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Old 6th March 2012, 11:48 PM   #1
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Default A better enclosure for JBL L100T

Hello Fellas,

I want to build new cabinets for my JBL L100T's. The existing enclosure has the volume of:

~ 36.6 X 86.2 X 29.8 = 94016.6 cm^3 =~ 94.0166 litre

I am going to make the cabinets ported in the front.

I am just wondering whether the existing cabinet volume is best for them, and if there is a better result with another enclosure volume.

The port diameter is 4". What is the optimal length for such a port?
I may use flared port.

Any help will be greatly appreciated.

Thanks
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Old 7th March 2012, 12:12 AM   #2
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In general, most of the "bookshelf" type JBLs are a bit small to be vented. Look at the L150, at twice the volume of the bookshelf 12" units, it has huge bass extension. My recommendation would be to go considerably bigger.

David S
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Old 7th March 2012, 12:28 AM   #3
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Quote:
Originally Posted by speaker dave View Post
In general, most of the "bookshelf" type JBLs are a bit small to be vented. Look at the L150, at twice the volume of the bookshelf 12" units, it has huge bass extension. My recommendation would be to go considerably bigger.

David S
JBL L100T is quite different from JBL L100. This is a 35.5" tall speaker.
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Old 7th March 2012, 04:51 AM   #4
GM is offline GM  United States
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Quote:
Originally Posted by raminaudio View Post
I am just wondering whether the existing cabinet volume is best for them, and if there is a better result with another enclosure volume.

The port diameter is 4". What is the optimal length for such a port?
Greets!

'Best' is what works best in-room, so no clue what's 'best' for you. Me, I like to have plenty of net volume [Vb] tuned to Fs in this driver's case as it tends to work well when near/at a wall or corner and allows a reasonable amount of tuning flexibility, so based on published specs, a Vb = Vas [~7.9 ft^3] seems reasonable with ~ 0.694x Vas [~5.49 ft^3] being about as small as I would want to go.

Note that a single 4" vent is a bit small for this driver's power rating and I'm guessing why JBL put it on the rear, so I'd want at least a 5" or dual 4".

The optimal length would be whatever tunes the cab to Fs or whatever performs best overall to you in your room.

GM
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Old 7th March 2012, 09:53 AM   #5
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Quote:
Originally Posted by raminaudio View Post
JBL L100T is quite different from JBL L100. This is a 35.5" tall speaker.
Missed the T!

David
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Old 7th March 2012, 03:21 PM   #6
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Quote:
Originally Posted by GM View Post
Greets!

'Best' is what works best in-room, so no clue what's 'best' for you. Me, I like to have plenty of net volume [Vb] tuned to Fs in this driver's case as it tends to work well when near/at a wall or corner and allows a reasonable amount of tuning flexibility, so based on published specs, a Vb = Vas [~7.9 ft^3] seems reasonable with ~ 0.694x Vas [~5.49 ft^3] being about as small as I would want to go.

Note that a single 4" vent is a bit small for this driver's power rating and I'm guessing why JBL put it on the rear, so I'd want at least a 5" or dual 4".

The optimal length would be whatever tunes the cab to Fs or whatever performs best overall to you in your room.

GM
0.694x Vas [~5.49 ft^3] is 3.81 ft^3. This is almost 4 cubic ft!
The internal volume of the existing cabinet is ~ 3.32 cub. ft, which I think it's already a little bit on the "too large" side ... the bass tends to get a little bit loose and too bassi for my taste. I want a little bit more accurate response in the low end.
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Old 7th March 2012, 03:36 PM   #7
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I haven't seen a frequency response graph of this particular speaker .. but going by the published spec's (35hz @-6db) it looks like the bass response would have a 2db peak just before dropping off quickly. If you'd like a flatter bass response, I think you'd be looking to loose about 1cu.ft. of Vb. (70l with a 39hz tuning).

I'm not an expert though, so take that with a grain of salt.
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Old 9th March 2012, 02:10 PM   #8
sreten is offline sreten  United Kingdom
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Originally Posted by raminaudio View Post
... the bass tends to get a little bit loose and too bassi for my taste.
I want a little bit more accurate response in the low end.
Hi,

Detune the ports to taste. Lining them with porous foam works well.

rgds, sreten.
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Old 10th March 2012, 01:15 AM   #9
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Quote:
Originally Posted by puppet View Post
I haven't seen a frequency response graph of this particular speaker .. but going by the published spec's (35hz @-6db) it looks like the bass response would have a 2db peak just before dropping off quickly. If you'd like a flatter bass response, I think you'd be looking to loose about 1cu.ft. of Vb. (70l with a 39hz tuning).

I'm not an expert though, so take that with a grain of salt.
So, 70 litre internal volume with a 39hz tuning needs a bass port of: 0.102m (diameter) and 0.151m (length). Is that correct?

How about 80 liter cabinet with a 34Hz tuning?
Isn't that a better idea?
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Old 10th March 2012, 01:22 AM   #10
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Originally Posted by sreten View Post
Hi,

Detune the ports to taste. Lining them with porous foam works well.

rgds, sreten.
Could you please explain. Thanks.
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