ported box design question: is exceeding the Vas of the driver bad?

[BrianGT]

I recently purchased a pair of Raven R2 tweeters, and Cabasse 21m18LB3/8 woofers from another member of the forum (thanks a lot, TimB), and am thinking about making a pair of speakers with them similar to the orca design on zalytron:

crossover:
http://www.zalytron.com/Schematics/990703_a.jpg
cabinet:
http://www.zalytron.com/Schematics/990703_b.jpg

The Vas of the driver is 53L, and the reference cabinet design is 53L. I have done some simulations with MJK's (www.quarter-wave.com) ported box worksheets, and the cabinet doesn't seem optimal. If I double the depth of cabinet, then I get a much better response. I have attached the image below.

Is having a cabinet size double the Vas of the driver bad practice? I noticed that on TL enclosures, this is often the case, if not more then 2x.

One more thing, if I change the box size, and keep the front baffle dimensions and driver placement the same, can I keep the same crossover?

--
Brian

 

[mikee12345]

www.diyaudio.com > bass reflex > EBS

:-D

 

[mikee12345]

Let me correct that link

let me correct that link!

www.diysubwoofers.org ! >ported > EBS

thats better!

 

[BrianGT]

Re: Let me correct that link

www.diysubwoofers.org ! >ported > EBS

Thanks for the link. It looks like I created an ebs cabinet without knowing what it was

Are there any real drawbacks to this design modification? I measured the impedence curves of the drivers in lab today, and I will do the calculations later to see how close the drivers match the published spec.

--
Brian

 

[mikee12345]

it means that possibly u may get a peak at resonance
pershaps some high group delay also at the peak..

www.linearteam.dk
try that


ive never built an EBS

 

[Variac]

I've seen lots of mentions that room gain bumps up the lower part of the curve, so maybe flat isn't what you want. Where does the room gain begin? Pprobably depends on the room and speaker placement.
Here's a link to a thread:


http://www.diyaudio.com/forums/showthread.php?s=&threadid=1261&highlight=room+gain

 

[herm]

Brian,

I am getting a different response than you are.
Here's my plot using WIN ISD (see link in Mikee's post)

Am I using the program wrong?

Green is 52.5 liter, Blue is 105 liter

An externally hosted image should be here but it was not working when we last tested it.

 

[BrianGT]

I have posted my results from the mathcad in html format, and you can view them here:
http://brian.prohosting.com/21m18/

I will go download WinISD and see what I get with it.

--
Brian

 

[BrianGT]

I get a fairly similar result with WinISD... check this out:

It doesn't seem to account for stuffing, or exact dimensions of the box, as the mathcad sheet does.

--
Brian

 

[BrianGT]

Here are the driver parameters that I am using for the Cabasse 21M18LB3/8 driver:

--
Brian

 

[herm]

Here's another graph, from Unibox this time.
I used xmax=6.5 mm per the documentation that I can find.

I don't think that the double volume will really help or hurt
you that much - especially when you look at that max spl line.
I cuts off most of the perceived benefit, except at lower volumes.

However, I do not know how loud 90 dB is, so I may be off.
Looks like I am going to have to buy an SPL meter if I am ever
going to understand all these graphs...

An externally hosted image should be here but it was not working when we last tested it.

 

[OMNIFEX]

BrianGT.

Just keep in mind once you increase the VAS beyond the woofers optimal enclosure requirements, you are at better risk of decreasing your xmax.


If your not running your speakers with low power, fine. However,
if your planning to operate them within its program rating, you'll run out of linear xmax.


Food For Thought.

Best Regards,

 

[mikee12345]

+-3db is just perceptable

110db is *loud*

ears are less efficient at lower freqs like below 50hz

double ur input power get 3db more sound.

if i was designing a sub i wud design it for eg : 110db at 35hz

i need to get a SPL meter also.


90db isnt very loud for bass >perceived as being even quieter..

 

[jleaman]

Cabasse 21m18LB3/

Now i have these Cabasse 21m18LB3 drivers and would like to do something with them. does any one have some ideas what i can do with these drivers ? ported sealed open baffle ? Id hate to have them go to waste.