Jump to content

University Classic/Dean Horn profile need driver choice help


Recommended Posts

Here is the drawing that I got from Moray James with which I based my dimensions from for the model (shown annotated in color).  I modeled it as 7 segments with starting and ending faces of the "waveguide" element shown in green. The distance (in red) units are in inches and refer to the cross-sectional areas and lengths.  Near the throat, there is a 3d expansion and the height of the channel (nominally 30in) is shown in parenthesis and dark blue.

 

Annotated sketch of model:

 

UniversityClassic Corrected Dimensions-Notes.png

 

 

Here are the driver parameters that Moray James provided me.  Probably a University C15W dual VC driver as measured using DATS:

 

Piston Diameter = 330.2 mm
* f(s)= 69.98 Hz
* R(e)= 6.63 Ohms
* Z(max)= 74.00 Ohms
* Q(ms)= 3.708
* Q(es)= 0.365
* Q(ts)= 0.332
* V(as)= 91.420 liters (3.228 cubic feet)
* L(e)= 1.41 mH
* n(0)= 8.19 %
* SPL= 101.20 1W/1m
* M(ms)= 58.27 grams
* C(ms)= 0.09 mm/N
* BL= 21.58

 

These simulations are for 2.83v of driver with mic at 1m away in 2pi space, with speaker sitting on floor and mic at exit mouth centerline height.

 

Freq response:

 

Unihorn1-James-Moray-FR.png

 

Cone displacement:

 

Unihorn1-James-Moray-Displ.png

 

Impedance:

 

Unihorn1-James-Moray-Impedance.png

 

Here is prediction for modestly priced ($160) modern 15 inch pro audio driver, the PRV 15W1600 which has a 0.37 Qts, is 100dB sensitive, and provides 7.6mm of xmax.  Instead of using the same geometry, if we simply extend the space from the throat to front of the horn and add a 11.5in stub (shown in light blue with yellow cross-hatch), we can extend bass response deeper at the expense of a little less max SPL and a more prominent dip at the first reflection null around 300Hz.  For many sub woofer duties or bass horn duties, this is perfectly sufficient.  Here is performance at max SPL with 96 volts drive.  I am running -24db BW high pass filters as needed to optimize the xmax.  Here, the HPF is set at 58.5Hz.

 

Freq response - the new fb is about 67Hz and if one were to EQ this flat at 133dB, the -3dB extension is 57Hz which is really quite amazing for a $160 driver and minor mod:

 

Unihorn1-PRV-15W1600-FR-Max-SPL-LS.png

 

Cone displacement:

 

Unihorn1-PRV-15W1600-Displ-Max-SPL-LS.png

 

Impedance:

 

Unihorn1-PRV-15W1600-Impedance-LS.png

 

I have tried one other driver, a budget Dayton PA for $70 and it works quite well still.  Given the excellent cone motion control of this design, it would be best to pick high thermal power rated drivers with high sensitivity.  Although lower priced drivers with less thermal capability can be an excellent choice for the budget minded user who doesn't need 130dB is also fine.  At 1 or 2 watts of drive is about all you will need for most home listening applications. :)

 

Hope this was helpful.

Regards,

xrk971

 

You can see more of my work on diyAudio in the Foam Core thread here: http://www.diyaudio.com/forums/full-range/223313-foam-core-board-speaker-enclosures.html

 

Current projects:

 

http://www.diyaudio.com/forums/full-range/268524-xki-xs-ab-initio-karlson-6th-order-bandpass.html

 

http://www.diyaudio.com/forums/full-range/271011-rockin-kazba-dipole-k-aperture-z-baffle-dipole.html

 

http://www.diyaudio.com/forums/full-range/239338-mini-karlsonator-0-53x-dual-tc9fds.html

 

http://www.diyaudio.com/forums/full-range/270614-subjective-blind-comparison-3in-5in-full-range-drivers.html

post-61083-0-87400000-1428580902_thumb.p

post-61083-0-44760000-1428584542_thumb.p

post-61083-0-26000000-1428584552_thumb.p

post-61083-0-88840000-1428584559_thumb.p

post-61083-0-53280000-1428584947_thumb.p

post-61083-0-98960000-1428584954_thumb.p

post-61083-0-93120000-1428584971_thumb.p

Edited by xrk971
Link to comment
Share on other sites

Here is the drawing that I got from Moray James with which I based my dimensions from for the model (shown annotated in color).  I modeled it as 7 segments with starting and ending faces of the "waveguide" element shown in green.

