Pro audio question for Craig please (copied from SSS)

[michaelhigh]

Hello, Craig, I am Michael Hy Yaffe, and I have a question concerning the pairing of separate LF and HF components with a particular crossover in a PA system. It will also be used as a home-stereo rig (with balls), and I would like to know your opinion, as I very much respect your expertise in this area. Firstly, I will run down the individual components. I have 4 JBL E-140's in Bag End II cabinets (see avatar) and JBL 2345 lenses. I am looking to purchase Selenium 220 TI compression drivers, mainly because they're comparatively inexpensive (cheap). I will be attempting to use a DOD 623 crossover between the two. I've been consulting with some people who use pro audio components in home stereo applications and one person in particular recommends a crossover design he has adapted from an Altec 19 design, and his reasoning is that it offers HF compensation that precludes the need for a tweeter in my case, with the horn/lens combo. Am I a victim of misinformation? Can I mate the E-140's with the Seleniums via the DOD 623 and not miss the compensation he mentions? Does the DOD offer the HF comp he describes being necessary or is he simply touting his own product? I look to you as a valuable resource, and anxiously await your response. Any additional advice would be greatly appreciated. Thank you in advance for your speedy reply, your time and advice.

[MrKnobs]

I copied this post over here from SSS. Be nice!

 

Terry D.

[soul-x]

Yeah I think the Old Altec passive crossover does have some compensation built in for the horn rolloff. But the same general effect could be achieved with active equalization.

 

Also Keep in mind that those newer style Selenium drivers are going to have a lot more extended frequency response than the old stuff.

 

Now help me a bit: I know there are a bunch of enthusiasts out there, but I still don't get these type of home systems. Is it a nostalgia thing?

[agedhorse]

The HF response of the 808 and 808 drivers on modern horns is pretty bad because the HF driver response rolls off pretty early. The reason it worked ok on the older horns is that they tended to beam at high frequencies and the narrowing of the HF pattern as frequency increased gave a form of acoustic compensation or lift.

 

I would expect that with no additional compensation, the modern drivers will be much more extended in the HF at a wider dispersion angle. This will sound much smoother and more useable.

[Craig Vecchione]

Do you mean the DOD SR823 crossover?

 

Regarding your question (are you being bamboozled);

 

I can't comment at all about a passive crossover modification without some details.

 

However, I can state that the JBL E-140 isn't going to go substantially higher than the 2.5kHz upper range of its specification. Is he stating you can use just the E-140 as a fullrange driver???????

 

Draw your conclusions accordingly.

[michaelhigh]

 

Yeah I think the Old Altec passive crossover does have some compensation built in for the horn rolloff. But the same general effect could be achieved with active equalization. Also Keep in mind that those newer style Selenium drivers are going to have a lot more extended frequency response than the old stuff. Now help me a bit: I know there are a bunch of enthusiasts out there, but I still don't get these type of home systems. Is it a nostalgia thing?

 

 

It's like this: I have 15's, and I was given 2345 lenses. I'm trying to mate those with 2 Crown power amps, a D-75 for highs, and a XLS-802 for subs. Nostalgia, maybe, bottom line is I have the majority of what I need to build a system I can use a bunch of different ways. My only question was will the horn drivers (Selenium 220TI) need HF compensation because a home audio guy mentioned it to me, and in all my years of fooling around with PA gear I'd never heard of it. I do, however, know how to balance a 2-way rig, I was just unsure about HF comp, that's all. That and the compatibility of the Seleniums with the JBL's and the DOD 623 crossover I have. The home audio guys recommend a capacitor to protect the horn if I accidently go below 800 hz, but I'd never heard of it's necessity in pro audio rigs. I'm asking questions in home and pro audio forums and trying to get as much factual info as I can and leave the subjective decisions to myself. So, yeah, nostalgia, if you want to characterize it as such. I'd rather find out if my idea is at all feasible and if I can assemble a rig that could be used as a PA one day and a DJ rig the next, then set it up in my living room for the down days. That's all.

[michaelhigh]

 

Do you mean the DOD SR823 crossover? Regarding your question (are you being bamboozled); I can't comment at all about a passive crossover modification without some details. However, I can state that the JBL E-140 isn't going to go substantially higher than the 2.5kHz upper range of its specification. Is he stating you can use just the E-140 as a fullrange driver??????? Draw your conclusions accordingly.

 

 

If the JBL goes up to 2.5 khz, and horns go down to 800 hz (and I will be using 1.2khz as a starting point for the horns and go down from there to somewhere above 800 hz), I should, in theory, have a full range rig without any frequency gaps. I was unsure about the Selenium's ability to handle the upper region, frequency-wise. I didn't have those particular specs or know how HF comp applied to active crossovers and using EQ's which of course I plan to do. Compatibility was the main issue of uncertainty.

[soul-x]

800 hz is a lot to ask of that driver if any significant power is going to be applied.

 

As for the top end, your biggest problem will probably not be how high in frequency it can go, but how beamy that horn is by the time it gets there.

[Craig Vecchione]

800Hz is below that driver's response range. The recommended crossover is 2kHz, and a 12dB/octave slope, to get 80w power handling. That's a good spec for a 1" driver.

 

The 2345 is a short-ish throw horn so it should work well and not be beamy. It's a good, if huge, horn for home use and smallish indoor venues.

