Simple Tapped Horn Tutorial using Hornresp - Page 3

Thanks for the tips. I've been looking at ARTA, but sort of lost interest when I found REW. Once I got that working, I just stuck with it. Guess I'd better check for an update to REW. Seemed like I installed it just yesterday (actually more like a year ago...).

Anyhow - here is phase from the Woofer Tester 2 sweep.



Sorry - I only have a Woofer Tester 2 (but I use it a lot...), I wish I had the Speaker Tester or Woofer Tester Pro.

OK, so I drug the example tapped horn into the living room this afternoon, set up the measuring gear, and recorded some in-room THD measurements. My method was to position the sub for a decent in-room response (have a huge dip in-room at 70 Hz), then set the mic at the listening position, and set up for some THD measurements using REW. I set the drive level for approx 90 dB at the listening position, which was approximately 3.3 volts drive to an 8 ohm load.

I used the REW generator and settings maxmercy and soho54 suggested, then stepped from 20 Hz to 120 Hz by 5Hz increments and recorded THD, THD+N, and 2nd-5th harmonics for each frequency. I have not plotted it up yet, but suffice to say, I could set the max for the axis at 10% and I wouldn't get close to the limit. I was pleasantly surprised.

So pleasantly surprised, I patched it into the system, grabbed a beer, and started playing music through it.

As it is an 8-ohm sub, I had to adjust the gain on the sub amp to match levels, but other than that - no Audyssey or anything like that - just as built - no tweaks, no nothing. It sounds great, and it plays plenty low (for a pair of cheap 8's).

I played a little bit of everything - Metallica to Junior Brown to Techmaster P.E.B. I heard a little complaint (though I couldn't duplicate it) when I was playing Mickey Hart's Umasha Strawberry Swamp Fever Remix at 105 dB (at the couch). Bass guitar sounds nice. Synth bass sounds incredible, and there is plenty of kick and chest resonance.

In a nutshell, I like it. My house sounds far worse than the sub. Everything rattles.

I'll get the THD and distortion components plotted up tomorrow. I just wanted to provide an update.

Well, for what it is, it performs very well.

Remember my comment about these cabinets needing a high-pass? I meant it. Without a proper high pass, I did bottom the drivers on a few of the explosion scenes in Batman Begins.

I kind of expected that, as I had the movie turned up pretty loud, and I'm pretty sure the bass is still a bit hotter than the mains, I'll RTA things tomorrow to see.

Thanks. One of the benefits of living on a hilltop in the Puget Sound region. There is something great to look at in most directions.

Thankfully - the neighbors are not that close. My poor house was rattling and shaking quite a bit tonight.

This one is just a prelude, honest. Proper drivers are ordered, and proper subs are in the works. Assuming these drivers test similar to the published specs, this is gonna get fun.

Honestly - I don't exactly know if I did the THD right. I'm still trying to figure out how to present it all on one graph, I have a few ideas. I'll post what I have once I get it all plotted up and let everyone pick it apart.

Looking forward to the results of your build as well. I'll second the recommendation for the W8-740P, though the MCM 55-2421 is no slouch in a front-loaded horn.

OK, so I couldn't wait.

Hopefully this effort was meaningful. If I've not done something properly, please chime in.

SPL and THD were measured at the listening position, approximately 10 feet from the corner the mouth of the sub was loaded into. Drive voltage (measured at 60 Hz with an 8-ohm resistor) was 3.38 V, about a watt and a half, which yielded an average SPL of 89 dB at the couch.

My house rattles. A lot. I'm sure the house rattles are part of the THD+N.

Once done with the measurements, I plotted up the SPL and then added a bar-chart showing my measured THD, THD+N, and the 2nd 3rd, 4th and 5th harmonics as determined by REW using the settings maxmercy suggested.

Anyhow - here's the chart. Hope the presentation is OK.



I also attached it as a pdf so the resolution is a bit better.

As you can see, my room is not at all sub-friendly (at least with only one). No EQ was applied and the amp gain remained constant. The amp used for the measurements is flat to below 20 (modified BASH 500). I used a different amp for the listening tests (and I still did not have enough of a high-pass in place...)

 

In room THD.pdf 8.173828125k . file

Very true. Note how the low corner drops even further when you make S2 larger (approx 280)? This driver behaves pretty well in a tapped horn, though the excursion does blow up with the real low stuff.

The box is pretty big,though that is to be expected with anything that has any sort of efficiency at 15 Hz. If you do one, be sure to use a good highpass with it.

Just got off the phone with Mr Haskins. My Anarchys (and a Shiva X2 ) are on their way to me in the big brown truck as we speak. Since I could drive there (and back) in an afternoon on a single tank of gas, I should have them in hand tomorrow. I need to look at mounting options - the driver is big enough (and the horn is small enough) that I need to take the motor structure into account or it will choke the horn slightly.

I'm generally happy with the design, though I'd like to clean up the impulse a bit more. I have got the phase just about right, and I have nearly got it to the size I wanted. I spent all night trying to get it folded up - and failed. I still suck at sketchup.

I'll keep trying on the folds. Tapped horns are a little more complicated, in that the throat and mouth have to line up, so you have to fold both at once. I'm using the maxmercy approved method, I am just painfully SLOW at it.

It is small - like under 2.5 cubic feet small. Not sure what the final dimensions will be - I'm going to let the fold sort of dictate that tonight rather than forcing things the way I have been.

With some damping and a typical plate-amp crossover, it should be usable to over 120 Hz, but no way to know till I build and measure and try a few alternatives. A good EQ might take things a little further.

A tall, skinny cabinet is tough - my L34 is really long. It will likely be rectangular. This one will not win efficiency contests, that is not what it is about.

Wood is cut - finally!

Each horn takes a full 5X5 of 1/2 baltic birch. I'd originally planned to use MDF, but found good baltic birch for less than $30 a sheet so I went that route.

I'll work on the layout tomorrow, but I won't be gluing anything up till this weekend. Probably won't be done till late next week. I'll do a build thread when I am done with the building and testing.