Coarse steel wool in near field speaker port?

[lbarratt]

This is something that has improved my BM15As. I have hated the ports as they have given me artificial bottom end. Can’t block them or the air can’t move. For a while now I have used coarse steel wool down the length of my speaker port. Anyone who comes into the studio from conductors to composers can hear the difference.(steel wool in/steel wool out) Thought I would finally share in a tip and secrets thread. No-one appears interested. Thought I would ask some higher end guys. (I also port my HR824s into the wall cavity.)

I am very heavily involved in writing some serious software and don’t have time to make up a marketable equivalent. Someone has already pointed out that you would have to watch out for steel fragments getting into your speakers. Coarse steel wool is very clean.
Thanks
LBarratt

[Eganmedia]

My BM15As shipped with foam plugs. Id use those before stuffing steel wool in there. Remember there are some awfully powerful magnets that will love to collect the iron dust as it breaks down. The foam plugs do tighten up the low end and stop the turbulance the ports can cause. I do like having the option to listen to them either way.

[John Willett]

The other option is to fill the ports with drinking straws - let's the air flow without the problems of a single large port.

[lbarratt]

Originally Posted by John Willett

The other option is to fill the ports with drinking straws - let's the air flow without the problems of a single large port.

Went out and got some straws. Haven't spectrafood it yet, but just according to my ears doesn't seem as good. The straws I got were very light,obviously not as dense as the coarse steel wool. Getting paranoid about these metal frags. I will put the steel wool in stockings. I will get around to spectrafooing one time.
This is a great community.
Thanks
Lach

[lbarratt]

Originally Posted by Eganmedia

My BM15As shipped with foam plugs. Id use those before stuffing steel wool in there.

The point is the foam stop air flow which affects the speakers ability to move. Haven't heard the proper foam.
I purchased floor stock-no foam. I have a dealer who really looks after me on price, but with a small price (no foam).
Thanks
Lach

[Bill@WelcomeHome]

You are in effect redesigning the speaker cabinet. If you like what you hear, so be it.

One possible problem (but probably not a big deal...) is the increased back pressure on the paper cones possibly affecting their lifespan and/or changing their response in frequencies above what the port brings to the table.

You may be hearing a better transient response... but you could be hearing just about anything as a couple of different parameters are altered by changing the port size.

And I have to wonder if you could not achieve the same audible result by moving the cabinets, as boomy bass on a known good cabinet design could have other causes, such as coupling to adjacent surfaces or the listener sitting in a room mode. The desk doesn't resonate? What happens if you change the vertical relationship between your ears and the port, do things smooth out?

Finally, you've queried the manufacturer about this? I'd be curious to hear what they had to say. Since all "full range" small speaker cabinets are compromises, maybe they gave up a touch of something in the sound in order to push the cabinet response to lower frequencies, and you've restored the 'better' design at the expense of a few Hertz in the low end.. they know all about it but had to make the compromise in order to put that extra few cycles of low end in their sales spec? If not, maybe they want to tighten up that port size to achieve the results you have achieved?

Interesting, in any event. Reminds me of the old idea of taping tissue over the NS-10 tweeters. I had one of the early pair, and they originally came with grille cloth... putting the original grille cloth back on the box achieved the same thing as taping the tissue over the tweeters... but it also disrupted the upper mids and was less pleasing over-all. We listened both ways and could not come to a solid consensus one way or the other, then Yamaha redesigned the tweeter to increase it's power handling, changes the stenciling to make it a horizontal box instead of a vertical box, and stopped supplying grille cloth. About that time the tissue-over-the-tweeter- idea went away.

[lbarratt]

I think acoustic design principles are changing. Years ago on gearslutz I commented on dividing corners with heavy flexible material to cancel out the bottom end. Some people joked about it, but now we have manufacturers suggesting dividing corners with thin bass traps.
Years ago some commented that sound was dissipated through heat. Now I think we are moving towards the idea that opposing sounds going into a material or down a fibre and the same sound going down the other end of the fibre or on the other side of the material will speed up the decay of that sound.

Put a piece of wood on a pillow and whack it. The vibration is absorbed by the pillow fibres. The idea of the steel wool is to absorb the vibrations and reduce the port resonating, but still allow as much air flow as possible. The resonating port will produce freq's according to it's length and width.

