Some design ideas for Dipole/OB needed?

[Mayhem13]

Re: Some design ideas for Dipole/OB needed?

The dome tweeter on both the 907 and 909 are DEFINATELY slightly waveguide loaded....



Its not much but the acosutic affects are there for sure.

[Deward Hastings]

Re: Some design ideas for Dipole/OB needed?

slightly waveguide loaded....

That looks like a pretty normal Revelator faceplate . . . if there's any "waveguide" effect it would only be above 10 kHz . . .

[Flint]

Re: Some design ideas for Dipole/OB needed?

BTW a new Jamo 909 will cost you US$18,000 a pair in Australia, cheaper in the States. This will give you some motivation to build your own pair...

I love this argument! "Yeah, well, at least it didn't cost $18,000."

Looking forward to seeing your project too. The world needs more Jamo R909 clones.

[Mayhem13]

Re: Some design ideas for Dipole/OB needed?

I don't think my space could fit a 909 clone......907 maybe..;)

The point i make for the tweeter and the WG loading is the advantage of the controlled directivity Looking at the pix more closely and in comparison to the formentioned Scanspeak revelator, the Jamo tweeter's dome is recessed even farther than the Scan, who mfgrs acknowledgments are as follows....

"The 130mm machined aluminum front plate has more controlled directivity (down to 2Khz)."

I'm just trying to find out if the benefit of CD is worthwhile in a dipole design. I could just wait for MarkK to finish his RS225/RS28F dipole but what fun would tha be?:D

And for MarkK, i have an extra QSC 10" waveguide that's not quite as deep as the PE version and has a much more 'oblate spheroid' profile if you'd like to try one. I would expect much less diffraction issues as well for it transitions to a flat baffle quite smoothly in comparison to the PE as well. Basically it looks like an oversized MCM guide.

[Deward Hastings]

Re: Some design ideas for Dipole/OB needed?

I'm just trying to find out if the benefit of CD is worthwhile in a dipole design.

It *may* be, in a room with highly reflective sidewalls. As John K noted above there is a "bloom" in the radiation pattern just above the MT crossover in ORION and his NaO designs. In my room placing an absorptive ring around the tweeter(s) (absorbing that "bloom") made no identifiable difference. Matching the rear radiation of the Mid (with a rear-firing tweeter) made a *significant* difference (again in my room, perhaps not in all). But just looking at and comparing the polars should give a hint "why" . . . there's obviously something significant missing with no rear tweeter.

[Mayhem13]

Re: Some design ideas for Dipole/OB needed?

Deward...i can't thank you enough for all of your help here (as well as all the other posters). The test baffle i mentioned has such a pronounced midrange spaciousness together with the directivity of the WG tdfc makes for a fantastic soundstage. I think the LR2 XO might be the key to the smooth blend....just speculation. Of course the single 6.5" midwoofer ran out of gas pretty quickly with a twist of the volume and HP filter to the subs. A pair of midwoofers or a larger driver is going to be needed but it's a start.

Jamo clone.........hmmmmm. Maybe a pair of 15's under the existing MT might do the trick. The Alpha's are certainly cheap enough and crossed in th 300-400hz range is a piece of cake for these. I didn't plan for a 60" tall speaker but who does really? If anybody knows of a 12" driver capable to 400hz or so with a high Qt, please point me in the right direction. I'm not sure just how high the Qt needs to be (as per MJK, the alphas are 1. something).

[markk]

Re: Some design ideas for Dipole/OB needed?

I don't think my space could fit a 909 clone......907 maybe..;)

The point i make for the tweeter and the WG loading is the advantage of the controlled directivity Looking at the pix more closely and in comparison to the formentioned Scanspeak revelator, the Jamo tweeter's dome is recessed even farther than the Scan, who mfgrs acknowledgments are as follows....

"The 130mm machined aluminum front plate has more controlled directivity (down to 2Khz)."

I'm just trying to find out if the benefit of CD is worthwhile in a dipole design. I could just wait for MarkK to finish his RS225/RS28F dipole but what fun would tha be?:D

And for MarkK, i have an extra QSC 10" waveguide that's not quite as deep as the PE version and has a much more 'oblate spheroid' profile if you'd like to try one. I would expect much less diffraction issues as well for it transitions to a flat baffle quite smoothly in comparison to the PE as well. Basically it looks like an oversized MCM guide.

I'm game to try one of the 10" qsc waveguides. IIRC these weren't that expensive. Is there a link to the qsc 10-probably just cheaper for me to order directly. Does qsc make an 8"?

