DIY Flat Panel Speaker Love

[Gary.M]

Although I am not exactly sure I think they are the same its just that the frog one has the plastic casing with the 4 legs around it while the HS does not. The reason I think that the exciters sound better with the plastic legs removed is because the exciter is suppose to move and flex the material its on but the extra legs holds the material so it does not flex as much. I just simply cut off the legs with a strong scissors.

I think others have removed the housing completely. I seem to recall it comes off easily.

[Unbiasedsound]

I think others have removed the housing completely. I seem to recall it comes off easily.

Oh ok, even better.......I was wondering does the Tectonic TEAX25C10-8/SP have the same amount of midrange as the Dayton DAEX25FHE-4 or is it less? From the exciters ive been using it seems the midrange starts to drop off when the exciter is 19mm or less....while the tectonic 13mm which is the smallest exciter I have owned has barley any bass or midrange and sounds more like a tweeter.

[Gary.M]

Oh ok, even better.......I was wondering does the Tectonic TEAX25C10-8/SP have the same amount of midrange as the Dayton DAEX25FHE-4 or is it less? From the exciters ive been using it seems the midrange starts to drop off when the exciter is 19mm or less....while the tectonic 13mm which is the smallest exciter I have owned has barley any bass or midrange and sounds more like a tweeter.

You can see from the graphs. Very similar midrange response between them...

[Unbiasedsound]

You can see from the graphs. Very similar midrange response between them...

Oh ok , I am no expert at reading those graphs but it seems like the DAEX25FHE has a slightly higher midrange then the tectonics.

[rmeinke]

I'm still not convinced. You have confused "motor". The voice coil and magnet assembly together are the motor, but the voice coil does the work. The magnetic field is what links them and the force is exerted through the magnetic field, not through the suspension.

Lets do a little thought experiment.

Take an exciter with a zero mass magnet assembly. (or at least close to) mounted to a DML panel.

Apply a voltage step to the voice coil, say 0V to 1V. Current will flow in the voice coil and generate a force, lets say the polarity is such that the magnet assembly moves away from the panel. It will move until the suspension restrains and prevents further movement.

The movement though has involved (almost) no mass, therefore (almost) no energy. The panel will not be moved.

The exciter can be fed a sinewave likewise and will oscillate, but because of the lack of mass will not exert any force on the panel.

Now consider the other extreme. Consider an exciter with a very high mass magnet assembly. Apply the same step. The exciter voice coil will move, pushing against both panel and exciter magnet masses. As the exciter magnet mass is so high it will move almost not at all, instead the panel will move away from it.

So there is an interaction based on the relative masses of the exciter magnet assembly and panel. The suspension will have a damping effect and will restrain maximum amplitude.

UnbiasedSound had noted that he thought the smaller exciters were better at high frequencies, perhaps there is a balance between small and agile vs large and sluggish? The Ultra is a large exciter with a lossy construction and large voice coil.

So far my finding is that the bamboo ply, with its higher mass and density, seems to allow high frequency to propagate much better than the lossy materials such as the doped cardboard. And a smaller exciter provides the most hf extension.

The Podium speakers use fixed and supported drivers (= to an exciter with very high mass magnet as it will not be moved by the voicecoil) attached to a very rigid panel. I think that material most likely also propagates high frequencies extremely well. Also as the exciter is restrained by the mounting it could be designed, or chosen, to have a smaller voicecoil and appropriate magnetic circuit parameters to work well at high frequencies while applying quite some force. Perhaps a stripped down tweeter mounted like this might work well?

After rereading my post, I totally butchered the term motor and seemingly use it inconsistently... my bad, was in a hurry.. got me. But Gary, I hope you can see the point of this discussion and the importance of the suspension in exciter design. It not inconsequential.

It is one of the discriminating differences between a traditional driver and an exciter and the primary reason why a traditional driver doesn't work well for DML constructions (along with the longer throw but that goes hand in hand with a much stiffer suspension). It also why we have those silly mounting tabs on some and why others that don't have mounting tabs as they have self-supporting suspensions.

Are you REALLY going to respond that you aren't convinced??? IIIIIIIIIiiiiiiiiii....

When we are talking about "better" high frequency response what are we talking about specifically. In my posts I'm talking about HF extension. I think HF extension is fairly well understood and doesn't vary much from a traditional dome tweeter.

