doityourself

"For a long time, the thought has been in my head to create a speaker based on the tractrix midrange horn. This is spurred by my dissatisfaction of the resonances and coloration inherent in my Cornwall's exponential horns." A bass horn is going to have all kinds of resonances and coloration. You'd better keep your Cornwall bottom end and concentrate on the midrange only.

My panasonic dvd recorder or a BD30 blu-ray player!

It depends on where the music falls in the audio spectrum. If it's concentrated in the 1-5 khz range it will sound piercing at even lower volume. That part of the spectum is where our ears are most sensitive. 105 db in the lower octaves won't be piercing.

Here's a graph by reversing the tweeter polarity and also reverseing the wiring to the midrange-tweeter. It solved the "suckout" at 3.5khz and caused a greater "suckout" at 300hz. I'm relieved now that the upper suckout is fixed. I didn't think my new "horn" rolled off that bad in the upper range. I'll see if it actually sounds different.

Here's a graph with the revised 3500 hz tweeter crossover. Still have a dip beginning at 2.5khz but new crossover did fill in dip somewhat. Dip is barely noticeable on 1/3rd octave white noise test. I can't say I hear anything lacking. The T35 has a noticeable rise from 3.5 to 8khz or so flattens and than drops. Some testing with only midrange horn running the response comes back at 5khz and extends to 6.3khz but is 4db shy of what it is at 1khz. I'm running a coil or roll off top end that is calibrated for an 8 ohm speaker at 5khz but this driver has about 15 ohm impedance at 5khz thus the coil isn't doing much.

Here's a chart I posted a yr ago or so. Not the same style of chart but you can see the dip around 4khz. I need to produce an updated chart with lower tweeter crossover freq.

I ran the T-35 down to 3500hz with a coulple of more capacitors to fill in the gap nicely in the 4khz range. Here's the finished product. Sounds nice.

I don't know about optimum mouth size is as critical as it sounds. I built a Table Tuba subwoofer that is horn loaded. It's a 13 ft length horn inside a 30x30 box 18inches wide. Mouth size is roughly 18inches by 22 inches. Sounds good down to 30 hz or so. Puts out more sound below 40hz than the khorn and it's only running an 8 inch Ford Explorer subwoofer! Corner placement is recommended but not necessary. Mouth size could be as narrow as 12 inches if used in a corner.

I found out by adding a 2 and 1 uf cap I could convert it to a 3500 hz 12db crossover that is identical to the X36 EV module. Sounds good. I doubt I'll burn out the VC since I don't play at part levels very often. I did burn up a set of diaphragms by running sine waves at higher wattage without realizing it! Smelled that burnt smell and that was it! The extra output in the 3-4khz fills out my hole real nice.

I have a hole in the 3-4khz range with my audax driver and tractrix horn and was thinking about running the t35 down to 3500 hz with a 12db crossover. Is this going to be safe? Only running a 60watt channel amp and hardly wide open. Is the hole being filled by the t35 going to be worth the risk? The audax with horn is too strong in the 5-6.3 range. I noticed when I built the low pass filter I figured on an 8ohm driver but the audax is more like 17 ohm at 5k. I need to change my coil to compensate.

The efficiency is rated at 100db/watt but some charts show only 95 db eff. between 400-1khz and than a rising response. There has been some conflicting graphs among the years. The midrang Edgar Horn article suggested using a JBL LE-5 driver with a 2inch throated horn (just longer than mine) for a 105 efficient horn. Not sure how hard those drivers are to get a hold of. The Audax is about $83 at Madisound. I saw a pair of Audax midranges (earlier model than mine but same model as Edgar used) that didn't sell for $35 on ebay a couple of weeks ago. Edgar mentioned that some cone midranges don't make good horn drivers but doesn't mention what models he tried. Just make a simple horn like mine on the first photo and experiment. Start off with a 2 inch throat and chop it off if needed.

Here's a freq. resposne graph. It does show the dip at around 4khz. My "unhorned" audax showed the same dip. Nothing to write home about but with 1/3 octave noise with my meter it shows within 2db from 500-2khz. Perhaps running the T35 down to 3500 and using a 12db filter on the audax would get rid of the dip.

I mentioned ringing but perhaps resonating is a more proper term. I haven't owned any midrange horns before to know of the affect. Here's a picture of the more finished product. Have to finish the outer corner trim, stain, and finish. Ran a freq. response with Audax sealed against horn and it is very flat except between 3-4khz but comes alive again at 6.3 (typical Audax response-perhaps a lower crossover to kill energy at 6.3 is needed). No horn coloration or maybe I got used to it already. The horn really helped the lower range of midrange (500-800hz). Balances nicely with the khorn upper midbass bump.

