Greets!
No need to apologize, I was just surprised at your remark since several folks have shown off different designs for this driver on various forums over at least the last couple of years. The only reason there's not more is few are willing to spend this much on a 'fullrange' driver, much less a Fostex.
FWIW, here's my Vb = Vas, Fb = Fs ML-TL based on my way of calcing them:
L = 45.22"
CSA = 133.5"^2
zdriver = 17.81"
rp = 1.25"
lp = 2.13"
zport = near/at the bottom
Obviously, this puts the driver too low, so a mass loaded bottom chamber is required, which can do double duty as stabilizing stand. This long a pipe needs a massive top also, whether multiple layers of wood, or my fave, a marble, slate, or similar decorative top plate.
Since MJK's WS's adds the flexibility though of what's possible with increased stuffing that I wasn't willing to explore on an experimental basis decades ago, a longer pipe to shift the driver up to ear level can yield most of the smoothness without what I consider the excessive damping required when the driver is placed near/at the top and the vent near/at the bottom typical of BR 'tower' designs:
L = 55.38"
CSA = 133.5"
zdriver = 20.2"
rp = 1.5"
lp = 2.13"
zport = near/at the bottom
In each case ~2.35 ohms series R is required based on published specs for a T/S max flat alignment.
GM
No need to apologize, I was just surprised at your remark since several folks have shown off different designs for this driver on various forums over at least the last couple of years. The only reason there's not more is few are willing to spend this much on a 'fullrange' driver, much less a Fostex.
FWIW, here's my Vb = Vas, Fb = Fs ML-TL based on my way of calcing them:
L = 45.22"
CSA = 133.5"^2
zdriver = 17.81"
rp = 1.25"
lp = 2.13"
zport = near/at the bottom
Obviously, this puts the driver too low, so a mass loaded bottom chamber is required, which can do double duty as stabilizing stand. This long a pipe needs a massive top also, whether multiple layers of wood, or my fave, a marble, slate, or similar decorative top plate.
Since MJK's WS's adds the flexibility though of what's possible with increased stuffing that I wasn't willing to explore on an experimental basis decades ago, a longer pipe to shift the driver up to ear level can yield most of the smoothness without what I consider the excessive damping required when the driver is placed near/at the top and the vent near/at the bottom typical of BR 'tower' designs:
L = 55.38"
CSA = 133.5"
zdriver = 20.2"
rp = 1.5"
lp = 2.13"
zport = near/at the bottom
In each case ~2.35 ohms series R is required based on published specs for a T/S max flat alignment.
GM
Scottmoose said:
Yes. Gif is a non-lossy format, so no artifacts. And if your software is powerful enuff (i recommend PhotoShop Elements to anyone doinfg casual raster file processing), you can force the gif to 2^n (n=<8) colors, in the case of the charts you are posting probably 8 colors, which makes picking out the red curve a 1 step process 🙂
dave
Thanks for the advice Dave -I'll definitely shift to gif images in future posts & I'll look ino Photoshop Elements too.
GM -as always, I'm in your debt for suggeting new (to me) ideas to consider, with other observations too: the over-damping part of having a driver / port too near the top / bottom is particularly interesting to me -I'll start to look into that. Could you expand a bit on your views in this? Many thanks once again for the input and advice.
Best
Scott
GM -as always, I'm in your debt for suggeting new (to me) ideas to consider, with other observations too: the over-damping part of having a driver / port too near the top / bottom is particularly interesting to me -I'll start to look into that. Could you expand a bit on your views in this? Many thanks once again for the input and advice.
Best
Scott
Well, it had to be done: I've just modelled GM's two MLTLs for the F200a in the latest MathCad sheet. Absolutely superb (as you'd expect). Here's the anechoic prediction for the shorter enclosure assuming just 0.25lbs ft^2 of stuffing (in gif format Dave!!!). As you can see, there's a slight decrease in the response just before cut-off which will likely make their in-room performance better ballanced than one with a peak or a completely flat anechoic response.
Attachments
I didn't run the in-room response for this one however, as Greg appears to favour the second, longer enclosure. Here's the anechoic prediction of that one with the same stuffing density (there will, however, be quite a lot more of it, by virtue of the longer line-length). A fractional increase will clobber the tiny wriggle, but personally, I wouldn't exactly be loosing any sleep over that whatsoever.
Attachments
And here's the in-room prediction. Don't set much store by this, because it's dependent upon many factors, not least the HxW dimensions used, and is not going to be optimal. Carpeted room, front baffle 32" from the rear wall, front port, nearfield and on-axis. Very, very good indeed I would say.
Attachments
Greets!
