I was just wondering why most horns / waveguides used with compression drivers are very deep with narrow directivity? I'm not talking about pro use, but rather in a domestic application.
Would a shallow waveguide like we see used with direct radiators not provide fewer response irregularities and wider dispersion while still having enough SPL capability?
Do the phase plugs inside the compression drivers not couple well to shallow waveguides?
Would a shallow waveguide like we see used with direct radiators not provide fewer response irregularities and wider dispersion while still having enough SPL capability?
Do the phase plugs inside the compression drivers not couple well to shallow waveguides?
The why just simply has to do with pro use.
In general there still seems to be the biggest unsupported taboo on compression drivers.
Which is interesting, because some of them perform miles better compared to expensive tweeters out there.
Plus you get the additional extra headroom with it.
About 10-15 years ago we all dove into compression drivers for home/domestic use, and some incredible results could be made.
But again, that faded away because of the incredible taboo.
In general all parameters are dialed in to optimize pro-usage.
So very often optimized for max sensitivity and efficiency.
Which isn't really needed for home-hifi = we can easily use 3dB less of that all to improve other things.
For example a much lower Fs, more optimized dome etc.
I personally think that phase plugs would be much easier to couple actually, as well as creating a lot less other issues.
The (roughly) 1 inch diameter of a regular dome tweeter often created issues.
In general there aren't many PA/sound-reinforcement type woofers that fit the home/studio market well.
Some perform great, but they just look like an absolute turd.
In general there still seems to be the biggest unsupported taboo on compression drivers.
Which is interesting, because some of them perform miles better compared to expensive tweeters out there.
Plus you get the additional extra headroom with it.
About 10-15 years ago we all dove into compression drivers for home/domestic use, and some incredible results could be made.
But again, that faded away because of the incredible taboo.
In general all parameters are dialed in to optimize pro-usage.
So very often optimized for max sensitivity and efficiency.
Which isn't really needed for home-hifi = we can easily use 3dB less of that all to improve other things.
For example a much lower Fs, more optimized dome etc.
I personally think that phase plugs would be much easier to couple actually, as well as creating a lot less other issues.
The (roughly) 1 inch diameter of a regular dome tweeter often created issues.
In general there aren't many PA/sound-reinforcement type woofers that fit the home/studio market well.
Some perform great, but they just look like an absolute turd.
90 degrees makes sense from a geometric point of view. In simplest terms that fits within a room corner.
Wider? That sounds like your choice of words, narrower would be the reason for a deeper waveguide. A high directivity index.
SPL is rarely a problem with compression tweeters and a deeper waveguide in a domestic situation.
Wider? That sounds like your choice of words, narrower would be the reason for a deeper waveguide. A high directivity index.
I mean that a shallow waveguide would have wider dispersion. That may or may not be desirable for home use, but certianly if a shallow waveguide could reduce diffraction issues and give a smoother response that would be attractive. The impedance plots on many of the Pro compression driver + horn combos is packed full of resonances.
I was museing about the possibility of B&C dcx464 coaxial mid/high compression driver in a smooth shallow 10" or so waveguide. (I mean something like those produced in ATH, not a wooden panel thing). I realise the shallow waveguide would give no gain at the manufacturer recommended 300hz xover. But maybe it could do 600hz or 800hz.
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A lower frequency as well.
Longer horn = lower frequency.
There are entire (and very famous) articles written on the most optical acoustic loading.
One of the reason why PA horns are often exponential, just to create a little bit more "boost"
With the idea that more = more better these days, the issues from back in the day are long gone.
None of that is really interesting for just good directivity.
One of the reasons why Geddes rightfully so was having trouble calling these things horns and decided to call them waveguides instead.
As far as I know that waveguide calculator tool from the "waveguide topic" also works just fine with compression drivers.
Really nice design for PA purposes, although a bit on the pricey side.
I think the (original) BMS coax is better.
(B&C and Celestion basically copied the patent and had them ready as soon as the original patent expired)
But both just really focused on PA purposes, not the cleanest.
If you design the horn well, you technically can just use that from about 200-300Hz and add some subs with it.
Quite a nice idea because there won't be any cabinet issues.
Although in return we'll get a pretty difficult horn to design.......
I have been using shallow horns and waveguides with wide dispersion for years. They have been around for a long time.
Started with JBL 2344/2342 moved on to PTH1010 and also the M2 waveguide.
Issues with the phase plug are driver dependent and not a universal issue.
They work well at home.
Rob 🙂
Started with JBL 2344/2342 moved on to PTH1010 and also the M2 waveguide.
Issues with the phase plug are driver dependent and not a universal issue.
They work well at home.
Rob 🙂
The size of the waveguide is probably less about the compression driver and more about what you want the waveguide to do. Generally people are interested in directivity, and the waveguide mouth must get larger as the cut-off frequency lowers, in order to maintain control. The same would apply to hifi tweeters, but compression drivers can often be used to much lower frequencies than hifi tweeters (especially at home-type SPLs), so therefore can be worthy of bigger waveguides.
