G'day again Ian
I'm not about to do an exhaustive search for drivers, but it strikes me the little Peerless 830564 will pretty much match, driver for driver, the beastly 18" BMS you used in your model, assuming the 12" is in a Tapped horn. Now I know both of us have not included thermal compression issues and you have not included your port losses. The Peerless driver is worth 1/2 what the BMS is worth.
Have a look at the following model. If you have a wall, or better, a corner you can use to load the sub into, you will find that the little tapped horn will actually beat the big dual 18" sub, with 1/2 the applied power. No, I know the Peerless 830564 is not going to survive a pro sound environment for long (It's a HiFi Driver) but a driver along the lines of the LAB12 with the same specs as the peerless driver would not be too hard to build. It would give more output too, because of a slightly higher x-max.
I'm using the 830564 tapped horn at home at the moment, and it is very strong, even compared to the two big 18LW1400 based Vented boxes, with a total external volume of 880L (shown above).
Fun little exercise, it'll be interesting to see what the others come up with.
Cheers
William Cowan
I'm not about to do an exhaustive search for drivers, but it strikes me the little Peerless 830564 will pretty much match, driver for driver, the beastly 18" BMS you used in your model, assuming the 12" is in a Tapped horn. Now I know both of us have not included thermal compression issues and you have not included your port losses. The Peerless driver is worth 1/2 what the BMS is worth.
Have a look at the following model. If you have a wall, or better, a corner you can use to load the sub into, you will find that the little tapped horn will actually beat the big dual 18" sub, with 1/2 the applied power. No, I know the Peerless 830564 is not going to survive a pro sound environment for long (It's a HiFi Driver) but a driver along the lines of the LAB12 with the same specs as the peerless driver would not be too hard to build. It would give more output too, because of a slightly higher x-max.
I'm using the 830564 tapped horn at home at the moment, and it is very strong, even compared to the two big 18LW1400 based Vented boxes, with a total external volume of 880L (shown above).
Fun little exercise, it'll be interesting to see what the others come up with.
Cheers
William Cowan
Attachments
Before anyone asks, here's the datasheet for the Peerless 830564:
http://www.cowanaudio.com/images/830564.pdf
It is a dual voice coil driver intended for automotive applications.
Cheers
William Cowan
http://www.cowanaudio.com/images/830564.pdf
It is a dual voice coil driver intended for automotive applications.
Cheers
William Cowan
cowanaudio said:
Hi William
Obviously thermal compression applies to all speakers, tapped horn, reflex or anything else
And if you're worried about this, 2 drivers in a reflex (needed to compensate for larger required driver displacement) will have lower power compression than 1 driver in a tapped horn...
Interesting you say the BMS drivers aren't up to the task (please explain, I'd love to know why) -- at least on their website they show response and distortion measurements taken at 1000W input power, which is more than I've seen from any other manufacturer.
Please don't get me wrong (excuse shouting) --
*** I THINK THE TAPPED HORN IS A GREAT IDEA!!!! ***
I'm just trying to figure out under exactly what circumstances it has an advantage over a more conventional design with the same size and cutoff -- because it doesn't seem to for the case I'm looking at, which makes me wonder where it does (maybe big arrays, maybe only for very high efficiency which means very big boxes -- where exactly?)
Tom's comparison of a tapped horn with a single driver reflex (on his website) unsurprisingly shows a big advantage for the tapped horn. My comparison with dual driver reflex seems to show no real advantage (excluding the possible port compression issue) , which is what I found surprising.
The tapped horn undoubtedly squeezes more out of a single driver than a reflex or similar box. But don't be blinded by this, in the real world you also need to remember that it takes a lot more time and effort (=money) to design, and the box is a lot more difficult (=time+effort=money) to build.
