The Science of Speaker Cabinet Design - Page 3 - AVS Forum | Home Theater Discussions And Reviews
Forum Jump: 
 12Likes
Reply
 
Thread Tools
post #61 of 181 Old 04-20-2017, 04:31 PM
AVS Forum Addicted Member
 
noah katz's Avatar
 
Join Date: Apr 1999
Location: Mountain View, CA USA
Posts: 21,589
Mentioned: 3 Post(s)
Tagged: 0 Thread(s)
Quoted: 1107 Post(s)
Liked: 387
My bad on two counts:

1) Yes, I erred in saying lower Q means higher amplitude; it's the opposite.

2) The chart *does* need some explanation; after 30 yr of referring to it regularly, I forgot what it was like the first time I looked at it.

The most notable feature is that the horizontal axis (freq) is normalized to the resonant freq.

w (actually omega, not "w", where w = 1/[2*Pi*f] ) is radian freq and w(n) is the natural (resonant) freq.

But no need to fuss with that; just know that 1 is the res freq, 2 is 2X res freq, etc.

xi is the damping ratio, which is also normalized, and is the % of critical damping (xi = 1/Q= .5).

Normalizing makes the graph universally applicable in a compact form.



Quote:
Originally Posted by tuxedocivic View Post
...the chart just says to me that as Q goes up, amplitude goes up IF bandwidth stays the same.

Isn't it apparent from the graph that BW increases as Q decreases?

Noah
noah katz is online now  
Sponsored Links
Advertisement
 
post #62 of 181 Old 04-20-2017, 08:34 PM
AVS Forum Special Member
 
michael hurd's Avatar
 
Join Date: Nov 2007
Posts: 2,412
Mentioned: 5 Post(s)
Tagged: 0 Thread(s)
Quoted: 165 Post(s)
Liked: 132
Quote:
Originally Posted by noah katz View Post
Shorting the woofers will help, but not completely lock them, and the cones will reradiate far more sound than the box walls, which is fine if it's cone reradiation that you want to test.
Absolutely the cones will pass more sound then the box walls, without a doubt. I suppose that one could substitute wooden circular plugs for the woofers instead. Not too hard to make with a router and circle jig.

This would also allow me to measure the quantity and bandwidth of sound that is radiated through ports installed on the front baffle as well.

95% Synthetic bass since Y2K.
michael hurd is offline  
post #63 of 181 Old 04-21-2017, 10:14 AM
AVS Forum Special Member
 
augerpro's Avatar
 
Join Date: Aug 2005
Location: Denver, Colorado
Posts: 1,940
Mentioned: 3 Post(s)
Tagged: 0 Thread(s)
Quoted: 137 Post(s)
Liked: 68
Looks like I probably won't be able to partner with anyone in Denver for this, so I thought I'd throw out what my plan was for anyone that might be able to go through with the experiment.

I would use a driver like the Peerless 830983 or 830985 due to their wide band response and shorting rings. Make a small box which can be attached to the test enclosure. First take a free air measurement to set the SPL at 90-93 dB or so and give a baseline response. Then attach the box to the front baffle of the test enclosure so it fires into the test box. This way the sound will reflect off the back of the box before going back through the dummy driver, just as if the dummy driver were making the sound. Speaking of that, I was going to use the SB Acoustics 15cm poly cone since it is pretty "typical" and I have the aluminum version on hand also to see how the diaphragm material effects re-radiation.

Now you can test various linings/absorption. I would test denim insulation, open cell foam like flooring backer, acousta stuff, etc. Frequency response, impedance, and possibly harmonic distortion would be of interest.

