Hello all,
I am currently working on a speaker where one of the design goals is to have a constant directivity and extremely low distortion.
A tweeter that has caught my eye is the SEAS H1499-06 27TBCD/GB-DXT. After some research I am quite fascinated by the use of constructive diffraction (instead of destructive). I want to use this wave guide, but I don't like the tweeter itself. I'd prefer to use a beryllium dome (I currently have my eye on the Scanspeak Illuminator D3004/66400).
I've been trying to get the dimensions from the patent but their margins are very large (ranges of >10mm, the angles are +- 2 degrees which is managable) (Patent can be found here: US8160285B2 - Waveguide unit
- Google Patents)
Based on pictures and the given datasheet I have made a CAD drawing. I am wondering if these dimensions are somewhat accurate (my cad drawing is attached) and am looking for someone that can confirm this.
The drawing is based upon the center of the waveguide. All lengths are there for radius'.
This project is strictly for a non-commercial product. I have already contacted SEAS about this issue, but they refer to the datasheet and the patent.
I have considered buying the DXT and then return it, but I don't think companies would like this.
Anyone who can help me out here?
Thanks in advance!
I am currently working on a speaker where one of the design goals is to have a constant directivity and extremely low distortion.
A tweeter that has caught my eye is the SEAS H1499-06 27TBCD/GB-DXT. After some research I am quite fascinated by the use of constructive diffraction (instead of destructive). I want to use this wave guide, but I don't like the tweeter itself. I'd prefer to use a beryllium dome (I currently have my eye on the Scanspeak Illuminator D3004/66400).
I've been trying to get the dimensions from the patent but their margins are very large (ranges of >10mm, the angles are +- 2 degrees which is managable) (Patent can be found here: US8160285B2 - Waveguide unit
- Google Patents)
Based on pictures and the given datasheet I have made a CAD drawing. I am wondering if these dimensions are somewhat accurate (my cad drawing is attached) and am looking for someone that can confirm this.
The drawing is based upon the center of the waveguide. All lengths are there for radius'.
This project is strictly for a non-commercial product. I have already contacted SEAS about this issue, but they refer to the datasheet and the patent.
I have considered buying the DXT and then return it, but I don't think companies would like this.
Anyone who can help me out here?
Thanks in advance!
Attachments
There used to be web site describing DXT and encouraging manufacturers to pay royalties to use it. I had a quick google but without success. Anyone?
SEAS are not the only ones to have used DXT waveguides. Acoustic Energy for example use it with a ring radiator. Others?
It is simply a set of diffracting edges and so is easy enough to simulate accurately using FEM or BEM. This would enable you to efficiently design for a particular tweeter.
SEAS are not the only ones to have used DXT waveguides. Acoustic Energy for example use it with a ring radiator. Others?
It is simply a set of diffracting edges and so is easy enough to simulate accurately using FEM or BEM. This would enable you to efficiently design for a particular tweeter.
I am aware of Acoustic Energy using the wave guide for their ring radiator tweeter.
I do not have experience in designing horns or using FEM.
Do you have any recommendations for software (preferably well documented software) that could assist me in FEM?
And about the website, do you perhaps mean this thesis: http://daim.idi.ntnu.no/masteroppgaver/005/5927/masteroppgave.pdf
?
The website was put up by the patent holder but it is likely 10 years or more since I saw it.
If you don't have access to commercial FEM software and are unfamiliar with FEM itself then you will have your work out for you to use the relatively unfriendly free software. You might be better off starting with BEM software like AKABAK (which gets discussed here) or acousto (which doesn;t much).
If you do want to browse free FEM software then have a look at Salome/CodeAster, Elmer and perhaps calculix. Although they can all likely be configured to perform acoustics calculations it won't be mainstream, will be fiddly and might have a detail or two that you need missing. I have not seen these free packages discussed here but a few have discussed commercial packages like COMSOL which can do a nice job.
