Diffraction - coaxial tweeter?

[Serow]

I have a 7 inch "full range" driver and a small tweeter that I'd like to mount coaxially in front of the full ranger, something like the following:

An externally hosted image should be here but it was not working when we last tested it.

From my reading, an obstruction with a size less than the wavelength of interest is basically invisible, as the sound wave will diffract around the object.

In my case, the size of the tweeter is about 4 cm and therefore theoretically should not affect the output of the full-range until around 6000 Hz. Do you think that mounting the tweeter in this manner will be detrimental to the sound of the full range driver?

I was also thinking of adding a layer of absorptive material to the back of the tweeter to reduce high-frequence reflections.

Thanks,
Eric

(P.S. planet10, the drivers look great and were packed superbly. Cheers.)

 

[sreten]

In my case, the size of the tweeter is about 4 cm and therefore theoretically should not affect the output of the full-range until around 6000 Hz. Do you think that mounting the tweeter in this manner will be detrimental to the sound of the full range driver?

I was also thinking of adding a layer of absorptive material to the back of the tweeter to reduce high-frequence reflections.

The results from the arrangement in the picture would be very poor.
But you say your tweeter is only 4cm diameter which should be OK.

One option is to remove the drivers dustcap and mount the tweeter
on an extended pole piece, airflow needs to be smooth.

But there are cogent reasons not to mount the tweeter in such
a fashion if you are running the main driver full range without a
crossover.

What crossover arrrangments are you thinking of ?

sreten.

 

[Serow]

Re: Re: Diffraction - coaxial tweeter?

But there are cogent reasons not to mount the tweeter in such
a fashion if you are running the main driver full range without a
crossover.

What crossover arrrangments are you thinking of ?

sreten.

Thanks for the reply. The crossover, if it can be called such, will be a series cap for the tweeter with a crossover point of 4000-6000 Hz and the main driver will be run wide open.

I was thinking that I should mount the tweeter as close to the main driver as possible. As far as lobing goes, where should the tweeter be in relation to the main driver - above, below, etc?

Eric

 

[sreten]

If the drivers are not too high directly below as close
as possible will probably give the best results.

You should also consider attenuation of the tweeter
for good matching.

sreten.

 

[planet10]

I've got a set of 8" whizzer full rangers, i was going to play with co-axially mounting the same tweeters to.

I was thinking of just building an "H-shaped" cross piece which the tweeter sits in the middle of, and adding ductseal to the back of the T to give it a nice smooth shape (even naked they aren't a bad shape). This assembly would then just velcro to the cabinet. I'll also probably continue my tweeter phase plug experiments with these.

dave

 

[SpeakerBob]

what about using 4mm metal rod rather than wood etc, and welding/ epoxying the tweet to that ? (possibly some kind of drawer handle could work?

The mounts for the Linn speaker's tweet/supertweet would be bigger than a rod.(I'll post a link in a sec..)

Rob

edit link and pic:

http://www.linn.co.uk/spec_sound/pr...speaker&refererURL=http://www.linn.co.uk/#174

 

[Serow]

Dave, I was initially planning on using an appropriately-sized metal door pull to mount the tweeters coaxially. Just bolt the tweeter on one side, and screw it to the enclosure right beside the FR.

Are you still using foam ear plugs to make the phase plugs for the tweeters? How does the existing dust cap come off?

Also, where did you find the ductseal - the stuff I've found has a quite liquid composition that wouldn't seem to hold itself together on the drivers.

ERic

 

[planet10]

Are you still using foam ear plugs to make the phase plugs for the tweeters? How does the existing dust cap come off?

Yes, still playing with them. I use a heat gun to lossen the glue and then pry it off with a knife.

Dusctseal should be avalable at heating/air conditioning supply wholesalers.

dave

 

[Brett]

I was thinking of just building an "H-shaped" cross piece which the tweeter sits in the middle of, and adding ductseal to the back of the T to give it a nice smooth shape

Something like this? They sound quite good, better in some ways than my 12" red.

 

[konut]

Heres a company that uses this technique for some very well reviewed pro studio monitors. http://www.me-geithain.de/index.html

 

[AJinFLA]

It can be done. Just hope when folks are trying this stuff that they have at least some measurement capability. The key is to match the directional output of the drivers in question as not to create valleys in your radiated power. Then again, if you like fullranges, this or time alignment, etc. may be of no concern. Good luck.

Cheers,

AJ

An externally hosted image should be here but it was not working when we last tested it.

An externally hosted image should be here but it was not working when we last tested it.