I know, but it doesn't always sound bad. The TH that I have (that I was talking about earlier) had a tuning near 20 hz, almost an octave lower than the FLH I was comparing it to. Maybe that's why it sounded so nice. Maybe it is a group delay issue. Maybe not, I don't know.
Matching phase between the top cabinets and the subs is very important for good transient response and realistic sound reproduction.
Although a sealed enclosure may have less phase shift over it's pass band than a BR, FLH or TH, all four can be phase aligned at the acoustic crossover point.
When done properly there is surprisingly little difference in the sound of the four different types of cabinets as long as they are equalized the same.
In the chart below, a sealed (IB) 2x12", a ported 2x12" and a TH (Keystone) are compared. From about 35 to 115 Hz the TH actually has the least phase shift of the three.
One class of subs that I have found generally don't sound good are band pass, the phase shift in the upper region is so rapid that it is not possible to get a good phase transition unless they are crossed well below the upper band pass, which leaves only about an octave of coverage left.
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I'm not an expert in this but I believe Danley addressed this years ago. I think he said that when you eq a TH to have flat response it will also have flat phase response. (That's not to say there's no shift, just that it's not spiky.)
Anyway, I don't think the amount of phase shift matters much as long as it matches the phase of the tops at the crossover point. Different crossover types and slopes will give different amounts of phase shift and different designs will have different phase response to start with, so you have to know what you are starting with if you want to get a good blend between the subs and tops. There's nothing wrong with mixing types and slopes of crossover as long as you end up with the frequency and phase response that you need.
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The Hornresp models seem accurate as far as phase response, though just as the measured frequency response of cabinets are not as "peaky" as Hornresp predicts, neither is the phase response.
The TH in my example has phase shift and frequency response similar to the DSL TH-118.
The ragged upper phase and frequency response of a TH makes them unsuitable for high crossover points, but within about a two octave range the phase can be comparably quite flat.
Although the Keystone TH phase response is still reasonably good for another octave higher than where it is crossed over, above 250 Hz it goes through dozens of 360 degree phase rotations.
A BR's upper phase response remains smooth as far as the frequency response does, so can be used over a much wider band width than a TH.
Both TH and FLH require the top cabinets to be delayed to be time and phase aligned, while BR may not require any delay.
The time alignment requirement often leads to "bad sound", as it is easy to get wrong.
Using a 24 dB per octave crossover, the HF rotations of a TH or FLH are of no audible consequence, as can be seen in the phase plot below of a TH time aligned with the top cabinets.
The crossover point is 100 Hz, the phase response of the LF and top cabinets align perfectly there.
Subjectively, there is no lack of "punch" in the crossover region compared to a BR.
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I just spent awhile looking for any type of real info on this mythic beast and couldn't find anything but marketing specs, regurgitated marketing specs, even more quoted marketing specs, and a couple pics of the cab. No frequency response charts, no driver t/s specs, no real info of any kind.
From a quick glance at a dimensioned drawing it seems that the path length is around 7 feet long and the throat comes to a point, so tuning is going to be very high - high enough that I would have trouble calling it a subwoofer.
Also it seems they are trying to cram way too much driver into a very small box so the frequency response is probably pretty bad. A large stack can fix that to some extent but I'm guessing it's just a bad situation.
I'm going to go out on a limb here, with no real info, and say that this is probably a bad horn using a low quality driver. I don't doubt that it's probably ear-bleeding loud but I think that's probably all it has going for it.
If you want a real reference, since you are clearly not afraid of building cabs, I'd suggest simulating and building a tapped horn vs flh using the same driver, same construction materials, same bandwidth, etc. In other words, a fair comparison. Use a small, cheap driver to keep size and cost in check and draw some real conclusions instead of comparing a completely unknown commercial flh against good tapped horn examples using much higher quality drivers.
It's not surprising to me at all that you have come to the conclusions that you have, considering your reference defacto benchmark.
