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Old 23rd October 2006, 07:13 AM   #1
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Default Driver suggestions for high output open baffle speaker

This is to mate with a sub bass horn for music and home theatre. My goal is to achieve a peak SPL of 110 db @ 3m for the mains and 120 db @ 3m for the sub. The sub can easily do 130 db at this distance, so I have quite a lot of headroom. This means 120 db for the mains at 1m, no mean feat!

The sound I'm looking for is dynamic, open, transparent. I want to reach live sound levels with a sense of ease. I prefer a relaxed sound, not too detailed, as I've found drivers such as Seas Excell are brilliant with well recorded material, but brutal with most pop and rock music.

I intend to do an active 3 way, probably with something like this:

W W MTM W W

1. Tweeter

This is what I find most difficult to choose. A CD in waveguide would do it, but I'm not sure I can pull it off with the same kind of sound I get from a good hifi dome. Essentially I want that sound on a larger scale.

Suggestions anyone?

2. Mid

I'd prefer a 6.5" or 8" driver like the Focal 7k from 300 - 2.4k. Looks are an issue here. I'd like to avoid something that looks like a typical pro driver. I like the look of the B&C PS21 (similar to Adire Extremis with inverted dustcap), but it looks like it has some uncontrolled breakup before the intended crossover region.

I'd like to find a good driver that is cheaper than the Focal but does the same job. Suggestions?

3. Woofer

Looking for a 12" driver with low distortion, reasonable excursion (7mm), decent power handling and a smooth extended response allowing a high crossover point. Currently the Peerless SLS seems the most cost effective driver I can find. Any other suggestions anyone?

It's more critical that the mid and tweeter reach the SPL target, but with the woofers, I can add on more later.

Why choose OB for a high SPL application? I have found from my prototype with existing drivers, that not that much eq is required. In fact, based on this I expect to be able to get down to 80 Hz easily without eq boost. For serious listening, I may lower the xo point to the horn sub to 40 Hz.
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Old 23rd October 2006, 11:19 AM   #2
DeonC is offline DeonC  South Africa
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Hi Paul

Have a look at Magnetar's OB speakers. I think that they would be what you are looking for. Here are two threads in which he discussed his system:

WMTMW Open Baffles

Big open baffle project

Enjoy,
Deon
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Old 23rd October 2006, 02:03 PM   #3
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Thanks, looking through it all ...
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Old 23rd October 2006, 09:37 PM   #4
ScottG is offline ScottG  United States
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Default Re: Driver suggestions for high output open baffle speaker

Quote:
Originally posted by paulspencer
This is to mate with a sub bass horn for music and home theatre. My goal is to achieve a peak SPL of 110 db @ 3m for the mains and 120 db @ 3m for the sub. The sub can easily do 130 db at this distance, so I have quite a lot of headroom. This means 120 db for the mains at 1m, no mean feat!

The sound I'm looking for is dynamic, open, transparent. I want to reach live sound levels with a sense of ease. I prefer a relaxed sound, not too detailed, as I've found drivers such as Seas Excell are brilliant with well recorded material, but brutal with most pop and rock music.

I intend to do an active 3 way, probably with something like this:

W W MTM W W

1. Tweeter

This is what I find most difficult to choose. A CD in waveguide would do it, but I'm not sure I can pull it off with the same kind of sound I get from a good hifi dome. Essentially I want that sound on a larger scale.

Suggestions anyone?

2. Mid

I'd prefer a 6.5" or 8" driver like the Focal 7k from 300 - 2.4k. Looks are an issue here. I'd like to avoid something that looks like a typical pro driver. I like the look of the B&C PS21 (similar to Adire Extremis with inverted dustcap), but it looks like it has some uncontrolled breakup before the intended crossover region.

I'd like to find a good driver that is cheaper than the Focal but does the same job. Suggestions?

3. Woofer

Looking for a 12" driver with low distortion, reasonable excursion (7mm), decent power handling and a smooth extended response allowing a high crossover point. Currently the Peerless SLS seems the most cost effective driver I can find. Any other suggestions anyone?

It's more critical that the mid and tweeter reach the SPL target, but with the woofers, I can add on more later.

Why choose OB for a high SPL application? I have found from my prototype with existing drivers, that not that much eq is required. In fact, based on this I expect to be able to get down to 80 Hz easily without eq boost. For serious listening, I may lower the xo point to the horn sub to 40 Hz.

Suggestions:

IMO you are thinking to conventionally for this requirement.

Think either a conventional driver line array.. OR,

..your point source compression driver/high eff. cone setup - which likely will not be MTM'esq (strictly speaking).



Since enough has been said on the line array (in other posts), I'll focus on the "pro-sound" design.

