Thanks a lot everyone for all of the suggestions!
The issue was that Joes had specified very specific density for the damping material, but I had indeed missed the comment re: using polyester.. I've currently opted for using two layers of the solen polyester for the 75mm thick areas (each layer 38mm), and the 25mm dacron that was posted from meniscus audio.. hope that will work okay...
Bonded Dacron - Meniscus Audio
Solen Electronique Inc. | POLYESTER
The issue was that Joes had specified very specific density for the damping material, but I had indeed missed the comment re: using polyester.. I've currently opted for using two layers of the solen polyester for the 75mm thick areas (each layer 38mm), and the 25mm dacron that was posted from meniscus audio.. hope that will work okay...
Bonded Dacron - Meniscus Audio
Solen Electronique Inc. | POLYESTER
It's nice to know that some people are in the same time zone.
If in Melbourne, may I say on behalf of the people of Sydney, thank you. We all look set to have a good summer, if nature and fires allow for it.
BTW, here is an interesting question, is it possible to make a 3-way speaker system that uses current drive on all three drivers, including LF? Even Stuart Ralston, who does use active current drive, does not do it. I don't think you will see an SGR speaker coming out doing that. But... do you think it is possible?
I will await your answer in the morning.
Goodnight!
.
If in Melbourne, may I say on behalf of the people of Sydney, thank you. We all look set to have a good summer, if nature and fires allow for it.
BTW, here is an interesting question, is it possible to make a 3-way speaker system that uses current drive on all three drivers, including LF? Even Stuart Ralston, who does use active current drive, does not do it. I don't think you will see an SGR speaker coming out doing that. But... do you think it is possible?
I will await your answer in the morning.
Goodnight!
.
Any box that has a significantly longer dimension than the other 2 will act like a transmission line.
The 4 distributed drivers (+ vent) will work to minimize the TL effect, but the Elsinore is probably best modeled with a TL modeler, but at this point i believe non have the capability of modeling multiple drivers — in multiple driver TLs the drivers are merged into a single driver at the “middle” of the driver array.
dave
How are you doing that? It is one of the myths of classic TL design that the damping slows the SoS, but it has been clearly demonstarted that this is not the case.
Joe, you will need to start thinking about modifying your theory of operation.
Elsinore is likely a hybrid system with the driver spacing working hard to blunt the TL action.
What is the tuning vrs a modeled version of the box? An MLTL needs to be tuned lower than a BR.
I was 1st introduced to resitive vented designs in the early ‘70s by a fellow who has done some of the most advanced research on aperiodic design than anyone else., and sold one of the most prominent brands selling resistive vent speakers in the day, the Fried R and Q (late 70s).
I have built many resistive vent designs, the end goal being to push the box heavily towards aperiodic.
dave
Certainly. You will have to be careful choosing drivers, bass drivers in particualr. You want as low a Qm as you can find and in an enclosure that works hard to decrease any resonance peak. An aperiodic seaker is likely the best approach.
dave
Sorry for interfering, I'm not a loudspeaker specialist... but if SoS stands for Speed of Sound, then Joe did not talk about that: he sais that he manages to slow the (air) velocity, before the vent, not the speed of sound...am I missing completely something?
Regards,
Loris.
Dave, you are selling me short.
We all know about getting the Qm low, this is also what Esa Merilainen proposes in his book. Everybody knows that. That's now old hat.
The Q of a system that defines the damping can also be defined by current versus frequency. When you are able to manipulate the current versus frequency, you can change the Qt of the system, in this case a sealed box. The irony is that you can only do this with current drive and you can actually get increased damping from current drive which you cannot a voltage source.
Oh yes, there is a trick, or should I say a technique. The fact that it works completely buries the idea of amplifier damping or DF.
Hi Dave
Yep. The lining of vented boxes was always just a 'rule' to me waiting to be broken.
Re the Elsinores, they are not a TL, have not claimed them to be. But again I think I am being misunderstood.
Make a box 75 Litres and fit a vent that tunes it to a frequency, say 45 Hertz. The Fb of the box is independent of the driver. Now add fill, don't change anything, and measure Fb of the box. Let us say it drops 10-12 Hertz to 33Hz.
Because you did not change the vent and yet it got tuned to 33Hz, you should perhaps be able to calculate that you have changed the effective volume to be equal to 100-110 Litres. You have made the effective box larger. This is the idea behind every vented box I have done for like twenty years or more. It works down to mini-monitor size. Just make sure that fill is kept away from the internal mouth of the vent.
Has the box volume been increased or has the velocity changed?
Maybe it's a relativity thing?
But what does the vent see looking back?
It's not something that I am going to sleep over. I have learned a 'magic trick' and sharing it. Others can do anything they like with it, even ignore it.
But my TL days are over. I still love the idea.
PS: Thanks for showing me the sub thingy.
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Not quite... not being picky on this, just chasing myths and vocabulary...
Speed of sound is the propagating speed of air vibration into that medium (mechanical oscillation around same position: only vibration propagates).
Air velocity is the speed of a moving quantity of air; depends on both frequency and amplitude of sound: slowing air velocity is reducing its (displacement/ time) rate, which is nothing else than attenuating: that's what damping (filling) material does.
You are not the only one.
They may not be claimed to be a TL, and the design elements will fight any TL action, but one cannot get around the physics of a box with an aspect ratio such that one dimension is sgnificantly greater than the other 2. Something, BTW, that was not analytically understood 20 years ago.