For the enclosure radiation it would probably be best to use a wood blank in place of the dummy driver. I would build test boxes of: 3/4" mdf, 3/4" mdf doubled up, 3/4" birch ply, 3/4" bamboo laminate, then some CLD methods. Maybe 1/4" mdf with 1/8" sorbothane pad in between. Maybe another with the 3M tape I mentioned. One made of urethane would be cool. Also coating one of the boxes with Acoust-X would be interesting. Certainly changes the "knuckle rap" test when I've used it. Measurements of interest: frequency response, CSD, harmonic distortion, impulse response.
augerpro is offline  
 
post #64 of 181 Old 04-21-2017, 10:42 AM
AVS Forum Addicted Member
 
noah katz's Avatar
 
Join Date: Apr 1999
Location: Mountain View, CA USA
Posts: 21,589
Mentioned: 3 Post(s)
Tagged: 0 Thread(s)
Quoted: 1107 Post(s)
Liked: 387
Quote:
Originally Posted by augerpro View Post
Now you can test various linings/absorption...

Why would you do this, unless you don't trust the plentiful published absorption coefficients?

Also, for the speaker-inside-a-box test, I'd make sure to isolate the inner from outer box by putting it on a few inches of foam, to eliminate direct mechanical transfer of vibration.

Noah
noah katz is online now  
post #65 of 181 Old 04-21-2017, 10:43 AM
AVS Forum Special Member
 
rhodesj's Avatar
 
Join Date: Apr 2005
Posts: 2,002
Mentioned: 38 Post(s)
Tagged: 0 Thread(s)
Quoted: 942 Post(s)
Liked: 533
Quote:
Originally Posted by tuxedocivic View Post
I didnt say damping doesnt lower amplitude. But you did say lower Q means higher amplitude. I dont see that being the case in your chart. Also, you havent provided enough details to explain how Q is proportional to amplitude. Can you provide more information where that chart came from? I think Ive seen it before.
Introduction to Loudspeaker Design has a method for measuring and calculating Qts for a driver. Same basic process is also here: https://web.archive.org/web/20160306...st.com/tsp.htm and that page provides this explanation: "The traditional way to measure Q is to measure the bandwidth between the -3dB frequencies, then divide the resonant frequency by the bandwidth"

So it's a ratio of the amplitude and width of the peak.
rhodesj is online now  
post #66 of 181 Old 04-21-2017, 10:55 AM
AVS Forum Special Member
 
augerpro's Avatar
 
Join Date: Aug 2005
Location: Denver, Colorado
Posts: 1,940
Mentioned: 3 Post(s)
Tagged: 0 Thread(s)
Quoted: 137 Post(s)
Liked: 68
Quote:
Originally Posted by noah katz View Post
Why would you do this, unless you don't trust the plentiful published absorption coefficients?
So I can see how far the radiated sound is down from the fundamental. I can wrap my mind around that better than a contextless absorption value.
augerpro is offline  
post #67 of 181 Old 04-21-2017, 02:37 PM
AVS Forum Special Member
 
tuxedocivic's Avatar
 
Join Date: Feb 2010
Location: Ladysmith, BC
Posts: 7,841
Mentioned: 188 Post(s)
Tagged: 1 Thread(s)
Quoted: 2202 Post(s)
Liked: 2078
Quote:
Originally Posted by rhodesj View Post
Introduction to Loudspeaker Design has a method for measuring and calculating Qts for a driver. Same basic process is also here: https://web.archive.org/web/20160306...st.com/tsp.htm and that page provides this explanation: "The traditional way to measure Q is to measure the bandwidth between the -3dB frequencies, then divide the resonant frequency by the bandwidth"

So it's a ratio of the amplitude and width of the peak.
On my phone looking at that but I think Ive figured out where the problem is.

Q is proportional to amplitude, but Q can change without changing amplitude. Im not sure if Noah agrees. If the bandwidth changes then Q changes. That was my original point about the resonance and being more audible if lower Q.

Going way back to the post Noah quoted, I was saying damping lowers Q, and lower Q is generally more audible if amplitude remains constant. That is well established. Of course damping also lowers amplitude so there is a benefit. I didnt mean to suggest there isnt. I was only showing the relationships between damping and stiffness given a constant wall thickness.

