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Look ma, no box !!


gainphile
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Another attempt for sonic purity. This time no h/u/w frame. Just plain old baffle for maximum uniform polar response.

4137486214_2182daa4ab_o.jpg

Tweeters are Hivi K1, L21 midrange, and the exotic Jaycar CW2119 I found last week from the rubbish :cool:

In pursue of the perfect polar response I have forgo some bass capacity. These are not friend-impressing speaker, but one to be enjoyed in very quiet night.

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The older brother (avatar) have more outright output thanks to the H-Frame. I have to increase the SPL of the new one to about +3db to compensate earlier rolloff so max spl is sacrificed. But I thought they were more coherent and faithful dipole radiators.

I'm thinking about how to finish the wood. Usually I use estapol satin, but the result is identical to unfinished pine. I wonder what estapol gloss would look like.

4136950475_d5fde3f57c_o.jpg

The top woofer is the "rubbish bin" speaker. Perfect condition. I don't know why people would throw these things away. Btw. that big brown rack and black "flower rack" were also from the side street.

One man's trash is another's treasure !! :cool:

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Be careful of Estapol Gloss. Before you apply it, you have to be 110% certain that you have sanded your finish as finely as possible. Check you have no cracks, or little bits of "fur", or any imperfections of any sort. Because once you apply the gloss - these things will show up.

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What are the main differences between a closed box and open such as yours?

The pluses:

- no box coloration, only the signal.

- uniform polar response, illuminate the room evenly. Speakers "dissapear"

- bass/lower freq. do not radiate to the sides -> no boomy sound.

The minuses

- Very inefficient below dipole=monopole frequency

- Very complex, requiring various filter slopes and multi-amps

- can be very expensive (4 tweeters, 4 woofers etc.). But not mine.

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Be careful of Estapol Gloss. Before you apply it, you have to be 110% certain that you have sanded your finish as finely as possible. Check you have no cracks, or little bits of "fur", or any imperfections of any sort. Because once you apply the gloss - these things will show up.

Thanks for the tip Keith. I had suspected the gloss requires some degree of perfection to the preparation.

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  • 2 weeks later...

After few sanding attempts I decided to stay with low-sheen finish. Just couldn't be bothered with the time it takes to have smooth surface. It will sound the same right :rolleyes:

More important is the structural rigidity. The simple baffle sways and vibrate very visibly on loud organ passages. So I took it outside for proper measurement with and without support.

dsc_1068.jpg

It was a real PITA to take equipments outside. But nothing beats ungated outdoor measurements...

dsc_1063.jpg

About 1.5m in distance and is a compromise between distance vs. earliest reflection. Measurement mic is a simple diy one. Very important is the platform stability as I've had speakers blown by the wind before. They act like sail!

The simplistic bracing:

Noname.jpg

Edited by gainphile
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Thanks... but not comparable to yours :rolleyes:

These are the measurement results. With full-range dipole system we can ignore the bass section (easy) and tweeter (achilles heel). That leaves the all-important midrange.

Raw response of wingless baffle:

compiledl21nowings10db.png

Raw response of baffle with support wings as above.

compiledl21withwings10db.png

Luckily the support wings resulted in negligible difference. The response is somewhat wider. These are typical of narrow-baffle dipole speaker. -6db/oct rolloff towards low frequency and then a peak.

Very important to observe is the even distribution of response going from on-axis (0deg) to off-axis. This uniformity ends at about 1.8khz, as shown on the bunching of lines. After this frequency (1st dip), the response will be awful.

The 1st dip frequency is directly related to the relationship between baffle size and cone diameter. The larger the baffle/speaker dimension, the lower the dip is. The golden rule of thumb is that baffle width should not exceed 2x effective cone diameter.

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And this is the final midrange response after the response have been shaped with 24db LR, 6db shelving lowpass, and notch filters.

compiledl21withwings500notch10dbcro.png

This polar response is one of many things which differentiates OB from normal speakers. It is directional and iluminates the room evenly. To the sides, it project -20db less sound. Compare with this wilson maxx (just picked randomly) at region for 100-1k. The normal speakers would have bunched lines, and then spreading (baffle step 4pi -> 2pi).

909WM3fig5.jpg

btw. for a very famous speakers and stereophile product of the year, the measurements is so bad for the maxx. Strange.

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Thanks... but not comparable to yours :D

Andy don't sell yourself short mate ,yours are running you do all your own

measurements and make your own active cross overs :rolleyes: plus you understand what your doing ,all I do is pay someone to do that .

Keep the great work coming :).

Cheers

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Thanks for the kind words Malcolm. Still, I am not inventing anything new here, just findings based on what others have done in the internet.

