Horn Loading RAAL Ribbon Tweeter --- Full Measurement Comparison

[Joseph Crowe]

I would like to share my latest blog post where I horn load a RAAL 70-21XR ribbon tweeter and provide a full measurement comparison against a regular speaker baffle.

https://croweaudio.blogspot.com/2020/06/horn-no-1155-for-raal-70-20xr-pure.html

 

[HooStat]

Very nice. Did you compare to the 1159? Seems like the 1159 has similar performance, better loudness, and lower cost (unless you use a more expensive tweeter)

 

[Vini darko]

That's a lovely horn design.

 

[Ericglo]

Excellent work.

I notice both the ribbon and SB tweeter on the comparison baffle have what looks like eyes at around 2k. Is that from the comparison baffle's shape?

 

[pozz]

Very beautiful design and results.

 

[gene_stl]

nice web page too.

 

[Absolute]

Excellent stuff Mr. Crowe, I love your website! I noticed you wrote that you vastly preferred the sound with the horn, which is interesting considering wide dispersion seems to be all the rage here at ASR at the moment.
Does that conclusion hold up even if you unplug the woofer and just listen to the tweeter?

 

[Kvalsvoll]

Nice horn, mahogani is a very fine material.

Measurements show that the horn has much smoother and even response (in 3D), so it really should not come as a surprise that it sounds better. and you also get a huge reduction in early reflected sound level. I have used horn loaded ribbons for many years, and they work quite well. You also get improved capacity at the lower end of the frequency range, where it is needed most. Compared to compression drivers or larger AMT drivers, you will get more distortion and the ribbans can never play as loud, but for many applications the output capacity may be quite sufficient.

 

[Arthurdent]

nice job

 

[Joseph Crowe]

Very nice. Did you compare to the 1159? Seems like the 1159 has similar performance, better loudness, and lower cost (unless you use a more expensive tweeter)

I did listen to both horns side by side (1155 & 1159) and the RAAL has more clarity overall. Looking closely at what measurement correlates to this was difficult. The RAAL has an extremely fast decay in the first 0.25ms compared to the SB dome but after 0.25ms they are pretty much the same. This can be observed in the CSD plot and step response. Otherwise there are no differences in the rest of the measurement set. Both the 1155 and 1159 measure and sound excellent, so it’s not a knock on the 1159. The RAAL is a contender for the same upper treble detail as the TAD TD-2001 compression driver but lacks the dynamic range of the TAD. In other words there is some minor compression on transient peaks with the RAAL, regardless of volume level. This would only be noticeable to certain people...somewhat as a “sin of omission”.

 

[Joseph Crowe]

Excellent stuff Mr. Crowe, I love your website! I noticed you wrote that you vastly preferred the sound with the horn, which is interesting considering wide dispersion seems to be all the rage here at ASR at the moment.
Does that conclusion hold up even if you unplug the woofer and just listen to the tweeter?

I didn’t know wide dispersion was all the rage currently. There seems to be a lot of interest in waveguides as well. One thing to note is that the 1155 horn provides wider coverage in the upper treble compare to the test baffle (100 vs 80 degrees) however in the midrange the horn is controlling coverage to match that of the treble.

 

[stevenswall]

I didn’t know wide dispersion was all the rage currently. There seems to be a lot of interest in waveguides as well. One thing to note is that the 1155 horn provides wider coverage in the upper treble compare to the test baffle (100 vs 80 degrees) however in the midrange the horn is controlling coverage to match that of the treble.

I think it's just "controlled dispersion" which is usually accomplished by waveguides. Some can control it really widely horizontally though. I imagine the Devialet Phantom would be like that.

 

[HooStat]

@Joseph Crowe
Is there any benefit to a horn for the 5" woofer (or a 4" one)? I thought I saw something on your website with that approach. Mainly, I was thinking it might help match dispersion to a lower frequency. But maybe lower frequencies are too omnidirectional to be affected.

 

[richard12511]

Measurements show that the horn has much smoother and even response (in 3D), so it really should not come as a surprise that it sounds better.

It still comes as a bit of a surprise, to me. According to Toole, wider dispersion is generally preferred, and waveguiding this tweeter is reducing the dispersion width.

