JBL L-200 upgrade

[macrojack]

I wondered about that time-alignment issue myself. And I found this tool:

http://www.mcsquared.com/wavelength.htm

I have to estimate this number but my horn diaphragm is about 16 to 18 inches behind my woofer dustcap. At 400 HZ. (my X/O point) the wavelength is about 34 inches. That means that my drivers should be 180 degrees out of phase. I can't hear that but it might be one of those problems you aren't aware of until it is solved.

It is true that this can be solved with my Drive Rack but I first have to figure out how.

I have a more annoying problem I would like to overcome. There is a low level hiss emitting from all 4 drivers whenever the amps are running. This occurs even when the preamp (JRDG Capri) is muted and it is not affected by the volume control when the mute is off. Any ideas?

I suspect it has something to do with my amplifier gain settings but I don't really understand how that works. My Rowland amp is 100 watts per channel (ICE power) and my woofer amp is 180 watt Perreaux. At my listening levels on pre-recorded music and movies, I can't imagine that clipping would be an issue, and indeed signal barely shows on my Drive Rack meters. This is apparently what amplifier level matching is supposed to prevent.

The Drive Rack is designed for live professional sound reinforcment applications and has many feayures I just don't need like feedback supression. Maybe the amp level matching falls into that category. Does it?

Thanks for the compliments. I'm from the high end audio world and have been used to much less performance for a lot more money. This project cost me just over $4K total including the Drive Rack, the second amp, and wire and connectors. And it is way more fun and exciting than prescribed, off the shelf packages.

[hjames]

Such hissing sounds like a noise floor issue ... your preamp feeds the dbx Drive rack, then that feeds the Perreaux and Rowland amps?

Do you have the hissing when the dbx is powered down? (not just bypassed but actually out of the circuit).
The dbx gear is a step above behringer, but its still lower end pro gear ... and that could be your noise ...
Have you tried using a higher end electronic crossover?
instead of the dbx Drive Rack PA, maybe upgrade to an Ashley (I use an XR 1001) or perhaps one of the Marchand units?

If you are talking about a driver being 180 degrees out of phase, thats easily cured by swapping the + and - leads to that driver - it was recommended that I do that for the 2235 woofer that runs on the low-side of my active split on my 4341s 4 ways). Made a difference in my system. Better to do that fix discretely than to do it digitally, if its 180 degrees out.

... my drivers should be 180 degrees out of phase. I can't hear that but it might be one of those problems you aren't aware of until it is solved ...

I have a more annoying problem I would like to overcome. There is a low level hiss emitting from all 4 drivers whenever the amps are running. This occurs even when the preamp (JRDG Capri) is muted and it is not affected by the volume control when the mute is off. Any ideas?

I suspect it has something to do with my amplifier gain settings but I don't really understand how that works. My Rowland amp is 100 watts per channel (ICE power) and my woofer amp is 180 watt Perreaux. At my listening levels on pre-recorded music and movies, I can't imagine that clipping would be an issue, and indeed signal barely shows on my Drive Rack meters. This is apparently what amplifier level matching is supposed to prevent.

The Drive Rack is designed for live professional sound reinforcement applications and has many features I just don't need like feedback suppression. Maybe the amp level matching falls into that category. Does it?

Thanks for the compliments. I'm from the high end audio world and have been used to much less performance for a lot more money. This project cost me just over $4K total including the Drive Rack, the second amp, and wire and connectors. And it is way more fun and exciting than prescribed, off the shelf packages.

[macrojack]

hjames - I'll try those experiments. Thank you.

Are my calculations re: the phase issue correct? It seems like the 180 out of phase is too easy and too convenient.

Then again, I'm not sure I'll even hear it. Will report back after testing.

The dbx unit provides more than XO. I bought the matching microphone and I find the RTA works pretty well. I also use the EQ functions as well as I can.
Aside from being a computer, which is to say incompatible with my aging brain, the dbx is quite comprehensive and convenient ..... and maybe noisy.

Would I be better off with a well-designed passive crossover?

[hjames]

I tend to think once you've gone to the hassles of biamping that you'd never be happy giving up the advantage of having the woofer directly coupled to a high quality amp with no passives to interfere with the sound.

