midrange enclosure

[jessegabriel]

Dear Sirs,
I recently purchased your Davis 100CKW8DF 4" Kevlar/Carbon midbass speakers. (Parts express-297-560). I am going to be using these as the midrange speaker in a 3-way cabinet (tweeter, midrange, woofer. I requested enclosure information from parts express, however, what they sent me was a bass box pro enclosure which included a port!!! First, let me say that this puzzles me, because as far as I can conjecture, they have mistaken the application of the speaker. (Why would a midrange need a port?) Can you tell me if a ported enclosure is appropriate for your speaker in my application?? Second, even if I was using them in a woofer application, I prefer sealed enclosures. Third, I don't think that I really want to spend the time building a box inside a box, with a port!

So, what I have in mind is to use a 6" pvc pipe as a means to enclose the speaker. (The next smaller pipe that is available to me is a 4", which I think will be too difficult to work with, considering the magnet is about 3 1/4 in diameter, and the mounting holes of the speaker are 4 1/2"). Here is where you come in.
1. Do you see any problem with using a 6' pvc

pipe to enclose the speaker?
2. If you don't see a problem with that, can you

give me an optimum length of the "cylinder"?

(Please consider that the speaker will be

mounted on 3/4' particleboard, and recessed

1/8 to 1/4" so the front of the speaker will

be flush to the face of the cabinet).
3. If you can suggest an optimum length, can you

tell me if this determination is based on

an "optimum" enclosure (sealed) volume? (In

other words, what criteria did you use
4. If there is an optimum sealed volume, what is

it? (I may try to find 5" pipe, if possible,

or feasible).

Other factors: Since the back of the magnet is 2 7/8 behind the front plate of the speaker, this means that shortest the pipe can be is 2 1/8. The inside diameter of the 6" pipe is 6". (O.D. 6 5/8)

I also intend to spray the inside of the pipe with rubberized car undercoating, to "absorb" and dampen the sound waves. What is your take on this, and, would I need to or want to add any other damping material? Other than what I have mentioned, do you have any other recommendations? Thank you, and I want to say I am very impressed with your speakers!

Sincerely, Jesse

[billfitzmaurice]

You can model the driver in WinISD just like any other driver. Make the rear chamber volume as small as is possible without upsetting response within the passband, stuff the chamber with poly batting or foam, anything beyond that won't hurt but also probably won't help.
As to why you were suggested a VB, even a four may work best in a VB if the intent is to use it to the lowest frequency possible.

[Dirk]

Provided Link: Keith Kidder's 411 (look at the midrange)


First off, welcome to the board. While this message board is owned by Parts Express, 99% of the posts and information will come from your fellow speaker building enthusiasts. Very few PE employees post, but they're always watching & ready to help when they can.

That said, you've chosen an interesting driver for your midrange (interesting in a good way). I can see why they'd want you to port it. In some respects, it could be used as a woofer in its own right. The Fs is very low for a true mid, and as such, Davis probably designed it to be used with very low crossover points. Well, in order to make something crossable that low, it's often a good idea to make sure that the requency response stays fairly flat; hence, the porting.

However, nothing says you couldn't use it in a sealed box. I like your idea of using the 6" pipe. Even more, I'd consider extending the tube right out the back of the speaker and then stuffing the willies out of the pipe. The woofer will be operating effectively free-air, and the stuffing will dampen the "transmission line" effects.
This will remove the majority of the box colorations from your mids. Now, without any sort of rear reinforcement, you'll want to cross it a little higher. Still, it'd be excellent for something like a 2nd order 300hz XO point. Just model it up in WinISD like Bill mentioned (or Unibox, if you prefer to use Excel) and model it in a HUGE box (something like 1000L). This will give a very close approximation of how the driver will respond "free air".

[ericanderson]

> Dear Sirs,
> I recently purchased your Davis 100CKW8DF
> 4" Kevlar/Carbon midbass speakers.
> (Parts express-297-560). I am going to be
> using these as the midrange speaker in a
> 3-way cabinet (tweeter, midrange, woofer. I
> requested enclosure information from parts
> express, however, what they sent me was a
> bass box pro enclosure which included a
> port!!! First, let me say that this puzzles
> me, because as far as I can conjecture, they
> have mistaken the application of the
> speaker. (Why would a midrange need a port?)
> Can you tell me if a ported enclosure is
> appropriate for your speaker in my
> application?? Second, even if I was using
> them in a woofer application, I prefer
> sealed enclosures. Third, I don't think that
> I really want to spend the time building a
> box inside a box, with a port!

