Hi all
Well I see that two kits are assembled now and are being evaluated with another pair delivered.
I look forward to the impressions.
I also see a significant amount of speculation happening as well as postulating about how the Tapped horn works.
So far as the White paper that was written near the beginning of the development and there have been several new wrinkles discovered since then which are part of the design now. For example, in a conventional horn the driver is facing the horn on one side and a sealed enclosure on the other. The horn, as it approaches it's low cutoff, appears to be a mass who's value increases with decreasing F. By choosing the back volume properly, the two reactance's cancel over a range of frequencies which extends the low corner (sometimes called Reactance annulling). The Tapped horn has no sealed back volume but the same reactance can be conjugated by choosing the drivers compliance and flare t for best results.
Immediately, one sees that the Tapped horn driver has a higher Fs relative to it's low cutoff than the more familiar alignments.
Keep in mind, that while there is a continuum of possible driver parameters, what one can build in real life is more limited. In the case of the DTS-10, consider the drivers Fs is an octave ABOVE the systems low corner.
How would one go about making a vented box with a low knee around 12 Hz?
Part of the strength of the approach is that for a given driver, one can get a significantly lower corner than when used conventionally conversely, drivers which are ideal for say 30Hz low corner, tend to be more like pro drivers, higher Fs, stronger motor.
Several people are speculating about what the DTS-10 can do as if it were customary to supply detailed measurements in home theater market or like we were making any claims about it.
Keep in mind the idea of a kit was sort of a wild idea that seemed like fun, it simply got more interest than we were expecting.
I saw the reference to the measurements Illka had compiled and the chart showing maximum usable output and that appears to me to be about as close as anyone has come to making universal comparisons.
If I recall, that was defined by 10% THD .
I have asked the shop to drag the prototype out to the parking lot and increase the level to 10% THD at the frequencies Illka measured.
At that point it will be possible to see where it stacks up so far at least in half space, as to level and THD.
Are there other comparable measurements of home subwoofers available?
Why a kit?
I grew up taking things apart and then later putting things together. As my mother still asks me occasionally 40+ year later did you put the back back on.
I did chores for my Grampa and earned enough for my first Heathkit and was hooked on building things for the next 50 years or so.
I was lucky in that loudspeakers and electronics were my favorite things since I was a kid, would turn out to be my job and then have my name being on the nameplate, weird!.
Bottom line, I like DIY stuff, it's how I got wherever it is I am now.
After Brandon's gtg where Ivan brought a TH-50, it seemed like maybe it would make sense to do a kit. Most of our efforts at work are in larger spaces than the home and scaling things down for home use has been something I wanted to do eventually.
Several times in the past I have tried to do DIY projects, the Lab sub& driver was the most recent one used in pro sound. I had thought how cool would it be to build something at the front edge of technology instead of an ancient design.
The problem is when a design is complicated; there are chances to change things enough so that it doesn't quite work. With a kit where all the wood working id done, and daddo joints being stronger as well as self locating, that seemed like the way to go.
Anyway Mike agreed to trying a kit, it kind of took off more than expected and here we are.
Intellectual property and copy cats;
Having worked with Horns most of my life, it seemed to me, given what several of them did, that the Tapped horn was something new and I have applied for a patent on it.
The idea came from thinking about the reflected signal one sees in the full range synergy horns we make. When you mount a driver on the wall of a horn, at the frequency where the distance to the throat is about a quarter wavelength, that signal reflects back being delayed 180 degrees, which cancels out the main signal, making a deep notch.
I thought what if I replaced the reflected signal with another source of the opposite phase (which I had in the rear radiation) and positioned it at the same 90 degree spacing..
If you look at the actual bass horn measurements in this thread, you will see what a conventional horns response looks like.
After making a computer model and a good deal of fiddling, I saw hints that it would work. Eventually I had arrived at a routine to design from and a set of rules to follow.
The idea here is that in the region where the first deepest notch is, in a Tapped horn, one has both faces of the driver being fully additive within the horn.
With that greater area at 2X the low cutoff, one can make the driver stronger and heavier than normal for properly driving a quarter wave stub and still filling in the dip.
