S11 OB - Revisiting Desktop OB design using Seas 8" and Tang Band Full-Range - diyAudio
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Old 19th September 2009, 03:18 PM   #1
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Default S11 OB - Revisiting Desktop OB design using Seas 8" and Tang Band Full-Range

I built some desktop OBs in the past, and this is to revisit the design using newly learnt stuff, mainly around polar response. One of the most promising of the previous built was this one. While it sounded ok at that time now I realise that running the full range down to lower frequency would result in not so smooth off-axis response.

In fact it should be the other way around. The larger woofer should have taken the lower frequency up to dipole peak.

So the idea here is:

- Seas L21RNXP from low freq - 800Hz, then TangBand FR for 800hz-20khz
- By crossing the alumunium cone L21 low enough the metal resonance may be eliminated completely.
- Still use thin baffle to obtain uniform response up to 2.5kHz


Some foreseen "problems" and compromises

- Excursion limit of 8" woofer. Can it provide satisfaction?
- Distance to the rear wall is 40-50cm max. Will it smear the sound?

The FR is TangBand W3-1364S. It's pretty and measures well. It has great opening at the back because of the small neo magnet.

Click the image to open in full size.


Seas L21RNXP. From previous project I learnt to deal with the metal resonance, but crossed at 1.5kHz it does not dissapear completely.

Click the image to open in full size.
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Last edited by gainphile; 19th September 2009 at 03:33 PM.
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Old 19th September 2009, 03:47 PM   #2
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Default Baffle

Pine wood is my favourite baffle material. It's not as dusty as MDF or chipboard, cheap, and smells nice. It's important to coat the wood otherwise it would change to yellowish colour. I use Estapol clear Satin.

Click the image to open in full size.

With OB the rear chamber needs to be as open as possible.
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Old 20th September 2009, 12:53 AM   #3
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The drivers installed and tested. The Seas works very.. very hard . Rattles everywhere on the baffle and my desk. Most have been eliminated but there's more.

Click the image to open in full size.

Click the image to open in full size.

Two pieces of foam underneath the speakers seems effective enough to decouple them from the desk.
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Old 20th September 2009, 12:57 AM   #4
CLS is offline CLS  Taiwan
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Looking good

TB's small magnet doesn't block the rear wave very much, so you can probably get a dipole response almost all the way to the top.
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Old 20th September 2009, 01:14 AM   #5
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Default XO

True. My the transition to that tangband is so smooth which makes me question my previous builds. I guess having 3 to 4 octave below xo frequency really helps. This warrants further investigation.

I've dialed the XO a bit but using the same thin baffle there's not much. It's still 1.5kHz and I wonder what kind of changes will bring by lowering it to 800hz.

The Seas is not too happy played at high SPL from 20-35hz. I think a 40hz or 30hz (but -6db) is a more realistic target. But I don't like non-20hz speakers

Le audiophile xo with pure copper jumpers

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Old 20th September 2009, 01:21 AM   #6
CLS is offline CLS  Taiwan
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Quote:
Originally Posted by gainphile View Post
...

The Seas is not too happy played at high SPL from 20-35hz. I think a 40hz or 30hz (but -6db) is a more realistic target. But I don't like non-20hz speakers

...

:LOL:

40Hz seems about right for an 8 incher. I've played with 8" widerangers on OB for a while. When playing (relatively) loud bass, cone movement was easily seen, maybe 5~6mm p-p. It still sounded OK even with such excursion.

For a desktop application, I think this would be the over the top hi-end speakers
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Old 20th September 2009, 11:39 AM   #7
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gainphile your experiments are always so interesting! thank you for sharing so in the details

perhaps what about adding an h-frame woofer under the desk? like a 2.1 system (you have amplifiers enough to do that ) would it work? or would it mess up everything due to phase?

hope you'll find some good 8" FR to test on the bigger baffles somedays, perhaps they could be a good match to the make with 3 woofers per side you did some time ago
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Old 21st September 2009, 07:06 AM   #8
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Default Finished!

Well that was a quick project which turns out nice.

Click the image to open in full size.

The speakers are really small. I attached a pic with my notebook as scale. Very pleasing.

About the bass... the optimum compromise between distortion, listening level, and excursion is 40Hz. That's pretty deep, dipole or not. The woofers are working reaaaaallly hard. Some 30Hz can be felt but not respectable. Below 30Hz is just asking for trouble. These metal cone makes horrible sound when bottomed . It's simply just physics and there is no way I could get more, except putting again a pair of 15" on my desk.

The problem down low is also related to materials. LP rips have those pesky subsonic rumble which drives the cone to excursion to maximum a lot quicker than the program material. A 2nd order highpass at 17Hz fixes that effectively at the cost of group delay. I could not hear it.

Aside from that the speakers makes really great bass, but you already know what dipole bass is all about. I think it's like a good espresso. Small in quantity but what comes out is pure. I have a Yamaha sub below the desk and while it can provide the extension to last octave, it degrades the quality of the whole system. I turn it off and perhaps will use it to watch movies.

The distance to rear wall is about 35cm. I did could not hear any faults. Comparing to my living room dipoles (which is 1m from rear wall), maybe a bit less soundstage, but that's really nitpicking. Phantom image is very scary, almost like the speakers making no sound and the music comes out of the wall. Listening to some classical recording I got goosebumps. If there is one best thing that stands out from them, it's the midrange.

The TangBand as tweeter, well this is new to me. It actually makes great tweeter and I can't hear lack of high. Even better, I think the transition from w-t is smoother than normal dome tweeter that I have been using. This warrants another investigation, perhaps using the TangBand as my livingroom tweeters. But I listen nearfield with these (1m - 2m) so maybe that's why it's ok. I did not lower the xo point as my listening so far can't hear any faults with 1.5kHz.

Thanks all for reading/comments. Now I'm going to listen to some music.
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Last edited by gainphile; 21st September 2009 at 07:12 AM.
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Old 21st September 2009, 08:34 AM   #9
CLS is offline CLS  Taiwan
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Wonderful !

Like I said, for a desktop system (or, for PC sound), this is just over the top! You're using active xover and 4 channels of amps, right? And you called that 'really small' ! :LOL:
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Old 21st September 2009, 05:10 PM   #10
Telstar is offline Telstar  Italy
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They are very cute! You have good carpenter skills
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