"bunging up" ported speakers a good or bad idea?

[dbbubba]

The people that design gear generally know what they are doing.
They don't design in ports for the hell of it.

I would leave them alone and divert your attention to something more worthwhile than customizing bass reflex speaker ports! (half kidding...)

[MarkRB]

Yeah, bit of a mad idea really. Without the port you will ruin the response of your drivers because it all operates in the same 'air'.

Are you using more than one set of monitors at a a time?

[dubrichie]

Originally Posted by MarkRB

Are you using more than one set of monitors at a a time?

not when i'm sober and actually working!

[MarkRB]

Haha, there's been loads of advances in recording by people saying "what happens when I press all the buttons at once?" and you know they were drunk or other at the time!!

[dbbubba]

Yeah, but a lot of people have been drunk or what-ever, pushed in all of the buttons tore up their gear.
Ask a good tech.

[MarkRB]

Originally Posted by dbbubba

Yeah, but a lot of people have been drunk or what-ever, pushed in all of the buttons tore up their gear.
Ask a good tech.

When you're drunk?

Tech's bore the shit out of me when I'm straight, let alone when it's 3 am and I'm feeling creative.

Should I ask a tech if I should use a guitar pedal on an insert or should I just do it and live with the consequences good or bad?

Each to their own and that, but I never subscribe to the "ask someone" school of thought unless the gear isn't mine and I think there is a fair chance I might blow it up.

For the record I've never blown a bit of gear except a tweeter trying to hear a 22kHz tone. Live and learn.

[Francis Vaughan]

Blocking up the ports can only make things worse.

The choice of driver and cabinet alignment (which includes cabinet size and ported or not) go hand in hand - you can't change one without the other. Blocking the port will simply wreck the bass alignment of the speaker, change the Q of the system and generally fritz with the sound.

The idea of smearing of sound with ported comes from the difference between a 2nd order and 4th order alignment. The group delay through a 4th order is messier than a 2nd order, but the designer still has a lot of freedom in the exact parameters chosen. Many ported speakers do exhibit a deliberate bit of added oomph by choosing a higher Q, but good ones don't.

The characteristics in the upper bass and up are not affected by the port at all. At these frequencies the port is acoustically invisible.

There is a remaining danger that the bass driver can be driven past its excursion limits if you block the port. The way the resonance of the speaker works changes between closed and ported, a ported system has minimum excursion at resonance, a close system has maximum. Thus high levels of bass can kill a closed speaker that was not designed from the outset to accept those levels. This change in excursion behaviour can also cause second order changes in the sound, which may or may not be perceived as beneficial.

[joelpatterson]

I jammed gobs of plastic bag material into the ports on the Tannoy Reveals I had set up once and it made them sound way better, like WAY better. Lost all of the murky, boomy action, and made them easier to listen to.

Of course, that was stupid, and evidence of criminal insanity... (and I showed such promise at one time!)

[dubrichie]

hmmm.

interesting.

tell you what, i'll give it a go and see if i like it.

[Jimbo]

My Dyn BM6 passives were shipped with foam plugs to use in the ports.

The manual said to use them:
1. to tighten up the bass
2. if the monitors are near a wall.

[seriousfun]

Plugging a port will change the LF rolloff, typically from 18 dB/octave (often with a bump around the resonant frequency of the port) to 12 dB/octave (no bump).

This can result in better interaction with a boundry (as above with the Dyns) or a subwoofer.

No assumptions can be made, but if you know what you are looking for you might give it a try.

[dbbubba]

I once had a pair of soffit mounted Tannoy monitors that were the rough equivalent of an Altec Big Red or a UREI 911 (I forget the model number.) Maybe it was SGM-15?

For some reason they sounded wrong in a very well designed control room that was based on VERY famous plans and specs.
After a few years of battling with these monitors we discovered that they we actually the front baffles of the Tannoy SGM15s (?) fitted into the enclosure or box of a UREI 911.

The UREI 911 box was actually a bit smaller than the Tannoy SGM15 enclosure, so the ports were wrong for the actual enclosure volume.
The difference in volume was not very much either.

The previous owner had inserted foam pieces into the Tannoy ports in an attempt to minimize the problems created by the mismatch.

In the end we were able to obtain the original boxes and re-attach new front baffles in a manner than were probebly stronger than the original design.
Tannoy in Kitchner, Ontoario assisted us in doing this.