My youtube channel: Impulse Audio
tuxedocivic is offline  
post #68 of 181 Old 04-21-2017, 03:13 PM
AVS Forum Addicted Member
 
noah katz's Avatar
 
Join Date: Apr 1999
Location: Mountain View, CA USA
Posts: 21,589
Mentioned: 3 Post(s)
Tagged: 0 Thread(s)
Quoted: 1107 Post(s)
Liked: 387
Quote:
Originally Posted by tuxedocivic View Post
Q is proportional to amplitude, but Q can change without changing amplitude. Im not sure if Noah agrees.
Nope

If you increase damping, the only way amplitude wouldn't change (decrease) is if you increased the input excitation.

Maybe it will help if I add to what I said about the misconception:

Lowering Q *does not* push down the peak and spread the energy over more freq; it only looks that way on a relative basis when you look at the response shape.

Again, lower Q reduces response at *all* freq, so there's no case in which lowering Q will make a resonance more audible.

Noah
noah katz is online now  
post #69 of 181 Old 04-21-2017, 03:22 PM
AVS Forum Special Member
 
tuxedocivic's Avatar
 
Join Date: Feb 2010
Location: Ladysmith, BC
Posts: 7,841
Mentioned: 188 Post(s)
Tagged: 1 Thread(s)
Quoted: 2202 Post(s)
Liked: 2078
Noah, we dont disagree that increasing damping means lowering amplitude. Of course you would have to increase the input to have Q descrease and amplitude stay the same. Ive stated several times, I was only offering some general trends between stiffness and damping.

Regarding your last sentence, if lowering Q reduces response at all frequencies, then you have either reduced the input or absobed (damped) the energy. So we do not disagree there. Damping lowers Q. Ive said it all along.

I feel like we are talking past each other. Perhaps you should just offer your insights about box building instead of nit picking about the definition of Q. I have noticed you tend to drop into conversations about box construction and come at me about details. Once was about buckling of slender braces. Another was about damping vs stiffness actually. I cited speaker dave and you scoffed. I had to inform you he was a Snell engineer before you backed off. Im sure other times. Whether or not Ive made a mistake about how Q works is quite irrelevent to the conversation. How do DIYers make the least resonant box given normal dimension, cost, and construction techniques? You can probably help in a meaningful way with this.

My youtube channel: Impulse Audio
tuxedocivic is offline  
post #70 of 181 Old 04-21-2017, 03:25 PM
wse
AVS Forum Special Member
 
wse's Avatar
 
Join Date: Mar 2008
Location: USA
Posts: 9,503
Mentioned: 10 Post(s)
Tagged: 0 Thread(s)
Quoted: 2204 Post(s)
Liked: 809
How about open baffle it would simplify everything!
wse is offline  
post #71 of 181 Old 04-21-2017, 03:49 PM
AVS Forum Addicted Member
 
noah katz's Avatar
 
Join Date: Apr 1999
Location: Mountain View, CA USA
Posts: 21,589
Mentioned: 3 Post(s)
Tagged: 0 Thread(s)
Quoted: 1107 Post(s)
Liked: 387
Quote:
Originally Posted by tuxedocivic View Post
Of course you would have to increase the input to have Q descrease and amplitude stay the same.

Ryan, I know I can be an annoying nit-picker, it's just that to a nerd like me, they're not nits.

Re the above quote, I don't know how to say this w/o further annoying you, but if you really understood that you wouldn't say

"Q doesnt mean higher amplitude, it means wider peak, therefore more area under the curve to hear" nor "Q is proportional to amplitude, but Q can change without changing amplitude."

Just noticed something that might help - in the first statement, note that the area under all of the curves decrease when Q decreases.

I don't recall what the topic was w/speaker dave, but I'm pretty sure I know what I'm talking about when it comes to Q.