[Pete Schumacher]

Re: Some design ideas for Dipole/OB needed?

I'm game to try one of the 10" qsc waveguides. IIRC these weren't that expensive. Is there a link to the qsc 10-probably just cheaper for me to order directly. Does qsc make an 8"?

http://yhst-93643794936312.stores.yahoo.net/sp000106gp.html

Currently out of stock according to the page.

Superceded by this:

http://yhst-93643794936312.stores.yahoo.net/pl000722ts.html

[markk]

Re: Some design ideas for Dipole/OB needed?

bummer...

I really want an 8". I'd even drop to the mcm before going larger. I mean, maybe a 10, but not a 12.

I know everyone dismisses the PE one, but-

The PE one isn't bad. I know everyone thinks the lack of a roundover is bad juju, but I'm not sure. I mean, it could be, but the diffraction seems not bad-if you think about the wavefront, it's expanded quite a bit by the time it reaches the bevel. And, it's more of a 45 degree bevel.

Hey, that's it. It's a 45 degree chamfer. It's a design feature...:D

Anyway, the ripple in the measurements is pretty controlled, even at 75 degrees off axis, and better than the 1" tweeter without a waveguide, so it still should be ok.

If I can ever finish it! I spent yesterday cleaning out my garage in preparation of someday getting to it...kids had swim team saturday, then took in a little minor league rivercats game. And, there's the weekend. Oh to have time for speakerbuilding...

[Deward Hastings]

Re: Some design ideas for Dipole/OB needed?

I didn't plan for a 60" tall speaker but who does really?

Brings us back to an advantage of the "H" frame . . . the ORION woofer (with two long-throw 10" drivers) assembly is 24" tall, and provides an appropriate-height platform for the MT panel. They have about the same swept area as two Eminence 15", so will produce essentially the same max SPL . But because of the cavity resonance in the "H" frame you need a relatively sharp and low crossover (LR4, not much above 150 Hz., ORION crosses at 120 Hz.), which puts an extra load on the Midrange driver (and is why ORION uses a W22).

It's all about tradeoffs . . .

[Mayhem13]

Re: Some design ideas for Dipole/OB needed?

I'm game to try one of the 10" qsc waveguides. IIRC these weren't that expensive. Is there a link to the qsc 10-probably just cheaper for me to order directly. Does qsc make an 8"?

PM me for the shipping info and i'll send you the 10" round one. I'm currently modding one for an AVS member with the SB29. I wonder if you wouldn't mind measuring up that combo as well?

[Mayhem13]

Re: Some design ideas for Dipole/OB needed?

http://yhst-93643794936312.stores.ya...p000106gp.html

Currently out of stock according to the page.

Superceded by this:

http://yhst-93643794936312.stores.ya...l000722ts.html

The only difference according to QSC is the addition of the gasket.:D

I know you'd like to the see the RS28F as well Pete!

[dantheman]

Re: Some design ideas for Dipole/OB needed?

Here's my measurement on the PE 10" WG w/ a selenium D220:

in 11.25 degree steps starting at 11.25 degrees off axis and going out to 90 sitting on top of a box.
This version shows the on axis dip and my first filter attempt:


Dan

[johnk...]

Re: Some design ideas for Dipole/OB needed?

I would not try to clone the 907. I f you have not seen measurements look at this:



In particular look at the green trace for the midrange. It shows the draw back of using a small driver on a wide baffle. The driver remains fairly omni-directional above the dipole peak (around 600 Hz) and as a result there is a dip (first dipole null) around 1.2k Hz. The mid to tweeter crossover would ideally be around 800 Hz max. This is just another case of where a commercial manufacture pays more attention to what it looks like as opposed to what it measures and sounds like. Here is the measurement of the complete system:



Here is a link to the complete Sterophile article. Note that the elevated low frequency response is due to near field measurement of the woofer, uncorrected for the dipole eq.

[martin]

Re: Some design ideas for Dipole/OB needed?

In particular look at the green trace for the midrange. It shows the draw back of using a small driver on a wide baffle. The driver remains fairly omni-directional above the dipole peak (around 600 Hz) and as a result there is a dip (first dipole null) around 1.2k Hz.

How did you determine that the single sharp dip at about 1.2 kHz in the green trace is due to a wide baffle?

Would a baffle diffraction issue above the hump result in a series of small peaks and dips that are more rounded, a ripple in the response. A sharp null like that looks more like some artifact of a system or driver resonance.