And Fremer, being the highly experienced speaker designer that he is, would know.
David Wilson, Johachim Gerhard, Franco Serblin, Stewart Tyler, Jeff Joseph, Albert von Schweikert, ++ know/knew a thing or two about how to make a good sounding loudspeaker, otherwise they would not have survived in the business (no, it's not all up to nice marketing and buying nice reviews), and Mr Fremer has had the privilege to have listened to more than a pair or two of their products, and I guess Mr. Fremer has observed that not two speakers look or work or sound the same, every designer has their own recipe and philosophie, and they differ largely from designer to designer. I think Mr. Fremer's description is valid; building well sounding loudspeakers is as much a "black art" as it is science, even today with measurment equipments and softwares all over the place.
The swept volume provides damping of the pipe at both ends. Velocity of air goes to zero at both ends, providing a resistive load. A nice idea, but seems prone to distortion.
There is quite a few nonsense statements floating in this thread. Interesting how many people lie for a living. Speaker designers included.
Remedy: get yourself educated and start using tools needed to get the work done properly.
Remedy: get yourself educated and start using tools needed to get the work done properly.
I belive that means Vb = 0.7*Vas
If correct, thats Butterworth 4th order, widely accepted as optimum compromise between box size, F3 and transient response. Pretty straightforward starting point.
Port area 30-35% of Sd? Very good compromise between port lenght and air speed inside.
Round port placed in front? Pretty straightforward.
Port opening inside box placed at small baffle? Thats very interesting. I guess point is to avoid sharp edge and reduce cavitation of air. I saw some ports with small flange at the rear for same reason. So, valid idea.
Driver Qts= 0.3-0.4 is straightforward too. Especially with modern HQ drivers mostly designed to give their best in BR cabinets.
Sd/Mms ratio of 7-8 cm2/g is very good choice for midbasses. Heavy enough to give stiff cone and low Fs without excessive Vas. And light enough to swiftly move to usual xo point at 2-2.5 KHz.
Heavy birch ply box, braced in such manner that bracings are used to control internal standing waves, so no stuffing is needed.
Sounds good to me.
But I agree that CLD construction is an overkill for average diy-er.
Many modern drivers have high Qms, so they depend more on electric damping and generate more return-EMF compared to low Qms drivers. So, amp with high DF and plenty current headroom seems like better choice for such drivers on terms of cone control compared to typical SET. Even if BR alignment is optimised in each case.
Iam surprised with number of "cold feet" OP received for this thread. Yes, his guidelines are simplified and generalized and word "perfect" is not something one should use lightly regarding speakers. But if someone wish to design his first high quality 2-way BR speakers this is pretty simple and straightforward way to do it.
I also thought the list of guidelines was helpful. The Area/moving mass ratio guideline might be a little too tight, and restricting a design to only round ports on the front baffle might be too restricting (many good sounding speakers do it differently). Still, these are guidelines that have worked for him. He did not claim this was the ONLY way to make a good BR enclosure, simply that this list is his recipe for success. Yes indeed, "Perfect" is a strong word... but we all are guilty of marketing our ideas 😉
Nice summary. I agree, for the most part. But, I've only been doing "it" for 49.75 years. Many disagree. So what?
I have done some of that, some of it is overkill. 3/5 or golden ratio is not that big a deal if the walls are not parallel. If thought out, 3/4 MDF is really as far as one needs to go. ( Quality matters) Having the brace behind the mid at an angle to reflect away is helpful. Believe it or not, I heard an audible difference radiusing the BACK cabinet edges. I have no explanation for this other than what heard. Instead of double Thich fronts, I have run a brace to the baffle between the drivers.
Round ports tend to have more of a resonance signature that slotted. One can get crazy and do a trapezoid slot.
One can do curved walls. One can do non rectangular baffles. All kinds of things
I have done multi-layer composites on sealed subs, but not found the need for a ported bookshelf.