 

[Joseph Crowe]

It still comes as a bit of a surprise, to me. According to Toole, wider dispersion is generally preferred, and waveguiding this tweeter is reducing the dispersion width.

The speaker that Floyd used as the narrow directivity speaker was an electrostatic panel that was down -15dB at 60 degrees off axis in the region from 2kHz-20Khz. This contrasts sharply to my polar map which is only down -5dB at 5kHz 60 degrees off-axis.

 

[richard12511]

The speaker that Floyd used as the narrow directivity speaker was an electrostatic panel that was down -15dB at 60 degrees off axis in the region from 2kHz-20Khz. This contrasts sharply to my polar map which is only down -5dB at 5kHz 60 degrees off-axis.

That's just a difference in magnitude, though. They're not as narrow as those electrostats, but they're still narrower than the non waveguided version, which, according to Toole, is a negative. Less of a negative, for sure, but still a negative.

Of course the improved dispersion consistency is an obvious positive, and I could definitely see where it's possible that the positive effects of the improved consistency outweigh the negative effects of the narrower beam. I guess it's just unclear to me where to draw that line. I know Dennis Murphy is against wave-guiding this tweeter. He favors the wider dispersion over the more controlled dispersion, but that might also be due to the wider dispersion woofer in the BMR.

 

[VeerK]

I have the 70-20XR in my DIY desktop monitors, great tweeter especially on the top of the range. This design looks phenomenal, I’m jealous

 

[Joseph Crowe]

That's just a difference in magnitude, though. They're not as narrow as those electrostats, but they're still narrower than the non waveguided version, which, according to Toole, is a negative. Less of a negative, for sure, but still a negative.

Of course the improved dispersion consistency is an obvious positive, and I could definitely see where it's possible that the positive effects of the improved consistency outweigh the negative effects of the narrower beam. I guess it's just unclear to me where to draw that line. I know Dennis Murphy is against wave-guiding this tweeter. He favors the wider dispersion over the more controlled dispersion, but that might also be due to the wider dispersion woofer in the BMR.

Here is a frequency response measurement of both speakers (1159 + test baffle) at 45 degrees off axis. I chose 45 degrees since this is the most likely angle to reach the listener as an early side wall reflection which contributes to the perceived source width in Floyd's study. Nobody would argue that they'd prefer the red response which is from the flat test baffle. Yes the green curve is down a few dB but I don't think a few dB is what Floyd's listeners objected to. The 'narrow' directivity speaker in his test was extremely narrow with a poor off-axis consistency. So it's certainly a stretch to conclude that anything less than 180 degree coverage window is a negative.

 

[Joseph Crowe]

I have the 70-20XR in my DIY desktop monitors, great tweeter especially on the top of the range. This design looks phenomenal, I’m jealous

Thanks, I’m sure the 70-20XR would sound amazing with near field.

 

[richard12511]

Here is a frequency response measurement of both speakers (1159 + test baffle) at 45 degrees off axis. I chose 45 degrees since this is the most likely angle to reach the listener as an early side wall reflection which contributes to the perceived source width in Floyd's study. Nobody would argue that they'd prefer the red response which is from the flat test baffle. Yes the green curve is down a few dB but I don't think a few dB is what Floyd's listeners objected to. The 'narrow' directivity speaker in his test was extremely narrow with a poor off-axis consistency. So it's certainly a stretch to conclude that anything less than 180 degree coverage window is a negative.

View attachment 71554

Honestly, I'm not so sure how much I trust the research that suggests wider directivity is better. The Salon 2 vs M2 blind really swayed me. The M2 was basically better in every way, yet it still lost because it had narrower dispersion. However, more and more, lately, I seem to be shifting towards preferring more narrow (and controlled) dispersion designs.

Like you said, those speakers in that test were different in many ways outside of just their dispersion widths. I think it's ok to say that the wider dispersion speakers were preferred, but it's not ok to say that they were preferred because they were wider. For a conclusion like that, I would think you would need speakers that were identical in every way except for their dispersion width.

Dispersion width preference is the aspect of speaker design I'm most interested in atm, and I'm here to learn. It seems like there are different opinions. Do you think this waveguide improves this tweeter in most loudspeaker designs? What about a speaker like the BMR?