Is this doable?

[pangea]

I've got so many great replies on my questions, that perhaps my main remaining question will be lost, so I hope you don't mind that I put it forward again and at the same time I have tried to isolate the most important question and also tried to clarify my question/problem.

A few days ago I received a suggestion on a first order x-over from an expert, which he said, would work and at the same time flaten out the frequency response on the 2445J driver

So, I'm asking for your help on this somewhat unorthodox x-over.

Will it work and will it reduce the hump and even out the frequency response between mid and high on the 2445J?

BR
Roland

[scott fitlin]

Giskard is the man for this question. I personally would not use less than 12 Db slopes on a compression driver. And not higher than 18 DB slopes.

First order filters are known for their excellent time domain characteristics, and excellent impulse response. But 6 DB slopes with a compression driver might be a bit shallow at the lower end of the operating range.

[Alex Lancaster]

And if You are planning on a cone speaker below the horn, why not xover at 1500 Hz, 6dB?, it would be even flatter, if the cone is flat that high.

Alex.

[pangea]

Originally posted by scott fitlin
Giskard is the man for this question. I personally would not use less than 12 Db slopes on a compression driver. And not higher than 18 DB slopes.

First order filters are known for their excellent time domain characteristics, and excellent impulse response. But 6 DB slopes with a compression driver might be a bit shallow at the lower end of the operating range.

Thanks, but could you pleas explain what you mean by "shallow"? I'm from Sweden you know!

BR
Roland

[scott fitlin]

6 db per octave is not as steep a rolloff as 12 dbb per octave, and you will have considerable overlap between the woofer and your horn. You are using a compression driver and since the rolloff is not that steep, if your crossover point is say, near the lower frequency limit of the driver, you might get too much low frequency below what the driver is rated for.

As Alex had said, with 6db slopes a higher crossover point might be a good idea, if you have a woofer that can go up high enough.

[pangea]

Originally posted by Alex Lancaster
And if You are planning on a cone speaker below the horn, why not xover at 1500 Hz, 6dB?, it would be even flatter, if the cone is flat that high.

Alex.

The x-over I was told, had the x-over point at around 5 kHz, because it would take away the big hump on the drivers mid section, but I don't know if it really does just that.

IF it does that, I guess I could insert a midbass driver just about at any x-over point.
I was thinking that maybe a, 2123H, 2118H or E 110 would work just fine in my small sub chamber up to around 3500 Hz, or am I thinking wrong here!?

BR
Roland

[pangea]

Originally posted by scott fitlin
6 db per octave is not as steep a rolloff as 12 dbb per octave, and you will have considerable overlap between the woofer and your horn. You are using a compression driver and since the rolloff is not that steep, if your crossover point is say, near the lower frequency limit of the driver, you might get too much low frequency below what the driver is rated for.

As Alex had said, with 6db slopes a higher crossover point might be a good idea, if you have a woofer that can go up high enough.

You think that it still would be a problem with a 6 dB slope when the x-over point is as high as 5000 Hz or higher?

BR
Roland

[scott fitlin]

Originally posted by pangea
You think that it still would be a problem with a 6 dB slope when the x-over point is as high as 5000 Hz or higher?

BR
Roland

No at 5000 hz it will not be a problem at all. But I dont think that using a 2445 from 5K on up is the best use, for this driver.

[pangea]

Originally posted by scott fitlin
No at 5000 hz it will not be a problem at all. But I dont think that using a 2445 from 5K on up is the best use, for this driver.

According to the person that designed this x-over, who stated that there would be a lot of energy left quite a bit down, because of the big hump on the 2445's frequency response. At least down to the one or two kHz region, that is IF this persons theory works as he said it would in this particular design.

BR
Roland

[Alex Lancaster]

According to the person that designed this x-over, who stated that there would be a lot of energy left quite a bit down, because of the big hump on the 2445's frequency response. At least down to the one or two kHz region, that is IF this persons theory works as he said it would in this particular design.

"the person" seems, IMHO, to have smoked crops sprayed with paraquat.

About Your Philosophy, no offense, Welcome to the planet!.

Alex.

[pangea]

Originally posted by Alex Lancaster
According to the person that designed this x-over, who stated that there would be a lot of energy left quite a bit down, because of the big hump on the 2445's frequency response. At least down to the one or two kHz region, that is IF this persons theory works as he said it would in this particular design.

"the person" seems, IMHO, to have smoked crops sprayed with paraquat.

About Your Philosophy, no offense, Welcome to the planet!.

Alex.

I don't know if he has smoked all that sprayed stuff you're suggesting, what I do know is that he has worked with the swedish JBL representative a few decades, so he should know what he's talking about. I just wanted a second opinion. I figured this would be the place to ask for it.

