Low down tweeters

[Covenant]

Why do some manufacturers defy the accepted wisdom that tweeters should be
near the top of speakers? :(
I have just got a pair of Mission 780SE and would have turned them upside down as the tweeter is underneath the bass driver but there is some damage to the finish on the underside. It's probably fixable but a nuisance to have to do it.

[Stratmangler]

In the Middle Ages it was accepted wisdom that the earth was flat, yet the Ancient Greeks (2000 years earlier) had worked out that the earth was round, so what does that say about accepted wisdom?

The designers at Mission have used D'Apolito (http://stereos.about.com/od/glossaryoftermsd/g/Dappolito.htm) configuration for quite some time, and have decided at some point that within the criteria of their design that it makes little or no difference whether the tweeter is above or below the mid-bass driver.

[hifi_dave]

Ideally, a tweeter should be at ear level, so in a tall speaker it might need to be some way from the top of the cabinet.

[Covenant]

Thanks chaps, the Mission speaker arrangement is to have the bass driver at the top, tweeter below and port below and to one side of the tweeter. Would this still be D'Apolito?

[Stratmangler]

Would this still be D'Apolito?

No, but the integration between the drivers would be similar to that of a D'Apolito configuration.

[walpurgis]

D'Appolito was just a bloke who stuck his tweeter between two driver, be they mids or bass mids. Hardly novel, or his own idea. It had been done many times before. I used the same layout myself, long before it was labelled with his name.

It has also been done with multiple drivers, with the tweeter central to three, four or more, bass mid units.

[Beobloke]

The acoustic centre of a (dome/ribbon) tweeter is flush with the front of the cabinet as the drivers themselves are so shallow, but the acoustic centre of a coned driver is at the top of the voice coil.

When the woofer is below the tweeter, the acoustic centres are offset as the woofer coil is a few inches behind the plane of the tweeter, so the overall sonic output of the speaker is effectively directed slightly downwards, whereas if you reverse this, it points slightly upwards. A D'Appolito configuration evens it all out and the normal acoustic plane of the speaker is in line with the baffle once more, or so the theory goes.

It's not a new concept - some old B&W speakers and the Leak 3000 series had stepped baffles, which aimed to achieve a similar result by bringing the cone drivers forward to line up their acoustic centres with the tweeters.

[Rare Bird]

Leak '3020'

[Sonority]

Are these upside down then ?

http://blog.stereophile.com/rmaf2009/Dynaudio-450.jpg

[hifi_dave]

Are these upside down then ?

http://blog.stereophile.com/rmaf2009/Dynaudio-450.jpg



Most probably - unless the listener is laying on the floor.

[Sonority]

No need to lie on the floor with those Dyns - The Consequence are designed that way ;)

[hifi_dave]

Obviously, or they wouldn't be made that way.

[Mr Kipling]

Back in the '70s (man), some manufacturers suggested using small standmounters either vertically (as normal) or horizontally (with the tweeters innermost). This was mentioned in the instructions that came with my Castle Richmond IIs. Trying it did widen the stereo image somewhat, but I went back to using them in the conventional way.

[walpurgis]

Just buy Tannoys and stop worrying!

[Reid Malenfant]

When the woofer is below the tweeter, the acoustic centres are offset as the woofer coil is a few inches behind the plane of the tweeter, so the overall sonic output of the speaker is effectively directed slightly downwards, whereas if you reverse this, it points slightly upwards. A D'Appolito configuration evens it all out and the normal acoustic plane of the speaker is in line with the baffle once more, or so the theory goes.
Spot on, due to the differences in the distances between the voicecoils & your ears the sound at or very near the crossover frequency tends to be beamed in one direction.

This can be counteracted somewhat by using an odd order crossover feeding the tweeter, such as 18dB/octave - which shifts the phase slightly.

[Covenant]

I tried turning the speakers upside down and it didn't make much difference. Must be something in the theory....

[Mr Kipling]

Spot on, due to the differences in the distances between the voicecoils & your ears the sound at or very near the crossover frequency tends to be beamed in one direction.

This can be counteracted somewhat by using an odd order crossover feeding the tweeter, such as 18dB/octave - which shifts the phase slightly.

The Scarlet Pimpernel!

Sorry if I've missed other postings, but been a bit distracted.

Hope your appearence is a bit more permanent!

[DaveK]

Jerry,
Reminds me of a recent post on here where someone (I forget whom ;) ) started a thread about why it was the generally perceived wisdom that tweeters and super tweeters should be at ear height and pointing directly at the ears.
Dave.

[Reid Malenfant]

The Scarlet Pimpernel!

Sorry if I've missed other postings, but been a bit distracted.

Hope your appearence is a bit more permanent!
:lol:

Yes it should be.. My lappy popped & I had loaned my other to a friend...

Needless to say I now have two other spare laptops, nothing like making sure eh? :rfl:

[Mr Kipling]

Found this for you, Dave.

[Covenant]

Jerry,
Reminds me of a recent post on here where someone (I forget whom ;) ) started a thread about why it was the generally perceived wisdom that tweeters and super tweeters should be at ear height and pointing directly at the ears.
Dave.

Well you can see I have a train of thought going through my noggin Dave. I have had a bit of time on my hands the last few weeks so have played around with speaker positions, diffraction etc. It's not cost much and it's been fun.

[DaveK]

Found this for you, Dave.

Gee, t'anks for that! ;) Somewhere on one of our PCs I have another pic of (my) same cat that I've been meaning to use as my avatar - I'll see if I can find it.
Cheers :cool:

[Stratmangler]

I have had a bit of time on my hands the last few weeks ...

Surely not?
I hadn't noticed ;):cool:

[Covenant]

Surely not?
I hadn't noticed ;):cool:

The joys of being self employed....

Off on a training course next week so that will put a stop to all this speaker fun!