Welcome to the forum. If you are looking at building the Imperial SO (Sub Only) from plans, you are going to have to wait until Steve D. puts them on the site. He is still working on them. Can't wait until he does post them.

If you are looking at building the regular Imperial it can be found at this link:
https://www.decware.com/imperial.htm

and then click on Get The Plans at the bottom of the page.

Hope this helps you out. I built the regular Imperial and use it as a sub for my PA system and it is great. Lots of tight fast bass with the 15" speakers in it (Goldwood and Peavey).

ok so if i buy these plasns i wont be disapointed with the results (provideing i biuld it correctly) and it will sound better than my current speakers which i stated in my first thread?

what do you mean by It demands attention at higher volumes? so i take it as its really loud if you say it will break my house, what is its lowest frequency?? and where can you find these bootleg Jenson plans? i want to learn as much as i can about the box and how it works, could someone post a link please? thanks

ok, i will buy it when i get some money handy, but if anyone finds the link please send it. i just want crazy amounts of bass like you hear in the clubs!! i cant wait to get building. so would you say its worth sacrifising the exta quality of the 15"s for the extra bass created by the 18"?

skeamah1516

this is footstonys site and has some stuff that helped me alot.
But it helped me understand Steves design.
But I would go with Steves design and do it right. and stay away from the corner imperial as a novice. You can't build it like the plans and expect it to work like the full size and not have resonence problems and the lows. It can only go one place and one place only. and may rattle itself to pieces under heavy use.

http://au.geocities.com/footstony/

Gex

if by spec you mean the sub, i am looking at a Eminence Sigma Pro 18 650W 18" Bass Driver and what is the corner imperial that your telling me to stay away from?  i will probably just end up making the normal imperial with the 2 15" subs as it will be less hassle

[quote author=skeamah1516  link=1130329857/0#11 date=1130367573]if by spec you mean the sub, i am looking at a Eminence Sigma Pro 18 650W 18" Bass Driver and what is the corner imperial that your telling me to stay away from?  i will probably just end up making the normal imperial with the 2 15" subs as it will be less hassle [/quote]

It was one of jensens downsized designs, and still very much an Imperial.
what you are planning is going to be much better. you might want to wait to see if someone pipes up about the single 18 or 2 15's and hear there thoughts.
did I mention the threads?

change_out- you must live very nearby! There in the workshop now? you lucky dog. a Zig built anything would be sweet.
with the IMP you got the icing and the cake and the baker along with it too.

Gex

Braggi,

I haven't built an 18" imperial, but  I suspect that the most likely sound you'd hear when a driver gets unloaded at low frequencies is the voice coil hitting bottom.  And that's an ugly sound!  

The Fs is the speaker's natural resonant frequency.  Below that the speaker doesn't couple to the air very well and will have large excursions without an air volume to load it, either from a box or horn.  Below about 40 hz the imperial horn doesn't load the woofer so you could get really drastic excursion.  I suspect the back chamber actually helps reduce this effect allowing the imperial to unload more gracefully than a base-reflex or OB.  I've driven my imperial with 20Hz tones and not bottomed the woofers but they do fly and the output is not tremendous although present.  At 30 Hz or above the imperials will have good output and really strong at 40Hz and up.

I hope this is useful info.  And here's to NEVER hearing the death rattle of your woofers unloading!!

Jim P

you could but you might want to make guides jigs etc to make better cuts.
you can't do it with a jigsaw thats for sure!

I am not all that great with a circular saw free hand. I have a 12" table saw, 12" chopsaw Etc Etc.

I think 60 did all his stuff without a table saw. In my book that takes skill.

Going to go ahead huh!
Take your time and get that circular saw wish I was there!!
My new garage got vetoed so no Imperials for me!

