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Hi Pascal, is it raining in France as well as in England today?

I would recommend the PR240Z0, it's a bit more expensive, but well worth the money!

I have them in use in my system, which is based on the World Audio KLS11 with redesigned cabinets for extra rigidity, and separate bass and mid/high enclosures.

I have used ported 47 litre boxes and measured in my normal sized (European not American!) room they are 3db down at 26 Hz, and I think you would struggle to get any lower whilst maintaining a reasonable box size.

I would be pleased to help if you require any more assistance


Hello Al,

no, the sun is shining in my city (Toulouse, in the south west). Ah, England, beautifull country....and beautifull music (Rolling Stones.....)

Thank you for your answer. I know World Audio, they make very goods things. I don't know the PR240ZO. I will get informations about. In fact I want to have bass renforcement for Fostex F208S+FT17H (I have found a pair of F208S for a very good price in deutchland spectrumaudio, 350 euros..... euh sorry 111,53 £). I had choose PR240MO for efficiency. I need basses with good efficiency in small box.
I'm not sure that the efficiency of PR240ZO is enough ?

Best Regards.

Pascal, not sure if your back issues stretch back this far...

World Audio Design (HiFi World) did a sealed box with the PR240MO called KLS8 in October of 1996 DIY supp 24.

Box was internally 50litres which gave a Q of 1.1 and a 2dB lift in the bass with -6dB at 42 Hz.

A 70 litre box drops the Q to 1.0 and the bass lift to 1dB with the -6 at 40 Hz.

Beware that the 240MO has strong break up above 1k (+5dB spikes at 3k) and will need to be well filtered to supress this.
Of course if you're only usig it to match with the fostex then it shouldn't be a hasssle as you'll start cuting it out about 200Hz or so.

Hope this has helped

BTW, looks like he 240mo isn't really ideal for a reflex box. Lots faster in a sealed cabinet anyhow.

Thank you Drew,

I'm afraid that in a sealed box, the basses are more fast but less deep. I need a driver with good response under 200-400Hz i can use with Fostex FE204. Now, I'm not sure that PR240MO is the best driver for that, I saw the SEAS CA25FEY H368 spec. and it seems to be good in a BR enclosure. Does somebody knows this driver ?

Best Regards.

Originally it looked like you were planning to use the 208Sigma not the 204.

If the 208/204 is anywhere near the speed of my 168Sigmas then I expect the speed will matter more than the absolute low end depth. If you are going for the incredible dynamics, coherence and impact of the high efficiency fullrange unit plus a bit of fill in at the top and bottom it would be sad to spoil it all by using a slower alignment.

Have you contemplated horn loading the 208?

Check the "Fullrange Driver Forum" and see what projects they suggest for the 208.

This all comes down to personal taste of course. My choice of compromises is that i'd rather have less low end and have it fast than have lots of low end and have it slow.

Enjoy the music
Thank you Drew,

I understand your point of view, but horn will not be the more adapted for the music I listen. For Maria Callas there is no problem, and i love, but i love too "the rolling stones", and the "bass" is important. I have studdy lot of Fostex drivers (i love there medium) and take a lot of informations on the net with very sympathetic boys who have take the time to answer me. The FE208 have one problem, it seems to work good only in horn, so i have studdy the FE204. It is similar, but have a more Xmax and is adapted for horn, bass reflex, open baffle,.... it have just one db less (95db).

Have you see the Fostex recommendation for FE168S ? They recommend to use a double bass reflex enclosure. Have you try it ?
I have asked to Fostex if they recommend the same for FE208S (with differents dimensions of course) but they don't answer :(.
If someone say me that yes of course I will use FE208S ;).

So if double bass reflex are not a solution for FE208S, after all, I will use FE204 wich can be use in numerous configurations. At this time I have two projects in mind and i must to choose one.
1) A FE208S in a double bass reflex enclosure (like FE168S recommandations)
2) A FE204 on open baffle put on top of a "bass box".
I'm not sure that my english is enough for you can understand me so this is a little quickly draw of what I think.

Best Regards, and thank you for all.



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My personal call is to go with the open baffle option.

I had an open back cabinet for midrange a few years ango and removing the box resonances from that section of the music did wonderful things.

As you say, if you are going down that road, a little more Xmax is desireable.

Trust me, your english is amazingly superior to my French.

How far from side walls?

Most definitely, you'll ge the best results with the fostex drivers used on axis and pointed straight at you.

You'll want the backs of the open baffles to be about 1.5 metres from the rear wall of the room, (more if possible).

If your room is wide enough then I'd try to have the sides of the baffles no closer than a metre to the side walls. Limit the rear reflections off side walls as much as you can.

are you planning to have any damping at all on the back of the baffle panel behind the driver or will you be operating as a full dipole?

