A better enclosure for JBL L100T

[raminaudio]

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

 

[speaker dave]

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

 

[raminaudio]

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.

 

[GM]

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

 

[speaker dave]

JBL L100T is quite different from JBL L100. This is a 35.5" tall speaker.

Missed the T!

David

 

[raminaudio]

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.

 

[puppet]

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.

 

[sreten]

... 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.

 

[raminaudio]

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?

 

[raminaudio]

Hi,

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

rgds, sreten.

Could you please explain. Thanks.

 

[puppet]

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?

What's better is what fits your needs. What are you looking for in bass response?

 

[GM]

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.

Not according to the driver's published specs, which way too often calculates a too small 'ideal' cab to begin with. Just from eyeballing some pictures and reading its marketing blurb, it appears to be tuned fairly high, a typical Altec, JBL alignment that earned them the 'west coast sound' moniker way back when, which would cause it to be a bit 'loose'/'bassy'. As sreten noted, it can be smoothed out by 'critically' damping the vent or you can tune it lower with a longer vent.

If you want more 'tight' bass extension though, you'll need the larger cab tuned down to around/at Fs.

GM

 

[sreten]

As sreten noted, it can be smoothed out by 'critically' damping
the vent or you can tune it lower with a longer vent.
GM

Hi,

That is not what I meant. Lining the port with foam tunes it
lower, it doesn't "critically" damp the port. The bass will be
"tighter" without needing a larger cabinet. There will be less
of it but the speakers will also go somewhat deeper.

rgds, sreten.

 

[GM]

Greets!

OK, one critically damps the vent by resistively loading it, which is what lining it with foam will do, i.e. lowers tuning, increasing system damping and any 'ringing' at Fb, so how did I misunderstand you?

GM

 

[raminaudio]

What are you looking for in bass response?

I want absolutely no "BOOM" and lots of punch and solid bass.

 

[raminaudio]

OK. The internal volume of the existing enclosure of the L100T is ~ 94 Liter. The port is 4" in diameter and a little more than 11 cm in length. So, if I am right (and please correct me if I am wrong), the tuning frequency of the enclosure must be: ~ 37 Hz.

Also, these a the parameters of the JBL 2214H woofer:

2214H tech sheet?

(These can be found in JBLPro website too.)

Using WinISD software, here is the Gain plot of 2214H driver in L100T cabinet:

According to this plot, there is a bump around 45.9 Hz. I think this is why the bass gets too "bassi" and sounds a little bit loose with some types of musics.

So, if I am right (and again, please correct me if I am wrong), if somehow I manage to flatten this peak, I have improved the sound.

With 80 liter internal volume, and a 34 Hz tuning, I get this plot:

This is much flatter to me, and it is still 36-37 Hz inside 3db. That's why I suggested this volume and tuning frequency. I think I need a port of 4" in diameter and 18.6 cm long.

I have only considered and compared Gain plots. I don't have the enough knowledge to considered other factors now... I think need some help to get it really right!

Thanks

 

[raminaudio]

I forgot to add that the cabinet dimensions of L100T3 (the later and improved version) are:
35 3/8" (tall) x 14 1/2" (wide) x 13" (deep)

I assume the wood thickness is 0.75".

So, the internal volume of this model is: 2.93 (cubic feet) ~= 82.97 (liter)

 

[puppet]

At this stage a guy could simply subtract volume and experiment with that in room. ... bricks, tennis balls, plastic milk/pop jugs, etc.