JBL 4842 Subwoofer double 18" 2245H drawings for DIY? - diyAudio
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Old 2nd July 2012, 01:48 AM   #1
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Default JBL 4842 Subwoofer double 18" 2245H drawings for DIY?

Hi Music lovers!

I have 2 jbl 2245H and Im thinking of building a monster subwoofer. I have found the JBL 4842 and I like the specs. Now the problem is I dont have any drawings.

Does any friendly soul out there have one or perhaps an idea where to find one?

Look forward to a reply!

Nick from Sweden
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Old 2nd July 2012, 06:15 AM   #2
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I don't have the Cabinet C4642A plans. Dimensions are given, construction looks basic. For gigs, the C4642A weighs over 200 lbs.

For home audio I always favor a pair of separate stereo woofers over a single double-speaker box. Stereo woofers improve the full stereo image.

1) JAES papers report that the listener can pick out the physical location of a bass speaker down to 60Hz. So a single box woofer would need to Xover at <60Hz.

2) Two physically separated woofers will smooth out the room modes. You can equalize a single impulse at the listener, but you cannot equalize room modes just smooth them out through use of multiple woofers carefully placed around the room.

If you want to build a single double-speaker box, it would make sense to orient the drivers to counter balance the moving mass.

Push-Pull-Slot-Loaded woofers (PPSL) have counter balanced moving mass and drive their air into a center single slot which has been reported to generate greater dynamics than standard push-pull woofers that drive their air into open opposite ends.

For home audio, sealed woofers are easier to equalize than ported, and also have a 6db/octave natural roll-off slope that is a closer match to most room gain effects.

The Altec Heritage forum recommends designing a modern enclosure for the 2245H with improved bracing, improved port placement, improved wide radius ports, and a lower bass tuning for home audio. They comment that most of the Altec cabinets were designed for movie theater efficiency over home audio deep bass.

Cabinet C4642A uses the newer port.

http://www.jblproservice.com/pdf/The...es/4642AGS.pdf
http://www.jblpro.com/pub/obsolete/4842.pdf
http://www.jands.co.nz/xfiles/JBL%20...inema/4642.PDF
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Old 2nd July 2012, 06:51 AM   #3
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Hi Linesource,

Thanks for your long and detailed message. You might think Im crazy but I also have 4 pcs 2235H in mint condition. If I would use them as well in seperate double speaker boxes, would this be an overkill? (I guess yes) I have a big room and the speakers will be powered with 2 6290`s and signal split by an active dbx filter.
The subwoofers will be used for both movies and music. I love all kind of music but I tend to listen mostly to club music. I wish to feel the bass and over all the impressive dynamics these speaker elements can provide.
I used to have a friend who worked at the agent for JBL in Sweden. This was long time ago and hes gone Im afraid. But he provided me with a calculation for an isobarik box. I have it somewhere. I will see if I can find it so I can scan it and then upload it. It also had the calculated signal curves printed as well. I remember I was impressed by the data. It played 138dB (if I remember correctly) and the volume was tiny. They whent straight down to 20Hz. I thought it was impossible to get that kind of specs considering the volume.

Maybe this is a stupid question but does it really matter if the 2245H is not placed exactly like the original speaker C4642A if you have the correct volume and the diameter and length of the vents? (Vents might be a wrong term, but you understand)

Final question. Is it a big difference between 2245H and 2241HPL?

Look forward to your reply

/Nick
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Old 2nd July 2012, 06:55 AM   #4
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I forgot to write that as I will have the two double speaker boxes with 2235H I could just let the double speaker box with 2245H play below 60Hz as you mentioned.
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Old 2nd July 2012, 09:26 AM   #5
bjorno is offline bjorno  Sweden
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Hi,

For use at home I suggest:

b
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Old 2nd July 2012, 07:07 PM   #6
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Default Bjorno and tip

Thanks Bjorno!

Im afraid the construction is not conveniant for my room although it would be cool to have

Thanks again!
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