I have given up on metal cone mids. Too hard to tame. Back to paper. I like the ER18 Seas, but the CSS and new Purifi are a big jump forward. Smoother and easier to implement. Lower distortion. The big deal on the CSS and Purifi is they are well enough behaved to actually reach where a tweeter should be crossed. So many people push the tweeter down to 2K or even lower ( yes Zaph, 1750 is too low!)
Funny how some reviewers cut on tweeters with plastic flanges. Well, they are a lot easier to cut to get closer to the mid! I understand n 1950 how plastic was considered cheap, but come on now, modern plastics can be fantastic. Criticize performance, not how yo got it.
I go back and forth, removeable front, or removeable back. I still am not happy with any grill cloth arrangement even though I would prefer to have them.
I disagree with Fremer. It is engineering. Many think it is an art because they have not done the engineering or don't know how. There is almost nothing new besides materials and CAD for motor design we did not know in 1950. Go read the AES papers. Like any engineering, some engineers are better, some have a better budget.
Round ports tend to have more of a resonance signature that slotted. One can get crazy and do a trapezoid slot.
One can do curved walls. One can do non rectangular baffles. All kinds of things
I have done multi-layer composites on sealed subs, but not found the need for a ported bookshelf.
I have given up on metal cone mids. Too hard to tame. Back to paper. I like the ER18 Seas, but the CSS and new Purifi are a big jump forward. Smoother and easier to implement. Lower distortion. The big deal on the CSS and Purifi is they are well enough behaved to actually reach where a tweeter should be crossed. So many people push the tweeter down to 2K or even lower ( yes Zaph, 1750 is too low!)
Funny how some reviewers cut on tweeters with plastic flanges. Well, they are a lot easier to cut to get closer to the mid! I understand n 1950 how plastic was considered cheap, but come on now, modern plastics can be fantastic. Criticize performance, not how yo got it.
I go back and forth, removeable front, or removeable back. I still am not happy with any grill cloth arrangement even though I would prefer to have them.
I disagree with Fremer. It is engineering. Many think it is an art because they have not done the engineering or don't know how. There is almost nothing new besides materials and CAD for motor design we did not know in 1950. Go read the AES papers. Like any engineering, some engineers are better, some have a better budget.
I think it's a very one sided view on speaker building. It can deliver good speakers i think, but it's certainly not the only way, or the best way to do it. But if you are happy with it...
I rather look at the goal and the specs of the parts used to determine the configuration. And i don't like the cheap plastic ports so many use here, as they vibrate also. A round port can work, but needs more solid material than a thin plastic piece i think. And a well executed slot is still easier to do for similar results and looks better. You just need to adjust the size of the slot for that.
I rather look at the goal and the specs of the parts used to determine the configuration. And i don't like the cheap plastic ports so many use here, as they vibrate also. A round port can work, but needs more solid material than a thin plastic piece i think. And a well executed slot is still easier to do for similar results and looks better. You just need to adjust the size of the slot for that.
The phenomenon is real, but the term "standing waves" is not a good description. I prefer the term Acoustical Resonance.
An acoustical resonance will occur whenever an internal cabinet dimension equals the half wavelength of a signal. For instance, if a cabinets largest internal dimension is 20 inches, the frequency with a half wavelength of 20 inches is 338 Hz. The SPL inside the cabinet can rise as much as 20 dB when this happens. This is very significant because the transmission loss (sound suppression) of a 3/4" layer of MDF or plywood is about 20 dB, so at 338 Hz, the sound coming through the cabinet walls can be nearly equal to the sound coming from the driver. This is not a structural resonance, this is just ordinary sound transmission.
And it is not just the inner dimension, it is the total path length. A complicated internal structure can create a longer path length than just the internal dimension.
What to do? Volume-filling acoustical damping is highly effective at bringing down the acoustical resonance. Fibrous stuffing and foams are very effective. Filling the cabinet will loosely fluffed wool or acoustistuff works extremely well, as does melamine foam. Augerpro has a giant thread on this subject.
Animal Farm is advising against volume filling damping, and he is not the first to point out that this reduces bass performance, I have heard this from many others. So if we remove the most effective tool to control acoustic resonance, it means everything else we do inside the cabinet becomes more important. That is why I like this discussion.