You misunderstood, placing them at the ends causes peaking at Fb since this is where the pipe's max gain is, and too much comb filtering between driver/vent in any decent length pipe IMO, ergo much more stuffing is required to damp it all down. For limited BW apps, this isn't an issue, but in wide BW apps it 'sucks' too much 'life' out of them for my tastes.
BB OTOH builds to a height limit, sets the driver as low as practical, then raises the vent to smooth it out somewhat to ~split the difference, so to speak.
Trade-offs, always trade-offs, so 'optimum' is in the 'eye of the beholder'. 😉
GM
You misunderstood, placing them at the ends causes peaking at Fb since this is where the pipe's max gain is, and too much comb filtering between driver/vent in any decent length pipe IMO, ergo much more stuffing is required to damp it all down. For limited BW apps, this isn't an issue, but in wide BW apps it 'sucks' too much 'life' out of them for my tastes.
BB OTOH builds to a height limit, sets the driver as low as practical, then raises the vent to smooth it out somewhat to ~split the difference, so to speak.
Trade-offs, always trade-offs, so 'optimum' is in the 'eye of the beholder'. 😉
GM
Ah, I see what you were getting at now -obviously not one of my brighter moments! I try not to have a driver mounted closer than 0.25 of the line length to So for similar reasons, as I refuse to go over 0.5lbs ft^3 of stuffing, and preferably no more than 0.35lbs ft^3 if possible. Unless it's an MTM design of course, when one driver will often be closer -I'll keep the taller options in mind now though as a way of avoiding that; good tip. As / when Martin gets his twin-driver additions going it'll be interesting to see the effects and if they need more stuffing than the current sheets predict.
Cheers
Scott
Cheers
Scott
DDF posted:
I don't fully understand what is being said about "fiber board". The material I'm aware of is referred to a "duct board" and used in HVAC installations. It is available in thicknesses of 1/2, 3/4, and 1". I believe it is available in greater thicknesses.
What would be the likely result from using this material at each end of the line? Damping? Attenuation?
I don't fully understand what is being said about "fiber board". The material I'm aware of is referred to a "duct board" and used in HVAC installations. It is available in thicknesses of 1/2, 3/4, and 1". I believe it is available in greater thicknesses.
What would be the likely result from using this material at each end of the line? Damping? Attenuation?
I assume it should damp out the higher harmoics a bit like stuffing -after all, that's the point of stuffing or lining the enclosure in the first place. Or at least, that's my view. Have a look at BB's comments on his Mk2 FE167E MLTL -scroll down a bit to get there; the first half of the page is all his original Mk1 stuff. He observes that the lined cabinet is 'over-damped' with the bass rounded off, but F10 remains the same, which pleases him (as it should) because it means that with the room factored into the game, the speakers are unlikely to 'boom'. Interesting.
http://www.geocities.com/rbrines1/Pages/FT-1600_MkII/Design_Details.html
Best
Scott
http://www.geocities.com/rbrines1/Pages/FT-1600_MkII/Design_Details.html
Best
Scott
It would seem Bob Brines is on to something. I'm going to consider leaving cabinet interiors accessible to allow changing the stuffing/lining approach during the prototype stage.
An alternate to the Hardi-Backer he uses is Durock. These cementitious boards are used as backing/underlayment for creamic tile.
Thanks for the references.
An alternate to the Hardi-Backer he uses is Durock. These cementitious boards are used as backing/underlayment for creamic tile.
Thanks for the references.
Speaking of accessibility, I've been wondering about this.
I'm wondering whether one can make an eye-pleasing cabinet which is designed to be easily accessible, like with screw handles or some sort of latching system.
A pressure-cooker latching system is what I have in mind. Add some sort of gasket material, and I wonder if the force of a latching system would create a better-sealed cabinet, or at least, a more-reliably sealed cabinet that would look cool.
But I think this departs from the topic. Dunno where to put these thoughts, since they're almost random.
Um...
Dave
I'm wondering whether one can make an eye-pleasing cabinet which is designed to be easily accessible, like with screw handles or some sort of latching system.
A pressure-cooker latching system is what I have in mind. Add some sort of gasket material, and I wonder if the force of a latching system would create a better-sealed cabinet, or at least, a more-reliably sealed cabinet that would look cool.
But I think this departs from the topic. Dunno where to put these thoughts, since they're almost random.
Um...
Dave
Scottmoose said:
Greets!
Thanks, but my default calculation is a T/S max flat, so I'm curious what specs you used since even the IB plot is a bit different.
As your room sim implies, it's typically not a good in-room alignment unless the room's quite large and the speakers are well away from any wall/corners, but it's what so many folks want/expect to see for comparison purposes that I've given up posting more room friendly ones unless specified. EBS alignments or vent damping works well to get a flatter in-room response for when Fb is down below the beginning of room gain and of course any sealed alignment with a <0.7 Qtc is typically room 'friendly'. In a perfect system though, the room will have a 12 dB/octave room gain curve and the speaker will have a complimentary sealed alignment with a matching F6 so that they sum flat.
