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Old 11th October 2018, 08:12 PM   #631
gmad is offline gmad  United States
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WF,

I was just guessing that keeping the holes to a minimum might make the resonance more broad (even), but maybe at the expense of making the instrument too soft(?) Anyway, I like your idea of the holes being in the corners. I think you should follow your instinct; I get the sense you have a good feel for this and I don't want to screw it up.
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Old 11th October 2018, 09:03 PM   #632
BYRTT is offline BYRTT  Denmark
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Quote:
Originally Posted by diyAchim View Post
...My opinion is, though, that the smallest volume approach is correct and I have very good behaviour of the B200 in it...
Hope not i'm irritating but why use the smallest volume do you use some smoothing EQ or have a room null to fill out there, back in post 610 i showed below prediction for B200 in 17,7 liters having a +6dB overshoot although i did manipulate or offset the original simmed 104Hz Fsc down to 91Hz just to be agreement with your impedance graph, about acoustics in normal indoor rooms and longer measurement window one would probably never notice that overshoot but its there and with Jeff Bagby's few milimeters centered nearfield measurement method it should reveal itself.

Click the image to open in full size.

Quote:
Originally Posted by diyAchim View Post
...FWIW, the impedance peak in the hypercube at 91Hz is fully in line with the simulation of a 17,7liters sealed box in the Visaton Boxsim software. So here we have no difference in behaviour...
Agree and use same software as planet10 that 91Hz is not inline with B200 into 17,7liter, could it be Boxim automatic adds say about 10-20% stuffing so it ends down at 91Hz instead of 104Hz at a clean 17,7 liters volume, if so your real world build should also have that stuffing installed else its not in agreement with Boxim software.

Quote:
Originally Posted by diyAchim View Post
...Sonce's shot at the lower impedance in the box makes no sense to me. I compared with simulation software and did not find that impedance in a box is modeled to be lower. Also, flexing walls would mean higher impedance like without enclosure, IMO. I may be wrong.

So lower impedance would indicate special behaviour of the hypercube. As far as I remember, Tesserax had some measurements done, maybe he can chime in.
Could be wrong but will imagine lower impedance means a overmuch stiffer spring and more amp power to move that point of stiffness, phenonem is probably caused by form of cone is more or less replicated at apex in back of enclosure so same spring pressure effect gets uniform loaded mostly all over cones shape verse a normal enclosure that has a plane back that will never load coneshape so hard because of weak angels and also into corners air can stand still and kind of isolated difuse aroud itself.

Last edited by BYRTT; 11th October 2018 at 09:11 PM.
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Old 11th October 2018, 09:50 PM   #633
diyAchim is offline diyAchim
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Thank you Planet10 and Byrtt,

indeed, I hadn't noticed that the enclosure definition added some stuffing without my intention, namely 6,7g/liters of stuffing.

When I remove this in the software, I get the same plots as you.

So this is really something - the hypercube behaves as if it was stuffed! I like this.

Here is the original sim (which is for the stuffing with 6,7g/l):
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Old 11th October 2018, 11:01 PM   #634
BYRTT is offline BYRTT  Denmark
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Quote:
Originally Posted by White Fang View Post
Thanks a lot BYRTT, I will look at it closely. BTW, what software did you use?

Cheers,

WF
Its all nice practical freeware stuff used although note such stuff has most often some learning/educating curve to handle but that should be no problem if interest really is there : ) its late so will get back tommorrow with some links.

Quote:
Originally Posted by White Fang View Post
I have been staring at your graph, BYRTT, I'm afraid I am trying to decipher it but I don't really understand it. The red curve is the one provided by the manufacturer?...
Yes red trace is manufactures pure datasheet curve, all i did to it is offset it +6dB so it stays clear in graph/plot of the others predicted curves.

