Two-way speaker system, WAY horn-loaded

Discussion in 'DIY' started by tubino, Feb 7, 2008.

  1. spkrman57

    spkrman57 wrongsideofthetracks

    To put things in perspective as I see it:

    Tubino posted:

    "Look at it this way: a BLH can be modeled as a ported box, where the port is a long expanding flare (horn) to maximize its LF capabililties. Viewed that way, isn't it easy to see how critical the minimum opening at the start of of the port is? If it's too big, as most BLH are, then you won't get an adequate compression ratio!

    To put it another way, it would seem not just possible but HIGHLY DESIRABLE to use the formula as a starting point to optimize chamber and throat size for a particular driver, with at least as much care as you would take to design size and length of ports!"

    I say when the proper throat size is not achieved that the BLH acts more like a transmission line than a horn at the mouth.

    Just my 2 cents of course!

    Regards, Ron
  2. djnagle

    djnagle Lunatic Member

    OK Guys, you are talking over my head. I am more of a builder/artist then engineer.

    Given that, T, what problems do you hear in your current set up? Also, I see the horn lenz you are using,,,,how does those compare to Edgarhorns?

    Dave, yes maybe we did not hear 10hz, but when it started playing Ross and I looked at eachother and said "DAMN!!!" I hope you feel better soon. Will you be at the SMAC meeting on the 21st?

    T, will you be able to make the SMAC meeting on the 21st?
  3. tubino

    tubino A guy with too many tubes

    I think the Altec 515E is working very well, just as it should, in the cabinet.

    The challenges I'm facing now are the ordinary ones with a new two-way: optimizing a crossover (Ron is guiding me, and I think I've got a pretty good one now) for LF and HF, and determining which HF driver and horn to go with, between the CD horn and 500hz Edgar. JBL 2441 is okay for now, Great Plains 399 might be better.

    I think the formulas might give some insight into what drivers work and why, and also how to do some optimizing of the throat and chamber for particular drivers. But as I say, it sounds DARN GOOD right now. I believe that using a driver with Vas of 4-5 cu ft (e.g. JBL 2226 or 136) would probably NOT work well in mine, as explained in the posts above, because they would want a much smaller throat. I'm curious enough to try the 2226 one of these days, though.

    As I said before, I'm aware from the Decware forums that not everyone has uniform success with drivers in the Dec Imperials, or the original Imperials like yours. I suspect using the formulas to determine the right throat size would be helpful. I could not get anyone there interested in discussing it, but might try again with my examples.

    Dennis, are you able to measure or otherwise determine the smallest area in square inches where the horn begins? That would be very interesting to know.
  4. djnagle

    djnagle Lunatic Member

    The horn mouth on mine is 85.25 sq. in. The back chamber is approx. 4.5 cu. ft. I was thinking about building a slide plate into the horn mouth to be able to adjust the mouth.....but I don't really have any complaints as is. The JBL 2441 is a bit sharp, but I am using the Radian replacement diaphragm with the mylar surrounds and that sound WAY better. Someone told me that the GP 399 uses the Radian diaphragm but I've never confirmed that. Cheers.
  5. tubino

    tubino A guy with too many tubes

    Here's a funny coincidence. Using that formula above, I came up with about 82 sq. inches for the Altec 515E. If you use the rough rule of thumb of a horn throat being about half the driver area of Pi* r*r, you get about 1/2 x 3.14 x 7 x 7 = 154/2 = 77. Pretty close! And either way suggests I might have a more linear response if I reduce the current throat by 15-20 sq. inches. If I have any problem I would be listening to improve, it's some humping or bass exaggeration I think is going on. I think spkrman57's observation would fit here.
  6. tubino

    tubino A guy with too many tubes

    You mean horn throat, right? So it's in the "normal" range of roughly half the driver area, but with the formula above, .8 x Fs x Qes x Vas, you get about that number with the Altec 515E, and something WAY WAY lower with the driver you're using. The formula indicates the driver you're using would want a throat of only about 20 sq. inches.

