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Old 29th January 2006, 01:32 AM   #1
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Default Acoustat Spectra Delay Line - Any Experts?

I just picked up a neat old pair of Spectra 3's and notice they use some sort of a delay line where the inside panels that run 'full range' or have the treble reponse and are delayed from the the two outside lower range panels. I've only had them hooked up for a few hours and am already getting curious in knowing more about this configuration. The speakers actually seem to be fairly full range with out the crappy little 10" bass driver - Maybe down into the low 40's strong. What I'm wondering is how is this delay done? What I planned on doing was biamping the panels and splitting the signal between the fullrange ond low range panels. Without measuring it sounds like around 400 cycles.

Has anyone here biamped to the delayed panel with the Spectra 3 or 4 Acoustats? (not the 10" woofer)??? Did you keep the delay intact? How are they wired for the delay?

The speakers sound pretty good stock, fast like my horns but a bit more coherant. Much better than the 1+1's, Innersounds or Martin Logans I've had - They reproduce the upper bass and low midrange very well - Sure suck some power! I'm used to 100 db+ sensitivity.. I'm just thinking about biamping and would enjoy any feedback.
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Old 31st January 2006, 08:25 PM   #2
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I took them apart - the only way to biamp them requires another pair of Medallion transformer per speaker. Seeing they are ultra expensive I don't think it's worth the expense to do this - just use a bigger amp........
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Old 2nd February 2006, 09:11 AM   #3
AW is offline AW  New Zealand
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Spectra "delay lines" are not delay lines at all. Only the QUAD 63 and it's new children use delay lines.

The Spectra solution is very simple. The inner panel is driven full reange - with the outer panel(s) driven through high value resistor(s) to roll off their trable response - adding their energy to the lower frequencies.

I have a pair of Spectra 11's that I use without the BS woofer - they sound really graet - especially for the $200 I paid for them!

Allen
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Old 2nd February 2006, 09:43 AM   #4
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Quote:
Originally posted by AW
Spectra "delay lines" are not delay lines at all. Only the QUAD 63 and it's new children use delay lines.

The Spectra solution is very simple. The inner panel is driven full reange - with the outer panel(s) driven through high value resistor(s) to roll off their trable response - adding their energy to the lower frequencies.

I have a pair of Spectra 11's that I use without the BS woofer - they sound really graet - especially for the $200 I paid for them!

Allen
There is a (claimed by acoustat) slight 200 ms (mid/bass delay in the Spectra 3 from the resistor network. These use a 3 panel system with fullrange, middle/bass, and bass only panels. Tone and projection size is very good but dynamics are muted though - or compressed. These serve as a good reminder of why I have gone to full range horns. I agree with the dynamic woofer - what a joke! The three panels have excellent bass up to a certain point then fall apart. I'm driving them with a 485 WPC/4 Ohm beefy SS amp. As they get turned up to live levels the dynamics compress. A very nice speaker for someone into jazz at low to moderate volumes - I bought these for $130.00
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Old 2nd February 2006, 05:18 PM   #5
gnnett is offline gnnett  New Zealand
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Hi Allen

Are you running the Spectra 11 transformer full range also, or using lower frequency cut off than factory to your sub?

Regards

Grantn
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Old 5th February 2006, 02:02 PM   #6
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Quote:
Spectra "delay lines" are not delay lines at all. Only the QUAD 63 and it's new children use delay lines.
Allen, of course the RC low-pass filter formed as a result of the series resistor before the Acoustat "bass" panels will have a group delay. And, as Magnetar mentioned, this was alluded to by Acoustat as a design consideration. By the same token, the delay lines in the Quad 63 and its successors also are low-pass filters, so that each concentric ring has more roll-off of high frequencies than the preceding adjacent inner ring. The combined effect of the delays and the frequency tapering yield the desired radiation pattern and on-axis response in both speakers. It must have taken a lot of iterations by Peter Walker to get it right in the more complex 63.

Still I agree that Quad made an attempt at a classic lumped-parameter delay line while Acoustat took the more traditional crossover approach.
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Old 7th February 2006, 07:25 PM   #7
AW is offline AW  New Zealand
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Grant,
>Are you running the Spectra 11 transformer full range<

Yes - even though Andy Svabo warms against it.

> or using lower frequency cut off than factory to your sub?<

Most of the time I don't even use a sub, but even when I do the ESL's don't get rolled off.

Allen

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