There is always more than meets the eye, never forget this.
About that journalist of yours, how hard can it be to go through
other people's dirty laundry? Nice people don't do that.
Of course you can use it, manufacturers are not idiots, you know.
You simply haven't opened up one yet to see for yourself.
As you introduce more of the stuffing in the box, the air gets stiffer
and the spl of the driver goes down. To produce the same spl like
with the unstuffed version, you need to increase the force to compensate
for the loss. Modeling programs do show how the effect of stuffing
decreases the spl and Qtc by lowering the Qms ( Fs peak lowered in magnitude).
Actually Lojzek, I have looked inside, and even built a few reflex speakers. You usually carefully place a bit of light BAF wadding or eggcrate foam near the sides in a reflex to control the midrange leaking out through the port in reality. Not to affect the bass.
The theory of reflex (aka Helmholtz Resonance) says let the air move freely from the bass to the port.
You CAN heavily stuff a reflex, but then it's not a reflex anymore. It's an aperiodic or damped reflex. Closer to closed box. FWIW, to damp the port you insert drinking straws! It can sound very good, and might even be the answer here.
But back on topic, acstcwrfrmn. I built a 30L box with a Qts 0.33 Reflex Driver and stuffed a sock in the port for giggles. TBH, it really didn't sound half as good as a proper old unobtanium Elac closed box driver in 30L.
But I don't see why you couldn't take a chance on some high Qms 8" reflex driver in 30L of closed box. After all, you just cut out a reflex tube and lower the bass coil value appropriately if it doesn't really win a cigar.
The theory of reflex (aka Helmholtz Resonance) says let the air move freely from the bass to the port.
You CAN heavily stuff a reflex, but then it's not a reflex anymore. It's an aperiodic or damped reflex. Closer to closed box. FWIW, to damp the port you insert drinking straws! It can sound very good, and might even be the answer here.
But back on topic, acstcwrfrmn. I built a 30L box with a Qts 0.33 Reflex Driver and stuffed a sock in the port for giggles. TBH, it really didn't sound half as good as a proper old unobtanium Elac closed box driver in 30L.
But I don't see why you couldn't take a chance on some high Qms 8" reflex driver in 30L of closed box. After all, you just cut out a reflex tube and lower the bass coil value appropriately if it doesn't really win a cigar.
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I will carry on, thankyou.
Funny where the muse leads you. The original poster is talking about closed box sound from 30L with drivers that don't quite fit the Qts 0.5 bill.
This SEAS CA22RNX looks reasonable, with a Qts of 0.41.
H1288-08 CA22RNX
The more I look at the aperiodic idea, the more I like it:
SEAS A26 Kit
Well, this has certainly been interesting and informative both. I've been busy the last several days and just now getting back into this. Sorry guys, I definitely screwed up! A thousand pardons as they say! On the PE site, if you type "rs225" or "rs-225" in the search bar, you get different returns (I was using the specs. for the new paper cone driver instead of the original aluminum one).
I have calculated box size and f3 for several drivers below: I've been doing this the ancient way with a hand calculator and the Dickason LDC formulas since the late 1980's. Anyway; here's what I get assuming a total added DCR of 0.5 Ohms
RS225P 25L, 65Hz
RS225 29L, 49Hz
Seas L22RN4X/P 18.4L, 52Hz
Seas CD22RN4X 17L, 54Hz
Motus UH205PW1 33L, 46Hz
Scan Classic 21W/8555-00 33L, 46Hz
SB23MFCL45-8 30L, 43Hz
SB23NRXS45-8 38L, 50Hz
SB23NACS45-8 36L, 48Hz
I'm a very slow typer so I hope I don't get logged out...to be continued
I have calculated box size and f3 for several drivers below: I've been doing this the ancient way with a hand calculator and the Dickason LDC formulas since the late 1980's. Anyway; here's what I get assuming a total added DCR of 0.5 Ohms
RS225P 25L, 65Hz
RS225 29L, 49Hz
Seas L22RN4X/P 18.4L, 52Hz
Seas CD22RN4X 17L, 54Hz
Motus UH205PW1 33L, 46Hz
Scan Classic 21W/8555-00 33L, 46Hz
SB23MFCL45-8 30L, 43Hz
SB23NRXS45-8 38L, 50Hz
SB23NACS45-8 36L, 48Hz
I'm a very slow typer so I hope I don't get logged out...to be continued
Continuing: Based on a TOTAL box size of 28L (1ft^3); the only 2 drivers above are the two Seas Prestige. These calculations are all net box volume; add in maybe 3, 5, 7 liters, etc. for the internal dimensions of drivers, X/O's, stiffeners, bracing, etc. Bringing the overall box size to my goal); All of the other drivers above won't work in my application UNLESS, box stuffing and/or using an aperiodic vent work their magic thus allowing for smaller enclosure volumes!
