Comments on 3 way bi-amped please ?

[fat_terry]

Hi,

Would anyone with experience please comment / suggest improvements to the beginings of the following design :

I plan to use :
Peerless 850146/CSX257 woofer crossed over with an active filter (and its own Amp) at 1060Hz.

Peerless P13W-H-00-08 mid and Vifa D27TG-45-06 with passive crossover driven with their own single Amp, crossed at 3KHz.

I plan to mount the woofer and mid in sealed enclosures, of 38L and 20L (plus bracing compensation etc) respectively.

I already have the BiAmps, Powersupplies and active filters (subject to XO frequencies) for this project.

I would welcome any suggestions/comments before I look at passive XO design and start ordering parts, but in particular :

I have chosen the Xover frequencies from general suggestions in LSD Cookbook and from the freq. responses. I feel there should be a better method, have I got them about right ?

Im a little concerned at the differing power handling characteristics of the drivers, being 100W and 40W for the woofer and mid. However the mid still shows a max SPL of 105dB, although somewhat less than the 111dB of the woofer.

I want to use a floor standing/tower design, however the calculated Vbs do not suggest a large enclosure to me.

Also the P13W-H-00-08 is listed as being suitable for vented enclosures. I had disregared this as being relevant only to LF response, until I saw an example of a vented mid in LSD Cookbook (mid and HF drivers, fig 6.5 page 107 in the 6th edition. This now has me puzzled and realising there is something I dont understand here. If someone could explain that one to me Id be grateful.

thanks for any input,

Terry.

 

[F1 FAN]

I have a similar setup but I triamp.I would suggest that you move your woofer to mid crossover down to the 300-350hz range instead of 1060hz.1060hz is to close to 3k and the w13 will have no problem running at 300hz but your woofer should not be run much higher than that.

 

[Andy G]

Try to use the P13Wh in an open back U-frame with about 2" of poly wadding behind. your ears will thanks you.
Your low x-o point will need to be around 200ish.

Also cross a bit lower on the mid/tweeter if you can.


ps: where in Aust are you ?

 

[fat_terry]

Thanks for your replies Andy and F1 Fan - I appreciate it.

Id applied the 2 octaves below resonance rule incorrectly - yes 300-350 looks far more sensible, thankyou !

Andy, when you say cross a little lower on the mid/tweeter I was a little lost in determining that XO freq. Except a note from LSDG saying the D27 range generally shouldnt be crossed lower than 2Kz, without saying why. Is there a specific reason you say this - experience perhaps ? Im just trying to learn a bit in the process .... so 2Kz sounds lake a better compromise perhaps.

I dont quite understand the open backed U frame bit ? Im placing the mid (well all drivers) in a sealed enclosure, you're saying to pad with 2" poly behind the mid ?

Im around the Hornsby area, not too far from you it seems ! Im often up around Port Stephens & Stockton.

T

 

[fat_terry]

F1 Fan,

many thanks for your reply - Im interested you have a similar setup, in fact I still cant decide whether to go the extra step and TriAmp it. How do you find the results ? How is your bass response, and did you use any sort of bass response modification like a Linkwitz Transform etc ?

Is your design all sealed elclosures ?

Is there anything you'd do different with hindsight ?

Terry

 

[Andy G]

Thanks for your replies Andy and F1 Fan - I appreciate it.

Id applied the 2 octaves below resonance rule incorrectly - yes 300-350 looks far more sensible, thankyou !

Andy, when you say cross a little lower on the mid/tweeter I was a little lost in determining that XO freq. Except a note from LSDG saying the D27 range generally shouldnt be crossed lower than 2Kz, without saying why. Is there a specific reason you say this - experience perhaps ? Im just trying to learn a bit in the process .... so 2Kz sounds lake a better compromise perhaps.

I dont quite understand the open backed U frame bit ? Im placing the mid (well all drivers) in a sealed enclosure, you're saying to pad with 2" poly behind the mid ?

Im around the Hornsby area, not too far from you it seems ! Im often up around Port Stephens & Stockton.

T

Hi Terry,
Yep, I have found that the P13Wh works much nicer when crossed around 2k - 2.4k than higher up. Reworking a 3-way using it at the moment.

As for the open back, its sort of like not having a cabinet at all. Just a baffle with a pair of shallow sides. Obviously bass response is sacrificed and if used for bass then big powerful drivers are needed, and eqed. But for use with mids.. well I guess you just have to hear ;-))
I find a full open back is a bit much, but padding seems to give just the right amount of reflected sound without affecting imaging etc. I haven't figured out why fully, but they are just work out nicer to listen to than sealed.

I'm in Newy. feel free to drop by (by prior arrangemnet if you want to catch me) for a cuppa and a listen if you are up this way. Always several pairs of speakers to listen to, of different styles ;-)) If you can get up here before you finalise your design, all the better !!