So it's only fair to allow more money to be spent on the drivers in a reflex compared to a tapped horn to make up for this -- after all, if this wasn't the case Tom's tapped horns would sell for less than decent double-18 reflex boxes, and this clearly isn't the case
For hobbyists who count time, effort and wood as free (which I guess includes me) this isn't the case -- and from an engineering point of view it's very satisfying to squeeze as much performance as possible out of a given driver.
On the other hand I started with the dual 18N850 design a couple of years ago (total design time, a few minutes), and have spent a lot of time since -- because I thought the tapped horn must be able to do better than something this simple -- playing with tapped horn designs with every driver I could find (and some I can't any more like the PA-5100), without being able to come up with anything better. This was all very interesting but without a positive result...
I'm not putting forward "the challenge" to get someone to design a better speaker for me which I can then rip off -- I already said right at the beginning why -- for my particular circumstances -- there was an advantage with a reflex (being able to pack the FOH tops inside) which obviously won't apply to most people.
I just want to figure out under what circumstances the tapped horn wins in a fair fight -- which means a better size/efficiency/cutoff/cost tradeoff, not just getting the most out of one driver in a big box.
Ian
cowanaudio said:
Hi William
Thanks for the figures -- I assume you're still just inside Xmax at 72V?
It looks like your efficiency is about the same as the reflex, maximum output is a couple of dB lower, cutoff frequency is about 10% higher.
Which is *exactly* the kind of annoying thing I kept finding...
Cheers
Ian
P.S. Like I said, the 18LW1400 is nowhere near the optimum driver for a 22Hz reflex, so it's not surprising your 830564 tapped horns beat it.
Iand, here is an image of your TH design from post #1219 and #1220, captured (in grey) with the same non tapped horn in the foreground. This was done by saying 'no' to 'do you want to do a tapped horn'.
I noticed this similarity when using Leach's formulas to design a front horn of 1000L (35' ^3). I converted it simply to a TH, and found the bass had comparable extension and level, the displacement and max SPL was similar etc.
If I changed the length of the TH and the front horn, the response/extension was compromised equivalently in both cases. I could not reduce the CSA of the TH without compromising the quality of the passband response, and reducing the front horn similarly produced a comparable increase in passband ripple.
As I believe MaVo was saying (before I interrupted with resonators), is there a magic combination of specs that can produce a TH of notable benefit?
I noticed this similarity when using Leach's formulas to design a front horn of 1000L (35' ^3). I converted it simply to a TH, and found the bass had comparable extension and level, the displacement and max SPL was similar etc.
If I changed the length of the TH and the front horn, the response/extension was compromised equivalently in both cases. I could not reduce the CSA of the TH without compromising the quality of the passband response, and reducing the front horn similarly produced a comparable increase in passband ripple.
As I believe MaVo was saying (before I interrupted with resonators), is there a magic combination of specs that can produce a TH of notable benefit?
Attachments
jnb said:
Your results show exactly what Tom has always said (and nobody is arguing with) -- that a tapped horn can have a much flatter response than a non-tapped one with a similarly undersized mouth.
My original post did show that the tapped horn is sensitive to lots of design parameters -- especially BL -- but that the correct choices can give a flat response, which was the design I posted (and you have been tweaking). In this sense there is almost certainly a "best set" or parameters for a tapped horn with a given specification -- I haven't managed to find a better set so far than the one I posted, which is why I asked if anybody else could.
So there are 2 questions here:
1. The easy one -- for this set of design constraints ("the challenge") can a tapped horn beat the reflex, and if so what driver parameters are needed?
2. The difficult one -- under what circumstances can an optimised tapped horn beat an optimised direct radiator (and presumably vice versa)?
(in a corner, big arrays, low cutoff, high efficiency, tiny box...?)
We know that a direct radiator has a fixed relationship between size, efficiency and -3dB point (and maximum output depending on driver construction) -- so we know that you need double the box size (or two boxes) to gain 3dB efficiency (6dB output), that an extra octave extension needs 8x the box size (I think?) and 4x the displacement, placing against a wall gains 6dB output and so on.