Noah

Last edited by noah katz; 04-21-2017 at 05:07 PM.
noah katz is online now  
post #72 of 181 Old 04-21-2017, 04:45 PM
AVS Forum Addicted Member
 
noah katz's Avatar
 
Join Date: Apr 1999
Location: Mountain View, CA USA
Posts: 21,589
Mentioned: 3 Post(s)
Tagged: 0 Thread(s)
Quoted: 1107 Post(s)
Liked: 387
OK, I've got a bit of perspective now; I forget that people are more interested in practical application and less in technical minutiae (thanks to the spell checker).

I haven't tried that many different methods myself, but I will offer that if using CLD, beware of making the viscous layer too thick.

I tried stiffening/damping some boxes by using Liquid Nails to bond 14 ga steel to the inside panels.

It didn't help as much as I expected, I believe because the LN was too thick.

Later reading highlighted that too thick of a layer just decouples the two outer panels and lessens the shearing/energy dissipation of the shear layer, and on commercial products that I've seen it's just a thin layer of adhesive like various self-stick products have.

Noah

Last edited by noah katz; 04-21-2017 at 05:06 PM.
noah katz is online now  
post #73 of 181 Old 04-22-2017, 07:00 AM
AVS Forum Special Member
 
tuxedocivic's Avatar
 
Join Date: Feb 2010
Location: Ladysmith, BC
Posts: 7,841
Mentioned: 188 Post(s)
Tagged: 1 Thread(s)
Quoted: 2202 Post(s)
Liked: 2078
Quote:
Originally Posted by noah katz View Post
Ryan, I know I can be an annoying nit-picker, it's just that to a nerd like me, they're not nits.

Re the above quote, I don't know how to say this w/o further annoying you, but if you really understood that you wouldn't say

"Q doesnt mean higher amplitude, it means wider peak, therefore more area under the curve to hear" nor "Q is proportional to amplitude, but Q can change without changing amplitude."

Just noticed something that might help - in the first statement, note that the area under all of the curves decrease when Q decreases.

I don't recall what the topic was w/speaker dave, but I'm pretty sure I know what I'm talking about when it comes to Q.
No big deal. I'm a nit picker too actually. It's in all us engineers. (I recall you're a structural engineer, I'm a civil). I admit you may have the technical definition correct. I just have a hard time understanding how your definition aligns with the prevailing belief that lower q resonances are more audible. I'm pretty sure this was even researched by Harman and Toole. That's the practical part. If lower q resonances are more audible, then damping can work against us.

Thanks for chiming in in any case

My youtube channel: Impulse Audio
tuxedocivic is offline  
post #74 of 181 Old 04-22-2017, 07:57 AM - Thread Starter
Advanced Member
 
Join Date: Dec 2015
Posts: 825
Mentioned: 29 Post(s)
Tagged: 0 Thread(s)
Quoted: 379 Post(s)
Liked: 198
A couple thoughts guys.

Noah, liquid nails was tested as a CLD damping compound in walls and found to greatly increase stiffness, slightly increas mass, and have little effect on damping. It behaved worse with transmission loss than a normal wall would. You might want to repeat the procedure with something different. For what it's worth silicone was also tested and didn't perform well. I don't see any reason why it wouldn't apply here as well.

Ok now as for tests. The studies I linked make reference to direct transfer of energy between driver and box being a mechanism for sound radiation from the box. If you decouple the inner speaker box from the outer you remove this variable. That is fine if all you want to test is the sound radiation through the box and not direct excitation. Direct excitation amplitude should be greater in a stiffer and more massive box but would be less delayed (if at all) and may not sound "bad."

This brings me back to an earlier point. You need to measure behavior over time and examine that more than the change in frequency response. The articles suggested that delayed energy even at lower amplitude would be perceived as more negative to sound than early stuff. Damping would have a bigger effect on this.

There seems to be a focus on resonance behavior. The resonant frequency is one of two regions at which direct and unabated as sound retransmission takes place, but it is not true that no sound transfers outside of that. Sound will also transfer in the region above the the box panel resonant frequency. Mass and damping (unrelated to change in resonance or amplitude or resonance) most impact transmission loss of a box wall at these points. Coincident frequency is also another point of complete failure to transmission loss and damping plays a big role here.

