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Old 11th December 2008, 02:31 PM   #2041
gedlee is offline gedlee  United States
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Soongsc

Short of my own work in this area you will find only "talk". I have met very few who really even understand the concepts let alone done scientific work on them. I have even seen them described completely erroneously.

Its not "manufacturing tollerenaces" that are the issue at all. Its the design that determines the bulk of the HOMs.
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Old 11th December 2008, 03:11 PM   #2042
soongsc is offline soongsc  Taiwan
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gedlee,

It was your identification of HOMs that inspired me to even consider looking into horns and wave guides, and I appreciate it very much. Looking at the frequency span of audio signals, it certainly seems that HOMs are unavoidable, but it also seems that the closer to the throat, the more critical the manufacturing tolerances, and the effected frequency seems to be in the top end of the spectrum. Additionally, the compatibility between driver and horn/guide becomes critical. Lots of work is required to optimize things, yet, the financial returns may not interest most profit orientated organizations. This is probably why not so much work is done in this area. Hopefully we whom don't have to do this for a living can push the envelope of application of this.
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Old 19th December 2008, 12:15 AM   #2043
Theo404 is offline Theo404  United Kingdom
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Default Vertical coverage

Firstly Id like to thank Dr. Geddes for sharing his invaluable knowledge with us all...

This may be going back many pages (just got to the end of this mammoth from start to finish) but Id just like to say something on the subject of many posts from wayne (the Pi speakers guy). He claimed many times that it would be desirable to limit the vertical coverage angle of the waveguide to within the nulls formed at the crossover with the woofer, however I would suggest that this would be undesirable. As Dr. Geddes points out many times, to get a good sounding system in a small room there needs to be a good ratio of reverberant to direct sound at the listening position, particularly within the crucial 2-6khz region. This limiting of the vertical directivity above the crossover point would surely weaken the reverberant field a fair amount?
Maybe its because I listen in a high ceilinged room, but surely at least ceiling (if not floor) bounce is going to be >10ms so not an issue?
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Old 19th December 2008, 12:29 AM   #2044
soongsc is offline soongsc  Taiwan
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How much room interaction is best is really subjective. If the original recording was done in a fairly dead environment, the room interaction is necessary. For live recordings, the original reverberation is also recorded, if there is too much room interaction in the playback environment, then it messes things up.
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Old 19th December 2008, 03:05 PM   #2045
gedlee is offline gedlee  United States
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Default Re: Vertical coverage

Quote:
Originally posted by Theo404
Firstly Id like to thank Dr. Geddes for sharing his invaluable knowledge with us all...

This may be going back many pages (just got to the end of this mammoth from start to finish) but Id just like to say something on the subject of many posts from wayne (the Pi speakers guy). He claimed many times that it would be desirable to limit the vertical coverage angle of the waveguide to within the nulls formed at the crossover with the woofer, however I would suggest that this would be undesirable. As Dr. Geddes points out many times, to get a good sounding system in a small room there needs to be a good ratio of reverberant to direct sound at the listening position, particularly within the crucial 2-6khz region. This limiting of the vertical directivity above the crossover point would surely weaken the reverberant field a fair amount?
Maybe its because I listen in a high ceilinged room, but surely at least ceiling (if not floor) bounce is going to be >10ms so not an issue?


It is correct that a tall room would not benefit as much from a narrower vertical directivity. I would prefer not to excite the vertical aspects of a room if possible because its mostly the horizontal reflections that add spaciousness.

My disagreement with Wayne is that it is not obvious that what he proposes would work in the simple way that he claims or that there would in fact be any improvement. I'd like to try it and find out but my suspiciian is that the difference will be negiligable, but the costs will be high. Not a good tradeoff.
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Old 20th December 2008, 12:03 AM   #2046
CLS is offline CLS  Taiwan
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I remember somewhere someone mentioned about the foam padded horn (WG) mouth by Peavey (do I remember it correctly? I can't find it now). The foam padded mouth is to "mimic" the effect of a real large radius round-over.

This is interesting, and should be easier (or cheaper) to do in some case.

So I tried this:
Click the image to open in full size.

Click the image to open in full size.

This is an 8" Dayton WG bought from PartsExpress. Its overall flare is quite smooth, but the mouth opening to the outer surface (baffle) is not very rounded over.

Here I cut some wool felt and stick them around the mouth, as the pictures above. This made it sound more open.

Originally this 8" one sounded more 'concentrated' and 'congested' than the 12" one of the same brand. I think it's because the different flare angle -- 12" one opens up more rapidly, thus wide and shallow in overall shape. In direct comparison, the 12" one sounds much more relaxed and open on axis and spreaded the treble in a wider listening area.

Now the padded 8" one got a similar performance as the larger 12" one -- very open sound and larger coverage. I can hear the treble coming from the opposite side of speaker smoothly and clearly when standing right in front of this side. (Of course it's getting some help from the large toe in angle, but it's still fresh to me.)

Sorry for all of the subjective descriptions and not providing any measurements. I have no proper instrument and software to do it right.

It's easy to do and cost almost nothing. So I hope someone with tools and skills of measurement would spare some time for this and share some data.

Any comments are welcome
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Old 20th December 2008, 01:27 AM   #2047
tinitus is offline tinitus  Europe
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Quote:
Originally posted by CLS
I remember somewhere someone mentioned about the foam padded horn (WG) mouth by Peavey (do I remember it correctly? I can't find it now). The foam padded mouth is to "mimic" the effect of a real large radius round-over.


http://aa.peavey.com/downloads/pdf/qwp1.pdf
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Old 20th December 2008, 01:44 AM   #2048
soongsc is offline soongsc  Taiwan
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Quote:
Originally posted by CLS


...
Sorry for all of the subjective descriptions and not providing any measurements. I have no proper instrument and software to do it right.

It's easy to do and cost almost nothing. So I hope someone with tools and skills of measurement would spare some time for this and share some data.

Any comments are welcome
I you want, I could probably drop by and do some measurements.

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Old 20th December 2008, 02:56 AM   #2049
gedlee is offline gedlee  United States
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Quote:
Originally posted by tinitus



http://aa.peavey.com/downloads/pdf/qwp1.pdf
That paper is such a sore spot with me. A complete rip-off of my OS waveguide and not a single mention of any of my work in the entire thing. The most disreputable piece of work that I have ever seen.
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Old 20th December 2008, 07:08 AM   #2050
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Love your work CLS.
Would have loved to see some FR plots or CSDs though.
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