If the rules are the same for both then if the tapped horn can win at one point against the reflex it can win at all points when optimised (hence question 1).
If the rules are different for a tapped horn then there will be cases where the tapped horn wins, and presumably ones where it loses (hence question 2).
Cheers
Ian
iand said:
Your challenge / comparison is not so straight forward as you might think. The problem is, that a tapped horn and a bassreflex need different drivers. What sounds trivial at first sight gets you into alot of problems when you want to evaluate the differences. Once you have different drivers, you have different xmax etc. This way, you can never be sure if you compare the enclosure benefit or the drivers themselves. You have to be much more specific in the aspect of what drivers you allow to make comparable results.
Easy answer to your question: Alot of xmax and power handling beats the reflex design. Thats probably not what you were after, but it shows, that you need to be more specific in driver specification. That brings you to the problem, how to compare different drivers. Maybe by choosing drivers with the same sd, xmax and power handling you come close, but as Tom sayed in http://www.danleysoundlabs.com/pdf/danley_tapped.pdf the driver for the TH will have more power handling and xmax, since it has to be a very different driver, compared to the bassreflex.
My bottom line is, this comparison is a little flawed, if you want to gain real knowledge about the different enclosures. The only way to accurately compare those devices is on an abstract mathematical level, where you can compute the gain of the enclosures without having to model a specific one, but i doubt someone on this board can do this.
Perhaps it would be better to look at what you can achieve with a tapped horn and then try to achieve it with a br or whatever design you like, since the good thing about a th is, that you can easily get designs, which will be difficult to get with an other enclosure type (very low and loud bass out of moderately sized enclosures).
Another thing is, i think so and said it once before, the most profit you can have with a TH is when the mouth gets really small in comparison to a normal horn. DTS20 has around 1000cm² mouth. The design you evaluate has a quite big mouth and is very near to a normal horn. This way, you dont use what a th can achieve, which is a tradeoff of bandwidth (you get around 2 octaves usable) for small enclosure size.
G'day again Ian, all
Perhaps another way we could attack this problem is start with a real, state of the art Tapped Horn, like the TH Mini on Tom's website and try to match those specs with a BR box. Same size, same efficiency, output and cutoff. It has 99dB efficiency at 40Hz, increasing to 101dB at 50Hz and up. All this in 133L. These figures are measured at 100W, so are pretty close to real. Speaking of which I really commend BMS for doing a high power plot on their spec sheet. I might be wrong but that plot only seems to show the port compression and not thermal compression. If the sweep were taken quickly from a cold driver, thermal compression would not show up. Also that plot shows there is a short fall from the target values at the lowest frequencies. Have a good look at the output at 40Hz. This is in a bigger box than the challenge called for, although slightly less power.
Check out the TH model of mine in the corner of a room, not 1/2 space as shown. The gain from the corner of the room is more than you will get out of a reflex, response is very flat like this too.
I think we might be having a fight with Hoffman.
Cheers
William Cowan
Perhaps another way we could attack this problem is start with a real, state of the art Tapped Horn, like the TH Mini on Tom's website and try to match those specs with a BR box. Same size, same efficiency, output and cutoff. It has 99dB efficiency at 40Hz, increasing to 101dB at 50Hz and up. All this in 133L. These figures are measured at 100W, so are pretty close to real. Speaking of which I really commend BMS for doing a high power plot on their spec sheet. I might be wrong but that plot only seems to show the port compression and not thermal compression. If the sweep were taken quickly from a cold driver, thermal compression would not show up. Also that plot shows there is a short fall from the target values at the lowest frequencies. Have a good look at the output at 40Hz. This is in a bigger box than the challenge called for, although slightly less power.
Check out the TH model of mine in the corner of a room, not 1/2 space as shown. The gain from the corner of the room is more than you will get out of a reflex, response is very flat like this too.
I think we might be having a fight with Hoffman.