In the end, the speakers were re-hung and coupled with the room perfectly.
They are still hanging in the room over seventeen years later.

Wrong enclosure to port ratio... inserting foam pieces... what-ever...
None of this made the speakers sound correct.

If you want to experiment... go right on ahead.

The person who did this modification in the first place was a VERY knowledge-able engineer/producer who's credentials reach back to 1958.
he thought he was doing the right thing, too.

[Francis Vaughan]

If you are the designer of the speaker, and in the case of Dynaudio, the manufacturer not of just the speaker, but of the drivers as well, you are able to design the speaker around the idea of multiple alignments. The design of the driver itself in such circumstances is constrained, not just the box volume. Also, the foam plug might not be a total seal, it may well be a resistive plug (something Dynaudio have a lot of experience with) that is precisely designed to work with the rest of the speaker design to yield a correct and different alignment to the ported version. There are examples of this idea going back decades.

[Neal]

Put a sock in it: advice from an expert:

Monitors Demystified, Part 1: Compromise & Approximation

[oldeanalogueguy]

Originally Posted by dubrichie

alrighty,

i am considering "bunging up" the ports on my Adam ANF-10 nearfield monitors.

i have always preferred the sound of sealed enclosures to reflex and only want the Adams for their mid-high frequency transient response and detail. my mid/mains are PMC TB2S-A in 2.1 with a TLE-1 sub. the room is very well treated and the speakers and mix position are optimized.

since i am not concerned with the bass extension of my ANF-10s and like the idea of reducing mid-range smearing and improving transient response would i be wise to bung their ports? would this adversely affect the overall tonal balance of the speakers, since it is forcing them to behave outside of what they were designed for?

i'd love to know, but don't know quite enough to figure it out right now.

thanks,

bad idea

they were designed to work that way
changing them will not make them better

if you like the otehr type design
then buy those

[ofajen]

Originally Posted by oldeanalogueguy

bad idea

they were designed to work that way
changing them will not make them better

if you like the otehr type design
then buy those

Precisely. Driver, box and type of system are designed as a whole. For a given driver, the optimal closed box size is typically considerably smaller than the optimal box size for a ported system, assuming the same total Q for the system (let's say both are critically damped with total Q of .7). I share the preference for a sealed designed, but the best course is to build or buy an optimal sealed design system. There are some excellent off-the-shelf sealed box speakers that are very reasonably priced.

Cheers,

Otto

[Karloff70]

I'm with Patterson, don't ask for permission, it isn't going to blow them up, just do it and you'll soon see if it makes them more useful to you or not. Report back findings please....curious.....

[Karloff70]

Originally Posted by ofajen

Precisely. Driver, box and type of system are designed as a whole. For a given driver, the optimal closed box size is typically considerably smaller than the optimal box size for a ported system, assuming the same total Q for the system (let's say both are critically damped with total Q of .7). I share the preference for a sealed designed, but the best course is to build or buy an optimal sealed design system. There are some excellent off-the-shelf sealed box speakers that are very reasonably priced.

Cheers,

Otto

If you feel the desire to name a few I wouldn't stop you at all......

[ofajen]

Originally Posted by Karloff70

If you feel the desire to name a few I wouldn't stop you at all......

Blue Sky and NHT come to mind, just to name two. They each have a range, and typically you pay more for a bigger box and lower 3 dB down point in the bass, though the Blue Sky systems are designed with an integral, sealed sub, so the difference is more in terms of how big of a room they can handle and where the satellite/sub crossover will be, and not so much how low they go. Also at the low end, Cambridge has a remake of the old classic KLH Model 6.

Cheers,

Otto

[Karloff70]

Originally Posted by ofajen

Blue Sky and NHT come to mind, just to name two. They each have a range, and typically you pay more for a bigger box and lower 3 dB down point in the bass, though the Blue Sky systems are designed with an integral, sealed sub, so the difference is more in terms of how big of a room they can handle and where the satellite/sub crossover will be, and not so much how low they go. Also at the low end, Cambridge has a remake of the old classic KLH Model 6.

Cheers,

Otto

Thanks for the tips, Otto!! On the slight lookout for closed boxes at reasonable cost to replace the job of the 10's which I can't bear anymore........Those Cambridge's look vaguely interesting....

[88fingerz]

I stuffed some white sweat sox into the ports of the new mackie MR5mk2...they now sound eerily similar to.....

NS-10s.

