Isobaric 8" expectations?!

Hi,
I am making a tapered pipe pair of speakers using a 16.5cm driver. I really like the description of them...we'll have to see what they're really like! The problem is, I envisage virtually no bass. My speakers I have at the moment use Audax AP210G6 8" drivers. Obviously I have two, and me being me (a cheapskate), would like to utilise these in a sub. I thought about an Isobaric sub. The room is medium size and the size of the enclosure is not a problem.

Could anyone tell me how low I could hope to reach with these speakers? Any other suggestions. FYI the 16.5cm drivers I am using in the TP speakers are Audax AP170Z0 and Audax TW025M0. (They're easily available!)

Thanks
Gareth
 
Hi,
Thanks, I'll look into this configuration. Will the bass from these still be 'punchy'. I love bass to add depth to music, but in moderation. It is of utmost importance that the bass notes hit when they are supposed to.

Will band pass provide this, because I've only been looking at sealed so far. I had thought about Isobarik because I had two 8" subs going spare, and I knew that this would reduce the box size by two and increase the power handling. That's all! ;)

Gareth
 
bandpass has its advantages and problems

1. the bass volume is good
2. the bass quality is not

i am not so sure about punchy bass (it depends on teh room, driver and design) but it will add a lot of foundation to the lower octave.

one reason I have used bandpass is to get bass out of a small box. also in places where the user does not want to see the driver.

a band pass sub can be hidden behind a sofa with min. difference to the sound.

regards
navin
 
Gareth,
I recently had a good look and listen to isobaric subs with each having two Vifa (or Scanspeak or something Danish) 8" long throw polypropylene cone woofers as the low end for some large ES panels.

The cabinets were about 22" square and 12" high or so.
These isobaric subs were crossed out at 150 Hz (? dB/Oct) and and tried with several high power tube, icepower and pro amps (600W/4 Ohm) in a very large room/volume.
Because of the sensitivity and power handling (flashover) of the ES panels max sustained power was around 300W on each of the bass amp Led VU meters.
The bass was utterly clean and powerful non boomy or resonant, and did not give a hint of bass nasties even when pushed hard (real hard).

On the downside perhaps are that they need horsepower and perhaps a little lack of attacking in the bass, but this may be a product of very dead polyprop cones or the product of usage with ES panels or the product of just plain clean response.
Either way they worked rather well and avoid totally the characteristically boomy/resonant/droning bass of commercial standard ported sub cabinets.

I suggest that since you have the drivers already, it is worth the investment in research, fabricating and tweaking.
I have seen designs where the cones are facing each other with minimal volume between them, and the rear of one cone radiating into the room, but I dont have any performance comparisons.

You have only time and particle board to lose. :)

Eric.
 
Hi,
Thanks for all of your great input! Does anyone know what I could expect from my tapered pipes? They have internal dimensions of 16.5cmx20.3cmx91.7cm or there abouts, and a 71cm tapered board that goes from the top of the 8.1cm opening.
I know this isn't very clear...For a rough idea of the shape, I did a quick render of my concept...

http://ena.brinkster.net/db/diyhifi

Any idea what this Audax combo will be like? (AP170Z0, TW025M0)?

Thanks
Gaz
 
I don't know if I arrived in time, but I like this bandpass configuration.
 

Attachments

  • isobp.jpg
    isobp.jpg
    15 KB · Views: 278
Hi Gaz,

When you get this sub finished you will have to let me come round and have a listen as i will be starting a sub as soon as i get sufficient funds (when Draeger pay me), Holly poop i will actually have money:eek:

By the way, sorry i dont have anything usefull to contribute:(

see you later.
 
TL bass is usually better defined than bandpass. there are exceptios ofcourse.

you have to choose your poison. if you are willing to have a big box TL might be teh way to go if teh woofers have a Fs in te region of 30-35hz you might have a winner.

only thing with TLs is that I am not sure if you can average the line lenght when you are using 2 drivers. Head says yes. heart says no.

push pull isobairk bandpass is another option sort of what sapito suggested but with the woofers facing each other.

Regards
Navin
 
Hi,
Sorry, I misread the post Navin; I thought that you were saying the 16.5cm drivers were for a TL...

How big would a TL sub be? It seems to be that the subs are around the correct specs (Fs of 33.7Hz).

I have done a 2-second sketch of what I understand by an isobaric TL...Can you tell me if I'm on the right track? What response could I expect from these?

Thanks!
Gaz
 

Attachments

  • tl.jpg
    tl.jpg
    4.2 KB · Views: 207
Rarkov,

Are you building a "classic" tapered pipe or have you modeled it to get an optimim design? The AP17 should work OK in a pipe but it would probably do better in a TL.

The 8s look best suited for a vented box, and as i am prone to do, i'd suggest a push-push arrangement. The prime purpose of isobarik is to reduce the box size (i think there are other, subtler benefits too) at the expense of efficiency and radiating area.

dave
 
Hi,
The design is taken from one of the books I have, I will scan it when I get home from work. It is designed for 'a' 16.5cm driver - It just so happens I have this one. I do not have a program that models Tapered pipes or Transmission Lines. What is there out there? If the formula are OK, I may write one...

Why would you go against the TL sub idea? I hadn't thought about an Isobarik TL sub - but now it's been mentioned, I quite like the idea...

Thanks,
Gaz
 
Rarkov said:
The design is taken from one of the books I have, I will scan it when I get home from work. It is designed for 'a' 16.5cm driver - It just so happens I have this one. I do not have a program that models Tapered pipes or Transmission Lines. What is there out there? If the formula are OK, I may write one...

A classic pipe like this has only a small chance of working well -- you'd be better off with a sealed box than this, particularily given you will have a sub.

Software is available starting here.

Why would you go against the TL sub idea? I hadn't thought about an Isobarik TL sub - but now it's been mentioned, I quite like the idea...

Because your driver's Q is too low to do well in a TL.

dave