Two-way speaker system, WAY horn-loaded
- Thread starter tubino
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tubino
A guy with too many tubes
Got the specs handy? I found that any of several Tannoys worked fine, but they all have low Fs, Qts in the area of .20 to .22. Other drivers with those specs, including Altec 515, work fine in mine.
I know that Steve is a good smart guy, but I can't help but think that his mods narrowed the range of drivers that work, and that possibly it takes a very different driver to work in his than in mine. I haven't measured it with any science, but I am getting PLENTY OF LOW BASS. I don't know where the -3db point would be, but honestly, I've got PLENTY for any recording I've put on, and in fact more would be TOO MUCH. (I've measured 110-120db in the horn mouth!) I see no problem with tinkering with easily-reversible stuff like constricting the throat a bit to see what happens, but I wouldn't want to try to "fix" mine by opening that chamber. I don't know what gain I would be hoping for.
I wonder if expanding the compression chamber so much requires greater excursion of the driver to really load the horn??? But maybe it kinda works with the right driver by changing the ratio of chamber to throat... sure would be easy to use some tape and wood blocks to try temporarily reducing the throat size before you cut the second one... In the name of science, please consider trying that before you saw the second one! Wouldn't it be something if you get the same LF loading to 20hz by doing that?
tubino
A guy with too many tubes
And in the name of science, I offer to try JBL 2226 in mine. It doesn't have the "rightest" specs, but ... I might learn something.
tubino
A guy with too many tubes
That's true! Confusing, ain't it?
??? Which ones do you mean there, and is the emphasis on SMALL? The ones I own (which I call Imperials, even though the plans don't say that) have a chamber, and it's BIG. I've seen the Decware plans (I paid for them through his site), and I see how Steve used that space to extend the chamber... but I am skeptical that that would be a good mod on mine.
tubino
A guy with too many tubes
I asked that question on the Decware forum and got no response. I don't know how to do it. I thought I might care enough to learn, but... I didn't. I sensed a big learning curve when almost none of the abbreviations made sense to me.
But I think it's a great idea.
tubino
A guy with too many tubes
OH! Now I get it. Can we call mine Jensen 1952s? Yes, mine have that sorta compression chamber with the constricted throat on either side. I keep meaning to try altering the dimensions with temporary wood blocks, but really haven't -- probably because it's already working well.
Depth: mine use 24" panels on the sides, plus back and front panels = ~25.5". That seems to be the same depth as in both of the plans you attached.
The difference in dimensions that I see is the height. Mine is 62", the "build-in" one is the same, and the corner one is 10" shorter.
tubino
A guy with too many tubes
Mine are built according to those 1952 plans from a Jensen bulletin. I've linked to it in this thread. A name would be handy, but I don't know it's possible to ID them any more thoroughly than the published paper and plans...
I live in West Toledo, not far from the University of Toledo. Short hop from 23 or 75 via 475.
tubino
A guy with too many tubes
The Importance of the Throat Formula in BLH
Way back in this thread (http://www.audiokarma.org/forums/showpost.php?p=1636856&postcount=3), I mentioned that Larry Moore pointed out that most old BLH designs have throats that are too large. In an issue of UltraFi Times, John Hasquin boils it down:
So let’s see how that works for my current setup. In that post I calculated the throat at 96 square inches. What would the Altec 515E want according to that formula?
Altec 515E: 0.8 x Fs 22.9 x Qes 0.19 x Vas 23.5 = 81.8 sq in
That suggests the current throat constriction is about 20% too large! (and once again, Larry is right...) Still, it could be worse. Let’s take a strong 15” driver that you might think would just need some horn loading for great bass.
JBL 2226: 0.8 x Fs 40 x Qes 0.33 x Vas 6.2 = 25.5 sq in
OOPS, wrong choice for this cabinet!
Seems for my cabinet, low Fs is fine, low Qes is fine, but then high Vas is needed. EDIT: I'm talking about fitting the THROAT proportions, not about the whole picture.
Way back in this thread (http://www.audiokarma.org/forums/showpost.php?p=1636856&postcount=3), I mentioned that Larry Moore pointed out that most old BLH designs have throats that are too large. In an issue of UltraFi Times, John Hasquin boils it down:
So let’s see how that works for my current setup. In that post I calculated the throat at 96 square inches. What would the Altec 515E want according to that formula?
Altec 515E: 0.8 x Fs 22.9 x Qes 0.19 x Vas 23.5 = 81.8 sq in
That suggests the current throat constriction is about 20% too large! (and once again, Larry is right...) Still, it could be worse. Let’s take a strong 15” driver that you might think would just need some horn loading for great bass.
JBL 2226: 0.8 x Fs 40 x Qes 0.33 x Vas 6.2 = 25.5 sq in
OOPS, wrong choice for this cabinet!
Seems for my cabinet, low Fs is fine, low Qes is fine, but then high Vas is needed. EDIT: I'm talking about fitting the THROAT proportions, not about the whole picture.
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dnewma04
The Healer
JBL LE15B might be a great option.
