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Joachim Gerhard 9th March 2010 01:52 AM

Mpl
 
3 Attachment(s)
I am planning to build a loudspeaker that complements my MPP. I have build a preamp and Brianco is doing a poweramp so in the next month a system will be made of Phonoamp, Preamp, Poweramp and Speaker for DIY.
The speaker is based on a wideband unit in a baffle.
Under 80 Hz it will be complimented by a dipol woofer and over 7kHz there will be a horn loaded Ribbon.
The wideband driver got developped over a period of one year.
It has a classical paper cone and Alnico magnet.
I got the finished samples some days ago and did some measurements.
The driver is designed for very low distortion.
It is under 0.5% up to 100dB in 1m second harmonic. Thirs id under 0.1%.
Today i will post some measurements.
The driver is in a 90cm by 125cm baffle placed asymmetric due to golden cut.
I will pulish photos and drawings later.
Impedance is 6 Ohm Re and sensitivity is 96dB for 1W/ 1m.

planet10 9th March 2010 09:42 AM

I'll be following this with interest Joachim. Something quite a bit different than your commercial efforts.

dave

graaf 9th March 2010 10:14 AM

Hello!

I can see typical nasty peak at around 3 kHz :(
Isn't there really any way to get rid of it? Not by means of ex post facto passive or active correction but by preventive measures? Are such peaks really unavoidable?

interesting what Hartley wrote in 1958:

Quote:

It so happens that many loudspeakers have a resonance at about 3,000 cps because of defects in construction
Audio Design Handbook, page 12

Quote:

A weak coil-cone joint usually gives a wellmarked peak between 2,000 and 4,000 cycles (usually at 3,000). This well-known fact is turned to good use in producing cheap speakers for cheap radios which have no real top; the peak at 3,000 gives a synthetic brightness to the reproduction.
Audio Design Handbook, page 153

best!
graaf

Joachim Gerhard 9th March 2010 10:40 AM

Quote:

Originally Posted by graaf (Post 2112584)
Hello!

I can see typical nasty peak at around 3 kHz :(
Isn't there really any way to get rid of it? Not by means of ex post facto passive or active correction but by preventive measures? Are such peaks really unavoidable?

interesting what Hartley wrote in 1958:



Audio Design Handbook, page 12



Audio Design Handbook, page 153

best!
graaf

You will not beleave it but 140 protos have being build over the years.
A version can be build without that peak. The version i have shown has the finished magnet system and membrane.
I also think the peak should go away because it is in the most sensitive area of human hearing. Other versions can be build that have more extended treble but for my profect i decided on an aditional tweeter so i will go with a variety of the shown driver.

graaf 9th March 2010 12:39 PM

Quote:

Originally Posted by Joachim Gerhard (Post 2112602)
I also think the peak should go away because it is in the most sensitive area of human hearing.

then why leave it? if "a version can be build without" it?

prohibitive costs? design-for-manufacturability considerations?

ribbon at 7 kHz and up would not help, even crossing at 3 kHz would not help :(
and we have been already sailing away from "Full Range" land into the waters of "Multi Way" :rolleyes:

50 years have passed, we presumably have all this hi-tech (from new materials to new measurements) unavailable to Hartley and His contemporaries and yet we can't fix those same old problems? :(

this is so disappointing :(

what is interesting speakers designed according to Hartley ideas are allegedly free from them
here is an example - Hartley speaker paired with a horn loaded ribbon filtered "6dB down at 10kHz and 12dB down at 5kHz":

Stereophile: Listening #37

yes, this example is outrageously overpriced, nevertheless the driver seems to be working according to the design principles 50 years old

so... then
why leave the peak?

all Hartley\'s patents expired long time ago, why not use it?

or ideas from Stewart Hegeman and others of "non-uniform asymmetric diaphragm treatment" or "differential wave impedance cone":
http://www.diyaudio.com/forums/full-...ml#post2088939

or Weber Rehde's patents and so on

why not?

best regards!
graaf

Joachim Gerhard 9th March 2010 05:11 PM

I will post measurements of a version without the peak later.
I know Richard Schmetterer of Hartley and also had the pleasure to spend time with the late Weber Rehde. I listened a lot to Shahinian speakers too that use ideas from Hegeman. Trust me, that peak will go !

Joachim Gerhard 9th March 2010 08:38 PM

other version
 
1 Attachment(s)
Here is another version of the wideband. Are you more happy with that graaf ?

planet10 9th March 2010 10:00 PM

Nice to see a waterfall with periods :)

The 2 charts don't seem to be the same driver thou. Top starts rolling off just shy of 10k, the waterfall driver i way down at 10k

dave

Joachim Gerhard 9th March 2010 11:00 PM

The fequency response is measured in 1m, the Waterfall is measured in the nearfield.

planet10 9th March 2010 11:43 PM

OK...

Be nice to see a waterfall in the far field.

dave


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