 

Interesting. Your dimensions are almost exactly the same as what I used to generate the Hornresp plots in my earlier post.

 

I did find one error in my models: somehow I calculated the back chamber as 80.43 liters but entered the model value as 173.2 liters (you used 106 liters for your akabak model). The smaller 80 liter value changes the response by about +1 dB at about 50 Hz, but otherwise has negligible effect.

post-20593-0-06800000-1428587090_thumb.p

Link to comment
Share on other sites

Edgar,

Are you applying a low pass filter?  As you don't have all that higher frequency hash that I have.  Thanks for the feedback and confirmation that my quick and dirty dimensions are within ballpark.  There is another easy mod to this box that can really bring the fb down.  Working on that now.

X

Edited by xrk971
Link to comment
Share on other sites

And here is the C15W in the Hornresp model, using xrk971's T/S values.

 

EDIT: revised "Eg" value in model.

 

Second EDIT: revised "Fr" value in model. Lots of moving parts here. Easy to miss one or two.

post-20593-0-64480000-1428594237_thumb.p

Edited by Edgar
Link to comment
Share on other sites

Edgar,

Are you applying a low pass filter?  As you don't have all that higher frequency hash that I have.  Thanks for the feedback.  There is another easy mod to this box that can really bring the fb down.  Working on that now.

X

 

No LPF. Just pure Hornresp. Hornresp does provide for some backchamber damping, but I essentially nullified that (the "40000" numbers that I used for the "Fr" parameter). I also set the backchamber depth to a very small number ("Lrc" = 10) so that Hornresp's calculation of internal reflection effects would be negligible at all but the highest frequencies.

 

I find Hornresp to be so much easier to use than akabak for "quick and dirty" comparisons like this. And the results usually agree pretty well. In fact I use akabak so seldom that I have to re-learn it every time.

Link to comment
Share on other sites

Edgar,

That's interesting that you don't have all those back chamber reflections by your setting the Fr large.  I am just in the opposite situation, I use Akabak so much that I have to re-learn HR everytime I use it.  I find its notation very cryptic and confusing - like what is the back chamber volume and area vs the front chamber volume and area.  Typically, I use more than 5 segments and often have complex multiple channel horns or drivers located at different locations (for example, a synergy horn with all 9 drivers and ports in a 3-way configuration with XO's).  My biggest stumbling block with HR has to be the TS parameters - manufacture data is very straightforward to put into Akabak and I keep a running base of all TS params that I have used (over 130 drivers and counting) and can cut and paste instead of entering into dialog boxes each time, and not having to convert the manufacturer's standard notation to Cms etc.  It's all what we are used to I guess.

 

The PRV 15W1600 is 5.3 in deep, so I set the rear chamber depth at a practical 6,5in for clearance and still get some variation that is different from HR (plotted out to same 20kHz upper limit as you have) - I wonder if this is due to the extra folds?  Of course, in reality, the woofer cannot move in pistonic mode up to 20kHz so it will follow measured response curve which falls off at 1.5kHz.

 

Regards,

X

 

Unihorn1-PRV-15W1600-FR-short-rear-cahmber.png

post-61083-0-14760000-1428590794_thumb.p

Edited by xrk971
Link to comment
Share on other sites

Edgar,

That's interesting that you don't have all those back chamber reflections by your setting the Fr large.  I am just in the opposite situation, I use Akabak so much that I have to re-learn HR everytime I use it.  I find its notation very cryptic and confusing - like what is the back chamber volume and area vs the front chamber volume and area.  Typically, I use more than 5 segments and often have complex multiple channel horns or drivers located at different locations (for example, a synergy horn with all 9 drivers and ports in a 3-way configuration with XO's).  My biggest stumbling block with HR has to be the TS parameters - manufacture data is very straightforward to put into Akabak and I keep a running base of all TS params that I have used (over 130 drivers and counting) and can cut and paste instead of entering into dialog boxes each time, and not having to convert the manufacturer's standard notation to Cms etc.  It's all what we are used to I guess.

