Is mounting a speaker on top of a sub a bad idea?

Yes.  Putting speakers on a vibrating subwoofer is always a bad idea and especially so when you’re talking about very expensive speakers like those Harbeths.  Subs can be very flexible in placement so I’d get creative with that to avoid having to use them as speaker stands.  

Thanks Soix.  You are confirming what my inner common sense is telling me.  

If you want your speakers above the subwoofers build a stand that straddles the subwoofers 

This is not a problem. Simply use a vibration isolation pad/feet between the speakers and the subwoofer. 

Think for a minute how many expensive large floor standing speakers have large, vibrating bass drivers in them. Too many to count AND they have no way to eliminate bass energy going throughout the speaker and crossover since they are connected to the same cabinet as one unit.

One other big advantage is the subs would be positioned properly for stereo image especially if using higher crossover levels. ( Subs set with slightly higher crossover can be locally identified)

You also gain an advantage to isolate the two cabinets in your set up  and still properly aligned. Highly recommended.

@soix  

+1 no speakers in top of subs. Also, for optimal sound you will have to move them around… optimal can be almost anywhere in the room. 

@ghdprentice    Don't do this? Wilson is doing it wrong?  BTW...these go down to 20 HZ.   B&W, TAD and many others do the same split configuration.

@gdaddy1 +1

Mike

You're placing your speakers in the optimal position for your listening. That doesn't mean that is the optimal position for the subs. Sub placement will be trial and error until you find the optimal placement.

Are those the 40.3 XDs?  Those must be some nice speakers!

The Wilson Audio speaker cabinets are designed to be mounted. The Harbeth isn’t.

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Excepted from this article.

Wilson Audio has long put much stock in the composite materials they make their cabinets from. X-Material, the primary material . . .

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The S-Material, which is used for the company’s front baffles, "provides a neutral and natural surface . . . "

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The new V-Material, which is used where two parts of the cabinet come together, "behaves like a vibration absorber," according to Wilson. It is used in the top panel of the woofer cabinet, where the objective, clearly, is to keep vibrations from the woofer cabinet from reaching the gantry and the lowest gantry-mounted driver . . .

Don't do this? Wilson is doing it wrong?

@gdaddy1  You’re really missing the point in this case.  The Harbeths were not designed to be placed on top of a sub, and the sub wasn’t designed to have a speaker placed on top of it whereas the Wilsons were designed to work that way.  Also, the best place to put subs for optimal bass in a room is pretty much never where the speakers are placed and in many cases it’s a poor place to put subs — any basic research on sub placement/room measurement will tell you that.  So for these reasons putting those nice Harbeths on subs is just not a good idea and should be avoided if at all possible for the benefit of both the speakers and the subs.

I think ignoring the fact that the woofers INSIDE the Harbeths actually woof renders objections to putting them on subs ridiculous. 

“Are those the 40.3 XDs?”   Yes. Paired with an Accuphase E800.  

If you're not using 4x subs in a dsp bass-managed array, what are you even doing with your life? (I kid, but seriously, if I didn't get the science of it I'd think it was witchery.)

@soix  What exactly is the "design change' allowing the Wilsons to have the speaker on top of the sub cabinet?

Maybe as @steakster points out... Wilson uses The new V-Material, which is used where two parts of the cabinet come together, "behaves like a vibration absorber," according to Wilson.

You can add a world class 'vibration absorber' on the Harbeth/subwoofer also!  Vibration absorption is not exclusive to just Wilson audio. Easily measured also.

'the best place to put subs for optimal bass in a room is pretty much never where the speakers are placed'

Then, according to this statement, you can conclude that the Wilsons can "never" be correct. Since the speakers are always connected to the subs and according to you, they shouldn't be.

Another thought is that subwoofers and speakers are different sizes, so placing your speakers on top of your subwoofers might make them too high or too low for proper listening.

FWIW, I would never put my speakers on my Sub.😀

It's not optimal, but it's far from the worst thing you could do.  A bowl of water can help give you a visual impression of how much vibration is present on the top surface of your sub.  It may not be a lot.  You'll have plenty of options on how to decouple the sub from the Harbeth.  I would start with rubber/cork HVAC pads.  They are a few dollars at most hardware stores, or you could go audiophile approved expensive.

Mijostyn made a good suggestion.

@gdaddy1 

Good counter example.

Then, according to this statement, you can conclude that the Wilsons can "never" be correct. Since the speakers are always connected to the subs and according to you, they shouldn’t be.

@gdaddy1 No, and as with most things in audio it’s a compromise. While the designer gets to implement the crossover and there are some advantages of things like potentially better impulse response, it comes at the high price of having to design/build much heavier/more expensive cabinets and placing bass where it’s not optimal and most likely creates significant bass problems in a room. And in this particular case, which is what we’re really talking about here, where the OP already has subs it would be both silly and counterproductive to place them where they most likely will not sound best and cause room-induced bass issues. Plus, putting a speaker on a big, vibrating beast if not necessary is just a stupid idea — vibrations negatively affect sound, so adding significantly more vibrations into the speaker is just never a good idea, period. And on top of that and as someone else mentioned, it’s also likely the speakers will not be at the proper height plopped on top of a subwoofer, so for all these reasons it’s just an awful idea to put those excellent and expensive speakers on subwoofers.

