My new Malibu's

[djgaloot]

I just picked up my new Malibu's. I was a bit worried since I bought them site unseen from Craigslist but they are in almost perfect condition. A few water spots and a couple of small veneer chips but overall VERY nice. I have not tested them much but they sound pretty nice connected to my Marantz 1060 amplifier. Next I will try them hooked up to my Fisher X-202 tube amplifier. Oh BOY!

[djgaloot]

This is a poor picture of them in the living room where they will not get to stay. I will be moving them to the basement rec-room and using them in my home theater/audio set-up.
Dave

[ChopsMX5]

Wow! Nice find indeed!

[Art J.]

Hello Dave. Really nice. Congrats.
If you still have them open, can you measure
the port openings on either side of the horn?
I have never been able to determine it from the plans.

I built an oversize set of Malibu's in the 70's using
a separate port based on the additional volume
and driver Fs. Never knew the original.
Thanks, Art

[djgaloot]

I will get the port size for you in a day or two. They are all closed up at the moment but I want to check the drivers for "goo" migration. The port opening is a bit 3-dimensional because it is formed by the horn flange standing off of the front baffle with spacers. I need to calculate it for my own project which is to build a center channel version.
Dave

[Art J.]

Thanks Dave, I gather from your picture and this detail
that the whole top of the horn is suspended in air and is
part of the port, along with the sides.
I can see that it will be difficult to calculate.
Thanks again, Art

[djgaloot]

Art,
Yes, correct. And the sides of the opening are wider than the horn flange leaving another gap.
I will figure the area out, BUT, "why did they do it this way?" It seems a whole lot easier to put a couple of rectangular/round ports next to the horn but here they have complicated the horn mounting and cabinet construction somewhat. I assume there is a good reason.
Dave

[00Robin]

ooohh! I am such a wood junkie. Man! They just look...playable and fun and big and really nice. LOVE the cabinetry(is that a word?)i get so excited when I see the new fun people get here.

I am in an awfully nice mood before going to the dentist this am,LHF must be a "good thing" for me.

[Art J.]

"why did they do it this way?" It seems a whole lot easier to put a couple of rectangular/round ports next to the horn but here they have complicated the horn mounting and cabinet construction somewhat. I assume there is a good reason.
Dave


Well, at that time, it seemed like the right thing to do.
But really, they had a very good reason. These are the grand 'old school' Base Reflex
enclosures, where the back motion of the cone is added to the front radiation.
That's why there is a large opening.
In the case of your Malibu's, the port size is going to work out to be about 40 sq inches,
or a rectangular port about 4"X10". (figured quickly without a refresher course)
Their is no room on the front for these so they recessed the horn.
The same 'cabinet tuning' can be achieved with a port tube, but their will be no
added 'reflex action' at all. Just a noise hole.
A brief overview here from the site library.

http://www.lansingheritage.org/images/altec/plans/1968-enclosure/page03.jpg

from the page;

http://www.lansingheritage.org/html/altec/plans/1968-plans.htm

[djgaloot]

Thanks for the reference. The given enclosure dimensions and given resonant frequency of 30 hz would indicate a port size of about 40 sq-inches. Also, according to the reference, "The location of the port in reference to the speaker cone opening in an enclosure is not critical, since the wave length of the frequencies in which the port opening is effective is much longer than the normal dimensions of the whole enclosure." So I guess the "noise hole" can be anywhere. Having it surround the horn may help blend the sound image more? For my center channel speaker, I am planning on more of a horizontal layout with the horn in the center and the two drivers on each side with a port beneath each one. I may reduce the cabinet volume a bit to save on room. I can use the referenced graph to re-size the port. Any thoughts on this?

[Zilch]

Those designs were conceived before the advent of T/S parameters and more comprehensive understanding of how box sizes, tunings and drivers interact.

By one view, the "hole" is a ducted port, with an equivalent duct length, in the simplest form, the thickness of the baffle material.

If the concept of "reflex" relating to ducted versus unducted ports has meaning in this context, I'd be pleased to hear just what that is, because I didn't find it in reading the reference cited.

I don't know the reason for porting beside the horn, other than that's how VOTTs did it when the horn was mounted within the box as opposed to sitting on top of it. It's certainly less complex to fixedly mount the horn and use ducted ports.

Altec moved from that scheme to ducted ports in the transition from Valencia 846A to 846B, for example, possibly subsequent to appreciating the teachings of Thiele.

In most every case where I've reviewed early reflex designs with rectangular holes in the baffles as ports, the tuning has been wrong, and they are indeed merely "noise holes," in large part. Their purpose seems to have been to accentuate whatever boom the particular driver was capable of producing.

I'm not saying that's the situation with Malibu, but when you start taliking about designing and making an equivalent DIY center channel with a different volume and different ports, it seems to me it would be worthwhile to figure out what is going on with the original design....

[Art J.]

I should be more subtle with my humor.

Dave,
There is the smaller Altec 9844 to consider with a 2"X10" port
if you want an old school center channel.

http://www.lansingheritage.org/images/altec/plans/1970's-lf-plans/enclosures19.jpg

Hi Zilch,
I remember many light hearted conversations in years past about the noise hole, but it was versus the sealed box.
What you read was just an overview of the more detailed writings of Badmaieff with Don Davis.
What was missing from that overview is that for the reflex action to be most effective, the port area has to be the same as the effective piston area of the cone.
In the case of a 15" woofer it is 133 sq in and for the 12" is 78 sq in.
With that large fixed port size and Fs, cabinet volume can be calculated for a full size reflex.
You can tell that the cabinet size ends up very very large.
So a half size reflex like the Malibu with 12 inch cone and 40 sq in, is still effective with good reflex action. Real nice classic speaker.
The quarter size 15 inchers like the Valencia 1 and Model 19 can be called noise holes if you wanted to. Quarter Ports were much more critical to tune, Bass rolled off quickly,and Fs of the cone would change with age. Just like todays ports.

http://webpages.charter.net/artj/chart.jpg

[djgaloot]

Art: The 9844 is closer to what I was thinking about. I know it used the same components as the Malibu.
Zilch: I will be the first to say I do not know anything about speaker design (yet!) so my 1st approach was to basically copy the old Altec design philosophy as outlined in the reference "Speaker Enclosures, Thier Design and Use" and hope it sounds similar to my Malibu's. I compared the volume and port size of the 9844 (after subtracting the components) to the graph in the reference and they seemed to match pretty closely. I'm sure there is a more optimum design but I was hoping to get reasonably close.

[smiley67]

Nice score. I check my local Craigslist every week and I never see any old stereo equip. I'll keep checking just in case.

[johnaec]

I check my local Craigslist every week and I never see any old stereo equip.

Good deals on Craigslist are snapped up in a flash! If you want to play in that game, you need to check several times a day. Mid and late evening and first thing in the morning are the best times to check, IMO, though stuff pops up all day long...

John