The effective box volume, we have real-world data that shows the velocity has not changed going thru the damping material.
dave
Hi everyone,
I found this old post regarding vent length and was just wondering re: the change.. The new vent length suggestion for 9mm is 100mm vs 88mm before - is this due to the new drivers or has this changed over the years due to optimization of the design? I ask because I was looking for a 3" PVC pipe coupling as previously described in this thread, as was able to find one with an ID of about 86mm, however it is 80mm in length.. that is close to the below figures but off of what seems it would be given the new guideline for a longer baseline vent length..
I found this old post regarding vent length and was just wondering re: the change.. The new vent length suggestion for 9mm is 100mm vs 88mm before - is this due to the new drivers or has this changed over the years due to optimization of the design? I ask because I was looking for a 3" PVC pipe coupling as previously described in this thread, as was able to find one with an ID of about 86mm, however it is 80mm in length.. that is close to the below figures but off of what seems it would be given the new guideline for a longer baseline vent length..
Hi Francois
Needless to say it is the inside diameter that is the important factor. The required length of the vent changes accordingly to maintain the same Fb. So here are the figures, use as a guide:
Internal Dimension = Vent Length:
90mm = 88mm - OK
87mm outside = 80mm - OK
85mm = 75mm - OK
82.5 = 69mm - Borderline
80mm = 63mm - TOO SHORT
77.5mm = 57mm - TOO SHORT
75mm = 52mm - TOO SHORT
What concerns me the most by those lengths is that 52mm for an inside diameter of 75mm means that the vent does not finish far enough into the box and hence the area in front of the internal main brace. Because of this I would not like to use any less than just over 82mm inside diameter.
The other consideration is the peak velocity in the vent should be kept under 0.1 Mach (velocity) @ Fb for a reasonable rated SPL. The larger the diameter the greater the SPL before 0.1 Mach is reached.
ALTERNATIVE:
You could use postal tubes from you local post office. These are usually cardboard - but I have used them. A good idea is to use something to coat them - even just white wood glue that dries clear - to stiffen them further and protect them from any possible air moisture. If the right PVC pipe is not available, this will do the job at a pinch.
Joe R.
You are saying that it is resistive in the sense that it attenuates. If so, OK. It is lossy.
But I am reminded about Einstein noting that light seemingly gets attenuated in speed near a large mass. But he disagreed with that idea, instead he said that it was time and not light that changed, indeed light is a constant. Or near constant... some would argue that point, but that is another story.
Since a filled 75 Litre box can be made to behave like 100-100 Litre box, then how should we explain it? Has it changed the apparent box size seen by the vent? By what mechanism?
This is not a trick question because it won't change anything that I already do.
Another thing re TL: Since most designs have that saddle in the Z, that means the end of the line is acting as a vent. I don't have any exact answer here and if anybody does, I would be grateful, but somehow TL's port seems to couple to the air in a 'better' way and that it may have something to do with the acoustic impedance.
Feynman once said that everything starts with intuition (paraphrasing) and mine tells me that something similar happens when we make the vented box volume more resistive, it causes it to tune down at a lower frequency that it would otherwise, that the vent is doing a better job of coupling to the outside air.
Beyond that, I don't know much.
But I do know this: The kind of bass I get tells me that something of my intuition is right.
So there you are.
.
A TL can be tuned/damped from a very bass reflex like double-hump impedance — (a faster roll-off traded for extension in a small line -- at resonance all the way to aperiodic lines -- very flat impedance and little to no bass output from the terminus.
Here an almost aperiodic TL (the line it is a bit short, so the hints of the hump):
With every loudspeaker many compromises need to be made, and you have massaged the set of compromises in this loudspeaker thru 6 major versions to end up with something that, given all the very positve feedback, is quite special.
dave
Indeed. It seems most commercial TLs have the saddle that indicate reflex action.
Some time I did a line that looked very much like it was a sealed box and I still have the Z measurement (took me a little while to find it) It was an 8" Peerless HDS driver into an about 6-7 foot single fold down-up filled line. It gave me a single define peak and no reflex action. The vent at the end just worked as a leak for the box? Your interpretation? See attachment.
Thank you for saying that. It's one thing what you think yourself, and I am a pretty hard task master, but when others build it, it gives you a nice fuzzy feeling that it was worth the effort.
PS: I just worked out, if you make an attachment, then make the browser display it in its own window, you have the URL address and you can edit the mesage and insert where you want it using that newly created URL. That is what I just did above.
Attachments
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Joe, don't modify quotes.. and retain context. Please take the time to familiarise yourself with the rules.
Consider a sealed box with no damping and take a look at the peak of the electrical impedance of the woofer. The impedance peak shows the resonance of the loudspeaker system, and the frequency of the impedance peak corresponds to the resonance frequency (which relates to the bass cut-off frequency of the speaker).
Now, add some damping materials to the box, which will add damping to the resonance of the loudspeaker. In other words, the addition of the damping material will modify (attenuate) the shape of the impedance peak. The damping effect is usually stronger at high frequencies than at low frequencies. Therefore, the damping will be more effective at frequencies above the impedance peak of the undamped box than at frequencies below the peak. This means that the damping will "eat away" more of the impedance curve above the peak than below the peak.
The result is that the maximum of the impedance curve of the damped box will be shifted to a lower frequency than the impedance maximum of the undamped box. This is why adding damping materials to the box lowers the resonance frequency (and hence also the cut-off frequency). I guess this is what you mean by "it appears as a bigger box".