I have written in past about my lack of love to the BMS drivers. The crazy, as far as I concerned “annoyingly wiling” angeloitacare brought this subject to this forum while he was galloping across Web, “picking from graves” about his new dB-Design’s Orphean horns. The Orphean horns use the coaxial drivers and it made me to pay attantion to them again.

I am not wiling to knock the dB-Design products. The dB-Design do whatever they do in the context of what they can, what they understand and in what they can sell to their mostly primitive and “lightly informed” customers. The dB-Design uses in their Orphean horns the coaxial BMS 4592ND driver. They claim that they highly modify the driver (whatever it means). I do not know the externs of the modification but I’m sure that wherever they do they keep the coaxial concept unchanged. I will leave alone other negative qualities of BMS and dB-Design and I would like to expend a little the coaxial concept itself.

Many companies in past made the coaxial drivers. Nowadays the car audio campmates love the coaxials drivers because the understandable space reasons. However, do the coaxial drivers in fact offer any SONIC ADVANTAGES in context of our larger space – the listening rooms? Obviously we are not talking about the specific BMS drivers anymore. The BMS was made for very different then Sound objective. If you see that BMS is very proud that their 112dB sensitively drivers can handles 1500W of power then you know in whish ass those drivers should be stuck up. Lets turn our attention form the elevator transducers – BMS to an enter family of the coaxial compression drivers.

Any company that sells coaxial drivers loves to tall story about point source sound. Sure it is the case but why it IS NECESSARY BETTER? In fact I feel that it worse as the unified acoustical centre does not allow learning that the crossover between the drivers does not work properly. However, the biggest problems I see when people try to merge the ides of coaxial drivers with horns.

It is known to anyone what dealt with horns the each frequency range there is an optimum size of horn. Make deeper horns and you loose response and transient at HF and pick some HF beaming. Make too shallow you have not enough LF equalization and your driver acts as a direct radiator. So, a small compression transducer with 2” throat will obviously run a horn profile for let say -500Hz…. and this profile is WAY too deep for any HF that might be radiated from THE SAME THROAT. Is it absolutely FUNDAMENTALLY IMPOSSIBLE to use coaxial compression drivers (with front horn) of am I missing anything?

Michaelz wrote:

Some drivers have a rising db curve from low to high frequencies.  The horn may help with flattening the FR.  If the FR of a given coaxial compression driver is flat, I would agree with your conclusion.

all cabperson drivers have rising db curve from low to high frequencies. The entire concept of compression driver (that is misleading name) is not that a diaphragm is loaded into a front chamber (actually in most case it is back chamber) but that the driver must use horn for external equalization. It is worthless to talks about frequency response of a compression driver without a horn and any rising of decaling db curve from low to high frequencies is juts improper selection of horn EQ for a given driver (or a defect of the gioven driver itself, which BTW is very common)

So, let see what the “bad” people do in the coaxial drivers. The LF part of the coaxial is presumably properly loaded but not the HF. In the BMS driver the HF kicks-in at 7KHz and for 7KHz the 300Hz horn is irrelevant- it is like the horn does not exist. So, the LF part of the coax is loaded but the HF part is shooting though with being loaded (or loaded with own small horn). However the 2” throat of the LF horn is VERY small opening and… this hole (though wish the HF driver shoots) is located… at the front of the mouth of the HF horn – this is VERY bad.

From my photography life I know that diffraction is a process of nonlinear bending of the source waves to the area of geometrical shadow. Interesting the diffraction become to be noticeable when the diameter of the hole is co-measurable with the length of the waves … It is exactly what should be doing on in the coaxial compression drivers.