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no bass from vented + floorstander 18w-8531- why?

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  • no bass from vented + floorstander 18w-8531- why?

    so.. i built another cabinet for the zaph zrt 2-way kit i bought, the first one being a sealed 20L design which had anemic bass (rolled off too much <100hz). The one i just built is a 38L cabinet and i followed Zaph's enclosure plans dimensions very closely, only difference being in the bracing placement.

    Well, this time round there is more bass but definitely not what i expected from a vented 18w-8531 floorstander design. I'm really clueless as to what's wrong, though i'm sure you guys will be able to enlighten me :D

    I went with the default 30Hz tuning recommended, and according to the tuning frequency response graph, it should be at least +/- 3 dB down to 50Hz... but somehow i'm not hearing it. Woofer is verified to be in phase. Test tones revealed that the speaker sounds pretty flat down to 80Hz but starts to roll off until output at 40Hz is almost non-existent. I have heard more than a handful of ported bookshelves with < 7" woofer that has more meaningful output at 40Hz than the speaker i just built. I can't help but think i did something wrong since the 18w-8531 is so highly raved about everywhere

    I clamped the front baffle on while adjusting the amount of stuffing.
    . With this method, there didn't seem to have much, if any, air leaks though i'm not sure if the amount of bass should be affected by that much?

    After trying out different amounts of rockwool and acousta-stuf stuffing, it didn't seem to make much of a difference. If it's not the woofers that are faulty, i'm wondering if it's a bracing/port problem.


    Circular cut-outs in 25mm bracing are 6.5" diameter. The only problem i can think of is how close the bracing is to the port, so there's not much air clearance near the port. I'm not sure if it affects anything. But even so, should the bass be affected by this much?


    The biggest questions on my mind are:
    1) Will the placement of braces relative to the port affect bass extension and output so much?
    2) Will excessive stuffing/fill amount alter and shape bass response drastically?

    Any suggestions are really appreciated, thank you!

    2)

  • #2
    Re: no bass from vented + floorstander 18w-8531- why?

    Do you have a woofer tester, or other way to measure impedance? If so, measure the woofer's impedance when it's installed in the enclosure to verify that you have the tuning frequency correct. Also, are you sure you're getting an airtight seal between the baffle and the edges of your box? If your braces stick out the front at all, there could be a small gap, which would cause air leaks and significantly reduce your low frequency output. An EXCESSIVE amount of stuffing will alter your tuning frequency, but you do not appear to have that much in there.

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    • #3
      Re: no bass from vented + floorstander 18w-8531- why?

      What are you driving them with? Is it possible that you are using a receiver set to "small" speakers? I would verify that the rest of your audio chain is up to snuff.

      -David

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      • #4
        Re: no bass from vented + floorstander 18w-8531- why?

        my guess is you don't have enough clamps on there to get an airtight seal. Try using some speaker caulk and some more clamps, or fabricate a gasket out of neoprene or some other material.

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        • #5
          Re: no bass from vented + floorstander 18w-8531- why?

          Originally posted by david_b View Post
          my guess is you don't have enough clamps on there to get an airtight seal. Try using some speaker caulk and some more clamps, or fabricate a gasket out of neoprene or some other material.
          Using Zaph's T/S measurements, that woofer should do low to mid 30's in your vented box (even if the baffle's not exactly nailed down).

          Are the woofer's in phase?
          You could do the battery trick. Hook it up back where the wires leave the amp and make sure both woofer cones move the same way with the same polarity.

          Chris

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          • #6
            Re: no bass from vented + floorstander 18w-8531- why?

            My guess would be checking for any air leaks. Somehow put your baffle on correctly so it doesn't leak. And I'm thinking that brace is mighty close on your port. Perhaps you could put an elbow there to extend it down & away from your brace.
            If dynamite was dangerous, do you think they'd sell it to an idiot like me?

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            • #7
              Re: no bass from vented + floorstander 18w-8531- why?

              Per your HTguide thread, you already found one mistake in your Madisound crossovers. Have you verified that the crossovers are now correct in circuit layout and component values, and that you have them hooked up correctly?

              Oh, and what are you driving these with?

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              • #8
                Re: no bass from vented + floorstander 18w-8531- why?