"Blackwood" is particularly nice.. its open back mtm using Vifa M11WH's.

you can get my email from my web site. http://users.tpg.com.au/users/gradds/

 

[F1 FAN]

F1 Fan,

many thanks for your reply - Im interested you have a similar setup, in fact I still cant decide whether to go the extra step and TriAmp it. How do you find the results ? How is your bass response, and did you use any sort of bass response modification like a Linkwitz Transform etc ?

Is your design all sealed elclosures ?

Is there anything you'd do different with hindsight ?

Terry

Hi Terry,I will describe my setup and actually it is more correctly a 4way active system because I use an active subwoofer to extend the bass below 50hz.

The tweeter is a SEAS H1212 metal dome.

For the mids I now use a SEAS CA17RCY/P (H571)but until very recently I used a Vifa M17SG.The mid enclosure is an 8litre sealed box.

The woofers are the 8"SEAS P21REX in a 1cubic foot vented box.
Because I use a sub the 8" woofers are hi pass filtered at 60hz.

The sub uses dual 10" woofers in a 3 cubic foot sealed box.I use an LT circuit to extend the bass.

The crossover between the mid/tweet is a 4th order LR at 2k and the crossover between the mid/woofer is a 4th order LR at 300hz.

I will add that I recently changed the mid/tweet crossover from a passive series design to the active one I now use and gained some very worthwhile improvements.

btw,I will make the same offer as Andy, you are welcome to stop by and have a listen but it is a bit of a long drive(flight).

 

[fat_terry]

Once again thanks guys, Im sure you remember when you first started out - you need all the pointers you can get !

Funnily enough F1 Fan, my first project was this same one but upon advice from this very board I ended up with a fantastic Adrie-based sub. I think I am up for doing the same as you have, ie 4 way also using the completed sub. Im guessing you werent happy with the Bass from the 3 ways, something I was concerned about with my proposed design.

I have been known to go to Canada, but only Toronto (which was fantastic apart from having to work during the day !). Newcastle is a more realistic proposition which I might take you up on if Im up there again - that's a great Web Site Andy, and some good photos of superb woodwork too (and good Aussie supplier links). I was wondering what systems you had in Newy, but the Mysystems link isnt working ?

Time to redesign the 3 way today I think ....

T

 

[F1 FAN]

Im guessing you werent happy with the Bass from the 3 ways, something I was concerned about with my proposed design.

I have been known to go to Canada, but only Toronto (which was fantastic apart from having to work during the day !).

The bass response of the 8" woofers was fine for music listening (about 45hz)but I also use these speakers for Home Theater.HT was to much for them to handle so I needed the extra bass extension and increased bass dynamics that the sub added.



So you have been to Toronto,I live 100 miles north east of there.
I would love to go on a trip to Aus it seems like an awesome place. (except it is the home of some nasty snakes.)

 

[Andy G]

that's a great Web Site Andy, and some good photos of superb woodwork too (and good Aussie supplier links). I was wondering what systems you had in Newy, but the Mysystems link isnt working ?

Thanks you Terry, not all the work is mine , just the Argos stuff. A lot of the curved speakers are done by others. (thanks for sharing, guys !)

That "MySystems" link should be working now btw.. somehow the page got left behind !!!

 

[fat_terry]

F1 FAN or anyone else that cares to comment, this is a generic triamping question.

Im not sure exactly how similar your triamped setup is (and Im redesigning for a triamped setup now), but one thing has me concerned, beginners comcern you might say :

The PW13 is a 40W unit. The woofer and tweeter Ive chosen are 200 and 100W units respectively. Unibox tells me the PW13 will have an SPL of around 105dB at 40W. Naturally the other drivers reach an SPL of 110+ dB at their maximum power rating.

Here's what Im having trouble understanding. While 110dB is probably overkill for a moderate sized living room, I can only guess that 105dB might be OK. But the huge difference in power handling capabilities (over 500% for the woofer) suggest to me these units should not live together and perhaps my design is flawed, or at best Im wasting having such a woofer in the design while I have the PW13 in there at only 40W.

However I have to remember Im triamping here. So Im really talking 3 units all being driven at lets say 40W ie the power of the smallest driver. But will this give me overall a higher SPL than if I was driving the whole lot with one amp ? See, Im confused.

Id just rather understand what's going on first that find out after construction my assumption was right, or wrong !

if you follow all that ?

T

 

[F1 FAN]

Hi Terry,I wouldn't worry to much about the power rating of the P13 . You will probably be crossing it over to the woofer in the 200-300hz range so power demands on it will be lessened because it will not be reproducing the bass range.
One of the advantages of active crossovers is that several db of driver sensitivty is not wasted in passive components so less power is needed.
The two different mids I have used (Vifa M17 and SEAS CB17) have about the same power handling as your P13.I use a 60watt Bryston amp on them without problems.
Also the 40 watt rating is long term power but the driver can handle more power for short dynamic bursts. Here is a link to some good info on bi and tri amping.

http://sound.westhost.com/bi-amp.htm