The B&C should probably not be used so close to its Fs =126Hz. [/QUOTE
Fs is usually less of a problem as long as the horn is loading the driver, it drops alot
Merry Christmas,
Anders
My experience with small throat size vs cone area is that it will ultimately result in narrowing of the usable bandwidth. You will have a narrower usable frequency range with an increased output but peak output in the center of that range. The small rear chamber on the back of the JBL follows the theory and practice of much earlier work done by Paul Klipsch. If you go back and read some of his papers you will find this along with the formula to calculate the back chamber volume. This rear chamber will extend the lower usable output of the cone horn combination by 1.2 times the normal horn cutoff calculation for an exponential horn. I am remembering this off the top of my head, but I think the formula was something like 2.9xA/R= volume of rear chamber. A is the area of the throat time the rate of expansion. It been 20 years or more since I used the formula so I may be off here. If I remember correctly this formula is in the RCA engineers handbook of old. I don't know where my copy is or I would look up the formula for you.
Bi-amped ESL/Altec 416 & Subs
Regarding the Altec 416, why the 16 ohm version chosen over the 8 ohm? Was that only because you maybe driving them with a tube amp?
I will be using Gary Dahl’s 3 cu. ft. (interior) sealed cabinets and limiting the response of these alnico midwoofers to between 700Hz and 70Hz, to minimize distortion.
Ever since I dared to pursue high end audio, full range ESLs have been the ultimate. Thus, what now drives me further to pursue this build is your likening of the 416’s presentation to “……. a wall-sized electrostat….”. So as full range ESLs must be the path not taken (i.e. low power First Watt amps are too cool to pass on ), I hope to succeed with this two-way system by using one of the painfully few HF/MF ESL drivers available anywhere.
SoundLab has very graciously offered to supply me with a pair of their MiniStats, along with the self-biasing circuitry-less the unneeded 6.5” woofer and crossover. SOUND LAB
SoundLab’s Roger West says the MiniStat’s ESLs have 92db sensitivity and are flat from 950Hz to 20kHz.
And I see here that John Sheerin has measured a pair of 416s “….in boxes outdoors as being fairly flat up to about 1kHz.” http://www.diyaudio.com/forums/multi-way/100392-beyond-ariel-781.html
So, between Rod Elliot’s comprehensive pair of articles on bi-amping BiAmp (Bi-Amplification - Not Quite Magic, But Close) - Part 1 and using this crossover http://www.firstwatt.com/pdf/prod_b4_man.pdf , I would think that crossing these stats with the 416s should be relatively easy, or at least without, much,
if any, compromise.
Also, can you hazard a guess over how the 416’s sensitivity will drop from
its datasheet’s 98db when placed in 3 cu. ft. (interior) sealed cabinets?
My one worry is what Rod Elliot seems to be saying about power requirements-regardless that with line level crossovers no amplifier power losses will occur. At 11 feet way, I don’t think that my ears can tolerate average SPLs much above 80 to 83db. So assuming the 416’s impedance won’t drop much below 98db, I would think that my First Watt F4 amp will have no problems driving them. It does 25 wpc/8 ohm and 40 wpc/4 ohms. But according to this table BiAmp (Bi-Amplification - Not Quite Magic, But Close) - Part 1 , for a 90db HF/MF driver, even if I crossover at ~ 800Hz, so that the Stats only require ~ 38% of the total power needed by them and the 416s (40 wpc??), it looks like the Stats will need ~ 15.2 wpc. The trouble is that my First Watt J2 amp does 25 wpc/ 8 ohms but only 13 wpc/ 4 ohms. Are my calculations, my interpretation Rod’s table or other reasoning in error?
Anything else about this HF/MF stat and GPA Altec 416 build that I may have overlooked?
Regarding the Altec 416, why the 16 ohm version chosen over the 8 ohm? Was that only because you maybe driving them with a tube amp?
I will be using Gary Dahl’s 3 cu. ft. (interior) sealed cabinets and limiting the response of these alnico midwoofers to between 700Hz and 70Hz, to minimize distortion.
Ever since I dared to pursue high end audio, full range ESLs have been the ultimate. Thus, what now drives me further to pursue this build is your likening of the 416’s presentation to “……. a wall-sized electrostat….”. So as full range ESLs must be the path not taken (i.e. low power First Watt amps are too cool to pass on ), I hope to succeed with this two-way system by using one of the painfully few HF/MF ESL drivers available anywhere.
SoundLab has very graciously offered to supply me with a pair of their MiniStats, along with the self-biasing circuitry-less the unneeded 6.5” woofer and crossover. SOUND LAB
SoundLab’s Roger West says the MiniStat’s ESLs have 92db sensitivity and are flat from 950Hz to 20kHz.
