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4.158.12.71
In Reply to: RE: Olsen Modified BLH monster posted by freddyi on June 22, 2007 at 06:36:07
Hi Fred
This project was a bit off the beaten path for me, but since my rig has been down since I started remodeling my listening room in Nov., I gotta live horns vicariously. You can see the scale of the various internal dimensions from the sketch. John is to be congratulated for transforming this rough sketch into reality. I suggested to John that he construct the cabs so the top panel could be easily removed for tuning. Note the chamber to the rear of the 15"er, which was made large for tuning options. Also note the rectangular holes down line in the 'W" top manifold which connect this manifold to the lower "S" bend of the bass horn. The size of these is another tuning option (thanks to Steve Schell for some thoughts on this, and some observations from his RCA studio monitors designed by The Master himself). Note the dashed lines in the top down view which picture some panels which also are another tuning option. Note that the horn mouth makes maximum use of the front cabinet space. The original sketch pictured the edges angled at 45 degrees to the sides of the direct radiator 15" front for baffle-step control. John built the speaker as a box (which is the easiest way to do it), but he could easily cut the triangular chambers off there. Some freq. resp. measurements would indicate if this is worth the trouble.
John originally wanted to use the BM-15CX38 as a driver, and at a certain point in the discussions it occurred to me that we were talking apples and oranges here. A web search turned up with three different spec sheets for this driver, all with different TS specs! This says either that the specs are rather loose, or that the manufacturer has changed the specs without changing the model number. I think the later is most likely, as the mid horn freq. resp. graphs were reasonably consistant between the different sheets. I was concerned that this driver needed a tweeter, as it's rather rough in the highs, going by the graphs. John seems quite happy with the Tannoy Golds as an alternative though, which look alot better going by the graphs for them.
This was a fun project, and a bit frustrating at times as John lives in Melbourn Australia and I live in Chicago. I would have started by testing the BM's TS specs to see just where they are, but John does not have any test equpt, so quite a lot of the project was "armchair engineering" guess work on my part. I tried my best to discourage John from building these monsters, and even sent him a birds-eye perspective drawing and stern WAF warnings, but he has pressed ahead regardless! I am genuinely impressed by his enthusiasm! This project is also a WAF engineering feat on par with the concrete and brick horn John Crabbe built in his dining room while his wife was pregnant in the 1950's. The stuff of legends!
Comments on the design anyone?
Paul
Follow Ups:
Paul,
Now you've done it! John's a goner.
Headlines: Massive Horn stack swallows Melbourne! Sydney next?
Eizik syndrome rumored.
Nice to see an old design reconstructed.
How does the this design work? Is it a dual chamber with reflex characteristics for the top half somehow tuned and coupled to a further horn expansion? Impedance plot might show.
Good luck on the remodel.
Tim
Hi Tim,
I think the enclosure functions basically as a back loaded horn. An exponential expansion is approximated in the series of sections with increasing width plus the continued expansion through the path down below. The chamber behind the driver probably works as a low pass filter. There was further filtering in the original Olson design from restrictions placed in the horn path.
Hi Steve,
Thanks for the response.
This is the first time I've seen a design such as this with a deliberate impediment to a continuous flare. Very interesting.
I guess my assumption has always been that numerous pathway bends would also provide the low pass function, without further need to create a port/aperture midway through the expansion and risk a reflection/response hiccup. "One never interferes with or deliberately obstructs the flare rate" kind of mentality at work here, you understand.
I would also assume that Olson would never publish a design that would contain any major flaw without explanation, and that the reflection is either non-existent or reduced to the inaudible through the combination of tuning devices provided.
In any case, a really neat project.
Tim
Tim
It's easy to follow the logic of not interfering with, or impeding the flare rate. Ben Rich, in his book "The Skunkworks", told the story of discussing the conical spikes in the intakes of the SR71 engines with a general once. The general said "I would think that the idea would be to get as much air in as possible" and Rich replied "Did'nt you ever put your finger over the end of a garden hose when you were a kid?". The restricted throat of a BLH is usually looked at as a necessary evil to balance the output of the horn and direct radiator, but compression mid driver designers use this all the time. The mid has a compression ratio and frequently a phase plug too to squeeze more bandwidth out of the driver. As to reflections coming from the aperture at the end of the manifold in the Olson BLH, these reflections have to pass back through the muffler effect of the manifold (against the "current" of the sounds tendency to flow from a high pressure area to a lower), and also through the low pass effect of the first air chamber before they could get to the cone and pass through it to cause any mischief in the output of the direct radiator.
