DIY multicell horn

[thevott]

Mirrophonic,
The 210 and 211 enclosures are bigger!!!
Actually, the 815 is a very similar, truncated cousin. The 211/210 horns extend several inches farther at the mouth though the width (flat panel to flat panel) is the same. Here are the horn dimensions (exluding the overall enclosure):

Width of 210 horn mouth (flat sides): 34"
Width of 815 horn mouth (flat sides): 34"
Height of 210 horn mouth: 59.5"
Height of 815 horn mouth: 44"
Depth of 210 horn: About 30"
Depth of 815 horn: About 23"

The other significant differences on the 815 is the absence of any bass-reflex chamber, a fully-enclosed driver chamber designed to reduce woofer travel, and the apperently thinner plywood on the curved panels to (my guess) reduce weight for shipping and suspending purposes.

As soon as I get my hands on some 210s and or 211s I'll A to B compare them with my 'opened-up' 815s.

After living with LF horns I simply cannot go back to direct radiating enclosures. I can only anticipate that the 210 will be that much more of a good thing.

MP

[thevott]

Mirrophonic,
Plans for all these enclosures are readily available. Check the Lansing Heritage site. They have a great Altec library there.

MP

[GM]

>After living with LF horns I simply cannot go back to direct radiating enclosures. I can only anticipate that the 210 will be that much more of a good thing.

====

FWIW, I had 515B loaded 210s at one time (three actually) and later turned two of them into corner loaded compression horns. Very impressive. Much later I sold them and put the four 515s into two 20 ft^3 vented EBS aligned cabs in the same corners and I can't really hear any difference beyond what you would expect due to the lower efficiency. Tonal balance, usable 'slam', transient response, etc., all sound the same except they require more power now (still within Xmax) and go two octaves lower (16Hz Fb).

For HIFI, an acceptable tradeoff IMO if you have sufficient/clean power and two corners available.

GM

[thevott]

GM,
Would you expound on that system as I am not familiar with EMS low frequency enclosures? The prospect of another octave is exciting to me as you can see on my avatar to the left.

The factors I cherish most about my Altec horns are the directivity and efficiency, the result being the reduction of the effects room acoustics and trademark transient response. Or simply really loud and clean!

MP

[GM]

EBS, Extended Bass Shelf. Basically, you make a cab that's a bit too large and tune it below Fs. This raises the F3, F6 points of course, but the corner boosts it some and if there's any room gain of note, the bottom end also. Without the corners, it has a response similar to a large sealed cab, though with a bit more gain.

If stuck in the corners, the corner is a conical horn of sorts, so there's not much difference in a typical size HIFI room. Where it becomes an issue is higher up, so you want a mids/HF horn that's 90deg or less. WRT transient response, there's a minor measurable difference between the modded 210s and the EBS, but I can't tell it. As for 'loud n' clean', well, dual 515s and a clean 110W/chnl is as loud as I care to go in my room.

Indeed, the 511s are the limiting factor and why I didn't mind parting with the 210s, which I got to fill a large 'great' room in a previous home. Actually, the cabs I'm using now were originally my 'subs' to fill in below the 210s.

GM

[Mirrophonic Sound System]

OK, I'm going to skip the separate thread because I've been doing
more quick caculations and it appears that the 210 is a fairly good choice
for a bass horn.

Initially I was concerned about the lack of depth which I suspected of
leading to an insuficiently low 'flare-rate frequency' - which should approximate
the cut-off frequency.

For reference I'm using Dr Edgar's design curves for "wall position" Tractrix
bass horns (the 210/ A4,A2 could be considered quasi 'wall-loaded'
because of those added baffle panels). To convert Tractrix to Exponential,
I add about 10% to the length.

With the 210's approx. 380 sq in throat area, and I make the cut-off freq ~80 hz,
the flare length can be as short as 30" (thanks to the large throat area
with dual drivers).

With the 'wall' loading, horn loading should extend to below 50hz
and with corner loading: who knows ? As GM said, they should be very impressive !

The avatar shows some floor-loaded concrete bass horns in Italy .
(click 'member rated' for enlargement)

[Datubie]

Mirro,

Looking at your new avatar..... What did you do? Accidentally turn the volume too high & blew up your house?

[Mirrophonic Sound System]

GM & VOTT,

Some good experimentation GM and the results are not a great surprise to
me.
The results being an undetectable difference between a good direct radiator
and a 210 theater horn.

I think the reason may be the compromises in theater horns which deserves a
separate thread and I will be Devil's Advocate by asking :
"Are Movie Bass Horns Any Good ?"

[thevott]

Mirrophonic,
Not only do your calculations support Altec's own data, they also suggests that Altec engineers actually knew what they were doing. Of course my ears have been telling me that for years.

It is the bottom octave, however, that I must solve. That's where the brick or concrete horn comes in!

MP

[Mirrophonic Sound System]

VOTT
In case you missed the picture of the Italian commercial
bass horns, I have reloaded it to the avatar.

I am thinking of similar construction for my bass horns:
Flat top & bottom wedge, curved sides with tractrix contour to reduce length,
single 15" driver with 0.6 throat-to-driver ratio.

Precedents:
Dinsdale: Tractrix bass horn
Babani: Simplified wedge construction for horns
Edgar: Design curves for Tractrix bass horns