Actually, not a bad thing IMHO. Nice compliment to my Dynaudio BM5as.

[ObiK]

Try it and see if you like it.

[Neal]

I also put socks in the ports of my Yamaha HS-80s and just can't bring myself to take them out now. Lost all the useless boom and gained so much definition.

The only warning I found was with the lose of some volume, you don't crank your speakers. That could hurt the drivers.

Phil Ward suggests this as a way to improve your mixes if you're stuck with ported speakers. Mike Senoir actually had a graft in his book Mixing Secrets For The Small Studio that shows a before and after of a ported speaker performing better with the port stuffed.

Next time I buy, no more ports.

[MarkRB]

Can anyone explain what is going on when you "stuff" a port with socks or whatever?

The logical side of my brain says that you would be restricting movement of the cone by not allowing the speaker to suck in enough air for it's needs.
Therefore slowing it down and restricting it's movement, which would result in slewed response and a significant drop in it's low end response.

Is there a good side to this bizarre practice?

[Panelhead]

Originally Posted by MarkRB

Can anyone explain what is going on when you "stuff" a port with socks or whatever?

The logical side of my brain says that you would be restricting movement of the cone by not allowing the speaker to suck in enough air for it's needs.
Therefore slowing it down and restricting it's movement, which would result in slewed response and a significant drop in it's low end response.

Is there a good side to this bizarre practice?

The sealed box, acoustic suspension, offers driver dampening, transient response, and slower roll off. You give up extension on the bottom and overall efficiency. A sealed box CAN match a ported or reflex design, but has to be in a much larger enclosure. Like four times more internal volume.
A larger cabinet has trade offs also. More radiating area, need for more rigid panels, and COST.
That is why most speakers are ported. It is just easier to make money building ported designs.
But AR revolutionized speakers with the AR-1. It offered bass in a smaller box. Just required more power.
I just switched from ported monitors to sealed box. Not going back. Horsepower is cheap.

George

[Neal]

Originally Posted by Panelhead

The sealed box, acoustic suspension, offers driver dampening, transient response, and slower roll off. You give up extension on the bottom and overall efficiency. A sealed box CAN match a ported or reflex design, but has to be in a much larger enclosure. Like four times more internal volume.
A larger cabinet has trade offs also. More radiating area, need for more rigid panels, and COST.
That is why most speakers are ported. It is just easier to make money building ported designs.
But AR revolutionized speakers with the AR-1. It offered bass in a smaller box. Just required more power.
I just switched from ported monitors to sealed box. Not going back. Horsepower is cheap.

George

May I ask what system you bought?

[ofajen]

Just for fun, I'll mention that you can pretty well predict the low end behavior you will get by blocking the speaker ports if you know the internal volume of the box, V(b), and the following three numbers for the bass driver:
1) the free air resonance, f(s)
2) the driver's resonant magnification at f, Q(ts) and
3) the air volume with an equivalent compliance as the driver, V(as).

Knowing the ratio V(as)/V(b) allows you to determine the ratio of Q(b)/Q(ts), where Q(b) is the resonance of the system. This allows you to determine Q(b) which tells you how "peaky" the response will be around the resonance, and, since you know f(s), it will also tell you what the resonance frequency of the system will be.

There are various calculators online to help work through this, though usually one is working in the other direction, with the driver parameters known and determining the optimal box size to generate a desired total Q for the system. I just use the charts in my old Radio Shack book on speaker design.

In this case, all is determined, and you get what you get. Too small of a box will be boomy with reduced bass range, too big of a box will give weak bass and reduced power handling. Of course, you might get lucky and the existing ported box will happen to be a good size for a sealed box.

Cheers,

Otto

[Panelhead]

Originally Posted by Neal

May I ask what system you bought?

They replaced a Quad 2.1 system with about the same size drivers. The Blue Sky System is designed to use a sub. The Quad is designed for stand alone use. So not apple to apple comparison.
The upper bass is much better controlled with sealed box. The Quads could get hooky if too close to a wall. The acoustic suspension monitors are less effected by placement.
But there are plenty of awesome ported and transmission line speakers. It is all design trade offs. One test I use is to rap the top of the speaker with my knuckles. This let's you hear the impulse sound of the cabinet.
Try a few sealed box and ported designs. See what they do to "color" the sound. The Quads were like a guitar thonk. Musical instrument type overtones. The BS SAT 6.5 Mk II make almost no sound.

George