Here's the TH-118 datasheet showing a pretty good phase shifting 60-200hz. That's what leads me to say it it would seem to be hard to get convincing kick drum sound out of a tapped horn.
http://www.danleysoundlabs.com/danley/wp-content/uploads/2012/04/TH-118-spec-sheet1.pdf
http://www.danleysoundlabs.com/danley/wp-content/uploads/2012/04/TH-118-spec-sheet1.pdf
The CV T36 FLH LF corner of around 45 Hz (in multiples) was fairly decent for the time it was introduced last century. The cone is pretty high mass, the cabinet rolls off pretty rapidly up high as well as below Fc. They can take a lot of power without burning up, but suffer from a lot of thermal compression. IIRC the newer units (or was it the B-52 copy of the T36) may have an aluminum driver cover and may be better in that regard.
Having used 6 of the old CV T36 outdoors and a pair of Keystone TH subs at the same venue (not at the same time) I'd say the six would be about equal in output to the Keystone above 50 Hz, while the pair of Keystones are far louder below 50 Hz.
Having used 6 of the old CV T36 outdoors and a pair of Keystone TH subs at the same venue (not at the same time) I'd say the six would be about equal in output to the Keystone above 50 Hz, while the pair of Keystones are far louder below 50 Hz.
I have convinced several engineers, dozens of drummers and thousands of people in audiences from 250 to several thousand that getting a convincing kick drum sound out of a tapped horn is quite possible when properly phase and time aligned with the top cabinets.
Since my horn loaded top cabinets have a similar phase angle to the TH in the crossover region, the TH actually has a smoother phase alignment than the BR cabinets they replaced. In the chest thumping 60-100 Hz kick range the TH are a winner, both in SPL and sound quality.
It took a while to get the alignment right, the first problem I had was with polarity, I ASSumed that since the cone was magnet out, the polarity should be reversed so positive voltage would make the cone move forward. This assumption was wrong, and could lead to a phase alignment using double the time delay (or no delay), in which case the sub would sound decidedly "slow".
At any rate, most of the systems I have heard where the bass is muddy were the result of improper alignment in the crossover region or bad rooms and positioning.
It amazes me in the days of cheap DSP that many users of FLH and TH still use no delay on the top cabinets.
Is this confirming that the phase of the rear radiation into S2 is the dominant output of the TH? i.e. much as a front loaded horn where the phase into the throat is the dominant output.
The driver diaphragm pushing towards the TH throat (S2) creates positive pressure at the mouth, as in a FLH.
Cone moves away from magnet (which is next to the mouth, usually), and you get positive pressure at the mouth.
Is this what you're telling us?
Time to rethink how I thought tapped horns work, I suspect.
Think about it like a tube of toothpaste. (That's probably a bad analogy but it works.)
Push in at the bottom of the tube and toothpaste comes out the mouth. It's hard to reverse that action in a tube of toothpaste but this is the idea.
I suspect a lot of people have no clue how tapped horns work. Tapped horns are back loaded horns. The ONLY thing the mouth side tap is doing is filling in a null higher up in frequency that's commonly experienced by back loaded horns. The mouth side tap does absolutely nothing to add bass anywhere near tuning, it just adds a spike at higher frequencies to fill in a hole in response.
Push in at the bottom of the tube and toothpaste comes out the mouth. It's hard to reverse that action in a tube of toothpaste but this is the idea.
I suspect a lot of people have no clue how tapped horns work. Tapped horns are back loaded horns. The ONLY thing the mouth side tap is doing is filling in a null higher up in frequency that's commonly experienced by back loaded horns. The mouth side tap does absolutely nothing to add bass anywhere near tuning, it just adds a spike at higher frequencies to fill in a hole in response.
Peaky, not stripey though in this case tb46, I had some time today while the warm up dj before Chingy hit the stage to check out the 3 segment version you posted. I also dumped it into autocad so I could directly compare your build against mine...I get what you mean now. Dramatically simpler construction, performance that is almost interchangeable, and under 1 sheet of ply long. Sweet variation on a theme!
I'm still not getting this. There's a delay from the front of the cone of L/c (L is the horn length, c is the speed of sound) before the front of the cone can have any impact on the pressure at the mouth. The rear of the driver is pretty much at the mouth, so it can almost immediately affect the pressure there.
Set the cone moving away from the mouth, and you must see low pressure at the mouth first.
I must be missing something, though. The above is very simple physics, yet it seems to contradict what you're saying.
Chris
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