Altec 511B horn compared to the GPA MR931

**MerlinVSM** · July 27th, 2012, 04:01 PM

How does the above horn sound when used in a high quality audio home system.

Any preference ?

Driver will be a GPA 902.

**gearfreak** · July 27th, 2012, 04:08 PM

Don't have 511's anymore, and have not had the MR931, but casually speaking I prefer CD horns.
I'd expect distance to the listening position to be a factor in your decision.

**fpitas** · August 14th, 2012, 10:32 AM

CD versus non-CD horns is often down to personal preference. Most audiophiles prefer non-CD these days, such as the tractrix or JMLC horns, which have a collapsing directivity with frequency. CD is preferred for PA use where you need to broadcast sound more or less evenly to the crowd in a club, but if you sit in a specific spot for listening, CD is not necessarily a good thing; all that power broadcast in other directions simply creates more reflected sound. CD horns in particular usually use a diffraction slot in some form, which can affect the sound by creating an internal reflection. That leads to ripples in the frequency response, which can be EQed out, but the reflections within the horn will emerge later than the direct sound causing time smearing. Still, it's a matter of taste, and some people are OK with that, and think it's a good trade-off for the better dispersion. Of course, if you want CD without using a diffraction slot, a waveguide is a good answer, since they don't have the constraints of a true horn.

I should add that I have 511s and am happy with them. I run them toed-in to a spot about a foot in front of my listening position, which helps the imaging. Used that way the limited dispersion over 10kHz isn't a big issue.

**VolvoHeretic** · August 14th, 2012, 11:00 AM

Originally Posted by fpitas

I run them toed-in to a spot about a foot in front of my listening position...

What, you use a laser sight to aim them?

**fpitas** · August 14th, 2012, 11:04 AM

Originally Posted by VolvoHeretic

What, you use a laser sight to aim them?

Nope, just sight them by eye. It's not real crucial as long as the apex is a little in front of the listener.

**cradeldorf** · August 14th, 2012, 03:47 PM

Originally Posted by fpitas

Nope, just sight them by eye. It's not real crucial as long as the apex is a little in front of the listener.

I stand against my speakers facing towards the listening position keeping myself square with the cabinet and aim my head straight and adjust the cabinet until I'm staring straight at the listening position.

**Panomaniac** · August 14th, 2012, 06:30 PM

Originally Posted by VolvoHeretic

What, you use a laser sight to aim them?

Believe it or not, I've done that. Green laser, in case you were wondering.

**Alien_Shore** · August 14th, 2012, 09:44 PM

I did some measurements tonight, since my test rig happens to be set up right now.

I took a 902 and measured from 1 meter, on-axis. Comparisons of MR931, 811, and 511.

The reason for the lower response from 0 to 120Hz on the 511 is the attic fan turned off (which was running during the other two tests and contributes some LF rumble).
If I am feeling motivated this evening, I'll take some off-axis measurements...

**Alien_Shore** · August 15th, 2012, 12:29 AM

Here are the off-axis (45 degree) comparisons:

GM · August 15th, 2012, 12:41 AM

Originally Posted by fpitas

I should add that I have 511s and am happy with them. I run them toed-in to a spot about a foot in front of my listening position, which helps the imaging. Used that way the limited dispersion over 10kHz isn't a big issue.

Yeah, a good rule-of-thumb for most rising on axis horns is to aim the left one to the far right LP and vice versa and if it's a solo seat, then at least 2 ft offset on each side.

GM