I've always had reservations about the implementation of back to back tweeters for dipoles. Yes they are better than single forward-firing tweeter as the tonal imbalances are fixed, but they have other problems too.
The imbalances with single firing tweeter is due to different radiation between front and back. And normally the tweeter levels are adjusted by ear to correct it to a certain degree (e.g. Linkwitzlab Phoenix). But what if instead changing tweeter levels we use the DSS filter ?
I've had this for sometimes now, and it seems to work quite well. Basically:
- Front firing tweeter only
- Some degree of directivity control using small waveguide
- Equalised to flat on-axis at 1m
- Subjectively adjust tweeter level to a correct level and note the attenuation
- Return to flat, and apply DSS.
The centre frequency is experimental, but the attenuation seems to correspond with the subjective attentuation.
The imbalances are corrected and sounds seamless. There is less sparkle as given by dual tweeters, but there is also much less room interaction and they seem to sound more truthful and direct. Much like listening to waveguide speakers, but with midrange transparency and that articulate dipole bass.
Here, the difference is seen between transition using tweeter level adjustments and DSS. It's quite an easy experiment and I hope to compare notes.
There are some other things I'd like to try sometimes in the future, for example placing the speakers much nearer to the front wall (now I have about 3m of space).
The imbalances with single firing tweeter is due to different radiation between front and back. And normally the tweeter levels are adjusted by ear to correct it to a certain degree (e.g. Linkwitzlab Phoenix). But what if instead changing tweeter levels we use the DSS filter ?
I've had this for sometimes now, and it seems to work quite well. Basically:
- Front firing tweeter only
- Some degree of directivity control using small waveguide
- Equalised to flat on-axis at 1m
- Subjectively adjust tweeter level to a correct level and note the attenuation
- Return to flat, and apply DSS.
The centre frequency is experimental, but the attenuation seems to correspond with the subjective attentuation.
The imbalances are corrected and sounds seamless. There is less sparkle as given by dual tweeters, but there is also much less room interaction and they seem to sound more truthful and direct. Much like listening to waveguide speakers, but with midrange transparency and that articulate dipole bass.
Here, the difference is seen between transition using tweeter level adjustments and DSS. It's quite an easy experiment and I hope to compare notes.
There are some other things I'd like to try sometimes in the future, for example placing the speakers much nearer to the front wall (now I have about 3m of space).
I'm frequently reading your investigation notes, these days. How does the polar plot look, in this case?
I'm quite interested in Rudolph's approach, too, of using a full range 2" to replace the tweeter. As a monopole, this should allow a low'ish XO, which could only be helped by a waveguide. Plus, if we want directivity, allowing the driver to beam a little should be beneficial, no?
EDIT: I see that popeye already proposed this at the Linkwitz forum. Any experiments?
I'm quite interested in Rudolph's approach, too, of using a full range 2" to replace the tweeter. As a monopole, this should allow a low'ish XO, which could only be helped by a waveguide. Plus, if we want directivity, allowing the driver to beam a little should be beneficial, no?
EDIT: I see that popeye already proposed this at the Linkwitz forum. Any experiments?
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please have a look at my experimentations with DSS and Plutos if interested in the subject in a more ample way (i.e. DSS in case of monopoles).
Here is the link to the post in the OPUG thread:
ORION/PLUTO/LX521 Users Group • View topic - DSS for Plutos: Phantom vs. Real Source Direction
(hoping it is ok to link back to another forum).
regards
giuseppe
Here is the link to the post in the OPUG thread:
ORION/PLUTO/LX521 Users Group • View topic - DSS for Plutos: Phantom vs. Real Source Direction
(hoping it is ok to link back to another forum).
regards
giuseppe
Obviously this is about hearing sensitivity compensation? The ear has sensititvy boost around 2kHz. It is general knowledge that this range is critical for sound localization eg. Most peakers also have xo around here, with many issues (phase, directivity, power response, peaks and dips etc.)
If a speaker measures straight here, it sounds harsh. BBC dip is 1-3kHz, is DDS similar? I could not find DDS mentioned in Linkwitz page.
If a speaker measures straight here, it sounds harsh. BBC dip is 1-3kHz, is DDS similar? I could not find DDS mentioned in Linkwitz page.
I disagree. That completely depends on the dispersion width of a speaker (and the room). With narrow dispersion designs the FR can be straight, omni even benefits from a peak here.
That is part of my findings when searching for the right eq. for my omnis.
Here is the link.
Interim Conclusions
The text is a bit lengthy but it does not only talk about omnis but wide vs. narrow in general.
I must clarify, that "straight is harshs"
- it is based on 0n-axis response!
My own listening experience and measurements and excercises with minidsp support what 2pi said - it depends!
I have found that I (like SL and Jon Marsh among many others) find most pleasing sound when on-axis has this bbc-dip and 15¤ off-axis is slowly descending to highs. This is largely because of high-end has usually more beaming
Like this: 1,2m on-axis and 15¤ horiz off-axis (60ms) and room response at 2,2m 10¤off-axis (500ms). My speaker is rather constant-directive but it has a widening peak at 2kHz.
