HiFi Subjectivist ¦ Audio Forum ¦ NVA User Group

Docfoster wrote: ↑Fri Oct 18, 2019 8:26 am

Simon Hickie wrote: ↑Thu Oct 17, 2019 10:37 am Soundstage implications are interesting. I have to say that my DIY OB speakers provide an extraordinarily big 3D soundstage that's high wide and deep - distinctly better than my semi-omnis. However, they need room to breathe with a meter or more behind them. Therefore, this would mean more rather than less speaker in the room.

My DIY sealed boxes (the ones with the 18 inch drivers) need about that distance behind them too. Maybe it’s partly to do with driver size as well as with the open baffle...?
I mean, how much bass energy can my sealed boxes’ 18mm of braced MDF absorb and internally reflect anyway...? (Similarly for wooden floorboards or plasterboard walls and ceilings.)
Maybe a lot of sealed / IB speakers are effectively semi-OB below a certain frequency! :-D

That's an interesting story, thanks.

karatestu wrote: ↑Fri Oct 18, 2019 8:39 am

Docfoster wrote: ↑Fri Oct 18, 2019 8:26 am

Simon Hickie wrote: ↑Thu Oct 17, 2019 10:37 am Soundstage implications are interesting. I have to say that my DIY OB speakers provide an extraordinarily big 3D soundstage that's high wide and deep - distinctly better than my semi-omnis. However, they need room to breathe with a meter or more behind them. Therefore, this would mean more rather than less speaker in the room.

My DIY sealed boxes (the ones with the 18 inch drivers) need about that distance behind them too. Maybe it’s partly to do with driver size as well as with the open baffle...?
I mean, how much bass energy can my sealed boxes’ 18mm of braced MDF absorb and internally reflect anyway...? (Similarly for wooden floorboards or plasterboard walls and ceilings.)
Maybe a lot of sealed / IB speakers are effectively semi-OB below a certain frequency! :-D

That's an interesting story, thanks.

Not my best, but thanks.

Docfoster wrote: ↑Fri Oct 18, 2019 8:47 am

karatestu wrote: ↑Fri Oct 18, 2019 8:39 am

Docfoster wrote: ↑Fri Oct 18, 2019 8:26 am

My DIY sealed boxes (the ones with the 18 inch drivers) need about that distance behind them too. Maybe it’s partly to do with driver size as well as with the open baffle...?
I mean, how much bass energy can my sealed boxes’ 18mm of braced MDF absorb and internally reflect anyway...? (Similarly for wooden floorboards or plasterboard walls and ceilings.)
Maybe a lot of sealed / IB speakers are effectively semi-OB below a certain frequency! :-D

That's an interesting story, thanks.

Not my best, but thanks.

Wooops. I meant to post that in the doping thread concerning your story about Goodmans.

I did wonder. :-D

I looked on a German hifi forum and they gave some of the T&S parameters for the 12" drivers as supplied to The Doc

Fs 35 Hz
Qts 0.65
Vas 73 Litres
xmax 5mm
RMS power 200W

If those figures can be relied on then i would say that Qts of 0.65 would be acceptable for use in an infinite baffle project. The Fs is good for a 12 incher as well.

The doping will have increased the Qts (don't know by how much) which makes it even more suitable and could possibly hit a target for Qtc of 0.7 (critically damped). The lowering of the Fs due to doping is also a good thing.

If i can make a true infinite baffle then in practice the Fs will only be increased by a factor of 1.02 rather than 1.4 when in an enclosure of 73L (Vas).

Anyone here heard a true infinite baffle loud speaker ?

One thing is certain. If i ever build this then they won't be going to any bake off's

Burglar proof as well (as long as they don't take the grilles off and take the drivers out).

I joined the cult of the infinitely baffled for some advice on this idea (thanks Lindsay). Still awaiting a reply.

There are some eye watering builds on there but mostly centred around home theatre and four or more 18" drivers built in array's or manifolds and mahoosive amplifiers, equalisers etc etc. You get the drift, the usual US over the top approach. Well over the top for hifi use only in small rooms at relatively low volumes. Not sure what SPL i usually listen to but it can't ever be over about 80 dB i would guess.

Small (12" ) drivers like mine with relatively small excursion limits (5mm) are said to be unsuitable as they will bottom out and self destruct. Surely that depends on how loud you listen and what you are asking it to do. Low frequency movie content (20 Hz and lower) at 100 dB or more would surely need a lot of displacement area, long throw drivers and high power handling. But i would not be asking for it to do any of that. All i want to do is listen to music with excellent quality low frequency content at low volumes.

Anyway, seeing as though i have four 12" drivers then i might as well use them all. That will help things. Doing isbaric infinite baffle is pointless so i would wire them up in the ordinary way with two drivers per channel, probably in parallel. With conventional speakers the output is generally limited by the power handling of the voice coil. With infinite baffle it is different - output is limited by the excursion limits of the driver (xmax).

What about a couple of 6x9 in foot well of your car open to the road- now that’s infinite!

karatestu wrote: ↑Fri Oct 18, 2019 1:07 pm Anyone here heard a true infinite baffle loud speaker ?

My Bozak Symphony speakers are not true infinite baffle speakers, but the spring effect of the air in the box is small enough for the drivers to act very similarly to an infinite baffle.

That still leaves the box though. Which is coupled to the floor through the 70kg mass of the speakers via castors. Which would be a different kettle of fish to a thick board screwed to a wall, or a smaller enclosure screwed to the floor with a whopping big hole in the floor.

Nevertheless, I am convinced that infinite baffles are well worth trying for anyone with the means to do so.

Home cinema optimum bass does seem to be about the extension and max power levels. Due to the amount of gimmicky low frequency bumps and thumps in modern Hollywood action films.

Whereas for music listening some of the extension and max power levels can be sacrificed for texture, definition, dynamics, the ability to start and stop quickly.