Selection of enclosure loss value (Ql)

[OdieM]

Hi

I am currently designing a set of two way bass reflex speakers. My design is based on the Thiele-Small method. To design the enclosure one must choose a value for the enclosure loss, named Ql.

One of my sources states that one should start with a value of Ql = 7, if the required volume is in the range of 2-3 cubic feet 7 is fine. If you arived at a smaller enclosure you should select a higher value and redo the calculations.

Taking Ql = 7 I arived at a volume of 35 litres. The next graph that is availeble is Ql = 10. If you however use the functions provided in Small's paper you can use any value in between.

Is there a more accurate way to choose a value for Q? Would using Ql = 10 in stead of Ql = 9 have severe implications on the design?

Thanks
Odie Malan

[David_Web]

Download Basta! and see for yourself. You can model both box and port losses amongst other things.
Basta

[OdieM]

Thanks

Downloading now, will work on it over the weekend.

Cheers
Odie

[David_Web]

I checked and you can model Q of box and Q of vent.
Not sure how the values relates to losses in numbers. The effect should be the same I think.
But if you want to model response and experiment then Basta! is one of the best IMHO.
Cone excursion is in RMS and not peak though, not sure if it is mentioned anywhere but good to know.

[richie00boy]

You don't know Ql until you build the box. My advice is build it and check Fb and Ql. If they are more than 20% off what you designed for then first listen and see what you think before amending the design. If less than 20% then don't worry about it. You can get all hung up on the numbers and simulations when in reality the differences aren't that massive to the ear.