Understand, our company is not some stockholder owned conglomo corp who has made it through the power of marketing, we are growing but still small in our industry, our products are often selected by side by side comparisons with some our industries larger naked emperors and all that requires hard work from a lot of people...
If the patent office grants the patent, then I will pursue the companies, which are infringing on the design and for this reason, I would ask all the kit assemblers to keep the specifics to themselves. Hopefully the opportunity to try something new makes that request trivial. Hopefully the issue of copy cats doesn't leave a bad taste in the office at work, I would like to see about doing some other DIY speaker kits if this works out.
So far as what does the DTS-10 do,
Subjectively, there are two kits out in the field working at the moment and the feedback is scant while they are being dialed in.
I have asked that the shop that when they have time to perform a measurement like Illka did, at least that will give some idea what one could expect.
Looking at the computer model, it would be a toss up if it's excursion or power limited at 12Hz, at 16 and 20, I would guess excursion limited, above 25Hz, power limited.
At 12Hz, it appears that it takes 10mm of cone excursion to reach 120dB @ 1 mtr with a Pe of 400w per driver and at the outlet about 8.6cm air motion at the horn mouth
Where it comes out in the real world remains to be measured.
Soho54 has modeled a tapped horn.
As one can see, the Lab 12 is not quite enough motor for that configuration.
With a stronger motor, the excursion and impedance minimum is more strongly driven, bringing up the response and low corner.
The thing one wants to maximize / optimize is the acoustic load on the driver, that acoustic load is sound radiated away. Here the throat area, taper, end area, tap location and front volumes and driver properties all enter into the final result.
A word about computer models in general is that they often over state the Q of resonances and in some case with a Tapped horn, can predict things which aren't present in a physical example. As a result, features are shown more sharply in a model than a careful measurement usually shows. For example, the swings of impedance, excursion and hf response will have less swing than the prediction does. Examine the measured impedance vs the predicted for example..
Also, at low frequencies how one parses the extra mass that each bend represents can cause the measured result to be different as in this case, I did not account for enough bend mass and the result was acoustically a little longer than my model and reality has more viscous loss than I estimated.
The usefulness of models is only to the degree that what is predicted is like what you measured when built. Making an accurate model is not easy and an accurate measurement always trumps a computer model..
DTS-10 placement;
In part it is not easy to model because to a much larger degree than a direct radiator, a horn can feel it's surroundings acoustically. A horn among other things is a high pass filter, horn loading begins above some frequency governed in part by how fast the path's area is increasing. For example, for a 30Hz exponential horn, the path area doubles about every two feet. For a 60Hz horn, the area doubles every foot and so on.
At the mouth of a DTS-10 or any horn, the horn action actually continues for a short distance outside the cabinet by virtue of the enclosure and floor limit the rate of the acoustic path's expansion. If one places the mouth in a corner, one has added a significantly larger external horn path. In fact, if you place multiple units together, you have also reduced the rate of expansion making the outside part of the horn larger.
I suppose the ultimate use of the DTS-10 might be one on the floor and one on each wall, all with the outlets in the corner. In a perfect world, to the horn, he wall becomes a seamless transition at the proper expansion rate. In practice, you get less than tha because there is a discontinuity and the source is too small BUT any gain you get is free and reduces the drive level needed to reach any given SPL.
In reality, try it where ever you think it might fit.
My assumption here was like the Spud platform, that one would normally use a pair of them too but the dimensions are such that one could also stack two high in a 8 foot room if one wanted to make a full height screen wall.
Each time you confine the radiation sphere with a wall / floor or wall / floor / corner you have confined the energy to a fractional space but also added to the external horn.
What do they say, your mileage may vary depending on your room.
MK, Ah Disney, have a lot of fond memories from there with my kids.
I have not seen the theater you mentioned though, next time.
Have fun with the construction too!
Are you going to have them in the front?
Best,
Tom Danley
Tom has a lot on his plate right now probably, if he posts we will get more headache. Scott is currently fending off some scammer from my country. LOL!
Hey I'm as guilty as the next most of the time, but this is just ridiculous.