 

The PRV 15W1600 is 5.3 in deep, so I set the rear chamber depth at a practical 6,5in for clearance and still get some variation that is different from HR (plotted out to same 20kHz upper limit as you have) - I wonder if this is due to the extra folds?  Of course, in reality, the woofer cannot move in pistonic mode up to 20kHz so it will follow measured response curve which falls off at 1.5kHz.

 

 

You are correct -- Hornresp nomenclature is very cryptic. It's evident that it started out as a simple program that got bigger and bigger and bigger ...

 

As for the T/S parameters, I usually just enter Sd, Re, Bl, and Le, and use the wizards for the rest. If you double-click on Cms, Mmd, or Rms, it will prompt you for Vas, Fs, or Qes, and figure the rest for you.

 

In the newer versions, it is possible to copy and paste driver parameters ... even from other files. (I have a whole library of variations upon the "Hornresp.dat" theme. The new versions of Hornresp can look inside those files and extract driver parameters from them.) I wish that it was also possible to copy and paste enclosure parameters, but the only way to do that is to use the "Add" facility, which is very inconvenient.

 

The high frequency anomalies that you show definitely appear to be reflections and/or resonances. That could be due to the fact that akabak can model the folds, while Hornresp cannot. Hornresp assumes a simple, straight horn.

Link to comment
Share on other sites

Doghouse models 5043 in3, very roughly 4200 after a driver is removed so the 80 L seems closer than 100 L.

The "doghouse" is the rear chamber?  Based on the triangle height of 23.5in (derived from geometry of 67 deg isosceles triangle with a 18.375in base) the volume is = base*height*depth/2 = 6477 cu inches = 106 liters. I don't see how a driver would occupy 26 liters of volume - that is almost 1 cu ft of driver.

 

What do you mean the models were wrong when you built it? It did not work as advertised?

Edited by xrk971
Link to comment
Share on other sites

 

The "doghouse" is the rear chamber?  Based on the triangle height of 23.5in (derived from geometry of 67 deg isosceles triangle with a 18.375in base) the volume is = base*height*depth/2 = 6477 cu inches = 106 liters.

 

 

The triangle height cannot be 23.5" if the leg is only 21.75". The height should be 21.75*sin(67) = 20.02". Also, the base is not 18.375" wide -- that is the external dimension, and we need the internal dimension, which is closer to 16.375". That makes a triangle area of 20.02*16.375/2 = 163.9 square inches. (My CAD program puts it at 163.5 square inches, eyeballing the corner locations on the drawing.) That makes for a volume of 4917 cubic inches or 80.6 liters.

Link to comment
Share on other sites

What do you mean the models were wrong when you built it? It did not work as advertised?

 

 

Yeah sorry for the confusion.  Not criticizing your work, X, just trying to say that I used different drawings when I was modeling the horn.  "Wrong" in the sense that the previously-posted plans in this thread don't match this official-thing which I deem "correct" due to provenance :)  Not a big deal in the cause to get Moray his 2-way wallhorn, just nit-picking.  

 

Edit to add the hard number to get for anyone playing-along at home. 

post-53574-0-12840000-1428625672_thumb.j

post-53574-0-30520000-1428626088_thumb.j

post-53574-0-52000000-1428626529_thumb.j

Edited by grindstone
Link to comment
Share on other sites

Thanks for the drawings Grindstone - great to see actual University blueprints!  I found a mistake in my area, your so-called, "hard number to get".  Isn't that just the area of a trapezoid which is the average of the parallel edge lengths times the height?  Or 0.5*(13.00+16.27)*6.25=14.63*6.25=91.47 square inches?  Your drawing shows 112 square inches.

