Romy,

Regarding your first illustration:

Some time ago I intentionally made two different boxes for my ScanSpeak drivers to see what will happen, because I do not believe in theories and trust only to my ears. The boxes had exactly the same internal volume and front baffle width, so the only difference was in their actual proportions (height and depth). The first one was very tall and very shallow, the second one was little in height but very deep.

There was HUGE difference in sound. The deep box sounded much more articulated and with ease at the dynamic peaks. The improvement in sound was most remarkable in the upper range of the driver. The only reasonable explanation I have for that is that the back wave form the driver bounce back to the cone and interfere with the front fired wave, adding delayed signal with high amplitude. If the back wall is very far from the driver’s diaphragm, the energy of the reflected wave is very low thus the sound is more clear and better defined. In comparison the sound of the shallow box was some kind of polluted at MF, loosing definition and dynamics (micro and macro), the midbass was quite excessive and unlistenable, although SS is quite nice driver.

So I think the depth of your box is of much greater importance than the exact location of the ports at the bottom and I definitely think the design “B” is going to have better sound.

My thoughts about your second illustration:

I’m not sure if my interpretation of the picture is right, but the port of speaker “B” seem veeery long to me. That means the tuning will be extremely low and the acoustic system should behave more like sealed box rather than typical bassreflex design. It is true if you tune it below approximately 20Hz but I hardly see any sound benefits from this kind of bass loading. The longer the port is, the lower the Fb will be and vice-versa (if the port area is the same). What is your motivation to use so long port?

haralanov wrote:

Some time ago I intentionally made two different boxes for my ScanSpeak drivers to see what will happen, because I do not believe in theories and trust only to my ears. The boxes had exactly the same internal volume and front baffle width, so the only difference was in their actual proportions (height and depth). The first one was very tall and very shallow, the second one was little in height but very deep. There was HUGE difference in sound. The deep box sounded much more articulated and with ease at the dynamic peaks. The improvement in sound was most remarkable in the upper range of the driver. The only reasonable explanation I have for that is that the back wave form the driver bounce back to the cone and interfere with the front fired wave, adding delayed signal with high amplitude. If the back wall is very far from the driver’s diaphragm, the energy of the reflected wave is very low thus the sound is more clear and better defined. In comparison the sound of the shallow box was some kind of polluted at MF, loosing definition and dynamics (micro and macro), the midbass was quite excessive and unlistenable, although SS is quite nice driver. So I think the depth of your box is of much greater importance than the exact location of the ports at the bottom and I definitely think the design “B” is going to have better sound.

I am sorry, you might mistyped. You meant to say the design “A” is going to have better sound, do you? The design “A”  has more deep box.

haralanov wrote:

My thoughts about your second illustration: I’m not sure if my interpretation of the picture is right, but the port of speaker “B” seem veeery long to me. That means the tuning will be extremely low and the acoustic system should behave more like sealed box rather than typical bassreflex design. It is true if you tune it below approximately 20Hz but I hardly see any sound benefits from this kind of bass loading. The longer the port is, the lower the Fb will be and vice-versa (if the port area is the same). What is your motivation to use so long port?

Well, I have no other motivation then juts to make it comprehensible that the ports lengths are different. I certainly am not planning to go it so long, but I was wondering how the length of the port and the most important the proximity of it to boundary affects sound. I might have the same port diameter and the same length but the port might stat from an open middle of the box vs. the port might start a few mm from an opposite wall. That what I was trying to depict. So, Petar, what would please to comment on it. Also, if the exit of the pot is important for pressure synchronization (you use horn-like profile and I like it) then can we presume that enters of the how might be benefited from gentile pressure transformation? Would in such case something like this to look overly ridicules?

Romy the Cat wrote:

...but I was wondering how the length of the port and the most important the proximity of it to boundary affects sound.

Lbjefferies7 wrote:

Now, as for your drawing of the exaggerated port flaires, it is excessive.  A port is not a horn and, from an engineering standpoint, I treat them very differently.  A port is a resonator.

Oh, sure I understand it and drew it excessively solely for the sake of illustration. I have see a few companies did the exit of the horn in semi-horn profile, so that lead to a question of the entrance of the Helmholtz resonator might be benefited from the semi-horn shape.

