New OB project

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After much research and maths I finally took to the saw bench. It seems to me the most discussed topic on OBs is bass response. In another thread some time ago, John (in CR) suggested an array of 6x9 car speakers on a W baffle as a bass helper.

Well, I had a couple of 6x9s laying about, so why not give em a go. The main drivers I have been working on for some time, so all that was needed was a crossover to try out the combo.

Standing 900mm high, and 450mm wide, tapering to 250mm at the top. The main drivers are 6" single cone Panasonics, with bitumen treated surrounds, several coats of PVA on the cone with a bias to stiffening the apex to extend the top end, and an extra magnet to increase sensitivity and improve transient response.

The helpers are nothing more than Sansui SB-3693s minus the pod mounted tweeters.
 

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The baffles at present are 10mm particle board. I expected some vibration from this, however, there is more life in the sound, compared to what I had when the drivers were mounted on 16mm MDF.

Cut from a 900x600 mm sheet, the triangular off cuts become the braces, forming a U-baffle at the floor.

This is the messy side, with prototype crossover.
 

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frugal-phile™
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yep.. just making sure.

If any one wants some like (or similar) to these let me know, I'm donating most of my collection to a friends kid (looks like we'll fill a small pick-up with drivers -- it is too much work to get $10-20/pr selling these on eBay).

Just pay shipping and a token for time to pack em up. Offer expires Thursday, cause they are gone after that.

dave
 
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Hey Geoff - any details on those 6x9s?

BTW, I've tried using the secondary of transformers as large inductor to shape OB bass response. My amp hated it! So no go for me. :(

Just wondering if an array of reasonably priced 6x9s on OB could give decent bass?

Edit: I see that they are Sansui units.
 
It takes shopping around to find suitable 6x9's. The problem these days is most 6x9's are mid woofers so you have to buy a sub too for your car. The lack of any specs is a real problem, so you have to listen to them in person to find something useful. It can be a very economical route to OB bass in a narrow arrangement that can double as a speaker stand. I wish I had 8 pairs of the big roll surround Mitzu 6x9's that I scored locally.
 
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Yeah John, kinda what I feared. You'd have to have a lot of drivers to listen to in open air.

If you were a car audio guy you could be on the lookout for stuff that comes thru the shop, but how is someone else going to find the right drivers?
 
panomaniac said:
Yeah John, kinda what I feared. You'd have to have a lot of drivers to listen to in open air.

If you were a car audio guy you could be on the lookout for stuff that comes thru the shop, but how is someone else going to find the right drivers?

Just go to the shops and listen to them. You want to see meaningful excursion. Things to look for are bigger roll surrounds and frequency response on the box starting at 30hz. If it says 50hz or 70hz on the box, it's definitely a mid woofer. Also, those designed specifically for rear decks and no huge magnets are good candidates.

I thought Tangband had a 6x9 with 14mm of Xmax, which also had a big Sd, but I don't see it listed at PE anymore. Their prices went up too. Before at $30 or so each, a pair or two per side could have made some nice OB bass augmenters with significant output.
 
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Yeah TB have three 6x9s IIRC. The flat one is know to be high distortion. Our buddy Salas in Athens uses some of the others in a box.

Then there is the strange 8x12 sub from TB. W8Q-1071F
27Hz listed FS, QT of 0.3 But I find that Tang Band drivers measure higher in FS and QT than specified. YMMV
 
panomaniac said:
Yeah TB have three 6x9s IIRC. The flat one is know to be high distortion. Our buddy Salas in Athens uses some of the others in a box.

Then there is the strange 8x12 sub from TB. W8Q-1071F
27Hz listed FS, QT of 0.3 But I find that Tang Band drivers measure higher in FS and QT than specified. YMMV

A great option would be to score 2 or more pairs of B139's. The advantage to the oval shape is the ability to stack more cone surface into a smaller profile. Then when you fold the baffle you can get more 2/1 rear wave travel distance and still retain a very small form. There are probably some suitable small drivers with good excursion used for computer speaker subs. Too bad there's no master list for all drivers in the world.
 
Hi guys, as John suggested, info is a bit scant. I measured the res freq at 50Hz unmounted, magnet on the floor. Figuring these were intended to be loaded by the boot (or trunk) of a sedan, the VAS would be high. The z peak at resonance was quite pronounced, so q was high. I didn't take measurements either side of Fo at the time.

Cupping the driver between upper and forearm gave some indication of the bass response. A bit of a gamble that paid off.

The are very similar in appearance to Aerpro-Extreme 6x9.

The frame is more closed than open. I haven't measured the openings in the frame, but area of such is less the the frame area. That may be a clue to the performance, even if not true OB.

I would class these as a mid bass. The tweeters on the pods were a 1.5" cone and a 1/2" dome.

Interesting comments Michael re the transformers on your amp. You may have been using too many turns. I was using the winding between the 7.5 and 12.6 v taps. I an now using hi quality auto transformers, the section from 4-8 ohm taps working well. The grain oriented laminations provide a cleaner top end.

I am wondering if you are using a T-amp.

As for stacking, yeah why not? The Aerpros retail for about $40 a pair. 4 a side is equivalent to a 15 in piston area.

2 on the baffle, and 1 on each side of a U or H baffle would integrate well with the main baffle.

My room is about 3.5 x 5.5 metres. These little OBs can reach average SPLs about 100 dB at 2 metres on a 30w / chan amp, on the verge of clipping.

Using music videos, I can hear base guitar is fairly flat down to an open E string, and it's tight. Next step is to build some baffles from decent material.
 
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