This is only a hobby for me; always has been, always will be that way. I don't want or need fancy software, testing and measuring equipment. I now use online calculators and test tones but that's about it. I have several test CDs and an old Radio Shack SPL meter. I have never made a penny on any design or build; just cost of parts and materials. My labor charges are usuall a few beers and burgers on the grill.
Thanks for showing me the error of my ways! Glad to know everyone is on their toes! regards.
I will carry on, thankyou.
Funny where the muse leads you. The original poster is talking about closed box sound from 30L with drivers that don't quite fit the Qts 0.5 bill.
This SEAS CA22RNX looks reasonable, with a Qts of 0.41.
H1288-08 CA22RNX
The more I look at the aperiodic idea, the more I like it:
SEAS A26 Kit
We are sort of thinking along the same terms. I have used various stuffing materials over the many years but only notice maybe a drop in F3 10% or less (small, closed boxes). I have been interested in Aperiodic vents for over 20 years but have never actually tried one. Dynaudio had some good white papers on this technique back in the day. Madisound seems to carry the Scan Speak equivalent. Maybe it's about time to give them a try!??
I used aperiodic with an Eminence 8 Alpha driver IIRC, years back in 30L of Wharfedale Linton cabinet I found in the street. Drinking straws in the port, a little stuffing and carpet lining. I was tuning by ear. I started with closed box and added a big adjustable plastic port later. It was one of my better speakers in the end. Sure went LOUD! A big Audax 1.5" TWO34 tweeter, IIRC.
Vtc=Vas divided by (Qtc/Qts)^2 - 1, IIRC. For closed box.
http://www.diyaudio.com/forums/diyaudio-com-articles/158899-arpeggio-loudspeaker.html
Quite a superb article IMO. Loudspeaker calcs made easy. Morgan Jones is a retired BBC engineer. Only one member here described it as BS. You can guess who that was!
TBH, I wonder if we've been making this more difficult than it is?
H1288-08 CA22RNX
Employed HERE: SEAS-3-Way-Classic
If I haven't lost my touch, that driver will be Qtc 0.8 in 30L. That's really not bad, and a smaller bafflestep coil with resistance will not only send the Qts in the right direction, but tone down the peak where it gets lost in room gain. I quote a Morgan Jones graph of speaker Qtc below. And being a staunch Steen Duelund fan, the only sensible thing is to employ well-behaved drivers like the SEAS CA22RNX with his mathematically perfect target curves.
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OK, guys; you REALLY got me thinking here about the relationship between Qt' and Vas. I did some examples for my own benefit which I will try to show here. I do type very slowly so may have to break it up. I don't have MS Office (word, excel, etc. so this is very old school just like myself!)
Let's fix Qtc at 0.707 Vb at 23L
For the first example; I'm setting Fs at 27 Hz.
Vas=130L Qt'=0.274 F3=70Hz
Vas=100L Qt'=0.306 F3=62Hz
Vas=75L Qt'=0.343 F3=56Hz
Vas=60L Qt'=0.372 F3=51Hz
Vas=45L Qt'=0.411 F3=46Hz
Vas=28L Qt'=0.475 F3=40Hz
To be continued; have to let the dog outside!
Let's fix Qtc at 0.707 Vb at 23L
For the first example; I'm setting Fs at 27 Hz.
Vas=130L Qt'=0.274 F3=70Hz
Vas=100L Qt'=0.306 F3=62Hz
Vas=75L Qt'=0.343 F3=56Hz
Vas=60L Qt'=0.372 F3=51Hz
Vas=45L Qt'=0.411 F3=46Hz
Vas=28L Qt'=0.475 F3=40Hz
To be continued; have to let the dog outside!
Continuing on: (second example)
I'll keep Qtc at 0.707 and Vb at 23L
This time let Fs be 20 Hz
Vas=130L Qt'=0.274 F3=52Hz
Vas=100L Qt'=0.306 F3=46Hz
Vas=75L Qt'=0.343 F3=41Hz
Vas=60L Qt'=0.372 F3=38Hz
Vas=45L Qt'=0.411 F3=34Hz
Vas=28L Qt'=0.475 F3=30Hz
Now; I'm not saying these will all be possible given my price range of $150 or less. Obviously, these are just examples of what I'm trying to do. Finding actual 8 inch drivers that meet these numbers (or, at least come close) is an exercise in and of itself! Some of these combinations of TSP's don't even exist in the real world (I realize that!). Perhaps my leading post was not exact enough. I'm looking for a box size close to 28L (1ft^3) total GROSS. I did not mean the net internal volume for the woofer only. Also, I mentioned trying to use a 4 to 5 inch fullrange for the mids. Most fullrange drivers in this size range have a (much?) larger Vas than dedicated midrange drivers of the same size. Since I want a low X/O between about 200Hz to 400Hz; this means using cone drivers vs domes (which usually need to be crossed a min. of 600Hz; more practical 800Hz or higher).
