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Old 23rd January 2003, 10:06 PM   #1
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Default time to redo the 16 cu ft subwoofer to fit an apt

I have (2) dayton DVC 15" drivers in a 16 foot box in my home right now, tuned to go flat down to around 20 hz ( dont remember exact numers). the problem with htis is that it is 16 cubic feet, almost as big as my fridge. Since I am moving to an apt, I want to keep these drivers and just make a much smaller enclosure. I was thinking isobaric in order to further halve my enclosure size. The only thing I know about isobaric is that it halves the required volume.. but how does it affect sound quality and efficiency in comparison to one driver, or both drivers side by side?
Also, since this sub is primarily for home theatre and video gaming, what would be better, still trying for the flattest curve I can get, or sacraficing a little low end in order to get some extra SPL in the 35-70 hz range?

secondly, I have always wired coils and drivers in parallel, as I heard that in series the voice coils act as inductors and affect each other adversely. Can anyone give me input on this?

thirdly, is there any sound quality difference between a round pvc port vs a rectangle/square MDF port??

fourthly - I see all the "retail" home theatre subs tend to be cubic. Is this okay to do? what about standing waves, ideal box ratio, etc?

fifthly - is it even worth it to consider a bandpass box for a driver this big?
thanks for any help you can give on any issues, i really just kinda want more experienced input before i commit to any set enclosure, so that i dont kick myself later when i find I cold have done substantially better.
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Old 23rd January 2003, 11:16 PM   #2
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Cubes are fine

Isobaric will equal efficency of one driver, and halve volume

These things model awsome in a bandpass, I think you can get like 122dB at 40Hz with a couple hunderd watts.

If you have a good enough amplifier that likes to work, do a linkwitz transform circuit on them and put them in about 5 cubic feet, and have the same output that you do now.

-Paul
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Old 24th January 2003, 12:02 AM   #3
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Default Re: time to redo the 16 cu ft subwoofer to fit an apt

Quote:
Originally posted by Jared
The only thing I know about isobaric is that it halves the required volume.. but how does it affect sound quality and efficiency in comparison to one driver, or both drivers side by side?
Also, since this sub is primarily for home theatre and video gaming, what would be better, still trying for the flattest curve I can get, or sacraficing a little low end in order to get some extra SPL in the 35-70 hz range?
IMO, Iíve always thought isobaric subs were a waste of a good woofer or a way to make a not so good woofer sound better. Granted, the isobaricís I have heard sounded decent, but not necessarily better than most good ported or sealed subs.

If you plan on doing any real listening with this system, you need to go for the flater response. You can always turn the level up on the sub if youíre watching a movie if you like that sort of thing, and your new neighbors wonít object.

It has always been my opinion that the real value of the sub is what it does for the mid range. It will clean up the mids like nothing else will.
Quote:
Originally posted by Jared
secondly, I have always wired coils and drivers in parallel, as I heard that in series the voice coils act as inductors and affect each other adversely. Can anyone give me input on this?
Parallel inductors are half the inductance and impedance. Series inductors are double/double.
Quote:
Originally posted by Jared
thirdly, is there any sound quality difference between a round pvc port vs a rectangle/square MDF port??
Ideally, no, but a square port will be more likely to generate noise than a round port. I would only use a square port for very large port areas.
Quote:
Originally posted by Jared
fourthly - I see all the "retail" home theatre subs tend to be cubic. Is this okay to do? what about standing waves, ideal box ratio, etc?
Ideally, itís not a good idea. That said, my sub/end tables are 22Ē square X 19Ē high inside the box. Practically speaking, if you use a lot of bracing and the right absorbing materials in the box, you can go a long way to making it a non-problem.
Quote:
Originally posted by Jared
fifthly - is it even worth it to consider a bandpass box for a driver this big?
It will depend on the driver and the type of alignment they are suited for. I wouldnít go out of my way to create a bandpass box. I think the best alignment is the simplest alignment.

Rodd Yamashita
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Old 24th January 2003, 01:34 AM   #4
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Cubes do work fine, at the frequencies that subs operate at, there is zero chance of a standing wave. Unless your cube is several feet long. I think the general rule of thumb is that once you cross the 4 foot mark with a sub box, you have to be careful for standing waves.

Personaly if you ask me, I would do is make two 2ft^3 boxes, put one driver in each one, except put it in upside down, so taht the magnet sticks out the bottom to get some more volume. Then build the lower part of the box to fit around it so that you cant see it, but at the same time it is well vented. Next get a pair of ~300W amps. Do a search for how to do a Likwitz transform on this driver. Search for FRD Consortium on Google and you will find a spreadsheet that will help you make one. By the way, these are sealed. Start trying them in different locations around your room, put one at 1/4 of the length of the room from one wall, and the other 1/3 of the length of the room from the oposite wall. Start moving them around untill you can get the flattest response down to 20 Hz.

