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View Full Version : should i chamber these?



PV Audio
10-30-2005, 01:06 AM
going to be designing some fronts for my father, and i am curious as to whether or not i should chamber a pair of these:

http://www.partsexpress.com/pe/showdetl.cfm?&DID=7&Partnumber=295-364

only reason i'm asking is i knwo a few people on here have used these and i'm sure they could give me informed insight. so should i have them in separate enclosures, or all in one? thanks.


-dave

PV Audio
10-30-2005, 02:32 AM
hello?

swc204
10-30-2005, 12:51 PM
:wave:

PV Audio
10-30-2005, 01:02 PM
yeah thanks lol, anyone with an answer?

PV Audio
10-30-2005, 02:14 PM
nobdy knows.......

adio
10-30-2005, 05:33 PM
chamber them

PV Audio
10-30-2005, 05:54 PM
why

thylantyr
10-30-2005, 08:50 PM
Make a ported test box.... then listen.

Plug the hole, now it's a sealed box.... then listen.

Which one do you like?

adio
10-30-2005, 08:53 PM
why
because they're small

PV Audio
10-30-2005, 09:06 PM
Make a ported test box.... then listen.

Plug the hole, now it's a sealed box.... then listen.

Which one do you like?
no no, i meant should i make seperate enclosures for both of them within the cabinet (so as to minimize canceling).

thylantyr
10-30-2005, 09:42 PM
If you do it right you can make non chambered and chambered work.
I can see pros/cons for both designs.

PV Audio
10-30-2005, 09:44 PM
care to give me insight?

thylantyr
10-30-2005, 10:26 PM
Sealed box: [Midrange sound] - sounds better in a over sized box with polyfill
or whatever recipe to let the sound inside diffuse through thick layers before it
hits the hard surface of the wall where it will reflect again.

If you chamber it you reduce the box size for each driver so the standing waves
will have to be diffused better. Usually it's better to make a deep box so the backwave gets to travel farther through these thick layers before hitting the
backwall which likes to reflect back. You can make both work just think about how
the sound is being diffused and if it's sufficient enough for your liking.

Do the echo test. Make the box, cut the driver holes, with empty box yell inside..
you will hear echo/reverb/etc. Add polyfill until you are satisfied that it's 'dead'
when you holler in a burst. No need for fancy test equipment, yell and listen.

Ported box: [Midrange sound] - same thing as above but it's not sweet to place
alot of loose polyfill as you affect port tuning. If you can only lightly stuff the box
then it's harder to diffuse that midrange sound. You need denser polyfill perhaps
attached to the walls leaving the inside chamber open for the port to breath
better. Ideally, double/triple the backwall polyfill as long is it doesn't block the
port.

Sometimes if you do chambers design you can model the woofers to see what
port size requirements are, maybe the scenario favors non chambered due to
port requirements or maybe you can do it in a chambered design too.
Run the numbers for both to see what you like. Chambered design is good for bracing as it is a brace too.

If you tune higher in a ported box, try to model for a large diameter hole with
very little port length, the standing waves exit the hole so there is less
reflections.

You can also try AcoustaStuf polyfill from PE. More expensive than ordinary
Walmarkt polyfill but the material is more dense, good for higher priced projects
where you want the best. You can make some excellent sound absorbing pillows
with this mated to ordinary poly battling, roll your own pillow and use 3M glue
to attach to the walls of ported boxes. For sealed box, no pillows needed.

You can go deeper into esoteric sound conditioning inside the box. For homes,
they sell this 'popcorn' type stuff that sprays on walls to make it course [chunky
foam type particles]. You can spray this stuff to the inside walls so the surface isn't flat to force these waves to take random paths on reflection. Add the poly
to the walls, thick.

This is all esoteric ideas, most people probably wouldn't notice but if someone
paid you top dollar to make a project do these things to justify the extra labor
costs so the customer feels special.

I think everything you do add up to make the box not sound like a box
for midrange frequencies. Lower cabinet resonance by using thicker walls &
bracing, condition the standing waves using those esoteric ideas using popcorn,
AcoustaStuf [or wool], fiberglass if sealed, not ported, pillows on walls if ported,
otherwise loose polyfill if sealed... etc.

People that make subwoofer boxes don't have to deal with these issues
except making a good stiff box with lots of bracing. But for midrange it's a new
ball game to make the midrange sound more clear and less boxy in sound.
Lots of people like open back design because they elimiated the standing wave
issue that you have to deal with with box designs. The idea is to make your box
design sound more like open back, when you do, then pat yourself on the back.

thylantyr
10-30-2005, 10:37 PM
DAYTON RS180S-8 7" REFERENCE SERIES SHIELDED WOOFER

The big complaint with the Dayton RS drivers, 6" and up, is the nasty cone break up
modes due to the metal cone. Some folks won't even tough these drivers unless you
use a low crossover point with a steep crossover slope.

Read about Jon's modula designs here;
http://www.htguide.com/forum/forumdisplay.php4?f=6

He did all the engineer work to make those midwoofers perform well with quality
tweeters. I believe he uses a CE type filter that mimicks 8th order slope to get the
best sound of these.

When I was recommending a Dayton RS 6" array mated to PT2 tweeters, nobody else
would even consider this combination because the crossover point would be closer to
2.5khz and many folks think the 6" Dayton needs a lower crossover point to get rid of
the nasty sound and/or a steeper slope than 4th order. The reason my suggestion to
use those two will work is because the PT2 could be crossoved over lower using LR 8th
order at 1.7khz.

When you think about loudspeaker design always think about the tweeter first and
what it can do well at whatever crossover/slope combination before finding a mate for it.
So.. if you have a killer dome tweeter you like but it needs a 4th order 2khz crossover
then you need to find a midwoofer that is friendy in this region. Some people won't
even touch a Seas Excel 8" or Dayton RS 7", maybe 6" with this requirement.

I'm not trying to dissuade you, but think about the crossover design too. If you want to
feel elite, invest in a Behringer DCX2496 for development work. You''ll be amazed at
how much elite you will be in loudspeaker design knowledge, the information learned
with this is worth the $250 shipped price tag.

You do your driver development with it to determine what is the best combination of
crossover points and slopes then try to take those numbers and make a passive crossover
Or use the DCX in your final system.

If you don't migrate to this methodology you will be playing the guessing game for
the rest of your life, asking people questions instead of being the one with the answers.

All you need is 2 amp channels and one DCX for development. /easy