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Thread: Heil with a JBL Woofer part 2 Back wave attenuation for best in room balance.

  1. #1
    Administrator Robh3606's Avatar
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    Heil with a JBL Woofer part 2 Back wave attenuation for best in room balance.

    Has anyone tried any attenuation of the back wave?? I was just listening to a live recording and was impressed with how well the venue ambiance came through. That said on non live recordings I also get a sense of space but it seems the focus is less clear compared to either the F 206's or my horn systems.

    I have been playing the the idea of trying to turn down the back wave just using some fiberglass batting to see if I can dial them in better. The goal is to increase focus but not loose the sense of space. I don't want to do an enclosure because of the potential of reflections back through the diaphragm just like putting a woofer in a box.

    Anyone else try this?? I am going to give it a shot too see what happens.

    Rob
    "I could be arguing in my spare time"

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    Administrator Robh3606's Avatar
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    This is worth playing with. At least in my room. I did a quick check to see what would happen using some 4" batting paper left on. It had a significant effect in room. Normally I couldn't hear a change in balance doing a sit down stand up test. I can now this did a great job of attenuation and effected the balance in the sweet spot. Better clarity more focus with little apparent loss of ambiance.

    It is clearly absorbing a great deal of the upper octaves but seems to be frequency shading the back wave and attenuating it as expected.

    With some experimentation I could reduce or increase the energy level but either increasing or reducing the thickness of the fiberglass behind the driver. Want to try and get some measurements to see exactly whats being shaded out and how much attenuation there is.

    Rob
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    "I could be arguing in my spare time"

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    Administrator Mr. Widget's Avatar
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    Hi Rob, I rotated your photo...

    Interesting idea. For some reason all of the better ESS systems and many of the AMT systems by others have left the AMT driver as a dipole. I wonder if a better solution would be to place some Sonex or heavy curtains directly behind the speakers on the near by wall.

    You may want to try both to see which you prefer.

    On a parallel topic, I was considering getting a second pair of ESS drivers and running them stacked since it would be so easy to do with a length of threaded rod. I think this would help with the vertical dispersion.


    Widget

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    Quote Originally Posted by Mr. Widget View Post

    On a parallel topic, I was considering getting a second pair of ESS drivers and running them stacked since it would be so easy to do with a length of threaded rod. I think this would help with the vertical dispersion.


    Widget
    Widget - see this crazy thread at Klipsch Forums - https://community.klipsch.com/index....-for-heritage/

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    Senior Member jmpsmash's Avatar
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    Quote Originally Posted by dkalsi View Post
    Widget - see this crazy thread at Klipsch Forums - https://community.klipsch.com/index....-for-heritage/
    Very cool. I did try to look at what can be done. A while ago someone managed to do a quad stack. 4 on each side but didn't provide any measurements.

    This one looks good except it still only go down to 500Hz with a fairly large "horn". Not high enough, not low enough. I hope he provide some distortion measurements too as that's one of the goal of going for an array.

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    Senior Member jmpsmash's Avatar
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    Back to the main topic.

    When I first read it, I thought you meant putting stuff at the front wall. I have tried nothing (just normal drywall), 2" absorption panel, and some wooden pattern paneling that scatters the sound (it is not strictly a diffuser as it is not diffusing sound uniformly like a QRD, etc).

    Dry wall: there are the most amount of ambience sound, creating a more live sound stage. I like that sound. However, instruments and voices are less focused mixing around all the backwave and front wave. My AMT is ~4ft from the wall. I have achieved better imaging with 6 ft from the wall but I have found that there are tons of low frequency issue with the speakers that far out.

    Absorption panel: Best imaging, but the magic of the dipole is very much diminished. A/B comparison the sound is dry and liveness.

    Scattering panel: Kinda in between, not the best of both worlds, neither the worse. but like 50% of each.

    Now I am tempted with a proper diffusion panel like a QRD. Those are crazy expensive. I need a long weekend to DIY one.

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    I had experimented with putting stuff (e.g., open cell foam) behind trying for a smoother frequency response, but settled on the wedgies. I may have to try again and see what the RTA says.

    There are some things/frequencies (cymbols) where you would swear that the Heils are located right next to your ears, like headphones. Very uncanny. When I happen upon on a selection that does this again (don't recall which do), I'll have to try the open cell foam behind to see what that does to it.

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    Senior Member jmpsmash's Avatar
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    Quote Originally Posted by toddalin View Post
    I had experimented with putting stuff (e.g., open cell foam) behind trying for a smoother frequency response, but settled on the wedgies. I may have to try again and see what the RTA says.

    There are some things/frequencies (cymbols) where you would swear that the Heils are located right next to your ears, like headphones. Very uncanny. When I happen upon on a selection that does this again (don't recall which do), I'll have to try the open cell foam behind to see what that does to it.
    Or a soprano singing at the top of her lung when her ran away lover came back to see her just moment before she dies.

    OMG my ears need some rest after that.

