Seas A26 kit

Discussion in 'Speakers' started by murphythecat, Dec 12, 2018.

  1. ultrabike

    ultrabike Measurbator - Admin

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    My understanding is that the use of polyfill or not depends on the woofer and port. In some cases the system may exhibit some peakiness in the bass area. Using polyfill reduces this issue.

    In some cases however, the bass is just right w/o any fill, and adding fill when not needed will only make the system loose bass w likely no benefit. In other words, using too much fill or fill when is not needed may essentially castrate the rig.

    I would forget about the back wave talk and all that. The box is more of a pressure chamber in my mind. And pressure goes on all directions inside the box. If the system is experiencing cancellation, it will show in your measurements.
     
  2. ultrabike

    ultrabike Measurbator - Admin

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    Here is what I mean:

    Stuff.png

    EDIT: This applies mostly to ported designs. Just found out this is more of a "leaky" sealed box.
     
    Last edited: Dec 19, 2018
  3. philipmorgan

    philipmorgan Member of the month

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    I used this 1/2" felt rug pad for interior lining on my bass cabinets: http://a.co/d/eEAXIeR cause Troels does it and I'm superstitious like that. Didn't verify it's effectiveness through measurements because I have other shit to do than un-mount and re-mount 18" drivers :)
     
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  4. ultrabike

    ultrabike Measurbator - Admin

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    Last edited: Dec 19, 2018
  5. ultrabike

    ultrabike Measurbator - Admin

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    Based on this:

    A26-freq-resistor.jpg

    I would probably also take either the 12 or 15 ohm resistor option.
     
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  6. ultrabike

    ultrabike Measurbator - Admin

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    More about the fill stuff.

    On looking at the specs of the box, it does not use a regular port. Instead it is more of a blocked slot. And depending on how you block that slot things will tend towards a sealed box (sort of a leaky one). This is not a conventional ported design. This is what they said:

    "The cabinet stuffing (50g) is distributed evenly inside the box. The highly damped vent acts as an acoustic resistor, resulting in a non-resonant (aperiodic) system. The quantity of polyfill stuffing used in the vent is 12 grams. We suggest mounting a piece of screening material over both sides of the vent to hold the stuffing in place. Decreasing the vent stuffing will improve the time response of the bass system, but will lower the bass output due to the lowered Q. If, on the contrary, more polyfill stuffing is used, the enclosure will behave closer to a sealed box and a higher Q will be obtained. However, the time response will be slightly deteriorated. We find 12 grams of polyfill to achieve the best balance between the time and frequency performance of the bass system. This amount of stuffing is based on measurements and extensive listening tests."

    Again, I would not think of this as a back wave cancellation and all that stuff. It is a pressure chamber and the blocking of the slot is giving this some control. They way they have it based on their listening tests and measurements seems pretty close to optimum. But if you want more bass increase fill. If you want more coherence decrease fill. There are obviously trade-offs.
     
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  7. purr1n

    purr1n Finding his inner redneck

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    I think murph is talking about increasing the fill to prevent soundwaves bouncing around inside the cab leaking back out through the front of the cone of the driver resulting in honk or shout. Won't see this in measurements and varying fill (within reason) doesn't change the effective internal volume enough to change bass response - but it does have very subtle effects on transient response and sound leakage back through the cone.

    These are the art or magickal things done after the measurements phase - which Seas has already perfected.
     
    Last edited: Dec 19, 2018
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  8. murphythecat

    murphythecat Friend

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    yes exactly. thanks ultrabike though.


    the foam in the port is not something I want to play with, i trust Seas there, and the kit came with the foam that you plug right in the "port" with the right density. I wont play with that

    I guess ill have to experiment with the foam inside the cabinet. to me, it makes little sense to allow the back wave to not be absorbed and then going back threw the cone. it for sure introduce colorations... why would absorbing the back wave would affect transients response?
     
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  9. purr1n

    purr1n Finding his inner redneck

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    Damping. Ultimately air can be model as a fluid (any people taking fluid dynamics or kids doing aerospace engineering?). More fill, more damping, like stiffer shocks in a car.
     
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  10. Priidik

    Priidik Friend

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    Damping material, like mineral wool, will slow down the wave propagation speed + will absorb (excite the fibers) in some bandwidth.
    The back wall will 'appear' further away and with a low pass mirror, effectively.
    This low pass effect is detrimental at times. So can the 'apparent increase' in cabinet size be not desirable.
     
  11. Serious

    Serious Inquisitive Frequency Response Plot

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    In my experience there's definitely a difference in FR with damping. Probably depends on the driver, internal volume, cabinet shape, etc. I did see less energy in the middle to upper midrange with more damping in the small desktop speakers I've built. It's not a minor change, either. I remember something like a broadband 2-3db change between 1-3kHz between no damping and quite a bit of damping.
     