> So, what I have in mind is to use a 6"
> pvc pipe as a means to enclose the speaker.
> (The next smaller pipe that is available to
> me is a 4", which I think will be too
> difficult to work with, considering the
> magnet is about 3 1/4 in diameter, and the
> mounting holes of the speaker are 4
> 1/2"). Here is where you come in.
> 1. Do you see any problem with using a 6'
> pvc

> pipe to enclose the speaker?
> 2. If you don't see a problem with that, can
> you

> give me an optimum length of the
> "cylinder"?

> (Please consider that the speaker will be

> mounted on 3/4' particleboard, and recessed

> 1/8 to 1/4" so the front of the speaker
> will

> be flush to the face of the cabinet).
> 3. If you can suggest an optimum length, can
> you

> tell me if this determination is based on

> an "optimum" enclosure (sealed)
> volume? (In

> other words, what criteria did you use
> 4. If there is an optimum sealed volume,
> what is

> it? (I may try to find 5" pipe, if
> possible,

> or feasible).

> Other factors: Since the back of the magnet
> is 2 7/8 behind the front plate of the
> speaker, this means that shortest the pipe
> can be is 2 1/8. The inside diameter of the
> 6" pipe is 6". (O.D. 6 5/8)

> I also intend to spray the inside of the
> pipe with rubberized car undercoating, to
> "absorb" and dampen the sound
> waves. What is your take on this, and, would
> I need to or want to add any other damping
> material? Other than what I have mentioned,
> do you have any other recommendations? Thank
> you, and I want to say I am very impressed
> with your speakers!

> Sincerely, Jesse

according to winisd beta the enclosure should be 115.9ci if you are using 6" pvc it would be approx 12.5" long adding some for driver displacement by the way winisd wanted to use a vented enclosure
eric

[Dirk]

> according to winisd beta the enclosure
> should be 115.9ci if you are using 6"
> pvc it would be approx 12.5" long
> adding some for driver displacement by the
> way winisd wanted to use a vented enclosure
> eric

That's based on the driver's EBP, which is just Fs/Qes. High EBP ( 50 > ) and it'll always suggest ported.

[billfitzmaurice]

> That's based on the driver's EBP, which is
> just Fs/Qes. High EBP ( 50 > ) and it'll
> always suggest ported.

It will also always suggest the best alignment for the flattest possible response to the lowest possible f3. Using it as a mid driver you must manually alter the box parameters as required to get the flattest possible response to the intended f3.

[Dirk]

> It will also always suggest the best
> alignment for the flattest possible response
> to the lowest possible f3. Using it as a mid
> driver you must manually alter the box
> parameters as required to get the flattest
> possible response to the intended f3.

Not entirely true. If I model a Dayton Quatro 15, it suggests sealed, but it can certainly work in a ported box (if you have 6 cubic feet of space you don't mind using).

[billfitzmaurice]

> Not entirely true. If I model a Dayton
> Quatro 15, it suggests sealed, but it can
> certainly work in a ported box (if you have
> 6 cubic feet of space you don't mind using).

The default is to what it calculates is the best alignment for that driver's specs. You can always override. The Alpha Pro version also offers the choice of various VB alignments for easy comparisons.

[Dirk]

> The default is to what it calculates is the
> best alignment for that driver's specs. You
> can always override. The Alpha Pro version
> also offers the choice of various VB
> alignments for easy comparisons.

After selecting the driver & number of them, it presents the sealed / ported dialog. This is based off the EBP. THEN it presents the screen you're talking about. My whole point was that just because the EBP suggests ported use, with a midrange, low frequency performance is (often) less important than crossover integration. There's no need to be flat to 60hz if we're crossing up in the "normal" low/mid XO region of, say, 300-600hz. We're way above Fs, so we don't need the power handling provided by porting.

I understand prosound having a completely different take on the matter. Being ported & crossing low is cool. But they also have the luxury of active XOs, which we can't assume here.