Except that exsisting SO concept might expand to a real one unexplainably without warning as soon as I have time

Gex

i built both my dbs from precut particle board. i ordered the material and the shop cut it to my specs. it was dirtcheap and VERY easy.
the imperial has lots of panels and it will be harder to work out a cut list but with a bit of maths involved, you can do it  ;).
if you're buying the material (btw, what are you building it from? ) then ask the people at the shop if they can cut it. the shop i bought the materials from cut everything for my db-12 in about 10 mins. work out the panels so that you only have to make the angled cuts.
i'll be using the same approach in building my wo

[quote author=JimP  link=1130329857/15#15 date=1130447745]
The Fs is the speaker's natural resonant frequency.  Below that the speaker doesn't couple to the air very well and will have large excursions without an air volume to load it, either from a box or horn.  Below about 40 hz the imperial horn doesn't load the woofer so you could get really drastic excursion.  I suspect the back chamber actually helps reduce this effect allowing the imperial to unload more gracefully than a base-reflex or OB.  I've driven my imperial with 20Hz tones and not bottomed the woofers but they do fly and the output is not tremendous although present.  At 30 Hz or above the imperials will have good output and really strong at 40Hz and up.

I hope this is useful info.  And here's to NEVER hearing the death rattle of your woofers unloading!!

Jim P
[/quote]

Yes, thanks for sharing. However, the warning with the Imperial is that drivers with an Fs lower than 40 will unload below 40Hz. Does this mean that drivers with Fs above 40 won't be unloaded below 40 Hz? it's a bit confusing to this dull boy. <Hand me another glass of wine. There now, thanks.>

The reason I specifically asked about 18" drivers is that I've never seen one with an Fs above 40.

-Jeff

I know it's hard to imagine, but the Imperial reacts more like a BR cab in the lowest frequencies. It has a volume of air tuned by a vent with a KILLER Tapered/Horn Loaded port. Unloading the drivers is related more to the volume and vent than the Fs of the driver. The danger is in having a driver unloaded at or near the resonance frequency. It seems, from what I've read here, that the Stock Decware Imperial is tuned to the 30Hz to 40Hz range and if you use a driver with a lower Fs it will not be supported at the critical resonance frequency. Any driver will be unloaded below the tuning of any vented box, but if the Fs falls in the tuning range, the control will be ideal. Higher Fs will also be loaded well, but a lower Fs than the box is tuned for is dangerous to the driver, even more so if it has to try to reproduce that range of freqs.

With that in mind, it should be possible to modify the chamber volume and vent circuit in order to support any driver. Extensive modeling and testing would be necesary to guarantee good results. If you just want to whip out (like it's some minor undertaking) some Imps, you're better off using drivers that have been proven in the past.

"... achievable ... ?"

Absolutely, since unloading doesn't happen all at once. Your driver doesn't just reach the edge of a cliff an fall off. At the tuning frequency, whatever the actual value is, there will be a useable range on both sides of the "cutoff".

One beneficial effect of using the horn shape for a port is that the actual cutoff rate (in dB/octave) is less steep, meaning it will resonate across a wider range, instead of just a narrow band centered around the actual tuning freq. Another benefit which we are all interested in, is that whatever energy reaches the horn, after loading the chamber, will be better coupled to the environment (amplified).

When considering reflex ports of all kinds, try not to think in terms of a few frequencies, but rather in octaves. Depending on (many) design factors, some ports roll off at slightly more than 6dB/octave, which is the natural driver rolloff in an infinite baffle, while others rolloff much faster, even 24dB/octave because the driver output and the port output are approaching 180 degrees out of phase with each other. In that case you will have a port which, instead of suppressing excursions, actually helps to cause extreme excursions.

Hornlover,

I really don't have a clue about the chamber differences between the two but keep in mind the Decware Imperial is different than the Jensen and the Jensen facts you stated may or may not apply.

