Paul W said:
Not looking into your question in depth, I believe that a plane wave tube is the power response (there are some caveats here at the upper end), but nobody that I know publishes plane wave tube data. Data is always taken on a horn, and ususlly one that is not CD. This gives them a "better looking response".
A true CD waveguide does not have a very flat response when unequalized and would not make for a very imperessive curve on a data sheet.
Earl,
The design and the polar measurements of my WG prototype are all linked in post #38 of this thread. Here is the main link again to the curves in the "Large midrange for OB" thread:
Post #293 Large midrange for OB
It's not professional grade data but should be ok for a first appreciation. Post #292 has the measurement setup.
The design and the polar measurements of my WG prototype are all linked in post #38 of this thread. Here is the main link again to the curves in the "Large midrange for OB" thread:
Post #293 Large midrange for OB
It's not professional grade data but should be ok for a first appreciation. Post #292 has the measurement setup.
Dr. Geddes,
I'm not ready to graduate to compression drivers, so I use wide rangers in my WG's (just a simple 90° square conical). This seems to really help balance the off axis response. Some of my wide rangers require assistance above 5-10khz and those with good high end extension need the top end replaced by a tweeter. Would it be a good idea to put a tweeter inside the same WG, or is that just begging for more problems?
I'm not ready to graduate to compression drivers, so I use wide rangers in my WG's (just a simple 90° square conical). This seems to really help balance the off axis response. Some of my wide rangers require assistance above 5-10khz and those with good high end extension need the top end replaced by a tweeter. Would it be a good idea to put a tweeter inside the same WG, or is that just begging for more problems?
Yes this first test was a bit limited. I used 75 cm measurement distance to keep it well over the dimensions of the WG, but this did not help my outdoors S/N ratio and made a 3 ms window necessary to get rid of the floor reflection. And this in turn limits the frequency resolution. I'll just have to find a better setup.
Which measurement distances, windowing and excitation signal would you recommend to measure this WG?
Which measurement distances, windowing and excitation signal would you recommend to measure this WG?
gedlee said:
I know a little company called JBL that publishes plane wave tube data on their compression drivers.
http://www.jblpro.com/pages/pub/components/2426.pdf
johninCR said:
Compression drivers have so many advantages over small tweeters you really should check them out.
I don't use JBL drivers as they are not cost effective, and I wasn't aware of seleniums data sheets. I wish more companies did this as I like seeing both sets of data.
As for measurements its always the greatest distance that wins, but this is always difficult. get as far away as your situation will allow. I used to use my cathedral ceiling living room for reasonable data, but not the factory has a very high ceiling so we get real far away - like 3 meters.
I've been following this and the "Beyond" thread. Both are interesting. I guess I have different design objectives from both EG and LO. Interesting threads though. Anyway, I put together an OS wave guide spread sheet that will accept throat radius, throat angle and exit angle and compute the correct profile and locate the X offset. That is, at the X offset the slope matches the input angle and the throat radius. You can down load it here: http://www.musicanddesign.com/codes/OS_wave_guide.zip
gedlee said:
Well that's getting pretty picky considering the accuracy of a wood lathe.
The throat radius only changes about 0.001" when you shave the back off enough for a 6.5 degree throat angle. But for the anal retentive, I included a note to use Goal Seek a second time to correct the nominal throat diameter so the real throat radius subtracts that 0.001". Now how you go about measuring the actual throat diameter and angle of the compression driver to 0.001" is left as an exercise for the reader.....
The accuracy of a lathe is in the hands of the turner. Several thousandnths is obtainable...though it probably won't stay that way. The movement of the wood after that is likely subject to ambient moisture changes. Just how significant is another exercise for the reader.
Mongo got a big laugh telling me once that the first part of analysis was........anal
Mongo got a big laugh telling me once that the first part of analysis was........anal
catapult said:
Well that's getting pretty picky considering the accuracy of a wood lathe.
I wouldn't worry about .001" either, but the thing is that my math doesn't agree with yours, I get different numbers which show a far greater difference in radius. I don't have the time to debug what you have done, but it doesn't set right with me.
DSP_Geek said:
HOM - Higher Order Mode, its a term that I coined to define waves that propagate in a waveguide that do not go down the axis, but travel by bouncing off of the walls. They are not predicted by the Horn Equation, so most people didn't even know that they existed (I was the first person to hypothesize there existance). The Waveguide Theory predicts them, and low and behold, it turns out that they are quite significant to audibility. Minimizing them yields a far better sound quality. But with "horns" its not possible to minimize them because you don't know what to do - the equations aren't rigorous enough to predict them so they are simply ignored.
Thank your for all the info - if in your opinion a 1" driver with say typical 60W program handling at 2k and recommended 1.6k x-o can handle this application down to sub-1000 Hz territory, it makes things a lot easier (and cheaper). I had assumed a 1.4" driver minimum.
As a DIYer one does not have the luxury of going through a gamut of options, it's more like on shot with educated guesses.
gedlee said:
I thought it might've been High Order Modes, but *what* modes were beyond me. Thanks.
I suspect HOMs might be related to the center annuli of phase plugs not coupling terribly well with the horn flare at higher frequencies. Have you had any experience with non-concentric phase plugs such as Altec's tangerine?
Dear Dr. Geddes,
Or the various attempts to form waves in a guide by sound reinforcement manufacturers, like JBL, EAW, Nexo, etc.?
From what I know about your work, you're not intending to mix up wave guides with what manufacturers usually phrase 'line array' or just 'line source'.
But I have always been wondering what's your opinion about these developments and what you think of them.
Cheers,
Sebastain.
Or the various attempts to form waves in a guide by sound reinforcement manufacturers, like JBL, EAW, Nexo, etc.?
From what I know about your work, you're not intending to mix up wave guides with what manufacturers usually phrase 'line array' or just 'line source'.
But I have always been wondering what's your opinion about these developments and what you think of them.
Cheers,
Sebastain.
sek said:
I have done several waveguides intended for line array applications. One does not use an axisymmetric geometry like OS for this, but good waveguide designs can be done which create a cylindrical wavefront rather than a spherical one.
Line arrays deffinately have their uses. For example, we have clustered Summas (ESP15), but beyond two, things don't "add-up" very well. So if you need more output than two Summas could provide what do you do? (Thats far more output than one would ever need in a home - even a small disco).
The line array is a pretty good solution when very high outputs (more than four enclosures) are required. But make no mistake these designs have a lot of compromises to them. Basically without very complex EQs they would be a disaster. And none of them has the sound quality of a well done small system. Its the tradeoff that you have to make for high output.
You have to be clear on what the goal is. What we have been talking about here is DIY stuff aimed at a more home listening environment. For very high output pro applications a completely different set of requirmements are required. I have done a lot of line arrays and the Ai ESP10 is designed to be "arrayable" but thats all another topic.