Mark. Nothing is hidden. The default flat driver model is given an 80Hz high pass. When you approach it from the low end, a low pass filter turns the rising response flat, and the flat response to falling.
This is old knowledge from the dipole enthusiasts, and it's also known among the subwoofer crowd.
This is old knowledge from the dipole enthusiasts, and it's also known among the subwoofer crowd.
Well I need to jump on that train cause I don't know how to use REW like that yet.
True. I would like to have the Waveguide experience is all. It is truer to the constant directivity idea, in particular, if I use a round one. I also propose an elliptical one. I would think an Elliptical waveguide would be desirable.
Thanks. Ok, i just built the same sim you did in vcad, and i get the same looking response graph you posted.
And i totally don't get it.
When i cascade those two filters in a processor, and measure the output....... i get exactly what i expect....zero output.
What on earth let's a sim show output with those two filters in play?
Mark, if one has a driver in a small box, it will raise it's Fs in box. Below that Fs number it will roll off at about 12 dB/Oct.
That's what the 2nd order at 80 Hz resembles in the sim. Just an ideal driver that rolls off below 80 Hz.
If we put a low pass on it, far below Fs, at say 20 Hz we create a level output above 20 Hz, where the driver was dropping off already.
And the output will resemble a low pass where the driver would regain flat response (at about 80 Hz) without any filter.
Next, we pump up the gain, say 24 dB 😉. And we have an output that resembles a subwoofer, created with a much
higher in-box Fs. And lowered the efficiency by quite a margin, hence the gain pump.
The crossover, together with the gain raise somewhat resembles a Linkwitz transform. Creating (flat) output below Fs. Not quite the same
naturally, but it's a trick to get a flat frequency below Fs.
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What is the purpose of having the waveguide be bigger? The driver is limited to about 800hz.... Lets say I aim for a 20" waveguide, can you make a freestanding ce360 that is 20" @fluid ...With a round wave guide, construction could be done a lot easier....either way If I am limited to 800hz by the driver then there is no use of going over 18" inches or so unless we are talking roll over area.
Thank you Ron, very helpful and very clear.
Yeah, i can get folks have learned all kinds of alchemy to make drivers dance in ways they probably aren't optimal for.
I have to say imho... examples of such are bad acoustic design...being altered by bad electrical design.
Personally when any passband needs more than +/- 6dB electrical adjustment, I count it as bad acoustical design and rethink/redesign it's physicality.
I cannot "make" anything anymore. I'm done with that, It's not what I do.
Remember a few things that are missing here. As the DI of the waveguide goes up, its coverage angle is going down. Then you have to consider that larger waveguides go lower if frequency. So, if you want a high DI your crossover point moves up. Remember that I said that you can't arbitrarily pick the crossover, you have to match the DI's of the upper and lower drivers. A lower DI - wider angle and the crossover needs to go lower to match. All this needs to line up or you will have a bad crossover region - exceedingly common unfortunately.
From what you say - I want more "direct energy" at the listening position - so do I. This means a high DI which dictates a higher crossover or a larger woofer (Mid in your case,) This is opposite of where your design is going - lower crossover means lower DI. I here almost no discussion on this critical point.
Yes, I know, you are just into teaching now, I was referencing Fluid and the model he produced
Maybe its the way I am looking at it....If we have a waveguide and measure its DI with no XO....the DI is not changed after applying a filter...so I cannot see what its trying to be conveyed with this perspective. The same is true with horn I am using....the DI of the horn does not change depending on where the xo is placed. What happens below the Xo filter, can change the DI....but if the the device on Top has higher di, than the device on the bottom, then it only makes sense to lower the XO.
This type of thinking changes when using the a 15" woofer into its beaming range....it almost seems that using a 15" so high is a compromise.
Time, patience and practice, I have spent a lot of time tweaking EQ's
Here is a comparison of a manual EQ I did by eye with a few filters vs a complete inversion
This is the ST260B designed for baffle mounting and could be scaled up.
https://www.diyaudio.com/community/...-design-the-easy-way-ath4.338806/post-6753006
https://www.diyaudio.com/community/...-design-the-easy-way-ath4.338806/post-6914654
Using bmc0's plaster method seems like a cheap and reasonable way to try something like this out.
The size is is determined by the length parameter in the Ath script, add more length get a bigger waveguide, it can be whatever you want it to be. Earl is describing being limited to 800Hz by the 1" driver he used, that limit would not apply to the Axi but the crossover frequency waveguide size and woofer directivity still need to be selected to avoid a directivity mismatch.
I displayed the woofer polar....I think the waveguide size should be as big as needed which in this case is sorta set my how low can the Axi play in a waveguide...Are we judging by Excursion? Should I look at my horns resp sim of the Axi and see where the xmax is reached without a horn?
"Bad" seems a bit dramatic to me, you seem to have no practical constraints on the size or cost of speakers that you make, most are not in that position.
All the best speakers I have made used much more than 6dB of EQ and I don't consider their acoustical design to be bad.
The previous polar did not look quite right to me, the final choice should be made from actual measurements anywhere from 500Hz should be quite practical with the axi. The OSSE termination lets go smoothly and loses directivity gradually making it quite flexible.
If you want a totally flat DI then build a 15" version of this.
https://www.diyaudio.com/community/...-design-the-practical-way.354772/post-6214298
That would be the best way to judge the waveguide and 15 together in a box designed to complement them.
I have bmc0's code and can make you a ruler flat DI OS with his termination for a baffle. All of this takes time though so you need to make your mind up what you want.
Ok, agreed...language a bit too strong....my bad lol 😉
How about i say compromised design, and by compromised i mean with one particular objective in mind, the objective of maximum linear dynamic capability.
Certainly not a major objective for everyone. It's one of mine, because it seems to clean up sound, even at lower listening levels.
I do wonder sometimes if folks are aware of the numbers it takes to accommodate boost, which is so often applied to achieve bottom-end extension and SPL.
I know you are, but just for general repetition's sake....power requirement doubles for every 3 dB increase.
So a 12dB gain for a particular frequency range needs 16x the power, vs the non-boosted range. (2^4th)
And +24dB is like wow...256x vs non-boosted. (2^8th)
It adds up quickly, if it's used. Most notes in music below about 40 dB aren't that loud anymore. Most, but not all.
If one really wants "the whole spectrum at high SPL, low distortion" it does seem a bit of a strange compromise to take.
Especially if it is added as a separate function (subwoofer) and the goal is maximum SQ.
If one really wants "the whole spectrum at high SPL, low distortion" it does seem a bit of a strange compromise to take.
Especially if it is added as a separate function (subwoofer) and the goal is maximum SQ.