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No port? But bass reflex, how do we work out enclosure alignment?

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  • Trdat
    replied
    Originally posted by billfitzmaurice View Post
    Vance's book is a good reference source for newbies, but everyone who's weighed in here is well beyond the newby stage. I can't give a time line for Paul, Chris, Dukk and Wolf, but I was designing speakers 20 years before Vance published Edition One. Ten years after that, in 1997, I joined Vance as a Contributing Editor at Speaker Builder Magazine. This ain't our first rodeo.

    Bill we are aware of your work and fully value your input. Obviously many of the others are also up there with their knowledge, its obvious their professionals. I am definitely not a newbie and the book will be to simple for me, so I agree with you there. At times post can get a bit complicated especially on the DIY forum while here its kept a little more simple. Many of the topics that are floating around have not been covered in a book, they are new concepts which aren't based on any research per se but rather taken from experience by experts which is not to say its not scientific. But a new book with clarification on these issues in particular on the questions in this post are needed for the next generation of speaker designers. Unless it exists and I have missed it...

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  • billfitzmaurice
    replied
    I'm 70 and still working, designing speakers and doing audio consulting. My knees won't let me ski anymore, so in winter I've got nothing else to do. In summer I play nine holes of golf five days a week, but that only keeps me busy until 11AM. New Hampshire doesn't have a caucus, we have a primary. After this debacle Iowa will go to a primary as well. The caucus system is as relevant today as a community barn raising, and they don't do that in Iowa anymore either.

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  • Dukk
    replied
    I'll be 50 this year. Built my first calculated speaker enclosure in 1989, then spent 28 years in retail electronic sales / car installations either full or part time.

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  • Chris Roemer
    replied
    hijack (PM for BF) - well, not THAT private !

    are you in your 70s Bill, (not that you'd have to answer, of course)?

    I'm 65 and sometimes wonder how many on PETT are retired.
    Actually I'd like to see a graph of the age distribution of the ("regular") TT users. Just curious.

    Hey, don't let 'em screw up the NH caucus (like they did in Iowa), okay?
    Take care.

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  • billfitzmaurice
    replied
    Originally posted by Regore View Post
    My recommendation is to purchase Vance Dickasons Loudspeaker Design Cookbook. Mine is the fourth edition. It will answer all your questions regarding various alignments pros and cons without the BS.
    Vance's book is a good reference source for newbies, but everyone who's weighed in here is well beyond the newby stage. I can't give a time line for Paul, Chris, Dukk and Wolf, but I was designing speakers 20 years before Vance published Edition One. Ten years after that, in 1997, I joined Vance as a Contributing Editor at Speaker Builder Magazine. This ain't our first rodeo.

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  • Wolf
    replied
    In a sealed box, a Qtc of 0.707 yields the lowest F3 you can achieve. If you build a larger or smaller box than that box with 0.707 Qtc, you have a higher F3 rolloff point.

    Later,
    Wolf

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  • Regore
    replied
    Hey Trdat; I like your comments and questions. You want the truth ! My recommendation is to purchase Vance Dickasons Loudspeaker Design Cookbook. Mine is the fourth edition. It will answer all your questions regarding various alignments pros and cons without the BS.

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  • Chris Roemer
    replied
    Look at these box recommendations (for 1 driver) here:
    https://www.soundlabsgroup.com.au/mm...&Product_Name=

    Your Mk3 enclosure falls in the middle of these suggestions.
    The largest box has the biggest hump (+2dB @ 40Hz), but look at the smallest box - VERY "lean" curve (low Q).
    Again though, since you must be high-passing these at 150Hz, none of this really matters...

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  • Chris Roemer
    replied
    If you're rolling your subs in @ 150Hz (and, then, I'd assume you're high-passing your (MASSIVE) Mk3s ALSO near 150Hz?), then the curve you're looking at in WinISD does NOT (really) make a bit of difference !

    Since you're using WinISD, go to the "EQ/Filter" tab and add a Highpass filter @ 150Hz. Look at your (bass) curve drop on your Mk3s ! !
    That 40-50Hz "hump" is NOW pushed down -20dB. You're not going to even notice that (prob'ly not even if your subs aren't running).

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  • billfitzmaurice
    replied
    Originally posted by Trdat View Post
    Your telling me when I switched from my closed box SVS sub at around .9 QTC to a .7 QTC DIY sub then improved that same DIY sub to a .58 QTC I was imagining things?
    Of course not. When you lower Q you lessen the possibility for boomy midbass, which tends to dominate the response, not in a good way. This assumes that all else is equal, which it seldom is.
    if I am crossing over the Visaton's to subwoofers around 150hz
    Crossing to subs above where the subs are directionally locatable isn't recommended, it severely limits where the subs may be placed. Using a pair of twelves to go to only 150Hz is a waste of driver capabilities and box size. For that matter if you're only going to even 100Hz the added size and complexity of a ported enclosure, and twelve inch drivers, doesn't make a lot of sense other than in very high output pro-sound applications. I fear that you may have chosen the Visaton design for the wrong reasons and may be trying to force a square peg into a round hole as a result.

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  • Trdat
    replied
    Okay I have done some hefty research on this including chatting to renowned speaker designers. Either I have totally misunderstood the concept or there is two sides of the coin and I only came across one side of it.