Lbjefferies7 wrote:

Using ports as anti-compression devices is just plain bogus, in my estimation.  Above the port's tuning frequency (Fb), the enclosure acts just as a large sealed enclosure.  Below the Fb, it acts as a quasi-infinite baffle system.  When the driver reproduces the Fb, the port "opens up" at the Helmholtz frequency...where the air masses in the box and in the port reach a "balance" where the output of the port is 365 degrees out of phase with the driver.  The responces of each resonator combine and create a greater overall response.  By tuning the port, the port's output can extend the sealed response of the acoustic system.  This is how I understand it, at least.

Yes, it is a perfect explanation and it is how I understand it but read below…

Lbjefferies7 wrote:

Now, Petar is spot on when he says that the Fb must not be below the resonant frequency (Fs) of the driver.  If it is, you will certainly get a horribly disgusting cone-flapping sound and may just fry your drivers.  The vision of murder will be dancing in your head...like sugarplums on steroids!

Ok, this is exactly where I am a lost. As long we keep the port’s resonance below driver’s resonance then I agree that we are at more or less save ground. Even I - the person who never experimented with poet in my live- have written about it at in past. However, if we accept this premise then we defeat the entire purpose of using ports. Of cause we would like to have LF EQ on the enclosure in compare to a sealed solution. Of cause we would like to drive the port’s resonance below the driver/enclosure resonance to get more bass out of the situation, without use of ultra low Fs driver and increasing the size of the box. Or cause we would have a sever driver reactance when the resonances “meet”. Aren’t they all the ideas of port use and isn’t it how it works in all bass reflex loudspeakers. I was under presumption that by embracing the horn idea we are by default let the amplification, filtration and other thighs to deal with driver “comforting” during the cone-flapping… If we keep the Fb above the Fs then why do we need to a port to begin with?

Romy the Cat wrote:

Of cause we would like to drive the port’s resonance below the driver/enclosure resonance to get more bass out of the situation, without use of ultra low Fs driver and increasing the size of the box. Or cause we would have a sever driver reactance when the resonances “meet”. Aren’t they all the ideas of port use and isn’t it how it works in all bass reflex loudspeakers. I was under presumption that by embracing the horn idea we are by default let the amplification, filtration and other thighs to deal with driver “comforting” during the cone-flapping… If we keep the Fb above the Fs then why do we need to a port to begin with?

I do not know what the Fs of the drivers that will be using. I did not measure them yet.  I have one of them in ¼ cub feet box with a port making 65Hz and two of them in 1/2 cub feet box making 38Hz. If I found more of the them then will be unit 4 of them per box, so I presume that I will be able to go quite low in 2-3 cub feet box. If I do have a notion in my head that the ported bass will suck anyhow then why do not get a full bass?

Well, here where I hit a problem. The “suck ported bass” is not a Boolean but it has moderation and it might be “the better crappy ported bass” and “worse crappy ported bass”. The keys in it are some kind of agreeable with subjective results moderation that would greatly depends of the specific implementation.   If you look at the LBJ, Petar and few others who try to help me in the MiniMe thinking then it is obverses that there are some “kinks” that would move the posted bass from “bad” to “horrible” but I am affair that without the trials and actual evaluation of the results it is very difficult to say how it will works, particularly if I am willing to get MORE bass and to drive the port resonance all the way down as far as the array of the 4 driver permits me.

So, at think moment I think where the get those drivers of mine and when I get them then I will come up with some kind of steel enclose the THEN will be bitching to anyone that it sounds very “porty”. However, the single 4” woofer that I found in ¼ cub feet with port (with temp tweeter), even those it has all characteristic of the “bad port sound”,  still does excellent in context of the requirement and defends I impose to the  MiniMe acoustic system. If I have in my final MiniMe version the same LF Sound that I am getting now from ¼ cub feet box (I hope to get less port noise due to 4 drivers and much larger enclosure) then supplementing with much-much better tweeter and spiced some interesting techniques the those woofer allow to employ (Some form of the “Resonant Oops”) I feel it will be happy like clam.

