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Old 31st December 2013, 02:15 AM   #1
Joekewl is offline Joekewl  United States
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Default Starting Questions for Big-Bass-Bench for HT

*****Edit/Update*****
I've decided to go with a 2x12" driver box for now. Dimensions are 48x22x18, with 1" board +bracing gives me ~8 cu.ft (230 lit). Since what I really need is low end response, should I go with an Isobaric build instead of the big box, dual down firing vented build I was thinking?

**********




Hello all, I'm new here so I will do my best to not show off my nubishness

I recently gutted and re wired a pure music stereo system with Two towers, a main chest and external sub for a grand total of 14 speakers, complete with crossovers, amps, cooling system, equalizers, CD/Record/Radio/Ipad/Bluetooth. It was quite a fun project that took about 6 months.

I say that to say this: on that project, I did everything but build the enclosures. This time, I am building a Bass-Bench for my HT (first step in a project to build a full 5.1, maybe 7.1, surround system from scratch). Basically, the electronics I understand, but I have no real experience with building enclosures. I've bought a couple books and have been reading around all over.

The task: I need to build the best box given a couple of set parameters.

--Drivers: I currently have 2x12" subs (Old Pioneer Car subs) and a 10" DVC subwoofer.
--Amp: I bought a sub amp that has only 100 watts but is 1 ohm stable (All drivers will be in parallel).
--Space: My wife will be upholstering the MDF and it will act/look like a bench for extra general seating...until it gets turned on. Maximum Dimensions are 46"x20"x18" (WxDxH).

My basic layout is going to be the two 12" (tuned to as low as I can get) on the ends both down firing, and the 10" in the middle, maybe down, maybe front firing. The plate amp will be on the back, or maybe in a hatch on top. This will be for pure HT and I have the alternate stereo for my music. My main listening area is approximately 18x20 but there is no wall between my kitchen/ dining room/sitting room so the entire downstairs (~1200 sq.ft) is open to suck up the bass.

My specific questions are:

1) I was considering having the 10" be in a sealed and front firing for the higher end bass (+~60Hz) and having the two 12" be ported for the lower boomy stuff. Is that a good, bad, or doesn't matter idea?

2) Since the two 12" subs will be tuned to the same FS and down firing, should they "share" the same air/space or should I have them sealed and ported separately? What would be the difference acoustically?

3) The ports I've calculated for the tuning I want on the 12" subs, are between 20" and 35" long (3"-4.5" diameter) depending on the volumes I use. I read somewhere that having a port length bigger than the box is bad, is that true? Could I not just have them run through the full box to the exit? Like, the tube for the left box runs through the full bench and out the right side. And, for HT, is it best to have the ports: a) down b) out each side c) forward toward audience?

4) I've read that adding insulation can make your speaker "think it's bigger". Since space is an issue ("Perfect" vented size for each 12" is like 10 cubic feet), should I use this stuff? How much is appropriate so that it doesn't restrict air flow?

Any and all tips/answers/links/comments are welcome, whether they address these specific questions or something I am not thinking of. Thanks in advance!

Last edited by Joekewl; 7th January 2014 at 03:04 AM.
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Old 31st December 2013, 01:08 PM   #2
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Hmmmm...

IMO, a two-way subwoofer like this probably isn't worth doing. A pair of 12"s will comfortably out-run a single 10", so I'd just give the 12"s the extra cabinet volume.

Do you have any T/S parameters for the 12"s?

Chris
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Old 31st December 2013, 11:28 PM   #3
Joekewl is offline Joekewl  United States
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Chris, thanks for the reply!

Yeah, it is kind of a cramp, I was a little off on the dimensions, it was supposed to be 48" wide, not 45". Even then, I think I measured the cabinet room (minus bracing, speakers, etc) to be about 7.5 cu.ft, which is 2.5 cu.ft more than the manufacturer suggested sealed volume for all 3 together.

I've tried running some sims on some freeware I've got, and I'm trying to decide a couple things. One of which, is how low can I tune them without sacrificing quality too much. The reason I wanted to add the 10", is that since it's a DVC, and the amp I got is 1ohm stable, I can run all "four" coils and suck as much out of it as possible.

One thing I MIGHT do (depending on how the wife takes it) is make two smaller benches to put a few feet behind our couches for the 12's and make a main front firing out of the 10", but just thought about giving that a try.

I got the specs on the 12's, I will list below. They are older, bought them in HS because they were a steal, like 75% off. They've held up in another enclosure I had really well over the years.


