Questions about compression drivers

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I have questions about the compatibility of some certain components, and would like to hear some impressions of those in the know here. I have 2 JBL 2345 horn lenses, and I am contemplating a purchase of suitable drivers for a system that could be used as a band PA or a home system when not gigging. I've been directed toward the Selenium D220TI 1" compression driver (bolt-on type) to go with the aforementioned lenses, and that choice was made by popular demand as well as for price versus performance reasons.

I'm going to ask some simple questions to confirm my almost-complete lack of hands-on experience with what I'm doing, and to form a basis with which to begin my journey into pro audio.

Question 1- Do the Selenium drivers, of the bolt-on variety, match up to the bolt pattern on the JBL 2345? I believe the 2345 has 3 bolts, 2" apart forming a triangle.
Question 2- Are there any other obvious choices that could be better for the same or less money?
Question 3- I understand that capacitors are recommended to protect the drivers from accidentally receiving too low a frequency, thus blowing the diaphragm... is this desirable/necessary?
Question 4- How do you set up the capacitor, if so? I am so green that I barely have a basic grasp of certain terms, not nearly enough to begin this, but I must start somewhere, and I have been talking to tech support at Parts Express (he helped me pick capacitors if needed) and hanging out at AudioKarma.

Admittedly a lot of this is over my head, but with some simple (rudimentary) diagrams and some patience, I know someone here should be willing to help me through some basics to get my system up and running. I cannot read schematics, so that's why I stress that my basic knowledge will slow me down without some patience. I currently have 4 JBL E-140's in Bag End cabinets, 2 per cab, and hope to integrate the horn lenses with some drivers and capacitors along with a Samson crossover for the PA/home system I'm ever so close to having complete.

When the horns are finished, I plan to build some boxes for the horns to sit on the Bag Ends. So- here's what I have so far: 4 JBL E-140's in 2 Bag End cabs for bottoms, a Samson crossover with CD compensation , and 2 JBL 2345 lenses. To power these I have a Crown XLS-802 for the bottoms, and a Crown D-75 for the horns. Needed are the drivers, capacitors, and patience to guide me through what will be easy for you here but still somewhat foreign to me, especially the math and tech lingo. I put these disclaimers out ahead of time so I don't assume too much and can let the wisdom that is obviously here come forth unfettered. Anyone?:confused:
 
Hi michaelhigh,

first welcome to diyaudio. Now, where to start... I guess it's good to mention that you seem like a very smart and humble person. I am surprised no one has answered yet. I cannot really help you with the particular driver/horn question (one of the reasons why I checked out this post is because I want to learn about these too) but I can help you understand the electronics side of it. I know this is probably going to sound like a bummer, but I recommend you learn electricity basics, more specifically: Ohm's law and Kirchoff's voltage law.
It's liek being able to tell a teaspoon from an ounce if you're a cook. because to understand the basics of crossovers and filters (that's what the aforementioned capacitor does) you need to know how current flows, and what components do to current flow.

In essence the capacitor yields the flow of electricity to the tweeter, sorry, the horn, whatever you want to call the high frequency driver. It does so because a capacitor's reactance Electrical reactance - Wikipedia, the free encyclopedia decreases as the frequency going through it increases. In other words, the lower the frequency in it, the more it will RESIST current flow.
but a single capacitor in series with the driver is, in my knowledge not sufficient as a suitable filtering element. A real component crossover circuit that has inductors and capacitors is what's needed.

So yes, a capacitor is necessary. If no capacitor is used, the low frequencies will damage the diaphragm of the tweeter. Euh, Horn. you understand!

The same goes with low frequency drivers: you must prevent high frequencies from exciting their voicecoil, because at high powers this can fry the voicecoil!

Ohm, I just read the last part of your post and found that you already have a crossover. Is it the type that you plug after the power amplifier, or before?

If it is after the power amplifier, then it does the job better than the capacitor you were talking about adding. Do not connect this capacitor after the crossover, it will sound horrible. Even though it won't damage your crossover, or horn. Ah, got it that time!

cheers,

gain-wire
 
Here's the basic signal flow. It starts at the source, whatever that may be (mic or line level) into an audio mixer, and from there to the crossover. Then the low goes to it's own EQ, then on to it's amp, and concurrently, the high goes to it's EQ, then on to it's amp. When I use regular full-range 2-ways on top I go full-range on top, bypassing the crossover completely, and at the same time run the subs through the crossover to whatever frequency sounds best, usually 80 hz or below, depending on how tight it needs to be. Now, I thought I might do the same in reverse- bypass the lows and tune the horns above 2000 hz or so. This is where the experimenting comes in. I've heard a good crossover point could ostensibly be anywhere from 1200 to 2500 hz as the E-140's go clear up to 2500. This is where the fun comes in! My ear ought to tell me where the crossover point should go, because the point will be where the sound is smoothest within the range, and then the gain controls are set for the most consistant gain structure following basic rules of thumb for unity gain. I use roughly 7 out of 10 as a reference, and set the power amps to the listening level. YMMV but that's always worked for me. Set the channels at 7, set the master at 7, use the trims to get the channels to total 7 on the main meter, and then the amps. That part I'm cool with. Also to figure in is the aux levels, which are structured similarly. I use two auxes, pretty common for a modest rig. If I stay at 7 or below, I can balance auxes with mains to achieve the final master level that gets sent on to the crossovers, then on to the EQ's, then I even compress if I want to before the amp(s). My compressor has a gate, so that comes in handy to tame open mics. I just need to get the last details I mentioned down, that of how to set up the capacitor if necessary and the drivers. I've got a basic understanding of impedance as it pertains to loudspeakers...I hope my long-winded description of gain structure makes sense to you. Like me with your advice, you might want to study it over if need be, I'll be spending time with your post to try to get it through my thick skull... Thank you for your response. :D
 
