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Old 27th December 2010, 06:53 PM   #21
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Quote:
Originally Posted by mondogenerator View Post
personally, i wouldnt be scared to use them in a sealed box. after many years of messing with both sealed and vented systems, i have come full circle and once again i prefer the small sacrifice in 'maximally flat' bass extension of a vented design to obtain the smoother, and transiently better response that a closed box will produce. room gain and the fact i listen within about 10ft mostly, means that often the result is better than the vented boxes i have. id even go as far to say that a low Qb (sub 0.707) sealed box can be even better, and ultimately flatter, when room gain is factored in. group delay on bass is noticable in many vented systems, and until recently i was sceptical about its audibilty. all these things combined with the fact you will sometimes be using a sub, makes me think that closed is definitly the way to go. ive often found jazzy drums and double bass sound far better, although less 'full' when i used the same driver in 'optimal' boxes both vented and sealed for comparison. and this is using the visaton AL130 which also has a very high EBP(pointing to a vented design) but the qts of 0.4ish means its a little more versatile. group delay in WinISD is cut from about 15ms to less than 6. ive also tried this with a old pair of audax ap130zo, with slightly less impressive results. the Fs of the audax is about 58hz thought, and the EBP way over 100 if i recall correctly.

i hope that maybe this is of some help
This is interesting. I wanted to come to this with my question. Today I will buy the wood, I'll make 10 liters sealed boxes, so there is room to bring reinforcements and padding. I have already bass reflex boxes I put together previously, then this is a matter of choosing which I like.
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Old 27th December 2010, 07:20 PM   #22
sreten is offline sreten  United Kingdom
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Hi,

This may be technically interesting, but I'm not remotely interested
in "optimum", i.e. Butterworth, vented boxes, I'm interested in what
is IMO the "optimum" way of using a particular driver for purpose.

Here I'd suggest detuning the vented boxes ports. Get some porous
foam, around ~ 8mm thick, cut into rectangles port length x 3 dia.
Insert into the ports, it will self support itself.

This IMO will be better than "optimum" sealed and vented.
Speaker design is the art of good compromises, not dogma.

rgds, sreten.

Attached is yellow = optimum sealed, green = optimum vented.
Driver = Qts - 0.35, Vas - 45L, Fs - 30Hz, ~ a good 8" driver.
I like the purple line at +8dB @ 20Hz over both the above.
Note the quasi first order slope of the purple line.
This gives quasi first order transient response, the best.
Look at F3, F6 and F10 for the green and purple lines.
Particularly note the slope of all of the lines at F6.
Compare the purple to the large/massive blue/red sealed box.
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Last edited by sreten; 27th December 2010 at 07:48 PM.
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Old 27th December 2010, 07:26 PM   #23
sreten is offline sreten  United Kingdom
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attachment
Attached Images
File Type: jpg model8ventedsealedcomparison.jpg (130.5 KB, 222 views)
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Old 27th December 2010, 07:57 PM   #24
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What program are you using?
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Old 27th December 2010, 08:06 PM   #25
sreten is offline sreten  United Kingdom
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Hi,

That program is the basic WinISDbeta, WinISDpro is more advanced but
more difficult to use, neither are particularly accurate, though they both
reflect the basic mathematics, for a real design I'd cross check with
say Unibox, which is apparently very good, but not as quick, at all.

They are both good for playing with the numbers, the latter also
does maximum SPL and power handling stuff, quite illuminating.
(Also does active pre filters for 6th order designs).

They are free, The demo version of Basta! is also worth a look,
if for nothing else, the free technical info/manuals available.

rgds, sreten.

To play with WinISDbeta you only need Fs, Qts and Vas.
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Last edited by sreten; 27th December 2010 at 08:16 PM.
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Old 28th December 2010, 02:52 AM   #26
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Today I bought the wood. I will make a sealed box about 9 liters, but there is also the option to open them to make it bass reflex, with the corresponding size for this application. Is a design that always used to be able to test so versatile. Tomorrow I'll start the assembly of the boxes. I estimate to complete them within ten days. As promised earlier, iŽll show you pictures
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Old 28th December 2010, 05:20 AM   #27
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Hello,
Good discussion of sealed boxes and bass reflex. Here is an effort at some of the reasoning or explanation with a stored energy bias.
Much of the discussion has been about driver Qtc and speaker (enclosure plus driver) total Q.
Pun included, it is a quality thing. Dampening is pretty much the reciprocal (1/Q) of Q. The higher the Q and the lower dampening the greater the stored energy and the more wobbly the bass gets. The trade off is greater dbs at lower Hz. The whole thing for extended Hz in a bass reflex box is stored acoustic energy compressed in the box and returned nearly 90 degrees out of phase as reinforcement. Sounds wobbly, fuzzy to me.
In my text book critically damped is Q=0.5.
DT
All just for fun!
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Old 28th December 2010, 09:17 AM   #28
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Quote:
Originally Posted by sreten View Post
Hi,

This may be technically interesting, but I'm not remotely interested
in "optimum", i.e. Butterworth, vented boxes, I'm interested in what
is IMO the "optimum" way of using a particular driver for purpose.

Here I'd suggest detuning the vented boxes ports. Get some porous
foam, around ~ 8mm thick, cut into rectangles port length x 3 dia.
Insert into the ports, it will self support itself.

This IMO will be better than "optimum" sealed and vented.
Speaker design is the art of good compromises, not dogma.

rgds, sreten.

I thnk youve maybe misinterpreted my meaning or my meaning wasnt clear.

i agree with your philosophy regards 'traditional' alignments, or at least the maximally flat butterworths. trouble is with stored energy. Chebychev is even worse. point being, all alignments are analagous to electrical filters (as we all know).

to the other poster, i have to agree, in a closed box system, provided power handling isnt too compromised, a total box Q of anywhere between 0.5 and 0.7 is where is aim, especially if i wanted seamless integration with a sub. thats just my personal opinion. plus it makes filters so much easier, and nicer phase wise-im sure even active has advantages using lower order filters-although to appease Sreten a little Weems book claims a cleaner upper bass from reflex designs than that of a closed box, but i cannot say i have noticed personally. having a reflex satellite crossed lower to a sub has its advantages, but the steeper filters needed, and the increased accuracy of their integration, are disadvantages. personally if i have a ported system with F3 = 45hz, i wouldnt even bother with a sub at all. maybe i have cloth in my ears

but i would like to see the group delay comparison with those curves Sreten, considering the gain between the HUGE closed box and the over damped vented box is due to the vent, coming with all the resonances, thru port reflections and phase issues that are inescapable. the vented alignment you show is interesting, I would use it for a main speaker system, but not for something to use with a subwoofer.

i essentially agree with you though. i would try and build a box suited for the vented alignment, with which you can tune the ports using foam, to varying degrees, to even aperiodic if needed. theres nothing wrong with playing around with stuffing or port sizes, or resisitive ports.
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Last edited by mondogenerator; 28th December 2010 at 09:33 AM.
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Old 28th December 2010, 09:25 AM   #29
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Incidentally, the best material to fill your boxes is natural fibre carpet underlay, Don't touch the horrid rubberised stuff.
regards
Henry.
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Old 28th December 2010, 09:58 AM   #30
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Originally Posted by toprepairman View Post
Incidentally, the best material to fill your boxes is natural fibre carpet underlay, Don't touch the horrid rubberised stuff.
regards
Henry.

it is good yes. not wanting to start a filler debate but in the end a composite of lots of materials is the best. foam fibre and felt....3 F's lol
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