Keith, the software is ARTA. It's a great free software which I found very easy to setup and use (free version can't save files). I tried SpeakerWorkshop before but it was too cumbersome to use. It's quite amazing what we have today. 15 yrs ago I had to do xo "by ear".

As mentioned before, The tweeter section is the achilles heel of typical dipole setup (and may I say all speaker measurements I've seen except CDs like geddes and horns). And this is why:

compiledk11.png

The response is quite awful both on and off-axis. We can blame some on diffraction effect, however the true culprit here I think is because we can't force back-to-back tweeters to radiate as dipole. Unless the baffle is made very small (like 1.5 inch). This in turns become very unpractical. A possible but long-shot solution is some kind of back-to-back horn.

Hence the search for ideal power response is not finished, and explains why in some area the Omnis like SL's Pluto is actually superior.

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Thanks Greg and all ...!

Final comment on the sound of these speakers. Well I put in a recording of my kids choir concert. It is from a large venue in Monash uni and I observed where the microphones are placed. Looked like simple pair of Omni setup.

Recording with dense spectrum and (hopefully) minimal mixing like this are ideal to assess speakers as the usual audiophile recording cannot reveal faults. Sparse guitar recordings and saxophone or some chick with piano will sound good anytime.

The sound from the OBs are open, wide and tall which was the characteristics of live unamplified concert. In this area the speakers were able to reproduce the venue somewhat accurately. What is dissapointing though is the timbre and "massed" sound. They do not sound like children singing. If I go to the other room or toilet I do not believe there are children singing in the living room.

More pronounced is if my kids sing in front of it. The difference betwen the speaker sound and my daughter's voice is massive.

Going back to the recording, there are missing reality cues from the surrounding venue and it became noticable after comparing with my memory watching the concert as live. All the coughing are now from the front, but this is a problem which surround system technology may solve in the future.

So, after all the efforts of removing distortion (box, standing waves, polar response) there is a long way to get to "sounds as real". It's much better compared to generic box speakers, but definitely not there. In fact it's a very long way.

ps. There was someone playing violin in front of Safeway, at the parking. It was an open space, very different from a concert hall. It struck me how sound reproduction technology have a really long way to go reproducing something like that. Truly beautiful.

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Thanks Greg and all ...!

Final comment on the sound of these speakers. Well I put in a recording of my kids choir concert. It is from a large venue in Monash uni and I observed where the microphones are placed. Looked like simple pair of Omni setup.

Recording with dense spectrum and (hopefully) minimal mixing like this are ideal to assess speakers as the usual audiophile recording cannot reveal faults. Sparse guitar recordings and saxophone or some chick with piano will sound good anytime.

The sound from the OBs are open, wide and tall which was the characteristics of live unamplified concert. In this area the speakers were able to reproduce the venue somewhat accurately. What is dissapointing though is the timbre and "massed" sound. They do not sound like children singing. If I go to the other room or toilet I do not believe there are children singing in the living room.

More pronounced is if my kids sing in front of it. The difference betwen the speaker sound and my daughter's voice is massive.

Going back to the recording, there are missing reality cues from the surrounding venue and it became noticable after comparing with my memory watching the concert as live. All the coughing are now from the front, but this is a problem which surround system technology may solve in the future.

So, after all the efforts of removing distortion (box, standing waves, polar response) there is a long way to get to "sounds as real". It's much better compared to generic box speakers, but definitely not there. In fact it's a very long way.

ps. There was someone playing violin in front of Safeway, at the parking. It was an open space, very different from a concert hall. It struck me how sound reproduction technology have a really long way to go reproducing something like that. Truly beautiful.

The old violin in the street epiphany.

Horns probably come closest.My open backed[dipole] Edgar horn can mimic such sounds better than any other speakers I have used.Most speakers can't energise the air enough-although I have heard large electrostats [Kingsound] that also come pretty close.So there is more to it than just dynamic range/sensitivity.Valve amps also help although in the case of electrostats this seems to be less important.

Edited by THOMO
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Thank you.

Unfortunately after living with the speakers for sometimes I conclude that the harmonics due to L21's 5kHz metal cone distortion is audible. This 5kHz metal resonance is similiar to W22s so I'm not sure why Orion users don't complain.

DistortionL21withmagn-2.png

The xo is steep (LR4) at 1.5khz, and the 5khz peak is notched using deep filter. However this only help at some level because the harmonics of lower frequencies are amplified by this peak. Looking at the distortion plot the 3rd order harmonics would be attenuated by the xo, but not 4th and 5th harmonics. Ideally this woofer should only be used below 800hz.

It is not readily audible. But it colours dense spectrum music (choir) as well as piano. Once identified it stick and I could hear it everytime.

I rebuilt my S9 (the avatar) to compare and sure the polycone mid is less coloured at that frequency, but does not have the outright resolution of L21.

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