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  • Steve Lee
    replied
    Glad you had this little epiphany and decided to go for a sanity check with the PA310 driver, Drew.

    Interested in your further findings as I am working a PA310 into a cabinet vol of 1.3 cu ft net right now . . .

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  • DrewsBrews
    replied
    I got the ports installed. I went to take a new set of measurements and had a facepalm moment. Hard to explain without making a whole paragraph, but it seems my receiver will auto split bass to both speakers and if I forget to unplug the other speaker it will skew the results. I've never noticed this before and don't know if I somehow enabled the setting while trying to get hdmi audio working for a dvd player I plugged in the previous week... or if it has always been doing that when I forget to unplug the other speaker.

    Once the other speaker was unplugged it became apparent the new port really wasn't making the difference I thought it was. The whole situation was frustrating enough that I put it all down for a few days to reflect.

    Today I decided to pull a Dayton PA310 and give it a try. I really hate to pilfer from a completed build, but they are currently not in use anyway. It seems a bit flatter and with better bass response. And without losing sensitivity. Not sure if the original port would have done better/worse. hmm....

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  • DrewsBrews
    replied
    Not much to report yet. Focusing my days off to do some drywall work at my home. Decided to cut out early today to keep from burning out my arms/shoulders... So I sanded out the silicone and paint from the port holes. Found my clamps were way too big to fit in there. Made a run for some tiny clamps so I can glue in little blocks to bolster the location for the precision port screws.

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  • DrewsBrews
    replied
    Messing around in WinISD with the new port... At say 35watts they breach the meager 3.75mm xmax at ~28hz, 96.6db. If xlim might be about double xmax, then danger zone limit for that power level is ~22hz @90db. Port air velocity at that power level peaks ~20.5m/s. Hopefully the double flares help handle that, if not then.. oah well I guess. The rest of the woofer output peaks @~109db by that point. Probably much louder than I would normally be listening to unless I was just testing the limits. Right now my listening distance is right around 2meters. Might add a couple feet once we rearrange the living room.

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  • DrewsBrews
    replied
    I think my point was missed.

    My resulting enclosure happened to be close to the calculated default enclosure size. Not saying it is actually ideal in any real sense.. I was just using the impedance peaks from that enclosure as a telltale leading to a theory that the actual woofer parameters are not too far off from the published specs.
    Last edited by DrewsBrews; 11-06-2022, 02:46 AM.

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  • Wolf
    replied
    Originally posted by PWR RYD View Post

    Where did this information come from? It may give the lowest possible anechoic F3 for a given woofer (in sims) but there are other important things to consider.
    Even peaks only seem to make tuning very close to box resonance, therefore tuning to the Fs of the box/driver system. This is known as the best way to keep Xmax to a minimum. It is not however the way to get the lowest F3, which usually involves tuning quite a bit below Fs.
    Agreed there are more things to consider.

    Wolf

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  • DrewsBrews
    replied
    3" double flare port seemed to do fine without chuffing during stress testing. Unless things rattling in the house just covered up any chuffing noise lol.

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    I've used 2" precision ports before and they have a nice satin texture on the mounting ring portion. The 3" version uses a much larger glossy texture that reminds me of cheapy blow mold tool cases. Neither that texture, nor the gloss of the rest of the port jived with the rest of the speaker. I sanded off the texture, then rubbed the whole thing down with steel wool to give the rest some tooth and sprayed a matte clear.

    Per the instructions: "Note: On Plastic Maximum paint adhesion and durability is achieved in 5-7 days.".... Ugh, better follow it or I bet the screw heads will crack the clearcoat.

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  • DrewsBrews
    replied
    Ever since I saw the port response, something kept telling me I had seen a similar response before...

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    (Example of the bottom end response of a transmission line)
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    So I've pretty much made a transmission line. Which, is not too surprising as that probably happens in most tower configurations to a certain extent. In the one tower I did previously I deliberately put the port about 1/3 up the tower in an effort to stay away from these kind of issues. This time I really didn't have a choice unless I did rear port. But at least now I know what it is I'm up against. The foam must be reducing the second plateau and completely killing the 3rd. It could be better though. Someone mentioned rock wool previously. I've got some fiberglass insulation I could replace the foam at the bottom of the enclosure with, and cover it with some scrap grill cloth to keep it somewhat contained. hmm.
    Last edited by DrewsBrews; 11-02-2022, 05:44 PM.

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  • DrewsBrews
    replied
    Originally posted by Steve Lee View Post
    It would be nice to apply some EQ and see what it needs in XO from ear experimentation . . .
    I am listening to it as I go, but just one speaker. I disassembled the crossover for the moment. I've got some days off the week after next off so I'll probably do my final tweaks and assemble the crossovers then.