Finding a major flaw in Olson's work? Yeah, I wish! I'd be off to the patent office in a jiffy ; )
Paul
Hi Tim
I've long felt that participation on this forum would serve one well when trying to cop an insanity plea. Lawyer: "Your honor, my client is clearly not in control of his imagination, and could hardly create a $300 clock radio which could seriously compete with the Bose company..." Ya never know when something will come in handy...
Your question as to how it works came up while looking into Olson's patent for this project. Olson attached some importance to the chambers and coupling apertures. A BLH probably has more room for adjustment here (as opposed to a double loader) due to the fact that the horn output has to be attenuated anyway to match the direct radiator output. I can't wait to try some of this out an my rig (which is buried behind a wall of piled up furniture now). It will be interesting to see if some bass extension is possible (probably at the expense of some bass output). An impedance plot will be interesting too, something I have spent little attention on previously. Great idea!
Thanks for your idea and well wishes as I go back down to the mine.
Paul
Hi all who have responded; thank you very much
Currently the tannoys i have a cross over ~1khz from my understanding. Unfortunately, it's a long story, but what I though I bought (ye, you guessed) from ebay, 2 'gold' drivers with the appropriate cross overs. Unfortunately I found out too late that one of the drivers is a HPD 385, and the other a monitor gold. Even worse, the monitor gold has been reconed to a HPD! Ok, can i get worse? Well, ye it does..........the cross overs are actually for monitor reds.
Oh well, the pitfuls of ebay.
Anyway, I have always been fascinated by the tannoys. I have been fortunate to locate a single HPD 385, so at least can match one of the drivers. I have to build a new cross over of course.
As Paul has mentioned in the replies, he based his diagram on the Paudio's initially. I did have the paudio's in an OB arrangement, but the lack of bass and the limited breadth/soundtage, led me to the 'next step'; horn enclosures.
i suppose it's a natural progression.
In any event, i don't think i really ever got them 'singing' at all, and especially with the cross over. The tannoys have much more info on them. I was particularly interested in the tannoy GRF autograph, a compounding horn. But as Paul said to me, he thought other designs would surpass the Autographs sonically, hence pressing ahead with this design by Paul.
I haven’t as yet fully grasped all the theory. Thanks again Paul for answering some of the questions raised. My problem is that I know no one here in Melbourne embarking or gone through horn systems. I don’t have a point of reference, and indeed as Paul has said, distance from opposite sides of the world has been helped with modern technology.
I don’t have any measuring equipment as yet, but hope to soon. I have the stereophile test CD’s.
I will however experiment with the sound with the ‘tuning’ section to put behind the driver. I will also try a smaller opening linking the manifold section to the ‘S’ area too. A smaller, or larger opening will, from my understanding, affect woofer sensitivity. How much will it affect bass extension? Which way?
May I ask advice from others too please, as to what the coupling chamber will therefore do to the cross overs of this dual driver (tannoy)? Do I look at a different cross over to what is recommended for the drivers? Ie, to take into account the coupling chamber? Also, do I look at possibly that the horn enclosure should be just for a bass driver eg JBL2235H?and use a seperate horn tweeter for the mid/top end? Would this be sonically superior to a ‘single full range driver’?
The tannoys cross over at about 1Khz. My understanding is that they area second order cross over, with a notch to stop a peak at 3khz.
The tannoys have a wonderful midrange so far. Playing organ music with the lows has never been better from what I have heard previously. And I haven’t began to find where it can be improved more
Thanks to all for your kind encouragement and support, it is greatly appreciated.
I look forward to your replies and suggestions
best wishes
john
ps, I have shown a pic of the opening from the manifold section to the 'S' area. It is ~7" long, and ~3 1/4" wide
Howdy,
I'm in Melbourne. I have a workspace out in Dandenong (a small factory). In the next week of so, I'm moving / downsizing to a local studio & workshop (Brunswick). If you are keen (and free in the near future), you could visit the factory for a listen, and to pillage my old enclosures. Most of what I have there will either be left behind, dumped, or broken up for materials.
I'd be interested, if possible, in comparing our coaxial-based systems.
The system I'm downsizing to uses 2*15" drivers for each channel: a coax and a helper woofer. They are simple sealed boxes, tower-style. I'm still sanding / painting the 2nd box, but the 1st is up, running, and reasonably well tweaked.
