NEW 1.5 inch horn for 4345 / 4343

[speakerdave]

I thought subwoof cut the 2307 for OA drivers to essentially include the throat length
that would already be there for the 2450... i.e., OA driver + custom horn being the
approximate equivalent of non-OA-2" driver + 2311 (in regard to throat+horn length). . . .

I think I've figured this out. I'm not sure the 2307 and 2311 have the same expansion rate. It doesn't add up anyway. Remember, the original setup had the full length of the 2307 plus a non-throatless driver. The 2311 plus the 2450 already compromises that. The "2313" with a throatless driver goes even further. Perhaps part of the merit of the original setup with the coated diaphragm is that the total horn length is what it should be. Best I've heard so far in this application is the original horn with a 1" TAD driver.

David

[4313B]

I think I've figured this out. I'm not sure the 2307 and 2311 have the same expansion rate.

As I've previously posted, they do.
JBL merely chopped a 2307/H91 down to make the 2311/H93.
It's the 2312/H92 that's "all wrong" for this kind of activity.

Best I've heard so far in this application is the original horn with a 1" TAD driver.

I think that TAD is a really nice driver.
G.T. had some input into this whole thing and I came to the conclusion after I messed with several combinations that the stock Al or Ti diaphragms with aquaplas applied and alnico cores offered the best balance and bang for the buck with the TAD being a very good option at increased expense. Of course, you guys are getting these 2435's and 2452's at substantially reduced costs so I can see why you would want to try them out in various scenarios.

[4313B]

heh.. well I've apparently killed too many brain cells...
went back and re-read post #1 where the 2311 and "2313" are listed as:
Wouldn't the 1.5" throat version need to be 7 1/2" (ala the 2311+2330) unless
the 2313 flare is now compound or otherwise modified?

Why? To maintain horn length? It simply doesn't matter, the system is jacked anyway in that respect so it just doesn't matter. I'd be more worried about the frequency response and impedance curve of any new combination so as to modify the network accordingly.

I guess it's moot. I'm not going to go cut up horns for this. Sorry for the detour.

Agreed. I'm not either and I abandonded the network design for the 1.5" 2435/435Be-based combo accordingly.

[subwoof]

The math involved in this horn mod was to simply get the horn cut off to the point that the resultant horn + small thickness of flange ( to be beveled later ) was equal to 1.5"

In my initial posting(s) I measured the actual phase plug to horn exit for all 3 combo's:

2307 / 2421 is 10 1/2 " ( 8 1/2 + 2 )
2311 / 2441 ( or 2450 ) is 7 1/2" ( 4 3/4 + 2 3/4 )
2313 / 2451 or 2435 ( and now 2452 variants ) is only 4 3/4"

I feel that the larger, more robust 4" diaphrams will handle any excursion / rolloff anomalies caused by the shorter horn. This isn't a football stadium, full power wide range app for this driver combo....

Remember that the "time alignment" issue for the long horn is also reduced to almost the depth of the 15 or 18 cone!

I have all of these horns and combo's - and the 2311/2330 had the same flare as the 2307 but the extra flange thickness ( and the fact the 2330 is for the ALTEC 1.4" ) changed the overall length a little.

The 2312 IS a different horn flare and should not be in this discussion.

In all this is just an experiment of modest goals - not the engineering pancea to re-invent the wheel..

sub

[4313B]

The math involved in this horn mod was to simply get the horn cut off to the point that the resultant horn + small thickness of flange ( to be beveled later ) was equal to 1.5"

And everyone should note that that is completely acceptable.

I feel that the larger, more robust 4" diaphrams will handle any excursion / rolloff anomalies caused by the shorter horn.

Not an issue given that you should cross them at 1kHz or higher. What you will do is play signal through the midbass driver and this horn/c.d. combo at the same time and measure the frequency response (make sure the horn/c.d. combo has its sensitivity brought down in line with the midbass driver using an L-Pad). Where there is a sharp dip in response you will place your intended crossover frequency. It should be around 1.2 kHz (If I remember correctly I got 1.275 kHz with the 435Be).

Remember that the "time alignment" issue for the long horn is also reduced to almost the depth of the 15 or 18 cone!

Only really matters with respect to the midbass driver, whatever that may be. The 2405/077 is what it is and jacked by design. No worries there. This stuff just works.

In all this is just an experiment of modest goals

Understood.

[Ian Mackenzie]

Interesting.

For what its worth I have heard the aluminium (2421), titanium (2425), acquaplas with titanium and stock Be diaphragms (Tad 2002) very recently in the 4345.

IMHO the diaphragm material is the key to improved performance, not the horn length or rear diaphragm piston area in this system. The coated titanium is better by an audible margin and Be (Tad) is noticably better again. They have more resolution.

Unfortunately the Tad 2002 has been discontinued. So the only option for you guys is the JBL Be equiped 2435 driver (0435) but it means modifying the 2307 as discussed by Subwoofer.

(I heard the Be 2435 at Rob's but with another JBL PT horn)

Ian

[4313B]

So the only option for you guys is the JBL Be equiped 2435 driver (0435) but it means modifying the 2307 as discussed by Subwoofer.

Yeah but it really needs another network mod too.

What does TAD have as a replacement?

[speakerdave]

. . . . G.T. had some input into this whole thing and I came to the conclusion . . . . stock Al or Ti diaphragms with aquaplas applied and alnico cores offered the best balance and bang for the buck . . . .

Certainly can't beat the price of that.

David

[subwoof]

Grumpy: The 2313 horns that I made have a flange thickness of 3/4 inch.

That is 1/2 an inch thicker than the flange on the 2311.

sub

[richluvsound]

but, you already figured that out.




Where do I measure from ? the front of the flange,the back of the flange , the front rim of the horn .

Rich

[subwoof]

Put said horn face down on a flat surface.

Measure vertical height to the surface the driver will bolt to.

Done.

This *is* the length of the horn.

Now the older model drivers have a short internal waveguide/horn/throat ( whatever term fits your definition ) that is located after the phase plug but before the exit and this *adds* to the effective horn length in this situation because it is after the phase plug and has the SAME taper ( slope ).

The newer drivers do not have this.

ok?

sub

[Mr. Widget]

What does TAD have as a replacement?

A couple of years ago they discontinued all of their studio monitors, last year they discontinued all of their horns and now they are discontinuing many of their woofers and compression drivers... it wouldn't surprise me if they discontinue the whole line in the next year or two.

It is really too bad... years ago they spirited Bart Locanthi away from JBL and now it seems they have spirited away some of JBL's bean counters too.


Widget

[richluvsound]

Hi Sub,

I want to double check before I give it the chop. It measures 4.75" I'll be welding the flange !

Rich

[subwoof]

Do not chop yet....

the cut-off point is on a section of the horn's inside diameter that is LARGER than 1.5" for my 2313 project.

If you look at the pictures I posted, you will see that the now-cutoff horn sits into a recess on the wood flange. The section of wood that is now between the horn and where the driver mounts has to be hand-beveled to get the correct 1.5" dimension.

IF you are going to simply weld a new flange on the horn, and made the new flange slide over the outside, then you would cut off the horn at a different point ( where the inside diameter IS exactly 1.5"

NEITHER of these lengths are 4.75" and until I re-check my templates and horn stash today, unknown.

I will post some additional info in a few hours.

sub

[richluvsound]

Hey Sub,

the patient is still intact.

I'm hoping as copies these horns maintain the original's wall thickness.



Rich