There are folks here who use Behringer and dbx RTAs for the digital tweaking capabilities they provide - but there is that trade-off with them having a heightened noise floor. Some folks use RTAs just as tools to check and see how their system is prforming, then they power it down and pull it offline for normal sound use. What works great for PA and commercial sound reinforcement use can be far too noisy for home use.

hjames - I'll try those experiments. Thank you.

Are my calculations re: the phase issue correct? It seems like the 180 out of phase is too easy and too convenient.

Then again, I'm not sure I'll even hear it. Will report back after testing.

The dbx unit provides more than XO. I bought the matching microphone and I find the RTA works pretty well. I also use the EQ functions as well as I can.
Aside from being a computer, which is to say incompatible with my aging brain, the dbx is quite comprehensive and convenient ..... and maybe noisy.

Would I be better off with a well-designed passive crossover?

[toddalin]

I wondered about that time-alignment issue myself. And I found this tool:

http://www.mcsquared.com/wavelength.htm

I have to estimate this number but my horn diaphragm is about 16 to 18 inches behind my woofer dustcap. At 400 HZ. (my X/O point) the wavelength is about 34 inches. That means that my drivers should be 180 degrees out of phase. I can't hear that but it might be one of those problems you aren't aware of until it is solved.

It is true that this can be solved with my Drive Rack but I first have to figure out how.

I have a more annoying problem I would like to overcome. There is a low level hiss emitting from all 4 drivers whenever the amps are running. This occurs even when the preamp (JRDG Capri) is muted and it is not affected by the volume control when the mute is off. Any ideas?

I suspect it has something to do with my amplifier gain settings but I don't really understand how that works. My Rowland amp is 100 watts per channel (ICE power) and my woofer amp is 180 watt Perreaux. At my listening levels on pre-recorded music and movies, I can't imagine that clipping would be an issue, and indeed signal barely shows on my Drive Rack meters. This is apparently what amplifier level matching is supposed to prevent.

The Drive Rack is designed for live professional sound reinforcment applications and has many feayures I just don't need like feedback supression. Maybe the amp level matching falls into that category. Does it?

Thanks for the compliments. I'm from the high end audio world and have been used to much less performance for a lot more money. This project cost me just over $4K total including the Drive Rack, the second amp, and wire and connectors. And it is way more fun and exciting than prescribed, off the shelf packages.

If your "Rowland" is really a "Roland," that could be your problem.

If you have RTA capabilities, this would be the preferable way to set your speaker component phasing. Check it both ways and see which provides the overall smoothest response. Forget about one frequency as the levels of some will come up while others go down.

I initially used to use a tone at the ~crossover frequency and use a sound level meter to determine which way was louder with the rationale that the louder setting would mean that the two speakers were in proper phase.

Well yes and no. Often this frequency could be louder, but other neighboring frequencies could be worse. Once I got the Behringer with the 62 bands of RTA, it was easy to see the error of my ways and now I look for the smoothest overall response.

[macrojack]

Todd - This is my amp and preamp: http://www.jeffrowland.com/CapriWith102-front.htm

I know for a fact that JRDG is among the quietest equipment on the market. It's fully balanced, dual mono and very well shielded. The chassis are made from a hollowed out aluminum billet.

hjames - My noise floor is pretty quiet. It doesn't interfere with program material at all. It's really quite faint even with my head in the horn. It reminds me of putting a seashell up to my ear - sounds like the ocean.

It's just audiophile anality that drives me to try and eliminate it. Oh yeah, my wife complains about it a little too.

By the way, you were right. It is coming from the dbx.

[macrojack]

Just out of curiosity, since my dbx is noisy, where's a brother to look for digital devices like the Drive Rack PA that will not be noisy. I've seen the words "a lot more money" used to describe the upgrade. So what brands might I investigate (dream about) and what do they cost?

And will I still find that analogue is better?

In my world, no kind of digital playback quite does what an LP can do.

[hjames]

Just out of curiosity, since my dbx is noisy, where's a brother to look for digital devices like the Drive Rack PA that will not be noisy. I've seen the words "a lot more money" used to describe the upgrade. So what brands might I investigate (dream about) and what do they cost?

And will I still find that analogue is better?

In my world, no kind of digital playback quite does what an LP can do.

Well, my decision to go with an Ashly crossover was based in no small part on the discussion here - http://audioheritage.org/vbulletin/s...?t=2316&page=9

Of course, that discussion started in 2004 and many of them have moved on to even better gear since then, but being on a budget, a used Ashly worked way better for me than a used JBL M552 had ...