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Multi-Way Conventional loudspeakers with crossovers

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Old 14th August 2003, 06:19 PM   #1
gary f is offline gary f  Canada
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Default tweeter offset: pros and cons

I wonder if there is any trouble associated with placing the tweeter a little off centered from the woofer.

I am designing a small two way and I wish to place the tweeter 2 or 3 centimeters on the left (or right) of the central axis. Why?
For 2 reasons

1- To have the tweeter placed at differents distances from the baffles edges to reduce baffle diffraction effects.

2- I think it is a way to achieve a better phases coherence at crossover frequency. Placing the tweeter closer or farther to the listener is a way of controling the path length to the listener and adjusting phases coherence.

BUT: Like everything, there may be some problems associated. Maybe the image is worst or anything.

What do you think??
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Old 14th August 2003, 07:17 PM   #2
qwad is offline qwad  Australia
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OFFsetting the tweeter has very worthwhile benefits IMO as I FOUND OUT JUST RECENTLY BUILDING A PAIR OF IPL TL 3'S F for a friend, the sound stage and stereo image really opened up compared to speakers I had built previously which due to laziness were just in line downthe centre of the baffle I never thought it would make so much difference, from now on I will be building all future projects of set, My next project a 3 way tl based on the mcdonald tl in HFN&RR featured in JULY'91 issue using the seas 10"csx high end woofer with 2" alloy dome mids by LPG I picked up on ebay prior to going on holliday to hungary last month and a pair of gold dome vifa / SEAS TWEETERS, THROUGH A FIRST ORDER SERIES XOVER.... cheers and best regards to all TC
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Old 14th August 2003, 09:57 PM   #3
Vikash is offline Vikash  United Kingdom
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Offsetting tweeters is common in hi-end speakers, and is done exactly for the first reason you mentioned. I'm not so sure about your reasoning on the second point though. I don't think the path length will be altered enough in this way for any audible effect. In fact, the path length won't be altered at all, it will still be the same distance from the woofer right?, just at a different angle. I think that keeping the drivers close together on the baffle plane is important to create a close sound source point. Offseting drivers to alter the path length is done on a different plane, usually by insetting the tweeter in line with the rear of the woofer.
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Old 15th August 2003, 05:49 PM   #4
gary f is offline gary f  Canada
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What I mean is that the path from the tweeter to the ears of the listener change when you offset the tweeter. In the image attached, (view from the top) the path A is longer than B so the signal from the tweeter has a few msec more delay. This can be used to adjust the relative acoustic center between the tweeter and woofer.

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Old 15th August 2003, 06:43 PM   #5
Vikash is offline Vikash  United Kingdom
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Well i don't know much about this, but I'm still not convinced. Firstly, this assumes that you will not be toeing the speakers in. I don't know the usable axis spread for your tweeter, but it would seem that due to tweeters being directional, this would not be the way to go. Of course, I could be wrong.

In all the examples I've seen (e.g. LDC - V. Dickason), the tweeter is offset rearward, in line with the woofer magnet to accomplish what you want. This implies a more complex cabinet shape, and so the other way is to slant the baffle so that the tweeter is further away.

Besides, reducing diffraction effects is reason enough to offset your tweeter to the side. And IMO it looks better too. Uniformity in aesthetic design stinks.
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Old 15th August 2003, 07:27 PM   #6
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Hi there,

New to this particular group. Hello!

Vikash, if you consider that the wavelength of 2KHz and up is a few centimeters and less, then moving the tweeter further or closer to the ear, as you say assuming no toe in, will dramatically alter its received (key word here. The phase angle at the ear will be changed) phase difference. Moving a tweeter one inch away alters the phase of 2kHz by about 180 degrees. I think. Something like that.

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Old 15th August 2003, 07:57 PM   #7
gary f is offline gary f  Canada
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Quote:
Uniformity in aesthetic design stinks.
I agree

I do not completely toe-in my speakers in front of me (I can see the interior side pannel a bit). Of course, this is a matter of taste and depends of the speakers. (My drawing skills could be improved a bit) Anyway

Even one cm may be enough to adjust the phase of +-35 deg aprox. at 3500 Hz for example. So it is a good way for acheiving a good phase coincidence sometimes (for fine tuning).

Soon, the Week end will come!
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