[soul-x]

I'm not remembering which specific horn that is. But short throw or not, the 70's horns tend to be pretty beamy at higher frequencies. That was actually a passable combination with the drivers of the day that rolled off pretty early and smoothly.

 

The newer compression drivers have a much more extended response but may be peaky towards the top end. Fortunately, the response on new CD horns tends to taper up high, so there's a decent match there, too.

 

What may need some pretty extreme eq to get sounding good is an old driver on a new horn (very dull) or a newer driver on one of the old horns (beamy).

 

But really, who knows for this combo? Just try it, be conservative, and make adjustments as necessary.

[agedhorse]

That's an old compact radial horn, it is somewhat beamy at higher frequencies. It's also designed for 1200Hz crossover frequency and if the HF driver is crossed at 24dB/octave to the LF driver then 1200Hz should be ok. At 12dB/octave then 1.6-2kHz is a better choice.

 

Note that your LF driver is not a sub, not even close. Be careful what terminology you use because you could get misleading answers. Don't worry about HF horn comp, that horn doesn't need it nor is it desireable.

 

It's most commonly used on 2" exit large format drivers to compensate for HF driver response droop along with CD horns that do not beam, meaning that there will be roughly a 3dB/octave power rolloff as frequency increases. Slope and knee point will vary with the driver and the horn.

[soul-x]

Here's the thing:

 

A pile of Bag End Cabs loaded with E-140s isn't really gonna thrill anyone here as a SR box: it's meh at best; a cobbled together mess at worse. On the other hand, there's some bassists out there to whom that's a dream cab. You'd probably get at least $200-250 a piece for them. So that could put at least $800 in your hand.

 

You could probably get another $350 for selling both your amps.

That's $1150

 

You were already going to spend $100 on your Selenium drivers, so keeping that in your pocket gives you $1250 to spend.

 

So you could get a pair of the sub-$400 powered Samsons, Wharfdales, or Yorkvilles that guys here on the forum are always bragging on, have a properly biamped rig with all the processing, horn eq built in, and none of the guess work. You could even get one of those $400 Proel subs to help out on bottom. If you bargain shopped, you might even have enough left over to spend a couple hundred on a decent pair of home theater speakers.

 

So then you'd have a nice tidy rig for your sound stuff that hides away in your closet and transports well, a decent home stereo setup that matches your furniture and doesn't look like an 8th grade science project, and both are properly configured, under warranty, and probably sound better at their respective intended purposes than your proposed Frankenrig.

[Craig Vecchione]

It's really not so beamy:

 

http://www.jblpro.com/pub/obsolete/radial_horns1.pdf

[agedhorse]

 

It's really not so beamy: http://www.jblpro.com/pub/obsolete/radial_horns1.pdf

 

 

Not as beamy as an exponential type horn but look closely at the units and you will see the problem...

 

In the vertical plane, the response is 10dB down at 30 degrees relative to 0 degrees at 10kHz. That's a 10x power difference.

 

In the horizontal plane, using 800Hz as a reference which is stated as -5dB, and is 3dB down at 45 degrees (as expected), now look at 7kHz which is 7dB hotter at 30 degrees through on axis. Then at 10kHz there is some form of throat/flair interaction as the horizontal pattern really tightens in and becomes -10dB relative to zero.

 

CD horns were designed to minimize this effect, and this gets back to why combining cabinets with this kind of horn may cause comb filtering artifacts that are much more audible than horns with smoother and more uniform patterns. I'll try to find a polar plot of a good CD horn to compare.

 

Here's a fairly nice example, each polat plot is one octave with 1/3 octave plots overlaid. Notice the uniformity of the response shape across the family of curves. Also notice the difference in shape between horizontal and vertical, this is because this horn utilizes a slightly different geometry in the vertical aspect of the throat and flair.

 

http://www.rcf.it/c/document_library/get_file?uuid=600cff79-5007-4f94-90ab-7f77090241cd&groupId=216492

 

Here's another, look at the horizontal beamwidth versus frequency, you will see that the roll off is pretty smooth and uniform, especially in the 5-15kHz range. I don't care for the vertical pattern on this horn though, certainly not for arraying in the vertical plane.

http://www.usspeaker.com/beyma%20TD-164-1.htm

[Mudcat007]

Here's the thing: A pile of Bag End Cabs loaded with E-140s isn't really gonna thrill anyone here as a SR box: it's meh at best; a cobbled together mess at worse. On the other hand, there's some bassists out there to whom that's a dream cab. You'd probably get at least $200-250 a piece for them. So that could put at least $800 in your hand. You could probably get another $350 for selling both your amps. That's $1150 You were already going to spend $100 on your Selenium drivers, so keeping that in your pocket gives you $1250 to spend. So you could get a pair of the sub-$400 powered Samsons, Wharfdales, or Yorkvilles that guys here on the forum are always bragging on, have a properly biamped rig with all the processing, horn eq built in, and none of the guess work. You could even get one of those $400 Proel subs to help out on bottom. If you bargain shopped, you might even have enough left over to spend a couple hundred on a decent pair of home theater speakers. So then you'd have a nice tidy rig for your sound stuff that hides away in your closet and transports well, a decent home stereo setup that matches your furniture and doesn't look like an 8th grade science project, and both are properly configured, under warranty, and probably sound better at their respective intended purposes than your proposed Frankenrig.

 

But that makes way too much sense and is way too practical. Where's the fun in that!