 

Anyhow, I reran the sim with 91.5 square inches and 80 liters rear chamber with an acoustical depth of 6.5in (will need baffles in there). This is with the original horn length (no additional stub). The output is much smoother now and reaches quite a high level when driven to xmax at  7.6mm with 110 volts. With a 65.5Hz HPF and 700Hz LPF (both -24dB/oct), this translates to a peak power of about 1.8kW.  This driver is not rated for that high so probably compression and overheating would prevent such high SPL's from being reached.  Now is the time to look for the expensive high end B&C monster drivers.

 

Here is the predicted SPL at xmax with no LPF:

 

Unihorn1-PRV-15W1600-FR-fix-volume.png

 

Here is the predicted SPL at xmax with 700Hz LPF:

 

Unihorn1-PRV-15W1600-FR-fix-volume-700Hz-LPF.png

 

Here is the predicted electrical power input with 700Hz LPF:

 

Unihorn1-PRV-15W1600-Elect-Power-fix-volume-700Hz-LPF.png

 

Here is a B&C 15SW115 pushed to max thermal of 1800 watts (only half of xmax reached):

 

Unihorn1-BC15SW115-FR-fix-volume-700Hz-LPF.png

post-61083-0-97360000-1428631179_thumb.p

post-61083-0-16880000-1428631214_thumb.p

post-61083-0-82680000-1428631222_thumb.p

post-61083-0-37640000-1428632030_thumb.p

Edited by xrk971
Link to comment
Share on other sites

Thanks for the drawings Grindstone - great to see actual University blueprints!  I found a mistake in my area, your so-called, "hard number to get".  Isn't that just the area of a trapezoid which is the average of the parallel edge lengths times the height?  Or 0.5*(13.00+16.27)*6.25=14.63*6.25=91.47 square inches?  Your drawing shows 112 square inches.

Um...I understood there'd be no math here today...

Well, the throat expansion pieces are actually compound-angled boards and I just model stuff that makes my head hurt like that and take what the nice computer says.

 

Yes re the Univ drawings but I just swiped them probably from here somewhere (WMcD?).  

Thanks for the work, X. 

 

I was looking at this thing a couple years ago but using the other driver data.  I also see I've made a transcription error so here's that.  I'm so happy I found my image-posting-holdup on this new board (gotta allow ajax.googleapis.com scripts to run or you can't "up" anything). 

 

post-53574-0-87320000-1428633494_thumb.j

Link to comment
Share on other sites

I think if you line the chamber with enough egg crate foam on all walls and add some polyfill, it probably won't "see" any of the parallel walls.  In reality, with appropriate padding and stuffing the output should be smooth.

 

Ok, no more math today. :)

 

Does anyone have measurements of a Classic to see if the predicts here are reasonable?  This is a pretty simple horn so I trust Akabak pretty much on this one that it is correct, as long as I put in the correct geometry.  I am pretty amazed at the SPL's this thing can reach if thermal loading was not an issue.  On the B&C driver, it is only getting to maybe 7mm for a 13mm xmax driver - but topping out on the 1800 watt rating at 7mm.

Link to comment
Share on other sites

Does anyone have measurements of a Classic to see if the predicts here are reasonable?  This is a pretty simple horn so I trust Akabak pretty much on this one that it is correct, as long as I put in the correct geometry.  I am pretty amazed at the SPL's this thing can reach if thermal loading was not an issue.  On the B&C driver, it is only getting to maybe 7mm for a 13mm xmax driver - but topping out on the 1800 watt rating at 7mm.

 

I think that, for the original purpose of the thread (as I understood it) -- i.e., finding the low and high frequency capabilities of the horn and finding an appropriate modern driver for it, the fact that the akabak and Hornresp models are so similar means that the results are reasonable. The truth is, as long as the throat area, mouth area, general contour, and path length are correct, the minute details don't really matter all that much with regard to the overall shape of the frequency response. For reflections and resonances, akabak is far superior to Hornresp, but the Classic is already an established design so I presume that any problems in those areas would have already been identified.

 

I find it a little amusing (in a good way) that you are trying to evaluate the max SPL capabilities of a 100+ dB enclosure ... 135 dB SPL in your living room will melt your picture windows! :)

Link to comment
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.
Note: Your post will require moderator approval before it will be visible.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

×
×
  • Create New...