small? Open Baffle question

[aceinc]

First, is this the right forum? If not hopefully a moderator will put it where it belongs.

OK, I would like to build an open baffle speaker using four 5" to 6" drivers per cabinet (baffle). The frequency range I want to cover with these drivers is 80-1500 hz.

Aesthetically I would like the baffle to be ~6" wide with wings at an angle starting at the width of the baffle, and spreading to ~16" wide at the terminus and the distance front to back (not along the hypotenuse) to be about 16".

So how do I find out based on a given driver, such as PE 299-065 what kind of freq response I can expect?

or

Based on the described dimensions could I ever expect to acheive the results I desire with any driver?

If true, how do I find the right driver?

I would like an SPL of > 90 DB 1 watt 1 meter.

Any thoughts?

Paul

[Rudolf]

Originally Posted by aceinc

I would like to build an open baffle speaker using four 5" to 6" drivers per cabinet (baffle). The frequency range I want to cover with these drivers is 80-1500 hz.

Aesthetically I would like the baffle to be ~6" wide with wings at an angle starting at the width of the baffle, and spreading to ~16" wide at the terminus and the distance front to back (not along the hypotenuse) to be about 16".

Based on the described dimensions could I ever expect to acheive the results I desire with any driver?

I would like an SPL of > 90 DB 1 watt 1 meter.

Download and read these two articles by Martin J. King about designing an OB system:
Passive two way OB system and Comparison of OB-, U- and H-frame systems
Those systems are aimed at 90dB/1W/1m. Martin uses the Eminence Alpha 15 driver with Xmax=3.8mm. That is roughly the same as the Xmax of the PE driver (3.5mm). The cone area of the 15A is ~7 times the area of the PE driver. So if you take 8 instead of 4 PE 299-065 drivers per side, we can start to think seriously about your idea.

To cover the range 80-1500 Hz you will need to split the OB (and the drivers) into two parts - one for bass (up to ~250 Hz) and one above that. Your proposal of 16" wings will develop a first quarter wavelength resonance peak below 100 Hz, followed by other notches and peaks. Above PDFs will help you to understand that.

Rudolf

[aceinc]

Rudolf, thanks for the reply.

I actually had read through the first item you posted, I had not read the second.

A few points,

1) The freq range I am trying to acheive, 80-1500 hz is a bit different than Mr. King's objective which I believe is to produce the lowest freq's possible at the highest DB. My goal is more of a midbass.

2) The H & U designs he studied were straight, not flared, and he indicates that he is unclear what effect that a flare would have.

The system I am designing is a 3 way system with a traditional box subwoofer and a planar tweeter. The part of the system that I am trying to tackle here is the area between 80 & 1,500 hz.

Has anyone done any work similar to M.L. King's excellent work using flared designs?

I am not opposed to a straight U or H design, if someone could point me towards info that would help me design for the freq range I am looking at.

Paul

[skorpion]

I think you could go ahead and build with your proposed units. It will be a cheap and cheerful project. Build according to your plan, perhaps widening bafflefront to 8" and about 28" high wings and above all: do not close the top end. It should be a 'Topless' kind of winged baffle then you will not get into resonance troubles. Some calculation show (MJK simulation) that you will hit around 90 dB with 1watt and 1 meter from 80 Hz and upwards with four units if you wire the speakers to 4 ohms impedance.

/Erling

[aceinc]

Thanks for the vote of confidence. The QTS of the PE 299-065 drivers is .8 and the efficency is 86.5. Would another driver be more suitable?

I was not looking for the cheapest drivers, but they seemed to have a high qts, which is one thing that is needed for open baffle designs as I understand it.

I would like to stay at 6" (150 mm) diameter or less.

Paul

[bjorno]

DIY:

b

[aceinc]

OK, I downloaded HornResp, which I used a few years ago to help develop a Tapped Horn subwoofer I built.

Unfortunately, I never used it for other projects, and what little knowledge I had has evaporated.

Could you you provide brief pointers on how to get to where you are?

Two of my drive parameter labels are different than yours, and I forget how to enable s2 - s4.

Paul

[skorpion]

I don't know what planar tweeter you have in mind but some calculations show that your aim could be fullfilled using two Peerless SDS 6.5" woofers,PE number 264 - 1088. Those are very good units. I could think of an MTM arrangement starting right at the top of a 44 x 32 " baffle, The 32 inch width including baffle ang wings. The corresponding 5.25 units won't make it excursionwise if you would like to go high but the 6.5" units will have a very good margin to play with.

HP filter will be mandatory for the woofers otherwise they will be to stressed by low bass.

/Erling

[bjorno]

Originally Posted by aceinc

OK, I downloaded HornResp, which I used a few years ago to help develop a Tapped Horn subwoofer I built.

Hi Paul,

HR have evolved a lot since then..There are quite a few new ways to model an OB in HR but since I recently have designed a couple of line arrays using the 'Template' I've submitted here-above, I just posted a sample screen using your driver TS.

...Unfortunately, I never used it for other projects, and what little knowledge I had has evaporated..Could you you provide brief pointers on how to get to where you are?...

Invoke the Loudspeaker Wizard at the Input Screen:Tools scroll-down menu. Click the Schematic scroll-down tab and choose response, then click on the 'Default' scroll-down tab and choose 'Combined'. You are now watching the FR sum from both the OB front an rear sides.

..Two of my drive parameter labels are different than yours, and I forget how to enable s2 - s4...

Se * here below + You may here alter the S1,S2 and S3 sliders that would alter the airways at the front of the driver only.

If changing the rear enclosure behind the driver: You must choose 'Schematic to invoke 'Chamber to appear where you can alter the contents of the rear hand sliders.


If you want to extend the front parts of the horn with an additional segment like a S4 area: You have to enter this new data at the main screen.

b

PS:
/Tip: *If you have a complete set of parameters and is confident with the values or previously done a consistency check, just enter all to the main input screen.
If not..Follow this procedure by letting HR do the consistency check:

Enter Re and Le then Sd and double-click Cms and enter Vas,
double-click on Rms and enter fs + Qms,
double click Mms.

Double click on BL and enter Qes. Double click on Sd to verify if the T/S looks right.
The key here is by not entering BL, always allow HR to calculate a rounded of value that is consistent with what you will find when double-clicking the Sd parameter./

Maybe someone can rewrite the instruction above using better English?...

[aceinc]

Bjorno, thanks for the tutorial. I will try it out at my earliest convenience.

Skorpion, Not a bad looking woofer, the truncated frame would try my woodworking skills a bit. The planar tweeter I was thinking about using in a dipole manner is PE 264-713. I really wasn't thinking MTM, and my baffle height will probably be no more than 32" as I want it to sit on top of a dedicated subwoofer per channel.

The main point of this exercise is to get a midbass that approximates the "speed" and efficiency of the planar. I was thinking that more magnet assemblies (drivers) moving smaller cones in a dipole configuration (open baffle) would have a better chance at acheiving the goal of "faster" response.

On a side note my consideration of drivers tends to give me more overlap in frequencies in order to allow me to play with the crossover.

Paul