yup, I think you pretty much understood my suggestion, but of course I blithely assumed that your existing system would have a pre-amp level line out - as the assumption was unilateral, only one of us was made an a$$.
Even though you have an existing sub (Polk) if you wanted to use the Advents as woofers - rather than retiring / selling them- there's no reason you couldn't use a small sub-woofer plate or stand-alone amp (such as the very nifty Dayton AP150) to power them.
Considering all that's transpired in this thread so far, I'd be inclined to recommend a Pensil with the Alpair10.3 or Ps if your budget could stretch that far. Relatively simple build, at approx 10" x 14" D, not much more floor space than I (vaguely) recall the Large Advents, and of course no stands required.
Even though you have an existing sub (Polk) if you wanted to use the Advents as woofers - rather than retiring / selling them- there's no reason you couldn't use a small sub-woofer plate or stand-alone amp (such as the very nifty Dayton AP150) to power them.
Considering all that's transpired in this thread so far, I'd be inclined to recommend a Pensil with the Alpair10.3 or Ps if your budget could stretch that far. Relatively simple build, at approx 10" x 14" D, not much more floor space than I (vaguely) recall the Large Advents, and of course no stands required.
Okay, after some long thought I have decided that, despite the great appeal of the Pensils, I am going for Fostex FF125wk in BR enclosures and try to run them with my Polk sub. A man from Moldova sells these nice enclosures for $150. Not DIY but something that I don't think I could build with the $80 baltic birch quote I got today locally, the cost of veneer, etc. The dimensions he quoted me (326x248x172) are a little larger than the Fostex recommendations, but I am hoping the extra volume will be a boon for my application.
http://www.ebay.com/itm/speaker-box-for-Fostex-FF-125-K-pair-/150970167612?pt=Speakers_Subwoofers&hash=item232685f13c
But if the Polk sub proves unappealing or intolerable, I am going to go with Plan B. Run the Fostex in a FAST with the Advents in the following way. I have a Adcom 5.1 channel preamp that I forgot about, so I can use the front preamp outs to run the Fostexs and the rear preamp outs (set to large) to run the Advents through the Dayton APA 150 that Chris recommended. I had no idea that thing has a low pass filter. What a great idea. Now I don't need to make passive crossovers for the Advents. Does anyone see problems going this route. Now that I think about it, maybe this should be my Plan A.
http://www.ebay.com/itm/speaker-box-for-Fostex-FF-125-K-pair-/150970167612?pt=Speakers_Subwoofers&hash=item232685f13c
But if the Polk sub proves unappealing or intolerable, I am going to go with Plan B. Run the Fostex in a FAST with the Advents in the following way. I have a Adcom 5.1 channel preamp that I forgot about, so I can use the front preamp outs to run the Fostexs and the rear preamp outs (set to large) to run the Advents through the Dayton APA 150 that Chris recommended. I had no idea that thing has a low pass filter. What a great idea. Now I don't need to make passive crossovers for the Advents. Does anyone see problems going this route. Now that I think about it, maybe this should be my Plan A.
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DoctorJ - if the signal processing is anything like the several 5.1 receivers I've played with recently, the rear pre-amp outputs would likely have very little LF output except in "5 channel stereo" mode.
Also note that the AP150 is bridgeable if you need more than the 75 WPC - which reminds me that I should try that myself ( I bought a pair of them for exactly this flexibility) , as well as a line out pass through for "daisy chaining" the unfiltered signal to additional amps. This would allow using the Adcom's main front L&R pre-outs, thereby maintaining the capability to use its surround processing modes now or in the future. It still would be very helpful to include some HO filtering for the Fostex - easily achievable with a simple PLLXO at that amp's inputs.
A question about the Advents - have the woofer surrounds been replaced within the past 10yrs or so? As with many commercial speakers of that vintage, the original foam surrounds were notorious for deterioration - they can limp along for years near approaching the edge of failure (brittle , slight tears and cracks), then one day simply crumble to dust.