    I am happy to break the myths, I am here to learn but I need to understand the concept that your proposing so I can get a take away from this.

    So from what I gather, when as for example Paul Carmody suggests a two option in the Amiga enclosure design one with a smaller box volume with a slightly larger port really only is reducing the low bass which in turn gives us better transients? Remembering that the Amiga enclosure is bass reflex and that decreasing box volume it does decrease low bass so that I understand. Paul O, essentially that is what your saying right, lower QTC less low bass better transient response? But I thought in a closed box larger box doesn't necessarily give you higher F3 it actually keeps lowering the F3 so for a closed box ive lost the concept.





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  • Trdat
    replied
    Originally posted by Chris Roemer View Post
    You can't mess around w/ANY closed box rolloff curve and duplicate the tuning you're looking at from your MK3s. THAT design is trying to achieve pretty high SPLs, and one thing they've done is (apparently) created a "hump" in the 40-50 Hz range w/their tuning. Yes, you CAN push that hump down (SIMILAR to lowering the Q of a closed box system) by making the port longer. You'll also lose extension..

    I am happy to loose extension. But what I would like to understand is if I am crossing over the Visaton's to subwoofers around 150hz would the cutting out the lower frequencies from the Visaton's have the same effect on 150hz and above if I was to make the port longer? Or would I still need to extend the port to get rid of that hump even though its crossed over?

    Essentially its just that hump that is not making it as transient as it could?


    I can stuff the port and essentially get a lower QTC and make it more like a sealed box, I will loose sensitivity and SPL but its an option. But the same question applies here, if I am crossing over with subs at around 150hz would what is above 150hz be effected by the stuffing of the port if the crossover will ultimately cut of the long wavelength frequencies?

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  • Paul O
    replied
    Lower QTC = less low bass = better transient response just like the article says. And as stated in the article and from what I have seen countless times drivers with weak motors don't have as much control over the cone as those with stronger motors.

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  • Chris Roemer
    replied
    Have you ever heard of "Q" (more of a closed box function than a reflex box) described as a "quality" factor? MOST people are okay w/a closed box Q above 0.7, up to about 1.0 before it starts sounding "boomy". (You've described changing the Q on other subs you've had by making the box larger.) You can SEE the diff. between a (closed box) Q of 0.50 vs 1.0 by modeling in your box program. While the rollofff curve shape (the "Q") of a closed box gets less "steep" as the box gets larger, it's ALSO (probably) limiting the system's extension. If you NEED 40Hz in a room, and you've got a box w/a Q of .80 but it's also got an F3 of 20Hz, you can make the box larger (lowering the Q) but still have adequate extension (maybe still down to 30). OTOH if you've got a box w/a Q of 0.80 (but its F3 is BARELY 40Hz) and you make the box larger, your Q WILL drop, but you'll probably also lose your 40Hz extension. (NOTE: MANY air-suspension designs of the 60s, 70s, 80s (think AR, KLH, and ADVE\T - all Henry Kloss designs) did NOT have Qs near 0.50, or EVEN 0.70 ... Qs of .80, .90 and even 1.0 were pretty typical. They kinda needed Qs that high to hit that 40Hz F3.)

    You can't mess around w/ANY closed box rolloff curve and duplicate the tuning you're looking at from your MK3s. THAT design is trying to achieve pretty high SPLs, and one thing they've done is (apparently) created a "hump" in the 40-50 Hz range w/their tuning. Yes, you CAN push that hump down (SIMILAR to lowering the Q of a closed box system) by making the port longer. You'll also lose extension.

    If you feel you can hear that "hump" (and don't like it), an easier way to TRY lowering the hump (rather than lengthening the slot vent) would be to throttle down your port cross-section, like by inserting a wood block the length of the port. Instead of doubling (or tripling) the slot length (sorta harder to try), just block off 1/4, or 1/3, or even 1/2 the width of your slot (but it's got to be the entire length(depth) of the slot, not just the opening at the front). Sure, at high output levels you'd expect chuffing, but by keeping the SPLs lower (to avoid chuffing) you should still be able to assess the "Quality" of your rolloff situation. If you find a rolloff curve you like better, monkey around in WinISD to dupe THAT curve (permanently) by THEN lengthening your port.

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  • Trdat
    replied
    Your telling me when I switched from my closed box SVS sub at around .9 QTC to a .7 QTC DIY sub then improved that same DIY sub to a .58 QTC I was imagining things?

    There was clearly an improvement in the overhang, sounded so much better that when putting the SVS sub against the my DIY sub I threw the SVS sub out to the trash. Tight bass is no overhang, I can't define it i am not an expert but its there when you lower QTC, I know it doesn't have as much to do with the higher frequencies hence it might be something I dont need to worry about on the Visatons especially if I am crossing over with a sub.The Visaton should be a well designed enclosure but I am designing the Visaton in accordance to my taste and want to make sure the trade offs are in my favor.


    How can transient bass not exist when clearly its obvious. What could I be hearing if it doesn't exist? I thought it was one of the most important parameters of designing woofer enclosures....

    I totally understand bass cant be fast but there has to be a way to choose how transient the bass is with box volume and port length or by other measures?

    Are you suggesting that this is something I don't need to worry about when designing an enclosure for woofers?







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