For the sake of helpfullness, I think that we may separate the differences of the ported speaker designs of myself and Petar.  What I have described is the standard, pedistrian model of a vented speaker.  Petar's is a hybrid aperiodic-ported design.  It is a less-than-vented design tuned to a particular frequency.  It's nice and can probably produce a nicer sound than a purely vented design, but in Romy's application (getting somewhat acceptable bass from 4 inch drivers) it may cut the effect of the port to severely.

Let me tell you about the small speakers that I built and had mentioned earlier.  They used the Peerless 830854 poly midwoofer with an Fs of about 75 Hz.  The goal of the speaker was essentially the same as Romy's...Small with relatively okay bass.  After a lot of modifications (including an Oops resonating soundboard back) to the origional design, it was successful.  I could play Bach's 2nd Cello Suite on them and enjoy it without the port farting out an indistinct noise.  They were very pleasant in the context of non-serious listening.  They measure just about 5.5 inches deep, 11 inches high, 7.5 inches wide (roughly) and I powered their 87 dB sensitivity with a barbarian Crown amplifier.  Once I have a place at home to set up, I'll be using them again, exactly as I did before...As my "its not a musical instrument but it won't piss me off" speaker.

I am very familiar with the ported M-Audio BX-5a "studio monitor."  Perhaps I am dimwitted, but I have no idea how these commercial companies can be so talented at making a port sound like a port!!!  Not only does the carbon fiber cone impart such a revolting, idiotic, tone, but the wildly flaired port blows and humms until my ears run with blood!  Not even in my days of dumpster diving for free drivers have I gotten such bad port sound as I have heard from nearly all commercial speakers.  It may relate to the thin walled plastic or cardboard ports they use.  My newer ports are made exactly like your horns, just with a straight profile...Stacked and glued MDF.  One difference of the port in my MiniMe speakers is that they are ABS pipe that have been damped and lined with an idea that I ripped off from B&W.  Their big thing is dimpling their flaires like the surface of a golf ball.  Not to be outdone (I was like that in those days), I spread on epoxy and lined the inside of the port with silica gel balls!  The damping effect of this treatment was probably much more beneficial that the aerodymic aspects, however.

Anyway, the best advice I can give is to make your enclosure very versitile.  With your drivers, with your amps, with your sources, with your goals, and your music, they are going to need to be very much your speakers...not mine or anyone else's.  Building a purely ported design could bring the results I think you are looking for. 

As for tuning the ports below the drivers Fs; give it a try... I've heard the "flapping cone" sound, I did some hands-on research.  I recently repaired the amplifier of a pair of self-amplified Bose speakers.  I pluged the passive speaker into my system and listened to it produce some really screechy, shouting, terrible sound.  Once I had the amp fixed, I fired them up to hear the really bad cone flapping drone without the shout or the peaky mid frequencies.  Obviously, Better Sound Through Research means using an equilizer to "fix" a fundamentally flawed speaker.  So, with the recent findings, I am reconcidering my "impossible to use port's below Fs" attitude.

Kindest Regards,
LBJ

Thanks, LBJ, I ma slowly getting into where I would to be in term of understanding, at least it is what I think I do. You are perfectly identified what I am shooting for: "its not a musical instrument but it won't piss me off", it is exactly what I would like it to be.

I few more questions. Take a look at the image below:

The difference would be juts the volume of the boxes and the consequentially the lower loading of the drivers in infinite baffle state, theoretically in larger box I might drive the driver have in “sealed state” but would be port acting in oversized box differently? I can make the box at tall as 72” but I do not think that my driver will be able to pressurize this volume. As I understand the port shell kick-in at the bottom of the acoustic suspension (hypothetically spanking). So, if I get 8 of those drivers then I can pressure-load a larger box and let the port to do less. Correct me if my assumptions are wrong.

 And one more question. What you feel would be a difference between those 3 cases?

Very good.  Raal 70-20XR...interesting.  Where are you planning to cross these over?

I remember the discussion about the internal balloon.  That is a very good idea and this may be the perfect opportunity to try it.  It will also be interesting opportunity to work on enclosure damping methods.  Being made of steel, they will probably make all kinds of noise without some help.  I have used frequency sweeps and a stethoscope to find the resonant modes in enclosures and strategically damped them out.  It worked out very well.  Today, I thought of something that may be worth trying.  With a steel enclosure, you might try glueing (silicone glue would be perfect) some hockey pucks over the most resonant areas.  It should work, they are easily removed if it doesn't, and best of all, hockey pucks cost 99¢ each.