And I see here that John Sheerin has measured a pair of 416s “….in boxes outdoors as being fairly flat up to about 1kHz.” http://www.diyaudio.com/forums/multi-way/100392-beyond-ariel-781.html
So, between Rod Elliot’s comprehensive pair of articles on bi-amping BiAmp (Bi-Amplification - Not Quite Magic, But Close) - Part 1 and using this crossover http://www.firstwatt.com/pdf/prod_b4_man.pdf , I would think that crossing these stats with the 416s should be relatively easy, or at least without, much,
if any, compromise.
Also, can you hazard a guess over how the 416’s sensitivity will drop from
its datasheet’s 98db when placed in 3 cu. ft. (interior) sealed cabinets?
My one worry is what Rod Elliot seems to be saying about power requirements-regardless that with line level crossovers no amplifier power losses will occur. At 11 feet way, I don’t think that my ears can tolerate average SPLs much above 80 to 83db. So assuming the 416’s impedance won’t drop much below 98db, I would think that my First Watt F4 amp will have no problems driving them. It does 25 wpc/8 ohm and 40 wpc/4 ohms. But according to this table BiAmp (Bi-Amplification - Not Quite Magic, But Close) - Part 1 , for a 90db HF/MF driver, even if I crossover at ~ 800Hz, so that the Stats only require ~ 38% of the total power needed by them and the 416s (40 wpc??), it looks like the Stats will need ~ 15.2 wpc. The trouble is that my First Watt J2 amp does 25 wpc/ 8 ohms but only 13 wpc/ 4 ohms. Are my calculations, my interpretation Rod’s table or other reasoning in error?
Anything else about this HF/MF stat and GPA Altec 416 build that I may have overlooked?
My memory's no better
, so from Badmaieff & Davis's book: A = V/2.9R:V = 2.9AR
GM
Thanks GM. I knew I was close but wasn't sure after all these years. It does extend the lower usable range of the horn by a significant amount. Goes against those who are using an open back on a horn, that is plainly the wrong direction in my eyes. A cone diver under those conditions becomes unloaded at the lower frequencies and that is why some complain that the cone will slam into the back of the horn. It can be a challenge to get a tight fitting chamber to fit around a driver but I have always been able to accomplish that. I do the same on my smaller mid-range horns, not to keep bass out from another device but to properly load the mid driver. If you look at a driver under these conditions even at high SPL levels you can hardly discern that the driver is moving. This is much closer to what you would see in a true compression driver, very small excursion vs output.
Since the system I'm building is somewhat similar to what's been talked about here, here's my latest incarnation. I added a super tweeter I designed based off a JBL 2402 to bring down the DI of the system above 10k (crossed at 9k). This worked pretty well despite the vertical polar response getting destroyed around crossover due to the large spacing and the tweeter's response not being too smooth above 10kHz. I don't really hear it going from sitting to standing though. Then I added a JBL 2225 in a sealed box between 80 and 800Hz, relegating my Sub1500 to 80Hz and down. This improved stored energy performance (measuring boinks ala Linkwitz) in the ~500hz - 800hz range where I was using the 2435 and LeCleac'h horn down towards the horn's flair frequency (380Hz). This was also pretty easy to hear - I had the same response and DI before and after this change and I was hearing a lot more detail in the low mids after the change. The response I posted is without the sub and before any room EQ was applied - I was just getting the system set up so it was easy to EQ. The max output of the system is actually 3dB higher than shown on the response plots - so about 114dB/1m for full scale output from my media server. It does this with essentially no power compression except in the sub at max output (like 1dB at max output).
There are still quite a few things to improve, but at the moment the single 15" sub is about 10dB low in output at 20Hz compared to the rest of the system even after including the 10dB of room gain I get below 40Hz. That's looking at distortion - if I look at power compression it's not quite as bad - I can probably about keep up with the highs before I see more than about 1dB of power compression. If I want to keep distortion limited output constant all the way down to 20hz, I could do 3 more sealed 15" subs or look at a corner horn. So far I haven't been noticing it holding things back too much.
I've also been thinking about adding a bigger LC horn for the low mids with a compression driver above the super tweeter. But at the moment I really like it - nice and punchy but well balanced, good detail, and not fatiguing unless I just have it cranked on something that's compressed. Now I need to finish the 2nd one so I can listen in stereo.
There are still quite a few things to improve, but at the moment the single 15" sub is about 10dB low in output at 20Hz compared to the rest of the system even after including the 10dB of room gain I get below 40Hz. That's looking at distortion - if I look at power compression it's not quite as bad - I can probably about keep up with the highs before I see more than about 1dB of power compression. If I want to keep distortion limited output constant all the way down to 20hz, I could do 3 more sealed 15" subs or look at a corner horn. So far I haven't been noticing it holding things back too much.
