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gaust 27th March 2008 02:37 PM

Adding a tweeter to full range
 
I have a feeling that I might be thinking about this too much and confusing myself so I was wondering if someone could put me straight!!

I have some 4" full range speakers and have recently bought some tweeters that I want to add to give some "air" to the top end. I intend to run the 4" driver full range and just use a capacitor on the tweeter to come in at a fairly high frequency. I have been doing some research to find suitable capacitor values but when I came to start thinking about hooking it all up I have started to get confused. So my questions are

1. What frequency would you recommend for corssing in the tweeter? - I was thinking about 8000hz, but I'd be interested to hear your opinions

2. How would I actually connect them up?
This is where I started to have problems; the full ranger and tweeter I have bought are both 6 ohm and with similar efficiency. What I am worried about is the impedence when they are both connected - do you connect them in series or parallel? My original intention was to use these for my home theatre set up (if they sound good enough) and my amp states that speaker impedence should be 6-8 ohms.

Apologies if these are stupid questions, but better to get them out there are asked than worry about them and not do anything

Cal Weldon 27th March 2008 03:05 PM

Hi,

I have used a tweeter with 2, 1.5 and 1.0 mfd caps added to full range units. You might want to get all 3 values in electrolytic caps to try out what you feel is best and then buy poly caps once you know which you like.

You wire them in parallel with your FR drivers. You don't have to worry about impedance drop as the impedance of the FR unit rises with frequency and you are cutting the tweeter off quite high so what the amp sees will be fine.

LineArray 27th March 2008 04:04 PM

Hi gaust,

may i ask you what kind of fr driver you use ?

What kind of enclosure or baffle do you use ?

In my setup i was thinking about using a tweeter too.
Then i decided otherwise and solved the problem by
equalizing www.dipol-audio.de

Lack of air on the top is often an issue with fr drivers.
To improve a good fr by adding a tweeter normally gives ambivalent results:

You add some air and brillance (is this an englisch word?) ok,
but often you lose homogeneity and proper impulse response.

If you can't avoid adding a tweeter you should choose one,
which has about the same radiation angle at the crossover
frequency like the fullrange.
This could be a horn or waveguided tweeter (ribbon) or a
dome tweeter of suitable diameter.
The tweeter has to be adjusted to the same output
level as the fr, usually this is done by a voltage divider.

The vertical distance between both systems should be as
small as possible at high crossover frequencies, to avoid
interference problems.

To avoid, that the tweeter comes too "early" and contributes
to good transient response of the system, you should mount the
membrane of the tweeter in the same plane like the dustcap or
whizzer of the fr, maybe even further back.
This is normally not achieved by front mounting both systems
on the same flat panel ...
Keep the offset variable so you can find the opimum offset
experimentally, it will vary with the crossover frequency chosen.

8 Khz may be good, if you can show me your driver, maybe i can give you some hints.

Cheers

gaust 27th March 2008 04:24 PM

Thanks for these quick responses and reassurances.

I had a feeling that there had to be something I was missing with just crossing in a tweeter with a capacitor as lots of people seemed to be doing it without a problem, and the rising impedance with frequency of full range drivers makes a lot of sense so my mind is at rest about that one, thanks Cal!!

I'm afraid that the fullrange driver is a bit of an unknown as it was bought off e-bay and I don't have T/S specs etc, but anyway it sounds quite good, and seems like a good place to start doing some experiments, which brings me to the using a helper tweeter.

The idea of getting the tweeter in the same plane as the FR drivers dustcap is not something I'd thought of but that seemes like a good idea. I was thinking about mounting the FR driver on a circular baffle that brought it slightly further forward than the tweeter.

As for the design again I was doing to experiment. My projects so far have included small sealed speakers using the Visaton FRS8, Cyburgs needle (FRS8 and Tangband W3-871) and Tabaq with the tangband. I was planning to try these in a sealed box to start with and then try them in a TL like the TABAQ and see what gives the best result.

LineArray 27th March 2008 05:18 PM

Quote:

Originally posted by gaust
.