Nom Dia--- 12"
Qts--- .556
Qms--- 9.542
Qes--- .590
Fs--- 25.7
Vas--- 4.74cu.ft (134.21 l)
Vd--- .0128cu.ft (.363 l)
Sd--- .542sq.ft (.0504sq.m)
Revc--- 3ohm
Levc---1.781mH @2kHz
Xmax--- .28in (7.2mm)
Zmax--- 53.55ohm
Bl--- 9.316 Tm
Rms---1.719 Ns/m
Mms---102.79g
Cms--- .0003737 m/N
Mg Wt--- 706g
Rms Power--- 150W
Max Power--- 450W
Sp Disp--- .053cu.ft (1.51 l)
Recom Encl--- 1.5 cu.ft (42.5 l)
F0 (in cab)--- 52.4
Q0 (in cab)--- .818

Thanks again,
Charles
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Old 3rd January 2014, 01:07 AM   #4
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Charles,
Using the two 12" vintage Pioneer Car subs with the available space, considering that 48"x20"x18" is the external dimensions and 46"x18"x16" (net) internal volume, this gives (13 248 cubic inch = 217.1 liter) 108.5 liters, sealed for each speaker driver, if that's the case of putting the two drivers in one enclosure, meaning no extra space for an additional driver besides the 2x12" Pioneers (F3 ~34 Hz/QTC ~0.88) what is not bad, considering.

You can not confuse the dimensions given by the manufacturer that are to work in a car environment with cabin gain and that for home design with the right dimensioning for a sub or speaker playing music or HT, they are different.
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Old 5th January 2014, 05:16 PM   #5
Joekewl is offline Joekewl  United States
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Inductor,

Yeah, I figured there would be a gap between how the subs work in a room for HT and how they work in a car. I just wanted to get some practice in working with the software and with the carpentry by doing a project that sounds as good as possible with the stuff I had already. I just don't know what exactly changes from one to the other and that's what I'm doing here. Hopefully to get a better idea and learn something.

I think I've decided to go with the just 2x12 speakers in one box and maybe build another box for the 10". I see a lot of different things on how low to go, and with my dimensions, and drivers, I think I can get to about 18Hz in a ported design in keeping the SPL curve decently flat at the tail. Most factory subs near my price range have a freq response that bottoms at 28Hz so I'm guessing that will be more than enough for now.

Since the EBP is just under 50, it says that the suggested enclosure is closed, but I cannot get nearly the low frequency response. It's still ok for me to go with the vented, right?
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Old 6th January 2014, 04:02 PM   #6
bjorno is offline bjorno  Sweden
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Hi,

FYI:

b
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File Type: jpg Old Pioneer Car_12inch-Driver.JPG (499.4 KB, 137 views)
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Old 7th January 2014, 01:35 AM   #7
Joekewl is offline Joekewl  United States
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Bjorno,

That's a lot of very pretty pictures! And, I appreciate you posting it... with that said, I'm a nub and not exactly sure what the key points of everything in that are. I kind of understand a lot of the numbers/figures but the context to which it applies escapes me. If you care to elaborate, I'd appreciate it greatly. If not, thanks again and I'll see what I can make of it all.

Charles
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Old 7th January 2014, 04:12 PM   #8
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DIY means well you know.
But, bjorno has shown a sim of a transmission line primarily done with Hornresponse.
You should download a copy of it, it is free.
You will recognise the input screen about half way down the left side.
BTW. make sure to click on the X in the bottom left hand corner to maximise the posting.
Put all of the numbers on that input screen into Hornresponse and play around with the software a little bit.
The speaker design that he is proposing is a Transmission line with an offset driver (OD) which means the driver is mounted partway down the transmission line.
The line also has a port to "load" it so the actual full name of this enclosure is an OD_ML_TL or Offset driver_Mass loaded_ Transmission line.
Right under the Hornresponse input screen is a "Schematic diagram" of the speaker box and there is a second schematic diagram on the right that shows 2 drivers at the offset driver location.
.
Transmission lines usually sound a bit better than simple Bass-Reflex boxes and are more easily ,IMO, integrated into a sound system.
Maybe someone has a simple box cross section to show what this kind of speaker would look like.
.
You may want to look at a post that is presently just a few below this one called " Lab 12 Based Offset Driver - Mass Loaded - Transmission Line (OD-ML-TL) Design by Bj "



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Old 7th January 2014, 04:47 PM   #9
Joekewl is offline Joekewl  United States
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Shadydave,

That's very helpful. I have seen a ton of posting regarding horn/transmission boxes, but didn't follow it all very well. They seem (for me) to look very complex. I will go check out the program for sure. I seem to remember a big issue with TL boxes being space hogs, is that correct?

Thanks,
Charles
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Old 7th January 2014, 09:49 PM   #10
troystg is offline troystg  United States
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Quote:
Originally Posted by Shadydave View Post
...
BTW. make sure to click on the X in the bottom left hand corner to maximise the posting.......
That has to be the best tip I have heard all year...

I never noticed that and have been squinting at the charts for months now...
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