I've also been thinking about adding a bigger LC horn for the low mids with a compression driver above the super tweeter. But at the moment I really like it - nice and punchy but well balanced, good detail, and not fatiguing unless I just have it cranked on something that's compressed. Now I need to finish the 2nd one so I can listen in stereo.
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Driver Measurement Gear
To run FR and impedance measurements on drivers (i.e. GPA 416-8B) with the ARTA software, is there a ready-made mic and preamp that might you recommend?
Also, regarding your sealed cabinets for the 416s, assuming they should be
as airtight as possible, did you run use (Gorilla?) glue between the Birch sides
that were butted together before you wood screwed them together?
To run FR and impedance measurements on drivers (i.e. GPA 416-8B) with the ARTA software, is there a ready-made mic and preamp that might you recommend?
Also, regarding your sealed cabinets for the 416s, assuming they should be
as airtight as possible, did you run use (Gorilla?) glue between the Birch sides
that were butted together before you wood screwed them together?
I used the MP-1r-KIT from IBF-akustik, and also built an ARTA Measurement Box.
Yes, the enclosure should be as airtight as possible. I used yellow carpenter's glue and clamps, no screws or other fasteners.
Gary Dahl
Yes, the enclosure should be as airtight as possible. I used yellow carpenter's glue and clamps, no screws or other fasteners.
Gary Dahl
Given the affected frequency range of pressure cycles within a speaker enclosure, say 20 - 200Hz, I never did understand why the often stated requirement for absolute airtightness is seen as being so important.
I would think that the kind of small leaks that might occur with a well fitting back panel, for example, that is screwed on but without a gasket would be roughly equivalent to a resistive port of maybe 2mm in diameter. I would think this is of no real consequence, but I stand to be corrected by anyone who has actually experimented with this.
I would think that the kind of small leaks that might occur with a well fitting back panel, for example, that is screwed on but without a gasket would be roughly equivalent to a resistive port of maybe 2mm in diameter. I would think this is of no real consequence, but I stand to be corrected by anyone who has actually experimented with this.
Absolute air tightness is not required or generally desired. If you hermetically sealed the cabinet, changes in atmospheric pressure would bias the cone in or out which could change the driver's characteristics depending on the magnetic circuit design. But most drivers and cabinets are not truly air tight. Certain size (small) leaks will cause audible noise when the driver is moving a lot and can be pretty annoying. You can get these around mounting bolts in woofers, for example. If you have a larger leak that doesn't cause noise, you're just changing the tuning of the box.
I agree with absolute air tightness is not neccessary. I tend to disagree with air tight being problemistic due to atmospheric pressure changes having much if any affect due to the walls typically being gas permeable. Only case this would be an issue is when the enclosure and driver is not gas permeable. Having built "acoustic suspension" type designs since the late seventies it has never been an issue. This was in "tornado alley" where it would have greatest effect.
So true. I drilled a very small hole in the bottom to equalize pressure on my sealed subwoofer with the Eminence LAB12 12". I think the volume was 37 L. But somehow there was a gap between the driver and the cabinet that started to make some loud whistling noise, when I tried to impress some relatives. Will need to take care of that soon. Maybe it will tune itself better.
Yes indeed we tend to demo at levels way beyond our usual listening level. Pano's voltage test is one quantification of this long standing audiofool tradition.
And we're often standing as we ignore how loud it is. Loud indicating distortion loud, I mean. And when I get my LAB 12 drivers reconed I'll just have to find out how loud they'll go. Can't wait!
Edit: they'll be the Bjorno ODMLTL hence very leaky
And we're often standing as we ignore how loud it is. Loud indicating distortion loud, I mean. And when I get my LAB 12 drivers reconed I'll just have to find out how loud they'll go. Can't wait!
Edit: they'll be the Bjorno ODMLTL hence very leaky
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Hi Gary, just a perception and only partly connected to the current focu of thread. With your marvellous opportunity as a conductor, you must have one of the best listening positions for the orchestra, and there are obviously other excellent positions to avail one of the best listening experience. This means perhaps up to 125dB during say Ravels Bolero
The point I am making is that this is a perspective that perhaps many of us ascribed to, as our target, or preference. So your finely adjusted bass unit, has been brought to your perhaps best match with that. This I believe, surely gives the confidence to expect that we would really be very pleased to own such a honed bass unit to the preferred loud be there live concert experience. Some may prefer the back of the hall. I prefer the clear but powerful front of the hall reproduction.
Great.