    What I noticed is that the Heil reall loads up the front wall so some sort of absorption to get rid of that high frequency energy is needed, otherwise it bounces back around and end up loading up the whole room.

    I have 4ft tall absorption panels almost covering the whole space between the two speakers yet the sound appears to come immediately above it.

  9. #9
    Administrator Robh3606's Avatar
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    Hello Widget

    Thanks for the picture fix. Running them in stacks! That’s interesting! Have you fired yours up yet?

    If not I would wait and see. With mine in full dipole operation there was no change in sit down/stand-up as far as the tonal balance. There was more than enough energy from the front wall reflections, behind the driver, to essentially mask any vertical directivity issues. It wasn’t until I tried the fiberglass that there was a change where you could hear a balance change out of the sweet spot.

    This is just my impressions in my room so grain of salt. The issue as I see it is I have a little too much of a “good” thing. I have a pair of L5’s in the next room and the difference is quite notable. Heil lots of space, uniform tonal balance, very open but much less focused and a bit grainy for lack of a better word.

    The L5 have them beat as far as focus and clarity which is why I wanted to see what would happen messing with the back wave. That’s a lot of bandwidth bouncing off that front wall and just like multiple sources it seems to be taking away from what they are truly capable of depending of course on what your goals are.

    I would like to keep openness and ambiance but increase focus, clarity and loose the graininess.

    Treating the front wall, behind the drivers, would be the more common approach but it’s expensive and hit or miss. I can easily change the thickness of the absorber as well as the absorbing material for a fraction of the cost and essentially have the same benefits. I should be able to measure the amount of attenuation and FR of the backwave to get a handle on what’s changing vs what changes I hear in the room response.

    I was listening last night and it was a step towards what I wanted. Have to see tonight if I still feel the same way and wasn’t “caught up in the magic of the moment”

    Rob
    "I could be arguing in my spare time"

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    Quote Originally Posted by Robh3606 View Post

    and a bit grainy for lack of a better word.

    Rob
    I often hear this, but wonder..., is it the Heils, or are the Heils are just revealing what's really there? Attenuating them a bit helps tremendously at removing the grain, but also removes a bit of HF detail. At least I have mine crossed over to keep the vocal fundimentals in the midrange, and just loose some sparkle and detail on those recordings when I turn off the HF switch and/or attenuate the Heil a bit.

    I prefer to run the L-pads "full bore" for best "coupling" and the crossovers allow for this, so long as the recording does. But many recordings require a bit of HF attenuation, and yes, I do get up and adjust the crossovers to the recording on a disk by disk basis as necessary.

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    Senior Member jmpsmash's Avatar
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    Quote Originally Posted by toddalin View Post
    I often hear this, but wonder..., is it the Heils, or are the Heils are just revealing what's really there? Attenuating them a bit helps tremendously at removing the grain, but also removes a bit of HF detail. At least I have mine crossed over to keep the vocal fundimentals in the midrange, and just loose some sparkle and detail on those recordings when I turn off the HF switch and/or attenuate the Heil a bit.

    I prefer to run the L-pads "full bore" for best "coupling" and the crossovers allow for this, so long as the recording does. But many recordings require a bit of HF attenuation, and yes, I do get up and adjust the crossovers to the recording on a disk by disk basis as necessary.
    I also would classify my Heil AMT as grainy. It is very apparent after swapping between the Heil and a Focal metal dome tweeter. Despite having even flatter frequency response the Focal is much smoother and has better clarity.

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    Senior Member jmpsmash's Avatar
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    My Heil have frequency peaks at 5k and 10k. After smoothing those out, they are less shouty than before.

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    Quote Originally Posted by jmpsmash View Post
    My Heil have frequency peaks at 5k and 10k. After smoothing those out, they are less shouty than before.
    Hence the wedgies in which we control these "mechanically" and through crossover component selection rather than through add-on electronic filtering.

  14. #14
    Administrator Robh3606's Avatar
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    Having some fun with this. Using hobby store black felt folded in layers of 2 and 4. Just took a 12 X 12 cut it in half and folded it to get 2 layers, then folded it again for 4. Works like a charm easy as hell to adjust and leave plenty of output even with 4 layers to get the ambiance and take the edge off. I have to try and measure this on the weekend to see what the deal is.

    Rob
    "I could be arguing in my spare time"

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    Administrator Mr. Widget's Avatar
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    Quote Originally Posted by Robh3606 View Post
    Hello Widget

    Running them in stacks! That’s interesting! Have you fired yours up yet?
    I did just before I had my Project Widgets up and running. I paired the AMTs with a pair of of PHL 12" woofers in some old test boxes. I ran them bi-amped at 800Hz and was not thrilled with the sound overall. I don't think the AMTs were the weak link there.

    I did have them out in the room and the back wave was allowed to do its own thing... when sitting the highs were pretty good, but when standing there was a significant roll off up top. That is what led me to think about extending them.


    Widget

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