Room response has dip around 800Hz, it is front-wall nulling. Also floor reflection and room modes are seen
- it is based on 0n-axis response!
My own listening experience and measurements and excercises with minidsp support what 2pi said - it depends!
I have found that I (like SL and Jon Marsh among many others) find most pleasing sound when on-axis has this bbc-dip and 15¤ off-axis is slowly descending to highs. This is largely because of high-end has usually more beaming
Like this: 1,2m on-axis and 15¤ horiz off-axis (60ms) and room response at 2,2m 10¤off-axis (500ms). My speaker is rather constant-directive but it has a widening peak at 2kHz.
Room response has dip around 800Hz, it is front-wall nulling. Also floor reflection and room modes are seen
Attachments
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OK, now I found it in SL's text
"Let's call this filter DSS (yes, it also de-esses), short for "Don & Siegfried's Shelf" because it may be unique to the ORION and /or to the two of us. The DSS works for us, but it also carries universal aspects. I suspect that the "BBC Dip" is related, because of its ability to control poor recordings."
"Let's call this filter DSS (yes, it also de-esses), short for "Don & Siegfried's Shelf" because it may be unique to the ORION and /or to the two of us. The DSS works for us, but it also carries universal aspects. I suspect that the "BBC Dip" is related, because of its ability to control poor recordings."
Again, and now we agree, it depends
Are you now talking monopole, dipole, or...?
Anyway, it is kind of fascinating how timbre changes with on-axis alterations in the 0.5dB range.
I can't find a reason why this kind of on-axis response shaping would have different effects on monopoles/dipoles/horns.
SL shows on-axis responses and is shaping that. Then suddenly in the closing phrase he talks about phantom images changing with this eq. His Orion uses back-to-back tweeters that are kind of dipole, they share same signal without delay or eq. Gino did the same for Pluto that has monopole dome tweeter. My tweeter is a ribbon in a horn. I can't see anything changing with DSS in front and back firing tweeters' relative response in Orion. Only the overall level changes. So - how could phantom image change?
If one want's do something for phantoms, backfire tweeter's delay, level or response should be changed.
SL shows on-axis responses and is shaping that. Then suddenly in the closing phrase he talks about phantom images changing with this eq. His Orion uses back-to-back tweeters that are kind of dipole, they share same signal without delay or eq. Gino did the same for Pluto that has monopole dome tweeter. My tweeter is a ribbon in a horn. I can't see anything changing with DSS in front and back firing tweeters' relative response in Orion. Only the overall level changes. So - how could phantom image change?
If one want's do something for phantoms, backfire tweeter's delay, level or response should be changed.
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It is in the sound power response. When you change it on-axis then you change it off-axis. So depending on the dispersion width, the timbre changes differently.
Secondly, there are various bands in the f range in which we hear that are associated with localisation. See Blauert bands.
With that the phantom image changes.
It is all in the link that I posted.
Secondly, there are various bands in the f range in which we hear that are associated with localisation. See Blauert bands.
With that the phantom image changes.
It is all in the link that I posted.
Here is a link to Blauert's original presentation of frequency bands contributing to sound localiszation of humans www.acoustics.hut.fi/.../blauert/...1a/SpatHear_1a.pps[URL="http://www.acoustics.hut.fi/.../blauert/...1a/SpatHear_1a.pps"][/URL].
His conclusions are mainly based on interaural distance and wavelengths. ie. ITD cues.
Range around 3kHz is very critical.
My point was - signal shaping does not change relation of direct and reflected sound.
However, 2Pi said in his link/web page that if some critical range's (like around 3kHz) relative loudness to other frequency bands is changed, perception of sound is changed. Timbre, spatial image..
Up to my logic, eq/response shaping does not change the signature difference of different types of radiators, but we perceive these changes with different magnitude. (understood? sorry English is a foreign language to me too)
Did I get it now?
His conclusions are mainly based on interaural distance and wavelengths. ie. ITD cues.
Range around 3kHz is very critical.
My point was - signal shaping does not change relation of direct and reflected sound.
However, 2Pi said in his link/web page that if some critical range's (like around 3kHz) relative loudness to other frequency bands is changed, perception of sound is changed. Timbre, spatial image..
Up to my logic, eq/response shaping does not change the signature difference of different types of radiators, but we perceive these changes with different magnitude. (understood? sorry English is a foreign language to me too
)Did I get it now?
That is correct but what I am also saying is, the magnitude and/or shape of eq. depends on the radiation pattern (wide vs. narrow) or sound power if you want.
The two extreme situations:
1. anechoic conditions or very narrow radiation => the FR can be flat/constant all the way up.
2. Omni => the required eq. deviates significantly from flat because of the timbre of the indirect sound.
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