[Andrikos]

Hello everybody,
I am working with a subwoofer driver manufacturer to build an OEM 18” driver for Infinite Baffle applications. This is not a full time endeavor for me nor am I in the ‘business’. I do have a day job and this is basically a side project for me. I’m not in it for the money, that’s why I expect to be able to offer the best $/liter displacement ratio in all of wooferdom. I’m doing it to prove to myself that I can do such a thing and in the process help the community use a driver that is specifically and exclusively designed for IB applications.


The main parameters we’re trying to hit by order of importance are:

Xmax > 20mm (more is obviously better but we’re also looking at linear, low distortion performance)
Fs < 20Hz
18” driver – Sd = 1400 – 1500cm^2. We feel that an 18” driver gives us the best chance of hitting our goals.
MAX SPL: >98dB at 10Hz, 110dB at 20Hz, 116dB at 30-80Hz unechoically per driver. Each doubling of driver number will add 6dB to this number. Room gain should add about 20dB more to the above numbers give or take, YMMV.

Pe = 500W single coil
Qts = 0.7- 0.8 (flat response for IB applications, not recommended for small enclosures sealed or ported).
Vas > 500 liters
Neodymium magnet
Foam surround (new and improved stuff not the foam from the 70’s and 80’s)

Our goal air displacement volume is >6 liters.
Our cost goal is <$50 per liter so as to have the most cost effective IB driver out there that is specifically designed for Infinite Baffle operations.

I do not care about aesthetics, bling factor etc. Every single cent will be dedicated towards PERFORMANCE! No fancy graphics/materials just to make a silly statement (i.e. this is NOT an automotive application focused driver )

This driver is aimed to DIY audiences that have the education, knowledge and experience to do a simple IB install with 1 or multiple of these drivers for UNPARALLELED bass performance.

For those who know IBs, the advantages are numerous and overwhelming:
1) Far lower cost than any commercially available subwoofer of an topology
2) Very simple structure (no fancy, expensive boxes required)
3) Out of sight, out of mind – High WAF
4) Did I mention the bass ROCKS? The house shakes, creaks and groans. Little children and puppies whimper in the corner. Neighbors file police complaints. You get the idea…
5) Perfectly blended and natural bass to the rest of your system.

Why am I writing this? Since I’m not a manufacturer, I would like the input of experienced IB owners and enthusiasts that are excited at the possibility of installing an Infinite Baffle in their home theater for a low cost. I’m a huge bargain shopper and the next step for me is to actually MAKE the drivers I want to buy. My potential ‘customers’ are NOT audiofools who spend $17k on a coffin sized sub with an undersized set of ports. My ‘customers’ are regular working stiffs like me with ‘real’ salaries and ‘real’ constraints because they need to include diapers and formula in their budget…

I hope my post wasn’t toooo long.
I’m looking for advice, desirable features, do’s and don’ts, lessons learned etc. etc.
I appreciate and thank you in advance for your feedback.

Andreas

[klh]

The IB market could definitely use a good 18" woofer. I have two 18" Avalanche drivers in an IB driven by a Samson S700 amp. I absolutely love the sound. The room is 3,000 cubic feet, and it fills it easily. When I checked it a few months ago, I hit 112 dB at 10Hz (at the seated position 14' away), and the drivers were moving no more than 1.5" (the limit is 3" peak to peak) and the amp was hardly working. The sound is so clean... and effortless. Total cost was $550+shipping for the drivers, $250+shipping for the amp, $10 bucks for 24' of speaker cable and $5 for a DIY 3' XLR-RCA cable.

If you can get this driver going, that would be great for the IB community.

[amplifierguru]

Hi Andrikos,

You will get up to 25% more performance from a vented design as the vent assist contributes. Also lower distortion as cone excursion is greatly reduced at around cutoff.
Further performance can be got with either type by using a Q=2 HP filter in the amplifier. This reduces out of band subsonic drive dramatically saving power and reducing large non-linear cone excursion (cone flapping)while extending response to 0.6fo before. This can be exchanged for smaller box size for greater strength for less resonance. It will also reduce out of band room modes.

I have built many such units (mostly JBL) for discos and night clubs, often capable of 126dB.

Cheers,
Greg

[_scotty_]

amplifierguru, you have brought up an interesting point when you mentioned
a vented system resulting in lower distortion due to reduced excursion at or near system resonance. What I have so far never seen is a measurement of distortion taken at the mouth of the vent. To assume that there is no distortion from output of the vent or a vent substitute probably incorrect.
Scotty

[Watson]

You will get up to 25% more performance from a vented design as the vent assist contributes. Also lower distortion as cone excursion is greatly reduced at around cutoff.

But as usual, there is a tradeoff:  higher group delay.  If you look at the research, group delay is more easily perceived at lower frequencies, and in my experience it's very audible in subs.  Infinite baffle folks love a fast, clean low end that's not achieved with stored energy.