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  12. spwath

    spwath Collegiate hijinks master

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    Right, from what I learned in acoustics class, a ported speaker just acts as a Helmholtz resonator, and a Helmholtz resonated just acts as a mass on a spring, with the air in the port acting as the mass, and the air in the speaker/container acting as a spring, so modifying the contents of the speaker will change the "spring constant", affecting other stuff.
     
  13. purr1n

    purr1n Finding his inner redneck

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    My statement was in the context of light touches / different approaches: loose fill, lining walls, specific walls, behind driver, combinations thereof - where FR measurements don't change or have insignificant changes within the bounds of human error, e.g., speaker / microphone placement.

    If we stuff a box so much to the point of notable FR changes before we notice "why does this thing sound dead?" then someone really screwed up.

    As an aside, critically damped sounds bad to my ears. A little overshoot is desirable.
     
    Last edited: Dec 20, 2018
  14. Serious

    Serious Inquisitive Frequency Response Plot

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    In that case it was just 2cm thick open cell foam (the cheap kind you can get at hardware stores, very soft) on the side walls, but I still have to try a lot more to see what sounds best. I certainly didn't expect such a big FR difference which is why I was interested what you'd say. I'll definitely have to try again to see what's going on. I have a few different materials now and ideas what I want to try so when I get the time I'll experiment with it.
     
  15. purr1n

    purr1n Finding his inner redneck

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    I just so rarely run into that situation because with small speakers, I crossover the tweeters low (1.6kHz) and use steep active filters.
     
  16. murphythecat

    murphythecat Friend

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    quick update. I got myself a new amp, the Ifi Retro stereo 50 amp; it has the Xbass option for speakers, and it really helped fill in the sub bass of the Seas a26. I now have satisfactory bass response.

    I will definitely play with some damping behind the drivers and see the results.

    Ive installed 15 ohm resistor and it gives a nice response, following closely the B&K curve. 18 ohm is slightly too rolled off for me but i might also use it depending on the mood.

    Yesterday we were listening to a movie, and the sound of a door opening sounded like it came from outside the room, my gf actually didnt realized it was in the movie and thought something was going on in the hallway. The transparency from that tweeter is excellent, it gives outside the speakers imaging and the feeling of a open window, sounds around your head sort of transparency. the Harbeth dont do that. Going back to the harbeth give a smoother sound but I feel like i can sort of start to "hear" all the filtering going on. serious comparison between shl5+ and A26 will happen very soon
     
    Last edited: Dec 24, 2018
  17. murphythecat

    murphythecat Friend

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    Ive compared a lot today the A26 vs shl5+

    Shl5+ have better depth of image, sounds are more separated. voices have more clarity. How voices sound is simply the best ive ever heard reproduced on any speakers, truly uncanny. even compared to Graham ls5/9, kef ls50, ref 3a decapo, AN-J, ECT.

    A26 have better bass, more of it, more understandable bass and you feel it, its a unforced bass, the shl5+ extend lower but its less clear, smaller and not as clear... better treble, less bright. The shl5+ is a tiny bit bright, too bright for my personaly taste.

    The shl5+ are clearer overall, the A26 mids have good detail as well, but not as clear and clean, I think what I can hear is lack of precision in the upper mids of the A26. There's some coloration on the A26 mids, it sounds not as crisp as on the harbeth. its only really noticeable when you compare directly with the harbeth.

    One thing we notice is that with harbeth we listen to the singer, while with the A26 you listen to the rythm section more. The A26 seem to blend the sound more, are more forward as well, are groovier. the Shl5+ are more impressive, you listen in awe, but I'm not sure if this is my bias but I find the shl5+ less involving or emotional, bit more laid back, impressive but boring on the long run.

    Both speakers sounds very different

    I'll miss the shl5+ but they are simply not worth, for me right now, 3 times more in terms of investments. I would buy the A26 again, so im quite happy with the results. They can play very loud, are coherent, natural and have good,effortless bass. They dont sound wrong either, my GF is very harsh and when I make her listen to a bad speaker, she will tell me. The fact they are a 2 way I think really helps in that it sounds cohesive and coherent, both drivers blend well and nothing sticks out as "wrong".
     
    Last edited: Dec 27, 2018
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  18. OJneg

    OJneg The Most Insufferable

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    Is this kit new? Wow. I built something like this a while back, but used crappy drivers salvaged from other projects. Lots of potential with quality Seas stuff.
     
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  19. murphythecat

    murphythecat Friend

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    ok, I still heard small coloration on the mids of the A26. it sounded sort of hollow, or rather not as clear as I wanted.

    so ive opened up the box, and put 4 inch Roxul Rockwool on the back panel, and ultratouch denim on the sides and the top cabinet.... what a difference

    this have removed the hollow feeling, the mids are now cleaner and I dont hear the upper mid colorations at all anymore.

    Im 100% happy with how the A26 came out
     
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  20. msommers

    msommers High on Epipens

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    Did you cover the entire back and sides or smaller squares behind the driver?
     

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