2 inches...

[scot]

If anyone cares, here is what two inches means.

Well that and discovering my sub still had a -6db curve applied. Fixed that as well, but the more interesting thing is how different the curves look when the only difference in the two is that I discovered my front left was measured wrong. I was measuring from the baseboard at the wall to the speaker to ensure exact alignment between the two, but forgot to subtract out the two in depth in a few measurements. Ended up that the speaker was just slightly angled wrong and a total of two inches different from the listeners head.

Fixing that made major differences in the quality of output.

(I noticed it by looking at the energy graph in small detail and saw two impulses. Close, but not quite overlapping.)


If you REALLY get into this graph you can see that I have two dropout ranges, 180-570 or so and a smaller one at 1-2.5k Those are real issues since it is in the spoken voice area. By playing sinewaves and walking around/measuring it seems the dropouts are caused by my l-shaped room. I am going to add a bunch of thin absorbers to the areas where I hear modes and see if that helps.

Playing around with some absorbers gave me 5-6db changes at different peaks so this should be an interesting experiment. BTW: green is where everything is aligned to <1/2".

[DrWho]

scot wrote:

If you REALLY get into this graph you can see that I have two dropout ranges, 180-570 or so and a smaller one at 1-2.5k Those are real issues since it is in the spoken voice area. By playing sinewaves and walking around/measuring it seems the dropouts are caused by my l-shaped room. I am going to add a bunch of thin absorbers to the areas where I hear modes and see if that helps.

I'm not convinced your room explains the behavior you're seeing. I think that if you did a similar measurement outdoors, that you would see some similarities.

What kinds of mains are you running? I'm gonna go out on a limb and guess that you've got some narrow towers with at least one 4kHz xover point and possibly another one around 600Hz.

I'm thinking the difference you're seeing is the polar response of the speaker and then the non-linear frequency response is likely related to the power response (as opposed to the frequency response).

Also, that 8dB broadband difference in the low-end doesn't look right either. Did you have a sub on when doing the green measurement and then no sub for the blue?

[scot]

Speakers are ribbons with dual scanspeak woofers, crossover is 1khz (12db up from the woofers, 6db down from the ribbons). Before you ask, yes the ribbons are fine down to 1khz, they are 43" long if I remember the distance correctly and are easily able to handle that range in sound. Near field measurements show they are pretty much flat, though they do drop off above 13khz. The mid dropout is not duplicated <1m, and you can walk around the room and hear major peaks and valleys.

Sub channel was set -6db on the blue, my outlaw audio 950 didn't save the 0db setting the first time I reset it for some reason. Once fixed that picked up the bottom end.


This is an L shaped room, from the room picture looking forward, the left side has a 6' bumpout. The right side you can see stairs going to the garage, and the back picture shows my big pile of bass tubes and the stairs to the rest of the house.

Ignore the mess please, and sorry that was with my 24mm wide lens... I need something wider to take a better indoor shot.

Ceiling height is 10'

[scot]

One more note, the window shades were open to get light in for the pictures. Normally I have cellular shades down to block light, so no worries about the slap echo all the windows would cause.

[DrWho]

scot wrote:

Speakers are ribbons with dual scanspeak woofers, crossover is 1khz (12db up from the woofers, 6db down from the ribbons). Before you ask, yes the ribbons are fine down to 1khz, they are 43" long if I remember the distance correctly and are easily able to handle that range in sound. Near field measurements show they are pretty much flat, though they do drop off above 13khz. The mid dropout is not duplicated <1m, and you can walk around the room and hear major peaks and valleys.

43" is the wavelength of ~320Hz....so you're gonna have crazy polars in the vertical plane at pretty much every frequency above that simply due to the shape of the transducer. Measuring in the immediate near-field won't necessarily show this because you're in a plane-wave region.

[scot]

Im sure there will be some amount of variance due to the length of the ribbon, but in all of the measurements I have seen (near and far field) they are minor enough to not be noticed and definitely not the fairly harsh and wide peaks and valleys from my measurements. As per the basic specs the speaker is +-2db 26-20khz (and I think +-3 to 25).

NFR 645. So it is a monopole ribbon, not dipole like the magnepans I have upstairs.