Hi Pascal,
Some folks hang carpet felt behind the driver to soak up some of the rear radiation. This prevents back reflections from stuffing up the soundfield.

On the other hand, Quads, Maggies and the like let all the rear radiation out and still sound great. Some sealed box builders (Wilson and Mirage) deliberately place drivers that produce rear radiation so I expect it may not be as much of an issue as it's commonly made out.

Build a nice wide panel with the driver mounted on it and have a listen. You can always add rear damping later on.


PS, consider using the fostex without the tweeter initially. You may find that you don't need it. Again, a tweeter hole can always be added later and the x over adjusted for it. The raw fostex shouldn't need anything more than a series cap to cut out the low bass.
diyAudio Editor
Joined 2001
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Hey Drew P

Pascal and I are building simiar speakers, if and when we stop having fun designing!As I mentioned, I am thinking of using the Fostex FF225 in an open baffle with a tweeter.It has flatter response than the 208 and I think that is due to the lack of a whizzer cone. Since I will have a tweet, it rolling off about 10k is fine with me.

I am very intrigued with your comments about fast bass. I was worried about the bass not integrating well with the full/mid driver.I was trying to solve this with a vented 15" pro driver because it seems similar to what the Fostex is. I also have the Basszilla plans, and it uses an expensive 15" to get high efficiency in the bass.

BUT I now realize I might have another option: I want the mid and tweeter to be very efficient, because I am using a small amp, but maybe I can drive the woofers with an active crossover and my old Hafler 220 with 125 watts/ch. I guess you are talking about a sealed cabinet with a Qtc of about 0.5 I'm just quoting thee Qtc stuff from an article I read - I reallly don't know much about it at all.

I don't need the bass to go much lower than 40hz so that might help. I also don't mind a reasonably large box

So..... I need a box/driver combo with great transient response
40hz to 200hz, Puts out about 103 dB? with 110 watts/ ch.
Driver cost best not to exceed $150 USD each.

There will be 2 boxes and total of 2 drivers. I prefer less Xmax if possible. SO, what is your advice? Drivers?, box size? An I asking for and unreasonable output? is 103 db enough? for a 18x 12 room with 10' high ceiling?

Thank you,
Mark, if you don't need the depth below 40Hz, then why not use the Audax 240MO in a 70 litre box (-6 @ 40Hz)

That means that your bass section will be 94 dB /watt efficient and won't need to be biamped.

(10 watts will give you that 104dB in the bass at 1 metre with only 1 channel driven)

70 Litres is largish for a little bass box but considering that you'll be building a wide panel you can use the extra width to your advantage(internal of cabinet say 40 - 45cm for a 50cm wide panel if the box is 25mm mdf). Given that you need spacing from the back wall there's no reason not to go backwards a fair way either (say 50-60 cm even).

At 45 wide and 50 deep the box only needs to be 33 high to give you your 70 litres. Domestically acceptable and with good boundary coupling to the floor and a rear panel far enough away from the drivier to limit the rear wall reflections.

A big flat box like this atthe bottom will give the open baffles a nice stable base to mount off and you could diagonal brace off the back of the bass cabinet to stiffen the panel up too.

Should work well.

diyAudio Editor
Joined 2001
Paid Member
Progress at last

Thanks for your response! I feel we are making progress!!

You understand the general cabinet idea exactly- My image is that of a panel speaker anchored by a deep bass box. I think that it will actually be pretty unobtrusive in the room (except straight on!) because it will be so flat from the side!

I will tell my wife that you guarantee that it will be domestically acceptable. I think you are safe from any reprisal from her because you are on the other side of the world! The only danger is if you ever want to visit. She's perfect except for hating motorcycles and big speakers (a little on the fence with sailboats too.. depends on water temp.)

One fly in the ointment is that I really meant FLAT to 40 hz so -6 db might not be good enough. The Fostex FF225 is more like 97-98 db efficient so 94 db is already down 3 db so that would be minus 9db at 40 hz. BUT you mentioned boundry coupling- does that boost the bass a bit? or are you already accounting for that?

Actually, the box could even be a bit bigger-say 25% Once you have a cube shape, more internal volume doesn't make it That much bigger! Will that get me the response? Maybe -3 at 40 might be OK.

Another way to look at it might be to try to get -3 dB at 40 with box size, then pad down the Fostex about 3db (blasphemy!)

This would give me the option later to play around with the bi-amp, and then take out the l-pad on the Fostex/tweeter

I know this thread started regarding the PR 240MO, but is that still the best speaker for this purpose?

Sorry to be so darned picky!
diyAudio Editor
Joined 2001
Paid Member
Think twice-write once

Sorry to keep posting but the questions don't stop!
The Pr 300mo is 97db efficient-pretty cool, but how big is the box?

