Physical speaker measurements: driver dimensions

[escape2]

Is there any sort of standard within the industry pertaining to how driver sizes are listed?

For example, if a speaker manufacturer states that their speaker includes a 6.5" driver, between which two points exactly is that 6.5" measured? Is it between the ends of the rubber surround? Is it the outside diameter of the frame in which the surround is housed? Is it the distance between opposing mounting holes and/or mounting bolts?

I've gotten a speaker recently that claims to have a 4.5" driver, but when you measure to the outside of the rubber surround, it's exactly the same size as another company's 4" driver. The only difference is that the mounting bolts are spaced further apart. Sounds like a pretty meaningless number, if they just measure bolt to bolt on the opposing end. I know tweeters are not measured like that at all.

Anyway, just curious.

Thanks!

 

[pozz]

I've noticed this too. I don't know about existing standards. It seems like another area to blur the line between information and marketing, like wattage or SNR.

 

[Beave]

I don't think there's an official standard, but most measure by the outer edge of the frame. The measurement is typically done in centimeters (since everybody but the US uses the metric system, and most drivers are made in Europe or Asia). Then, for the US market, the result in centimeters is converted to inches, and typically rounded *up* to the nearest half inch or inch.

A more standardized measurement of a driver size is its Sd, a measure of the cone area. You can see the Sd given in many driver specs, but not in many speaker specs.

 

[3125b]

Interesting question, I never thought about that.
I just measured Mackie MR524, the rubber of the woofer is 12cm in diameter, wich equates to 4.72" - they advertise 5.25", so they must mean the frame. The total surface area would be 113cm².
The supposedly 6.5" drivers of the Focal Alpha 65 are really 14,5cm or 5.71" in diameter, wich is really far off. The total surface area would be 165cm², 46% more than the MR524.
These non-standard measurements are something that actually seems to be more or less common with headphones as well.

 

[MZKM]

Yeah, I have 2 towers, one is spec’d at 7” at the other 6.5”, the latter though is actually larger from surround to surround and screw to screw.

 

[Vini darko]

Reminds me of bicycle tyre measurements. Essentially abitary.

 

[escape2]

4.5" (advertised) driver from Energy:

4" (advertised) driver from Dayton:

 

[pozz]

This is a good idea for a comparitive study, if someone wants to make an effort.

 

[pozz]

These non-standard measurements are something that actually seems to be more or less common with headphones as well.

Headphones too? Can you give an example?

 

[mhardy6647]

There used to be standards -- EIA standards -- that applied to the cutout diameter, mounting circle, stuff like that.

I believe, e.g., that these very vintage EV drivers are "EIA-compliant" (as we'd say nowadays)
I'd like to think that at least some components still cleave to it

This is a good idea for a comparitive study, if someone wants to make an effort.

One could just look at datasheets from, e.g., https://www.parts-express.com/ or https://www.madisoundspeakerstore.com/ and whup up a little comparative spreadsheet (were one suitably motivated, that is).

This one (for the record) -- is not

 

[3125b]

Can you give an example?

The AKG K371 (wich I just got) would be an example.

 

[Frank Dernie]

When I built my first speaker in 1968 I used an 8" unit and I seem to remember the 8" was the OD of the unit, though it might have been the pcd of the fixing holes.
The 9" bass unit in my Proac EBS speakers is the pcd of the fixing holes.

I don't think the quoted diameter has ever been the cone itself, though the dome of the 3" dome unit in the Proacs is the actual dome itself, the chassis cutout hole is 6" diameter.
These are both ATC drivers, there is obviously no "standard".
I have a pair of Devialet phantoms and they have 2 unusual layout bass drivers with a domed effective piston with its suspension roll inside, so one can't see it, the effective driver area is huge compared to many speakers.

 

[Juhazi]

Don't know about standards, but looks like NO. Even loudspeaker driver manufacturers use haphazard measurements.

For simulations, to determine actual Sd (radiating surface area) of a circular unit, diameter should be taken from middle of surround roll. All drivers spec sheeets give dimensions and also Sd, but I haven't checked if Sd is right. Safer to measure diameter or estimate from the picture.

An example from SEAS http://www.seas.no/index.php?option...le&id=92:h1456-08-er18rnx&catid=44&Itemid=461

and SB Acoustics Satori https://sbacoustics.com/product/6½in-satori-mw16p-4/
and SBA https://europe-audio.com/datasheets/sba/SB17NRXC35-4.pdf

SEAS is advertized as 6½" and SB as 6 or 6½" and they have thicker surround roll than the SEAS

frame diameter half of roll ¤ Sd on datasheet Sd calculated by https://www.mathsisfun.com/geometry/circle-area.html
SEAS 176mm 135mm 136cm2 143cm2
Satori 165mm 125mm 119cm2 111cm2
SBA 170mm 125mm 118cm2 109cm2

 

[hardisj]

I have tested over 100 drivers in the last 10 years. The answer is: no.

Sometimes the size is based on flange, sometimes half-surround, sometimes who knows. They generally just shoot for an approximation. You’re best served to use SD to back out the size (which should be half-surround based).

 

[MarkWinston]

I onow its an old thread but I was shocked to see how small the drivers were on my new Wharfedale Diamond 12.2. It was claimed 6 1/2 inches on the spec sheet but when the speaker arrived it even looked smaller than some of my 5 1/4 inch woofers. So I messaged Wharfedale and they told me 6 1/2 inches from one end of the chassis (basket) to the other. The cone is just barely 5 inches, definitely not moving as much air as some 6 1/2 inches should.

 

[Katji]

Is there any sort of standard within the industry pertaining to how driver sizes are listed?

They normally - most of them - work in millimeters, and then convert to early 20th century units for the large USA market, and the conversion gets rounded, so as to avoid giving measurements like 6 11/16".

 

[RobertMoore]

In 1968, when I made my first speaker, I utilised an 8-inch unit, and as far as I can tell, the 8-inch measurement was the outside diameter of the unit (OD), albeit it may have been the center-to-center distance (ccd) of the fixing holes. My Proac EBS speakers have a 9" bass unit, and the pcd of the mounting holes is equal to the pcd of the speaker's tweeters.

Although the dome of the 3" dome unit in the Proacs is the real dome itself, the stated diameter has never been the dome itself, and the chassis cutout hole is 6" in diameter.

There is certainly no "standard" when it comes to ATC drivers like these two.

The effective driver area of my Devialet Phantoms is far larger than that of most speakers, and the speakers themselves have a distinctive architecture due to the use of a domed effective piston that hides its suspension roll within.

 

[Grotti]

In 1968, when I made my first speaker, I utilised an 8-inch unit, and as far as I can tell, the 8-inch measurement was the outside diameter of the unit (OD), albeit it may have been the center-to-center distance (ccd) of the fixing holes. My Proac EBS speakers have a 9" bass unit, and the pcd of the mounting holes is equal to the pcd of the speaker's tweeters.

Although the dome of the 3" dome unit in the Proacs is the real dome itself, the stated diameter has never been the dome itself, and the chassis cutout hole is 6" in diameter.

There is certainly no "standard" when it comes to ATC drivers like these two.

The effective driver area of my Devialet Phantoms is far larger than that of most speakers, and the speakers themselves have a distinctive architecture due to the use of a domed effective piston that hides its suspension roll within.

This resembles #12: is it you, @Frank Derney????

 

[Frank Dernie]

This resembles #12: is it you, @Frank Derney????

No he isn’t.
I was somewhat surprised to see this unattributed slightly (wrongly) re-quote of my post.

 

[Curvature]

You’re best served to use SD to back out the size (which should be half-surround based).

This is worth repeating.