The idea of getting the tweeter in the same plane as the FR drivers dustcap is not something I'd thought of but that seemes like a good idea. I was thinking about mounting the FR driver on a circular baffle that brought it slightly further forward than the tweeter.


bringing the fr forward by an additional spacer baffle is ok.

The edges surrounding the fr due to baffle or cabinet shape
should not be circular but asymetric. A protruding circular
spacer should not be a big problem, if the main baffle is asymetric
and larger as the spacer. Try to make the whole for the
fr conical to the back to provide as much free space between
magnet and baffle as possible. Otherwise you build a resonator,
its like a box in the box ... i say this because with the spacer
the whole might get very deep. Another solution is to
make a larger whole in the baffle, which just fits to the spacer
but is bigger than the fr basket diameter.
Try to design the spacer in a way, that the vertical distance
between fr and tweeter can be kept small although.

Cheers

RaphTube 6th January 2010 10:29 AM

Same Project
 
Hi, I'm about to do the same thing.
-add a tweeter to a full-range driver.

Unfortunately, like gaust my fr's are unmarked.
For interest's sake though, I'm using a ML-TQWT Enclosure.

I've never really fiddled with any sort of crossovers before (I usually stick to full-range), so I have little knowledge, and no experience here.

Those cap values are helpful, thanks.
But the tweeter's output is just too high.

Quote:

Originally Posted by LineArray (Post 1467955)
The tweeter has to be adjusted to the same output
level as the fr, usually this is done by a voltage divider.

How would this work?
Could I put a resistor across (parallel with) the tweeter, and the cap in series with both?

What about guideline resistor values?

Quote:

Originally Posted by gaust (Post 1467955)
Apologies if these are stupid questions

Always ask.
-Stupid questions are easier to handle than stupid mistakes.

LineArray 6th January 2010 05:48 PM

This is an example calculator for a voltage divider:

Voltage divider - loaded and open-circuit dB calculator damping volts potentiometer circuit impedance damping pad decibel dB voltage impedance bridging matching - sengpielaudio Sengpiel Berlin


The use of a parallel resistor for smoothing the impedance peak
of a super tweeter at its resonant frequency is allowed too,
but then there will be no attenuation in the passband of the
capacitor. In the crossover region attenuation may work, and
if the sensitivity of the tweeter matches it may be a minimalistic
and good choice even for the top end.

Everything is allowed as long as one knows what he wants to achieve.

Most important is to choose an appropriate crossover frequency for
the tweeter.

What is the difference between "assisting" a fullranger in the brilliance
region and building a conventional 2-Way ?

If your fullranger delivers a good presence region and the tweeter should
only add some "brilliance" the crossover frequency should be above
say 6 Khz ... attenuation and slope should be chosen in a way, that
the tweeter is not heard as an additional sound source.

To have the tweeter radiating from the same plane (or set back carefully)
is helpful.


Kind regards

chris661 6th January 2010 06:10 PM

For a crossover (component values) calculator, the best I've found is Passive Crossovers, Capacitor and Coil Calculator

There's even wiring diagrams (somewhere) on there for you aswell

PS, I'm keeping an eye on this thread. My recent floorstanders need more sparkle.

InclinedPlane 6th January 2010 08:20 PM

Quote:

Originally Posted by Cal Weldon (Post 1467912)
You wire them in parallel with your FR drivers. You don't have to worry about impedance drop as the impedance of the FR unit rises with frequency and you are cutting the tweeter off quite high so what the amp sees will be fine.

Well I'll be dipped in ****. I never knew that. And looking at the plots, they do indeed do that. If your fullrange driver is 13ohm at 6khz then you're all set!

dcathro 20th January 2010 12:27 AM

I am about to do this as well - add atweeter as a helper to a Supravox 215 OB EXC.

I have two tweeters that I can try a pair of Seas Exotic T35 1.5" Alnico domes with 94 db sensitivity, and a pair of Saba 4" alnico paper greencones that I have bought on ebay to try - no idea of the efficiency.

I am thinking of trying to have the -3db point at 6K where the 215 is losing power. I would also like to do this without using resistors.

If anyone has any ideas or suggestions, I would love to hear them.

Thanks

David


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