Here is something I don't fully understand. The formulas and physics that deal with barrier transmission loss should apply equally to a room wall or a speaker box wall. I don't see why they wouldn't. In a speaker we talk about raising the resonance frequency through stiff, increasing mass, and here we discuss adding damping to dissipate the sound transfer before it can exit the box. In a room we decrease stiffness to lower the resonant frequency. The reason is that mass no longer dictates transmission loss below the resonant frequency and walls transfer low frequency sound nearly unobated. The resonant frequency is thought of as a high pass filter to transmission loss. With the coincidence frequency we also lose transmission loss above it. Stiffness tends to dictate these two behaviors and stiffness is the enemy. Why is it different in a box. The idea that a higher resonance is more easily dissipated makes sense to me, the articles discuss the amount of damping proportionally increases as frequency goes lower for the same dissipation effect. Discounting that one detail though, it would seem adding stiffness isnt a good thing, yet it is?

The first study I referenced dis conclude that the stiffer and more massive box radiated more sound than the less stiff box. It's time behavior was a little better however. That's the only thing I can think of, that by connecting the walls we increase the masses being used to dissipate the energy so that whole more surfaces now reradiate sound the also dissipate the fixes energy more quickly. If that's right then it still point to a lot of damping being key.

What Noah says is perfectly in line with the literature I've read on CLD. Its supposed to be a very thing layer. Thick isn't better. Dr. Geddes uses a layer of urethane rubber that he spreads to a thickness roughly equal to what you so for green glue. I would say it's about .5-1mm at most. It is my understanding that if you want more damping you add more layers of MDF and damping compound. You don't make the damping layer thicker.


Sent from my iPhone using Tapatalk
Mpoes12 is online now  
post #75 of 181 Old 04-22-2017, 08:09 AM - Thread Starter
Advanced Member
 
Join Date: Dec 2015
Posts: 825
Mentioned: 29 Post(s)
Tagged: 0 Thread(s)
Quoted: 379 Post(s)
Liked: 198
I also think a box construction technique that might have promise would be one where the baffle is composed of 4-5 layers or 1/4" MDF with a viscoelastic layer between each spread thin. It would be high mass and heavily damped. You could take advantage of this so that the driver sits on a CLD layer or two along with adding some decoupling. It might reduce the energy transfer to the front baffle and thus all other panels.

Kef is using a CLD brace. I think this would be interesting as well. I think a mechanism for benefit would be that as the wave transfers across the brace the damping behavior would dissipated before it hits the next connected panel.

I also like the idea or multiple layers of absorption/damping inside the box. Something that gradually increases in acoustical impedance. It would potentially increase absorption as sound travels inside the box and if it does decrease likelihood of reflection, then becomes more likely to be dissipated in these damped high mass panels.


Sent from my iPhone using Tapatalk
Mpoes12 is online now  
post #76 of 181 Old 04-22-2017, 11:21 AM
AVS Forum Addicted Member
 
noah katz's Avatar
 
Join Date: Apr 1999
Location: Mountain View, CA USA
Posts: 21,589
Mentioned: 3 Post(s)
Tagged: 0 Thread(s)
Quoted: 1107 Post(s)
Liked: 387
Good, glad there's no hard feelings

Quote:
Originally Posted by tuxedocivic View Post
I just have a hard time understanding how your definition aligns with the prevailing belief that lower q resonances are more audible.
I wasn't aware that that is the prevailing belief, but per the above discussion and can only mean that along with decent damping, stiffness is relatively low and allows relatively high displacement; MDF comes to mind.

Noah
noah katz is online now  
post #77 of 181 Old 04-22-2017, 11:48 AM
AVS Forum Addicted Member
 
noah katz's Avatar
 
Join Date: Apr 1999
Location: Mountain View, CA USA
Posts: 21,589
Mentioned: 3 Post(s)
Tagged: 0 Thread(s)
Quoted: 1107 Post(s)
Liked: 387
Mpoes,

Liquid nails in walls would be just adding a parallel structural load path between the wall panels and the studs in addition to screws/nails, so it would increase stiffness and reduce damping by not allowing the panels to rub against the studs when excited.