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Thanks for your reply. In answer to your question, the crossover comes before the power amp. I can give you more info about system and gain structure, I think I just typed a big long post on it but it appear to have dissapeared. Entirely possible. The tech at Parts Express said I can wire a capacitor between the female 1/4" jack and the driver lug, on the positive lead, and get protection from low freq accidents. I could be wrong, or he could be wrong, but he said he had plenty of experience with that and it did offer protection. YMMV. If you need details on signal flow or gain structure let me know. I have that part down, I just need to know if I really do need a cap in between the jack and driver lug, and details about driver and horn compatibility. Most of it makes sense to me but, I'm still trying to nail down all the details. Better that way before it starts costing too much in unnecessary repairs. Edit: I'm being moderated, hence the double post. Sorry.
 
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Question 1- Do the Selenium drivers, of the bolt-on variety, match up to the bolt pattern on the JBL 2345? I believe the 2345 has 3 bolts, 2" apart forming a triangle.
http://www.jblpro.com/pub/obsolete/Radial_Horns1.pdf

Selenium D220Ti-OMF-8 1" Titanium Horn Driver 8 Ohm 2/3 Bolt | Parts-Express.com

Yes, very likely.


Question 2- Are there any other obvious choices that could be better for the same or less money?
No. There are better choices for more money, however.


Question 3- I understand that capacitors are recommended to protect the drivers from accidentally receiving too low a frequency, thus blowing the diaphragm... is this desirable/necessary?
Yes, you need a protection cap in series with the compression driver to protect it from turn-on/turn-off transients, DC on the amp output, or operator error.


Question 4- How do you set up the capacitor, if so? I am so green that I barely have a basic grasp of certain terms, not nearly enough to begin this, but I must start somewhere, and I have been talking to tech support at Parts Express (he helped me pick capacitors if needed) and hanging out at AudioKarma.
Choose a value that rolls off an octave lower than your anticipated crossover frequency given the driver impedance. Read up your active crossover manual, or Section 3-2 here:

http://www.jblproservice.com/pdf/Vintage JBL-UREI Electronics/JBL-5235 manual.pdf
 

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The Selenium D220Ti-OMF-8 is Bolt on.
The Selenium D220Ti is Screw on.
http://www.selenium.com.br/site/assets/produtosfinal/292_pdfManual.pdf
Measures are in metric but I think they are the same. Confirm on your side (JBL's).
(Note: PE shows wrong (link) pdf for Ti/screw on).
Thank you...I see the triangulated screws. Another question- When I connect the capacitor, do I do it between, say, a female 1/4" jack positive lug and the positive driver lug? I plan to build a box to hold the lens and driver, so I can connect the speaker wire with a 1/4 male plug. Do I have this part right, or is it someother way I am unfamiliar with? Thanks in advance...
 
Answers #1 & #2

I have questions about the compatibility of some certain components, and would like to hear some impressions of those in the know here. I have 2 JBL 2345 horn lenses, and I am contemplating a purchase of suitable drivers for a system that could be used as a band PA or a home system when not gigging. I've been directed toward the Selenium D220TI 1" compression driver (bolt-on type) to go with the aforementioned lenses, and that choice was made by popular demand as well as for price versus performance reasons.

I'm going to ask some simple questions to confirm my almost-complete lack of hands-on experience with what I'm doing, and to form a basis with which to begin my journey into pro audio.

Question 1- Do the Selenium drivers, of the bolt-on variety, match up to the bolt pattern on the JBL 2345? I believe the 2345 has 3 bolts, 2" apart forming a triangle.
Question 2- Are there any other obvious choices that could be better for the same or less money?

