Home » Sponsored » Pi Speakers » HF Compression driver without horn flare?
HF Compression driver without horn flare? [message #47150] |
Sun, 19 June 2005 05:13 ![Go to next message Go to next message](/forum/theme/AudioRoundTable/images/down.png) |
Paul Holland
Messages: 13 Registered: May 2009
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Chancellor |
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Hi folks, The following link describes a boutique / audiophile speaker, made here in Sydney, with similar design concepts to some of the pi speaker range, ie 2 way, ported, 15" woofer with compression driver, pro audio components.I have not listened to them , and are afraid to enquire about the price, but my efforts to reverse engineer an affordable DIY version has brought me to the pi site (here to stay!) Anyway despite my divergence from the original plan, ( I will probably build a pi 8) I am curious about the designers using the TAD TD4001 sans horn flare. Has any pi constructors tried this? Is this common or uncommon practice? Does this practice only apply to the TAD TD4001? Opinions welcome. http://www.deepaudio.net/html/product_info.htm Other interesting construction details include aluminium / MDF sandwhich panels with minimum bracing or damping. Has anybody experimented with laminated / composite sandwich panels? Cheers, Paul.
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Re: HF Compression driver without horn flare? [message #47152 is a reply to message #47150] |
Sun, 19 June 2005 08:27 ![Go to previous message Go to previous message](/forum/theme/AudioRoundTable/images/up.png) ![Go to next message Go to next message](/forum/theme/AudioRoundTable/images/down.png) |
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Wayne Parham
Messages: 18748 Registered: January 2001
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Illuminati (33rd Degree) |
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A compression driver used without a horn is basically a dome midrange/tweeter. The TAD 4001 has a beryllium 4" diaphragm, a 5 slit phase plug and a 2" diameter throat. Do you know if Deep Audio removes the cover and phase plug and radiates off the diaphragm side, or do they leave the plug installed and output through the throat when using the device as a direct radiator?As for models of π Speakers, there are three basic types. The one π and two π speakers have a direct radiating cone woofer and dome tweeter. The tweeter is designed with a wide surround and is capable of relatively high excursion, making a first-order crossover possible. The woofer becomes increasingly directional as frequency goes up, but the crossover range is very wide because of the use of a first-order crossover. So there isn't an abrupt change in directionality due to the fact that the woofer and tweeter share a wide common band. Three π and four π loudspeakers use DI matching between the cone woofer and horn loaded tweeter. Crossover is done where the woofer directionality narrows to match that of the horn tweeter. This prevents a sudden change in in directionality because the woofer and tweeter are about the same at the crossover point. The five, six and seven π loudspeakers use the room's corner to confine woofer radiation to the 90° wall angle. This is matched by the midrange and tweeter directionality, since both also use 90° flares.
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You might ask them [message #47156 is a reply to message #47155] |
Mon, 20 June 2005 09:22 ![Go to previous message Go to previous message](/forum/theme/AudioRoundTable/images/up.png) ![Go to next message Go to next message](/forum/theme/AudioRoundTable/images/down.png) |
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Wayne Parham
Messages: 18748 Registered: January 2001
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Illuminati (33rd Degree) |
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Compression drivers are designed to be used with a horn. They are a lot like dome mid/tweeters but since they are designed to be used mounted on a horn, they are optimized for that application. A horn reduces excursion, so without a horn, diaphragm excursion will increase for a given drive level.You might want to ask them what they've done to address these issues in their application. Maybe they did some excursion measurements during R&D and found the limits of a TAD 4001 when used without a horn. It would be interesting to know what frequency and power causes the diaphragm to move too far in that application, and whether the coil moves out of the gap, the surround fails or the diaphragm hits the phase plug when the excursion limit is exceeded. You sure don't want to shatter one of those beryllium diaphragms. The Deep Audio loudspeaker has some things in common with one π and two π speakers, and other things in common with three π and four π speakers. I imagine it sounds good, but I am concerned about their choice to omit the horn. I cannot help wonder about it, and can only assume they have derated the device appropriately and made it work for them in that fashion as a dome tweeter. At its simplest level, a horn is a way of pointing the sound. Instead of wasting energy sending sound out to the sides and the rear, a horn directs sound into the room, where it is needed. This not only helps focus the sound making it more powerful on-axis, but it also reduces reflections. If directionality is matched throughout the audio band, then the reverberent field is made uniform too. So really, using a horn to point the sound where it is wanted is a good application of a very simple and useful acoustic device. Basically what I'm saying is that I can't see any reason to forego the use of a horn on a compression driver. High frequency horns are simple and effective acoustic devices, they aren't terribly large and they have no downside I can see. To omit the horn is to use the compression driver in a mode it wasn't designed for, and throws away the advantage of controlled directivity. It also requires increased excursion from a device that was intended for limited excursion.
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Re: You might ask them [message #47159 is a reply to message #47156] |
Tue, 21 June 2005 15:19 ![Go to previous message Go to previous message](/forum/theme/AudioRoundTable/images/up.png) ![Go to next message Go to next message](/forum/theme/AudioRoundTable/images/down.png) |
spkrman57
Messages: 522 Registered: May 2009
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Illuminati (1st Degree) |
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Compression drivers for horns are rather expensive to take chances on destroying the diaphrams. Even a short horn is better than no horn at all! Just my 2 cents worth! Ron
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Re: You might ask them [message #47161 is a reply to message #47156] |
Tue, 21 June 2005 23:35 ![Go to previous message Go to previous message](/forum/theme/AudioRoundTable/images/up.png) ![Go to next message Go to next message](/forum/theme/AudioRoundTable/images/down.png) |
Paul Holland
Messages: 13 Registered: May 2009
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Chancellor |
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Well, in the faq section they state subjectively, they prefer a circular expansion of hi frequencies, so fair enough. They have also voiced the cross-over for the speaker be used only with a direct on axis listening position, so that's what they like as well. Wayne, I appreciate your explanation, my curiosity has been satisfied for now. Thanks, Paul.