LBJ

Lbjefferies7 wrote:

Very good.  Raal 70-20XR...interesting.

Oh, yes, the 70-20XR is very interesting. I did not have this driver but Alex allowed me to experimented with some elements of it’s design in context on my “Water Drop” tweeter and it was quite remarkable. I end up do not use those “elements of it’s design” with “Water Drop” as my tweeter has different objectives but in context of the 2-way MiniMe the 70-20XR’s “elements of it’s design” shell show themselves vey very positively.

Lbjefferies7 wrote:

Where are you planning to cross these over?

You have no idea how loaded this question. The crossover point with the MiniMe is not a tactical question but actually the very strategic question of the entire speaker, let me to explain why. The woofers that I use are fairly bizarre – they are what made me to think about the MiniMe. They have diaphragms made with reinforced fabric, the outer suspension is rubber. However, the reinforced fabric is semi-soft in the similar elasticity as the outer suspension. So, it is not a piston motion (like in foolish ceramic drivers) but rather motions with a lot of break ups – the right motion in my books. But then is the kink of the driver- the dust cap. The dust cap is inverted dome of aluminum and it the way how it placed makes the dust cap as the literally keystone of the diaphragm resonance. It is sort of the resonance’s lighting rod – if you see the driver then you understand why I got enthusiastic about it. Now, the woofer goes up, let say to 4K-5K and the dust cap begin to ring. The similar effect to JBL LE8 that also has metal dust cap. Here is where I will be playing with my woofer – to tune by ears the dust cap’s resonances. You see, that dust cap ring in a very measured dosage is in fact very good (in context of these speakers) as it works like the “Oops-resonator”. I will damp the dust cap by painting the driver with volcanic ash (no speaker white cones in my home!!!). That will extend the safe operation of the driver for 500-1000Hz up but the primary tuning tool for me will be the crossover point. So, I will be searching for crossover point by just listening the Oopses with witch the woofer’s dust cap will resonate – where it will become too much Oops then I will cross right there… Well, here is the question: how the woofer’s dust cap will behave if I have 6-8 woofers per channel and the excursion of each woofer is substantially minimized? I have no answer now but I think I will found another 2K of response. Then we have the HF’s cancelation coming from the line-array configuration… It will eat the HF but will it each the dust cap Oops-resonances with the same appetite? I have no answer now… How the “not eaten” residues of the HF woofer resonances will be “subjectively friendly” to the distortions of the 70-20XR tweeter’s lower knee? I have no answer at this point. I need to found the woofers, to build the box to screw the array of the woofers and the tweeter in and start to run the crossover point up and down, to hear how it will work all together. I have no planning to cross at a specific point I will cross it wherever it will be, I anticipate that it will be somewhere between 2K and 6K, most likely a second order.

Lbjefferies7 wrote:

I remember the discussion about the internal balloon.  That is a very good idea and this may be the perfect opportunity to try it.  It will also be interesting opportunity to work on enclosure damping methods.  Being made of steel, they will probably make all kinds of noise without some help.  I have used frequency sweeps and a stethoscope to find the resonant modes in enclosures and strategically damped them out.  It worked out very well.  Today, I thought of something that may be worth trying.  With a steel enclosure, you might try glueing (silicone glue would be perfect) some hockey pucks over the most resonant areas.  It should work, they are easily removed if it doesn't, and best of all, hockey pucks cost 99¢ each.

Hm, in interesting idea – to offset the box resonances by targeted mass-damping – sort of rotationally balance a car’s wheel by adding mass on one side. I think it might work with light enclosures. I do not think it will work with heavy and stiff enclosure as I am planning to do. As you understand from my previous paragraph it will be a lot of active resonances radiated out of this speaker, so I presume that the enclosure resonances will be a least of my problem. I do not decided with steel finally. I know that I am not willing to do anything myself with enclosure. I will design it (after I know how many woofer I will be able to fish out), get a quote for my machinist and then see what other material are available. It will not be 1” of wood but a few mm of something very strong- steel, aluminum or architecture plastic (Perhaps the material-savvy Jessie could advise something). Anyhow I will try to keep the dimension of the baffle as little as possible….