    And I'm just wondering if yours now works better because you greatly expanded the chamber, which maybe corrects the ratio of chamber to throat (compression ratio) for that driver. What would have happened if instead of increasing the chamber, you had either reduced the throat size, or used a driver with low Fs and low Q but much higher Vas, to match the throat?

    I don't understand why the Decware guys are so keen on drivers with Vas of 4-6 cu ft. A driver like the 515E with Vas of 23.5 cu ft is a better match on the numbers, and sounds great in mine with it's smallish chamber.
  7. tubino

    tubino A guy with too many tubes

    Edgarhorns vs. CD horns

    Sorry, I blabbed on without answering this. Yes, I'm currently using a constant directivity horn, namely B&C ME60 2" 60x40. Parts Express #294-624
    ; Minimum frequency: 800 Hz *Throat diameter: 2" *Dimensions: 9.3"H x 10.6"W x 7.9"D.

    One of the things I love about my 1952 Imps (is that a reasonably accurate label?) is the way the whole hornloaded range takes over the room the way live music does. It's BIG all the way down, and I can walk around the room and enjoy it. I loved that about the Tannoy dual concentrics in the BLH's, but the 1" Tannoy driver and wave guide HF couldn't keep up with the bottom, IMO. So when I think about a HF to keep up with the Altec 515 in there, I think it's gotta be 1.4" or 2", and ought to sound with wide dispersion. Well, to be honest, spkrman57 figures it out way before I do, but I was getting there! So spkrman57 loans me these horns that bolt right on to the 2441's, and once I mount them properly on a baffleboard at about ear height under the woofer, I find I like it. I can sit smack in the middle and the imaging is there, but off-axis is nice too. If this basement system and room evolve as I want and expect, having a whole couch of seats of good sound would work out REALLY WELL for a bigscreen theater between the big-sound Imperials.

    The Edgarhorns image better if you want to sit right in the sweet spot, but I've got another system coming along where that would be more appreciated, so ... that's probably how that's going to work out. The fact that the Edgarhorns don't need a baffle is a little added plus to keep the speaker size kinda reasonable in the living room.

    I don't know if SMAC Feb 21 will work for me. Kids' birthday parties to attend, some big home projects, trying to set up a workshop, cleaning out the basement area where this giant speaker project is developing.
  8. tubino

    tubino A guy with too many tubes

    Calculating compression chamber for a particular driver

    Okay, using John Hasquin's formula suggests some benefit to slightly reducing the current throat. It's easy to try, so I will. Now, what about the compression chamber volume?

    I don't understand this stuff, so I'm still only seeing a bunch of parts instead of a SYSTEM. So taking one part, I read* that the volume of the compression chamber works like a low-pass filter (6dB/oct.), so the higher the frequency the higher the attenuation. The crossover point (-3dB) can be calculated with this formula:

    Fhc = 2 x Qts x Fs (Vas/Vf) where Vf = chamber volume. Note that a larger volume lowers the crossover frequency, so a large Vas driver with small chamber will keep working higher up in frequency. Conversely a low Vas driver with a very large chamber will only work at very low frequencies. (Using djnagle's numbers, where Vas is close to Vf and the other numbers are low, I came up with something close to a dropoff STARTING at 10hz!)

    I calculated my chamber size as 7.5 x 15.5 x 16 = 1860 cu inches = 1.08 cu ft.

    Working that out with my cabinet and an Altec 515E : 2 x .19 x 22.9 (23.5/1.08) = .38 x 22.9(21.76) = 189 hz is where it starts dropping off at 6db/octave as frequency increases.

    I'm sure there are a lot more factors at work with chamber size, but like I say, I can only manage one part at a time!
    *Source:, where the guy says he got it from these two:
    Design Factors in Horn-Type Speakers. Daniel J.Plach (October 1953) from "An anthology of articles on loudspeakers from the pages of the journal of the Audio Engineering Society".

    Low-Frequency Horn Design using Thiele/Small driver parameters. D.B.Keele jr.. Preprint of the Audio Engineering Society.
  9. djnagle

    djnagle Lunatic Member

    Hey T, I understand about the sweet spot of the Edgarhorns. In my situation, I have my listening chair right in the sweet spot and if I listen to tunes when not in the chair, I am doing dishes or some other project on the table and not paying attention to the nuances of the music. You are right though, it is one hell of a lively system. Sorry you can;t make the SMAC this weekend. We will have to ge togather something though.