Remember, that a sub that models flat down to 20 Hz will have dips and peaks of about 10-15dB. Using two separate enclosures can greatly reduce this effect, and smoot the bass response.

Lastly, one thing to consider is to use your subs nearfield. Dont place them near any walls, and as close as you can comforatably to the listening position. For example, put one on each side of the listening position, but make sure that they are >6ft from any walls.

This will create a complete nearfield listing experience, and from my experience (eventhough you may loose ~6dB of output), the bass is of very high quality.

-Paul
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Old 24th January 2003, 02:31 AM   #5
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Paul - is is an error in WinISD that when I switch to an isobaric design the efficiency drops by 3 db? I kinda thought it was going to be 3 db greater, but you say it stays the same, and winisd says it drops 3??
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Old 24th January 2003, 02:53 AM   #6
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im so glad i made this thread !! I never heard of a linkwitz transform sub equalizer before !! from 3 minutes of reading it sems to me this is a tailored active equilizer to a driver/enclosure combination in order to boost the low freqs by a correct amount to "fake" a flat response down to lower frequencies. Does this cause issues with excursion and maximum power handling tho? For exampl in a sealed box I know this sub will hande 600 RMS, with this Linkwitz, and a 600 watt amp, wouldnt I run out of amplifier power at low frequencies befroe high frequencies and end up with distortion and overexcursion??
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Old 24th January 2003, 07:20 AM   #7
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Quote:
Originally posted by Jared
Does this cause issues with excursion and maximum power handling tho?
I expect it would just force the excursion to be what it would have been if it were in a big box instead of wimping out in a small box. It would take extra power to do this, maybe 12dB extra watts per octave below resonance?
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Old 24th January 2003, 08:41 AM   #8
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First:

Two drivers beneath each other in the Same box = double volume and doble efficiency compared to a single driver.

Two drivers behind each other in the same box (isobaric) = half the volume and half the efficiency compared to a single driver

=> There's no free lunch !


The excursion issue is depending on the source material. For the average music recording there is usually not much going on at subbass frequencies. But it is nice to be able to reproduce these contents. For music purposes, equalized closed box subwoofers offer great sound and versatility.
Sometimes, a system that goes lower with good accuracy, can have more slam subjectively, than one that doesn't go as low but is capable of much more SPL.

Because you

1.) ... move to a smaller appartment where power requirements might be smaller

2.).. already have the most expensive parts (i.e. drivers and amp)

you can build two closed-box subs with linkwitz transform (or ELF), as a try, with little effort !!

Just my two pence

Regards

Charles
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Old 24th January 2003, 11:08 AM   #9
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Default linkwitz

linkwitzlabs.com

i think he does some work on these filters

quite good

but yeh excursion cud get abit scary
a shiva with 15mm xmax i wudnt mind trying sometime.

www.geocities.com/sc00byd0159

i have some articles on this from a magazine ,one is sealed,the other is ported,,and one uses motional feedback using the dual voice coil,the other is plain linkwitz i think.

(the ported one is interesting cos the port phase is different and changes more gradualy loading the cone more down low)

From the articles:
if ur speakers have got the excursion its not bad
for some reason ppl say the power requirements arent as bad as u wud expect for 10db boostage etc

cooledit 2000 shows that my *bassy* songs have no output below 30hz.only test tones and movies i wud expect.

the lowest my normal songs go to is 40hz and my basstest ones to 32hz or so.

20hz is nice ,but il just wait til i get an 18inch.(til i can afford an 18inch more like)!

next project : vega12
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Old 24th January 2003, 12:19 PM   #10
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mikee12345 - this driver I am using is a Shiva clone.. it does have 15mm xmax... http://www.partsexpress.com/pdf/295-190.pdf
good luck with your vega 12! I had a vega seres 15 in an auto at one time, its now in my fiance's sisters jeep. My fiance has a veaga series 12 in her civic. I think they are absolutely wonderful subs. With the 15 and 600 watts RMS I went to an SPL contest for fun.. I got 139 db with a little bit of cliping. was in teh 137ish range with clean sound tho.. those subs are brutes !!

thanks for everyones input, I am definately going to go with the linkwitz in a small sealed box, as even if it does not sound to my liking I will have a 2 cubuc foot enclosure that I can add the other driver to for a plain jane sealed isobaric. If it does sound great I can make another !
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