[Newbie] Modifying speakers

[Bylie]

Hello all this is my first post so why not make it a big one

I've got a bit of a question, about 3 years ago I made my own bookshelf speakers + subwoofer. Now these don't sound bad but I'm in the mood for modifying my current speakers. The current specs of my bookshelfs are :

Tweeters - Monacor DT-252 75Wrms 8 ohm 85dBspl
Middle/bass - Monacor SPH-135TC 60Wrms 4 ohm 98dBspl (they have a dual voicecoil 8 ohm in parallel => 4 ohm)

My subwoofer :

Woofer - Monacor SPH-250TC 100Wrms 8 ohm 90dBspl (also a dual voicecoil, left and right channels are on one voicecoil)

Amplifier :
Yamaha AX-592 140Wrms

Filter used in the bookshelfs :
Tweeter = 18 dB/octave with -- 3,3Ohm -- 1,5µF -- 0,36mH(parallel) -- 4,7µF
Mid = 6 dB/octave with -- 0,4mH --

Now I was thinking of "expanding" my speakers by building two the same bookshelfs without the tweeters and placing them underneath my current, that way the I can achieve a better dBspl.
I also would be wiring my current dual voicecoils inline so they would have 16 ohm and them put them in parallel with the new mid/woofers so they'd be 8 ohm again which would also be better for my amp. Also the resistor in front of the tweeter would be replaced by another one to adjust to the added mid/woofer.

Now my question is would this be a good idea and aren't there any catches??

thanks and a picture wich might explain some things a bit better :

 

[planet10]

Tweeters 85dBspl
Middle/bass 98dBspl

The sensitivities you have speced are somewhat suspect. if accurate your tweeter is not contributing much.

If you are going to add the other woofer and run it over the same bandwidth as the original you might want to flip the originals upside down to give yourself an MTM. 1st order XO on the woofs might be a bit shallow for an MTM.

The other way to approach it is to do a 2.5 way but with the impedances present it might be tricky.

dave

 

[Bylie]

Dammm big typoos there, I was a bit in a hurry.

Tweeters : 92dB
Mid/woofers : 85dB

That's one of the reasons I'm considering adding an extra mid/woofer because then the spl of the mid/woofer would go up by approx 3dB.

Btw : isn't an MTM system the same as a d'appolito??

 

[planet10]

Btw : isn't an MTM system the same as a d'appolito??

Yes. I like the more descriptive term MTM. And the fact that i was building them 5 years before Joe made the design popular. (my 1st was a triangulated TL with two English made (Harbeth?) clear poly 8" midbasses and a tweeter probably a Philips but that detail is lost in the mists of time.

dave

 

[naqref]

That's one of the reasons I'm considering adding an extra mid/woofer because then the spl of the mid/woofer would go up by approx 3dB.

Well the SPL would go up 6dB...

A least with a contant voltagesourse like an amplifier.

 

[planet10]

Well the SPL would go up 6dB...

A least with a contant voltagesourse like an amplifier.

You are assumming a quality Solid State amp.

You actually get 3 dB from the doubling of the cone area. And then you may get as much as another 3 dB if you have a constant voltage amp that actually doubles its output power into 4 ohms vrs 8 ohms (the cheaper the amp the less likely this is -- some actually put out less power into 4 ohms). With a tube amp you change the taps and you get the same power.

Here things are complicated by the wiring scheme which will change the impedance from 4 ohms to 8 ohms. If he has a constant voltage amp that is capable of delivering the required current into a 4 ohm load, by adding the speaker and changing the impedance there will actually be NO gain in levels (3 dB more from the 2nd speaker and a loss of 3 dB from the amp). There will be a decrease in distortion thou.

dave