Cheers
William Cowan
cowanaudio said:
Hi William
There are several difficulties with doing comparisons with a real tapped horn like the TH Mini (or the TH-115):
1. Not knowing what drivers are used (maybe), or the exact design of the horn (Tom's secret sauce?)
2. Not knowing if Xmax is exceeded within the passband at rated power
For example, I think the TH-115 uses the B&C 15TBX100 which has Xmax=9mm, rated power is 1000W continuous (133dB) which it might just handle, 2000W program (136dB) which I'm almost certain it won't, at least not everywhere in the passband.
(incidentally, if you look at the TH Mini curves it's under 92dB at 40Hz, 99dB at 50, 101dB from 60-100Hz)
I'll see if I can come up with a reflex box to equal this (not with a single 12" driver, obviously
, but without knowing what the Xmax limits are (maximum SPL vs. frequency) for the TH Mini it's difficult to do a fair comparison, which is why I'm suggesting using simulation with known driver parameters as a basis for comparison.So we either need to start with a reflex design that we know is optimum and come up with a tapped horn to match it, or vice versa. I suggested the first option, we could also do the second one but only if we knew exactly what the optimum tapped horn starting point was -- so if you know exactly what's inside any of Tom's tapped horns we could do also it that way
It's difficult to know the reason(s) for the LF SPL shortfall in the BMS plots (though as you say, it's pretty brave of them to show such a plot, I've never seen anyone else do it!) -- it could be port compression, it could be thermal compression (shows up most near minimum impedance), it could be a bit of both.
I know the efficiency of a tapped horn goes up more in either multiples or in a corner than a reflex, but that's kind of moving the goalposts -- all Tom's measurements are in half-space with a single box and the tapped horn is claimed to give higher SPL under that condition, so that's what I'm trying to prove (or disprove).
So far I haven't found a tapped horn that wins (for this particular set of design parameters), and neither has anyone else (yet...) with either real or imaginary drivers.
Cheers
Ian
P.S. If it turns out that in half-space there's little or no difference but in a corner the tapped horn wins -- that's exactly the kind of data I'm looking for, where the real advantages of the tapped horn lie.
iand said:
Hi Ian,
By way of explanation:
1. At very low frequencies you get a theoretical +6dB improvement in SPL response each time the solid radiation angle is halved. 3dB is due to improved acoustical loading conditions (enabling twice the power to be radiated), and the other 3dB is due to the doubled power radiating into half the space. Going from free space to eighth space gives an 18dB increase overall.
2. At very high frequencies (assuming constant directivity) you get only a +3dB enhancement. The acoustical loading conditions do not change when the solid radiation angle is halved. Going from free space to eighth space gives only a 9dB increase overall.
3. With a directional horn, at very high frequencies there is no change in the on-axis SPL as the solid angle is halved. This is because the sound radiates in a "beam" fully contained within the defining solid angle boundary.
4. Room reflections are ignored in this model.
Hornresp-calculated results are consistent with the above.
Kind regards,
David
David McBean said:
Thanks David, this makes complete sense -- but also shoots down in flames the argument that the efficiency of a tapped horn goes up faster than a reflex when placed against a wall or in a corner !!
Another way of showing that there shouldn't be any difference is to consider that as far as the room is concerned the tapped horn I came up with is a 320l box where all the sound (from both sides of the cone) comes out of a single 45x45cm hole with about 99dB/w efficiency.
If I build the reflex box with the two drivers face to face (one in, one out) in a triangular recess with the port exiting at the bottom, this also looks like a 320l box where all the sound (from both sides of the one) comes out of a single 45x45cm hole with about 99dB/w efficiency.
Since the room neither knows nor cares what's inside the box (so it's a "black box", ho ho ho) the room gain will be the same in both cases.
Back to you, William...
