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Old 18th August 2012, 01:27 PM   #1
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Default what can i do with four of these ?

Hi , I picked up four of these a little while back because they were bit of a bargain and after many hours of googling i can't find a suitable sized enclosure to build. Most of the builds I've found are somewhere around 10 cft per driver which is fine with me but not the other half.

The subwoofers are jbl gto 1514 car drivers specs I could find are

Vc 3.8 ohm
Mh 3.05
Sd 830cm2
Bl 17.13
Vas 153.5l
Mms 257g
Free air res 25.1hz
Qms 7.08
Qes 0.52
Qts 0.49
Power handling 350w
Sensitivity 93db
Frequency res 23-300 hz

These will mainly used for home cinema use, but also for music in my living room which is approx 5 x 5 x 2.4 m and my other speakers are four of the mercia design from the planet 10 website using a pair of mark audio chr-70. My centre also uses a pair of mark audio chr 70 in a bass reflex enclosure . These are currently crossed over at 80hz on my onkyo receiver.

I don't mind building a pair or four enclosures and not too fussed on overall output as im not a loud listener most of the time . Free phone app dos'nt show above 90db at my listening position even when im listening at the loudest I would . 95% of the time it would be a lot quieter though .

I reckon I could get away with four enclosures of 6cft or a pair of enclosures of 12cft and still keep the other half happy . Maybe a pair of isobaric could be a good idea, my understanding is the half the enclosure size with good low end extension ?

I've no windows based pc at the moment so am unable to use winisd etc , I've not found anything for android yet .

Any help would be greatly apprieciated .
Thanks
Steve
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Old 18th August 2012, 02:14 PM   #2
tb46 is offline tb46  United States
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Hi Steve,

I'll attach a Hornresp Input screen for an isobaric bass reflex (two drivers in series). V_net=3.3ft^3. By the time you have the isobaric configuration, bracing, etc. accounted for you might be around 5ft^3. A simple trials box could be build from 2'Dia. sonotube, some like the sound of isobaric boxes, some don't, so some experimenting may be in order. Another possibility would be bjorno's T-TQWTs.

Regards,
Attached Images
File Type: jpg JBL_GTO1514_BR_Iso_Input.jpg (36.2 KB, 241 views)
File Type: jpg JBL_GTO1514_BR_Iso_SPL.jpg (28.8 KB, 237 views)
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Last edited by tb46; 18th August 2012 at 02:21 PM.
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Old 18th August 2012, 06:02 PM   #3
sreten is offline sreten  United Kingdom
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Hi,

Two 3.5cuft (clamshell) isobarics tuned to 20Hz are not too shabbly.
(6 cuft and 20Hz will give you flat to near 20Hz and a very sharp
roll-off, which is not good transient wise. The smaller box has a
more rounded roll-off, better for transients, and generally the
smaller boxes airload will better linearise the driver distortion.
4 cuft and 20Hz gives you -3dB @ 20Hz isobaric.)

rgds, sreten.

Placement just over 1/3 along the back wall and just over 1/3
along the furthest side wall usually gives the best overall result.
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File Type: gif guff.gif (20.7 KB, 217 views)
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Last edited by sreten; 18th August 2012 at 06:20 PM.
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Old 20th August 2012, 02:41 PM   #4
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Hi thanks for the replies and sorry for the delay in responding . Been working to many hours and then catching up on some much needed sleep .

I don't have my heart set on isobaric enclosures , if anything I'd prefer four seperate enclosures of 2ft x 2ft x 2ft maximum outer dimensions so I could spread them round the room . The reason I thought isobaric was all the builds I could find were using 10cft per driver .

I do have suggestions of two sealed ppsl enclosures of 6cft and a simple transmission line for each subwoofer , length 2.3m , open end 0.042m2 , close end 0.249m2 .
I've no experience of either ppsl or transmission line and have only heard one clam shell isobaric setup in a car once .

Good to hear that both of your designs come in under the size I need to adhere too . I will Google the bjorno t-tqwt's as well . Lol been looking for a supplier of sonotube in the UK for ages without any luck , I've stacks of old mdf to knock up some trial enclosure though .

Sreten , what's the port area and length on you design please?

Thanks for your time
Steve
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Old 21st August 2012, 01:32 AM   #5
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bandpass ?
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Old 21st August 2012, 02:13 AM   #6
GM is offline GM  United States
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Quote:
Originally Posted by steve71075 View Post
.......a simple transmission line for each subwoofer...........
This was going to be my suggestion if it could be tall.......

GM
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Old 21st August 2012, 05:07 AM   #7
Djim is offline Djim  Netherlands
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Hi Steve,

Since you seem to have an almost square room (5m x 5m) that is also half wide high (2,5m), you will have pretty strong room resonances to deal with. You don’t seem to care much about high output. This info considered I wouldn’t go for a resonant system but ‘simple’ closed boxes with compensation EQ. That way you can keep them relative small and ‘spread them round the room’ to deal with your room resonances. If you don’t use more than 150Watts per driver you don’t even need a low cut off filter and you should be able to get 110dB at 20Hz and about 99dB at 10hz without room gain from four 100 litre cabs (3.5cft) and 600 watts total. These figures are based on 3dB system losses. That's all well within your requirements and enough to upset someone. Of course you can also build 100 Litre basreflex (+ port volume and driver volume) cabs and 'fill' the tubes completely to see what you prefer.

Last edited by Djim; 21st August 2012 at 05:12 AM.
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Old 21st August 2012, 02:00 PM   #8
sreten is offline sreten  United Kingdom
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Hi,

The choice between isobaric or not is essentially two boxes of a given
volume (say 2.5 to 4 cuft) or 4 boxes each double the size (5 to 8 cuft).

The 8 times the volume increases max SPL and efficiency by 6dB for
the same bass extension. Essentially isobaric gives you two 87dB
drivers with half the Vas sutable for smaller boxes.

IMO if isobaric goes loud enough, here it is your best choice, as you
will have converted some car subs to parameters more typically
used in domestic subs, but its your call.

A big room with efficient speakers might need the extra SPL.

rgds, sreten.

Port sizing of subs and speakers is a contentious issue. IMO
they are often oversized compared to what you actually need
for typical programme material rather than test signals.

4 cuft tuned to 20Hz is a 4" diameter x 18" port acording to WinISD.
(or a slot 15"x 0.75" x 13" deep). Flared ports complicate matters.
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Old 21st August 2012, 02:38 PM   #9
tb46 is offline tb46  United States
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Hi Y'all,

Post #7: "...‘spread them round the room’ to deal with your room resonances."

Post #8: "... Flared ports complicate matters."

The are some great papers on both subjects, here is one source:

Harman - Scientific Publications

On multiple subs see: "Welti and Devantier" (#2 in the list), and one I like on ports is "Maximizing Performance from Loudspeaker Ports".

A reference for multiple subs here on diyaudio is:

Multiple Small Subs - Geddes Approach

Start with the link in Post #5.

Regards,
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Old 21st August 2012, 02:50 PM   #10
jwmbro is offline jwmbro  United States
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Quote:
Originally Posted by GM View Post
This was going to be my suggestion if it could be tall.......

GM
Yeah, if tall and skinny is okay, could always go for a T-TQWT, about 1 x 1.5 x 4 ft external, or 130liters internal.

Click the image to open in full size.

You're not getting much output below 20Hz though, you may want to go deeper for home cinema.
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