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Originally Posted by White Fang View Post
...I see some of the later curves produce horrible comb filter effects, I guess this is from room reflections, right?
...
Its when going off axis on a relative big diameter piston we loose high frequency program more and more the worse the axis and reminds why drivers are manufactured in different sizes and some build multi way systems, problem is not there being situated pure on axis but bigger diameters as this BG 20 can for example only hold 20khz within a very few degrees off axis and called it beams as crazy : ) Up to about 1500Hz it radiate perfect uniform 180 around also called it radiate perfect into half space, from about 1500Hz and up it starts beam and comb filtering as seen below for 10/20/40/80 off axis. Mostly because beaming is a problem at all hang together that room reflections mix with direct sound called power response and here a 165mm piston will sound kind of dull because for example say it adds about 40% to direct sound below 1500Hz but almost nothing as frq goes up above 1500Hz and more. Then again multi way systems have kind of same power response problem even they use a perfect small tweeter piston down at say 20 mm diameter but their power response problem sits only inside XO region where tweeter hand over to midrange and spacing distance between those two drivers is the culprit, where had it been a coxial driver with same acoustic center then power response can get kind of perfect. That said in your use for musical instruments beaming can maybe be good enough feature or maybe better or at least if one knows of it one can take care where to physical place the stuff on the scene or in rehearsal room.

20dB down there is kind of traffic going on ...
Hypercube Loudspeakers-7012b-png
Quote:
Originally Posted by White Fang View Post
...Could you tell me if an enclosure larger than 27 litres would be any better? I mean, I have seen one site saying the ideal sealed enclosure for this driver would be something like 1.66 cubic feet (46 liters) and then I used some software that says the ideal would be 74 liters.

Could you simulate those volumes and explain to me if I would gain anything?...
Five simulations below and guess for guitar use the smallest one are fine but don't go smaller then overshoot on blue trace probably gets too hot/colored and maybe starts conflict with some other room gains and can sound really nasty, then again this is not for a smooth flat reference but musical instruments so who will know : ) for bass guitar and acoustic guitar use with reference to light green trace in post 624 will suggest some EQ filters somewhere in chain to flatten out a smoother and lower reaching response but guess for distorted electric guitar it doen't matter so much : )

Hypercube Loudspeakers-7013b-png
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File Type: png 7013b.png (110.0 KB, 123 views)

Last edited by BYRTT; 11th October 2018 at 11:13 PM.
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Old 12th October 2018, 11:12 AM   #635
White Fang is offline White Fang  Belgium
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Wow, thanks a lot BYRTT, I don't quote the whole message because it will fill in too much space, but I read it carefully.

I wished I understood better these things, but I am already overwhelmed by the amount of articles and books I want to read, and stuff keeps on piling and the pile getting bigger... So I guess I will leave speaker design for another life! Although building them seems like fun, and anyway, I already have the drivers.

My respect to everyone here who understands fully all this info, and thank you so much for the simulation.

From it I gather that there is a trade off in enclosure volume, when the volume is smaller, the bass drops earlier, and it creates some kind of resonance, almost like if you applied a "highpass" filter with "resonance", borrowing from synth-talk.

With bigger volumes, the bass response is flatter, and it extends more into the bass region, things that are both desirable, but then again who will want a 400 liter guitar cabinet to carry around?

So, I think I will opt for the 'reasonably' bigger volume, and not use the smallest box where the drivers could fit.

I will love to give back to this community some test results, I have a "supposedly" flat response test mike somewhere, but I will probably need some coaching on how to proceed.

Thanks to all of you for your feedback, cheers,

WF
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Old 12th October 2018, 11:26 AM   #636
White Fang is offline White Fang  Belgium
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Just wondering, is there a reason the ~70 volume performs so bad? It is really so, it extends no further into the bass than the 45 l. version, and it starts rolling off earlier.

From the graph, the 26.5 l and 45 l seem like the best options. Actually 45 seems a good compromise, the bass response is flatter and you get some extended bass, plus 45 l. is quite manageable. BTW, there is a website that says this is the best option:

"Optimum Cabinet Size (determined using BassBox 6 Pro High Fidelity suggestion): 1.66 feet^3"

Visaton BG20-8 8" Full-Range Speaker with Whizzer Cone 8 Ohm

The builder recommends 30 l., so I guess that is the optimum range for these drivers (~30-45 l.).

