Lockwoods in da house! - advice please

[JohnJo]

Just typed a whole load of stuff in here then accidentally deleted it - raging

Anyway, quick recap and update for those that are interested.

In many ways these speakers have been a mixed blessing, a bit like Turkish Delight, full of (eastern) promise but not very palatable at times.

They have worked best at low volumes where the bass has been in best proportion to the mids and treble but with rising volume bass output didn't seem to keep up. Took me a long time to work out that it wasn't necessarily bass *weight* but more importantly dynamism. I found myself sticking with the richer recordings in my collection but I was missing a lot of good, not so well recorded, stuff.

Other things that were bugging me were centred around amplification. When guys who's opinions I thoroughly respect like Geoff (Walpurgis) who have a lifetime's experience of Tannoys were recommending solid state amps and working with 20watt SS amps themselves how come every SS amp I tried sounded dead as a door nail and 25watters like the Firstwatt M2 were totally under-powered? And why was my Primaluna with it's low damping factor the only amp to bring these speakers to life when guys like Paul at RFC were saying that HPDs need an amp with a high DF? I've tried some SERIOUS amps with these and the Primaluna trounced them which made NO sense at all, Luxman 590AX, Albarry etc. Last straw was last weekend when I tried a Naim Supernait 2 which is also known to be no slouch but again no magic

The virtually unique thing about this incarnation of big Tannoys is that they are a sealed design and hence heavily acoustically damped. The only other unported ones that I know of are the equally rare Tannoy Mansfield. The Lockwoods are also heavily lined inside with wool sheets about 2" thick adding to the effect. In a moment of inspiration I took the mounting screws out of one side of the crossover panel and pushed it inside the box, creating an opening of about 5/8" x 3" in the rear of each speaker and pressed play
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1. Seemingly increased volume (higher sensitivity?) but subsequently checking using a db checker on my phone showed peak levels the same at a given position on the volume position for sealed and open cabs I'm certainly listening with the volume control in a considerably lower position now.

2. Increased bass weight and POWER.

3. Improved sound stage width and depth. Also imaging has taken on a new level of in-the-roomness for vocals and particularly instruments.

4. Richer, more natural tonality overall along with an ease in the presentation that's hard to put into words.

5. Improved resolution and detail. Breaths and movement of performers are suddenly noticable.

6. Once CDs go on now they play to the end

7. The amp is now sounding how you would expect it to, full and fruity, particularly in the bass and I can't help thinking SS is the way to go.

The whole thing just seems to breathe now in a way it never has.

So, how do you calculate an optimum bass port diameter, length and position?

[walpurgis]

Interesting result John.

There numerous port calculators online, such as this: http://www.mh-audio.nl/reflexboxcalculator.asp

[JohnJo]

Interesting result John.

There numerous port calculators online, such as this: http://www.mh-audio.nl/reflexboxcalculator.asp

Ah, that looks complicated

The Academys are virtually identical in size to the Tannoy Berkeley which uses the HPD 385 driver too. They seem to have a couple of what look like 2" ports on the front at the bottom.

[Qwin]

I didn't realize Tannoy did sealed enclosures for HPD drivers.

Tannoy's specification says the HPD 385 has an Fs of 22Hz and a Qes of 0.2

This gives it an EBP (Efficiency Bandwidth Product) of 110 (Fs/Qes)

Roughly speaking a figure of:
0-50 is meant for sealed only
50-90 is for either
90-200 is for ported only

So based on the Tannoy figures the HPD 385 is best suited to a ported enclosure.

On Hans Hilberink's site he also shows some measured results after a re-cone, using the added mass method of Fs14.7 Qes0.19 = 77 EBP which would suggest it would suit either type of enclosure. But nothing to suggest the driver/surround was run in before testing.

Make what you like of those figures.

Normally, if keeping a flat response with Qtc 0.707 an optimum ported enclosure would be much larger than an equivalent optimum sealed design. The ported version would go considerably deeper though, up to an octave in some instances, dependant on the port tuning of course.

The on-line calculator Walpurgis links to isn't as daunting as it first appears, once you start populating the fields.
There are others which look friendlier, but you will still have to enter box volume, desired tuning frequency, number of ports, etc.
The airspeed, to avoid port noise, adds extra parameters and if you are going to flare the port entry/exit you will need to take this into account for overall length. All the information you need is out there in one form or another.

[JohnJo]

Thanks Ken, that's great info. I'm out and about today but will hopefully have a go at the calculator later using these values then report back to get your advice if that's ok?

[Qwin]

There are plenty of people on here with more experience than me, but I will help where I can.

[JohnJo]

Right, here we go, bear with me as this may contain nonsense

Here's the original brochure for the Lockwood Academy, admittedly with the DC 386 driver but cabinet dimensions are the same.

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If we subtract 20mm all round for the cabinet this gives internal dimensions of 47 x 22 x 72.5 cm which equals 75 Litres. The brochure quotes 68L so I assume they are assuming 7L for the driver, crossover, bracing etc. which seems reasonable. We will input this data into the online calculator.

Here are the T&S parameters from Tannoy. We will use this data since my drivers were completely reconed by Lockwoods and should be close to factory specs, rather than using the measured values of a driver with replaced foam but original soggy suspension. The only measurement I am using from this table is the driver diameter of 32cm as I can't be bothered to open up the cabs to take my own measurement and it sounds about right anyway. These tables are both from the hilberink site.

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[JohnJo]

Plugging these into the online calculator we get:

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I've manually inputted the port diameter of 9.9cm as this was the closest commercially available size to the 9.61cm originally suggested by the calculator.

How does this look to everyone?

[JohnJo]

Just ran the data for the sealed cab on the simulator. The dimensions are different from my actual speakers in both the sealed and ported examples as it suggests these itself once you put in the volume but don't think it matters as the volume is the same. Can anyone explain the expected differences between the ported and sealed cab from the results of these models? I don't understand the meaning of the "calculated performance" figures. Thanks.

P.S. Good simulator Geoff and thanks Ken for getting me started with the data

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[Qwin]

Hi John
I ran the same program last night, only I guessed the cab volume and got similar results to you.

I have heard it said that Tannoy drivers don't model well and that what works in the real world can be substantially different.
This would seem to be the case as it is suggesting an ideal ported volume of 68L, for a 15" driver!
Also the performance calculator shows an F3 of 58.63Hz which is not deep at all, my 4" Quad bookshelves will better that.

Increase the cabinet volume to say 90L (you can force it) and the F3 point comes down a bit, but still not great.

In case you do not know what F3 is (apologies if you do) it is the industry standard for stating how low a speaker will go.
All speakers will produce fairly deep bass, but it is the level of output that is important, as to whether we hear it. The frequency response will tail off in volume the lower you go and the industry decided that at a point 3dB below the nominal flat level, this would be the point to quote in the specs as a standardized and realistic audible level.
A 3dB reduction will half the volume level.
So that's the bass level quoted in the calculations.

This might be of use to you, Tannoy used to do DIY kits for the HPD series, you could buy the drivers/crossover and build your own cabinets.
They supplied dimensioned drawings for these including ports and based the 15" cabinets on Arden(175L) and Berkeley(98L) equivalents, presumably tuned for the same or similar results.
Find the HPD Technical Manual here: http://www.teknomage.co.uk/tannoy/
Check out the first two cabinet drawings.

As built by Tannoy:
The Arden had an F4 of 30Hz
The Berkeley an F4 of 35Hz
(Tannoy used a figure of -4dB in those days)

Hope that helps in some way.