#1 - Getting "Hi-Fi" sound from a pro setup requires broad horizontal dispersion (for a horn) up to about 7 kHz (..and the higher the better). Most 1 inch dome tweeters have about 160 degrees of dispersion up to 4 kHz. Furthermore the spl off-axis isn't that strong for these drivers up to about 7 kHz.

Now then, you just won't find a good horn that does this, BUT anything over about 100 degrees should be decent. So here is where you start your system design. Not with a driver, but rather with a horn!

IMO there is an excellent maker of horns at what is a relativly modest price from DDS. What you want to look at here is the polar plot and how "constant" the dispersion pattern is higher in freq.. Note that the smaller "circles" on the polar plot indicate the very highest freq.s for the spec'ed passband. Again, we are really concerned with HORIZONTAL dispersion, NOT vertical.

http://www.ddshorns.com/catalog.php?page=products

So then going through their list picks up these with greater than 100 degrees horizontal coverage:

http://www.ddshorns.com/catalog.php?page=CFD1110Pro
http://www.ddshorns.com/catalog.php?page=CFD14110Pro
http://www.ddshorns.com/catalog.php?page=CFD15110Pro
http://www.ddshorns.com/catalog.php?page=CFD2110Pro

Notice that NONE are really an actual 110 degrees of dispersion constant. They are ALL down about 6 db at even their lowest freq.s at the 110 marker. (..thats OK, functionally that gets us just about 100 degrees).

The next step then is deciding what type of Compression driver to use AND asking yourself how low/steep are you going to use the driver and how high do you want the driver to go (..bearing in mind the increasing loss of sound pressure off-axis at higher freq.s)? (..the questions are inter-related.)

For instance IF you go lower in freq. (often less than 1 kHz) then you'll likely want a 2 inch driver. IF you go higher in freq. then it will prob. be 1 inch driver. A 1.5 inch driver basically provides you with something "in-between".

Generally:

The lower in freq. you use a compression driver - the cleaner and more detailed the sound (provided you use an appropriate/steep filter).. Additionally, the lower in freq. you use a smaller diameter compression driver - the greater the distortion. The higher in freq. the driver operates the greater the dispersion pattern and the more stable the imaging AND the greater the apparent subjective sense of "air".

To add to this consider tonal balance and diaphram/suspension material, AND driver "break-in".

IF a driver has a considerably greater loss in spl off-axis at higher freq.s - THEN the sound will be a little "duller" ***UNLESS*** you listen to the thing O N - A X I S. IF you listen ON-AXIS then the thing will likely be painfully bright. To compensate you can either "to-in" or "toe-out" the driver when listening (and each has their own advantages and disadvantages).

Driver material-wise.. Titanium is genererally the "brightest" sounding material, but it can often sound a little "closed-in" due to the transition between diaphram and surround. At the other end of the spectrum is coated paper/phenolic which can sound a little "dull". (..the most costly - Be, can be more detailed than any other diaphram material, but usually has less "impact" at lower freq.s due to its reduced mass.) Aluminum and Mylar seem to provide a middle-ground. ANY type will likely sound "closed-in" without a *SERIOUS* amount of "break-in" time. ANY suspension on a compression driver needs to be "fatigued" to loosen them up and achieve a more spacious sound. Then you can compound the issue with magnetic field integrity, (basically hysteris), of the magnet and its material. The best is typically provided from a good field coil, the worst from a ceramic ferrite. Next to a field coil would be Alinco, then Neo (usually). I think this has more to do with processing and crystal structure on these permanant magnets more than the material itself (..but its a guess). Additionally, the higher the field strength typically the cleaner the sound.

On last thing to comment on with driver selection is the use of an additional driver as a super tweeter. Here you can extend the off-axis disperion by utlizing a smaller driver. The thing you need to be carefull about here is the off-axis dispersion at the crossover for the compression driver and how much power vs. distortion the super tweeter can handle (..i.e. the lower you crossover the super tweeter the more trouble it gets "in").

OK..

With all of that my suggestion is the following bearing in mind all of the above factors AND cost:

1. Go as low as you can with the horn: More detail = better sound and this isn't a case of more "fatiguing" sound. To me then the horn to select is clear =

http://www.ddshorns.com/catalog.php?page=CFD2110Pro

2. Now you need a good 2 inch driver for it that doesn't cost a fortune (..though you don't want to "skimp" here either). I want to stay away from titanium - to bright for your tastes. You also want it to have good off-axis performance to higher freq.s. Additionally, you'll want a fairly flat impeadance curve. My suggestion is:

http://www.bmspro.info/index.php?sho...10281&id=54367

Mylar diaphram, decent impeadance, low "fs", decent dispersion, strong magnet, reasonable cost. (and Brett here has commented on them favorably.) You will of course need LOTs of "break-in" for them.