Most rooms become increasingly transparent with decreasing frequency though, so to get a ~flat alignment to very low frequencies normally requires some peaking at Fc/Fb/Fp, so huge IB, BP, or TL loaded with very low Fs drivers has historically been the preferred way to do this. Today though, mass quantities of power and drivers that can handle it combined with digital EQ can be had relatively cheaply, so has become the new 'standard' in this 'brave new world' of miniaturization, shrinking room size true sub systems (as opposed to the typical LF systems being pawned off as 'sub' systems) into 2 ft cubes. Just like comparing optimum Vs 'small' horns though, something gets 'lost in the translation'.
GM
Port Location
Hello Scott and GM:
This is a very interesting thread with much of the dialog over my head. I have noticed the GM likes to put the port at or near the bottom while Scott has been locating it 3 or 4 inches up. I have built designs with the port exiting the bottom. With the cabinet on "legs" of 1.5 to 2 inches. Could either of you discuss the impacts on the sound of these port locations.
I like the port out of the bottom as I do not like the large hole in the cabinet look of front or rear baffle mounted port.
Great discussion
Hello Scott and GM:
This is a very interesting thread with much of the dialog over my head. I have noticed the GM likes to put the port at or near the bottom while Scott has been locating it 3 or 4 inches up. I have built designs with the port exiting the bottom. With the cabinet on "legs" of 1.5 to 2 inches. Could either of you discuss the impacts on the sound of these port locations.
I like the port out of the bottom as I do not like the large hole in the cabinet look of front or rear baffle mounted port.
Great discussion
Ed Lafontaine said:
Greets!
FYI, BB uses this as a consequence of preferring to build with MDF, so if building with a much more rigid/less massive material such as no-void plywood, then you're 'shooting yourself in the foot' by adding something massive unless isolated by a non-hardening, lossy glue to make a constrained layer panel isolation system. I don't know for sure, but I doubt the only glue I know of that otherwise suits the app is strong enough to keep the panels from falling over time/movement and any solid means of support will defeat most of its damping ability. Instead it will basically just lower the panel's Fs, the exact opposite of what you want to do, so bracing to further increase the cab's rigidity is the way to go, then any minor resonances left are easily damped to below the noise floor with the interior reflection's absorption lining.
GM
kneadle said:
Greets!
FYI, I used Dzus fasteners and nema 4/4x rated neoprene gasketing for quick access with superior sealing on electrical switch, etc., boxes in racing apps, so will be almost 'overkill' in a speaker app: http://www.southco.com/product/default.aspx?cid=7514
The gasket material should be available from your local electrical jobber supply house.
GM
shazzam! But does your enclosure look good? Or does it look like a test enclosure?
Thanks,
Dave
Thanks,
Dave
Re: Port Location
Greets!
Hmm, Since I prefer to put the driver at the pipe's focal point to damp the 3rd harmonic, the vent needs to be an extension to the pipe, ergo short as practical, otherwise it audibly shifts the focal point and I don't know how to factor this in my simple calc, and as I noted in post 127, with the driver placed between this point and the closed end of the pipe, the vent needs to be raised to offset some of the consequences to the FR.
WRT floor loading, I'm a big fan of it when it's practical to use it since you can tune its Q via the box/floor or base gap and why the few designs I've done that Dave has made nice drawings of are bottom exit.
Sound wise, it's all about getting the flattest in-room response, so whatever works, but it's been my experience that a low Q vent alignment sounds best overall, i.e. 'sealed with gain' as I like to describe it.
GM
SCD said:
Greets!
Hmm, Since I prefer to put the driver at the pipe's focal point to damp the 3rd harmonic, the vent needs to be an extension to the pipe, ergo short as practical, otherwise it audibly shifts the focal point and I don't know how to factor this in my simple calc, and as I noted in post 127, with the driver placed between this point and the closed end of the pipe, the vent needs to be raised to offset some of the consequences to the FR.
WRT floor loading, I'm a big fan of it when it's practical to use it since you can tune its Q via the box/floor or base gap and why the few designs I've done that Dave has made nice drawings of are bottom exit.
Sound wise, it's all about getting the flattest in-room response, so whatever works, but it's been my experience that a low Q vent alignment sounds best overall, i.e. 'sealed with gain' as I like to describe it.
GM
kneadle said:
Greets, part deux! 😉
No, obviously there was no need, but if you look at what all Dzus has available, you'll see that they have a number of systems that will suit your needs. Anyway, I would make the entire back the access panel, so unless these will be seen from the rear, it's not much of an issue.
GM
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