Corey

Stv,

I'm in the middle of teaching my unit on sound and resonance so all of my equipment and the Imperials are set up in my classroom.  I will try to do some frequency analysis of the speakers.  One thing i would like to try is a FFT analysis of the spectrum for white (or pink) noise.  We have a computer-based system that can do a frequency analysis up to about 11kHz.  For the Imperial I would be happy with up to 1kHz.  I just have to find the time, but now seems like the best opportunity.  I should have the resolution to pick up any big dips of peaks in the response although room effects could be a problem.  I'll mic it close to the horn mouth.

If I can get this done I'll report back.  Maybe by this weekend.  I'm curious to know how much output there really is below 40hz.

By the way, 2 Imperials in a classroom is a guaranteed conversation starter with the kids!  And the neighbors might start complaining - we were doing sine sweeps today so the kids could get a feel for what 20-20,000 Hz really means.

Later,

Jim P

OK,

Here is what I found.  But first, a few disclaimers.  They test system is not calibrated.  Frequency identification is right on but the intensity scaling is relative not in dBs.  The sampling rate it uses is 11Khz so it can only give measurements up to 5500 Hz.  I looked at the range up to about 1kHz, but mostly concentrated on th erange up to 250 Hz.  The mic was placed at the mouth of the horn at its center.

The results (full size imperial):

There are noticable peaks at 70-75 Hz and less so at 100 Hz.  Also a peak around 250Hz.  The 250 I could hear and was gratified to find that when I engaged my equalizer (set by ear), the response got much flatter, although a bit heavy on the bass.  What can I say, I like a little bass.

As for the 75 Hz peak, it showed up in almost all configurations of the mic and speaker placement.

My imperial has one Dayton Pro 15" and one Eminence Gamma 15".  The Dayton is fs= 36 Hz, Qts = .37; the Gamma is fs= 33 Hz and Qts= .30

I also made use of an SPL meter and my old Carver test CD with 1/3 octave centered pink noise and measured the spl at about 1 meter from the speaker  .8 m from the floor.  Here are the  results:

Frequency (Hz) / SPL (dB)
25 / 60
31.5 / 63
40 / 66
50 / 70
63 / 73.5
80 / 74
100 / 73
125 / 73
160 / 76
200 / 79
250 / 81
315 / 81
400 / 82
500 / 84
600 / 85
800 / 85
1000 / 84.5

This is with the Imperial in the middle of the room, no corner or wall help for the bass and no equalization.

I found it interesting to note that I was picking up measurable subsonic output from the imperial during pink noise testing, and it wasn't from background noise.  Like 5-10 Hz!

What does it all mean?  Perhaps the higer Fs driver will help avoid the 70 Hz peak.  In listening that peak is not that noticable and almost never objectionable sounding.  The peak that I hear and dislike most is the 250Hz.  That's probably something going on with the back chamber or a cabinet resonance.

We'll I could keep writing but instead I'll wrap it up and answer any questions about what I tested you guys might have (that is if I can).

Jim P.

ps.  I had a student stop in after school because he wanted to hear the Imps turned up, something I can't really do during the school day.  I had Gary Glitter's Rock and Roll part whatever which is far from HI FI but has some decent bass.  I think he was stunned at the sound.  Now he's trying to figure out how to get one in his car.

Stv,

No standing waves noticed the way I had the speakers configured for testing, although I wasn't specifically looking (or listneing) for one.  The room is 30' wide by 50' long with lab stations in half an desks in the other half.  Tile floor, acoustic ceiling tiles and drywall walls.  Pretty reflective overall but the bass seemed pretty uniform.  Louder near the walls and corners as expected but no big nulls or antinodes.

Jim

Braggi,

I used 2 measurement methods.  The table of values was with a dB meter reading 1/3 octave pink noise.  I think this method was less sensitive to narrow peaks, smoothing the overall appearance of the response.  The FFT method showed very narrow bands of frequency almost individual frequencies, and with this method a peak showed up at 250 hz and also at 70Hz.  The 250 hz peak doesn't seem to show in the spl meter data, but it is there.

Jim P