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Pros and Cons of larger compression drivers


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I am still struggling to understand the benefits of speakers with larger compression drivers.

 

For some time I've been interested in the RCF HD32-A which I am considering as a replacment and hopefully a step up from the PRX612 that I currently use (with subs). The HD32A is at least 50% more expensive than the PRX612 and the main reason for this appears to be the compression driver.

 

The compression driver in the HD32-A has a 3.0" voice coil with a 2.0" exit. The crossover frequency is 800 HZ.

 

When I checked the spec's on the PRX612M it says 1.5" diaphragm. It doesn't give figures but I believe it has a 1.0" exit but i am not sure of the size of the voice coil. Crossover is 2kHz

 

I assume from the crossover point that the compression driver in the HD32-A is doing a lot more work than in the PRX612. Will this result in a better (more even) spread of sound and a longer throw?

 

Any other pros and cons.

 

Cheers

 

 

 

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I am still struggling to understand the benefits of speakers with larger compression drivers.

 

For some time I've been interested in the RCF HD32-A which I am considering as a replacment and hopefully a step up from the PRX612 that I currently use (with subs). The HD32A is at least 50% more expensive than the PRX612 and the main reason for this appears to be the compression driver.

 

The compression driver in the HD32-A has a 3.0" voice coil with a 2.0" exit. The crossover frequency is 800 HZ.

 

When I checked the spec's on the PRX612M it says 1.5" diaphragm. It doesn't give figures but I believe it has a 1.0" exit but i am not sure of the size of the voice coil. Crossover is 2kHz

 

I assume from the crossover point that the compression driver in the HD32-A is doing a lot more work than in the PRX612. Will this result in a better (more even) spread of sound and a longer throw?

 

Any other pros and cons.

 

Cheers

 

 

Andy would know more, but off the top of my head ....

 

The larger diaphragm is harder to design without distortion to the HF. My experience has been that these drivers are smoother; however, it could just be that they are more expensive and have better materials in them.

 

The positive side is that they can cover lower frequencies that are still too high for a 12" or 15" woofer to reproduce well.

 

In my own limited experience, 3 way speakers do the best job, but are generally bigger, heavier, and more expensive. This may also be incorrect since depending on the implementation, each cross-over could have issues at the cross-over frequency depending on how well the OEM designed things.

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With regard to the exit size, some of the original RCF 2" exit designs were reworked down to 1.4". With these changes, HF response was extended upwards as well as the higher frequency distortion lowered. It's the identical driver with a new throat/phase plug. It really has nothing to do IMO with lying. Many of their horn flairs are 1.4"/2" throats depending on the transition piece used.

 

One of the biggest challenges with 2" throats is that the larger diameter affects the higher frequencies much more significantly, BUT it handles lower frequencies much better. It's the biggest trade off in HF device design.

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With regard to the exit size, some of the original RCF 2" exit designs were reworked down to 1.4". With these changes, HF response was extended upwards as well as the higher frequency distortion lowered. It's the identical driver with a new throat/phase plug. It really has nothing to do IMO with lying. Many of their horn flairs are 1.4"/2" throats depending on the transition piece used.

 

One of the biggest challenges with 2" throats is that the larger diameter affects the higher frequencies much more significantly, BUT it handles lower frequencies much better. It's the biggest trade off in HF device design.

 

 

 

I disagree. The specific driver being discussed is only found in the HD-32A where it is advertised in press releases, spec sheets, and the RCF website as a 2" exit driver. Look up the driver by itself and the spec is 1.4".

 

My own 522A..... Advertised as 2" exit, but when I measure it, it's 1.4". How is that not lying? Heck, if it was 1.5" they could at least claim they rounded up.

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Unalaska has it correct, it depends on the throat it's deigned to work with, some drivers can use either a 1.4 or 2" throat horn depending on the specific throat exit adapter used. It allows the same basic motor to be optimized based on what the designer deems most important. RCF HF drivers are great drivers, I really prefer the 1.4" exit myself and that's what I design around when I use these drivers.

 

Some horns are available ONLY in 2" or ONLY in 1.4" so this set-up gives options that are otherwise not possible. Perhaps the marketing folks didn't grasp this whole concept, it appears that it's not all that clear to others too.

