BillFitzmaurice.info

Hi all.
Quick question reguarding crossover parts in Australia.
Im gathering a list so i can start buying parts.
Omni 15 tall boy. Planning on doing the single 15”
So, if i use a single 4ohm speaker. Do i buy components to suit
The 2 speakers, 4 ohm load in the drawing? (Page 18)
Also, i am struggling to find a 5mh coil but with small gauge wire
And less than .5ohm dcr.
Hopefully i have sufficiently explained myself.
Thankyou everyone

Hi, RRFB.

I had a similar question here: viewtopic.php?f=3&t=25549

The short answer is, it depends:
1) The ohm rating (4, 8 etc.) of speakers is nominal. It's quoted by manufacturers as a standardised number, since the actual resistance in actual use changes a lot depending on power put in to the speaker, among other things.
2) One "4 Ohm" speaker doesn't necesarily have the same resistance behaviour as two ""8 Ohm" speakers in parallell. It might, or it might be close enough, but it might not.
3) Also, the TS parameters for a 4 Ohm version of the same speaker might vary a lot from the 8 Ohm version.

In the link above, I proposed the 4-Ohm version of the 3015LF for an Omni 15 Tallboy.
Bill pointed out that based on the driver specs, the nominal resistance was closer to 6 ohms.
He provided some suggestions for crossover values, which I used.

But not before checking myself.. There are only two parts in a low pass filter of this type, and without knowing the theory there seems to be a linear relationship between the inductance values of the coil and the capacitance value with the nominal resistance of the speaker.

So you have to look at the spec sheet for the driver you intend to use. What is it?

rrfireblade954 wrote: ↑Sun Dec 12, 2021 5:37 am So, if i use a single 4ohm speaker. Do i buy components to suit
The 2 speakers, 4 ohm load in the drawing?

Yes.

Also, i am struggling to find a 5mh coil but with small gauge wire
And less than .5ohm dcr.

Read it again: The 5mH coil is the smallest available gauge with no more than 0.5 ohms DCR.It doesn't say that it must be small gauge wire, it says use the smallest gauge you can find with less than 0.5 ohms DCR. For instance: https://www.parts-express.com/5.0mH-18- ... or-266-568

speakerbug.com.au has a 21AWG 4.7mH air core.

Also, my copy of the plans states: The 5mH coil shunts to ground and doesn’t need either low DCR or high current capacity, so here use the smallest available gauge.

It doesn't say that in my plans. How old are yours? As I vaguely recall at some point someone used a circuit board mount inductor that probably had 50 ohms or more DCR,and maybe 0.1 amps capacity, so I had to be more judicious in the coil specs. That was probably when I added pictures of coils and caps so that newbies would know what they look like.

The "last modified" date for the pdf file says 5/30/17 6:56AM. Is there a newer version? If so, I think I may just order a new complete set so I can get the new TT and 21 simplex plans in my library too.

Thankyou for the replies
Here is the speaker im planning on using.
https://thespeakerfactory.com.au/produc ... 33fc&_ss=r
My amp is capable of minium 2 ohm load. So I figure i will be ok
There.
Am i able to use air core for the low pass? Im struggling to find
Solid/iron core. In Australia anyways.
Getting there….
Thanks guys

Righto,
I have the crossover components sorted… i think.
My next question is,
Are the drawings for the bp filter and hi pass to suit 8 ohm
Speakers. (I realise i have both options for the woofer 4 or
How does this affect the total rating of the cabinet?

It doesn't. The only pass band where the impedance is of concern is the woofer range.

A crossover question for OmniTop 15 running bi-amped. The capacitor for dc-protection, is the value crucial or does it have a range? Would a 22uf work? Changing the crossover point to about 450 hz first order. My guess is it still protects dc with a higher value but are there more to it?

Also, since its recommended when running bi-amped to run the signal through the low-pass passive filter, would it work with bi-amped, crossed, signal through the high pass filter too if i build that one?

(i run bi-amped at home but when moving them or lending them, it would be easier with passive x-over and I wonder if i need to turn the hp-filter off when i use it bi-amped)

Thank you

When bi-amping eliminate the low pass filter on the woofer and the 22uF and 5mH coil on the midrange bandpass filter. All else remains the same.

Bill Fitzmaurice wrote: ↑Tue Nov 28, 2023 2:40 pm When bi-amping eliminate the low pass filter on the woofer and the 22uF and 5mH coil on the midrange bandpass filter. All else remains the same.

It appears his questions are for OT15, not Omni15

Seth wrote: ↑Tue Nov 28, 2023 3:41 pm

Bill Fitzmaurice wrote: ↑Tue Nov 28, 2023 2:40 pm When bi-amping eliminate the low pass filter on the woofer and the 22uF and 5mH coil on the midrange bandpass filter. All else remains the same.

It appears his questions are for OT15, not Omni15

He said OmniTop, but his question discusses the midrange driver......some clarification would be good as this thread started with and Omni 15TB

Yeah, it definitely should have been started in a new thread either way.

Yep, I assumed it was the Omni, not the OTop, as he mentioned running a 450Hz crossover, which is not an option for the OTop.