expensive open baffle woofer solutions: AE LO12 or ScanSpeak 32W/4878T11 or 4x Purifi PTT8.0?

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#101
CharlieLaub said:
I don't think that using two larger "value oriented" drivers will be comparable or superior to the Purifi PTT10. You can certainly get more total displacement, but that will likely come at a cost of a higher distortion level. I have built plenty of subs with lots of displacement, but few that sound really clean and that is what the PTT10 seems to offer more than just about any other driver, especially in the 10" size. This is especially the case for the particular type of loudspeaker I build, so YMMV on this.
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Well, if you look at the usual distortion mechanisms, BL(x), BL(i), Le(x), Le(i), Kms(x), Sd(x), etc., all of them are reduced in some fashion by splitting the load and/or cancelling asymmetry with multiple drivers (where the drivers sum acoustically). It's not inconceivable that the mitigation of these various distortion mechanisms, through multiple "OK" drivers, would ultimately provide less audible distortion than a single SOTA driver.

In the end, of course, using multiple drivers might be a non-starter for you. Also, the Purifi is a really sweet driver, so that carries a lot of weight too 🙂
 
#102
It is true that we can find drivers with good true BL(x), BL(i), Le(x), Le(i), Kms(x), Sd(x).
Charlie is also no stranger to using multiple drivers.

But a combination of these plus smooth response out to 600Hz (ideal minimum) for a 300Hz crossover, AND good x-max? That’s challenging to find.

And he no is no stranger to large woofers. Eg. Faital’s 18” neo (sub)woofer) 18XL1800. Nice TS parameters for BR or sealed box. Geometric x-max 15.5mm. Looks like it might fit the bill for OB? Unfortunately first breakup (destructive interference dip) around 300Hz.

He is also no stranger to using multiple drivers.
Do we have many options?

I went for twin drives for increased voltage sensitivity and lower distortion. I also needed a 300Hz crossover. I ended up using the 830845, which has a first dip at around 500Hz, which is not ideal:

https://products.peerless-audio.com/transducer/207

In the end I accepted that it was the best option for my design goals.

Great driver + Great price = Outstanding
But had to recommend (NLA)
 
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#103
I’ve just watched a YouTube vid by PresentDayProductions in which they show the construction of their MUM monitor, which use what must be 3 of the best drivers on the planet, including the 8” Purifi woofer. They are effusive about how good it is. Equally interesting is that they are designing a matching sub. Their original plan was to use the well regarded Dayton RSS 12” subwoofer. However they tried it with their monitor and whilst the low bass was very good, there was a distinct disparity between the quality of the Purifi bass from the monitor and that from the sub, so much so that they concluded that their only choice is to ditch the RSS and use a Purifi woofer for the sub as well - probably the 10”. They have chosen to do this despite the much higher cost of the Purifi woofer vs the RSS.
This to me speaks volumes (see what i did there 🤣). Seriously though, this just confirms that Purifi have really moved things on with these woofers.

As an aside, I bet those MUM monitors sound great.
 
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#105
CharlieLaub said:
In my designs I aim for a crossover point between woofer and midrange of 300Hz, so Mr Crowe's 1.2m x 1.2m baffle is too large, and is causes the dipole peak to occur too low in frequency. I need to cross over at 300Hz to limit the demand put on the midrange, which in my designs is "nude". When I keep the baffle smaller I can push the dipole peak out to about 300Hz so I can achieve a 3-way design with mid and tweeter used nude.

For example, the response of a panel measuring 0.55m x 0.55m using four 8" drivers is shown below.
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Charlie,

what is your take with the 15OB350 is used on a 55" baffle (this is, with sealed subs below and crossing to mids between 200 and 300 Hz)? If you were to choose a reasonable priced driver (<200 USD), what would you choose for this application?

And a second question, subjectively, do you miss the OB special character when crossing to monopoles at 70-80hz?
 
#106
Sounds OK to me.

Honestly, I have heard too many OB/dipole systems that have bad sounding low bass (below 60Hz) because the drivers must be pushed hard to get decent SPL unless the baffle is large. This includes for example the LX521, which I have heard many times, and every time my first impression on hearing the system is that the bass is flabby/not clean and the bass level too high. Crossing over to non-dipole subs relieves the driver of having to reproduce the lowest frequencies with large excursions, so it should sound better overall. A monopole can pressurize the room at LF, which I like, and it has about 4.75dB more acoustic power for the same on-axis SPL, so you can get plenty of low bass output on recordings that have it.
 
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#108
@Studley I was originally planning to go for the Purifi 10, and the design I was using calls for eight of them. It looked great on paper until I saw the price of the PTT10s! Eight of them is not really in the realm of affordable for me... in the meantime I already own eight SB Acoustics WO24P and some other drivers that are not quite as good but will work just fine. I'm currently way behind getting going here in Germany after moving from the US and am still doing some construction on the listening space I will use, and this has halted my speaker building. Once the room is ready I will first set up a system that I brought from the US with a only little bit of re-building involved and then after that I want to build a multi-pattern woofer system. Maybe after that I will get back to dipole woofer systems but at this point it is not clear if I will revert to my original plan or try something else.
 
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#110
CharlieLaub said:
Sounds OK to me.

Honestly, I have heard too many OB/dipole systems that have bad sounding low bass (below 60Hz) because the drivers must be pushed hard to get decent SPL unless the baffle is large. This includes for example the LX521, which I have heard many times, and every time my first impression on hearing the system is that the bass is flabby/not clean and the bass level too high. Crossing over to non-dipole subs relieves the driver of having to reproduce the lowest frequencies with large excursions, so it should sound better overall. A monopole can pressurize the room at LF, which I like, and it has about 4.75dB more acoustic power for the same on-axis SPL, so you can get plenty of low bass output on recordings that have it.
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Dear @CharlieLaub

Some years ago, you presented a project with a very big (24"??) long stroke subwoofer in a H-frame. How did this unit compare to sealed subs? Or other examples of open baffle bass that worked well compared to sealed subs?

I ask because I believe right away that sealed subs will do better (way more output in less physical volume) in the lowest octaves, but in our flat I really can't allow for the room pressurizing, so still interested in an open baffle solution that would work well as low as possible.

Many thanks!
Erik
 
#111
That was a high-excursion 18" subwoofer, with 36mm Xmax, Fs=24Hz or so and Qts=0.72. I had a pair of these in H-frames in the US, just before I had to dismantle everything before the move. Now THOSE produced some pretty impressive dipole bass - I used an amp that could deliver 1200W to each of them and I could not bottom the drivers out. I still have the drivers and hope to use them together in a slightly different configuration as a mono dipole subwoofer. Of course these could not pressurize the room, but my home in Michigan was very large with an open floorplan, so neither could multiple sealed subs. The volume of the space was just too large to notice much LF pressurization. In that sort of listening space the dipole bass was superior in many regards, but it really takes a lot of displacement and/or baffle area to get down into the low 20s. These drivers have displacement in spades, and are well designed for home HiFi use.

If you want to check out the drivers, here is the linky:
https://www.oneaudiousa.com/product-page/ib3
Make sure to click on the tab for the 18" version when checking out the TS parameters in the table at right.

Not sure if the drivers can be shipped directly to your location but there is a dealer in the UK. You could inquire at One Audio if you are interested.
 
#112
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