But it is a choice, you can use compression drivers with smaller waveguides or even none, just like a hifi tweeter. If you aren't interested in controlling their directivity or wanting to use their lower frequency potential.
Anther reason for large and deep waveguides are where people want to add significant horn-loading (e.g. to allow higher SPL, and/or potentially even lower crossover). Those need to do more than control/restrict directivity; the loading is related to the horn expansion rate and profile, and in general requires more depth. Again, you don't 'need' to do this, and there are some potential drawbacks to deep horns in hifi so many people don't; it is just another thing which compression drivers are well suited for, if you want it.
But it is a choice, you can use compression drivers with smaller waveguides or even none, just like a hifi tweeter. If you aren't interested in controlling their directivity or wanting to use their lower frequency potential.
Anther reason for large and deep waveguides are where people want to add significant horn-loading (e.g. to allow higher SPL, and/or potentially even lower crossover). Those need to do more than control/restrict directivity; the loading is related to the horn expansion rate and profile, and in general requires more depth. Again, you don't 'need' to do this, and there are some potential drawbacks to deep horns in hifi so many people don't; it is just another thing which compression drivers are well suited for, if you want it.
Even among "regular horns" there are ones that aren't that deep to begin with.
As soon as those are "constant directivity" they are relatively shallow.
Just some (non particular) examples are something like a FaitalPRO STH100, which is around 85mm deep.
Or something like a BMS 2193, which is only 70mm deep.
If you design a proper CD/OS waveguide for a regular dome tweeter you will roughly reach the same dimensions.
Here you'll find quite some more examples;
https://www.diyaudio.com/community/threads/geddes-on-waveguides.103872/
https://www.diyaudio.com/community/threads/geddes-on-waveguides.103872/
How would we calculate the max SPL something like the B&C 464 could output in the lower range if not receiving any horn gain? Say we pop it in an 8" waveguide on a 12" baffle. Could we xover around baffle step of 500Hz while being able to output enough SPL for domestic use? The waveguide will not provide gain below about 1KHz, but at least we have half-space radiation until 500Hz.
Hello
That seems like a small waveguide for 500Hz. Why the 8" limit? Why are you worried about max spl? As long as you have enough SPL down low to support a proper crossover you should be fine.
Chances are there is no way you are going to know for sure until you slap on the waveguide and do some measurements.
Rob 🙂
I mean that it might be possible to xover at 500Hz if we accept 95dB max output level, but if we want 110dB max output level the driver may hit xmax at 500Hz (xmax is very small for compression drivers, since they rely on horn loading to achieve the high SPL pro audio requires). For example if the typical pro audio horn on driver X can give us 125dB at 500Hz max SPL, I would happily trade -6dB for a smaller waveguide with a smoother response in a domestic case.
For a piston direct radiator SD and Xmax give us an easy SPL calculation. I'm not sure how it works for a compression driver with no stated Xmax and a compression chamber + phase plug + user definable horn.
Hello
I can't see you ever causing a compression driver to hit the phase plug in a home situation unless something is very wrong.
Look at it this way when you set-up the system you are doing low power measurements. So no worries there. If you go passive or active you are going to have to pad the CD. So right from the start significantly less power into the CD. So lets say it works out to 10db that's significant and it could be 13db so 1/20th power.
When you measure on the waveguide you will clearly see where the knee is. If you are 6db down at the crossover point a couple of hundred Hz away from the knee you should be fine. If in doubt just cross a bit higher. Until you have an actual measurement it a guess where to crossover.
Not getting into matching DI at the crossover point. That for sure will dictate where it S/B.
Rob 🙂
I can't see you ever causing a compression driver to hit the phase plug in a home situation unless something is very wrong.
Look at it this way when you set-up the system you are doing low power measurements. So no worries there. If you go passive or active you are going to have to pad the CD. So right from the start significantly less power into the CD. So lets say it works out to 10db that's significant and it could be 13db so 1/20th power.
When you measure on the waveguide you will clearly see where the knee is. If you are 6db down at the crossover point a couple of hundred Hz away from the knee you should be fine. If in doubt just cross a bit higher. Until you have an actual measurement it a guess where to crossover.
Not getting into matching DI at the crossover point. That for sure will dictate where it S/B.
Rob 🙂
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No, wider dispersion would not be better if narrow is what you want. A deeper waveguide will not help with diffraction and it will not help with a smoother response. It is challenging to build a deeper waveguide and it is worth the effort if that’s what you’re looking for. Why would you bother with a shallow waveguide?
You may be thinking of horns. If you take an existing waveguide and stretch it to a longer axial length, it will perform less good at the lowest frequencies holding to the new narrow angle.
yes, it even says longer horn 😎 😉
If you stretch out a waveguide it basically becomes just a horn, but we are getting very pedantic here.
Mostly because the line between the two is rather gray and not black and white/a discrete step.