JBL 2245 is a Compact, Short-Throw, Radial Horn. It is not designed to work with an Acoustic Lens. Also, these horns do not have the bi-radial profile of subsequent designs. See
http://www.jblpro.com/pub/obsolete/Radial_Horns1.pdf

[1] A JBL 2426H/J Compression Driver (current model) may be mounted to this horn. It has a 1" dia. throat entry port centered in a 1-3/8"-18 male threaded spigot. A 4-1/4" circular flange (snout) containing (3), 1/4"-20 threaded mounting holes equally spaced on a BCD of 2-1/4", is screwed onto the driver. See:
http://www.jblpro.com/pub/components/2426.pdf

Note that older JBL, compatible, but obsolete, drivers may also be mounted to this horn. These include 2410, 2420, 2421A/B, 2425H/J, 2461, & 2470.
If you're buying old drivers, with the plan to have them re-magnetized and re-diaphragmed, Brush Wellman makes superior replacement diaphragms from beryllium (Be al la TAD) for this purpose. At the moment only 4" dia. diaphragms are being offered. In the near future, product line is to be extended to the smaller sizes as well. See:
http://www.electrofusionproducts.com/docs/EQF3023_PrecisionBerylliumDiaphragm.pdf

Other candidate drivers include those from P-Audio:
P.Audio System Co., LTD

[2] P-Audio PA-DE34
P.Audio System Co., LTD

[3] P-Audio BM-D450
http://www.paudiothailand.com/pdf/products/BM-D450.pdf

[4] P-Audio BM-D440
http://www.paudiothailand.com/pdf/products/BM-D440.pdf

[5] P-Audio BM-D446
http://www.paudiothailand.com/pdf/products/BM-D446.pdf

[6] P-Audio PreNeo-450N1
http://www.paudiothailand.com/pdf/products/PreNeo-450N1.pdf
The Selenium drivers you are considering are documented here as well:

[7] Selenium D2200Ti-OMF
http://www.selenium.com.br/site/assets/produtosfinal/292_pdfManual.pdf

[8] Selenium D2500Ti-Nd
http://www.selenium.com.br/site/assets/produtosfinal/304_pdfManual.pdf

Note: There are small differences in the mounting dimension due to the measurement standard used for design of a particular driver. Some require M6 Cap Screws (metric), others require 1/4-20 cap screws (English) for fasting the driver to a horn, and the BCD's very 0.005" or so. These differences should not present a problem when fastening drivers to the horns. All listed here have a 1" dia. throat exit.

Regards,
WHG
 
My horn is a 2345, you typed that it was a 2245 but sent me the lit for the 2345. Does that change your response, because I'm interested in all the input I can get, once the proper facts are assembled. Suggest a driver for the 2345 and give me your impressions on the D220TI or recommend something cheaper that might sound better. Remember that this is a potentially short throw application, and small to medium sized clubs at best. Thanks for taking the time to respond.
 
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Typo! & Beef

My horn is a 2345, you typed that it was a 2245 but sent me the lit for the 2345. Does that change your response, because I'm interested in all the input I can get, once the proper facts are assembled. Suggest a driver for the 2345 and give me your impressions on the D220TI or recommend something cheaper that might sound better. Remember that this is a potentially short throw application, and small to medium sized clubs at best. Thanks for taking the time to respond.

Typo! Should Read 2345 to be consistent with the reference given. I like the P-Audio drivers better than the rest. If you compare the response graphs you can see why. Then look at sensitivity and power handling. For club venues, beefy is better. The folks like it loud and you will want it clean.

Regards,
WHG
 
Point well-taken, Flaesh. I've heard nothing but good about the Selenium, it's just a matter if it mates well with the 2345. When I speak to someone who has used the 2345 they can describe it's native characteristics to me and that will make the difference. Since my primary goal is to have a PA rig I can use in my house and locally I want it to serve both purposes equally well, but on a budget of less than $100 for HF. I ought to get in just under the wire with the JBL horns free and the Seleniums for just under $100. Thanks for your input. I know how manufacturers inflate claims to sell gear. The other two names come well-recommended.
 
You need a lot MORE than "a cap" to protect your compression driver.
I would not use LESS than a 24db/oct (4th order) xover in a PA/SR situation.
That's two caps and two coils.
You can make ur own, cheap, fwiw.
You do not need fancy caps - you can "steal them" from old CRT computer monitor chassis, etc...


You should also employ some sort of power limiting/clipping protection, unless you like lots of
distorted hash and fried VCs in ur new drivers.

The simplest method for protection is a lightbulb (yes) in series with the driver. It works.
Do a search for it?
The next better method is a soft knee limiter before the power amp, set to prevent more power than the driver is permitted and the amp clipping.

Of course, the usual thing that happens in a semi-pro PA is that it is set up to max SPL and then the band plays LOUDER... the result is either distortion, blown drivers, or IF there is limiting, massive compression of the sound.

Diffraction lenses tend to reproduce hash very well...they add their own too it seems.

If you can handle the extra weight (doubtful) run tube amps on the horns... they clip much more gently and don't tend to make as much hash...

You can use an electronic xover, of course, but then unless you literally GLUE or cover the controls for the HF settings, somebody could or it accidentally could be turned and cause ur stuff to fry...

The JBL E-140 are less than optimum for bass use, especially given the availability of very high power drivers today at reasonable prices... there more "tone drivers" for instrument amps, imo. If they're not fried you might resell them and buy one of the newer bass drivers.

Realistically, if you want a great PA sound you need to divorce the midbass/midrange from the bass section.

But run whatcha got is what people need to do - but keep ur eyes open for the future...

_-_-bear

PS. make sure you do NOT clip the Crown D-75 - it makes nasties when clipped... you might search for a better amp...
 
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