While I finish the 2nd box, left channel is-
Sub: 4*15" in a 2cubic metre concrete BR box, with a corner-mounted baffle.
Main: coaxial in sealed box, with oversized corner-mounted baffle (no baffle-step correction needed).
...and right channel is-
Sub: 250litre sealed box, using a single 15".
Main: coax+helper box (the helper is for baffle step correction).
I have a couple of other abandoned experiments as well, including a fullrange 10" in a rather large front horn.
Hi John
I would'nt take the mix up with the drivers too seriously, it's just a road bump in the developemental process (both models are painted gold). Problems with used drivers are common, even from reputable sources, as you don't know who had the drivers before that. Tannoy only guaranteed that the specs would be within 10%. The specs on the Tannoy Gold site for the HPD 385 were apparently obtained from drivers which had the surrounds replaced. Anyway, they are not drasticly different from the Golds. Fs is 22 Hz to the Golds 26 Hz. EBP is 110 to the Gold's 118, so they should still be able to drive a BLH. Mass roll off is 220 Hz for the 385, and 236 Hz for the Golds, which is a non-issue in a BLH with direct radiator front output. If you like the midrange, you likely have a winner. If you hate the midrange, you would have a difficult path ahead at the very least, even with good suporting performances by the highs and lows.
With the Stereophile Test Disc, you should be able to tell where the bass response of the horn drops off. Set the CD for the midrange test track, and adjust the volume to a comfortable level, the ear is most sensitive to the 3 to 4 K Hz range. Next set it to the bass test. As the signal drops lower you should be able to hear where the horn drops off sharply, somewhere below 50 Hz. A -3dB downpoint is usually the area of interest here, but can be difficult to hear by ear, but the steep mechanical roll-off of the horn should be obvious, especially with the 20 Hz tone. This is best done when home alone, which may be the most difficult part ; )
Don't get discouraged!
Paul
Let's try that again...
And once more, without the bottom chopped off (hopefully, as it looked okay in the preview)...
here that is enlarged - ya know, somehow David McBean fits into the holy horn hierarchy
Fred
It kept croping the bottom of the drg. off untill I sized it down. This was weird because the drg. always came out okay in the preview.
As to David McBean, I believe it was revealed on this very august forum that the famous Hornresp program was originally modeled on Olson's Dynamical Analogies, and existed in some form pre-dating the pioneeering Keele, Small and Leach AES papers.
All roads lead to Olson
Paul
first stole your image - removed unnecessary boarder -scaled 210% to maximum width of ~580 pixels that fits between advertisements (don't seen those today - haha) then uploaded image.
can't out why your image got cropped - a big image should post and if ads are present at the right frame in this forum, can post below those when not using a browser in full width
David McBean's simulation engine is good thanks to Saint Olson and a lot of work on David's part - its so compact.
my hard drive died and lost everything but seems like posted larger version of one or two of your designs in a thread - can't remember which thread - might be buried in "Olsonology" -?
Fred
Yes, awhile ago you kindly posted the drawings of the Melow Monster from the 1962 Popular Electronics, which formed the basis of my horn rig. The similarities between the M.M.'s and Olson's BLH from the late 30's are obvious. For John's speakers, I just scaled up Olson's BLH, added the angled corners, and made the mouth as big as the space in the front of the cab would allow. It appears that uploaded images here have to be scaled down or they get truncated at the bottom (how come everyone knows this stuff but me!?). Olson is both the father and the holy ghost, and we are but mediators in the Great Horn continuum.
Rev. Paul
I have a set of Hedlund Horns built using with 1 inch to 1 1/2 inch thick MDF. Despite the greater thickness of my BLHs, the bass still GREATLY benefitted by serious reinforcement of the compression chamber, back horn and horn opening. Try reinforcing the boxes for much improved bass.
Retsel
hey Paul -- looks like something I'd like
whats your offhand guess of flare type, path length, chamber volume and mouth size? What adjustments to response and to "tone" can be made by adjusting the manifold's panels? --- is that mainly tackling overtones fed into the horn whihc end up suming with the front which ends up as overall sound to the listener?
