Eminence Alpha 15" has bass in OB?

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Hi,

I know that eminence alpha 15" is one of the most popular speaker for OB.

I was looking around for a potential woofer for a new OB project so why not start looking at the alphas.

When I look at the datasheet, I got a shock.

http://www.parts-express.com/pdf/290-407s.pdf

The bass rolls off at 100Hz and by the time it reaches 30Hz, it's already down by 20dB...

So how can a speaker like that be good for bass? :confused:

One can easily get a 6" woofer with better bass response than that, so what gives.

According to the datasheet, it should sound horrible as a woofer, much less an OB one.

Anybody care to comment on that?

Oon
 
Before we get any further on this topic, do most people introduce a bass boost to the speaker either by passive means or active means by biamping?

From what i know in loudspeaker theory. A bass reflex will introduce a hump and can move the -3db point lower. Sealed box if done properly can introduce a steeper slope. Open baffle just cuts the bass. I believe the measurement is done in infinite baffle. So unlikely the bass performance in open baffle will be better.

Yet i am aware that many people have measured their OB system with this speaker with frequency response down to 40 hz or so. So what's the catch, seems to contradict manufacturer's datasheet...

Oon
 
When I look at the datasheet, I got a shock.

http://www.parts-express.com/pdf/290-407s.pdf

The bass rolls off at 100Hz and by the time it reaches 30Hz, it's already down by 20dB...

So how can a speaker like that be good for bass? :confused:

One can easily get a 6" woofer with better bass response than that, so what gives.

According to the datasheet, it should sound horrible as a woofer, much less an OB one.

Anybody care to comment on that?

Oon

A few things

- With varying baffle width you change the frequency response of a dipole.
- A 15" barely has to move to produce sound
- 97db/w/m
- qts = 1.26

NOw what does that mean?

It means

- This driver won't have to move. Less excursion can be better than more excursion, even if it takes more power to do it.
- the high qts will affect the frequency response even in an OB. So if there are dipole losses, they are "offset" by the high Q "gains"
- We don't need 97db @ 1m. Let's say you have an 85db midrange. Now when you low-pass the 97db/w/m woofer, you have 12db :eek: of headroom to "offset" the dipole losses again.

Remember, if it's 97db @ 200hz, and -12db @ 50hz in an infinite baffle - That's still 85db of IB efficiency you have @ 50hz. That's not bad for an OB, especially since higher frequencies have more bass content. Some other 15" drivers may look "flatter" but are less efficient 80hz to 200hz. That means more EQ boost is needed above 50hz. If you have the same efficiency at 50hz, and more efficiency above 50hz, i say keep it :p.

...Now consider using two in parallel.
 
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Hi Rock Lee,

If you look at the graph from the link I put up in the first post, sensitivity is only about 73dB/W at 30Hz.... even though it is 92dB at 100Hz. That is why I can't get why it is possible to get any bass from that speaker.

Quite insufficient to match most "normal speakers".

MY other guess is that people might be driving it with valve amps, since there is a fairly high output impedance, the source become a little bit of a current source. I think the sharp rolloff is the high increase in impedance around Fs. Increasing to about 40 ohms. With a current source like amp, the increase in impedance is not felt so much. in other words the voltage will be automatically be boosted to compensate for it and hence producing more bass.

Any thoughts?

Oon
 
If you look at the graph from the link I put up in the first post, sensitivity is only about 73dB/W at 30Hz.... even though it is 92dB at 100Hz. That is why I can't get why it is possible to get any bass from that speaker.

That graph itself doesn't seem right to my eyes in the bass, which was probably incorrectly spliced around 300hz - that looks like a very smooth Q < .5 rolloff of a different driver.

A Q = 1.4 /Fs = 40hz woofer like the alpha 15 would have a rather different IB rolloff. Just run the ts paramters through any sealed box sim for an extremely large sealed box ie 15000L - and you'll see that response should peak near free air resonance 40hz not have a shallow rolloff.
 
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Hi Rock Lee,

If I want a more accurate source, this is the direct one from Eminence..

http://www.eminence.com/pdf/Alpha_15A.pdf

I know this doesn't make any sense, which is why I started this thread, but this is the manufacturer's datasheet from their website.

The Deltapro 15 has a similar graphical response.... strange isn't it..:confused:

http://www.eminence.com/pdf/Delta_Pro_15A.pdf

So at this moment I am still tryoing to figure out why the world of difference between what the forum apparently observes and the supplied datasheet...

Oon
 
So at this moment I am still tryoing to figure out why the world of difference between what the forum apparently observes and the supplied datasheet...
Look at these simulations which start from the published TSP: Open Baffle vs. Closed/Vented Box Speakers

From what I know they are more in line with reality than your deductions from the manufacturers data sheet. This will not keep many people from finding the remaining efficiency unacceptable.
 
Hi,

Its best to assume all Eminence measurements below say 100Hz are inaccurate.

rgds, sreten.

Eminence measurements are accurate for the specified measurement condition:

The microphone is mounted 1m from a 2 ft. X 2 ft. baffle built into the wall with the speaker mounted flush against a steel ring for minimum diffraction, in a 2700 cu.ft. chamber with fiberglass on all six surfaces (three with custom-made wedges) driven by a Hafler P1500 Trans-Nova amplifier.

Whether that measurement has any correlation to a usual environment is certainly open to discussion, but it allows for comparison of their different drivers under the same test conditions.

That said, anyone concerned about having enough low bass should not be considering OB as a solution;).
 
On a personal note i believe the measurements are real but need not agree with the t/s parameter. T/s parameters is just an attempt to model the behaviour of the driver based on a mass and a spring with a dampener, does not take into consideration the acoustical properties of the cone, flexing of the cone etc.

I believe the t/s parameters will bring us closer to understanding the properties of the speaker but is no a substitute for the real measurement. There is more to play. After all you can get all the t/s parameter without having a microphone. You can even get a t/s parameter of a loudspeaker without a cone. I see you try to get that to sound....

Oon
 
On a different note, do you guys think that eminence is measuring their speakers differently from other manufacturers, and hence they disadvantage themselves? Kinda strange.... if it was done by one of us i would sincerely doubt the result, but since it is done by a manufacturer i am sure he did it properly.

One discrepancy between their measuring technique and our living room is their measurement is done in an acoustically dead room, anechoic chamber. Our living room will definitely have more reflections off the walls, and bass is certainly more reflective, and less likely to be absorb, the bass response should certainly be better....

Oon

Oon
 
On a personal note i believe the measurements are real but need not agree with the t/s parameter. T/s parameters is just an attempt to model the behaviour of the driver based on a mass and a spring with a dampener, does not take into consideration the acoustical properties of the cone, flexing of the cone etc.

I believe the t/s parameters will bring us closer to understanding the properties of the speaker but is no a substitute for the real measurement. There is more to play. After all you can get all the t/s parameter without having a microphone. You can even get a t/s parameter of a loudspeaker without a cone. I see you try to get that to sound....

Oon

Hi,

Beliefs based on personal opinion with no technical basis are just that.

Technically you don't have a leg to stand on, and your making no
attempt to answer the OP's question, just muddying the water.

rgds, sreten.
 
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Another thought comes to mind. This is a high effienciey speaker with fairly low x-max. So there is a possibility the coil that is moving out of the magnetic gap and the experiencing poor linearity. In other words. It might be experiencing soft clipping at 1w. So it might have a response much close to its t/s parameter at 0.1W. Which is still pretty loud....

Oon
 
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