Protip: Using a sub? Plug your mains

Pro tip. Indeed.
 

Merry Christmas. 

You need to be able to control the rolloff of the main speakers. You cant do that by just plugging the port. Some woofers dont work well in sealed boxes. What you really want is a high pass filter. That will enable you to tune the rolloff point and slope so that it integrates with the sub. And it will also prevent any issues with excursion below port tuning frequency. If you follow eriks advice, you will end up stressing the driver cone as all you are doing is causing the driver to be pushed against the air pressure in the box and stressing it. 

On the other hand if you dont listen to heavy bass music then it doesnt reallly matter whether you plug the port or not. 

Some drivers can handle both ported and sealed enclosures, some cannot. Also, when plugging a port, you want to plug the whole length. That applies to more than just speakers ;-)

Isn’t that we have crossover slopes in both the sub and main speaker to ensure a smooth handoff of the frequency?

Hey @testpilot - So main speakers have their own natural rolloff and that a lot of audiophiles forego the use of, or can’t, put an electronic high pass filter in line with the main amplifier. As a result, the main speakers go pretty low and the bass can get messy. By plugging the port you raise the -3 dB point, letting the sub handle more bass.

The critical thing, for me is this: By plugging the ports you prevent excessive excursion below the port frequency, hopefully reducing distortion. This benefit exists whether or not you use an electronic high pass filter.

If you are using an electronic high pass filter this becomes less of an issue.  I'm doing a project soon I hope to better document why this work.  Stay tuned.  I have lots of solder and breadboards to go through. :)

Makes perfect sense to me. The driver ends up operating more in line within its capabilities, reducing heat and distortion. Every little bit helps.

All the best,
Nonoise

It seems the high pass filter should be enough.  I have read that plugging ports can mess with the speaker performance intended by the designer.  Could plugging the ports affect frequencies above the intended level at which the mains cross over to the subs?  I guess the only way to know is to try it.  In my system, I believe adding a HPF (Marchand XM446XLR) improved SQ when playing the system at higher volumes, but I do not perceive any difference at low-mid playback volumes.  My current speakers are not ported so I cannot comment on the effect of both a HPF and plugging the ports.

It seems the high pass filter should be enough.  I have read that plugging ports can mess with the speaker performance intended by the designer.  Could plugging the ports affect frequencies above the intended level at which the mains cross over to the subs?  I guess the only way to know is to try it. 

@mitch - It is true that you can't just willy nilly pick to port or not, and the size of a cabinet to ensure optimal performance. In terms of the overall frequency response, you are only changing the lower part of the woofer's response.  The upper part is dominated by other factors.  The big benefit is reduction in distortion by minimizing excursion, an especially important thing in 2-way designs as it can affect the clarity of the midrange a great deal.

The other big benefit is ths woofer will distort less at higher output.

A line level crossover, when significantly higer than the port tuning frequency, should be enough. :)

@erik_squires How does plugging the port keep the amp from trying to play down low? I don't have any high or low pass filters in my system. I want to try your suggestion but can you explain why physically plugging the port will change the amp's output? I realize it will change the outcome, but why would it change the out put?

@erik_squires 

You recently accused me of vague unprovable positions and a complete lack of evidence. Don't you think its hypocritical to claim without evidence that there is a reduction in distortion and excursion by plugging the port? Let us all see some evidence of this claim. None of us want to risk damaging our expensive speakers by following your advice.

You have also claimed that:

This combination increases the dynamic range, and reduces distortion, especially when used with a line level high pass filter.

What evidence do you have that using a line level high pass filter and then plugging the port brings additional benefits than just using a high pass filter alone?

It also often makes integrating the subs easier thanks to less overlap. 

Does it? Do you have any evidence of this ease with which the sub can be integrated? Or should we just take your word for it? Isn't it hypocritical of you to accuse me of being vague when you are being just as vague when you say that it becomes easier to integrate the subs?  Would this integration be done by ear or is it measurable?