[amplifierguru]

Hi Watson,

The research is summarily (7 studies) reviewed in -
"Phase Distortion and Phase Equalizing in Audio Signal Processing - A Tutorial Review" by D.Preis JAES (Abstracts) Vol29, p938-, concluding that "a perceptual threshold of 2.5mS group delay at 100Hz for non-reverberant conditions and double that for reverberant conditions"

and quoted in "Subwoofer Performance for Accurate Reproduction of Music" by L.Fielder and E. Benjamin JAES V36 No8. which considers a number of possibilities, and states "no perceptual studies have been done below 100Hz"

Cheers,
Greg

[Andrikos]

Hmmm, interesting.
IB with a port?
Never heard of that one before...

Are we sure we're talking about the same thing?
Thanks,

[Watson]

AmplifierGuru, I haven't had access to the AES archives for a while, but take a look at the Krauss paper at AES 88 (1990).  

In my experience, having built both types of sub, there is an obvious difference in bass quality.  You may not view lower group delay as the appropriate tradeoff to make, but others do, and that's a legitimate engineering choice.  This was the reason, btw, why Linkwitz chose a sealed design for his Thor subwoofer:  "I did not consider alternate approaches to subwoofer design as acceptable for meeting my goal of accurate sub-bass reproduction. This includes vented, passive radiator and acoustic bandpass woofers. They all rely on resonant energy storage to increase efficiency and to reduce size."

[JLM]

Using an 18 inch limits built-in applications to attics as typical house floor and wall framing is 16 inches on center (leaving 14.5 inches clear) versus attics that are 24 inches on center (leaving 22.5 inches clear).  

IB bass is only cheaper if you have the cavity (or warm climate) to vent into.  Obviously being built-in limits it to long term home owners.

Your design goals appear to be aimed more to the HT or electronica crowd as response below 30 Hz is rarely needed in most musical forms.

[Andrikos]

Hi JLM,
You're absolutely right.
This is solely aimed for the HT nut as we're aiming for very high SPL levels of 10Hz frequency content. Many naysayers will complain: "But we can't hear it!".
Welll, the house will definitely let you know and it add to sheer realism while watching movies that a regular commercial movie theater cannot approach.

[mcgsxr]

wow, and I thought I was a basshead...!

[Andrikos]

Hey Mark, you can never have too much BASS my friend!
You know that...

[brj]

Using an 18 inch limits built-in applications to attics as typical house floor and wall framing is 16 inches on center (leaving 14.5 inches clear)

Good point.  Andrikos, once you get the 18" version worked out, might a 15" version be possible to allow more installation options?  You can always use multiple drivers to move more air!

[JoshK]

Shoehorning 18" drivers between 16" studs has already been solved by some cult members.  Look on the cult of the infinitely baffled page for examples.  Basically the mouth is a little small than the driver in one of the dimensions.

I am looking to add an IB into my floor using the basement.   This will be with 15" avalanches though....

[klh]

IBs sound very fast, very good, go very deep and take up very little space within the room. Obviously they have several limitations. One must have open space adjacent to the music room, and one must do their homework WRT finding the ideal location. It's pretty hard to go back after you cut holes in your wall/floor/ceiling. And, there is the whole portability issue. It takes a special circumstance to have an IB, but the vast majority of those who end up installing one are extremely happy with the outcome.

[Andrikos]

Couldn't have said it better my self klh!

[amplifierguru]

Andrikos,

10Hz hey! thats low enough to shake your foundations. Yes IB's don't have a vent and they make a bloody good use for skimped magnet 'budget' drivers. I simply misinterpreted your take on 'performance' thinking it might have included lower distortion.

Of course that 10Hz second order IB will have an associated 30mS group delay. Don't tell Watson.

[Andrikos]

Haha! 30ms group delay eh?
I have a feeling a structure as large as a house would take a bit longer to react (groan) to a >120dB 10Hz stimulous...

[markC]

Hmmm... this is interesting. The wall at the back of my 12x21.5x7.5 ft. listening room seperates it and the rest of the basement from the crawlspace, (sidesplit design). The crawl is about 3.5x24x30 ft. So maybe I wouldn't have to build a box to get a sub that I could be happy with. I'm a 2 channel guy, so 10 hz is not necessary, but 25 or so  would be cool!

[Andrikos]

Hmmm... this is interesting. The wall at the back of my 12x21.5x7.5 ft. listening room seperates it and the rest of the basement from the crawlspace, (sidesplit design). The crawl is about 3.5x24x30 ft. So maybe I wouldn't have to build a box to get a sub that I could be happy with. I'm a 2 channel guy, so 10 hz is not necessary, but 25 or so  would be cool!

You, my friend, are the perfect candidate for IB.
There's a ton of already available drivers to achieve this.
25Hz is nothing for these bad boys.
It starts to become interesting below 20Hz where ported subs are all spent, out of breath and honking...