Paging Mike V @ PE

[jims]

Hi,

I posted this a week ago and didn't get an answer for questions 1 & 2 below. Seems beyond the knowledge of the denizens of the board, as one would need complete product specs that aren't readily available. Could you give it a shot?

Thanks!
Jim

Original message:

I have the Dayton SA240 sub amp and have three questions:

1. Does this amp have a subsonic filter? If it does, what are the cutoff frequency and order of the filter? I'm concerned about driver overexcursion at low frequencies in a vented sub. Some other folks have suggested that a lot of sub amps have a subsonic filter, but there's no switch on the amp for defeating one, and there's no mention of it in the specification sheet that came with the amp.

2. If it doesn't have a subsonic filter, I am considering building a line level passive filter that would be inserted between my HT receiver and the low-level input of the SA240. To do that, I need to know the input impedance of the SA240 to design the filter properly. Can you tell me that?

3. I've found that the sub amp is warm all the time, even when it's been switched fully off (not on "auto") for a couple days. Is that normal?

Thanks!
Jim S.

[ren]

> Hi,

> I posted this a week ago and didn't get an
> answer for questions 1 & 2 below. Seems
> beyond the knowledge of the denizens of the
> board, as one would need complete product
> specs that aren't readily available. Could
> you give it a shot?

> Thanks!
> Jim

> Original message:

> I have the Dayton SA240 sub amp and have
> three questions:

> 1. Does this amp have a subsonic filter? If
> it does, what are the cutoff frequency and
> order of the filter? I'm concerned about
> driver overexcursion at low frequencies in a
> vented sub. Some other folks have suggested
> that a lot of sub amps have a subsonic
> filter, but there's no switch on the amp for
> defeating one, and there's no mention of it
> in the specification sheet that came with
> the amp.

> 2. If it doesn't have a subsonic filter, I
> am considering building a line level passive
> filter that would be inserted between my HT
> receiver and the low-level input of the
> SA240. To do that, I need to know the input
> impedance of the SA240 to design the filter
> properly. Can you tell me that?

> 3. I've found that the sub amp is warm all
> the time, even when it's been switched fully
> off (not on "auto") for a couple
> days. Is that normal?

> Thanks!
> Jim S.

1. 20Hz -6dB
2. See #1
3. The amp is always ON, but it's just muted when in standby.

[MikeV@parts-express.com]

I will have to get with the product manager of that part in order to verify what REN has stated, but I believe his statements to be true.

I'm pretty sure that most plate amps have a low frequency high pass filter to increase efficiency and decrease heat output, extending longevity of the amplifier. As far as your worries about the warmness when not in use, all I know if that if it is plugged in it draws power. I wouldn't worry about warm though.

I wouldn't suggest relying upon the LF high pass to protect your subwoofer, especially if your are using this in a home theater application. Many studios are incoporating infrasonic information into the sound mix of their DVDs. Here's an except for proof:

"Of all the test selections, I was most eager to see how the Bag End would cope with the brutal 7Hz and 18Hz drones in the infamous "F'ing Irene" scene of Black Hawk Down (Fig.C3). At approximately the same overall playback level you'd experience in a good commercial cinema, the lower of the two subsonic components was nowhere in evidence perceptually (it won't be in that cinema, either). The 18Hz component made its presence known palpably, if not quite as pants-flappingly as with the Genelec HTS6 reviewed in Part 1 or the ServoDrive in this installment. To gauge audible distortion, I disconnected the main speakers and just listened to how cleanly these three infrasonic champs rendered the 18Hz chopper rumble. The Bag End came in second in this particular face-off, edged out by the massive Genelec, though it should be noted that when I played the scene with the main speakers reconnected, the distortion products of all three were masked by higher-frequency chopper noises. This suggests that, in actual practice, all three might well sound equally clean on this passage."

That passage was taken from <A HREF="http://www.ultimateavmag.com/feature...ay/index2.html">http://www.ultimateavmag.com/feature...ay/index2.html</A>

Let's say you are listening to SPL levels of around 110 dB (loud, but not unheard of). In order to achieve that with a generic subwoofer of 86 dB @ 2.83V/1m sensitivity, you would need around 256 watts of power. The LF high pass filter would limit the power at 20 Hz to 64 watts (arbitarily). At 10 Hz, you would still have 16 watts of power reaching the speaker.

That may not sound like much, but is more than enough power to drive an average subwoofer past Xmax.

If you are worried, BassBox predicts where the subwoofer would reach failure with relation to power and frequency. Linear Team's WinISD Pro may also do this, and since it's free, I recommend checking it out. <A HREF="http://www.linearteam.dk/">http://www.linearteam.dk/</A>.

As far as the input impedance, I'm not sure that spec would help as it fluctuates with frequency. I doubt that engineers have provided the input impedance response graph that would be required to build an appropriate filter.

That being said, you could always do the listen and gain adjust method using the referenced track from Black Hawk Down above.

Now you see why I only recommend sealed subwoofers for HT DVD LFE playback.

[jims]

> I will have to get with the product manager
> of that part in order to verify what REN has
> stated, but I believe his statements to be
> true.

Thanks! It would be great if you could verify that.

> I'm pretty sure that most plate amps have a
> low frequency high pass filter to increase
> efficiency and decrease heat output,
> extending longevity of the amplifier.