Romy the Cat wrote:

It will not be 1” of wood but a few mm of something very strong- steel, aluminum or architecture plastic

Romy the Cat wrote:

You have no idea how loaded this question. The crossover point with the MiniMe is not a tactical question but actually the very strategic question of the entire speaker, let me to explain why. The woofers that I use are fairly bizarre – they are what made me to think about the MiniMe. They have diaphragms made with reinforced fabric, the outer suspension is rubber. However, the reinforced fabric is semi-soft in the similar elasticity as the outer suspension. So, it is not a piston motion (like in foolish ceramic drivers) but rather motions with a lot of break ups – the right motion in my books. But then is the kink of the driver- the dust cap. The dust cap is inverted dome of aluminum and it the way how it placed makes the dust cap as the literally keystone of the diaphragm resonance. It is sort of the resonance’s lighting rod – if you see the driver then you understand why I got enthusiastic about it. Now, the woofer goes up, let say to 4K-5K and the dust cap begin to ring. The similar effect to JBL LE8 that also has metal dust cap. Here is where I will be playing with my woofer – to tune by ears the dust cap’s resonances. You see, that dust cap ring in a very measured dosage is in fact very good (in context of these speakers) as it works like the “Oops-resonator”. I will damp the dust cap by painting the driver with volcanic ash (no speaker white cones in my home!!!). That will extend the safe operation of the driver for 500-1000Hz up but the primary tuning tool for me will be the crossover point. So, I will be searching for crossover point by just listening the Oopses with witch the woofer’s dust cap will resonate – where it will become too much Oops then I will cross right there… Well, here is the question: how the woofer’s dust cap will behave if I have 6-8 woofers per channel and the excursion of each woofer is substantially minimized? I have no answer now but I think I will found another 2K of response. Then we have the HF’s cancelation coming from the line-array configuration… It will eat the HF but will it each the dust cap Oops-resonances with the same appetite? I have no answer now… How the “not eaten” residues of the HF woofer resonances will be “subjectively friendly” to the distortions of the 70-20XR tweeter’s lower knee? I have no answer at this point. I need to found the woofers, to build the box to screw the array of the woofers and the tweeter in and start to run the crossover point up and down, to hear how it will work all together. I have no planning to cross at a specific point I will cross it wherever it will be, I anticipate that it will be somewhere between 2K and 6K, most likely a second order.

So, it is no luck for me and I need to hunt in used market the speakers and get my woofers from them (that why I do not divulge the brand and model under which Mission sold my woofers).  Well, those guys who do mass production of speakers – they are in so cool state – the can make any specification for any diver then want…

Wojtek wrote:

Funny , I visited a guy who  ususally picks up audio stuff from the curb (garbage picking) and noticed some 4 small Mission midbass woofers with crossovers. He said cab wasn't worth to save . What are the serial/ type numbers on yours, maybe they are what you're looking for ?. REgards, W

The 6moons’ Srajan Ebaen published a writing about Austisn David Haigner’s loudspeaker where David goes into some extend taking about his implementation of the bass reflex idea. The article made as Srajan’s narrative but in fact it is obvious that the “review” is juts David’s dictations. With the same success Srajan might juts record the Haigner’s comments and to attach to the review as mp3 file (you will see this practice coming very soon). The Srajan’s review has no comments about the sound of the Haigner’s loudspeaker. Sure why to make any comments! If to say that it sound not good then David would pull out the advertising from 6moons site. If to say that the speaker sounds very good then somebody not-deaf might buy the loudspeaker and to witness that Ebaen is a full of blabbering shit. Probably it is better to make sexy still-life pictures and publish the transcripts of the word of other, presenting it as own “wisdom”. Here is the way to go Mr. Reviewer!

Anyhow, if somebody is interested in the David Haigner’s thinking then here it comes:

http://www.6moons.com/audioreviews/haigner/rho.html

http://www.6moons.com/audioreviews/haigner/sidebar.html

I find it interesting but not too useful for myself as I do not fell that David connect subjective character of Sound with technical-measurable data. I presume that Mr. Haigner has some methodologies how to deal with it but it did not make in his commentaries to the 6moons’ guy.