My sub has the ability to contour/adjust the levels of specific audio bands (parabolic equalizer) so that I can integrate the sub with my mains.  With the use of a microphone, I can plot the frequency response of my room.  Not sure what the benefit would be with plugging the rear ports. 

@erik_squires Wrote:

Protip: Using a sub? Plug your mains

I would not block ports on my main speakers without first asking the manufacturer's advice. Blocking the ports would change the tuning frequency of the speakers. Keep in mind, if your speakers did not come with port plugs the woofers may not be designed to use them. 😎 See below:

Mike

@ditusa - Read the last paragraph of the article you quoted. It's pretty much what I'm saying, only the author of the article doesn't consider in his writing the benefits of a plug when using a sub and not a  line level filter. :)

@erik_squires Wrote:

 It's pretty much what I'm saying, only the author of the article doesn't consider in his writing the benefits of a plug when using a sub and not a  line level filter. :)

I agree! :-) 

Wow onother idea. I just install the pioneer modified yesterday? They do complement my KLH model 9 nicely. 

One thing worth clarifying: Not all drivers will work well ported, but all drivers will work sealed. Yes, this is no longer "as intended" by the designer, but that doesn’t mean this isn’t a better match with a sub.

You are playing with the bass response here. You raise the -3 dB and make a gentler slope.  You are not making the "ideal" sealed speaker.  There are differences.

Generally speaking, an "ideal" sealed speaker uses a smaller volume of air vs the ideal ported speaker, so if you just plug a ported speaker, without reducing the volume you end up with a speaker that is normally orveramped...  BUT!! ... in this case you are doing so specifically for a subwoofer, which means overdamped is fine.

Also, therefore, lastely and soforth:

This is a tip that is easy to try and reverse too. :)  Try it and listen.  No good, no damage.

@erik_squires , thanks so much for this tip! I felt compelled to chime in with positive results. Used a couple of sock pairs to plug port in right Tekton Enzo XL. It has really cleaned up and tightened bass. Plugging both speakers was a little bit of overkill.

I have single REL sub, and could never get bass dialed in. Bass trap, cross-over/gain adjustments, speaker/woofer positioning... nothing seem to eliminate bloat in room. Plus, I don't know the science behind it, but midrange SQ is improved too.

All the best, and happy listening!

Thank you for that, @strateahed - That's pretty innovative of you, I'd not have thought to only do one or the other but it makes sense.

Glad you were able to get what you wanted out of your system now. :)

@erik_squires How does plugging the port keep the amp from trying to play down low? I don’t have any high or low pass filters in my system. I want to try your suggestion but can you explain why physically plugging the port will change the amp’s output? I realize it will change the outcome, but why would it change the out put?

Hi @hilde45 - I’m sorry if I mistyped but you are 100% correct. The amplifier’s output is a function of it’s input, for the most part. If you mean, why does dynamic range get improved, it is because the speaker’s excursion below the original tuning frequency is no longer as big. That means there’s more excursion left for the music above that Hz.

As you have guessed though, the amplifier's voltage swing for those notes remains the same.

Very interesting post Erik thank you. 

Socks everybody has them give it a try, I did some time ago but went 

back to wearing them. Lots of variables will affect the results.

It all depends on what you want.  I do not recommend filling the port or reducing the volume of your enclosure unless your speakers are poorly designed in the first place (or if they are designed to be optionally plugged).

I use a small REL sub using the high level inputs and turn it down (level and crossover) 'til it sound good.

Note:  I seldom listen above 70-75dB.  If you want louder with more thump I don't know what to tell you.

It all depends on what you want. I do not recommend filling the port or reducing the volume of your enclosure unless your speakers are poorly designed in the first place (or if they are designed to be optionally plugged).

Hey @kahlenz,

I think what few enough audiophiles understand is how much bass there can be from a pair of speakers once they are actually in a room, regardless of the specifications. We think we know based on the specs what is happening, but we don’t. Based on my experience as a speaker builder, and in-room measurements the advice I’m giving is solid, and best of all, easy to try and/or reverse.

This article I wrote may help some.