my new 604 cabinets I'm building.

Well it sounds like you don't need any help at all !! Great Job BTW ! :Thumbs up:

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Originally Posted by Altec Best

Well it sounds like you don't need any help at all !! Great Job BTW ! :Thumbs up:

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Thank's AB, I really don't have a clue what I'm doing just rehashing all the info I read on the net. Eventually it kinda makes sense and if I get enough of the same opinion I feel like I can pretty much trust that it's true. :) BTW that Martin J king stuff goes over my head like the space station. I don't think I would be able to understand it if Martin himself was telling it to me himself one word at a time.

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Originally Posted by Altec Best

You need to be exact with the numbers to be accurate with the results. I think you said 12.44 cubic feet in an earlier post.But from that .jpg looks like you put in 12 cubic ft.IIRC you have 2 different 604's that you had GPA recone correct ? If so what did they recone them as 604 g,h, ???

He came up with the 41 Hz from your port dimensions I think.You may need to add length to the port to lower it some. 25-30 Hz port tuning is more in line for HiFi/HT I think GM was getting at.

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I do have 2 different 604's a"C" and an "E" GPA did not recone them as they said they didn't need it and I would be better off leaving them alone so I did.

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Originally Posted by cradeldorf

I just don't know how he calculated the 41 hz box tuning frequency? I just used this online one and came up with 29.4836? Not sure If I'm doing it right, but it looks right. Did you read the link I posted in post #32 by
John L. Murphy Physicist/Audio Engineer?

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Easy, I used well-proven math for vented alignments, not the formula for a heavily stuffed sealed alignment as this calculator does.

Yes, I?m familiar with it; the basslist threads I was usually a part of prompted many of his tech topics. For the record though, his generalizations are just that, a ?vents for dummies? tutorial since at the time few of us on the forums that understood most/all of the ramifications didn?t want to part with our hard won knowledge just so folks could go off and use it for profit.

Anyway, if anyone is serious about DIY speaker design as a hobby or business, I strongly recommend you use MJK?s MathCad software [please pay the business fee if applicable] as it?s the most accurate I?ve ever used and not nearly as hard to learn in depth as AkAbak.

FWIW, the math I?ve used for decades to calculate vents match right up with his calculations when a lightly damped golden or acoustic ratio cab is simmed and his MLTL vent calculations line up with the measured results of some of my old designs I still had final details of, so confident enough that any other alignments would be too, though if I needed it to be tuned to Fs I would cut the vent[s] too long and do the measurements to fine tune it.

GM

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Originally Posted by VolvoHeretic

I'm still quite confused on this, especially after reading my Radio Shack "Advanced Speaker Design" book three times and doing all of the math long hand. Isn't the only frequency coming out of the port the box/port resonance and at Fb the speaker is motionless and all of the air motion is in the port and in faze with the woofer? Doesn't aiming the port out the rear, bouncing off of the wall make it out of faze with the woofer? :)

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It?s a narrow pass-band of frequencies with its width [Q] being determined by the vent and system Q which in turn determines how ?locked up? the driver is at Fb. Consequently, it?s only in acoustic phase at Fb, rotating increasingly out of phase on either side as shown on an impedance or transfer function phase plot. This animation does an excellent job IMO of visualizing driver/vent interaction: Essay

This is addressed in JM?s tech note. Still, I?ve used rear and bottom firing to good effect and in many cases preferred bottom firing for MLTLs, using adjustable feet to fine tune vent loading.

GM

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Originally Posted by GM

Easy, I used well-proven math for vented alignments, not the formula for a heavily stuffed sealed alignment as this calculator does.

Yes, I’m familiar with it; the basslist threads I was usually a part of prompted many of his tech topics. For the record though, his generalizations are just that, a ‘vents for dummies’ tutorial since at the time few of us on the forums that understood most/all of the ramifications didn’t want to part with our hard won knowledge just so folks could go off and use it for profit.

Anyway, if anyone is serious about DIY speaker design as a hobby or business, I strongly recommend you use MJK’s MathCad software [please pay the business fee if applicable] as it’s the most accurate I’ve ever used and not nearly as hard to learn in depth as AkAbak.

FWIW, the math I’ve used for decades to calculate vents match right up with his calculations when a lightly damped golden or acoustic ratio cab is simmed and his MLTL vent calculations line up with the measured results of some of my old designs I still had final details of, so confident enough that any other alignments would be too, though if I needed it to be tuned to Fs I would cut the vent[s] too long and do the measurements to fine tune it.