Note that there are other possibilites here - most notably "vintage" drivers. But I chose to stay with current production drivers for the selection.

Now you COULD go with the Co-axial versions for your super tweeter bandwidth.. BUT it won't really "gel" with the dispersion pattern and will have relativly high losses off-axis - so I wouldn't recomend it for this wide-dispersion design. So that brings us to the super tweeter.

For the super tweeter I want something that pretty well matches the dispersion of the Horn/Mid at the crossover freq. and to at least 11 kHz. I also want something that goes to about 4.5 kHz with a LR 4th order crossover. Current production there is one clear choice: The Beyma CP25.

http://profesional.beyma.com/ENGLISH/producto.php


***** There is one aspect of this design that should be clear - notice that the 100 degree horizontal dispersion pattern is VERY similar to the frontal "lobe" of a dipole. I.E. this design will come close to a *true* constant horizontal directivity for most of the operating passband, unlike virtually every loudspeaker *****

http://www.linkwitzlab.com/rooms.htm


I may continue with this latter for suggestions on the dipole mid/bass drivers.
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Old 24th October 2006, 01:13 AM   #5
Greggo is offline Greggo  United States
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Scott,

I thought you were a big fan of the 1.4 or was it 1.5 kHz crossover point? Or do I have you confused with something someone else posted, maybe Thylanter, back in the "percieve" thread.... Anyways, just got back from RMAF in Denver and I was really impressed with a couple of systems using the DDS ENG-1 90 waveguide, and the best in my opinion was one using the 1 inch BMS 4552 or something like that.

Paul,

I would look real closely at the combination above, shelved down just a bit up to around 12-16k and then left alone so as to get as much top end out of it as possible and bring the upper-mid / lower tweeter response down closer to a typical cone SPL. Not much choice in my opinion for a single cone that will give explosive dynamics in an open baffle without looking at the pro drivers. The implementation I heard that was very dynamic and yet still smooth and imaged like crazy was from Emerald Physics, and his system coupled the above CD/horn with a pair of Ciare 8" per side, and then had a separate bass panel system with Eminence 15s. If I was gong with a single cone mid below the waveguide, I would look at the Volt BM2500.4 and see how it would hold up on an open baffle run down to 200Hz, and then cross to a subwoofer system, and yes, the Peerless XXLS still seem like the best way to go from all reports, especially if you want to avoid aluminum drivers.

Personally, I am thinking about a computer based crossover and DRC so I am looking at the same kind of set up you are thinking about but will probably cross from whatever mid I end up with to a sealed sub between 100 and 200 hz. After listening to around 5 or 6 open baffle mid drivers (Rick Craig at Selah Audio was showing a great new system with Accuton mid on open baffle and what I think was a sealed sub below and ribbon tweet above) I am convinced that even if I can control room nodes reasonably well with DSP rather than brute force multiple drivers in a dipole sub configuration, I still want that dipole midrange sound, it just sounds so right to me I don't think I will ever be able to put a mid or midbase driver in a box (unless it was a really good dome, and they all seem to be self-contained anyways so the box is just there to hold em in place and give them a baffle as needed..).
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Old 24th October 2006, 07:30 PM   #6
ScottG is offline ScottG  United States
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Quote:
Originally posted by Greggo
Scott,

I thought you were a big fan of the 1.4 or was it 1.5 kHz crossover point? Or do I have you confused with something someone else posted, maybe Thylanter, back in the "percieve" thread.... Anyways, just got back from RMAF in Denver and I was really impressed with a couple of systems using the DDS ENG-1 90 waveguide, and the best in my opinion was one using the 1 inch BMS 4552 or something like that.

It all depends on the application.

Thy was really big on that, BUT so am I in most circumstances - the thing thats really different is the use of a horn, and that calls for re-thinking of the design.

Its funny you should mention liking the 1 inch BMS driver in particular.. One of the distributors for the US (who has heard all BMS compression drivers), ALSO liked that one the best overall - but it IS more limited in its application. Note that it is the 4540ND, and costs a reasonable $100 US. The waveguide also only costs $70 US.

Notice however that the waveguide is not a constant directivity design:

http://www.ddshorns.com/catalog.php?page=ENG190Pro

..and that poses some serious limitations with respect to imaging and loudspeaker placement.. and also tonal balance.