    Maybe it is time to start measuring the Imps and gettting some hard data about what works and why. Cheers.
  10. tubino

    tubino A guy with too many tubes

    Yes, we must get together, and YES on data, but trying to correlate with theory -- it's hard with so many variables! It's one thing to pretend a BLH is a horn, but ... that would be a lot more accurate picture IF you flipped the driver to fire into the horn, AND sealed a chamber around the back, where the front used to be.

    But then I read Hasquin's piece in UFT, where he says,

    And I remember how little I know.

    I never really had much problem finding powerful low Fs Low Qts woofers to really load the horn and show minimal excursion and minimal excursion at high output levels of low bass. How high? My speakers are in the basement. The speakers came with the wrong drivers, but the first time I hooked in the right kind of driver, I put on Chemical Brothers with 20 watts of 845 power per channel. The cones were barely moving, but I had 120db peaks on the Radio Shack meter, and it sounded CLEAN. When I went up to the SECOND floor of the house, I could feel the furniture move with each bass beat. In the basement, of course, stuff was dancing off shelves. So I know what these can do!

    I put on a Dub collection a few months back at live-performance levels, and things were rattling around, let me tell you.
  11. djnagle

    djnagle Lunatic Member

    I have the same experience with mine. Although I am on a slabe so the sound just comes at me instead of being wasted transmitting through the structure. I like the 845 tube. I am building an amp to driver my woofs using 807 tubes.
  12. tubino

    tubino A guy with too many tubes

    Heh. I'm not normally listening to music two floors up, but I confess to having a little juvenile fun when it was all new to me. Mine are on a concrete floor too, so I'm definitely getting some reinforcement there!

    807 amp is a good plan. PP or SE? What OPTs?
  13. djnagle

    djnagle Lunatic Member

  14. tubino

    tubino A guy with too many tubes

    A friend of mine read this post and my response, and offered to loan me a pair of LE15s! Nice friend, eh? So he brought them by today, and I quickly popped one in. Great bass in the horn mouth, but ??? Everything else was haywire till I reversed polarity to match the compression driver and other channel (I had the JBLs hooked up red to positive at first... that darn JBL...). Ah, but then it was good.

    I measured the other one on Woofer Tester 3, and got Fs of 30, Qts of .23. Sometimes I wonder if woofers ALWAYS drift in that direction, or if WT3 is less accurate (in this way) at the low end of Qts..

    But as I say, initial response was very positive! Sounds quite good, and I'm all JBL now.
  15. dnewma04

    dnewma04 The Healer Super Mod Subscriber

    Very interesting. LE15B model? Or some other LE15 version?
  16. tubino

    tubino A guy with too many tubes

    Yup, LE15B. I'm scrounging around now for the right crossover parts for this much lower impedance woofer.

    I'm kinda thinking I need to talk my friend out of these...
  17. Zilch

    Zilch Curve Junkie Subscriber

  18. tubino

    tubino A guy with too many tubes

    The pair I'm using were taken from L200 cabinets, and those cabinets now have 2226 in them. So far it seems like a win-win. The 2226 like the ~4cu ft cab, and the LE15B are happier in my horns.
    Last edited: May 3, 2009
  19. dnewma04

    dnewma04 The Healer Super Mod Subscriber

    Yep, the LE15B seem like they were designed to reside in big horns. :) Too bad JBL used them in the L200...
  20. jaybird

    jaybird AK Subscriber Subscriber

    This is the first I've seen this this thread. I have been using 4530's that I built in 1981 and they where over built, 3" screws every 3 inches, tons of glue, much more solid the the JBL's we copied and the sound noticably fatter, better low end. I was using 811b's and 2345's and 2405's crossed over at 800 and 7k, but a few weeks ago I put the $10.00 waveguides,from my econowave efforts, onto my 2420's and this is the best it has ever sounded! Now you can resume this wonderfull discussion!

Share This Page