OK- here is the question: Which needs more xmax, excursion?
An open baffle, sealed box or Bass reflex? Probably like all questions-it depends. We a re still agonizing over the Fostex FF225 vs FE240
Of course the open baffle rolls off about 200 hz about 12db octive. I guess to make it fair, lets compare to a sealed box or bass reflex also cutting off at 200 hz

240: Much greater travel, whizzer cone which makes the response more uneven, which I don't need because I'm using a tweeter, 95 dB efficient $75

225 Very short travel, but soft limit to over excursion, low distortion, Very flat response. This one seems more like a what a planer speaker is but much smaller area of course. rolls off at 10k very cleanly so interacts fine with tweeter. 96+ db efficient $95
Cripes! I leave the computer for 1/2 a day and I've got a flood of questions to answer.

For bass, Xmax will be biggest on an open baffle, medium on reflex and low on sealed.

Efficiency will be highest on reflex, medium on sealed and low on open baffle as it requires equalisation at +6dB/octave once the back wave starts cancelling out.

Due to no box resonances, bass can be fastest, deepest and most precise with an open baffle for bass (a dipole subwoofer) but it needs to be in precisely the right spot and alignment is an issue.
Of course the precision comes with the previso of a really low Fs, very efficient (read bloody expensive) bass driver, the need for equalisation and a bucketload of amplifier power.

Again, if you can track down some back issues of hifi world from around late 95 to mid 97 you should find the plans for a diy dipole sub.

If your wife would put up with Magneplanars then we may be on safe territory here. Wide open baffles take up the same width as big panels. They are working with similar physics regarding cancellation.

Stay away from cubes for bass boxes. You get all your resonances at the same frequency. try to keep the dimesnions all different. A medium width, very deep and quite low height box will be best. It makes the precieved height of the big box smaller (which pleases wives) makes things more stable and reduces backwave reflections.

Sounds like the 225 in a biamped system is the way to go. Youll need to do this if you are matching efficiencies, as you say padding down the Fostex is silly. You'll definitely need to biamp if you go for a diploe sub but i doubt your wife would like it.

Remember that big panels don't have to be wood coloured. You can build a frame and put coloured cloth over them. They could be a "decorative feature" of the room. Brighten things up a little! When you get bored or re-decorate, just change the colour of the grille cloth.

The precise amount of boost from boundary gain I don't know so I won't pretend. I've never worked with the 300 so i can't comment on it either.

I ran it through WinISD and to get -5dB at 40 will require more than a 100 litre box. These pro series drivers are more for pro rigs where cabinet size doesn't matter.

Hope this has all helped a little

diyAudio Editor
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Cripes! I leave the computer for 1/2 a day and I've got a flood of questions to answer.
Well only from me! everyone else is at the beach with their familys :)
For bass, Xmax will be biggest on an open baffle, medium on reflex and low on sealed.
I was asking this regarding the mid.
Efficiency will be highest on reflex, medium on sealed and low on open baffle as it requires equalisation at +6dB/octave once the back wave starts cancelling out.
Again, this is for the mid, We will have about a 45 cm wide baffle, to keep the mid happy, then when it rolls off, the boxed woofer takes over.
Sounds like the 225 in a biamped system is the way to go. Youll need to do this if you are matching efficiencies, as you say padding down the Fostex is silly.
Might not be silly in the interim until I get the biamp worked out. The PR300MO is looking pretty tempting at 97 dB.
I ran it through WinISD and to get -5dB at 40 will require more than a 100 litre box. These pro series drivers are more for pro rigs where cabinet size doesn't matter.
Well...... maybe not so bad... 45cm wide x 60 cm deep x 70 tall
= 189 liters right? or am I being an idiot Yank? You know them there centimeters and all. Would this get me a much flatter response?
Hope this has all helped a little
A lot, but I've got to get a box calc program. The one I found on the web needs Excel 2000 I've just got '97

Thanks again for your help- this is starting to sound like something that might work!

PS: Just downloaded Win ISD
Mark, be aware that the responses shown in WinISD don't take into account rolloff in the drive units.

If you are never pushing energy below 200Hz in to the drivers then i don't think that Xmax is going to be an issue. It's in the bass where all the big movemement goes.

Yes, 45 x 60 x 70 will give you a 189 litre box. but that's a bass enclosure that's (allowing an inch either side for the 25mm panels) a box 1ft8inch wide, 2ft2 deep and 2ft 6 high.

That's a pretty big box but it's your spouse you gotta convince. just don't blame me.

To put this in context a 44 gallon drum is about 200 litres.

"Hey honey, it's a bit smaller than a 44. You won't mind two of them in the loungeroom will you?"
I can see it now... :D

This cabinet by my calcs will give you minus 4.3dB at 40Hz.

If you got a bit of room gain and padded down the mids by a couple of DB it should match well.

Continue at the risk of your marriage...

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