Also note that the AP150 is bridgeable if you need more than the 75 WPC - which reminds me that I should try that myself ( I bought a pair of them for exactly this flexibility) , as well as a line out pass through for "daisy chaining" the unfiltered signal to additional amps. This would allow using the Adcom's main front L&R pre-outs, thereby maintaining the capability to use its surround processing modes now or in the future. It still would be very helpful to include some HO filtering for the Fostex - easily achievable with a simple PLLXO at that amp's inputs.
A question about the Advents - have the woofer surrounds been replaced within the past 10yrs or so? As with many commercial speakers of that vintage, the original foam surrounds were notorious for deterioration - they can limp along for years near approaching the edge of failure (brittle , slight tears and cracks), then one day simply crumble to dust.
Hi, Chris. Yes, I had the surrounds professionally refoamed about 1.5 years ago, so they are good to go. I like your daisy chaining idea (again I didn't realize that you could do that with the AP150), though I maybe can still get away with using the Adcom in 5 channel stereo mode.
In regard to "HO filtering," could you elaborate on what you mean? Why it might be necessary? Are you talking BSC? Or something else?
In regard to "HO filtering," could you elaborate on what you mean? Why it might be necessary? Are you talking BSC? Or something else?
"HO" = typo, S/B HP ( High Pass) although at much lower frequency than would be considered the norm in most commercial 2-ways, which are often in the middle of the most critical mid-band area.. IINM, the Advents were at 1000Hz, which could well explain the tremendous failure rates of earliest generation of the wonder but overtaxed tweeters - I was in the trade off and on for a good part of the mid 70s to late 90s, and when rode hard and put up wet, tweeters on the Advents failed famously long before the foam surrounds started rotting
For example, when using FR drivers of approx the same weight class as the FF125WK, I tend to use between 100 - 150 for summed/ mono bass in 5.1 systems, and as high as 300 or so for stereo bass. As woofers, I think the Advents could easily be operated as high as 300-500 without any issues.
With careful enclosure design / placement, and selection of XO points to coincide with the step loss frequency (which is dependent on the baffle dimensions), the need for any additional BSC can probably be avoided.
For example, when using FR drivers of approx the same weight class as the FF125WK, I tend to use between 100 - 150 for summed/ mono bass in 5.1 systems, and as high as 300 or so for stereo bass. As woofers, I think the Advents could easily be operated as high as 300-500 without any issues.
With careful enclosure design / placement, and selection of XO points to coincide with the step loss frequency (which is dependent on the baffle dimensions), the need for any additional BSC can probably be avoided.
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Thanks again Chris. That makes much more sense now. I think 300-500hz for the Advents would be fine: the only reason I know this is b/c I just ran into a guy at a resale shop who said he used to cut open Advents with crappy utility cabinets, disconnect the tweeter and just run them open as quasi open baffle speakers. He said they sounded very good (i.e., open) but with not much on top. I suspect the reason for doing so is that with just the mids and highs going to the Fostex drivers I can push them a little harder with rock music and home theater? But the Dayton's low pass only goes to 150hz, so I am kind of stuck there, right? So the HP filer would have to start there?
It wouldn't be hard to fabricate a 2-way PLLXO for whatever frequency you decide, and run the AP150 or any available power amp full range
For a simple 1st order 2-way, the maximum part count for such an XO would be 2 caps and 2 resistors per channel - the little box and RCA connectors will likely cost more.
I used the calculator imbedded here:
TLS.org | Passive Line-Level Crossover
There's also a link on this page to Passive Baffle Step compensation design by Paul Joppa - something that I've never personally played with
Passive Line Level Baffle Diffraction Step Compensation
For a simple 1st order 2-way, the maximum part count for such an XO would be 2 caps and 2 resistors per channel - the little box and RCA connectors will likely cost more.
I used the calculator imbedded here:
TLS.org | Passive Line-Level Crossover
There's also a link on this page to Passive Baffle Step compensation design by Paul Joppa - something that I've never personally played with
Passive Line Level Baffle Diffraction Step Compensation
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