Determining Drivers for a Sealed Box?

[squidbait]

For my first project, I am looking to do a mid-cost HT system for a secondary TV room in house. To keep it as simple as possible I will start with 2-way front speakers in a sealed box.

My question is, how do I determine which speakers are best in a sealed box, vs. a ported box. Or will all speakers work well both ways? In the Loudspeaker cookbook, when talking about LF woofers, he mentions fs/qes should be around 50 for a sealed box, and 100 for a ported box. He also says it should have a larger x-max. When looking at 5 - 6.5 inch speakers, most are around 100.

Any help would be apreciated.

[rabbitz]

Well done in researching the LDCookbook. Nice to see someone doing their homework.

I'm no expert on closed boxes but you should look for a driver with a low Fs, EBP around 50 (up to 80?), Qts >0.3 and a long Xmax. Also look at the manufacturer's data sheets as this can often tell you if it's suitable.

The Peerless 6 1/2" CSX (850122) works in a closed box of 10-15 litres (EBP=67 to 83 depending on whose info you look at) and is recommended by Peerless for vented or closed.

Hope this helps.

[squidbait]

Thanks for the info. Looks like I am on the right path.

[mikee12345]

go to www.adireaudio.com

see the SHIVA and TEMPEST
they are good sealed box subs...they can work in low tuned ported also..but are used alot in sealed box

Value for money woofers.


Low fs
Mid Q
xmax=~15mm

higher Q can work too-but less damping,larger box required.
I like my low Q high damping woofers

also winisd pro from www.linearteam.dk will show response
Cheers!

[Pjotr]

Hi,

One of my objections to Dickason is that you already need to understand what is it all about to understand the book.

You can put almost any speaker in a closed box. If it is your first project then start with a simple 2 way. Then a 17 cm mid-low speaker is the best way to go IMHO. You don’t get that low but you get most times good results.

The formulas are simple. What you need is VAS, Qt and Fs of the speaker unit. Then with the volume of the box (in liters) you can calculate the Q of the box, Qb and the new resonance frequency of the speaker+box, Fb:

Qb = Qt*SQRT((Vas/Vol_Box)+1)

A Qb between 0.6 and 0.71 gives a reasonable good alignment.

Fb then becomes: Fb = Fs*Qb/Qt

It is obvious from the above formulas that with a low Qt you can do with a smaller box but that Fb rises a lot above Fs. With a higher Qt you need a bigger box but you can get lower in frequency. With most 17 cm speakers box size doesn’t become a problem. Try several speakers and see which one suits your needs most.

You can simulate a lot of speakers but to make an optimum selection I found it useful to put the above formulas in Excel for all the speakers of interest for comparison.

Cheers

[squidbait]

I agree with you fully. I was expecting more backround when I purchased the book, but it's very technical. I have read the same things over and over and still don't understand. That's why I am here!

Thanks for the response.

[Doug Kim]

After some experimenst, I found a sealed box, placed against the front wall, and listening in near-field position works best for me. They sound just like a car-stereo, which I really like.

So I'm thinking of building a wide-baffle shallow-depth square sealed box using a pair of 5-6.5" drivers.

Before I figure out myself according to other's tips, are there any driver especially known as good for 15 (or so) litre sealed box?

Thanks

Doug

[sreten]

http://www.zaphaudio.com/BAMTM.html

Hi,

You could build the sealed version of the above.

Though if a sub is not being used the
floorstanding vented is a good option.

As stated in the original post not many drivers are optimised for
sealed use nowadays, The BAMTM covers excursion issues to a
degree by having two bass drivers.

/sreten.

[Doug Kim]

Thanks for the reply as always, Sreten.

I was looking up all the driver parameters and I came up with this guy which has not been mentioned too often.
What do you think this one for sealed application?

Tang Band 6.5 inch driver

Doug

[sreten]

Hi,

The TB is an interesting driver but no-one has measured it yet.
It will work in 15L sealed but no bass, unless Eq'd.
~ 30L tuned to ~ 30Hz has a lot more bass.

/sreten.