article about speaker ports that may interest listeners

Thanks for the link, Mike. That's some good reading.

My only problem with the bass-reflex design is simply that it's not flat throughout the lower end of its range. Having lots of bass isn't the same as having accurate bass.

It's a reasonable trade-off for most applications. The design is fine for a bass guitar rig or a PA system. After all, an equivalent enclosure with the same bass extension that wasn't ported would be impractically huge.

I was in a band once with a bass player who built his own speaker cabinet using conventional formulas for non-ported enclosures and a single 18" speaker. It did sound great, but would not fit through the back door of the van!

The article is aimed at audiophiles rather than critical listeners, or it probably would have stressed the nonlinearities that are inherent in ported enclosures. For casual listening, it's a reasonable trade-off to get more bass from a smaller box in exchange for marginally less-than-accurate bass response.

Of course, as I sit here looking at my ported nearfields and my ported subwoofer, I realize why most studio monitors are ported: these speakers would be 3' wide otherwise, and very difficult to mount on stands!

Drew, I'll have to re-read that in context but at first glance those numbers seem whacky.


"bitflipper


The article is aimed at audiophiles rather than critical listeners, or it probably would have stressed the nonlinearities that are inherent in ported enclosures. For casual listening, it's a reasonable trade-off to get more bass from a smaller box in exchange for marginally less-than-accurate bass response.

Of course, as I sit here looking at my ported nearfields and my ported subwoofer, I realize why most studio monitors are ported: these speakers would be 3' wide otherwise, and very difficult to mount on stands! "

Bit,
I have often fantasized about creating a regionally based speaker construction business that specialized in very large and great sounding speakers meant for the hi end South Florida mansion market. The idea is that shipping costs prevent all those poor rich people form enjoying good sound... and I can help. The business would be built around a dedicated delivery service so that all the logistics of shipping were included in the pricing structure. I like the idea because you might be able to work with out off shore competition dumping into your market and killing you off. The shipping costs will keep the importers out of that market segment. Of course most of the boat yards in Miami are selling yachts made n China... go figure... so my shipping cost theory may be full of holes. :-)


In any event, seeing how I am predisposed to appreciating all the best that ported design can offer I am sincerely curious to learn more about this non linearity that you speak of.

I understand that the a ported design, ideally, will allow the speaker to reproduce lower frequencies... but with significant roll off. The sealed design may be a bit flatter looking on a response graph but it doesn't even have any low bass (unless it's an ideally sized cabinet with a driver designed to produce low bass) so how is hat really any flatter. The extra bass offered by the bass reflex design is closer to the flat line than no bass at all... ???

So I must be missing something... and I'd like to learn your perspective.

One thing I was looking for yesterday but could not find is credible info about ports and the claim that out of sync sound blows out of them no matter how well designed. I was also curious about the front and rear location debate. I have too many experiences with well designed ported cabinets to think there's noticeable problem with a well designed port... and I've also seen *undesigned* ported systems that had all the problems.

Years ago when my LaScala bass horns needed new woofers I ported the sealed box in the middle with appropriate sizing after I had selected the fresh drivers. Those thing will thump you in the chest at 200 yards... they are like a weapon. I put the ports on the bottom... no one ever knew ;-).

I have a few ginormous bass boxes as well... goodness all that stuff is so big it lives in the shed.


best regards,
mike

edit spelling

mike_mccue


Drew, I'll have to re-read that in context but at first glance those numbers seem whacky.


 

Looking at it in retrospect, it's true that 10*log(200) = ~23dB

But I'm so used to "20*log()" style dB's (i.e. the squares of the ratio, not the ratio), in which case 24dB = 10^(24/20) = ~16, not 200.

But it's possible he's technically correct, as I don't think he defines what he means by "output" (so I don't really know which dB interpretation is correct). But if we are talking about the ratio (rather than the square of the ratio), then 10^(24/10) = ~251, not 200, anyway.

As always, I could be wrong...

I think the thing here is that very accurate monitors can be designed and they can be either sealed or ported so it does not matter that much. But thanks Mike for the link to that article. Interesting reading and good to understand a bit more about how it all works. I do agree with Dave though that if your speakers are going to be close to a wall, then a sealed design might be better for you, compared to rear firing ports or passive radiators.

Back in my Hi Fi days we definately preferred sealed enclosures and one of the best was the Britich Leak design.  I think ported designs were perhaps not as good then as they are today.

At the moment I am listening to ported monitors and they sound great. Especially since mounting them on the heavy concrete stands. A lot of low end colouration has gone away and the monitors sound very smooth down there and more like a sealed enclosure now. I can't believe how far an 8 " driver can go down.

Also Dave I am not sure I agree about the lowest frequencies being around 50 Hz in film soundtracks. As someone who has written music for film, one of the oldest tricks in the book is to drop in very low frequency sounds into the soundtrack to create a sense of impending doom. Well below 40 Hz for example. I think theatres are well equipped to handle frequencies well below 40 Hz.  Even 20 Hz is quite noticable and sub bass frequencies (octave down from normal bass octave) are also often dropped in. Some of the FX tracks would go below 40 Hz as well I am sure.

