Bill Fitzmaurice

[quote] I will be building the 1x12 very soon and intend to put a piezo in it. [/quote]One is insufficient. Part of the reason why commercial cabs with piezos sound bad is that they don't use high pass filters, the other is that they don't use enough of them. At the minimum you want two piezos per woofer, vertically aligned, wired in series for one pair, banks of series/parallel for more than one pair.

[quote name='Kevin Dean' timestamp='1472980546' post='3125674'] How hard can it be ? [/quote]A lot harder than you think. First off, I'd use either a midrange driver or a tweeter that can run to 2kHz. The usual tweeters used in bass cabs go no lower than 3.5kHz, if that, making them more useful for creating hiss than anything else. Then there's the matter of the crossover. Designing a crossover is a skill only perfected with years of experience. Yes, there are off the shelf crossovers, but they aren't very good. There are on-line crossover component calculators, but they're far too elementary to give a good result.

[quote name='tauzero' timestamp='1472736162' post='3123771'] I think they missed a trick not making it bridging. [/quote]It was bridged. Each 250w amp consisted of two bridged 62.5w amps. You can't bridge twice, and even if you could the minimum impedance load would have been raised to 8 ohms anyway.

They're not optional, they're critical. I should imagine your tone is very boomy without them.

That would work.

[quote name='bassman7755' timestamp='1472300606' post='3120158'] IME even budget floor standers sound much better than quite an expensive subwoofer + shelf/satellite speakers setup. [/quote]That's the opposite of my experience.

I use one channel of a Fly into an 8 ohm 1x12, but it's a high sensitivity Jack 12 cab, not your garden variety box. Depending on what your Hartke are a pair of them, one per channel, may be OK.

[quote name='Biglump' timestamp='1472301376' post='3120163'] I'm thinking of making my own because there doesn't seem to be any 4 ohm 100 watt extension cabs around. [/quote]Why 4 ohm? And why 100 watt?

[quote name='bagsieblue' timestamp='1472203893' post='3119363'] I'd like to think it's a debadged readily available option.... [/quote]It may be, but we can't look inside your cab. Confucius say "picture worth thousand words".

[quote name='Helderius' timestamp='1472133508' post='3118777'] Yes, it is open back. [/quote]I'd suspect the speakers.

In that case it's not a microphonic tube. Is this an open back '59 Bassman reissue? Despite the Bassman name they're guitar amps, useful for bass only at very low volume.

The short answer is that you want to use your bass speaker as part of a hi-fi, and where both response and low frequency extension are concerned bass speakers are very low-fi. Use the right tool for the job, in this case a hi-fi powered sub.

[quote name='MoonBassAlpha' timestamp='1472042537' post='3117929'] That's not quite what I meant Bill, I meant the rear-facing speaker is also open to the air, just facing backwards, or even upwards or downwards. [/quote]Without a picture I can't be sure of what you mean, but on the face of it that's not an isobaric alignment.

Possibly a microphonic tube. To test turn the amp on with no instrument plugged in, volume halfway, gently tap each tube with a pencil. If you have a microphonic tube you'll hear it.

[quote name='MoonBassAlpha' timestamp='1471871112' post='3116532'] Could you run an isobaric cabinet with the speakers magnet to magnet, one facing forwards, one facing backwards, both emitting sound? [/quote]Technically they don't both emit sound. The area of only one cone is exposed to the air, so the maximum output with two drivers isobaric is the same as with one in a standard configuration. The only advantage is a halving of the Vas, but due to the space taken up by the second driver and the connecting plenum chamber the net cabinet size is not halved, while cost is greatly increased by using two drivers. That's why manufacturers in general have not jumped onto this particular band wagon.

[quote name='Twincam' timestamp='1471788894' post='3115857'] I'm using maths and a very simple port tuning program. [/quote]Why? I could see it to some extent if modeling software was a major investment, but as it's free I can't comprehend not using it.

The tuning is the same as with a standard cab. The modeling software will take into account that it's an isobaric alignment.

Having done studio work during that period my first hand experience was that studios dumped most of the valve gear because they didn't want to be perceived as having fallen behind the technology curve. This was during the same period when they were changing to 16 and more track tape decks and consoles that were designed for the studio, rather than broadcasting. There was a 'clean sweep' attitude, and to their later regret many a perfectly good baby ended up tossed out with the bath water.

[quote name='Beer of the Bass' timestamp='1470841717' post='3108873'] Will they, though? It seems there was a period of uncertainty from the mid 80's to some time into the 90's when US and western Europe stopped production, but if anything they seem to have undergone a resurgence since then. It's not just Russia and China either - JJ are successfully making them in Europe under all of the environmental restrictions that go with that. So I would be surprised if they disappear within my lifetime. [/quote]The only use for them is in amps. As demand for valve amps goes down prices on valve amps and valves will continue to rise, further reducing demand, further reducing production, further increasing price in a literal death spiral. That can only make vintage valve gear, or at least what will be vintage someday, appreciate in value. A comparison can be drawn to Fairchild valve compressors, the studio standard of the 60s and 70s. After SS took over the compressor market studios literally tossed Fairchilds into the trash bin. Now those which remain command the same price as a very nice car. For instance: http://www.analoguetube.com/#!Vintage-Fairchild-670-For-Sale-44000/c1czm/5576e3fc0cf2312d79783c31 I doubt that valve amps will appreciate that much, but one never knows. .

[quote name='M@23' timestamp='1470836822' post='3108832'] Really? They're not exactly hard to come by and seem to sell 2nd hand for the standard 60% (ish) of retail. [/quote]Wait 20 years, when valves have gone the way of the dodo.

Keep it, if only to hide it away and appreciate in value.

It won't go as loud down low as a driver with more xmax. The difference between a small vented cab and the Jack would lie in the midbass and low mids, where the horn of the Jack greatly increases sensitivity. If you want to get a lot more output down low you'd have to go to a longer xmax driver. A 3012HO, for instance, would have 6dB more output down low, the equivalent of two EVM. If it was me I'd sell the EVM, they do bring a good price from guitar players.

[quote name='MoonBassAlpha' timestamp='1470133430' post='3103429'] Would an EVM12L work well in a JackLite 12 Bill? [/quote]It will, about the same as with a 3012HO as far as response goes, although the 3.3mm xmax is less than optimal.

The DL15x was a later version of the EVM15B. A good driver, though weighty. Specs are Fs 42Hz, Qes .3, Qms 4.5, Vas 195L. xmax 4.1mm. Pe 400w. It would be fine in the Simplexx 15 or Jack/JackLite 15 cabs.

[quote name='Huge Hands' timestamp='1469775844' post='3100925'] What, bury him in a car park? [/quote]I was thinking of giving a headsman a bit of work, but the parking lot will do.