GM

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I love how you force us to learn, it kinda feels like your a professor and were your pupils. It truly is a good feeling and as my dad used to say nothing worth earning is free. I have the winIsd at home on my puter so I'll fire it up and see if I can remember from the last time I tried using it. As always Thanks Greg.

Wow--lots of great info for all of us to absorb here--thanks GM! I was about to put an SOS message on this thread (Save Our Speakers)! Much of this goes over my head but I'm going to do some reading and see if I can make (more) sense of at least some of it. Greg, I know this stuff is not always completely black and white, but do you think Cradeldorf is "better off" putting the port on the front or the back of his cabinets? Also, 65 square inches seems awfully big to me for a port size if he wants to get a "modern hi-fi" tuning for his cabs (as you alluded to)--any suggestions (even a ballpark suggestion?) as to what port dimensions may get him a nice low tuning--say closer to the tuning of the Model 19 cabinets?

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Originally Posted by cradeldorf

I'm mulling over filling all the voids between the braces with 2" egg crate foam. I hope the 2" is the total height of the foam plus the eggs and not just the foam itself.

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Originally Posted by Altec Best

I'm not sure foam is a good dampening material internally in the cabs.Good old Fiberglass insulation performs better IMO.YMMV

Maybe someone else could help out with this decision and chime in.I only ever use insulation.

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Anyone have any preferences/ideas that they'd like to share as far as this "egg crate" foam vs. more conventional insulation?

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Originally Posted by cradeldorf

I think you would be astonished at how much bass my as101's make Vott. they literally shake the fillings in my teeth. :; <---see one tooth fell out already. :D ......

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I'm not saying that the current tuning of your AS 101 cabs with regard to being used with 604's isn't resulting in enough bass. Quite the contrary, from this post and some of your other posts in other threads, I think the fact that those cabs were not tuned with 604's in mind may be giving you way too much mid-bass response which is throwing off the ratio of midrange to midbass to the "lowest" bass your speakers can produce and resulting in a "mess" (yes, I know, a very technical term) and the "shelf" that someone added in a failed attempt to implement DBR tuning may be reeking havoc with the tuning/sound quality as well in ways I can only imagine since I haven't heard them. Hopefully these new cabs, once tuned/ported/insulated/etc. "properly", will sound great!

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Originally Posted by cradeldorf

I think you would be astonished at how much bass my as101's make Vott.

I wish Greg hung out here more....

I think I'm gonna split the back board so I can just replace the bottom half with a different one with a different port size in it.

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Bass or mid-bass? Vintage tunings typically were mostly mid-bass, same as most prosound still are, not to mention most recorded music peters out quickly below ~40 Hz or higher in older recordings.

Regardless, without response measurements at the listening position [LP], need to know how much series resistance there is as well as room acoustics to zero in on what you?re hearing, so mostly a rhetorical question unless you have perfect pitch.

Circumstances has forced me into a ~ one [more like half] man ?crew? doing a whole property rehab on a shoestring budget, so at best probably won?t have much quality time for at least another year to spend much time on the forums, PMs, etc.. The rain has stalled me till probably tomorrow and should be doing indoor stuff, but you know how it is with hobbies??..

Good plan, I typically recommend a removable/gasketed vent panel to allow easy tuning changes. That, or use heavy cardboard or PVC pipe vents left extended enough to easily swap them out, using blu-tac or similar to temporarily seal them to the baffle.

GM

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Originally Posted by cradeldorf

I'm mulling over filling all the voids between the braces with 2" egg crate foam. I hope the 2" is the total height of the foam plus the eggs and not just the foam itself.

I don't think I need dampening, That's only for small boxes that you want to make sound larger than they are. What I want is to break up the standing waves and keep the mid frequency waves from bounding all around the inside of the cabinet and coming out through the port or cone.

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I’m no fan of foam, but would only use open cell, otherwise the closed cell will reduce net Vb somewhat, but no clue how much. Also, it’s my understanding that it works best when spaced away from the walls, though don’t know how far, and any braces must be covered also; so hanging a full length ‘blanket’ of it diagonally across the cab *plus damping the inside of the top* seems the best solution overall.

Your cab’s internal dims falls within the acceptable room ratios, so I normally recommend using Altec’s, i.e. lining one wall, back and end opposite the vent with 1” acoustic fiberglass insulation or if polyfil stuffing [AKA damping] is preferred, starting with ~1.67x the fiberglass’s calculated lbs/ft^3 stuffing density and adjust more/less to ‘taste’. My SWAG is that this equates to a ~0.25 lbs/ft^3 polyfil stuffing density using MJK’s software.

GM