    I tried an open box GRS 12PT-8. It was a little flatter on the response peaks and didn't seem to have the 70-80hz peak, but lost too much sensitivity to be acceptable to me.

    I've got some 3" precision port flares that have the exact same flange OD as these 4" ports.. Since the MCM woofer picked up so much low end with the extended port, I'm thinking of just linking together the 3" port flares for a roughly 3"x5" port and using that.

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  • Steve Lee
    replied
    It would be nice to apply some EQ and see what it needs in XO from ear experimentation . . .

    Leave a comment:


  • DrewsBrews
    replied
    I went outside and did some quick and dirty measurements. I'm not equipped for this really. Different amp, so wouldn't be a 1-1 comparison. Brown: 7.5" cardboard tube. Green: original 4" port.

    I did a super dirty measurement about 2ft away aiming at the woofer (holding the mic) just to see what that gave me. (violet)

    So the ~100hz peak in the measurements up to this point appears to be a room mode. Makes sense as my room is just a few inches over 11ft wide. Most of my measurements are within 1ft of the center between walls. Except the measurement I did against one of those walls, which did not have the 100hz peak at all.

    But the mid 70s peak must be something internal.

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  • DrewsBrews
    commented on 's reply
    I really don't know. Most of what I learned was over the past 15+ years poking around the internet trying to piece together information into something that seemed to make sense. I only tend to get a build in every few years due to the cost and, well, life so a lot of that "knowledge" is probably pretty stale.

    I still learn a ton from each build. And that's kinda how I like it.

  • PWR RYD
    replied
    Originally posted by DrewsBrews View Post

    From what I've gathered in the past: The closer the impedance peaks are in amplitude, the better matched the box is to the woofer.

    Where did this information come from? It may give the lowest possible anechoic F3 for a given woofer (in sims) but there are other important things to consider.

    Leave a comment:


  • DrewsBrews
    replied
    Originally posted by Chris Roemer View Post
    MY WinISD (using T/S parms from the newark site) shows a 2.26cf box w/a 4"id x 4" long port tunes to 46Hz.
    YOUR (inbox) z-plot shows a tuning (Fb) of 44? Hz. By definition, the Fb IS the "valley" between the 2 peaks.
    This should correlate to a bottom-end rolloff (F3) in the mid to upper 40s - just about all the bass you'd need (for music).

    Also, (WinISD shows) this rather short port tube has the 1st (main) port resonance near 1.7kHz - NOT the "boom" you seem to be getting near 80Hz or so. It's just a coincidence that your upper z-peak is also right in that range. Maybe a room mode?
    Thank you Chris! I didn't expect anyone to track down the specs and do all that. Though your input does help immensely in confirming and correcting my understanding of things.

    I started off in WinISD before ever making sawdust and got the same results that you see. I was hoping the specs weren't too far off as I don't have a DATS yet.

    From what I've gathered in the past: The closer the impedance peaks are in amplitude, the better matched the box is to the woofer. In this case the peaks seem pretty dang close. That would correlate to the WinISD suggested box specs being very close to my real box volume and tune. So, I suppose I can infer the published specs aren't too far off.

    ​I haven't had a problem with this from other builds. Though this is the first time having a woofer and port so low to the floor, so it could be finding a new mode. I imagine it must be pretty potent if it influences the nearfield port measurement so much. Entertaining the idea of taking the laptop and a little amp outside to get some rough measurements to compare to.. at a time when there isn't a dang train on the tracks 1/4mi away lol.

    ---

    Last night I rolled up a piece of cereal box to create a ~7.5" long tube and shoved it in the existing port, which should drop the tune to about 39hz factoring in its slightly smaller diameter.

    Blue is the first port measurement, Green is the "extended" port. Not sure if I had the volume up higher on the amp the first go than I normally have it set. Orange is room response before, Red is after extending the port. Dramatic boost to the bottom end but nothing else drops down.

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    Last edited by DrewsBrews; 10-28-2022, 05:28 PM.

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  • Chris Roemer
    replied
    MY WinISD (using T/S parms from the newark site) shows a 2.26cf box w/a 4"id x 4" long port tunes to 46Hz.
    YOUR (inbox) z-plot shows a tuning (Fb) of 44? Hz. By definition, the Fb IS the "valley" between the 2 peaks.
    This should correlate to a bottom-end rolloff (F3) in the mid to upper 40s - just about all the bass you'd need (for music).

    Also, (WinISD shows) this rather short port tube has the 1st (main) port resonance near 1.7kHz - NOT the "boom" you seem to be getting near 80Hz or so. It's just a coincidence that your upper z-peak is also right in that range. Maybe a room mode?

    Leave a comment:

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