Never mind on the why you call it diffraction question, found it in the B&C Compression Drivers thread.
noah katz said:
JBL made a 2-way that seems to have been inspired by the Summa. Here's a pic:
An externally hosted image should be here but it was not working when we last tested it.
I have a pair, they're quite nice. If you're going to use a JBL waveguide, I would think this would be a better candidate than what's being used for the "econo-wave."
Having said that, I retired them after buying the Summas. The JBL can't hold a candle to the Summa in the imaging department.
"The JBL can't hold a candle to the Summa in the imaging department."
What about harshness?
And to be fair, anything compared to Geddes' WG's should have the foam.
What about harshness?
And to be fair, anything compared to Geddes' WG's should have the foam.
noah katz said:
Well the harshness is caused by HOMs. If you use a good waveguide, the need for the foam is less. That's why the foam works so well in Sheldon's Unity horns; the Unity uses a sub-optimum waveguide.
And the JBL M-Series uses a waveguide that's VERY close to oblate spheroidal.
I'm not saying it's perfect, but I challenge anyone to show me a commercial speaker with a better waveguide. The only one that's better is made by a German company, and costs around $20K. I bought my JBLs for $400/each at Guitar Center!
Again, not saying they're as good as the Summas, they're not. But for the money? They're quite competent. And the waveguide is a million times better than anything I've seen in a commercial product.
Do you know about the compression drivers that BMS makes for JBL? There's another angle to the M-Pro series that's worth discussing, but read this first:
http://www.audioheritage.org/vbulletin/showthread.php?t=6368&page=7
My real burning question is how Dr. Geddes concludes from his measurements that the JBL econWG sounds harsh.
noah katz said:
I bought a pair of Econowave WG, using Selenium D220Ti, they are ok. Haven't heard the Gedlee WG, far to expensive for me.
I think the RCF H100 horn($28 each, a bargain) with B&C DE250 combo is far superior. Loudspeakers Plus used to sell them but pity no longer. Very little or no equalization is required with this combo. I am still listening to them.
Cheers.
"I think the RCF H100 horn($28 each, a bargain) with B&C DE250 combo is far superior."
In what ways?
"Very little or no equalization is required with this combo. I am still listening to them."
Do you mean EQ to give a generally smooth response, or high freq EQ for CD?
If the latter, that says it's not CD.
In what ways?
"Very little or no equalization is required with this combo. I am still listening to them."
Do you mean EQ to give a generally smooth response, or high freq EQ for CD?
If the latter, that says it's not CD.
noah katz said:
Most horn and compr driver combo will NOT produce a flat frequency response. Equalisation is required, usuallly to lift the frequency up from 8Khz onwards by about 3-4dB(This is a gross generalisation) using high freq. shelving circuit, see econowave x-over as an example. A particular combo ie horn and comp driv. a different HF shelving is required.
There you are not simply as a plonking the compr dr. on the horn. If you are keen I like to suggest using a DCX2496 and equalization is very easy indeed.
noah katz said:
The whole idea of a waveguide is to provide pattern control, and mate with a woofer. The problem with the "waveguide" used in the econo-wave is that it's a compromised design. First of all, the coverage angle in the vertical axis and the horizontal axis is different. That's compromise #1.
The bigger problem is that it narrows in the throat, which will cause the coverage angle to collapse at high frequency.
Does that make sense? It's just a compromised design.
The speaker that I mentioned, the M-Pro, has a much better waveguide.
If you don't believe me, just look up the data. I downloaded it for you, and you can see it here:
You can see from JBL's own published data that the M-Pro has smooth controlled directivity, all the way up to 16khz.
I doubt you will get a direct answer. However, if the on axis response transitions smoothly through the freqeuncies, then you can generally expect the sound will not be as harsh.noah katz said:
Actually the wave guide relies on the small throat to obtain wider dispersion in the higher frequencies. If the throat were larger, then the beam width would not be wide.Patrick Bateman said:
soongsc said:
A wide throat yields a narrow beamwidth?
You must be making horns on Bizarro World.