The honeycomb panel that Podium uses I'm sure does very well in the upper registers. Katz states a panel should "ring like a bell"... I believe a material's damping properties may likely be a key aspect for improving HF sound quality (and thinner would be better than thicker). Of course it needs to be light and rigid. No, high mass is not good.

btw... a stripped down tweeter won't work well in a DML construction because... what for it... what for it... its very compliant suspension.

[rmeinke]

In summary, I've been aiming for a panel that can go from about 200-300Hz on up, with an open baffle woofer filling in below. I may have what I want. Certainly a listen to this single bamboo panel was very impressive.

Glad you are digging your bamboo panels btw. Looking at the graphs, the recessed low freq. response suggests an overly rigid panel (not that it is bad given your design parameters). In your search, did you come across a thinner (more flexible) bamboo panel?

[Gary.M]

Are you REALLY going to respond that you aren't convinced??? IIIIIIIIIiiiiiiiiii....

When we are talking about "better" high frequency response what are we talking about specifically. In my posts I'm talking about HF extension. I think HF extension is fairly well understood and doesn't vary much from a traditional dome tweeter.

Yep, I stick to my guns. Suspension is not the determining factor. By HF extension I mean exactly what you say... better high frequency response. The techtonic exciter on the 3mm ply is as close to perfect as I would want. No eq needed and flat enough out to 20k.

[Gary.M]

Glad you are digging your bamboo panels btw. Looking at the graphs, the recessed low freq. response suggests an overly rigid panel (not that it is bad given your design parameters). In your search, did you come across a thinner (more flexible) bamboo panel?

Thats fine, I'm not looking for low frequency response. I have a 15" open baffle woofer to deal with that. :-)

[Gary.M]

The honeycomb panel that Podium uses I'm sure does very well in the upper registers. Katz states a panel should "ring like a bell"... I believe a material's damping properties may likely be a key aspect for improving HF sound quality (and thinner would be better than thicker). Of course it needs to be light and rigid. No, high mass is not good.

Don't place too much faith in quotes from Shelley Katz. I have it on very good authority that he is no longer with Podium, in fact hasn't been for some time. He also was never a technical man as far as the design goes... He was a good story teller and marketing man.

[Gary.M]

btw... a stripped down tweeter won't work well in a DML construction because... what for it... what for it... its very compliant suspension.

Have you tried it? And note that I'm talking about a driver that is mounted to a beam behind the panel... not using it as a self supported exciter. Its on my list as something to try, and I have an open mind. I think it might work, but I could also be wrong. Let's not discard anything that hasn't been tried.

[rmeinke]

I think others have removed the housing completely. I seem to recall it comes off easily.

I have this exciter and was going to do a project with it however getting the case removed required carefully cutting as the legs and the outter body and part of the exciter assembly itself. Its possible and may be worth the effort though. It only connects in 2 locations so once you slowly cut off the plastic outer body its possible to just snip at the 2 connection points and at that point its pretty clean.

The old buyout exciters from 5-6 years ago is what Gary is likely referring to. Those were just glued on.

[rmeinke]

Thats fine, I'm not looking for low frequency response. I have a 15" open baffle woofer to deal with that. :-)

It certainly wasn't criticism... just an observation I think the bamboo panels and OB will be excellent together!!

[rmeinke]

Yep, I stick to my guns. Suspension is not the determining factor. By HF extension I mean exactly what you say... better high frequency response. The techtonic exciter on the 3mm ply is as close to perfect as I would want. No eq needed and flat enough out to 20k.

Didn't mean to sounds rude in my posts... I just didn't want folks to think that the only purpose of suspension was to "hold things together".

[Gary.M]

Didn't mean to sounds rude in my posts... I just didn't want folks to think that the only purpose of suspension was to "hold things together".

No problem. We're all hear to share and learn. :-)

[rmeinke]

Have you tried it? And note that I'm talking about a driver that is mounted to a beam behind the panel... not using it as a self supported exciter. Its on my list as something to try, and I have an open mind. I think it might work, but I could also be wrong. Let's not discard anything that hasn't been tried.

No I have not tried it and think experimenting is always a great learning experience. Unfortunately, you will find out very quickly what role suspension plays in exciter design my friend. :-)

A traditional tweeter's suspension is designed to support a VERY lightweight diaphragm. On bamboo (or any other material we are currently using) the force of the powerful motor acting to move the weight of the panel will damage and likely tear the suspension in short order. Alignment of the tweeter and panel would also be difficult due to the fragile suspension and tight tolerances.

Best bet would to connect the voice coil to a material like mylar or some other very light weight material. That would probably work fairly well I imagine