical outcome of X are made-up and tested. Presumably you don't want to fall into the circle of wasting time testing your latest efforts, rather than listening to the super bowl's anthem correctly ;-)

 

[Goldhamster916]

The resonance ist determined by volume and port area like Fr ~ sqrt(area/volume). Closing one of two would half the area, leading a shift to Fr(new) ~ 0,707 Fr(orig). Thing is, this would only work if the drivers operate in the same shared volume - I don't know if that's the case. Even if so, there could be some minor effects dpending which of the two to be closed.

You need a measurement equipment anyway. Such a device is, and with an appropriate equaliser at hand the more, the cheapest tuning for your listening experience imaginable. In regard to your questeion, the operations are easily learned. At least easier than sensible speculations over a hypothetical outcome of X are made-up and tested. Presumably you don't want to fall into the circle of wasting time testing your latest efforts, rather than listening to the super bowl's anthem correctly ;-)

I searched their white papers and turns out they partitioned the cabinet into smaller enclosures to push the standing wave frequency of the LF driver higher. So I guess I either use them as they are or try my luck with sealing both and then apply eq (and more power) while using a in line limiter to not overextend LF driver excursion.

 

[Heinrich]

I searched their white papers and turns out they partitioned the cabinet into smaller enclosures to push the standing wave frequency of the LF driver higher. So I guess I either use them as they are or try my luck with sealing both and then apply eq (and more power) while using a in line limiter to not overextend LF driver excursion.

Getting analytical equipment at your hands, today that's a cheap mike alone, will change everything. 100 vs 10K++ is a factor of 100, one percent. Speculating and doing something won't help you as much.

 

[levimax]

To me the only reason to plug the ports on a well designed ported speaker like the KEF's is if you are going to add a sub. The slower roll off and reduced group delay will make it easier integrate a sub.

 

[ssashton]

I searched their white papers and turns out they partitioned the cabinet into smaller enclosures to push the standing wave frequency of the LF driver higher. So I guess I either use them as they are or try my luck with sealing both and then apply eq (and more power) while using a in line limiter to not overextend LF driver excursion.

If you look at the graphs I shared, the ported option still has more output than the sealed one well below the tuning frequency- down to 26hz. So unless you really, really care about that <26hz content I wouldn't go plugging the ports.

Just get a measurment mic and EQ like MiniDSP. Ask for advice on that if you don't know what to get.

 

[Heinrich]

To me the only reason to plug the ports on a well designed ported speaker like the KEF's is if you are going to add a sub. The slower roll off and reduced group delay will make it easier integrate a sub.

Well designed 'ported'. The tuning should be set close (~15%) and above the lowest frequency to be played. EDM recordings cut at about 40Hz, more artsy content at 30Hz. Movies may go way deeper. (For the fun of it.) If the tuning is chosen to be higher** than 40Hz, or 30Hz respectively, and playing relevant bass content, a low cut filter is mandatory. It shall block all content below the tuning frequency.

When designed like that, an equaliser is an easy tool to use for room integration and foremost setting all just right to taste. The subjective judgement involved may depend on each individual recording--there's nothing wrong with that.

To change a given design from ported to closed has implications. Depending on the alignement of tuning with bass content, it may or not be beneficial in terms of max output: at frequency X limited by distortion and intermodulation, or even limited by self destruction. To recommend a yes or no requires some deeper knowledge about the speaker design, type of bass content and peak (!) sound pressure level.

That's why I recommended to get into measuring objectively any outcome, before and after the fact. Too many parameters unknown. A mike is very cheap compared to the speakers in question. The expertise is not, I know. But it will be at least as valuable as anonymous internet advice anyway, and would hold a lifetime, and it is free..

** possible reason for doing so: the speaker is that small, that even if it would play a deep note within its max capabilities, it won't be heard due to equal loudness / hearing threshold

 

[Goldhamster916]

I already have a UMIK, Multi EQX, Dirac and REW. Will do some testing when i buy the speakers. I appreciate the advice fdrom everyone!

 

[Heinrich]

I already have a UMIK, Multi EQX, Dirac and REW. Will do some testing when i buy the speakers. I appreciate the advice fdrom everyone!