This is very different than adding plates/panels.

As for the rest, I really don't understand a lot of what you said.

> Direct excitation amplitude should be greater in a stiffer and more massive box but would be less delayed (if at all) and may not sound "bad."

Agree about less delay.

IMO higher stiffness would make the driver reaction force to try to move more of the box mass and therefore reduce displacement. Also more mass means less displacement.

> The resonant frequency is one of two regions at which direct and unabated as sound retransmission takes place

What's the 2nd region?

> Coincident frequency is also another point of complete failure to transmission loss and damping plays a big role here

What is coincident freq?

> The resonant frequency is thought of as a high pass filter to transmission loss.

Maybe I'm not understanding, but usually it's a LP filter, same as a port attenuates high freq. exiting it

> I would say it's about .5-1mm at most.

> I thought it was more like .015 in.

On multiple layers, I'm not sure more layers is better, as for the same total thickness you might have significantly less stiffness, and max shear is at the neutral axis (usually the center plane) so shear dissipation is most effective there.

Noah
noah katz is online now  
post #78 of 181 Old 04-22-2017, 01:02 PM - Thread Starter
Advanced Member
 
Join Date: Dec 2015
Posts: 825
Mentioned: 29 Post(s)
Tagged: 0 Thread(s)
Quoted: 379 Post(s)
Liked: 198
http://www.acoustic-glossary.co.uk/sound-insulation.htm it should have said coincidence frequency. Sorry for the typo.


Sent from my iPhone using Tapatalk
Mpoes12 is online now  
post #79 of 181 Old 04-22-2017, 01:05 PM - Thread Starter
Advanced Member
 
Join Date: Dec 2015
Posts: 825
Mentioned: 29 Post(s)
Tagged: 0 Thread(s)
Quoted: 379 Post(s)
Liked: 198
http://wiki.naturalfrequency.com/wik...d_Transmission see this and http://www.mne.psu.edu/lamancusa/me458/9_trans.pdf for discussion of these zones. Mass dominates between the resonance frequency and coincidence frequency. Not above coincidence or below resonance.


Sent from my iPhone using Tapatalk
Mpoes12 is online now  
post #80 of 181 Old 04-22-2017, 01:14 PM
AVS Forum Addicted Member
 
noah katz's Avatar
 
Join Date: Apr 1999
Location: Mountain View, CA USA
Posts: 21,589
Mentioned: 3 Post(s)
Tagged: 0 Thread(s)
Quoted: 1107 Post(s)
Liked: 387
Interesting, thanks.

Noah
noah katz is online now  
post #81 of 181 Old 04-22-2017, 01:35 PM - Thread Starter
Advanced Member
 
Join Date: Dec 2015
Posts: 825
Mentioned: 29 Post(s)
Tagged: 0 Thread(s)
Quoted: 379 Post(s)
Liked: 198
Noah much of what you discuss deals with what would matter for a sub enclosure

https://books.google.com/books?id=jD...20loss&f=false

Below the resonance frequency mass has little impact on transmission loss. Stiffness dominates. Doubling the stiffness leads to a 6 db increase in transmission loss. At resonance the damping matters. Above resonance mass matters. With a full range speaker that produces everything you can't just build stiff or massive because all of he zones, including coincidence would come into play.

I think maybe for different boxes different ideas might apply. For a main speaker it might make sense to get the resonance below its operating range by keeping mass high and stiffness relatively low, with high damping to reduce the amplitude decay of the resonance (which would be unlikely to be excited in this scenario). With a sub box it probably makes sense to get the resonance frequency high and get stiffness up as high as possible. In this case stiffness matters but these articles indicate mass does not matter so much. Damping would matter only to reduce the effect of the resonance.