I hope everyone has a very Merry and safe Christmas too.

Ever wonder how those little ear buds get frequencies down to 30 - 40 hz?..Because it has very little to do to the size of the driver. It has to do with efficiency and balance . A 5" woofer has just as easy a time wiggling at 40 Hz as does an 18" woofer. It's just that larger woofers can match the efficiencies of high frequency drivers with less power when listening loudly in a large room. So if you wish too have a full range system with a 5" woofer you need to lessen the power to the high frequency driver in relation to the woofer...then use them near field, or , double up on that 5 " . It's not about the size of the low freq, driver..but about how much air it pushes in relation to the high freq. drivers.

All the talk is of ported or sealed enclosures, but what about transmission line techniques. Back in the late seventies I ended up building 6 pairs of DAlines (decoupled anti-resonant transmission lines) using KEF B110s, T15s and STC 4001Gs, not all for me. Bass extension flat down to the mid 20s (Hz). Great for organ pedal and Grand Cas. See here: http://www.tech-diy.com/LS_Articles.htm .

SysExJohn.

All the talk is of ported or sealed enclosures, but what about transmission line techniques. Back in the late seventies I ended up building 6 pairs of DAlines (decoupled anti-resonant transmission lines) using KEF B110s, T15s and STC 4001Gs, not all for me. Bass extension flat down to the mid 20s (Hz). Great for organ pedal and Grand Cas. See here: http://www.tech-diy.com/LS_Articles.htm .

SysExJohn.

Enclosures that employ a Transmission Line design are often used in full range driver systems (i.e., 1 driver in the speaker) ...

... and not to go off topic but the things I was surprised to see coming over to this thread were the magic plant stands.

It was just pictures not much talk about the actual design:

http://forum.cakewalk.com...;m=2146353&mpage=6

post 154

post 164

Some photos just for fun:

This was an early venture into speaker building for me.  The plan for the folded horn design was purchased from Speakerlab and was built in senior woodshop (’82) using 2 sheets of plywood.  The driver inside the horn IIRC was a 15” PAS.  My goal really had nothing to do with fidelity … strictly volume!  The “system” used an EV X-over and a Peavey horn and driver on top.  At the time budgetary constraints limited me initially to a simple stained plywood finish but a few years later the Peavey horn was removed and the cabinet was refinished with a wood veneer.  Unfortunately (and I really wish I had other photos of this speaker), this is the only existing photo I have of it and the expression on my face is ridiculous so you get the “head removed” version of the photo.  Note that the corner of the cabinet captured in the foreground is an EPI 100.



This is a dorm room circa ’84.  The turntable is a (still functional) Dual 606.  The plinth is essentially just a plastic box.  The turntable simply sits on springs making the thing very susceptible to vibration.  Again, my goal was not fidelity but to keep it from skipping.  This is the only photo I could find of it … apparently either before I had access to a lever or before I sobered up.  And I do remember using rubber automotive bushings which are not in this photo so I must have made some mods at some point.  Note that the Onkyo receiver pictured was given to my father sometime in the late 80’s or early 90’s and has been in constant operation since.



Warning: I am a chemist by training and have no business with a soldering iron so if you have a weak stomach you may want to avoid the next 2 photos … that said:

I really don’t have a lot of time to pursue speaker building now so I try to do a little dabbling once in a while.  Here are photos of the guts of a recent (2010) project; a pair of Ohm C2’s that were acquired fairly cheaply on e-bay.  The C2’s in their day were one of the biggest selling consumer bookshelf speakers.  The wood veneer was perfect but the speakers themselves had issues.  The top photo is the original X-over and the bottom photo is a reverse engineered homebrew X-over.  I am using these speakers in a system that consists of a 70’s era Crown preamp, an 80’s era Phase Linear (series II) amp and a 90’s era Micromega CD player.  This project is still a work in progress … I still need to tweak the X-over by experimenting with the resistor.

The choice of a driver goes beyond just size and the use of multiple drivers to achieve a larger surface area like any aspect of speaker design has its advantages and disadvantages. A speaker is in part, characterized by its free air resonance F(s) and this will be a function of the mass of the cone and the compliance of the suspension (spider and surround), these are analogous the m and k in the equation for a spring with a weight on it. If you plot impedance vs. frequency there is a peak at the speakers F(s).

That is exactly true..... and in practice the F(s)  goes out  the window as soon as you place the driver in a cabinet and place it in a room. That is the function of cabinet design and room treatment. But it also has a lot to do with local reflection/coupling. My point being that the F(s) has a lot to do with the actual system design but very little to do performance after integrating a properly designed cabinet and install location.

" At a given F(s) for a given speaker size and given speaker design, a choice (or compromise) has to be made wrt to Q and other characterizing parameters."

In other words you can make a 15" driver sound like a 3" TV speaker if screw up the design well enough...and conversely you can make a 5" driver sound like a 15" with the correct design and proper monitoring levels. What I think is over simplified is that a larger driver equates to better low end response, but I think that a whole lot more goes into it........most of which is user defined by monitoring levels and placement.