Short port: 38Hz - 45kHz
Long port: 35Hz - 45kHz

You may opt for the long port and equalise to taste in-room. The low tuning, fit for even 'artsy' recordings, without chuffing noises, in absence of port resonances or other leaks is only one of KEF's significant achievements in the last decade. Let's see if there is any argument left in favour of sealed- I personally don't expect one.

(There are additional low-frequency components originating from impact noises, see Fourier Analysis etc. Measuring them is challenging due to the block-based digital analysis, which causes spectral leakage. Overall, it seems that 30 Hz of an f3 and tuning say at 35Hz is sufficient at even elevated volume levels. Alas, one won't get people into a collaboration to investigate deeper. If I did it alone myself, only few would accept the results, the others would talk it down vigorously as to practice 'science'. Lots of work, nothing gained ... )

Have fun!

 

[mikessi]

To the OP: At such a low listening level, your own hearing become considerably non-linear, especially at the lower frequencies. Chances are, the close-wall positioning will help compensate for your own reduced bass sensitivity. Plugging the ports could also have unexpected results not just in the low end but higher up in frequency. You're paying for a well designed speaker with a particular set of compromises chosen presumably by experienced pro engineers: Why undermine that? If you think it's not perfectly well suited for your needs, why not find one that's better suited?

(Being an inveterate speaker DIYer, I'd build my own, of course. )

 

[Goldhamster916]

I agree with the sentiment that the speakers are very carefully designed especially for this configuration and that it might affect the speaker in a way which is hard to predict when you plug the ports. My current plan is to let them run with the long port, which will give me close to 85db at 30hz with wall reinforcement, which is more then enough for music at my listening levels. To get the last 10 hz down in home theatre applications i will rather cross them over at 40-50hz with a subwoofer then trying to plug the ports and add power.

Thanks everyone!

 

[Chrispy]

Hi,

following scenario: the KEF Reference 3 Metas have two ports with a tuning frequency of ~40 Hz and two 6.5'' high excursion woofers each. I would listen at 1.5m at low volume (~60DB), speakers placed within a few inches to front wall. As you can see I really don't need the SPL the Reference 3 provides. The idea is to seal the ports to have the air inside behave like a spring and decrease woofer distortion which, in the ported configuration, increases a lot under the ports tuning frequency. Apart from that i would maybe try to apply a few DB bass boost to get, combined with the more gradual role off from the sealed design, a flat FR till ~30hz. I would then try to find a way to limit SPL below ~100HZ. Amp has 250W (hypex based), power handling of the speaker is 300W.

1. Are there any flaws in my reasoning?

2. would i get the desired results?

3. would there be group delay or other non FR related issues with this approach? if yes would it be audible? in case of group delay: would linear phase filters be a solution?

4. From what i have read about KEF i would assume the Reference 3 and all components within are modeled specifically with this exact port in mind. would the effects of a sealed cabinet negatively interact with/contradict design choices on other parts of the loudspeaker and therefore lead to negative effects on sound quality? Dampening and motor structure for example are parts i can think of which might be moduled to this specific design.

KEF Reference 3 Meta CEA2034:

View attachment 481283



I think I basically try to emulate what many active speakers do with a passive speaker, like here on the LS60 but at even lower SPL. I would be happy to have a headroom to ~70DB at 30hz. the question is if there is anything in the Reference 3 design which makes it unsuitable fo this approach.

LS60 low frequency compression:
View attachment 481282

I appreciate anyone who takes his time to answer my questions!

Basically the box is more intended for one or the other, taking a ported box and blocking ports isn't really an ideal sealed setup for lowest frequencies.

 

[CJH]

Does using the KEF foam plugs really seal the port, Doesn't it rather just attenuate the sound coming out of the port with some leakage. In order to effectively seal the sub, one would need to shove some type of closed flexible ball (hand ball, racket-ball or stress relief ball) into the port hole. Comments?
CJH

 

[Goldhamster916]

I don’t think they completely seal the port, it’s probably still lossy to a degree. Note that the Reference series doesn’t come with foam plugs, the r Series does (not sure about the lower end ranges). Which might be an other indicator that the reference series isn’t designed to be used in any kind of sealed configuration.

 

[Frank Dernie]

Does using the KEF foam plugs really seal the port,

Almost certainly enough to no longer be a Helmholtz resonator, yes.