"Large throat". Not "deep throat" either.Patrick Bateman said:
Is this a classic or newly published?
noah katz said:
Uups,
Seems that Mr. Geddes defined a standart. There's a lot to question with his waveguides. To the most part of it an understanding of higher mathematics is required. That for the end user has a hard time to distinguish some advertising claims from real engineering.
It is true that OS waveguides are a solution to the wave equation. But - they are not the only one. As a practical waveguide has to be finite - is has to end somewhere - even the OS shows severe "HOM". Example given the wide dip around 8kHz. That IS interference, that IS "time delayed energy" etc. Ripples are apparent all over the spectrum, but Geddes averages them away partly. There is no data above 10kHz - mmh!? The 18sound XT1086 performs at least as smooth as Geddes' OS. And it has not tht huge 0° dip, that bashes useability for me personally with Geddes' OS. The foam seems to be a gimmick. Did anybody verify it's use objectively?
Mr. Geddes is a vendor in the most of it. He's not that much an engineer anymore. Both, Geddes and Bose habe a PHD. Would anybody remind A.Bose as a trusted leader to excellence? People learnt to take Boses claims into question. What came out was a normalisation of respect for hm. You have to question Geddes too. What will come out, we will see. It is not meant as "name calling" or bashing Geddes. But, please, dare to question it when he prescribes You a costly foam plug.
"We are only in it for the money." F.Zappa
xpert said:
Sounded better to me in my system. It did (to my ears) eliminate a slight "horn character" in my Unity's. I didn't attempt to analyze it further, as I only have to satisfy me. I think I'm a pretty objective listener. I don't have a personal stake in any outcome. I haven't heard any real differences rolling tubes, capacitors, resistors, cables, etc., or much difference between tube and transistor gear, for that matter (assuming good quality designs properly applied, and decent quality parts in all cases). So I'm no golden ears. But I did hear a difference here. And the foam was better.
xpert said:
Engineering is technology applied towards a specific goal. Bose's target has mostly been adequate sound in an small form factor, and profitable. So, yeah, I'd say he's done an excellent job in achieving his objectives. It's not going to satisfy critical listeners, but that's not the target audience.
Sheldon
noah katz said:
Harshness has no concrete deffinition, but here is what I sense when I listen to an older diffraction device. The HFs are colored and don't sound right, although the sound is very dynamic with low compression. Further, as the device plays more loudly the "harshness" gets greater.
I spent a lot of time with different horn designs etc. and there is one thing that comes through very clearly. A regular string of resonances in the pass band and the impedance curve indicates a strong internal reflection which can be from the mouth or a diffraction slit, either way it is a problem and elliminating it goes a long ways towards improved sound quality. The JBL horn had such a periodic progression of resonances and as such it woul fail even my first test of sound quality.
But further to that I have studied the effect of alternate path waves in waveguides and even without reflections from discontinuities these waves will exist. It can be shown (I have done the psychoacoustic studies on this) that delayed resonaces, such as would occur with HOM (alternate path waves) are audible AND that they become more audible with SPL level.
Since nothing was done in the JBL device to improve these HOM I would content that they would be an audible problem.
Yes, the polars were OK, they always are for diffraction devices, thats not their problem. The problem is the diffraction that is used to get these polars creates more problems than it solves.
This was a brief 2 min. discussion of what has taken me 20 years to learn myself, so its going to be lacking in many respects. SOme things that I note in measurements are not so easy to define, but herin lies the basics.
xpert said:
Rude as always I see.
Bose's PhD is not in Acoustics, mine is. I know him and his understanding of Acoustics is limited. His expertise is in digital communications theory.
Question all you want, but readers should know that it has turned out that you were seldom correct in your accusations.
The 8 kHz hole is not a result of HOM. It is a result of mouth diffraction from a circular mouth. An elliptical of square mouth will not exhibit that effect, nor will a less coherent waveguide. Since no one ever listens to my waveguides on-axis it is not a real problem, only one that people like you like to pick on.
The foam is hugely effective - don't make guesses without some data to support your position, and you have none.
And I am now and always will be a better engineer than you appear to be.
Your rudeness is a real turn off, so don;t expect me to respond to your junk comments any longer.
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