On my 15A when ported I can't mix cello, dist guitars, kick, bass ,etc because the port tells me that there is a thick dull bottom end and I should not add anymore bass. I try to clean up the bottom end with outboard, but because it is a pipe that is resonating due to many freqs(including higher ones) I start to destroy good parts of my sound to stop the resonance. My other speakers in the same place do not have that problem.

Pleae excuse-Some of my ideas are experimental and maybe crazy, but hopefully that is the idea of gearslutz. To explore our craft.

Thanks
Lach

[Bill@WelcomeHome]

Originally Posted by lbarratt

...
Pleae excuse-Some of my ideas are experimental and maybe crazy, but hopefully that is the idea of gearslutz. To explore our craft.

Thanks
Lach

" I think acoustic design principles are changing...."

less a matter of that than the average guy accepting principles which were previously scoffed at on these boards. The principles always held true and have been known for a long time, this audience just wasn't ready for the truth. (And in some cases, technology was unable to supply the required product to fit the known answer. Line arrays are far from a new idea, but technology has finally made them practical. )

"Years ago some commented that sound was dissipated through heat...."

a mis-stating/misunderstanding of the principle.

" The idea of the steel wool ..."

I understood immediately. I commented on the unstated... when you change the port size, which stuffing it with steel wool will do, you've changed the response. This may improve the bass but it may (or may not...) have other audible consequences. But it should have consequences. Otherwise we're saying that port size is immaterial, just cut a hole and let'er rip. (Not being a speaker designer, this may be true.... but I doubt it. I'm sure that there is a loose-truth there, because years ago when I was working on a ported stage monitor I asked the speaker company how to calculate the port size, and the answer was very unscientific.)

We get 'bright ideas', and on occasion they are brilliant in their simplicity and work very well, but seldom are they new untried ideas and usually a deeper look into all the aspects of what is happening reveals the underlying problem and a more practical solution.

(A tube packed with steel wool is a suppressor.....)

[Steve_B]

Placing drinking straws in the port was a fad that came and went in the ‘80s. Perhaps it is time for a comeback.

If you assume that straws, steel wool or foam acts as an acoustic resistance, its presence will lower the port’s Q. This has the disadvantage of causing increased cone movement.

[Petrus]

If somebody wants the tighter bass response of an acoustic suspension speaker, why not buy or make such a monitor? Like Yamaha NS1000M. Trying to turn a reflex speaker designed as such into a closed box, why? Speaker design is not only deciding between a box with a tube or without, the ideal bass driver specs are also different.

Another matter is that there are a number of badly designed and calculated bass reflex systems, and modifying them might not matter much and even improve them...

[lbarratt]

Originally Posted by Bill@WelcomeHome

" I commented on the unstated... when you change the port size, which stuffing it with steel wool will do, you've changed the response. This may improve the bass but it may (or may not...) have other audible consequences.

Wish I didn't have to change the volume of the port. If I hold an empty tube to the side of my speaker and do a sine wave sweep I will get resonant tone. This is the part I want to kill.

I am no genius. Just curious. I think we have lost a little in our understandings since we no longer have generations of a passed down knowledge from father to son in a trade and since people revere science rather than intuition(which I think is really hyper intelligence). The example is the guy who can think of Pi by staring at fractal patterns in nature. Give me an old well designed room to record an Orchestra in any time.

I did't know the straw thing. Wasn't as impressed with it's impact.

Thanks for all your helpful and possibly correcting thoughts.

Lach

[ray_subsonic]

Originally Posted by lbarratt

If I hold an empty tube to the side of my speaker and do a sine wave sweep I will get resonant tone. This is the part I want to kill.

Lach, What frequency is this cabinet resonance that you've found when you do this sweep? It's possible that frequency of this resonance may not correlate with the Bass Node you're hearing at The Sweet Spot.

In designing bass-reflex enclosures (using Thiele-Small parameters), the chamber of the cabinet is intentionally tuned to a certain resonant frequency/wavelength (to match the mechanical impedance of the driver). The port is again tuned separately (as the source of the majority of the volume velocity). Yet again, this may not necessarily be the same frequency/wavelength that is being reproduced at the Sweet spot. So, are you clear on which resonance you're hearing? Is the Bass emphasis your hearing (In the Sweet spot) in the 30-60Hz region, or sometimes higher up in the Bass register? (suggesting harmonics of the sub frequencies).

