[Arctos]

Greetings,
Can anyone tell me in laymans terms what the relationship is between speaker cabinet volume and damping material?  If you calculate the proper volume for an enclosure, does adding damping material make the enclosure seem smaller or larger to the driver?  I know this is a newbie question, but I am a newbie, after all  .

Also, what is the relationship between port volume/length and enclosure volume?

Last question: is there an easier way to calculate enclosure volume than using unibox?  The reason I ask is that I find this program to be a little too technical for me, and I cannot figure how to enter the proper statistics for a driver that is not already listed in the driver choices (I'm trying to calculate for a Tangband W3-871).

Regards,

RDS

[JohnR]

If you calculate the proper volume for an enclosure, does adding damping material make the enclosure seem smaller or larger to the driver?

For a sealed box, it makes it seem larger. For a ported box, adding damping seems to have the effect of reducing the Q and making the bass response slope down a bit earlier. *In general* it's recommended not to heavily stuff a ported box.

Last question: is there an easier way to calculate enclosure volume than using unibox?  The reason I ask is that I find this program to be a little too technical for me, and I cannot figure how to enter the proper statistics for a driver that is not already listed in the driver choices (I'm trying to calculate for a Tangband W3-871).

It's not hard, you just need to enter the parameters near the top left of the spreadsheet. Specifically, Fs, Qms, Qes, Sd, and Vas. The others are good to enter if you have them but won't affect what you are trying to do right now. Give it a go and then come back with more questions

JohnR

PS I suggest downloading version 3 of Unibox, it's faster and easier to use than version 4 and you won't need the features of version 4.

[Arctos]

JohnR,
Thanks for the info!!  I have been playing with Unibox 4.02 and 3.01 today and tonight with some interesting results.  I tested them against each other and found the results to be very close but not exactly the same.  I thought this was a pretty good sign.

Now here is my issue:  If I use the "standard design" values, they tell me that the optimal volume for a ported box for my little 3" tangband driver is 7.8 liters and the F3 point is 58hz!!  I find this hard to believe.  I then checked out the "design by Vb, Fb and Q" section, and was confused, as I thought that for each driver there was an optimal volume, and this software is supposed to be used to calculate it, among other statistics.  I did play with it and entered a more reasonable sounding volume of 4.5 liters for this driver and the F3 point came back sounding reasonable at about 70hz.  I spent alot of time double checking my inputs and believe them to be correct for this driver.

The port lengths for both calculations came back sounding reasonable; somewhere in the neighborhood (for a 1" diameter port, or 2.54cm) of .75 to 1 inch long.

Any insight?

Thanks,

RDS

[JohnR]

These drivers have a fairly high Qts which makes them a bit tricky to get sensible results from them. Drivers designed for ported boxes (larger ones) have a Qts around 0.3 or so, typically. I must be using different parameters than you because I get different numbers, but the basic results are not far off. If you look at the curve with the "ideal" box and tuning you'll see a peak around 70 Hz, which is because of the high Q of the driver.

When I used the W3-881s, I reduced the box size and set the tuning low. Also, set the damping to "heavily stuffed." This resulted in making a small driver sound like there was some reasonable weight at the bottom, without it being boomy. IMHO, YMMV etc. For example, try Vb=5L, Fb=60.

Then, when you build it, put a 0.68mH coil in parallel with a 0.47 ohm resistor, and put these in series with the driver.

JohnR

[Arctos]

Thanks John,
I would like to back up a bit, as my knowledge of speaker design theory is lacking.  It sounds as if the cabinet volume is not as critical as I once thought when designing a speaker.  Is this true?  If so, what should I look for when trying to decide on a volume for a particular driver?

You mention a peak at 70hz; what does this mean?  Also, is 70hz a bad place for a peak, and what is a better frequency for this peak?

Also, what would be the purpose of adding the coil and resistor to the circuit?  I originally thought that with a single full range driver there would be no crossover-type components.

My original plan was to come up with something that has similar frequency range and characteristics as the nOrh 3.0.

I must apologize, as I really am a novice when it comes to this stuff, but I am having a blast learning and building these things!!

Thanks for your patience and help,

RDS

[Arctos]

John,
As further info, here are the figures I am using:

Fs - 125Hz
Re - 6.6 Ohms
Qms - 6.24
Qes - 0.76
Sd - 45.07 cm2
Vas - 1.35
Xmax - 5mm
Le - 0.313
Nominal Power - 15 watts

I am using 1 port that is 1 inch inside diameter.  I don't really understand what is meant by "port end correction", but when I played with it the effect was on the suggested port length.

Regards,

RDS

[JohnR]

It sounds as if the cabinet volume is not as critical as I once thought when designing a speaker.  Is this true?

It depends on what are want to achieve. There's not any single "right" answer... With my Jordans, I made the box a little smaller than required for a flat response, and tuned a little low to get a smooth rolloff. I was trying to follow the type of tuning recommended by Adire:

http://www.adireaudio.com/tech_papers/enclosure.htm

One of these days I'd also like to try an EBS (extended bass shelf) tuning. This is used to give deeper bass at the expense of power handling. Some info here:

http://www.diysubwoofers.org/prt/ported5.htm

You mention a peak at 70hz; what does this mean?  Also, is 70hz a bad place for a peak, and what is a better frequency for this peak?

If you look at the graph you'll see it. I personally don't really like the idea of peaky bass response but some speakers are designed that way on purpose to make it sound like they have more bass.

Also, what would be the purpose of adding the coil and resistor to the circuit? I originally thought that with a single full range driver there would be no crossover-type components.

Heh, I guess it depends who you ask . That is baffle step compensation, more info here:

http://www.t-linespeakers.org/tech/bafflestep/index.html

Audibly the effect is to make the speaker sound less "thin". If you get hold of some cheap coils and resistors and some clipleads from RadioShack then you can experiment. So far I've preferred to have it than not.

HTH

JohnR