LE8t port question

[bldozier]

hello all,
just considering a surround cabinet build, the box is 44Liter
i had considered using the Lancer44 combination, but have read i may
also consider a single driver, in a ported configuration. I have JBL 2.75 ports on
hand as we as a 4" can anyone recommend a port length, i get 2.3" w/ the 2.75"
but i have read that a deeper port is need to drive them down to 35hz.
these will probably be used in a 3 way configuration.

thanks.

[Horn Fanatic]

hello all,
just considering a surround cabinet build, the box is 44Liter
i had considered using the Lancer44 combination, but have read i may
also consider a single driver, in a ported configuration. I have JBL 2.75 ports on
hand as we as a 4" can anyone recommend a port length, i get 2.3" w/ the 2.75"
but i have read that a deeper port is need to drive them down to 35hz.
these will probably be used in a 3 way configuration.

thanks.

Greetings -

With an Efficiency Bandwidth Product of 69.32, you may want to consider loading your LE 8T in a sealed enclosure. With a free air resonance of 45 Hz, trying to get it to reproduce 35 Hz may be a bit of a stretch. It's not a good idea to force a speaker into doing something it was not designed to do. Trying to get 35 Hz out of a 1.5 CuFt enclosure with an LE 8T doesn't make much sense.

Just sayin'...

Good luck, H.F.

[bldozier]

thank you for your references, I'm just trying to use the boxes i have already, I'm not currently thinking of making anything
new just what i have.

the 44l cabinet was a left over L88 plus that wanting me to modify it, as i don't have any need for a 12 inch driver in my current system.
as you quoted maybe 34hz is not fully achievable from this size cabinet, but this is not really helping in my search for a port.

if i need to tune its enclosure, its going to be on that side with the le8t, i do own a pair of pr8s which i would like to use but after my research,
on the decided a single speaker would grant better surround fidelity, i will again read into this further.

so with your jedi - like le8t knowledge could you bring me up to date on how to use them in a 44 liter cabinet. i've read sealed, but can you adversely give me a port length, or comment on HOW the pr8 would function,

[bldozier]

thank you for your references, I'm just trying to use the boxes i have already, I'm not currently thinking of making anything
new just what i have.

the 44l cabinet was a left over L88 plus that wanting me to modify it, as i don't have any need for a 12 inch driver in my current system.
as you quoted maybe 34hz is not fully achievable from this size cabinet, but this is not really helping in my search for a port.

if i need to tune its enclosure, its going to be on that side with the le8t, i do own a pair of pr8s which i would like to use but after my research,
on the decided a single speaker would grant better surround fidelity, i will again read into this further.

so with your jedi - like le8t knowledge could you bring me up to date on how to use them in a 44 liter cabinet. i've read sealed, but can you adversely give me a port length, or comment on HOW the pr8 would function,

http://www.audioheritage.org/vbulletin/showthread.php?14161-LE8T-H-PROJECT-HELP

[RMC]

An LE 8T (not H version) has a Qts of 0.49 according to JBL's table of T/S parameters and that is another yellow flag in favour of a sealed box as per Horn Fanatic's comments. Difficult to add more common sense than what he already provided you with...

That being said, a QUICK modeling of LE 8T in Winspeakerz V. 2.5.2 for a 44 liters (net) box tuned at 35 hz indicates:

- driver general sensitivity of about 89 db at 1 w/1 m from about 100 hz and up
- response progressively dropping below 100 hz to 84 db around 34 hz (i.e. - 5 db compared to driver's general level of 89 db)
- for a 2.75" vent diameter, I get a vent length of 6.456 inches.

If you tune the same box at 40 hz instead, then the following happens in the same software:

- Slight level increase in the bass range to almost 90 db
- response again progressively falling but this time from about 60-70 hz and you get 84 db at about 35 hz (i.e. almost -6 db compared to level of almost 90 db in the 70-100 hz or so range)
- for a 2.75" vent diameter, I get a vent length of 4.472 inches.

That means a 40 hz tuning gets you a shorter vent by 2" which may be of help if space is tight inside the box, and performance will still be comparable (i.e. not that much different).

Richard

[bldozier]

thank you sir.

my box is just a bit over 71L, i made a boo boo.
but thanks

[RMC]

A quick modeling of the LE8T with same software but in a 71 liters (2.5 cu. ft.) box isn't bad either. Response is also reasonably flat in the larger box, probably because of the driver's higher than usual Qts number of 0.49 for a vented box.

Some scenarios modeled for that box size are:

Fb 35 hz, F3 33 hz, Dv 2.75", Lv 3.24"
Fb 40 hz, F3 36 hz, Dv 2.75", Lv 2"
Fb 37 hz, F3 35 hz, Dv 2.75", Lv 2.688"

That last one (Fb 37 hz) appears to be the best for a little deeper bass but flat response as well. However, one must not forget this is a driver rated at 25 W (Pe). Don't expect very high output level in the bass range from such a driver. According to Winspeakerz, it will reach X max at 30 Watts at 50 hz (at 104 db or so). And the best you can do at 35 hz is about 101 db since you are limited by the 30 watts at 50 hz. In theory, one could do somewhat better than 101 db at 35 hz because of vent help, but in practice you can't because the driver hits the wall (Xmax) sooner at the 50 hz mark than at 35 hz. Naturally, using a steep high pass filter from 35 hz and below will help such a driver survive longer...

Richard