what can i do with four of these ?

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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
 
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,
 

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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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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
 
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:).
 
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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.
 
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:

http://www.diyaudio.com/forums/subwoofers/134568-multiple-small-subs-geddes-approach.html

Start with the link in Post #5.

Regards,
 
Hi,

That HK paper is routinely trotted out regarding multiple subs
when its simply not applicable to the cases being discussed.

THe HK paper is about minimising seat to seat differences,
not the overall frequency smoothness, and then using
advanced digital EQ to smooth the overall response.

Fair enough, but the suggested placements are not good
(in fact they are bad) if your after the flattest response.

Given most will mount subs on the floor up against a wall
The simplest option is two subs, one placed around 1/3
along the back wall and the other ~1/3 furthest side wall.

rgds, sreten.
 
After checking with the other half another four towers in the living room is a no :) apparantly four enclosures standing around around 1.4m tall is enough .

Got a couple of days off later this week so am going to try a couple of the isobaric designs first I think , can always seal up the port as mentioned and remove the outer driver from the isobaric configuration to see what sealed sounds like . Would the auto audussey in my onkyo receiver be suffiecent eq if i try sealed?

What kind of power should I be looking at providing for a pair of the isobaric enclosures? I'd like to build an amplifier (my first one) to power them . I do have a plate amplifier to use as a temporary
measure , only 150w @ 4ohm or so but worked really well on my old box with three jl audio 15w6 tuned to 21hz if i remember correct .

From reading I see my room is less than idealy shaped , its actually more like 5 x 6 x 2.4m but not far from square . I have two locations I can put the enclosures , 1st is on the front wall either side of the AV rack under the projector screen around 1.5m from the corners which would be preferred or 2nd choice is around 2/3 along the sidewalls towards to the back of the room and my seating postion .

Thanks for the links , I will have a read when I have some spare time and thankyou for the suggestions . Will let you know how they sound

Steve
 
Hi,

A 140W / 4 ohm plate amplifier should be fine for two isobaric enclosures.

Simple fact is it likely will be loud enough for your typical usage, if it isn't
you can increase power but only by say +3dB to 300W or +6dB to 600W
but these are marginal gains on Max SPL and your overall Max SPL levels.

I severely recommend against trying to build a high powered subamplifier
as your first amplifier project, it likely will go horribly wrong, typically.

Simply having two boxes (4ohm) versus one (8ohm) ups the efficiency
in room by 6dB, i.e. two boxes with 150w will better one box with 600W
easily, simply by having a lot lower distortion at any required SPL.

Sealed versus vented depends on the alignment you choose, and FWIW
the isobaric sealed will probably outperform a single driver sealed in the
same box, so there is little point in removing a driver from isobaric.

rgds, sreten.
 
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I have a 12" Boston car sub in use in my living room. Sucky acoustics, lots of standing waves and no way to optimize.

Sounds like a good time to test a dual rear sub: wide and tight against the rear wall, perhaps even cone outward (think 3-4 " deep, 2 feet tall or so and however long it needs to be, perhaps blending the drivers int an end table or what have you.); and put the other 2 in an isobaric loaded TL or other horn-type near the front.

Iso = half the cubic volume and same db levels as a single driver.
hmmm, time to research isobaric loaded 8th order bandpass enclosures...
 
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