Do you think I'm mis-applying any of these factors to a speaker box. I noted earlier some of these wasn't totally clear to me. Either I don't understand transmission loss as well as I think some of what we say about full range speaker boxes may not be right.


Sent from my iPhone using Tapatalk
Mpoes12 is online now  
post #82 of 181 Old 04-22-2017, 01:46 PM
AVS Forum Addicted Member
 
noah katz's Avatar
 
Join Date: Apr 1999
Location: Mountain View, CA USA
Posts: 21,589
Mentioned: 3 Post(s)
Tagged: 0 Thread(s)
Quoted: 1107 Post(s)
Liked: 387
I didn't say a thing about transmission loss.

What I did say is relevant to mains; sub boxes can be built stiff enough to put f(n) above the passband.

Though we should be careful not to paint with too broad a brush; note from the amplitude ratio graph that amplification starts to become significant at an octave below resonance.

Re transmission loss in general, I don't see the sense in pursuing it for speaker boxes, since sound leaking out will be dominated by what gets through the driver cone.

Benefits of mechanically isolating the driver cone depend on what proportion of box panel vibes are from that vs. from SPL inside the box; I don't know the answer to that.

Noah

Last edited by noah katz; 04-22-2017 at 01:55 PM.
noah katz is online now  
post #83 of 181 Old 04-22-2017, 02:00 PM - Thread Starter
Advanced Member
 
Join Date: Dec 2015
Posts: 825
Mentioned: 29 Post(s)
Tagged: 0 Thread(s)
Quoted: 379 Post(s)
Liked: 198
The purpose of this post was to discuss re-transmission by the enclosure.

I am sure you can debate the negative impact but the significance of the transmission through the enclosure is discussed in various articles I cited earlier. Using very sophisticated methods they found hat the enclosure radiated sound very loudly, and at certain frequencies louder than the fundamental after a certain time passed. It was noted that this loud delayed transmission is likely to be detrimental to sound.

I've asked to physicist that I know studied this if the data can be shared. One is on vacation and said he would let me know when he gets back. I know the gist of the study, they applied the same effect to a signal through headphones in an abx study, but I have never seen the data. All I know is the results lead to a preference for no box radiation effects.


Sent from my iPhone using Tapatalk
Mpoes12 is online now  
post #84 of 181 Old 04-22-2017, 02:04 PM - Thread Starter
Advanced Member
 
Join Date: Dec 2015
Posts: 825
Mentioned: 29 Post(s)
Tagged: 0 Thread(s)
Quoted: 379 Post(s)
Liked: 198
Sorry I did not mean to say fundamental. I meant sound coming from the speaker. That's not the fundamental. Also I meant to write two physicist, not to. I'm not a very good phone typer with a 2 year old around.


Sent from my iPhone using Tapatalk
Mpoes12 is online now  
post #85 of 181 Old 04-22-2017, 02:22 PM
AVS Forum Addicted Member
 
noah katz's Avatar
 
Join Date: Apr 1999
Location: Mountain View, CA USA
Posts: 21,589
Mentioned: 3 Post(s)
Tagged: 0 Thread(s)
Quoted: 1107 Post(s)
Liked: 387
Not sure you mean post or thread, the title of which is The Science of Speaker Cabinet Design.

> Using very sophisticated methods they found hat the enclosure radiated sound very loudly, and at certain frequencies louder than the fundamental after a certain time passed.

Yes, no arguing that; I've seen similar in loudspeaker design texts.

Just thought of something; a box made from NidaCore panels might perform well.

It's a honeycomb core made of viscoelastic plastic over which you bond face sheet material of your choosing.

Even better if you make the panels curved.

https://www.google.com/webhp?sourcei...F-8#q=nidacore

Noah
noah katz is online now  
post #86 of 181 Old 04-22-2017, 02:47 PM - Thread Starter
Advanced Member
 
Join Date: Dec 2015
Posts: 825
Mentioned: 29 Post(s)
Tagged: 0 Thread(s)
Quoted: 379 Post(s)
Liked: 198
I've wondered about materials like this for home walls too. I'd love to play around with fancier materials for speaker enclosures but cost is often really high and availability difficult.