BG 20 - 8 Ohm | Visaton

Thank again, to all of you, for the your suggestions and commentaries posted here in this forum, cheers,

WF
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Old 12th October 2018, 01:58 PM   #637
xrk971 is offline xrk971  United States
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I don’t think 70L curve looks bad at all. That’s a nice smooth roll off. Why do you say it is bad? Vas is 110L and you can make a sealed cabinet up to Vas and it will work fine. Basically the softer the suspension is coupled with a weaker motor, the larger the Vas.
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Old 13th October 2018, 01:39 AM   #638
BYRTT is offline BYRTT  Denmark
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White Fang funny you wonder about the yellow one because its the magic 2nd order butterworth curve hitting a Q value of 0,7071 which gives widest amplitude flatness compromise before rolloff and its corner frq is exactly at -3dB point where the higher or lower Q values relative to 0,7071 number will give some amplitude overshoot or undershoot also called over and under damped, and by the way these filter grades are exactly the same that happens into electric circuits combining a capacitor and inductor. Some builders would probably mean its magic to hit that Q of 0,7071 using impedance measurements and adjust physical volume with stuffing and bags of rice inside enclosure until impedance measurement number is exactly at 0,7071, thoughts behind it is probably it would then mean friction to move cone in inwards verse outward direction is then same and in kind of symetric balance, but then again there exsist some published advanced Klippel tests of various drivers and here many drivers even the most costly ones don't look in very good or perfect linear balance and are often offset mechanical somewhere by purpose so not shure its worth go for theoretical symmetry.

Another lesson is in a way its probably not free to pick between those extensions because system acts as a spring and Q value numbers in a way is springs tension and will dictate lenght of stroke when pushed with a certain power, in previous plot curves show power of 1 watt at 1 meter, below is at 25 watt power and includes a red line showing limit of linear excursion (length of stroke) at 4 milimeter point, and as seen on the 5 times red traces its actual only the small one that goes below limit at 25 watts but then again system now outputs +106dB SPL and that high SPL is probably not needed so try find a balance. Visaton don't tell milimeters for highest mechanical excursion limit any where so we don't know where unit will hurt or detroy itself mechanical therefor think use either the blue or purple volume value to keep stoke within some predictable limit. Last thing is if you add dampening material it adds virtual volume that driver incuding spring effect will see, it is said up to about 30% more volume if enclosure is hard stuffed.

Hypercube Loudspeakers-8000-png
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Last edited by BYRTT; 13th October 2018 at 01:46 AM.
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Old 13th October 2018, 08:05 AM   #639
White Fang is offline White Fang  Belgium
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Thanks BYRTT, what I like about the purple curve is that it extends somewhat more into the bass with a gentle boost or resonance before. The "magic" .707 curve might be flatter, but is outperformed clearly by the blue and purple ones in the bass. That being said, the smaller volume might create too much of a boost there at around 120 Hz.

I will follow your recommendation gladly, also, in case the driver kills itself by going too far, well, these are not very expensive ones anyway.

I will start building them and report on how is everything going along the way. I wish a nice weekend to the whole diyaudio "team". Cheers,

WF
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Old 13th October 2018, 08:10 AM   #640
White Fang is offline White Fang  Belgium
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Quote:
Originally Posted by xrk971 View Post
I don’t think 70L curve looks bad at all. That’s a nice smooth roll off. Why do you say it is bad? Vas is 110L and you can make a sealed cabinet up to Vas and it will work fine. Basically the softer the suspension is coupled with a weaker motor, the larger the Vas.
To me the extra flatness of the curve seems at the expense of the bass performing less, so I don't get why this is an ideal situation at all.

I was yesterday tuning the harpsichord for Handel's Resurrezione, I noticed the concert hall had every wall covered with diffusing panels.

Did anyone tried that on speaker walls? Is it worth to add some texture to the surface? Not that very hard to do with a router. Just a few passes at different levels, you won't even see it from the exterior.

Cheers,

WF
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