Could you find out if it's a first or 2nd order filter? What is the cutoff frequency? Is it the same as the boost circuit? I have the unboosted version of the amp, but I know that the settings can be changed using the table posted online.

As far
> as your worries about the warmness when not
> in use, all I know if that if it is plugged
> in it draws power. I wouldn't worry about
> warm though.

Ok.

> Let's say you are listening to SPL levels
> of around 110 dB (loud, but not unheard of).
> In order to achieve that with a generic
> subwoofer of 86 dB @ 2.83V/1m sensitivity,
> you would need around 256 watts of power.
> The LF high pass filter would limit the
> power at 20 Hz to 64 watts (arbitarily). At
> 10 Hz, you would still have 16 watts of
> power reaching the speaker.

> That may not sound like much, but is more
> than enough power to drive an average
> subwoofer past Xmax.

> If you are worried, BassBox predicts where
> the subwoofer would reach failure with
> relation to power and frequency. Linear
> Team's WinISD Pro may also do this, and
> since it's free, I recommend checking it
> out. <A HREF="http://www.linearteam.dk/">http://www.linearteam.dk/</A> .

Yes, I actually did model this in WinISD Pro. That's how I identified this issue to begin with. The model shows considerable xmax exceedence at low frequencies.

> As far as the input impedance, I'm not sure
> that spec would help as it fluctuates with
> frequency. I doubt that engineers have
> provided the input impedance response graph
> that would be required to build an
> appropriate filter.

> That being said, you could always do the
> listen and gain adjust method using the
> referenced track from Black Hawk Down above.

> Now you see why I only recommend sealed
> subwoofers for HT DVD LFE playback.

Yes, it does make some sense to use sealed subwoofers for HT. However, I think a vented one will be ok as long as I'm aware of the issue.

Thanks again,
Jim S.

[Brent_S]

> Hi,

> I posted this a week ago and didn't get an
> answer for questions 1 & 2 below. Seems
> beyond the knowledge of the denizens of the
> board, as one would need complete product
> specs that aren't readily available. Could
> you give it a shot?

> Thanks!
> Jim

or teach the man to fish. Most likely, since the answers you seek are readily available on PE's product page for the SA240, no one felt like doing the reading for you.

<A HREF="http://www.partsexpress.com/pdf/300-804boost.pdf">http://www.partsexpress.com/pdf/300-804boost.pdf</A>
<A HREF="http://www.partsexpress.com/pdf/300-804r.pdf">http://www.partsexpress.com/pdf/300-804r.pdf</A>


(Originally posted by: Brent S)

[jims]

There's no link to the 2nd article from the product page. I'm not sure how you found it. Others responded to my post last week, and an earlier post, and from their responses it seems they weren't aware of the article either. Since it states a different power output (200 watts vs 240 watts), I wouldn't be 100% sure it's up to date.

I did previously find the boost table link on the product page.

Jim S.

> or teach the man to fish. Most likely, since
> the answers you seek are readily available
> on PE's product page for the SA240, no one
> felt like doing the reading for you.

>
> <A HREF="http://www.partsexpress.com/pdf/300-804boost.pdf">http://www.partsexpress.com/pdf/300-804boost.pdf</A>
>
> <A HREF="http://www.partsexpress.com/pdf/300-804r.pdf">http://www.partsexpress.com/pdf/300-804r.pdf</A>

[Brent_S]

> There's no link to the 2nd article from the
> product page. I'm not sure how you found it.
> Others responded to my post last week, and
> an earlier post, and from their responses it
> seems they weren't aware of the article
> either. Since it states a different power
> output (200 watts vs 240 watts), I wouldn't
> be 100% sure it's up to date.

> I did previously find the boost table link
> on the product page.

> Jim S.

My apologies, that did come off a bit more harsh than I intended.

Only the title of Darren's review says 200 watts while saying 300-804 at the same time. All other references are appropriate to the SA240. PE doesn't appear to reuse part numbers so there's only one 300-804, the SA240.

Darren's article is on the "Reviews" tab of the SA240 product page. <A HREF="http://www.partsexpress.com/pe/pshow...4&ctab=11#Tabs">http://www.partsexpress.com/pe/pshow...4&ctab=11#Tabs</A>

Peace.

-Brent




(Originally posted by: Brent S)

[jims]

No big deal, and thanks, because the article has a lot of useful info in it. I wouldn't have found it otherwise.

You're right that it only says 200 watts in the title. Maybe just a typo? I did find one other inconsistency - the article says the variable low pass has a range of 40 to 160 Hz, but the amp itself and the current spec sheet say 40 to 180 Hz. Could just be another typo or a minor design change.

I should also make it clear that, when I said that no one on the board had answered my questions, I wasn't trying to be critical of the people who participate here. My point was just that the info didn't seem to be readily available. I even checked the Dayton web site and did a general google search before posting, and the info didn't pop up anywhere.

Thanks again,
Jim

> My apologies, that did come off a bit more
> harsh than I intended.

> Only the title of Darren's review says 200
> watts while saying 300-804 at the same time.
> All other references are appropriate to the
> SA240. PE doesn't appear to reuse part
> numbers so there's only one 300-804, the
> SA240.

> Darren's article is on the
> "Reviews" tab of the SA240 product
> page.
> <A HREF="http://www.partsexpress.com/pe/pshow...4&ctab=11#Tabs">http://www.partsexpress.com/pe/pshow...4&ctab=11#Tabs</A>
> Peace.

> -Brent