@gdaddy1 First of all, those Wilson's are incapable of projecting 20 Hz into a closet. Frequency response specs are extremely misleading being taken at one meter. In short, they are not subwoofers which for the majority are poorly designed, cheaply manufactured and vibrate like crazy producing vast amounts of distortion. 

Having said all that there is absolutely nothing wrong with placing a speaker on top of a subwoofer as long as nothing rattles. Isolation feet are for the most part a joke. I would put some self adhesive felt feet under the speaker so that both surfaces are protected from abrasion. Make sure the subwoofer is dead horizontal or the speaker might walk off with the vibration.   

We can take the “height” issue off the table.  The Tontregers place the tweeter too low for my application.  The optimal height to raise the 40.3 is pretty close to the height of the sub. 

@soix 

vibrations negatively affect sound, so adding significantly more vibrations into the speaker is just never a good idea, period.

Agreed, but that's NOT what I'm suggesting. I want to eliminate all vibration going to the speaker and it's absolutely possible. I agree that the tweeter height must be within range of your ear height. If it's too low the speaker can be adjusted higher using stands. The only problem would be if they are too high. You are assuming this mismatched condition is "Likely" when it hasn't been measured and we don't know.

@mijostyn   

Isolation feet are for the most part a joke. 

Believe it or not there is big difference in the dampening affect from different materials used in vibration control. It's not a joke, it's science.

Don't Set Your Subwoofer In The Corner see here!

Mike

@lewl28  Too low can easily be raised higher by the simple use of some speaker stands. I cut mine to an exact height.

What crossover do you set you subs? 

A thought to ponder... when I move subwoofers around a room I could always, easily detect where the sound was coming from. I could always point at their location. The higher the crossover the easier it was to hear their location. If used in a stereo application this can affect the stereo image negatively. By placing the Harbeths in straight vertical alignment with the woofers will retain the stereo image and depth. They will still be adjustable. Initial placement YOU control, change the phase, change crossover level, change the volume, toe them in or out.. Plenty of adjustments. For me the center image was more important than attempting to find the last ounce of bass and separating the subs and have two speakers off the center image. 

Many others feel this way also.

@gdaddy1 Yes, and it applied to items like automobiles. The job of loudspeakers is to create vibration. If the speaker enclosure is designed correctly it should not vibrate. Any vibration of an enclosure is audible and called distortion. Those feet are usually a hoax although there are some that actually work. When you change the height of a loudspeaker you change its relationship to the room and even a few inches can change the sound for better or worse. Only mechanical items like turntables and transports might be adversely affected by vibration. The best turntables have an isolating suspension.

@ditusa That is BS of the highest order. Subwoofers are up to 9 dB more efficient when placed in corners. The cone does not have to travel as far to create a given sound pressure level and that lowers distortion and conserves power. One subwoofer only in any location is a nightmare. The minimum is two. I place 4 subwoofers with a total of 8 drivers along the front wall ending in the corners creating a subwoofer line source. There are no room modes at all. Bass is even throughout the room except for a 2-3 dB increase a the boundaries. 

I side with @soix on this. A speaker balanced on top of a sub is going to move. It may even fall off. This is avoided in 3-way systems by bolting, gluing, or otherwise fastening the sections together in the optimal configuration, which of course depends on the crossover. Which of these attachment methods should be used with an expensive speaker? I say, "None."

Then there’s the problem of stabilizing the sub on the floor, with an added weight on the top, raising the centre of gravity - it goes on. I wouldn’t touch it. YMMV.

not ideal and looks like a kludge but if you really enjoy the sound....

just make sure you have good iso dots under the speakers. 

Definitive pioneered combining loudspeakers and subs in the same cabinet for decades and Golden Ear is doing this as well. I haven't seen any complaints about them.

in the same cabinet

being the operative words.

I have enjoyed my Sony M7 sitting on top of my SVS SB16 ultra without any issues of vibration 

https://youtu.be/iiZ8xf2pDco?si=THxlHfGQ1wxOgDwe

Another one Usher BE 718 on top of SB16 ultra 

https://youtu.be/E8sSmmDkjfo?si=BC2J9uxHtICoiAyT

Another one

https://youtu.be/snCrObvQcyI?si=lhvMrnBz5_Z83wXE

Definitive pioneered combining loudspeakers and subs in the same cabinet for decades and Golden Ear is doing this as well. I haven’t seen any complaints about them.

The optimal location for a subwoofer (low bass transducer) is usually never at the optimal location for a speaker (imaging and so on). The primary objective with a subwoofer is to get it married to the room...not anything else...

Golden Ear didn’t defy any physics and produce some kind of acoustic miracle.... What it does is a awkward compromise to cater to some low info dinosaurs who believe music listening should be done without subwoofers...

If you are placing speakers on top of a sub (at the same spot), it is a wasted opportunity in most circumstances.