I have been experimenting with different fill/stuffing/lining of a 2 way BR cab. Based on lots of impedance sweeps of different configurations I've come to my own conclusion that it is impossible to kill all the resonances while also retaining the full performance of the port. An empty cab has the best bass performance, and a totally filled cab has the least resonance. Finding the best compromise was interesting. Placing acoustic foam and poly stuffing in different places in the cab and different amounts and thicknesses all have very real implications. Adding more fill material in some cases made the resonance worse depending on where it was placed. My current leader in the house is a single acoustic foam pad covering the top panel of the cab, and two stacked foam pads directly behind the driver but not reaching out to the edges. Nothing on the left and right sides or anywhere near the port. It is much less fill than I had thought was needed, but measurements say otherwise.
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I don't want to get too far involved as I don't have time today, but re the above: damping material is at its most effective at Vmax (i.e. the point of maximum air-particle velocity), and least effective where pressure high and air velocity low. That isn't always practical for various physical reasons (vent, bracing, duct or driver position etc.) but any point where velocity is high is usually a good starting point. In practice though, for most vented boxes of decent proportions, you should be fine lagging non-opposing faces with OC-703 or an equivalent, & making what adjustments you want via the old click test, unless you are using the damping to help achieve a particular alignment. In general, I avoid acoustic foam -there are some good examples, but most is mediocre - poor.
Yes. And he's so full of stupid myths so that if he ever did learn any actual engineering it would take forever, or Gitmo style 'encouragement' for him to come back to basic physics.
That's because many use it incorrectly and don't consider it beyond, "I'm just gonna fill this space up". It should be part of the initial design.
Your ideas for designing a ported woofer enclosure seem very sensible to me. I have never had much luck getting a ported system to sound right so I just might try your approach. Thanks!
I thought that adding absorption to a BR cabinet was a trial-and-error exercise. Is there a way to accurately simulate or calculate this?
Experience, and thinking about how it works and what you're trying to achieve with it.
No way I'm aware of to simulate how I do it.
A long time ago, I was looking for a light, stiff material with which to make an accelerometer housing.
I looked up the formula for stiffness of a beam. You want high Young's Modulus of elasticity for a stiff beam.
I then then plugged in the constraint that mass of the beam had to be fixed, allowing me to compare structures made with different materials, but all weighing the same, all intended to do the same job.
If you use a denser material, you have to make the beam cross sectional area smaller, to keep it from getting heavier. It turns out the penalty paid by doing this is heavy.
From this simple analysis, I found out that the best material is the one with the highest ratio of Youngs modulus to density.
This applies to loudspeaker cones just as well as to beams. A loudspeaker cone should be light and stiff. Again, when choosing a material from which to make the cone, you want a material that has a high ratio of Young's modulus of elasticity to density.
Then I looked up those material constants for dozens of materials, and ran all the numbers through a little program I wrote, to calculate the ratio of Young's modulus to density, and sort the materials in order, with the best materials for making a light, stiff structure at the top.
Guess what material topped the list?
SPRUCE! Wood. The same stuff used to build early aircraft, which had the same need to be light, stiff, and strong. Those pioneer constructors knew what they were doing!
Paper also did very well. It's basically wood pulp, and has the same combination of high Young's modulus and low density as spruce.
Metals did very poorly. They have very high Young's modulus, but also very high density. The latter outweighs the former. They are poor choices for making loudspeaker cones. (They are great for bridges, where you don't care about how heavy they are.)
Most plastics did not do well. Too floppy, too dense, compared to spruce or paper.
In short: metal speaker cones are not a good idea from an engineering point of view. In fact, a properly designed paper cone will outperform it. Which is exactly what you found out by experiment!
I have a new respect for paper-cone loudspeakers since then.
Plastics are inherently not as good cone materials as paper, but may have other advantages (such as being waterproof, or having more internal mechanical damping to calm down breakup modes.)
-Gnobuddy