Well, things are really starting to come together. I know it
seems like slow work, but I have to fit the construction of
the Imperials in with everything else that comes my way - eating, breathing, doing things around the house for my lovely wife etc.

All but completed the speaker enclosure/chamber, with drivers installed. Was putting some low level stuff through them, just sitting on the patio, just to warm up the drivers. No high frequency components at all, but you know, with the correct port, you'd have a helluva subwoofer pair, without the horn.

My query regards an earlier post (Getting ready to climb the mountain) where Braggi warned me of possible 'speaker decoupling', due to the woofers' low Fs.

Before I cut the bottom panel of the enclosure and hence establish the horn input vent (approx 60mm by my clacs guys), is there any way to circumvent decoupling by either increasing or reducing the gap? Should I load the chamber up with more filler or less?

Cheers,

Gary.

Glad you can see the light at the end of the Imperial tunnel, Gary. Some things to consider: are you using your speakers full range, for home use? PA or DJ? Sound reinforcement for live music? Low power tube amp or major wattage sand amps?

I do occasional DJ stuff and very small scale sound reinforcement. I never turn my power up since I'm usually in fairly small spaces or outdoors where high SPL would bring the cops quickly. I'm not worried about trashing my woofers. However: I read a JBL white paper that stated as fact: ..." if you send bass to your speakers below the tuning of the box, you WILL break woofers." (emphasis theirs) They recommended high pass filters with serious rolloff a few Hz higher than the tuning of the box. That's why so many pro audio components have 40Hz filters built in. (Also to protect speakers and amps from the occasional dropped mic.)

They were talking about bass reflex boxes but the point is more general than that. I think horn decoupling should be considered nearly as seriously, although I think the cost will be bad sound quality long before destruction of woofers. At low volume levels I can't imagine you'd ever break your speakers but we have to imagine you'll want to turn them up at some point. Be careful when you're doing initial testing and you should be OK.

I think I'd try no stuffing at all in the chamber and see if you like it that way. Posts I've read recently suggest a small amount of stuffing, such as stapling a single sheet of fiberglass insulation over the insides of a speaker box is roughly equal to no stuffing at all. Other opinions may vary.

Keep us updated and just be careful with the watts until you're confident your drivers are performing in a way you like. Glad the project is coming along.

Thanks again guys,
Definately a case of wait and see, thats the beauty of our game. At the moment, we are lining the interior with a thin layer of dimpled foam, I don't see the point actually, to many people it is just the done thing. My first set of the speakers, big floor standers with 15" woofer (approx 130 litre volume, no port) had no stuffing and the bass was great. In its latest guise, my new floorstanders (see website) has stuffing and I would say the bass is not any better. I'm considering taking it out.

The Imperials will be used as part of a full range system, eventually using active co's with co points ~700 Htz and 5000.

No worries, we will take it nice and easy, do various frequency checks at low volume. I have a great test cd, with tones starting @ 20, 30, 40 etc and on up.

Cheers,

Gary.

[quote author=DirtDawg  link=1130286952/0#3 date=1130429622]
... Dropping a mic is very bad and so is having Judas Priest drive a Harley on stage and putting one of your $400 wireless mics in the pipe and revving up the bike! You need an oil filter for that one. I recommend a low cut for any live mic situation ......... but, dropping somone else's mic sounds very cool if you have the headroom.
[/quote]

Good God, man! Have you had some experiences! Dawg, I'm so glad you're here among us. I straddle this audiophile/pro sound interest which the audiophiles think is crazy and frankly, doesn't seem serious enough for the prosound forums. It's great to hear comments from someone who's been there and is still having a great time experimenting.

Thanks for your input. By the way, have you considered writing a book of your experiences along with tips for the pro sound crowd? Two books maybe? I'd buy 'em. And maybe the film option.

Well, just to let you all know, Jake came down yesterday to do a bit more Imperialing, fit a few more panels together, drill a few more holes, and one thing led to another. We thought, what the  ;) and we ended up putting one of the horns together, screwed, but not glued (yes, did I not tell you we are screwing these beasts together), and minus the braces in the rear of the cabinet. The panel fit was near perfect, so that put a big  :) on my face.

Jake cobbled together his laptop and a thirty watt Technics 'A' class amp (interesting amp this one, I want to look into it a bit, for an 'A' class it runs surprisingly cool?). The first bit of sound was one of Jake's own pieces of dance music. The Imperial was sitting on my patio - steel roof etc. Immeadiately everything started to vibrate, the sound is owerwhelming. Later today, we will drag the speaker onto the lawn and give it a bit of a workout. Pics will be on the website shortly. Then, after a play, it will be dismantled for final finishing.

Thanks for your help so far, it's been exhausting but fun, and now we can hear what all the fuss is about.

Cheers

Gary.

Gary
did you ever say what you were using for drivers in the Imperial and any tweaks like the lining?
I still collect information on successes on the Imperial just in case the opportunity arises.

thanks
Guy

G'day Guy and guys!

Quoting from an earlier post - Getting ready to climb the
mountain, I provided the following on the drivers...

They are made in Taiwan and are branded - Redback.
The cones are reinforced paper. 15" diameter.

The following parameters are supplied...

Rated Input      100W RMS
Max Input         150 W
Impedence @ 300Hz   8ohm
Response         28 - 1.5kHz
Resonant Frequency  28Htz
Sensitivity 1w-1m     94 dB
Voice Coil Diam   49.5mm
QMS    4.29
QES     0.44
QTS     0.4
VAS     314.6L
Nett weight  5kg    approx 11 lb
Magnet weight  1.4kg   approx 3+ lb

The forum provided great advice regarding the driver
horn loading, i.e. the resonant frequency is too low for
the horn, and careful use of the volume knob will be
needed to avoid blowing up the drivers. With that in mind,
we decided to delete most of the wadding in the speaker
chamber, using a layer of dimpled foam in the apex of
the chamber only.