When installed an air bag "clock" spring in a Ford product they used to give you a small container of paste that you put on the terminals. Can't remember the name but that's what I'd put on a wire that is not making postive contact. I've got some in my toolbox and use it occasionaly.

Here's a full length picture. Bottom unit is the later Speakerlab model that has been scaled down on the outside but internals same dimensions as Khorn.

Here's a more finished product. I couldn't see myself cutting up the old boxes yet so I removed the T35 and put it on top of the speaker and added a baffle to horn and painted it flat black (need to do some more painting). Made the otherside one and listened and like it! I may finish these off in a box of their own or leave it alone and remount the tweeter back in the box horizontal to clear the horn roof. Not a perfect job by any means. I'm not going to reinforce the sides as the 1/8inch masonite is in stress and plenty "stiff". Don't think I detect any "ringing".

I put a 10x10inch baffle on it last night and sealed against the speaker it didn't change the readings much. You can tell when you get with 2 inches of the speaker the sound changes. In Edgar's paper he actually preferred a 1inch gap between and older model audax and baffle to kill a 500hz spike. Can't decide how to finish the project.

I just ran the test. My meter was about a meter in front of speaker. Turned tweeter all the way off-woofer still running. The horn starts to come alive at 630 hz (up 5db) and is generally up about 3db over the rest of the midrange (using 1/3rd white noise) but at 4khz actually looses 3db! My wife just held up the horn to the speaker. In Edgar's paper he said best results were with a 1 inch space between the speaker and throat. I'm thinking I need the speaker sealed tight to help out the very low end of horn fs. He was getting a peak at 500hz he was trying to tame. I was looking for an average 3db gain and I think this got it. Edgar came up with aprox. 5db gain (at least he rated the horn with an earlier version of my audax as a 105 db efficiency horn). I just need to add the speaker board and stiffen up the sides of the horn. The sound reminds me of an altec horn system (thinking movie theatre or an model 19 Altec). Not sure I'll like the "horn" sound but I'll build another horn and tweak the bass unit crossover with just one 5.4mh coil, increase the tweeter output and do some listening.

Well, all of this talk of the tractrix horn made me want to build one for my audax midrange. Got one built tonight from Edgar's paper on using a horn with cone speakers. It's the 300hz horn (9x18inches-6inches deep). Will run some freq. response tests later tonight. My thinking is that if the midrange was stronger I might be more willing to put with the bass unit's strong upper bass hence the horn. Should increase db output by 5-7db. We'll see.

My homebuilt khorn plans from speakerlab has a bass contour control and am wondering if it's more than an L-pad wired in with the woofer. I'm running the 100db Audax midrange but know that the bass has a pronounced bump in the 180hz range. I've tamed mine somewhat with a couple of coils wired in series for perhaps a total mh of 9 to help roll off some of the midbass. I've thought about designing a notch filter centered on 180hz. Perhaps just a 100watt Lpad and cutting the woofer output by 4db might sufffice. Any thoughts?

I just built the Table Tuba from Bill's designs and am very impressed. The horn exhibits the same bump in the 125hz range as the Khorn but running a subwoofer amp with lower crossover dampens any upper bass. I built it 18inches wide and used an 8 inch subwoofer out of a Ford Explorer I had laying around. Output below 40hz way better than the Khorn! Is on par with my 12inch ported 3.5 ft box with 200 amp plate amp. I'm running a 100watt plate amp with it right now. If you need more output you can run 2 8inch MCM drivers for $35 each or a 10inch Eminence subwoofer that will handle 300 watts.

I'm a bit confused on the venting of the bass bin from khorn to speakerlab. I was under the impression that early Khorns were vented and that speakerlab also vented their earlier versions but the later Khorn and Speakerlab discontinued this practice. I do know the Speakerlab plans I used had no extra venting but I almost bet that the extra space by venting will lower the resonance slightly for lower bass but perhaps less output slightly above the resonsant freq.

Wasn't the K43 used in the industrial/Cinema Khorns with a reported -5db at 29hz spec.?

I do have chart without any crossover. Here it is. With both chokes in the bass bin the speaker is listenable without any eq. or subwoofer running but the subwoofer fills in the lowest octave nicely. Probably the extra reistance of the coils reduces the output of the bass driver sufficiently to balance it a little better. The freq. response with both chokes on the right speaker does still show some increase in the 150hz range compared to the chart I posted.

Here's the second chart with both coils hooked in series.