JBL 2397 with 2405 time aligned

[Dr.db]

Thanks a lot for your guidance!!


Would you have any suggestions for the placement of the 2405 ontop of a 2397 or smith-horn ?

[Horn Fanatic]

Thanks a lot for your guidance!!


Would you have any suggestions for the placement of the 2405 ontop of a 2397 or smith-horn ?

The photo of the bracket used by a chap in Canada HJames posted on the 7th looks very cool. As for time alignment? By the looks of the bullet placement it doesn't look like it. I noticed two chaps on Face Book discussing the time alignment issue recently. One of them is of the school that the voice coils aren't always require to be on the same plane. His reasoning appeared to be sound, but that is just one opinion. If I can find the discussion I'll post it here so that others may review it.

However, I would use some type of damping material on the top of the wooden horn you end up building, to eliminate reflections from the top of the horn should you mount the 2405 within proximity of the horn throat. Perhaps some felt, it's cheap!

Good luck. Post pics of your horns when you make them.

[Dr.db]

That would be nice, looking forward to that discussion!


Actually I´d like to avoid any kind of damping material on top of the wooden horns. Simply because of the looks.
So I would try to mount the tweeter high enough so that it will beam completly above the midrange-horn.
Could this height be determined by simply using the diffraction-characteristics of the 2405 ? It has 25° vertical diffraction, so 12,5° up and 12,5° down from the horn-mouth. This is about 1inch down per 4"inch lenght.... If the 2397 is 13,5inch long plus the 2328 adapter with 4inch of length this would be a total of 17,5inch which the 2405 is mounted in behind.
17,5inches divided by 4inches = 4,375inches
So the horn mouth of the 2405 has to start at least 4,4inches above the midrange horn to avoid reflections, right ??

I hope this wasn`t too confusing.

[Mr. Widget]

That would be nice, looking forward to that discussion!


Actually I´d like to avoid any kind of damping material on top of the wooden horns. Simply because of the looks... So the horn mouth of the 2405 has to start at least 4,4inches above the midrange horn to avoid reflections, right ??

I agree that a pile of absorbant material on the horn would be hard to pull off and make it look good.

Realize that the dispersion spec is at -XdB, it isn't absolute. I think you will need greater separation to pull this off without absorbant material.

Also on the voice coil alignment discussion be aware that time alignment must take into account listening position relative to each driver's acoustic center... Meaning if you stand up or move back you will need a different alignment than a lower or closer listening position so simply lining up voicecoils will almost never be correct.


Widget

[ivica]

I agree that a pile of absorbant material on the horn would be hard to pull off and make it look good.

Realize that the dispersion spec is at -XdB, it isn't absolute. I think you will need greater separation to pull this off without absorbant material.

Also on the voice coil alignment discussion be aware that time alignment must take into account listening position relative to each driver's acoustic center... Meaning if you stand up or move back you will need a different alignment than a lower or closer listening position so simply lining up voicecoils will almost never be correct.


Widget

Hi Mr.Widget,

Not to mention the influence of the (usually applied networks). As comb effect (dye to the time delay mismatch) can be seen on the FR measurements, an experimental work would be easier way, I think.
I have here one question for You ( as a man of great experience and knowledge): using "brick-wall filters" (in VHF/UHF sections) would it help or not?

Reagrds
ivica

[Dr.db]

That´s correct; time alignment always depends on listening position.
I think the height of sitting in a couch is allways about the same, just the distance varies considerably.
But it has to be considered, you´re right!


I`m going to use an active-crossover, but this will still affect the time alignment, won`t it ?


With which equipment could I actually determine the correct position in a field-test ? I´ve nothing for measuring so far and I don`t want to spend a lot money either...

[Fort Knox]

I've already been though all this horn alignment business ...
and your better off w/2 way system and some serious eq..FK

[Mr. Widget]

...using "brick-wall filters" (in VHF/UHF sections) would it help or not?

With regards to comb filtering absolutely, regarding improving basic impulse response (the goal of time alignment) I'm not sure. Since there are several other variables, I guess it would depend on the application.


Widget

[ivica]

With regards to comb filtering absolutely, regarding improving basic impulse response (the goal of time alignment) I'm not sure. Since there are several other variables, I guess it would depend on the application.


Widget

I agree that impulse response would be the best measure, but for sure, in such situation , a kind of time-delay, compensation has to be applied.

regards
ivica