attenuation problem.

[Arty]

First of all, hello everyone, I'm new to this forum.
I would like to ask about tweeter attenuation.

The long story is:
I em not a hi-fi high end seeker.
My setup consist of my computer with its integrated sound device,
and a simple TDA1557Q amplifier. No volume control, no nothing.
Chip glued to a heatsink, capacitors directly on the pins. No pcb, no nothing, only a switch to turn it on or off.
Powersuply is a 40 VA rated unknown DC suply, no idea if its regulated or not. Says 15 V DC / 40 VA max. nothing else.

For me, it is a high-end audio amplifier, as it suits me just fine.

So anyways, my gradpa age speakers are slowly going to die.
Gotta make new ones.

I found a suitable set of 4 midbass drivers, and a pair of tweeters.
So the idea is to make 2 speakers, eatch having 2 of the midbass drivers, and 1 tweeter.
Simple way setup, 2nd order x-over.

For now, let us assume I can deal with the box, and find a crossover freqvency.

Details that may need to be known to gain an answer to my question:
The midbass units have 90 dBL sensitivity, they are 8 Ohm rated.
The tweeters are 91.7 dBL sensitivity, and 4 Ohm rated.

The question is, if i wire 2 of the midbass drivers in paralell, to get 4 Ohms, by how many dBL would i need to attenuate the tweeter?
Baffle stepp corresction should not be included in the answer, i did not yet design the box, and as so i do not know the size of the baffle.


I found a topic with a simular question, but unfortunate.. after reading all 10 pages, there was no clear answer. And my setup is a bit different to that one.

Thank you for the answers.
I think i suplyd all the details, if not, please feel free to ask. At least if it is revelant.

[sreten]

Hi,

Given your numbers you have to include baffle step, otherwise your tweeters
are not loud enough. For a MTM two way nearfield the bass mids will be 96dB*,
so around 3 or 4 dB of Baffle Step Correction will align them to your tweeter.

I don't recommend full 2.5 way BSC for nearfield applications, only farfield.
In this case the tweeters need attenuating around 2dB for 90dB/1V/1m.

rgds, sreten.

* simply put I find it highly unlikely small bass/mids are 90dB/1V/1m.

[AndrewT]

What is dBL?

[Arty]

Originally Posted by sreten

Hi,

Given your numbers you have to include baffle step, otherwise your tweeters
are not loud enough. For a MTM two way nearfield the bass mids will be 96dB*,
so around 3 or 4 dB of Baffle Step Correction will align them to your tweeter.

I don't recommend full 2.5 way BSC for nearfield applications, only farfield.
In this case the tweeters need attenuating around 2dB for 90dB/1V/1m.

rgds, sreten.

* simply put I find it highly unlikely small bass/mids are 90dB/1V/1m.

I see. So it would give +6 dBl for near field. both of the speakers would be approx 1.5 meter from me, so based on Your advice MTM configuration would not be wise.

Allso, the midbass units are 210 mm diameter ones (includes the foam edge too), they are not realy small. Suposedly they would e both very close to walls, i read somewhere that bafflestepp has less effect in that case.

Never had imagine that one day i would have to think about attenuation network for midbass, rather than tweeter.

anyways, based on Your opinion, i would be just fine with one midbass and one tweeter for eatch loudspeaker. Sounds good, cheaper that way. That is never a problem, makes things a bit less complicated.

hmm.. this is getting a bit off topic. o well
//btw, if You have any opinion on my choice for xover point feel free to comment.

[sreten]

Hi,

For nearfield I'd go for wide and not deep speakers, assuming wall mounting.

2 x 8" MTM's for nearfield is ridiculous. I'd go with one 8" and a mid/treble FR.

The Fountek FRR 88 EX c/o at the BS frequency to a 8" driver,
using first order series could work well, 8" issues are avoided.

rgds, sreten.

[ByronInLawrence]

Hi Arty,

I'd like to suggest a different approach. It sounds like this is your first speaker project. There are many small and inexpensive kits available from vendors such as Parts Express and Madisound. Many are available without cabinets, they don't cost any more than buying the parts individually, and they have already been built and tested, and tweeked.

Of course, designing your own is more fun. If you insist on going that rout, I recommend downloading Speaker Workshop
Speaker Workshop Download
and SPL tracer from here SPL Tools
Use SPL Tracer to make *.zma and *.frd files to import into Speaker Workshop. In Speaker Workshop you can model your crossover with resistors for attenuation. An even better suggestion is to build a Wallin Jig Eric Wallin's Internet Homepage which is inexpensive and generate your own *.zma and *.frd files for Speaker Workshop.

Good Luck,
Byron