Why would you want to, or even be in the position to welcome me, to a planet on which I have already been a resident for over fifty years? No offense!

BR
Roland

[4313B]

Originally posted by pangea
Will it work and will it reduce the hump and even out the frequency response between mid and high on the 2445J?

What horn are you using? Flat-front bi-radial? Exponential as mentioned in your other thread? What is the model? Did the guy in Sweden come up with his solution based on a specific horn?

[pangea]

Originally posted by Giskard
What horn are you using? Flat-front bi-radial? Exponential as mentioned in your other thread? What is the model? Did the guy in Sweden come up with his solution based on a specific horn?

I'm using a Brasilian made exponential horn made by Selenium model HL 14-50 it is 131 mm long, 160 mm mouth.

I told this person I'm using an exponetial horn, but I'm not sure if we discussed specifically which horn I was using.

BR
Roland

[Robh3606]

Hello Pangea

All of the biradials like the 2360 and 2380 series require compensation to flatten the curve. Basically reducing output in the lower range of the curve. The 4430/4435 used passive compensation with the 2344 and the 4425 with the 2342 horn. All these horns give you flat/uniform power response as such they must be equalized electrically to be flat on axis or anywhere else for that matter. The directivity remains constant with freguency. Take a look at the horn curves WITHOUT eq./compensation, Also look at the directivity curves.

An exponetial horn will compensate the driver so on axis it is flat but the power response is not. The directivity changes and gets higher the higher in frequency you go. Basically you go from wide beam to spotlight.

The idea about the first order network is theoretically it can match the roll off of the driver. So depending on where you choose to make the hinge point on the crossover you will reduce the lowend response at a rate that closely follows inversely what the driver is doing. This will work with a CD horn.

Take a look at the 4430/4435 crossover. Then take a look at the 4722 crossover. The 4722 has the idea in it purest form. Please note that these are 12db networks not 6db

You have to know what type of horn you have and what its directivity is to do the compensation. Any published specs on the horn you are using??

Rob

[Earl K]

Hi Pangea

I use that horn. For my purposes, I find it very nice with no horn coloration that I can make out. I use 2441 diaphragms in 2440 magnets some parts of the week - and other times a 2450SL diaphragm in one of those 2440 magnets. Right now I'm listening to one of each. The 2450SL is more extended with a nimbler / tighter response all through its' response curve. My second 2450SL diaphragm has a fit problem that effects its response curve - I may have a defective diaphragm , I'm slowly researching this ) .

I biamp my system, crossed at about 750 hz ( LR, 24db per octave ). I use a simplistic RC network to bump-up the HF response a little bit. A simple 1.5uf cap strapped across a 16 ohm resistor is all the EQ I use. I'm not after ruler flat response - and - well, this RC network just won't deliver "flat" - but it is very musical sounding . I've tried 3uf and larger but those weren't to my liking.

Today, I just tried a 12ohm resistor strapped across the driver with a 2.35uf cap inline ( as in your drawing ). That setup, also won't deliver "flat" HF response. Also, it's not as musical or as open sounding as the simple RC network ( at least with my Bryston 2B-LP ) . Though that setup does have a significant db drop or padding effect - perhaps more than you're after. A tone generator and a cheap SPL meter would tell you all this info .

For the $ 5.00 it'll cost you to buy the 2.2uf cap and resistor - try this out yourself - you won't blowup your amp as long as it can handle a 6 ohm load ( and if you don't create any short-circuits when you're messing about ).

The 2441 driver on that Selenium horn has an AC impedance of about 12 ohms across most of the range in question ( actually 10.5 to 12.5 ohms ). The paralleled 12 ohm resistor gives a working circuit impedance of 6 ohms. The 2.2uf cap "sees" or is reacting with the 6 ohms of AC impedance . After a bit of my math, I figure that gives a cornering frequency for that cap of about 12000 hz ( with 6 db per octave rolloff for the frequencies below ). I also assume that horn with a JBL driver is about 109 - 110 db (with 1 watt at 1 meter). Selenium rates it at 108 db with their older line of drivers - but these drivers were always a bit less effiecient than JBLs .

I'd ask your JBL contact to redesign the HF portion of the network. Offer him some money to do it. Ask him to incorporate a 16 ohm Lpad for some level matching. ( An Lpad in the 2123h portion of the circuit would likely be useful ). Suggest he look at the S3100 HF circuit for some "ideas & inspiration" in circuit design. That S3100 is designed for a CD style horn driven by an 8 ohm nominal ( 3.2 dcr )2426h driver - so he will have some scaling of values to accomplish . Still it's a nicely designed circuit for the DIYer .

That's what I suggest .

regards <> Earl K