Just came into 4 large format Manta-Rays, several questions

[dhook17322]

Two are very long (almost 6' long) large format Mants-Rays (2' x 3' mouth) and two are shorter wide angle models large format units. They are fiberglass construction painted black and in good condition, but the labels are painted and looks unlikely they will be readable if the paint comes off yet. I have several questions on their use which will be with a pair of 210's in a 30' x 40' building.
1.- Unlike the metal horns, these do not appear to ring but do have a marked resonance at a mid-bass frequency. Do they require additional damping to make them more innert?
2.- Are there any special procedures to hang them? They don't appear to lend themselves to sled mounting on top of speaker cabs if you keep the voice coils in the same plane. They will stick out well in front of the bass cabs unless you use electronic delays.
3.- Will these perform better than multicelled horns (e.g. 1003's and 803's) with large format drivers (288K's)?
4.- The response curves of these drivers appear to be weak on the extreme high end (above 15K Hz.). Would it make sense to add a pair of these with small format drivers which claim to be good to 22K Hz.?
Thanks much for any help.

[joyspring]

Dave H:

I'm guessing the two long ones are probably 40x20 from the dimensions you provided. Here are some dimensions on circa 1986 fibreglass MantaRay horns:

<pre>
MR42A 61cm H x 86.4cm W x 152.4cm L
MR64A 61cm H x 71.1cm W x 71.1cm L
MR94A 61cm H x 86.4cm W x 71.1cm L
</pre>

Onwards to your questions...

1. Damping won't hurt but won't necessarily help either, assuming that you will be crossing them over above 500 hz.

2. The MR42As are probably not an appropriate match for the 210 cabinets in a cinema / hi-fi setting; they're really intended to be clustered for long-throw public address. The DI (directivity index) definitely will not match a single 210 at any reasonable crossover frequency.

Your other horns are probably a much better match for your 210s.

As for mounting, you could make a custom bracket that attaches to the junction of the horn throat and body.

[3 and 4 are closely related and deserve some background info before some of you accuse me of denigrating superior `vintage' technology...]

All compression drivers have decreasing energy output with increasing frequency, eventually assuming a mass-induced -6 db/octave rate; this is pure physics at work. Plane wave tube measurements bear this out.

Without electrical EQ, compression drivers mated to standard horns have increasing directivity with frequency; for example, while a 511 sectoral (radial) horn with an 802 driver may be flat to 14 kHz on-axis, it will have a falling response 30 degrees off-axis. That is, it has a flat frequency response but falling power response.

Constant-directivity horns have a flat power response (equal energy output within its rated bandwidth within its specified coverage) but have a falling frequency response that ideally mirrors the compression driver's plane wave frequency response.

Therefore, constant-directivity horns require electrical EQ (+6 dB/octave) to yield flat frequency response on-axis (and off-axis, which is the CD horn's primary benefit). Many active crossovers have CD horn compensation as an option, or you will have to add a series RC bypass to the HF section of a passive crossover.

3. Power response-wise, the MantaRays are clearly superior to older multicells.

Todd has previously mentioned the problem of `apparent apex' in constant-directivity horns caused by the axial displacement of horizontal and vertical breakpoints but that may or may not be objectionable to you.

However, the MantaRays will definitely not have `fingering' which may occur with increasing frequency in multicells, nor will it have any diffraction problems at the horn mouth either.

Soundwise, I'll leave that up to you. Personally, I greatly prefer well-designed constant-directivity horns; Altec MantaRays are amongst the best.

4. As I mentioned above, you will need to add electrical equalisation to compensate for the MantaRay's flat power response. Adding an additional HF horn/driver will defeat the purpose of using constant-directivity MF horns, unless the HF horns are also constant-directivity and have the same horizontal and vertical coverage angles.

BobR

[dhook17322]

Thanks much for the great information. What I have is two MR 42's, one MR 64 and a MR 94 and 288K's. Obviously I will need to find another of the wider angle MR's. The system I have to run them is an all Rane system with:
MP 24 mixer/preamp
ME 60 graphic equalizer
MA 6s 6 channel amp, 100w @.
SAC 22 crossover
RA 27 analyzer
PCA
Cd player, turntable and tuner
I plan to do a lot of experimentation with these and a couple 1003's with the 210's biamped plus 2 subs with the 3182's I have. Hopefully it all works out - at least should provide plenty of inside work for winter. Any suggestions are very welcome.

[Richard C.]

Bob R.,

You said:
"Todd has previously mentioned the problem of `apparent apex' in constant-directivity horns caused by the axial displacement of horizontal and vertical breakpoints but that may or may not be objectionable to you."

What does this (apparent apex problem) "really" sound like, and what would be the worst sound source that would show this up? Does a CD horn sound equally flawed up close and at a distance? Is it something that only certain people can hear? I know many people that are bothered by multi-cell lobe patterns, and wouldn't EVER listen to one. But, on this hostboard, there are several people that must just overlook this little flaw - and love these horns for ALL the other advantages.

Richard C.

[stpower]

Dave,
BobR pretty well summed it up in his post. Since I am using 210's also, I can add the following;
I would recommend the MR-94. I use this horn with a 290 driver for midrange in my system with excellent results. I previously used 1003's. The 1003's have a bit better loading in the lower midrange, but the lobing between the individual cells is very noticable in a home HI FI environment and is annoying. The Mantaray is more smoother across the dispersion angle and sounds the same when moving your head. To me the Mr-94 is more easy to listen to in the home.
I don't recommend the one size fits all active EQ for CD horns on crossover units. Each horn and driver need different amounts at different rolloff points. You will need to do a lot of measuring and experimenting to get the EQ right, but it will be worth the effort.
You may want to experiment with 1003 vs Mr-94 to see which you prefer.I sure like the looks of the multicell better, the coolest looking horn ever,I think.

stpower