Fred
Fred
My offhand swag is that this is kinda close to a hyperbolic expansion sorta (mostly). As in most bass horns, it's what fits inside the box and winds up being close to being recognizable to one of the known horn expansions. The mouth size is about 1050 square inches, the path length is about 12.5 ft., and it should be able to go down to about 25 Hz. The Tannoy Gold is a bit of a wild card here (as were some of the BM iterations) in that it has a rather lowish Fs of 26 Hz, unlike the usual suspects/musical instrument drivers usually put to work to drive bass horns. I would expect some ripple at the bottom end as a result, along with some difficulty going up to the mid crossover freq, but measurements will tell if these concerns are valid. Can't find my notes on the front chamber, bit it is about 3" deep, about 19" high and about 33" wide. Subtracting the triangular ends, it comes out to about 1805 cu. in. (not fuguring in the mass the rear of the 15" driver occupies). This was made as large as possible to accomodate tuning the volume. This type of chamber is ususally of concern in where it starts to limit the high freq. output of the driver as Fhc: Fhc=(2Qts)Fs(Vas/Vfc). However, if you make the chamber large enough it can begin to act as a notch filter as Olson has shown in his Dynamical Analogies, as can the area where the horn throat begins. The hole which determines the horn throat is adjustable, and is generally "choked" in a BLH in order that the bass horn does'nt overpower the direct radiator front output. I had originally conceived the coupling holes between the top manifold and "S" section to be merely useful as another adjuster for attenuating to output of the horn, but after some of Steve's comments and looking at the Olson patent again, I think it it's more complex than that. If you make these holes smaller than what would seem optimum for maximum output, the top manifold would begin behaving more like a vented box or a TL. The overtones created by the manifold panels should fall in the 900 Hz region, while the output from the bass horn itself should roll off under 200 Hz, so this is a non-issue due to the muffler effect of the manifold. Quite a few perameters to adjust in this design, but that's the fun of an experimental horn!
Paul
if you throw away the wood, now much air volume would the horn have? - or maybe another way is to ask its external bulk and ~how many 4x8 sheets went into it?how big is the throat area -?
heres a sim Tty One
26Hz is pretty low - horn mass load can shift things- got AJ-Horn for toy but not sure if cna do it right unless the epansion is fits one what it wants
Hi Freddy,
from memory I needed ~4 sheets to make this. I was fortunate enough that the local hardware shop to me was able to cut the MDF to my measurements, and I must say, he did a great job, most being exactly as ordered. To see this big box take shape and fit together was great. I also had spare MDF left over. Now thats for my next project, a dolls house for my little girl. Of cousre to have next to the horn cabinets so as she can listen music too!
best wishes
john
Fred
25 Hz is indeed low, like: "best case scenario"; "down hill with a tail wind"; "give er 5 dB down cause she's a horn" etc. The AJ sim predicts about 45-50 Hz , about what my rig will do, but that's a very big mouth and long horn on John's rig. As a sidebar, I recently wondered why measurments of my rig from the early 90's showed 45 Hz -3dB, while later ones showed more like 50 Hz. After I measured my Ampex 402 pre-amp I stopped wondering (in the early 90's I ran Hafler S.S.). Anyway, 50 Hz of horn bass beats 30 Hz of direct radiator bass, with bass dynamics being the deciding factor.
The throat is about 12" diameter. That's an interesting proposition of considering the mass of air in the horn minus the wood, which would affect the point where reactance with this mass would raise the bass response above what the mouth/horn length would indicate. This however ignores the contribution of the manifold and folds along with the various other tuning variables. John has anounced his intention to obtain some measuring equpt, and it should be interesting to see how the D.U.T. compares with the sim. I assume the sim can't compensate for variations from between the lines of the horn continuum: i.e. specify a mouth area/termination and horn length, and then name that horn expansion. John would have to say how many 4 X 8 sheets (to the wind?) this horn takes.
Paul
Paul
~105dB halfspace for 2.83v/50Hz ain't too shabby and should kick like a mule with drumkit (does it "kick" or just sound clean??)
John should have a real nice horn rig. I'm sorely lacking in that dept. (although have 3-k-horn & 2-Sentry IV carcasses)
re:kickdrum - what do you think's the highest cutoff which will get most of the sound and feel? Karlson in the "middle" of my yard which drops off 8 feet behind the mic is about F8-F10 around 50 - I want to drop the size even more so it can be carried.
I';m not overly fond of reflex and hate to see their cone flap in the wind on hard transients - my K will get pretty lood in a little room with 1/8" peak to peak and ~300W peak
Fred
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