Is this stuff available to consumers? I often have a hard time sourcing these exotic materials. Dr Geddes was using urethane sheets for his composite enclosures for a while and when I tried to get some I had a hard time. It was going to be something like $500 per sheet and a minimum order of 10 sheets.

I've not seen it done but I do think there could be merit in using green glue as the viscoelastic layer. It's a proven product for a highly similar purpose. It's cheap and easy to get. They have at my local menards even.


Sent from my iPhone using Tapatalk
Mpoes12 is online now  
post #87 of 181 Old 04-22-2017, 02:54 PM
AVS Forum Addicted Member
 
noah katz's Avatar
 
Join Date: Apr 1999
Location: Mountain View, CA USA
Posts: 21,589
Mentioned: 3 Post(s)
Tagged: 0 Thread(s)
Quoted: 1107 Post(s)
Liked: 387
I don't think it's hard to get; a lot of people that build their own boats use it.

When a fiberglass boat hits a pier, it punches a hole in it; with a Nidacore hull it just deforms and bounces back.

Also they say it makes the boats much quieter vis a vis engine noise, and I believe it's the case that fiberglass is better than wood in that respect, i.e. better damped, which is relevant here.

I'm going to use it for a monocoque car (trike actually) body.

Noah

Last edited by noah katz; 04-22-2017 at 03:01 PM.
noah katz is online now  
post #88 of 181 Old 04-22-2017, 02:54 PM
AVS Forum Special Member
 
augerpro's Avatar
 
Join Date: Aug 2005
Location: Denver, Colorado
Posts: 1,940
Mentioned: 3 Post(s)
Tagged: 0 Thread(s)
Quoted: 137 Post(s)
Liked: 68
Mpoes12> that critical or coincident frequency is very interesting, I've never read of that phenomenon before. However I don't understand it, heh. I'm assuming the bending wave of the panel is related to the distance of any unsupported area? So smaller boxes would directionally push that frequency up, as would more bracing (to effectively shorten the length of the panel that would flex)? If so, then we are talking about frequencies where the wavelengths are on a similar scale to the length of any "free" panel area? Back of the envelope tells me that is pretty much the entire midrange for the range of typical loudspeakers. Intriguing.

I think you are correct to think of this as different modes or zones, and each has a different solution.

Noah> NidaCore very cool!
augerpro is offline  
post #89 of 181 Old 04-22-2017, 03:05 PM
AVS Forum Addicted Member
 
noah katz's Avatar
 
Join Date: Apr 1999
Location: Mountain View, CA USA
Posts: 21,589
Mentioned: 3 Post(s)
Tagged: 0 Thread(s)
Quoted: 1107 Post(s)
Liked: 387
Brandon,

Yes, and there's more coolness:

Nothing much sticks to polyethylene, so the core has plastic mesh fused to both sides.

When the face sheets are applied, resin flows around the strands and locks them on mechanically when cured.

Also, the core is very flexible and can be formed into compound curves, though I assume face sheet material limitations apply, about which I'm not very knowledgeable.

Noah
noah katz is online now  
post #90 of 181 Old 04-22-2017, 03:30 PM - Thread Starter
Advanced Member
 
Join Date: Dec 2015
Posts: 825
Mentioned: 29 Post(s)
Tagged: 0 Thread(s)
Quoted: 379 Post(s)
Liked: 198
Yeah I clicked the link. Its very cheap and seems easy to buy. I want to mess around with some. My next speaker projects are surrounds and subwoofers as I have no need for different mains. This might be a nice front and rear baffle damping material.


Sent from my iPhone using Tapatalk
Mpoes12 is online now  
Sponsored Links
Advertisement
 
Reply DIY Speakers and Subs

Thread Tools
Show Printable Version Show Printable Version
Email this Page Email this Page


Forum Jump: 

Posting Rules  
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off