Time To Try Open Baffle

[Mutley666]

I've been following the many threads on the forum, and have read the massive site the is www.linkwitzlab.com , and I decided that its about time I try this open baffle thingy for myself.

So not wanting to waste vast sums of money, and being the kind of person I am, not wanting to copy someone elses design, I searched for the cheapest drivers around, to have a play with.

I've collected a couple of 15" woofers, a couple of 6.5" mids and a cheap silk dome tweeter, with the intention of throwing 1 speaker together, to see what I can realistically achieve.

The drivers so far have come to a total of £70.00 ($126 US), and they arrived this week.

I've created a 420mm baffle with 160mm wings at 90°, and will have the 2 15" woofers at the bottom and the 2 6.5" mid/woofers in an MTM arrangement at the top. I'm going to aim for cross over points of 200Hz and 2500Hz.

Progess so far? Just about got the baffle together and the woofer in.

[gvinson]

I'm interested in dipole bass as well. Please let the forum know if you get viable results or take measurements.

Good Luck.

Ribbon Project

[Mutley666]

I'm just waiting for my mic preamp and parts for the Wallin Jig, once they arrive I'll get some measurements done.

Should be interesting to find out what can be achieved with these cheap drivers!

[sreten]

Originally posted by Mutley666
I
I've created a 420mm baffle with 160mm wings at 90°, and will have the 2 15" woofers at the bottom and the 2 6.5" mid/woofers in an MTM arrangement at the top. I'm going to aim for cross over points of 200Hz and 2500Hz.

Progess so far? Just about got the baffle together and the woofer in.

Hi,

just an observation :

given the 6dB roll-off of open baffles sensitivity is a moot issue.

Its more likely you would get good results with one 6.5" driver.
(Space it unequally from the 3 edges to smooth diffraction effects)

You could then crossover to the top 15" near baffle transition.

Hopefully the (presumably) higher sensistivity 15" would then
compensate for the initial baffle roll-off.

You could then bring in the other 15" lowerdown, this would
compensate one octave (6dB) of roll-off.

Presumably below some point you'll need 6dB/octave active boost.

/sreten.

[Mutley666]

Sreten, so your suggesting a 2.5 way approach using two 15" woofers, one 6.5" mid/bass and a tweeter?

An interesting idea, and I feel there may be some potential.

As this is really just an experiment at this stage, I'll surely give it a try!

[sreten]

Hi,

I'm suggesting more than a 2.5 way, a 3.5 way.

The 0.5 way on the 2 bass units will compensate for one octave of baffle loss.

If one bass unit is more sensitive than the mid unit, then if the
bass/mid c/o point is a shallow 1st order around the point that
baffle loss begins then the sensitivity diffrence could compensate
for some initial baffle loss.

Note that without measurements this is partly conjecture.

A driver in the centre of a baffle can exhibit strong diffraction ripples.

It may be better to allow a carefully placed mid unit to go somewhat
lower with some active boost, and bring in the bass units lower when
there is already significant baffle loss but below the frequency the
bass units exhibit significant ripples.

In this case you might need a two stage bass boost arrangement.

/sreten.

[Mutley666]

Once I get my measurement equipment together , I'll run some frequency response tests and see what is what, but I think you maybe on to something there!

[Rudolf]

Originally posted by sreten
... there is already significant baffle loss but below the frequency the bass units exhibit significant ripples. ...

sreten,

my OBs are developing along similar lines as Mutleys: two 15"woofers, conus mid and horn tweeter. But I don´t see where the bass units could exhibit significant ripples if they are x-overed below 500 Hz. Could you explain? Is it edge diffraction? Floor reflection? Anything else?

Rudolf

[sreten]

Originally posted by Rudolf


sreten,

my OBs are developing along similar lines as Mutleys: two 15"woofers, conus mid and horn tweeter. But I don´t see where the bass units could exhibit significant ripples if they are x-overed below 500 Hz. Could you explain? Is it edge diffraction? Floor reflection? Anything else?

Rudolf

Hi,

I've seen plots of speakers on open baffles with significant peaks
and dips, typically a dip then peak going downwards in frequency
into the 6/dB octave transition region.

500Hz ? I think you'd need to be a lot lower to avoid ripples, but
it is possible the overall response of the 2 15's is relatively smooth.

This would be because the large cone area has more variation of
distance to the baffle edge than say a small centrally mounted driver.

Ripple frequency is lower for wider baffles.

As I said my comments are partly conjecture, I'm no expert on open baffles.

8" MTM on a small baffle (~12" wide) (from linkwitzlab.com):



Here the ripple effect is clearly illustrated by the tweeter,
and somewhat smoother for the two 8" drivers.

/sreten.

[sreten]

By the way Mutley, where did you source the 15's ?

Are they from Skytronic ?

I'm curious as to the drivers parameters.

/sreten.