A better design (at least to 4 kHz) would be the Supravox Pavillion 1:

http://www.supravox.fr/anglais/haut_...av_1_pouce.htm

It goes a little lower in freq. and has a MUCH wider dispersion character. THAT and the BMS 4540ND might work very well with a normal sealed or bass reflex midbass.. AND a super tweeter like the Fostex FT96H:

http://www.madisound.com/cgi-bin/ind...2.8199&pid=349

(the only problem there is that the fostex doesn't go *quite* as low as needed for the design for full dispersion character - even with a good LR4th order crossover).
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Old 24th October 2006, 11:52 PM   #7
Sjef is offline Sjef  Netherlands
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With the DDS waveguide or other horn/waveguides you get a very difficult if not impossible job in combining them to open baffle speakers due to the totally different in room power response. Tried lots of them with my open baffle speakers and only the very undeep shallow waveguides seem to match. I'm experimenting at the moment with the BMS 4540nd drivers in different waveguides. For better power response and great match to open baffle sound you can also have a look at the Mundorf AMT tweeters.

Compression drivers can sound as good and most of times even better than lot's of dome tweeters out there and at the levels you want to play with them they will surely sound a lot better.
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Old 25th October 2006, 12:24 AM   #8
ScottG is offline ScottG  United States
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Quote:
Originally posted by Sjef
With the DDS waveguide or other horn/waveguides you get a very difficult if not impossible job in combining them to open baffle speakers due to the totally different in room power response. Tried lots of them with my open baffle speakers and only the very undeep shallow waveguides seem to match. I'm experimenting at the moment with the BMS 4540nd drivers in different waveguides. For better power response and great match to open baffle sound you can also have a look at the Mundorf AMT tweeters.

Compression drivers can sound as good and most of times even better than lot's of dome tweeters out there and at the levels you want to play with them they will surely sound a lot better.

A Waveguide and a Horn are not the same with regard to dispersion.

What I described above *should* be comparable in the forward plane (give or take a db at 45 degrees off-axis). This would NOT be the case with waveguide. (..and note this same problem has a corelary when combining front loaded horns to normal omnipolar midbass designs - i.e. you'll find LOTs of people with a very similar response to yours for a rather different design.) Its also why I mentioned the waveguide is more suited to an omnipolar midbass design.

Now there will be a deviation in power response due to the reverse phase (and additional room reflections) of the dipole driver. All thats required then is some attenuation.

Another thing of concern is that the dipole driver is in fact operating as a dipole at the crossover freq. so that the forward plane is a *true* CD design. This can be modeled effectivly in the Edge (freeware):

http://www.tolvan.com/edge/

..and note that while I really didn't go "into it" - there are several reasons for having a lower crossover for the horn here that are related to these issues.
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Old 25th October 2006, 07:19 AM   #9
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Quote:
Compression drivers can sound as good and most of times even better than lot's of dome tweeters out there and at the levels you want to play with them they will surely sound a lot better.
I'd like to believe that this is true of high end domes at moderate SPL, but I have yet to experience a CD that I would say achieves this. This could be merely because I haven't heard it done right. Anyone in Melbourne with some speakers along these lines they would like to demo?
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Old 25th October 2006, 10:55 AM   #10
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Hi Paul,

I like the way you specify your design goals. Starting with what you are looking to achieve and then selecting the most appropriate technologies and techniques to achieve it.

However, I wonder if some of your assumptions are correct. 110dB peak SPL at the listening position isn't as difficult to achieve as you might be thinking. Remember that you have 2 speakers contributing to the sound field, you are listening within a reverberant environment, music has a high crest factor and also that the spectra of recorded music reduces amplitude as frequency increases.

110dB peak at the listening position of 3m is equal to 120dB peak at 1m in an anechoic environment. For a typically semi-reverberant listening room, 3m approximately corresponds to the critical distance where the reverberant sound field makes a roughly equal contribution to the direct sound. There's more detail about this on my web page:
http://www.aeronet.com.au/Acoustics.htm
So 120dB peak drops to 117dB peak.

2 speakers further drops the requirement to 111dB peak.
Music typically has a crest factor (ratio of peak to RMS) of 6dB or more. It depends on the kind of music of course. Heavily compressed music might only have a crest factor of 2-3dB, whilst classical music might achieve 20dB or more, but for typical contemporary music 6dB is a good figure to work with. Average SPL now drops to 105dB per speaker.

Considering that the spectra of contemporary music falls at approximately 2dB/oct above 100Hz means that the mid needs to output a little less than the broadband average, the tweeter less still, and the woofer proportionally more. Of course the crossover frequencies play an important part in determining how the energy is split between the drivers and the exact type of music will also be a factor. Assuming crossover frequencies of about 300Hz & 2kHz will mean that the woofer will need to produce something like 106dB average SPL, the mid about 104dB SPL and the tweeter about 98dB SPL.

So now the problem is a more manageable. 98dB is easily within the reach of a 1" dome tweeter. And the midrange and woofer only need have moderate efficiency. Of course in the above analysis I have assumed a 6dB crest factor which implies the amplifiers be capable of 6dB more than that required for the maximum average SPL.

Cheers, Ralph
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