tuga
Major Contributor
What is the reasoning behind choosing a rectangular mouth instead of a round one?
-
WANTED: Happy members who like to discuss audio and other topics related to our interest. Desire to learn and share knowledge of science required. There are many reviews of audio hardware and expert members to help answer your questions. Click here to have your audio equipment measured for free!
Evidence-based Speaker Designs
- Thread starter Ilkless
- Start date
What is the reasoning behind choosing a rectangular mouth instead of a round one?
It has to do with directivity. Round horns don't exhibit constant directivity but beam a lot and is likely one the reasons they often sound very colored.
An OS waveguide could would work well, but becomes encredible large and tall if you want CD low in frequency. The waveguide of the Geddes Summa you see below would be way too small.
OP
- Thread Starter
- #1,223
What do you think of the SEOS profile? Don't really seem them around much for complete speakers.
tuga
Major Contributor
I understand the problem of maintaing narrow directivit at low frequencies. Bass horns are indeed quite large beasts:
But a speaker can beam and exhibit constant directivity, a constant narrow-directivity speaker.
An Avangarde or some electrostatic speakers exhibit quite a radical amount of beaming but doesn't the Dutch & Dutch 8c also qualify as a constant narrow-directivity speaker?
What is the dispersion angle value below which it is considered beaming?
What are the downsides of beaming besides making stereo a one person experience?
Ha, after "only" ten thread pages we now have the possibility to search all information together to at least approximately simulate the floor bounce of your speaker. The floor bounce for the listening position at 3m distance and 1m height should be at 400-500Hz.
Since the crossover frequency is 500-600Hz, the floor bounce should still be noticeable.
Depending on how well the vertical directivity of the mid-bass horn still works at this frequency, the sound pressure dip caused by the floor bounce will result.
A possible candidate for the floor bounce would be the sound pressure dip at 470Hz in the 3m room measurement.
To verify this, the floor bounce would have to shift to higher frequencies at longer measurement distances.
Conversely, a shift to lower frequencies should take place at a shorter measurement distance and the sound pressure dip should also decrease depending on the directivity of the horn.
I had the biggest SEOS waveguide. I think it's a rather mediocre design.
tuga
Major Contributor
In what way, measurable, audible, both?
Guess it depends what you define as constant directivity. A speaker that changes the directivity a lot in the area between 500 Hz and 10 kHz isn't constant IMO. The result other than a smaller sweetspot is a change in the spectral content because the reflective energy will vary in frequencies. Some beaming very high in frequencies is on the other hand not a big issue.
The floor bounce will depend on the directivity as well as you mention. It can also be minimized with absorption if one feel the need to do that.
Both. Measurements and sound quality correlates to me.
tuga
Major Contributor
As far as I know only omnis, dipoles, cardioids and (really huge) horns can avoid the transition from direct to omni.
I don't know if Toole mentions this in his research but I agree that a sharp transition from omni to narrow in the low- or mid-midrange, as is typical in many 2-way woover and horn designs, would not be particularly desirable...
If you were doing room EQ based on this response would you EQ that circled dip or not?
Perhaps you minsunderstood me. When I'm talking about "low in frequency" I'm not referring to the frequency area below Schroeder. Below Schroeder room modes will dominate not matter what. Obviously the Schroeder limit isn't always very definite and it can a transition zone and SBIR also come into play. For instance, with the midbass horn I can see that the frequency area around 150 Hz is more even compared to other speakers.
But generally you want constant directivity down to the Schroeder frequency. If you look at round horns you will see a beaming pattern often starting quite early and going all the way up. It's constantly getting narrower, thus the overall change in directivity in a very audible range is quite large.
tuga
Major Contributor
Would it be possible to EQ-off a cancellation?
Yes, as that is not a "perfect" cancellation. If you push it up by app 5dB with the filter with appropriate Q it will practically dissapear with 1/6 smoothing. The question here is would it sound better or not.
tuga
Major Contributor
I have posted an example above where that doesn't seem to happen, and here is another one:
https://www.stereophile.com/content/avantgarde-acoustic-uno-nano-loudspeaker-measurements
If I'm not mistaken the increased narrowing can be eliminated by using more ways.
But this makes speakers a lot more expensive and less domestically acceptable size-wise, for example:
Last edited:
You should keep in mind that the floor bounce is always position dependent (listening position height and distance to the loudspeaker) and the cancellation cannot, as already mentioned, be filled up with EQ.
tuga
Major Contributor
Makes sense.
In regard to your question, do you mean it could sound worse because you are not dealing with a "perfect" cancellation or because some people might like the effect of a dip in that range?
You can add more stacked horns to combat the beaming, but which again leads to new serious issues IMO.I have posted an example above where that doesn't seem to happen, and here is another one:
https://www.stereophile.com/content/avantgarde-acoustic-uno-nano-loudspeaker-measurements
If I'm not mistaken the increased narrowing can be eliminated by using more ways.
But this makes speakers a lot more expensive and less domestically acceptable size-wise.
tuga
Major Contributor
Wouldn't a dipole interact with the room differently than a forward radiating box below Schroeder?
