Long wire from XO: midbass OR tweeter?

[ro9397]

IIRC this issue affects audible performance.

An estimated 30" long wire must connect the PXO output to the midbass OR the tweeter. (The opposite driver will run 16" wire.)

XO: 2.2 kHz
HP: 1st order
Drivers: 8-Ohm Dynaudio
HP: 1st order w/ resonance control
Active HP XO: High quality 80 Hz (active subs)

30" wire to MB/16" wire to tweeter...or vice versa?

If time allows, why?

TIA!

[infinia]

The tweeter is to have the longer run since it is resistively padded down anyhow, right. I would just split the crossover in half if you are really worried about something like this? Your question really doesnt compute in any app I can think of. ie the midbass and tweeter should be closer than 1/2*30". Philosophy student... hmm.=, we have a potential thread starter like "I don't believe cables make a difference".

[ro9397]

Thank you. You are correct: tweeter pad is 3.3 Ohm series followed by 15 Ohm parallel.

I had an intuition this may lead to a question about the application. I'll be surprised if this is not one of the strangest speaker designs crossing your path: a dual box bipole that can be converted to a single box monopole use. The upper box houses the two front-firing drivers (one MB/one tweeter) & the rear firing tweeter. The lower box houses only the rear-firing midbass.

Each box is about 1/2cf internal, separated by a stand about 15" tall.

Two smaller boxes rather than one larger box were chosen for several reasons: the upper box can be detached to employ separately as a single monopole monitor. The professional hired to assist w/ the design specified a particular relationship of width to depth for the lower box, providing a low-enough fs before the rear wave folds back to the front. (Remember the system is actively HP Xd around 80 Hz.) If one large box was employed the upper box could not be detached for monopole monitor use. Also, the entire single box would be either too wide for good image/stage performance or too narrow for the rear-midbass.

Now, on to the impedance load issue. Two drivers wired as a simple monopole are 8 Ohm nominal/5.3 Ohm minimum. As a bipole, w/ twice the number of drivers, the minimum load must be either 10.6 Ohm (drivers in series) or 2.65 Ohm (drivers in parallel).

The amp currently employed will likely favor a 10.6 Ohm series load. But the ability to separate the upper box (in this case the rear-firing tweeter will be disconnected & not employed except to seal the hole in which it resides) requires two separate isolated XOs (one each for the front & rear firing drivers). Also, separate XOs allow a 16 or 4 Ohm nominal load w/ choosing either series or parallel input wiring, thus accomodating a wider range of amps.

The advice to run a longer tweeter wire is welcome because it is consistent w/ my plan to install two identical 8 Ohm PXOs, one each in the upper/forward firing box & another in the lower/rear-firing box. The long tweeter wire will directly exit the lower box's terminal board (no binding posts because the lower box is never employed alone) then couple to separate/dedicated binding posts in the upper terminal board & on to the upper/rear firing tweeter.

Are you as confused as I am?

[infinia]

Hi
Sounds like a very special speaker indeed. What dynaudio drivers are you using?

[ro9397]

Good ole 17WLQ & D-260.

The separate upper box looks great w/ classic proportions. But as a bipole you can imagine it looks a bit strange: the boxes are identical in size but the upper box is narrow across the width (image/stage performance) while the lower box is turned to be shorter in height & wider L to R (prevents fold-around).

A 1/4" thick 8+ lb steel ballast screws to the bottom of the upper box for 37 lbs total mass (ballast has 3 spikes contacting the stand separating the two boxes). The system is stabilized by a large pedastal base w/ 3 spikes contacting the floor.

As if the speaker was not weired enough: System is three-channel across the front, pure analog Trinuaral by James Bongiorno, 2.0 in, 3.1 out.

Four subs employed per Duke LeJeune/Earl Geddes multi-sub approach. Counting each front bipole speaker (2 boxes each) as one speaker (3 total) + 4 subs = 7 speakers total.

The speakers might best be described as a poor man's German MBL Rhadialstrahler. The Trinaural is probably best described as a pure analog version of Meridian's classic Trinaural DSP (in both cases the center is NOT summed mono but rather processed & the result of algebraic formula; the L/R are effects/ambience channels).

[infinia]

Nice
we love to see images.
how do you do the LF sub/s and active xover?

[ro9397]

I'll scan the drawing & take a picture of the sum total one prototype upper enclosure already built.

In an earlier thread I was surprised there was little feedback specifically addressing the chosen panel material, 5/8" real slow-growth batlic birch ply bonded over 5/8" original particle board. About 18 mos ago Stereophile described this new composite from a GB speaker company; also mentioned were theoretical advantages & postitive listening tests. I was sold; I realize builders have their favorite panel materials.

Within a few days the above panel material will be compared to solid 1-1/4" thick ovangol (prohibitively costly) employed in my favorite standmount production speaker being cloned.

Advice is sought for constructing the stand separating the upper/lower boxes.