Questions about compression drivers

michaelhigh · 29th November 2010, 09:01 PM

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?

gain-wire · 29th November 2010, 10:31 PM

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

michaelhigh · 11:33 PM

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.

michaelhigh · 11:45 PM

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.

ZilchLab · 30th November 2010, 12:19 AM

Quote:

Originally Posted by michaelhigh

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.

Quote:

Originally Posted by michaelhigh

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.

Quote:

Originally Posted by michaelhigh

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.

Quote:

Originally Posted by michaelhigh

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/Vin...5%20manual.pdf

michaelhigh · 30th November 2010, 12:23 AM

Thank you, Z.

Inductor · 01:06 AM

The Selenium D220Ti-OMF-8 is Bolt on.
The Selenium D220Ti is Screw on.
http://www.selenium.com.br/site/asse..._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).

michaelhigh · 30th November 2010, 01:41 AM

Quote:

Originally Posted by Inductor

The Selenium D220Ti-OMF-8 is Bolt on.
The Selenium D220Ti is Screw on.
http://www.selenium.com.br/site/asse..._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...

michaelhigh · 30th November 2010, 04:25 AM

Anyone else on the mounting of the cap? How?????

ZilchLab · 30th November 2010, 04:37 AM

Quote:

Originally Posted by michaelhigh

Anyone else on the mounting of the cap? How?????

You snip and strip the ends of one of the driver leads and wire-nut the cap in line. Buy a suitable-size cable/conduit clamp at the hardware store and screw that to the baffle. Done.

29th November 2010, 09:01 PM	#1
michaelhigh diyAudio Member Join Date: Nov 2010 Location: Belleville, IL	Questions about compression drivers 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?

29th November 2010, 10:31 PM	#2
gain-wire diyAudio Member Join Date: Nov 2004 Location: NCR	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 __________________ Trans-directional-servo-logamp non-zerocrossing autogain compressing thingamajig

29th November 2010, 11:13 PM	#3
michaelhigh diyAudio Member Join Date: Nov 2010 Location: Belleville, IL	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. Last edited by michaelhigh; 29th November 2010 at 11:33 PM.

29th November 2010, 11:26 PM	#4
michaelhigh diyAudio Member Join Date: Nov 2010 Location: Belleville, IL	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. Last edited by michaelhigh; 29th November 2010 at 11:45 PM.

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30th November 2010, 12:23 AM	#6
michaelhigh diyAudio Member Join Date: Nov 2010 Location: Belleville, IL	Thank you, Z.

30th November 2010, 04:25 AM	#9
michaelhigh diyAudio Member Join Date: Nov 2010 Location: Belleville, IL	Anyone else on the mounting of the cap? How?????

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