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Mullard speaker box strange impedance resonances
Mullard speaker box strange impedance resonances
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Old 14th March 2019, 06:50 PM   #11
turk 182 is offline turk 182  Canada
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well if the original size of the box is too big as in too much bass reduce the cubic volume (either cut the box size down or start filling space with solid objects to reduce the volume)

without a proper understanding of what U-U-U-U is i'll have to assume that it's either resonances or breakup modes that are occurring because the driver is not adequately damped at low frequencies in general (forget driver resonance for the moment) what your looking for at the moment is to find a volume of air that acts like a spring against the back of the driver to prevent it from flying to the end of it's travel at low frequencies and yes the resonant point of the driver does generally turn out to be the first place it occurs but if the "air" spring doesn't increase as the frequency decreases it will cause driver damage or go active and high pass it.
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Old 14th March 2019, 06:54 PM   #12
turk 182 is offline turk 182  Canada
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when these thing where designed "tubes" where the standard and "variable damping" was the new "in" thing...

i really have been around tooo long....scotch time!

Last edited by turk 182; 14th March 2019 at 06:56 PM.
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Old 14th March 2019, 08:26 PM   #13
planet10 is offline planet10  Canada
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Mullard speaker box strange impedance resonances
If what i remember of the 9710 their high Qt means they are not suited to reflex enclosure which is what the impedance curve indicates. THis box is a poorly designed attempt at periodic but they did not go far enuff (and as a vented box i expect poorly designed (ie from before T/S made it a lot easier). You need to stuff the crap out of that box to push it towards or make it aperiodic.

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Old 14th March 2019, 09:12 PM   #14
Galu is offline Galu  Scotland
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An aperiodic enclosure would produce a single impedance hump of low amplitude.

In accord with Dave's suggestion, but instead of stuffing the c**p out of the box, you could convert the large open vent in the original enclosure design into a resistive vent.

This can be done by stapling a thick sheet of acoustic fibreglass over the inside of the rectangular opening. If found to improve the bass, a more substantial resistive vent can be fashioned by sandwiching the fibreglass between metal mesh sheets.

Having said that, my recommendation to block off the vent entirely to see how the speakers behave in a sealed box still stands - that's worth trying first as we're fumbling in the dark here!
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Old 14th March 2019, 09:22 PM   #15
freddi is offline freddi  United States
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Mullard speaker box strange impedance resonances
9710 should be nice in a Karlson 12
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Old 14th March 2019, 10:37 PM   #16
VaNarn is offline VaNarn  Australia
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Mullard speaker box strange impedance resonances
Firstly, the Mullard/Philips enclosure designs are from a period when T & S parameters were basically unknown.
Secondly, the Philips 9710, whilst being an exceptionally good speaker design for its day, will have aged and possibly be in need of some remedial attention. This would require new braided tinsel wires, checking that the corrugated wave spider has not collapsed inwards and painting the outer paper surround with a suitable latex coating.
Based on the parameters from the Troels' site , the enclosure internal volume should be in the vicinity of 125 litre, for two speakers in the one enclosure and this should be 'tuned' to around 40 Hz.
As far as adding damping material to overcome the high Qts figure, the safest way to do this is to fix a wad of Tontine fibre (25mm thick) directly behind the speaker frames, just like a teapot cosy. This will alter Qm slightly and on the downside will add to the box losses; however this is less of a tradeoff than killing the vent output.
The 9710 can be a little forward in its' sound characteristic at the higher frequencies and a slot diffuser of a modified Kolster-Brandes type as described by Gilbert Briggs
in his book ''Loudspeakers" is a useful tweak.

Last edited by VaNarn; 14th March 2019 at 10:37 PM. Reason: grammar
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Old 14th March 2019, 11:39 PM   #17
planet10 is offline planet10  Canada
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Mullard speaker box strange impedance resonances
Quote:
Originally Posted by Galu View Post
An aperiodic enclosure would produce a single impedance hump of low amplitude.
If it were perfect it would almost completely flatten the impedance bumps.

Click the image to open in full size.

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Old 15th March 2019, 12:24 PM   #18
Galu is offline Galu  Scotland
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Quote:
Originally Posted by planet10 View Post
If it were perfect it would almost completely flatten the impedance bumps.
Absolutely - nice illustration!

For Powerpz's benefit I'll explain that 'aperiodic' means 'without period' - i.e. 'without frequency' of resonance. In practice, aperiodic loading reduces the height or 'Q' of the impedance hump exhibited by a driver when it resonates at its natural frequency. True aperiodic loading would eliminate the resonance hump entirely.

Powerpz may care to experiment with the suggested methods of reducing the 'Q' in his enclosure - i.e. either by employing a resistive vent or, as helpfully suggested by VaNarn, by stapling a pad of wadding tightly over the rear basket of the drivers.

Basically, he has to fool the drivers into thinking they are in a larger enclosure.
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Old 15th March 2019, 01:23 PM   #19
turk 182 is offline turk 182  Canada
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gotta ask...would reducing the enclosure volume be worse because if i'm incorrect i'd like to know!?
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Old 15th March 2019, 03:38 PM   #20
Galu is offline Galu  Scotland
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Quote:
Originally Posted by turk 182 View Post
gotta ask...would reducing the enclosure volume be worse because if i'm incorrect i'd like to know!?
Referring back, powerpz said his enclosure volume was 93 litres. Then VaNarn said the volume should be 125 litres.

From the above information I assumed that the enclosure required to be bigger rather than smaller.
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