Have you been able to possibly A/B with a different set of monitors (rather than Mackie HR824's, again a near-field monitor with hyped bottom end) in the same position as the Dynaudios? Maybe a smaller Infinite Baffle (Non-Ported) designed monitor like an NS-10 might work? Maybe try de-coupling the Dynaudio's from the surface they're sitting on? Mopads? More Broad or More Tuned Bass Trapping along the wall behind your monitors?

Is your monitoring position (and your Dynaudio's) close to one of the walls in your room? What are the approximate Dimensions (Or the Volume m3) of your Control Room? Have you done any calculation of Room Nodes and Anti-Nodes?

I'm not trying to overwhelm you by asking all these questions. Your answers would provide immediate clues. It could be that the Dynaudios may be literally the wrong monitors for the room .. But conversely, there just might be a better solution to take excess bottom end energy out of the monitoring position, based on a few small changes. I'll be interested to hear your answers ..

Cheers

[Eganmedia]

Originally Posted by ray_subsonic

Is your monitoring position (and your Dynaudio's) close to one of the walls in your room? What are the approximate Dimensions (Or the Volume m3) of your Control Room? Have you done any calculation of Room Nodes and Anti-Nodes?

That was my question as well. Not to presume too much about what you know, but I have seen a lot of people complain about the bass response of a speaker without taking the room into consideration. Are you sure the resonance you hear when you sweep tone is the resonance of the speaker box and not the room?

[Bassmec]

Originally Posted by lbarratt

This is something that has improved my BM15As. I have hated the ports as they have given me artificial bottom end. Can’t block them or the air can’t move. For a while now I have used coarse steel wool down the length of my speaker port. Anyone who comes into the studio from conductors to composers can hear the difference.(steel wool in/steel wool out) Thought I would finally share in a tip and secrets thread. No-one appears interested. Thought I would ask some higher end guys. (I also port my HR824s into the wall cavity.)

I am very heavily involved in writing some serious software and don’t have time to make up a marketable equivalent. Someone has already pointed out that you would have to watch out for steel fragments getting into your speakers. Coarse steel wool is very clean.
Thanks
LBarratt

MONEL WOOL is what you want to stuff up your orifices!. if you absolutely must old chap.
Its non magnetic and does not corrode.

[lbarratt]

I love my 15As.
I am not the first to have a slight problem with a lack of clarity on the bottom end on the 15As especially-or other ported speakers.

I want a ported nearfield. I think non ported speakers are slightly more floored as far as nearfield design goes. An enclosed cab really does appear to affect the speakers ability to move because air pressure within the cab does not equal air pressure outside the cab when the speaker is moving.
I was just suggesting a slight compromise in design that works for me. I will pursue other materials rather than steel wool.

I have done extensive treatment and testing on my room for years after the one year build. It is a full on floating design. Tried different speaker placement over many years, etc. I am happy with my speaker placement. Yes my speakers are close to the wall, but I wasn't 100% happy with the 15A sound when it was placed off the wall(I still like the sound, just wanted to fix it a bit.) The Genelec installer in Aust has extensive arguments as to why your nearfields should be close to the wall. I happen to agree. My whole room is designed around this placement. Some gearslutz had me convinced otherwise for a while, but I now agree with this guy.

I would love an infinite baffle nearfield, but Dr Who Tardis technology isn't available to speaker designers yet.

The resonance I was talking about was if I hold an empty tube to the side of the speaker. I was suggesting that the port might act like this. I was suggesting the port might act like a guitar body and it may be helpful to dampen it whilst still allowing the bass freqs from air flow to continue.

Sorry I am not gifted in communication.

Love the discussion. Please don't get frustrated with me.

Thanks
Lach

[Liquid360]

I did that before, but it was a pair of socks stuffed in the ports. I was trying to make a "manual crossover" so the low frequencies wouldn't clash with my subwoofer. Worked.

[pan60]

why not sell them and get some monitor that would be more to your liking?
but definitely no steel wool: o~
straws, LOL sell-em: )~

[u b k]

Socks over here, gently rolled into loose tube shapes.

I will try monel wool, sounds fascinating. I too love experimenting, hearing the tradeoffs, and going with what my ears and experience conclude.

Seems so simple. It's probably not. Either way, I do what I do.


Gregory Scott - ubk