Cheers
Ian
iand said:
Not necessarily so, as what David talks about are ideal values. As the room can extended the horn to be physically bigger than the box it occupies (i am thinking of something like this: http://www.servodrive.com/SPL-bdeap32.html ), the acoustic loading of a horn in a room will be nearer to the ideal value which David described, than that of a bassreflex, which will have a rather big discontinuity along its path, where box ends and room begins. I think the br will have a less ideal impedance matching than the horn, resulting in less than ideal behaviour. Combined with port compression, which you ignore up to now, the horn seems to have several benefits above the br.
MaVo said:
There's nothing magic about added acoustic loading increasing the output of a horn; especially in a tapped horn the discontinuity is massive because the flare rates are completely different, you can also simulate this easily for BDEAP-type configuration and see the effect (the end flare rate is much too rapid for a 30Hz horn, only really works down to 50Hz or so -- see BDEAP32 plots).
If both boxes (reflex and tapped horn) have the same half-space efficiency and same acoustic exit size the effect due to room loading (efficiency increase) *is* the same for both -- the room doesn't have some magic way of seeing inside the box, if the electrical - acoustic gain is the same for both then so are any reflected impedance effects which might change efficiency.
In this case the tapped horn and the reflex both behave the same way with extra room loading, which is what Hornresp shows clearly without any "I think" or approximations involved
I really wish Tom hadn't called his invention the "tapped horn", because people are extrapolating all sorts of things from full-size horn behaviour which don't necessarily apply to the tapped horn, they simply don't work the same way:
Full-size ("true") horn
-- large mouth area, inversely proportional to LF cutoff
-- essentially non-resonant above cutoff
-- presents a high resistive (non-reactive) acoustic impedance to the driver
-- very high efficiency due to impedance matching (acoustic transformer)
-- expanding exponential or similar profile to give gain (impedance matching) over wide bandwidth
-- flat response with very little sensitivity to varying driver parameters (e.g. BL)
Tapped horn
-- small mouth area independent of LF cutoff (see DTS20, TH50, TH115...)
-- resonant operation over operating bandwidth
-- presents highly reactive acoustic impedance, small resistive component
-- increased efficiency mainly due to multiresonant behaviour (like a bandpass box) not impedance matching
-- conical or similar profile gives poor acoustic impedance matching
-- very sensitive to driver (e.g. BL) and horn parameters, flat response needs precise alignment of resonant peaks and dips to avoid severe ripples
In other words it might look like a true horn with a small mouth -- but by definition this removes the operation mode that a true horn uses (non-resonant wideband acoustic impedance matching).
Cheers
Ian
jnb said:
The reason for the ripple you've got is that the driver/horn parameters are not correctly matched. If you look at the responses posted by me and William you'll see it's possible to get a flat response up to 100Hz or so (which is what I meant), usually with two high-Q resonant peaks above this (130Hz and 190Hz in my simulation) -- these are the ones that are notched out by the resonators in the DTS20.
Ian
I've been reading over this thread for quite some time now and I have a few q's.
When it is recommended that a driver with a high Fs be used compared to the cutoff frequency, how high is too high? To me, a driver with a 30 hz Fs would work better in a 25 hz tapped horn than let's say a driver with a 50+ hz fs.
And does anybody have trouble running akabak or hornresponse in Windows Vista? I cannot run them at all and it's quite frustrating.
When it is recommended that a driver with a high Fs be used compared to the cutoff frequency, how high is too high? To me, a driver with a 30 hz Fs would work better in a 25 hz tapped horn than let's say a driver with a 50+ hz fs.
And does anybody have trouble running akabak or hornresponse in Windows Vista? I cannot run them at all and it's quite frustrating.
Virtualy
Do you have XP?
If so Download,http://www.microsoft.com/windows/products/winfamily/virtualpc/default.mspx,
and install XP on a virtual machine. Its good for Windows and Linux. I do it for Wavelab 5.0.
iUSERTLO72p
Do you have XP?
If so Download,http://www.microsoft.com/windows/products/winfamily/virtualpc/default.mspx,
and install XP on a virtual machine. Its good for Windows and Linux. I do it for Wavelab 5.0.
iUSERTLO72p