Hope this clears up my original target design goals! Regards!
I'll keep Qtc at 0.707 and Vb at 23L
This time let Fs be 20 Hz
Vas=130L Qt'=0.274 F3=52Hz
Vas=100L Qt'=0.306 F3=46Hz
Vas=75L Qt'=0.343 F3=41Hz
Vas=60L Qt'=0.372 F3=38Hz
Vas=45L Qt'=0.411 F3=34Hz
Vas=28L Qt'=0.475 F3=30Hz
Now; I'm not saying these will all be possible given my price range of $150 or less. Obviously, these are just examples of what I'm trying to do. Finding actual 8 inch drivers that meet these numbers (or, at least come close) is an exercise in and of itself! Some of these combinations of TSP's don't even exist in the real world (I realize that!). Perhaps my leading post was not exact enough. I'm looking for a box size close to 28L (1ft^3) total GROSS. I did not mean the net internal volume for the woofer only. Also, I mentioned trying to use a 4 to 5 inch fullrange for the mids. Most fullrange drivers in this size range have a (much?) larger Vas than dedicated midrange drivers of the same size. Since I want a low X/O between about 200Hz to 400Hz; this means using cone drivers vs domes (which usually need to be crossed a min. of 600Hz; more practical 800Hz or higher).
Hope this clears up my original target design goals! Regards!
Not sure what you really mean by this. To say it is pointless to try a high Vas driver in a small closed box is only accurate if the Qt' is ALSO high. My exercise shows that a high Vas driver with a low Qt' can work in a small, closed box with a lowish F3. Likewise, a low Vas driver with a high Qt' will also work in a small, closed box with a lowish F3. This is my design goal for this particular project. I am retired; I think up different ideas weekly, sometimes daily. There is nothing wrong with my methods, not fancy I agree!
I really don't want or need high tech software or hardware. The basic formulas have not changed. I have had many successful designs and builds doing it the old fashion way (ie good, predictable results; with verifiable, in room measured data). Again, this is a hobby only. If I were doing designs and builds for paying customers on a regular basis then, of course, I would use SOTA software and hardware.
Hi,
You do protest far too much. Insisting on low Qts and Fs and high Vas
drivers for small boxes is pointless. I never said it wouldn't work, it does.
Being pedantic about the actual box volume and no stuffing smacks
of self justifying backtracking to me, your not open to possibilities.
Simple fact, as most would agree, is the RS225-8 is a VFM no brainer.
rgds, sreten.
You do protest far too much. Insisting on low Qts and Fs and high Vas
drivers for small boxes is pointless. I never said it wouldn't work, it does.
Being pedantic about the actual box volume and no stuffing smacks
of self justifying backtracking to me, your not open to possibilities.
Simple fact, as most would agree, is the RS225-8 is a VFM no brainer.
rgds, sreten.
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I lost interest when I read this:
-such a waste.
Even a small child would have the follow-up question of "where/how can I get modeling software?"
..and then there are those things called "search engines".
-such a waste.
Even a small child would have the follow-up question of "where/how can I get modeling software?"
..and then there are those things called "search engines".
OK, I'll keep going. Here is what I am basing this on, pure and simple:
RS225 56.8L, 28.3Hz, Qt' of 0.41. I get very close to 29L NET, F3 49Hz.
Seas L22RN4X/P 93L, 21Hz, Qt' of 0.29 about 18.4L NET, F3 52Hz.
Seas CD22RN4X 108L, 20Hz, Qt' of 0.26 about 17L NET, F3 54Hz.
Again, net volume for woofer only based on about 23L so I can add in everything else internal bringing the total up to about 28L. The external box size is governed by the space I have available. If I COULD exceed 28L (gross/total) external; I surely would!
RS225 56.8L, 28.3Hz, Qt' of 0.41. I get very close to 29L NET, F3 49Hz.
Seas L22RN4X/P 93L, 21Hz, Qt' of 0.29 about 18.4L NET, F3 52Hz.
Seas CD22RN4X 108L, 20Hz, Qt' of 0.26 about 17L NET, F3 54Hz.
Again, net volume for woofer only based on about 23L so I can add in everything else internal bringing the total up to about 28L. The external box size is governed by the space I have available. If I COULD exceed 28L (gross/total) external; I surely would!
Hi, thanks! Yep, egos getting in the way here of pure physics! Anyway, take a good look at the Motus 8 inch. The guys at Solen said they really liked it. It has MANY good (desirable) specs. like Fs, Vas, SPL, X-max, higher frequency extension with a well behaved roll-off, etc. At least worth a look. Not sure if it is an Excel or Revalator equal though! regards.