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Old 14th August 2006, 04:19 PM   #1
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Default Box specs, port, and room gain questions

Hey guys, new to the forum, but have been reading quite a bit on it. probably about a month away from ordering all my parts. Wanting to do a subwoofer mainly for home theater use 95/5 split between ht and music. I've decided on the dayton quatro 15 with an existing amp i have soon after to upgrade to 240 watt pe amp. wanting to model my sub to look like the wilson watch dog sub. i've come up with, using 3/4" mdf, an 8.5^3 ft box with 2-8x2 rectangle ports 25.21 inches long to decrease on the possible port noise. this gives me, in winisd pro, around -1.6 db at 20 hz. this is about where i want to be at the price i want to be at. questions are, do these specs sound like they'd make a good sounding sub suitable for home theater and also does anyone have any objections or suggestions for using the rectangle ports instead of just buying flared ports from somewhere? also thinking this looks pretty good on paper, i never really took into account room gain. reading some posts from i think aaron gilbert(?) i start to doubt my design a bit. i won't have any eq for quite some time probably, but i still want to get the cleanest, lowest sounds i can from the box without any extra port noise or distortion. I know this is a pile of questions, but i'm a guy who does a ton of research on just about everything i purchase because i'm always extremely tight on money. thanks in advance and this is a GREAT forum.

Brandon
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Old 16th August 2006, 04:39 PM   #2
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nobody wants to jump in?
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Old 18th August 2006, 01:21 PM   #3
sreten is offline sreten  United Kingdom
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Hi,

You can bet the Wilson Watchdog doesn't have 3/4" walls.

Your design used for music I'd expect to sound bloated, looking
at the driver I'd use it 3 or 4 cuft sealed, room intergration would
be far better. But I'm no HT fan, some people love overblown bass.

/sreten.
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Old 18th August 2006, 11:17 PM   #4
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You think? i'm using winisd pro and getting a pretty flat response. but this doesn't take into account for room gain which i'd still like to find out more about. All i'm wanting is flat response and better sounds than my current rca 10" sub i've had for 5 years. I may be able to be pushed into one of the new hi fidelity subs, which i really like, but mone restraints (government job, wife, 3 kids) keep me from splurging on anything extra.
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Old 19th August 2006, 09:45 AM   #5
AndrewT is offline AndrewT  Scotland
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Hi,
pity no one wants to enlighten us.

Maybe the information is kept a secret.

Or worse, maybe no one here knows anything about room gain and guess instead.

Hope someone is getting real annoyed and jumps in to put me in my place!
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regards Andrew T.
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Old 19th August 2006, 01:16 PM   #6
Notax is offline Notax  Montenegro
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Quote:
Originally posted by brandonnash
You think? i'm using winisd pro and getting a pretty flat response.
Who says its like that in real?
Like Sreten, I think 3 cu.ft. closed would be the best.

If you insist at BR, 4,5 cu. ft. and Dt=130-150 mm (5-6"), Fb=21 Hz, tunnel lenght depends of Vb, Fb, Dt, so calculate. Anyway, you should try different lenghts around that calculated. Can be problem: Vb=127 L, Fb=21 Hz, Dt=150 mm than Lt=815 mm. Very long.
Minimal Dt is about 115 mm. If you go with Dv=140 L, Fb=21 Hz, Dt=115 mm than Lt=411 mm. But, in (this case of) BR group delay is almost 30 msec. at 18 Hz. Because of that its not bad to go with smaller BR box (around 100 L) and Fb=25 Hz. Smaller excursion, group delay 19 msec. at 19 Hz. (Vb=100 L, Fb=25 Hz, Dt=120 mm, Lt=440 mm)
Very important are dimensions of your room and some other caracteristics.

However, for someone with no expirience in this, again, its better to go with closed.

After 1/2 hour I noticed recommendations od manufacturer. No everyones are good, but this are not based on simulations, but obvious in real tests. I like it.

2,5 cu.ft. sealed, light stuffed Qtc=0,68 - thats it!
or

vented 5,5 cu.ft. Fb(F3)=24 Hz, Dt=4", Lt=12,75" (I would say little bigger Dt and Lt)
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Old 19th August 2006, 03:21 PM   #7
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As far as the wilson goes, yes i'm sure that it doesn't have 3/4 " walls. i'm going to use either 3/4 or 1 " mdf with some bracing because i don't have access to composite materials like their m or x materials. I'm just going for the look of it. I'm sure i won't have the sound quality of it. I want to get something substantially better than the little sub i have now. sreten, do you think it will be bloated sounding because of the design or because you prefer sealed boxes? i've always prefered sealed when listening to music, but it doesnt have the deep extension of a ported for ht. just for kicks one night i brought in a jl audio 15w6 i had in a sealed box to see what the sound would be like in my ht. it was great with music after some setup, but it didn't have what i wanted for movies. i'm kind of basing my comments broadly around that experience.
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Old 19th August 2006, 07:23 PM   #8
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sorry i must have been replying when notax was replying. I do have plenty of experience with sealed boxes. I've probably made 15-20 of those for custom car installations anywhere from 8-12 years ago. i've made 1 ported box for an spl competition for a car when i was about 18 and managed 138 db from 3 10" woofers. I'm decent at woodworking, but i've never made a ported box for quality home theater applications. i'm not wanting a box that'll be used only for music. i watch probably 10-15 hours of movies per week and only listen to music 2 or 3 times a week or when it's in the movies. I'm wanting something that will get as close to or below 20 hz flat as possible. all of the research i've done has shown that i'll have around -10 to 15 db at 20 hz and flat response to around 40 hz using a sealed. I think i'm getting that now with a 10" ported sub.
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Old 19th August 2006, 08:19 PM   #9
Notax is offline Notax  Montenegro
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For that what you want is best to go with active system with equalization at lowest (see Linkwitz site) or other bass unit for BR box, to get -3 dB at 18-20 Hz.
Maybe to try with Dayton Titanik 12" (or 15").
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Old 20th August 2006, 09:53 AM   #10
sreten is offline sreten  United Kingdom
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Hi,

AFAIK anything flat to 20Hz will sound bloated in a room.
HT may be OK but music probably would not, of course
this also depends on the upper cut-off frequency used,
if it is low, say 50Hz, then it would sound much flatter.

It all depends on the adjustability of the system.
Subamplifiers with the option of bass boost can be good,
either to get low bass or have different music and HT settings.

Personally I think any design using a box bigger than the Vas of
the driver is not good, working round the limitatations of a 3L Vas
4" driver is one thing, an 8.5 cuft subwoofer box quite another.

When I look at the parameters of the driver it obvious to me
it should be used sealed, used reflexed = very big boxes as
Qts is marginal for reflexing.

For a vented sub I'd choose a driver with slightly lower Qts
such that box volume ends up ~ 50% of Vas to ~ 80% Vas.

Like I said, I know about music subs, not much about HT subs.

/sreten.
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