Open baffle speakers

When I was shortlisting speakers for a 10w amp, I was looking at several pairs from Decware including a couple open baffle designs like these ZF15Ls


Ultimately, the required acres of space behind them killed that idea.

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Why do low wattage amps work well in some cases with OB speakers?

Gorgeous!

Partly the fact that there is no enclosure providing opposing pressure so the cone is easier to move and the out of phase energy is not absorbed but part of the output. Reflected off a rear wall it arrives in phase.

But it shouldnā€™t be overlooked that many (not all) open open baffle speakers are large single driver designs. That contributes a lot to the easy of driving and has nothing to do with open baffle. Such designs may have extremely simple or no crossover at all.

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As a bit of fun, I decided to make (with my 6 year old son) a pair of small open baffle speakers over the Christmas period. They are very low budget units using Pioneer coaxial car speakers (there are reasons for this) and most of the materials were from B & Q. These are the finished items. Granted they wonā€™t win any beauty awards but it was a fun project and the results are quite enlightening really.



The list of parts are:
A pair of Pioneer TS-G400 4 inch coaxial drivers (Ā£20 for a pair) from Halfords.
2 x 8mm thick flooring sample boards for the baffles - Ā£2 each.
3/4 inch MDF for bases.
QED Qudos Micro speaker cable - I had it in stock and it fitted the spade terminals perfectly.
Speaker terminals
Silent Coat automotive sound dampening panels - the silver stuff on the back of each baffle.

Reasons for choosing the Pioneers:

  1. I had them in stock.
  2. Being coaxial drivers, they are effectively point source and theoretically, donā€™t need any additional crossover work.
  3. Not many specs are available but I figured that being car speakers, they are designed to be pretty flexible about mounting/cabinet type/free air use etc.
    Pioneer also offer this series in 5.25 and 6.5 inch versions which will no doubt give greater bass response.

Originally, I planned to stick two flooring boards back-to-back for the baffle but, despite leaving them clamped overnight with the type of glue that normally works really well, they separated when I started assembly so I went the sound dampening route instead.

So, to the sound. Powered by an Arcam FMJ A18 (Arcam Alpha 5 CD player as the source) they sounded very clear but also ā€˜disappearedā€™ acoustically. The downsides were a forward balance (though not too bad) and a significant lack of bass output/tonal richness. The latter and most of the former was fixed by adding one of the passive bass modules that I made using a Dayton Audio Classic 6.5 inch driver and fed by a subwoofer amplifier. This really does make a pretty effective small room speaker system considering their DIY nature and very low overall cost. My father also had a listen to them on Christmas Day and he was complimentary on how they portrayed musical instruments within a recording.

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A fun expt.

40 years ago I made a tiny box speaker with a car back shelf speaker driver, the box was made of 6 pieces of wood about ten inches square.

It sounded quite bad, but I used them occasionally as extra speakers in my first mainly Marantz stereo system.

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Those may be the worst pieces of industrial design that Iā€™ve ever seen.

Did the designer draw inspiration from an old fashioned egg timer?

I look at the egg timer, your time of speech just expired :joy:

It would have been interesting to build them with the 6.5 inch versions. Due to their ā€˜modularā€™ :grin: construction I could easily change the baffle to find out should I spend Ā£30 on the 6.5 inch versions at some point. Ultimately, I wanted to experience some of the benefits of open baffle without spending much at all. Ref bass output, there is clearly a reason why serious OB speakers use 12 - 15 inch plus bass drivers, though my DIY upward firing bass module (the grey object in the last picture) does a good job in my office.

I also built these for use at school as, being open backed, they will allow children to see how a speaker works. We do magnetism as part of Forces in Y3 and Sound in Y4. Previously, I have used one of my subwoofers to demonstrate sound/vibration at different frequencies - the pupils loved that.

I might also try these with my Arcam Solo Movie 2.1. Similar to the Uniti Qute and IIRC, the original Uniti, this is one of the few integrated stereo ā€˜ampsā€™ (it is also a DAC and DVD/SACD player) that has bass management built in. In this case, it has an adjustable LP and HP filter that can be varied between 40 - 150 hz so the speakers can be high passed - this might help with power handling and the slightly forward balance of the OB speakers.