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Short of having a 3 way box IMO 2" throat horns are much smoother in the all important vocal range. Yes the trade off is the extreme HF but in SR this is often not as much of an issue (how much HF "smear" is there in most rooms anyway :-). Another benefit is MOST 2" exit setups also use a larger diameter voice coil (more power handling ability). True it is also usually crossed over lower but they still seem to be more bullet proof than smaller drivers. One big 6k squeal and a 1" will stop working but a 2" seems to take it in stride. This is a generalization and solely based on my observations (and the number of diaphragms I've replaced over the years :-).

 

My .02

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Short of having a 3 way box IMO 2" throat horns are much smoother in the all important vocal range. Yes the trade off is the extreme HF but in SR this is often not as much of an issue (how much HF "smear" is there in most rooms anyway :-). Another benefit is MOST 2" exit setups also use a larger diameter voice coil (more power handling ability). True it is also usually crossed over lower but they still seem to be more bullet proof than smaller drivers. One big 6k squeal and a 1" will stop working but a 2" seems to take it in stride. This is a generalization and solely based on my observations (and the number of diaphragms I've replaced over the years :-).

 

My .02

 

Good point. According to the spec sheet the voice coil in HD-32 is 3" and is bigger than the one in the woofer which is only 2.5". With a 800 Hz crossover the compression driver would be doing a lot of the work.

 

Given the spec's of these speakers they should be fantastic but I haven't read any raving reviews. I also haven't heard anything negative, so perhaps they are just too new.

 

I like em on paper but would really like to hear them in action before I cough up any hard any cash.

 

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Unalaska has it correct, it depends on the throat it's deigned to work with, some drivers can use either a 1.4 or 2" throat horn depending on the specific throat exit adapter used. It allows the same basic motor to be optimized based on what the designer deems most important. RCF HF drivers are great drivers, I really prefer the 1.4" exit myself and that's what I design around when I use these drivers.

 

Some horns are available ONLY in 2" or ONLY in 1.4" so this set-up gives options that are otherwise not possible. Perhaps the marketing folks didn't grasp this whole concept, it appears that it's not all that clear to others too.

 

 

I get the throat can be shrunk, but I'm talking about increasing the size. Did you look at the spec sheet I referenced? It's clearly a 1.4" exit driver. Then when they put it in the HD-32A it's suddenly larger. The exit can never be any bigger than it starts out.... right?

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My EAW boxes are all 2" exit B&C compression drivers.

 

I prefer the vocal clarity of a box with a larger 1.4" or 2" exit and lower xover points.

 

Back in the old days JBL had the 2" exit and typically the bullet or slots were used on top.

 

Altec always stuck with the 1.4" exit and better HF extension.

 

The tell is using a 500hz-800hz xover with a 2" exit.

 

There was a technical reason Altec moved away from the 500hz xover and moved it up to 800hz I cant remember why but

I think it was time alignment.

 

JBL had a 2inch exit compression driver with phenolic diaphagms that were great but lacked HF extension.

 

A 1" exit driver wont last long at those lower frequencies and especially when you pump some power into them.

 

It is all a trade off and how well the cone driver behaves on higher frequency dispersion at the xover point

and the overall design and power handling etc.

 

Heck there is a LOT more that goes into the overall design and choice of drivers, box size, ports, xovers and the list

goes on!

 

 

 

 

 

 

 

 

 

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I get the throat can be shrunk, but I'm talking about increasing the size. Did you look at the spec sheet I referenced? It's clearly a 1.4" exit driver. Then when they put it in the HD-32A it's suddenly larger. The exit can never be any bigger than it starts out.... right?

 

I see where you are coming from, but there were some specialized horns RCF used that adapted the 1.4" exit to 2" before the horn flair. The exit is not the active area ot the phase plug, often there is a 2:1 difference to try and maximize HF extension.

 

Here's the 1"-1.4" product where the same horn flair is used with 2 different driver exits through the use of a transition. http://www.rcf.it/en_US/products/precision-transducers/horns/hf94

 

There are also drivers that may use the same motor but a different exit assembly (that's the black area of the return plate) and they may call it the same number for OEM purposes (you can't buy it anyway) though it is functionally different. May have a different manufacturer's part number even though it's the same model. As long as it uses the same diapragm, that's all that matters to the end user.

 

I can think of a JBL product that was offered this way, the 2425 was offered as a 2 bolt for both finished products and raw driver sales but there was also a 2425 thread on that wa only available in a finished JBL product, though both were called 2425's. Since you couldn't buy the thread-on driver as a raw driver and both used the same diaphragm and had essentially the same specs (exit was 7/8" IIRC) the only differentiation was at the part number level and not the model level.

 

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