I'm laid up post surgery right now, but I can measure the VAS in a couple of weeks when I can start lifting decent weight up again.
These are the specs I got for the samples I have.
Re: 3.3-3.6 ohms
Fs: 24-26hz
Qts: .1633 - .1859
Qes: .1803 - .1950
Qms: 4.172 - 4.763
When I completed the measurements, my first thought was that they would love to be placed in a BLH.
I'm laid up post surgery right now, but I can measure the VAS in a couple of weeks when I can start lifting decent weight up again.
These are the specs I got for the samples I have.
Re: 3.3-3.6 ohms
Fs: 24-26hz
Qts: .1633 - .1859
Qes: .1803 - .1950
Qms: 4.172 - 4.763
When I completed the measurements, my first thought was that they would love to be placed in a BLH.
tubino
A guy with too many tubes
I'll give you a HELL YEAH! on that.
Yep that one might work well. All the Imp users I've talked to say that low fs, low qts, high sens. and working well in a 3 to 5 square foot cab is what you are looking for. The JBL 136 or pro version, 2231, has a fs of 16hz, qts of .2, is 96db, and needs 4 sq. ft. cab.
I think I am a bit lost though......are you not getting good bass out of yours T?
I think I am a bit lost though......are you not getting good bass out of yours T?
dnewma04
The Healer
I eluded to it earlier but never really completed my thought. Horns only work like horns if the wavelengths of the sound they are producing don't exceed room dimensions. So, if you had a room with a longest dimension of 27', your BLH won't work like a horn, anymore. It will act like a direct radiator. At that point, the room is in control and no woofer replacement will fix what is broken. A different speaker location might, EQ can help at one particular location, or you could add more woofers in the room to fix the nulls. Above the rooms corner freq, horns can do some magic.
When you say you can hear 10hz, I presume you are just feeling air moving around and hearing higher freq vibrations/harmonics. We have these pesky ears that limit our ability to actually hear below 25hz in most cases.
When you say you can hear 10hz, I presume you are just feeling air moving around and hearing higher freq vibrations/harmonics. We have these pesky ears that limit our ability to actually hear below 25hz in most cases.
tubino
A guy with too many tubes
Why calculating throat and chamber size matters, again
I'm getting terrific bass. I got terrific bass out of almost any low Fs low Qts drivers.
But it seems very likely to me that throat dimensions are typically overlooked, and as a result there is a lot of unnecessary flailing in the dark with BLH!!!
Just look at those numbers in the formula for Altec 515E vs JBL 2226 or the one you give -- there is difference of a factor of 3 or more!!! in the indicated throat size!
Look at it this way: a BLH can be modeled as a ported box, where the port is a long expanding flare (horn) to maximize its LF capabililties. Viewed that way, isn't it easy to see how critical the minimum opening at the start of of the port is? If it's too big, as most BLH are, then you won't get an adequate compression ratio!
To put it another way, it would seem not just possible but HIGHLY DESIRABLE to use the formula as a starting point to optimize chamber and throat size for a particular driver, with at least as much care as you would take to design size and length of ports!
Yet this is almost never done in the stuff I've read. Usually people start with a box, then flail trying to find drivers to match. Or flail with the box to make it work, without using the simple formulas at all.
The thing is, with a box like mine, it isn't any big deal to use wood blocks and other fillers to dink with the chamber volume and throat size.
I'm getting terrific bass. I got terrific bass out of almost any low Fs low Qts drivers.
But it seems very likely to me that throat dimensions are typically overlooked, and as a result there is a lot of unnecessary flailing in the dark with BLH!!!
Just look at those numbers in the formula for Altec 515E vs JBL 2226 or the one you give -- there is difference of a factor of 3 or more!!! in the indicated throat size!
Look at it this way: a BLH can be modeled as a ported box, where the port is a long expanding flare (horn) to maximize its LF capabililties. Viewed that way, isn't it easy to see how critical the minimum opening at the start of of the port is? If it's too big, as most BLH are, then you won't get an adequate compression ratio!
To put it another way, it would seem not just possible but HIGHLY DESIRABLE to use the formula as a starting point to optimize chamber and throat size for a particular driver, with at least as much care as you would take to design size and length of ports!
Yet this is almost never done in the stuff I've read. Usually people start with a box, then flail trying to find drivers to match. Or flail with the box to make it work, without using the simple formulas at all.
The thing is, with a box like mine, it isn't any big deal to use wood blocks and other fillers to dink with the chamber volume and throat size.
tubino
A guy with too many tubes
Calculating chamber and throat size
View of mine from the top, right behind driver. Here is how I calculated the existing throat constriction as about 3" w x 16" h on each side = 48 x 2 = 96 square inches.
Maybe some drivers want a larger chamber, but I KNOW that the formula indicates a lot would want smaller throats!
View of mine from the top, right behind driver. Here is how I calculated the existing throat constriction as about 3" w x 16" h on each side = 48 x 2 = 96 square inches.
Maybe some drivers want a larger chamber, but I KNOW that the formula indicates a lot would want smaller throats!