The Arcam is a really flexible piece of kit (effectively a DV135 DVD/SACD player, an Arcam A18 amp and decent DAC combined in one chassis) and IMO a bargain on the used market. Hook it up to a compact streamer or the digital output of a TV with a fire stick and you have the basis of a compact, flexible and capable bedroom system. I use mine with some Piega TS3s.

Great Christmas project. You could try hanging just the speakerā€™s (without the wooden bits) from the ceiling you would get a feel for the influence of the baffle then.

Sounds like you like an experiment!

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Could be worth a try!

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Here are mine. For scale, the TV between them is an old school 50" Plasma.
These were driven as 3 way with active crossovers implemented in DSP.
They were an interesting experiment at the time, but ultimately I prefer the sound of a box loudspeaker and they were never going to stay in our living room, were they?

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They look good, Roog.

Did you buy them, or make them from a kit?

How far out from the wall did you have them at the furthest?

Did they sound better the further out they came?

What did you do with them?

For dipole (open back) speakers they look much closer to the back wall than I would expect to be necessary for best sound.

Also the right speaker looks as if almost touching the side wall, so effectively extending its right hand baffle and modifying its sound relative to left speaker far more than a similar layout with closed baffle speakers.

Thank you Jim, I thought that as they were going to appear in our living room from time to time I should make a bit of effort.

I made them from oak veneered panels of about 20mm thick. I copied a number of fairly typical open baffle designs which are out there.

I tried all manner of arrangements, most of my ā€˜testsā€™ were conducted in our previous property which had a bigger living room and offered greater flexibility for placement. As far as I am concerned such designs are not effective open baffle designs, as the baffle needs to be of significant size to prevent cancellation at bass frequencies. Mine are not big enough and I knew this before I commenced construction but it didnā€™t stop me from wanting to do the experiment anyway.
Pushing them up against walls is supposed to increase the effective baffle size and should help with bass response, I found this to be a marginal effect.

My feelings on this approach are that the bass is fast if rather light, despite using high efficiency twin 15" drivers and having the ability to boost bass response through the 3 way active crossover, although during speaker break-in I fed the bass units between 10 to 100Hz at high levels and managed to shake the windows in my living room, at the right frequency the room resonated quite disturbingly!
In all configurations bar one, more on this in a mo, I found the sound stage very poor, almost non-existent, I suspect this is down to the comb filter effect you get from interference between the rear and front waveforms. Based on my experience, movement of the listener does nothing to improve this.

My best experience of them came from when I had them stored in our box room, I set them up as a near field listening experiment, in this configuration they sounded a lot better if somewhat intimidating and very impractical. It was like using very large headphones. I suspect the improvement which for the first time included a sound stage, was due to the limited cancellation occurring under near field conditions, no more than a metre!

When I had taken all of the measurements I wanted and ā€˜listening testsā€™ that my wife could stand, I sold them to someone else who seemingly wanted to do the same. :slight_smile:

My conclusion is that open baffle might work if you can accommodate a very large baffle, just as the maths suggests, but that the principle is flawed in most practical installations. I wouldnā€™t bother, but donā€™t let me stop you from having a play, they are easy to make even if you do have to have oak veneer, finished openings and stainless steel stands, all courtesy of Ikea.

I prefer the sound of boxes, in my case they are sealed, infinite baffle!

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Thanks Roog

Thatā€™s an excellent experiment you conducted - and a very informative write up of the results.

If Iā€™m honest, it does put me off homemade OB speakers.

But itā€™s a long way off because I love my SL2s and plan to move house before I would make any change of speakers.

Thanks
Jim

You know, there were nostalgic reasons for my experiment, if thatā€™s a bit grand, I remember the seemingly huge oak open baffle speakers with a gold coloured expanded metal grill which we had in my primary school. They would play us educational radio programs and records of classical music, using this kit.

I believe the equipment was sourced from a common manufacturer located in or around Worcester UK.

At my school it was all classical music (and chapel music), but a music teacher once played the Bonzo Dog Doodah Band.

I didnā€™t particularly like it, but it did stick in my memory.

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I loved - and still very occasionally play - Iā€™m the Urban Spaceman!

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They look very nice though. Albeit, the tweeters stand out a bit. Did you ever get to try them in a space with a couple meters behind them and the same to any side walls?

I can totally imagine how in a certain type of large home, with matching tweeters, they could in fact be quite aesthetically pleasing.