                Originally posted by Chris Roemer View Post
                Using Zaph's T/S measurements, that woofer should do low to mid 30's in your vented box (even if the baffle's not exactly nailed down).

                Are the woofer's in phase?
                You could do the battery trick. Hook it up back where the wires leave the amp and make sure both woofer cones move the same way with the same polarity.

                Chris
                Good call for BOTH woofers to be in wired correctly. I was nervous & proud to demo my speakers to some family & friends who almost never come around. They thought is was "nice". After they left that comment was bugging me. Sure enough, 1 of my 4 woofers was out of phase! Of course now they probably don't believe me after explaining this to them. Who knows when I'll get to re-demo again.
                If dynamite was dangerous, do you think they'd sell it to an idiot like me?

                Comment


                • #9
                  Re: no bass from vented + floorstander 18w-8531- why?

                  You should check out page 2 of Robert's thread on his ZRT's. He had issues with bass response on his, might be helpful.
                  "If you cannot find the truth right where you are, where else do you expect to find it? - Dogen

                  "Why are you wearing that stupid human suit" - Frank

                  "We spread the time as we can, but in the end the world takes it all back" - Roland

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                  • #10
                    Re: no bass from vented + floorstander 18w-8531- why?

                    I've been working with that woofer a lot lately. It has a TON of bass, even sealed.

                    First off, I don't think slight air leaks would cause the kind of bass response he's talking about. If you don't believe me, model some air leaks in Unibox.

                    I think the problem is probably either related to the playback gear (someone mentioned "small speakers" setting on the amplifier), or something mis-wired on the crossover.

                    Did you try just hooking the woofer straight up to the amp (bypass the XO, and no tweeter)? Sure, it might sound a bit weird, but it should definitely have some of the bass response that woofer is suppsed to get.

                    Also, maybe just do a battery check on the woofer terminals; make sure they're not mis-labeled.
                    Isn't it about time we started answering rhetorical questions?

                    Paul Carmody's DIY Audio Projects
                    Twitter: @undefinition1

                    Comment


                    • #11
                      Re: no bass from vented + floorstander 18w-8531- why?

                      This problem has been present in two different cabs. I doubt it is the cab. Crossover or signal source is the problem I think. OP says he has verified polarity.

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                      • #12
                        Re: no bass from vented + floorstander 18w-8531- why?

                        Maybe this is "dumb" but how close to a wall/lining is the internal entrance to the port? I can't really tell from your photos but if that end of the port should happen to be really close to the back wall, flow to it could be severely altered/restricted. The rule of thumb is there should be at least one port diameter clearance.
                        Paul

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                        • #13
                          Re: no bass from vented + floorstander 18w-8531- why?

                          Okay, i managed to try out the speakers with another amp. The bass response is similar. I also tried them out full range without the XO. Same result. So i tried something else.

                          All this while i have been listening to them at quite a high height; the tweeter is about a head's length below my ears. So i sat on a smaller chair with the tweeter at eye level this time. And there is a lot more bass, the tonal balance being much better. But it still doesn't sound rich/articulate/blabla the way most people describe the 18w 8531. Sounds like it might just be a room acoustic issue. I will try the speakers out in another room tomorrow (bigger room) to see how it sounds there.

                          Paul, when you say there's a TON of bass - even sealed, do you mind being more descriptive in terms of frequency response and corresponding output? Your wealth of experience with this woofer will be really helpful for me.

                          There is another thing that bugs me though - why does the port output sound so... for lack of a better word, restrained? It feels like it wants to pump out more air but can't do so. I am really wondering if it's a result of the bracing being too close to the port, and i'm thinking of getting rid of the middle bracing.


                          But at the same time, i'm worried it'll make the cabinet ring much more

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                          • #14
                            Re: no bass from vented + floorstander 18w-8531- why?

                            Cut a hole through your brace where the port is. This will have the port see nothing behind it and eliminate any restrictions. Cut the hole, or section out, the same size or bigger than the port.
                            If dynamite was dangerous, do you think they'd sell it to an idiot like me?

                            Comment


                            • #15
                              Re: no bass from vented + floorstander 18w-8531- why?

                              After looking at your pics again, it would seem that the port may be up against the back wall. If so, never mind previous post. Try putting an elbow on the port turning it down.
                              If dynamite was dangerous, do you think they'd sell it to an idiot like me?

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