Beer budget "Version" of $10,000+ Jamo Open Baffles

[sreten]

Hi,

This is all purely theoretical, but may be of interest to some.

I was thinking about how one might go about this, and it sort of all
came reasonably together, so I thought I'd share my thoughts on this.

The starting point is MJK's excellent article :

http://www.quarter-wave.com/OBs/OB_Design.pdf

You can find reviews of the Jamo R907 and R909 online.

MJK's article outlines a strategy, high Q bass units ~ 6dB greater
senstivity than the mid treble, and an offset electrical c/o points
of 200Hz and 500Hz L/R to give an effective acoustic c/o point of
around 400Hz, these can be actively or passively implemented.

Here come one dodgy point of my thinking as I can't check it,
using twin 15" drivers and extending the height of MJK's baffle
won't change MJK's conclusions much, and you can use his c/o.



It is a very big loudspeaker, but for some that is the point ....

My first thoughts were what would you use for the mid/treble
section and what c/o ? Anything out there that fits ?

ZA5.2iw - 2-way in-wall system :
Zaph|Audio - ZA5 Speaker Designs with ZA14W08 woofer and Vifa DQ25SC16-04 tweeter

Careful chamfering of the rear for the mid unit is needed ....

Seems to fit the bill, I guess you could find other in-wall designs.
Again assumptions are somewhat dodgy, will it still sound balanced
with the extra rear radiation ? R3 = 6 ohms may be the best option.

Perhaps a smaller driver would be better, but sensitivity will
usually suffer, here its 87dB, 2dB down on the Jamo's, but
not a huge loss given the relatively beer budget.

So we need a bass driver +6 to +10dB sensitivity, the lower the
sensitivity the higher the Q somewhat to mate to the mid/treble.

As this is a paper exercise, somewhat better than just buying
drivers and a off the shelf c/o and hoping it will be alright,
here IMO is where you compromise performance for the price.

That is, what you should end up with is great for the price,
rather than hoping they will be great for the money you spend.

It turns out just about the cheapest option will work in the bass end.
GRS 15PF-8 15" Paper Cone Foam Surround Woofer 292-415
You can do a lot worse for $30 .....

Two of these will be 93dB sensitive albeit 4 ohms impedance.
So MJK's bass c/o will need converting to 4 ohms to work.

That is basically it, the outline of a 20" wide plain open baffle speaker.

Ideally I'd say the modelling should be checked, ideally you'd
want to c/o to the bass as low as possible, to make the best
of the ZA14 driver, and limit the effects of the bass drivers,
but its a starting point for a cheap ambitious project.

I don't think there is much to add to the mid/treble c/o,
but modelling of the finer details of the bass to mid and
driver placement options could yield a better option.

Its not a practical design for my domestic environment,
but if nothing else its food for thought for speakers.

rgds, sreten.

[woody]

You may want to reread his articles. I think he did one with 2 of the Alpha 15's per
side to use with a Lowther. But doing this he had to change the crossover points a
lot. This is all from memory but I think he had to use 200hz on the woffers and 250hz
on the Lother.

[sreten]

Originally Posted by woody

You may want to reread his articles. I think he did one with 2 of the Alpha 15's per
side to use with a Lowther. But doing this he had to change the crossover points a
lot. This is all from memory but I think he had to use 200hz on the woffers and 250hz
on the Lother.

Hi,

I don't think so. The Lowther system uses huge width open baffles, not 20" wide.
The only reason being to get the Alphas up to the Lowthers sensitivity, not elegant.

MJK

Finally, reviewing the Lowther OB speaker system documented on my site
reinforces some of the observations made in the preceding paragraphs.
The Lowther OB speakers are a great sounding system but they are HUGE.
The front baffle with wings extended measures 40” tall by 60” wide.
It requires two Eminence Alpha 15A woofers and still needs bass boost
from the active crossover. The baffle size, the number of woofers, and
the bass boost were all driven by the approximately 98 dB/W/m of the
Lowther PM2A full range driver. The minute I selected the Lowther drivers,
I had backed myself into a huge speaker system with multiple woofers and
an active crossover. A great sounding OB system but I learned about OB
design trade-offs the hard way by constructing a brute force design.
I am going to be smarter with the next OB design that I design and build.

rgds, sreten.

[sreten]

HI, FWIW 4 or more of the bass drivers are $23 each ..... rgds, sreten.

They'll get nowhere near the Jamo drivers, but the mid/treble drivers certainly will.

[MJK]

Another good candidate, Goldwood 215/8 15" woofer.

Goldwood GW-215/8 15" OEM Woofer 8 Ohm 290-345

You can extend flat to 30 Hz ($36 for four) in a 20" wide baffle if the T/S parameters are accurate.

[bjorno]

Originally Posted by sreten

HI, FWIW 4 or more of the bass drivers are $23 each ..... rgds, sreten.

They'll get nowhere near the Jamo drivers, but the mid/treble drivers certainly will.

Hi, Good idea, A few years ago I tested this approach:

Dual woofers in OB v single

Surprising result...the OB's sounds ...very good... and my intension was to give these to my son..But I didn't, By the way: I'm listening to the OB's mostly in a horizontally speaker setup!

b

[NYCOne]

Originally Posted by MJK

Another good candidate, Goldwood 215/8 15" woofer.

Goldwood GW-215/8 15" OEM Woofer 8 Ohm 290-345

You can extend flat to 30 Hz ($36 for four) in a 20" wide baffle if the T/S parameters are accurate.

Martin,

Have you had direct experience with these?

I, too, would like to try an OB with some interesting tweeter (fullrangers), but find myself having a hard time finding the right woofers. I'd like to see a driver that can do 30-1Khz in an OB.

[Pano]

Good project.

John Busch is working on a similar idea but with the GRS woofers. I'll soon be building a version with dual 15" GRS woofers - so closer to this. Definitely beer budget. Cheap beer.

[sreten]

Originally Posted by MJK

Another good candidate, Goldwood 215/8 15" woofer.

Goldwood GW-215/8 15" OEM Woofer 8 Ohm 290-345

You can extend flat to 30 Hz ($36 for four) in a 20" wide baffle if the T/S parameters are accurate.

Hi, TBH the GRS unit looks a far better bet to me, and its cheaper, rgds, sreten.

Due to room gain and stuff, I tend to like a tapered bass roll-off, flat is not always good ....
(If tapered suits the room you end up with a higher real max SPL before bass overload.)
Flat is good for wooden absorbing type structures, tapered suits more rigid constructions ....

Are my tenuous assumptions about two drivers in a higher 20" wide baffle correct ?
Well I know they not "correct", but is it reasonable ? Is there not much difference ?

[jerome69]

Hi,

Clones were done :
Jamo R909 Passive Open Baffle Project

Big passive OB project

Your mid-tweeter is a good option.
20" width is not an absolute need, if you accept a lower sensitivity, the width could be 16". I don't want something larger in my living room. With active equalization, 11" is enough.
You can also use 12" or 10" drivers

Cheers.