From here, it will be a matter of careful listening tests
to decide what the final internals will be.

The Imperials will be augmented by seperate mid+treb
enclosures and actively crossed over. My linear arrays
will do a handsome job for the initial 'play' , Jake is
assembling his own enclosures, still deciding on final
configuration.

Darn, why do I have to sleep. But if building the Imperials
is like chipping away at a mountain, then I'm chip happy.

Cheers

gary

[quote author=Valiant_ap6  link=1130286952/0#12 date=1131455777]G'day Guy and guys!

Quoting from an earlier post - Getting ready to climb the
mountain, I provided the following on the drivers...

They are made in Taiwan and are branded - Redback.
The cones are reinforced paper. 15" diameter.

The following parameters are supplied...

Rated Input
100W RMS
Max Input
  150 W
Impedence @ 300Hz   8ohm
Response
  28 - 1.5kHz
Resonant Frequency  28Htz
Sensitivity 1w-1m     94 dB
Voice Coil Diam   49.5mm
QMS    4.29
QES     0.44
QTS     0.4
VAS     314.6L
Nett weight  5kg    approx 11 lb
Magnet weight  1.4kg   approx 3+ lb

The forum provided great advice regarding the driver
horn loading, i.e. the resonant frequency is too low for
the horn, and careful use of the volume knob will be
needed to avoid blowing up the drivers. With that in mind,
we decided to delete most of the wadding in the speaker
chamber, using a layer of dimpled foam in the apex of
the chamber only.

From here, it will be a matter of careful listening tests
to decide what the final internals will be.

The Imperials will be augmented by seperate mid+treb
enclosures and actively crossed over. My linear arrays
will do a handsome job for the initial 'play' , Jake is
assembling his own enclosures, still deciding on final
configuration.

Darn, why do I have to sleep. But if building the Imperials
is like chipping away at a mountain, then I'm chip happy.

Cheers

gary


[/quote]
You could use this
http://www.sound.westhost.com/pcb/pp99.htm
But with a higher cutoff if you wish you can adjust the cutoff easily with a cap,should completely cure the over excursion.

Ohh, that chilly, chilli beer. Yeh, it's still chilly here, well relatively speaking of course. Fired up the new PC tonight, what a ripper, so just letting you know how things are going.

fantastic! One of the Imperials is more or less completed, painted in and out. Awaiting only the fitting of speaker connector, lifting handles (still not sure what to do with this one), and a plaque that will read 'Decware modified Jensen Imperial, by Jake and Gary 2005.'

The second speaker panels have been painted internally and are now ready for screwing and gluing together and finishing externally.

Pics you say....soon. They will be presented in all their glory on my website. Jake will hopefully pop down again before Xmas and we'll put in another few days labour and sorted.

Cheers,

Gazman, Chilli Beer drinker and Imperial builder.

What a difference a Jake makes  :).

My man made it down here last week, and even though he was feeling a little unwell, he put in a big days work, and now we have the second cabinet finished, all bar the filling and painting, which I can do now, at my leisure.

We fired them up of course, in tandem with my arrays, in 3 way active mode. Played only a few songs with the wick turned up, didn't want to hassel the neighbours. Generally just played around with a few tunes. Annoyingly, the music started to cut out a high volume levels, leading me to think my Playmaster amp was clipping, or worse - failing  ??? Then I realised, the CD player (we are using my son's Playstation 1 as a source, don't want to drag my Yamaha outside), was skipping from the vibration. Lesson: Dont use PS 1 for a source, place your CD player on a layer of foam or toweling.

So here they are for the moment, try this link. I will give a full write up on completion. Note the three back braces. The speaker chamber front panel will be enhanced with a nice cut of laminate surrounding the drivers, stained and varnished.

http://members.iinet.net.au/~toffees2/Imperial1.jpg

If the link fails, try my www.

Cheers,

Gary

Howdy Guy,
yeah, the weather is nice here, it's like this all year round. Sorry to rub it in. This summer has been our coolest by far, other parts of Oz have been sweltering. Even a bit of rain hasn't gone astray.
The dimensions are as per Imperial, minus a couple of mm to allow for the fact that we used 18mm chip, i.e. the horn dimensions are pretty much to plan, had to use some 22mm chip on the rear of the speaker chamber to bring the horn shape back into spec.
Jake is such a top lad, shame he and my daughter are no longer an item, but that is life, we progress and I'm sure that Jake will. He has good music plans, and now, he will have the speakers to deliver all his ideas in Kodachrome sound. They will probably be shipped up to his pad in Perth around the end of the month, though I'm sure that if they need a baby sitter, if he goes travelling, they will have a nice spot back at my house.
On the subject of 'house', I'm thinking I might grab the 'Housewrecker' plans off Steve, probably go for the 2 x 15" cabinet. The drivers in Jake's Imperials, though some might say are a little underpowered (120 or so watts rms), should be ideal for a loungeroom, and from what I have read, I could probably design the box to shape up as a nice bit of furniture.
These plans by the way are going to go on hold until at least 2007. A trip to Europe (I was born in England), World Cup soccer, and an attempt to manufacture, cast, plastic telescope mirrors is my next venture. Its worth a shot, isn't it.
Wish me success.
Oh, by the way, Jake bought me a plunger Router for Christmas, what a tool it will be, can't wait to fire it up on the new project.

Cheers,

Gary.