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OK, heck, I'm curious as well so I will ask them... [message #47170 is a reply to message #47164] |
Wed, 22 June 2005 20:24 ![Go to previous message Go to previous message](/forum/theme/AudioRoundTable/images/up.png) ![Go to next message Go to next message](/forum/theme/AudioRoundTable/images/down.png) |
Greggo
Messages: 36 Registered: May 2009
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Baron |
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I just sent them a note via their web site contact page, with a link to this forum and a request for some thoughts if they have any they are willing to share with us. If they just reply back to me and there is anything that will add to our discussion here, I will post it myself. Regards, Greg Jensen
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Re: OK, heck, I'm curious as well so I will ask them... [message #47172 is a reply to message #47170] |
Thu, 23 June 2005 02:30 ![Go to previous message Go to previous message](/forum/theme/AudioRoundTable/images/up.png) ![Go to next message Go to next message](/forum/theme/AudioRoundTable/images/down.png) |
16
Messages: 4 Registered: May 2009
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Esquire |
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Hi Guys, I am the designer of the Model 16 loudspeaker system. The question has been raised about our choice to use a compression driver without a horn. Well, firstly it must be realized that, as Wayne rightly states, a horn is a device that directs acoustic energy. When drive-units move and pressurize air, those pressure changes move outwards in space. If we were to mount a diaphragm on an infinitely large baffle, then that energy would only go forward in a 180 degree half-hemisphere as defined by the baffle...i.e. into "half-space"...it wouldn't be able to spill behind the drive-unit. Therefore an infinite baffle is somewhat like a "180 degree infinite-length circular horn". As such, it "loads" a driver to a small degree but to an infinitely low frequency. As soon as we use a baffle that is not infinite in size, then at some low frequency limit, defined by the size of this non-infinite baffle, the energy will start to spill behind the drive-unit and into a "whole-space" environment. In this case the drive-unit becomes "unloaded". Now, if we start to bend the walls of this baffle forwards into a horn, the magnitude of the loading increases. So now we can see a simple relationship forming, the longer the horn walls the lower the frequency the loading will be maintained to, and the tighter the angle the greater the "severity" of that loading. Now, just to make things a little more interesting, the tighter the angle the more the horn resembles a pipe, and of course pipes have resonances at discrete frequencies, and so it occurs that these resonances also "load" the driver and there will be specific centre-frequencies of peak loading. Once you understand all this you realize that short horns will provide very little loading below what will inevitably be a fairly high cut off frequency. Now, as a consequence of loading, the on-axis sensitivity of the loaded frequencies is increased, and this allows the possibility of electrical filtering or attenuation of those frequencies because now we may have a little extra acoustic energy to burn. Hence, in theory we can reduce the excursion requirements of the driver over the loaded frequencies, and hence the idea that loading ultimately helps to protect the driver. It is also true that the loading itself reduces driver excursion; the extent to which this happens is dependant on the magnitude of the loading. In the case of the Model 16 however, it is first and foremost a domestic hifi speaker rather than a PA system or studio monitor and as such it was never intended to be foolproof under the wild dynamic demands of uncompressed live instruments common to those environments. When used sensibly in near-field domestic situations it is more than capable of providing satisfying SPL without exploring the maximum safe output levels of the compression driver. The TAD4001 driver is rated at 30W with the TAD recommended filtering and assumed horn loading. It has an efficiency within the meat of its pass-band of 110dB per watt at one metre. So even with a tiny current flowing through its coil this driver is capable of sufficient safe output for me. We chose the 4001 driver for its sonic presentation…its tone…its musicality. We wanted to design a system that delivers a particular musical message, rather than a system that will impress people who want explosions or faithful recreations of space shuttle launches. Having a pair of Model 16s facing you at 1.5m in a quiet lounge room is like driving a 400hp car around town…you don’t ever really use the full wack…well…at least I don’t with the type of program material I listen to. Finally, we feel that there are some very real subjective virtues that we have been able to manifest by avoiding a horn, and for what it is worth we did prototype some horn systems, including going as far as modifying a TAD4001 by cutting out its conical plastic throat, filling behind it with resin and then re-machining it out so as to begin a perfect Tractrix expansion curve immediately from the phase plug!!!Hmmm....
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Pipe modes [message #47174 is a reply to message #47172] |
Thu, 23 June 2005 04:59 ![Go to previous message Go to previous message](/forum/theme/AudioRoundTable/images/up.png) ![Go to next message Go to previous message](/forum/theme/AudioRoundTable/images/down.png) |
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Wayne Parham
Messages: 18748 Registered: January 2001
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Illuminati (33rd Degree) |
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Regarding horns, I agree with you about pipe modes at low frequencies. An infinite horn is essentially a constrained space and pipe modes are avoided. But as a horn gets smaller in respect to wavelength, the pipe modes become more and more pronounced.On the other hand, measurements of appropriately sized horns show no response ripples, provided the frequency is high enough that the horn is of wavelength dimensions. For the TAD4001, a large horn is not required to avoid pipe modes because of the frequencies involved.
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