If you don't have access to commercial FEM software and are unfamiliar with FEM itself then you will have your work out for you to use the relatively unfriendly free software. You might be better off starting with BEM software like AKABAK (which gets discussed here) or acousto (which doesn;t much).
If you do want to browse free FEM software then have a look at Salome/CodeAster, Elmer and perhaps calculix. Although they can all likely be configured to perform acoustics calculations it won't be mainstream, will be fiddly and might have a detail or two that you need missing. I have not seen these free packages discussed here but a few have discussed commercial packages like COMSOL which can do a nice job.
You can still acces his website via the "wayback machine" (an internet archive). I can understand that different tweeters need different horns to perform optimal, but I figured since they are both domes of 1", the waveguide would have a similar effect.
Anyway I am going to look into the software you mentioned.
Thanks a lot!
Yes, the cone and surround matching is critical. I read a lot od DXT ten years ago and have MarkK ER18DXT monitors. I can't see or hear anything magical about SEAS DXT, but it is smooth above 3kHz. But it has no boost below 4kHz and no added directivity below 2kHz because it is so little.
Dave Pellegrine used to make custom waveguides and adapters which are top!
Copy these instead and prepare to difficulties trying to find the optimal driver and adapter. SB29RDC on Pellegrene waveguide
Check this too Wave guides & horns
Dave Pellegrine used to make custom waveguides and adapters which are top!
Copy these instead and prepare to difficulties trying to find the optimal driver and adapter. SB29RDC on Pellegrene waveguide
Check this too Wave guides & horns
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It will be difficult to build a constant directivity speaker with these tweeters, because extending their narrow 90-100 degree pattern to lower frequencies is hard to achieve with woofers. That would require at least three sources, each with its own DSP channel.
Does anyone know why the DXT waveguide is stepped? Similar waveguides seem to achieve similar performance without these steps.
Does anyone know why the DXT waveguide is stepped? Similar waveguides seem to achieve similar performance without these steps.
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It is stepped in order to have a tweeter with a waveguide that is pretty much the same size as a tweeter without. The steps create strong uneven diffraction effects which is why several of them of different sizes are needed to smooth things out. A larger conventional waveguide is gentler and smoother in guiding sound waves and offers control over a wider frequency range. If you are not strongly constrained by space then a DXT is probably not what you want.
Google found this Norwegian paper of waveguides, using DXT as an example. FEA design approach.
http://daim.idi.ntnu.no/masteroppgaver/005/5927/masteroppgave.pdf
The DXT brochure is out of this world, marketing babble, diamonds from heaven. But notice that they show response only above 3kHz, expect good match with a 4" midrange! http://www.seas.no/images/stories/prestige/pdfdatasheet/dxt_seas.pdf
http://daim.idi.ntnu.no/masteroppgaver/005/5927/masteroppgave.pdf
The DXT brochure is out of this world, marketing babble, diamonds from heaven. But notice that they show response only above 3kHz, expect good match with a 4" midrange! http://www.seas.no/images/stories/prestige/pdfdatasheet/dxt_seas.pdf
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I mentioned it earlier. Now that I know that you can't just copy paste DXT waveguides for the same result, I am going to use a similar design aproach.
I googled a bit and found the following article:
Open source Waveguides for CNC & 3D printing!
The forum he refers to is very helpful and is what I initially was looking for. I am going to try to simulate the waveguide with the parameters given on that forum!
Thanks alot!
Gentle diffraction on waveguide steps broadens the beam in top octave at the expense of slight deterioration of energy decays in this range.
So you do that.
Link i posted wasn't for you. I posted it to be seen how DXT waveguide cooperates with 5,5" midwoofer regarding directivity.
I forgot to quote Juha so i get the confusion.
How about using one of the commercially available waveguides like the Visaton WG-148R (148 mm diameter) or the Monacor WG-300 (168 mm diameter)? Heissmann Acoustics has tested several tweeters on these waveguides with very good results. LINK. Troels Gravesen also has information on using the Monacor waveguide with various tweeters, including the ScanSpeak D3004/660000 and D3004/664000. LINK
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